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Sample records for photon multileaf collimator

  1. Evaluation of multileaf collimator design for a photon beam.

    PubMed

    Galvin, J M; Smith, A R; Moeller, R D; Goodman, R L; Powlis, W D; Rubenstein, J; Solin, L J; Michael, B; Needham, M; Huntzinger, C J

    1992-01-01

    Various aspects of multileaf collimator (MLC) design are examined relative to clinical requirements. The characteristics studied included: (a) irregular field edge definition or "effective" penumbra, (b) optimum field coverage for the multileaf portion of the field, and (c) leaf velocity. A film dosimetry technique was developed to measure the rapid 2-dimensional change in dose at an edge defined by a multileaf collimator with the segments staggered. The method applies a correction factor which allows for the changing ratio of scattered to primary photons at the field edge so that the energy dependence of the film is corrected. Stepped lead alloy blocks were irradiated with 6 MV photons to obtain films simulating a double-focused multileaf collimator, and the results were compared to films of fields shaped with standard divergent blocks. The effect of the shape of the leaf face (the end of the leaf) on penumbra was also studied. Proper shaping of the leaf ends may eliminate the need to exactly match beam divergence so that the mechanical of the collimator system is simplified. Leaves having several different end shapes and moving horizontally to intercept a vertical beam were compared to the divergent design where a straight face moves along an arc. The measurements showed that the "effective" penumbra (measured as the distance from the 80 to 20% isodose lines) for the multileaf collimator is a function of the angle between the direction of leaf motion and the edge defined by the leaves. In addition, all leaf end shapes showed some increase in penumbra compared to standard divergent blocking and also had increasing penumbra width as they moved over or back from the field center line. A total of 459 treatment fields and six disease sites were examined to determine the percentage of fields potentially shaped by multileaf segments of specified length. This study showed 93% of the fields had lengths of 30 cm or less and 99% had widths of 25 cm or less. A study

  2. Validation of modulated electron radiotherapy delivered with photon multileaf collimation

    NASA Astrophysics Data System (ADS)

    Klein, Eric E.

    There is a challenge in radiotherapy to treat shallow targets due to the inability to provide dose heterogeneity while simultaneously minimizing dose to distal critical organs. There is a niche for Modulated Electron Radiotherapy (MERT) to complement a photon IMRT program. Disease sites such as post-mastectomy chest wall, and subcutaneous lymphoma of the scalp, etc. are better suited for modulated electrons rather than photons, or perhaps a combination. Inherent collimation systems are not conducive for electron beam delivery (in lieu of extended applicators), nor do commercial treatment planning systems model electrons collimated without applicators. The purpose of this study is to evaluate modulation of electrons by inherent photon multileaf collimators, and calculated and optimized by means of Monte Carlo. Modulated electron radiotherapy (MERT) evaluation was conducted with a Trilogy 120 leaf MLC for 6-20 MeV. To provide a sharp penumbra, modulated beams were delivered with short SSDs (70-85cm). Segment widths (SW) ranging from 1 to 10cm were configured for delivery and planning, using BEAMnrc MC code with 109 particles, and DOSXYZnrc calculations. Calculations were set with: voxel size 0.2 x 0.2 x 0.1cm3, and photon/electron transport energy cutoffs of 0.01 MeV/0.521 MeV. Dosimetry was performed with film and micro chambers. Calculated and measured data were analyzed in MatLab. Once validation of static fields was successfully completed, modulated portals (segmented and dynamic) were configured for treatment and calculations. Optimization for target coverage and OAR sparing was achieved by choosing energies according to target depth, and SW according to spatial coverage. Intensity for each segment was optimized by MC methods. Beam sharpness (penumbra) degraded with: decreasing energy and SW, and increasing SSD. PDD decreased significantly with decreasing SW. We have demonstrated excellent calculation/measurement agreement (<3mm). Equal dose profiles were

  3. Delivery of modulated electron beams with conventional photon multi-leaf collimators

    NASA Astrophysics Data System (ADS)

    Klein, Eric E.; Mamalui-Hunter, Maria; Low, Daniel A.

    2009-01-01

    Electron beam radiotherapy is an accepted method to treat shallow tumors. However, modulation of electrons to customize dose distributions has not readily been achieved. Studies of bolus and tertiary collimation systems have been met with limitations. We pursue the use of photon multi-leaf collimators (MLC) for modulated electron radiotherapy (MERT) to achieve customized distributions for potential clinical use. As commercial planning systems do not support the use of MLC with electrons, planning was conducted using Monte Carlo calculations. Segmented and dynamic modulated delivery of multiple electron segments was configured, calculated and delivered for validation. Delivery of electrons with segmented or dynamic leaf motion was conducted. A phantom possessing an idealized stepped target was planned and optimized with subsequent validation by measurements. Finally, clinical treatment plans were conducted for post-mastectomy and cutaneous lymphoma of the scalp using forward optimization techniques. Comparison of calculations and measurements was successful with agreement of ±2%/2 mm for the energies, segment sizes, depths tested for delivered segments for the dynamic and segmented delivery. Clinical treatment plans performed provided optimal dose coverage of the target while sparing distal organs at risk. Execution of plans using an anthropomorphic phantom to ensure safe and efficient delivery was conducted. Our study validates that MERT is not only possible using the photon MLC, but the efficient and safe delivery inherent with the dynamic delivery provides an ideal technique for shallow tumor treatment.

  4. Design of a fast multileaf collimator for radiobiological optimized IMRT with scanned beams of photons, electrons, and light ions.

    PubMed

    Svensson, Roger; Larsson, Susanne; Gudowska, Irena; Holmberg, Rickard; Brahme, Anders

    2007-03-01

    Intensity modulated radiation therapy is rapidly becoming the treatment of choice for most tumors with respect to minimizing damage to the normal tissues and maximizing tumor control. Today, intensity modulated beams are most commonly delivered using segmental multileaf collimation, although an increasing number of radiation therapy departments are employing dynamic multileaf collimation. The irradiation time using dynamic multileaf collimation depends strongly on the nature of the desired dose distribution, and it is difficult to reduce this time to less than the sum of the irradiation times for all individual peak heights using dynamic leaf collimation [Svensson et al., Phys. Med. Biol. 39, 37-61 (1994)]. Therefore, the intensity modulation will considerably increase the total treatment time. A more cost-effective procedure for rapid intensity modulation is using narrow scanned photon, electron, and light ion beams in combination with fast multileaf collimator penumbra trimming. With this approach, the irradiation time is largely independent of the complexity of the desired intensity distribution and, in the case of photon beams, may even be shorter than with uniform beams. The intensity modulation is achieved primarily by scanning of a narrow elementary photon pencil beam generated by directing a narrow well focused high energy electron beam onto a thin bremsstrahlung target. In the present study, the design of a fast low-weight multileaf collimator that is capable of further sharpening the penumbra at the edge of the elementary scanned beam has been simulated, in order to minimize the dose or radiation response of healthy tissues. In the case of photon beams, such a multileaf collimator can be placed relatively close to the bremsstrahlung target to minimize its size. It can also be flat and thin, i.e., only 15-25 mm thick in the direction of the beam with edges made of tungsten or preferably osmium to optimize the sharpening of the penumbra. The low height of

  5. Design of a fast multileaf collimator for radiobiological optimized IMRT with scanned beams of photons, electrons, and light ions

    SciTech Connect

    Svensson, Roger; Larsson, Susanne; Gudowska, Irena; Holmberg, Rickard; Brahme, Anders

    2007-03-15

    Intensity modulated radiation therapy is rapidly becoming the treatment of choice for most tumors with respect to minimizing damage to the normal tissues and maximizing tumor control. Today, intensity modulated beams are most commonly delivered using segmental multileaf collimation, although an increasing number of radiation therapy departments are employing dynamic multileaf collimation. The irradiation time using dynamic multileaf collimation depends strongly on the nature of the desired dose distribution, and it is difficult to reduce this time to less than the sum of the irradiation times for all individual peak heights using dynamic leaf collimation [Svensson et al., Phys. Med. Biol. 39, 37-61 (1994)]. Therefore, the intensity modulation will considerably increase the total treatment time. A more cost-effective procedure for rapid intensity modulation is using narrow scanned photon, electron, and light ion beams in combination with fast multileaf collimator penumbra trimming. With this approach, the irradiation time is largely independent of the complexity of the desired intensity distribution and, in the case of photon beams, may even be shorter than with uniform beams. The intensity modulation is achieved primarily by scanning of a narrow elementary photon pencil beam generated by directing a narrow well focused high energy electron beam onto a thin bremsstrahlung target. In the present study, the design of a fast low-weight multileaf collimator that is capable of further sharpening the penumbra at the edge of the elementary scanned beam has been simulated, in order to minimize the dose or radiation response of healthy tissues. In the case of photon beams, such a multileaf collimator can be placed relatively close to the bremsstrahlung target to minimize its size. It can also be flat and thin, i.e., only 15-25 mm thick in the direction of the beam with edges made of tungsten or preferably osmium to optimize the sharpening of the penumbra. The low height of

  6. Dosimetric verification of modulated electron radiotherapy delivered using a photon multileaf collimator for intact breasts

    NASA Astrophysics Data System (ADS)

    Jin, L.; Ma, C.-M.; Fan, J.; Eldib, A.; Price, R. A.; Chen, L.; Wang, L.; Chi, Z.; Xu, Q.; Sherif, M.; Li, J. S.

    2008-11-01

    Modulated electron radiotherapy (MERT) may potentially be an effective modality for the treatment of shallow tumors, but dose calculation accuracy and delivery efficiency challenges remain. The purpose of this work is to investigate the dose accuracy of MERT delivery using a photon multileaf collimator (pMLC) on a Siemens Primus accelerator. A Monte Carlo (MC)-based inverse treatment planning system was developed for the 3D treatment planning process. Phase space data of 6, 9, 12 and 15 MeV electron beams were commissioned and used as the input source for MC dose calculations. A treatment plan was performed based on the 3D CT data of a heterogeneous 'breast phantom' that mimics a breast cancer patient, and delivered with 22 segments, each associated with a particular energy and Monitor Unit value. Film and ion chamber dosimetry was carefully performed for the conversion from measurement reading to dose, and the results were employed for plan verification using the heterogeneous breast phantom and a solid water phantom. Dose comparisons between measurements and calculations showed agreement within 2% or 1 mm. We conclude that our in-house MC treatment planning system is capable of performing treatment planning and accurate dose calculations for MERT using the pMLC to deliver radiation therapy to the intact breast.

  7. Matching extended-SSD electron beams to multileaf collimated photon beams in the treatment of head and neck cancer.

    PubMed

    Steel, Jared; Stewart, Allan; Satory, Philip

    2009-09-01

    Matching the penumbra of a 6 MeV electron beam to the penumbra of a 6 MV photon beam is a dose optimization challenge, especially when the electron beam is applied from an extended source-to-surface distance (SSD), as in the case of some head and neck treatments. Traditionally low melting point alloy blocks have been used to define the photon beam shielding over the spinal cord region. However, these are inherently time consuming to construct and employ in the clinical situation. Multileaf collimators (MLCs) provide a fast and reproducible shielding option but generate geometrically nonconformal approximations to the desired beam edge definition. The effects of substituting Cerrobend for the MLC shielding mode in the context of beam matching with extended-SSD electron beams are the subject of this investigation. Relative dose beam data from a Varian EX 2100 linear accelerator were acquired in a water tank under the 6 MeV electron beam at both standard and extended-SSD and under the 6 MV photon beam defined by Cerrobend and a number of MLC stepping regimes. The effect of increasing the electron beam SSD on the beam penumbra was assessed. MLC stepping was also assessed in terms of the effects on both the mean photon beam penumbra and the intraleaf dose-profile nonuniformity relative to the MLC midleaf. Computational techniques were used to combine the beam data so as to simulate composite relative dosimetry in the water tank, allowing fine control of beam abutment gap variation. Idealized volumetric dosimetry was generated based on the percentage depth-dose data for the beam modes and the abutment geometries involved. Comparison was made between each composite dosimetry dataset and the relevant ideal dosimetry dataset by way of subtraction. Weighted dose-difference volume histograms (DDVHs) were produced, and these, in turn, summed to provide an overall dosimetry score for each abutment and shielding type/angle combination. Increasing the electron beam SSD increased

  8. Multileaf collimator for Coline medical accelerators

    NASA Astrophysics Data System (ADS)

    Harasimowicz, Janusz; Plebański, Grzegorz; Sajna, Krzysztof

    2008-01-01

    Multileaf collimator (MLC) allows advanced field shaping for radiation therapy delivered with medical accelerators. In this paper theoretical considerations and scientific studies of a new MLC design are described. Considered multileaf collimator model comprises of a multiplicity of tungsten leaves of 1 cm width projected at isocenter plane. To ensure compatibility of a new MLC solution with different accelerator types as well as to assure high reliability in irradiated environment and presence of strong magnetic field, a complex and independent control system had to be developed. It comprises of two modules - one placed in the accelerator treatment head and the other one placed in the control room. Both of them ensure high reliability and treatment quality while working in harsh conditions. Mechanical design and leaf shape optimization algorithm based on a ray tracing method are also described in details. Adapted solutions allowed providing minimized and uniform radiation penumbrae in the full range of leaves positions which is crucial for modern advanced radiotherapy.

  9. Initiation of multi-leaf collimator conformal radiation therapy.

    PubMed

    Powlis, W D; Smith, A R; Cheng, E; Galvin, J M; Villari, F; Bloch, P; Kligerman, M M

    1993-01-15

    Clinical studies have been initiated in conformal radiotherapy using a computer controlled multi-leaf collimator. Quantitative dosimetry and treatment planning studies comparing field shaping by lead alloy blocks and the multi-leaf collimator demonstrate the clinical acceptability of the multi-leaf collimator. Sixteen patients with tumors in multiple sites have received some part of their treatments with both blocking systems. Studies of dosimetry and field shaping show that the multi-leaf collimator produces clinically acceptable blocking for most field shapes and disease sites. The 80-20% penumbra was characterized for a wide range of shaped beams. For straight edges perpendicular to the leaf travel, the penumbra of measured dose distributions from the multi-leaf collimator is equal to conventional divergent blocking. When the multi-leaf collimator leaves approach a contour at an angle, the penumbra increases. At forty-five degrees, the maximum angle of approach, the penumbra is approximately 4 mm wider than that for divergent blocks. Three-dimensional treatment planning demonstrates that equivalent dose distributions can be obtained from the two field shaping systems. The multi-leaf collimator can be used effectively and efficiently to treat a variety of disease sites. Its optimal utility may be in treating complex fields--five or more shaped coplanar or non-coplanar beams. It is well suited for conformal therapy applications.

  10. The Performance of Multileaf Collimators Evaluated by the Stripe Test

    SciTech Connect

    Sastre-Padro, Maria Lervag, Christoffer; Eilertsen, Karsten; Malinen, Eirik

    2009-10-01

    The performance of 3 multileaf collimator (MLC) systems (Varian Medical Systems, Elekta, and Siemens Medical Solutions) mounted on 7 different radiotherapy linear accelerators was investigated by a stripe test. The stripe test consisted of 8 adjacent multileaf segments of 2.5 x 40 cm{sup 2}, enclosed by all leaf pairs. With 6-MV photons, the segments were used to irradiate Agfa CR films. The optical density profile of the irradiated film in the travel direction of the MLC was used to estimate the short- and long-term leaf positioning reproducibility. The short-term reproducibility was found by analyzing 6 consecutive stripe tests. The long-term reproducibility was obtained by performing 3 to 5 stripe tests over 2 months. The short-term reproducibility was mainly within 0.3 mm for all systems. For the long-term reproducibility, the Varian and Elekta MLCs were within 0.4 to 0.5 mm, while the Siemens MLC showed a wider distribution, with values up to 1 mm for some leaf pairs. The inferior long-term reproducibility of the Siemens MLCs was mainly due to a decrease of the segment size with time. In conclusion, the stripe test is a useful method for evaluating MLC performance. Furthermore, the long-term reproducibility varied among the MLC systems investigated.

  11. The performance of multileaf collimators evaluated by the stripe test.

    PubMed

    Sastre-Padro, Maria; Lervåg, Christoffer; Eilertsen, Karsten; Malinen, Eirik

    2009-01-01

    The performance of 3 multileaf collimator (MLC) systems (Varian Medical Systems, Elekta, and Siemens Medical Solutions) mounted on 7 different radiotherapy linear accelerators was investigated by a stripe test. The stripe test consisted of 8 adjacent multileaf segments of 2.5 x 40 cm(2), enclosed by all leaf pairs. With 6-MV photons, the segments were used to irradiate Agfa CR films. The optical density profile of the irradiated film in the travel direction of the MLC was used to estimate the short- and long-term leaf positioning reproducibility. The short-term reproducibility was found by analyzing 6 consecutive stripe tests. The long-term reproducibility was obtained by performing 3 to 5 stripe tests over 2 months. The short-term reproducibility was mainly within 0.3 mm for all systems. For the long-term reproducibility, the Varian and Elekta MLCs were within 0.4 to 0.5 mm, while the Siemens MLC showed a wider distribution, with values up to 1 mm for some leaf pairs. The inferior long-term reproducibility of the Siemens MLCs was mainly due to a decrease of the segment size with time. In conclusion, the stripe test is a useful method for evaluating MLC performance. Furthermore, the long-term reproducibility varied among the MLC systems investigated.

  12. Neutron beam characteristics from 50 MeV protons on beryllium using a continuously variable multi-leaf collimator.

    PubMed

    Brahme, A; Eenmaa, J; Lindbäck, S; Montelius, A; Wootton, P

    1983-08-01

    The dose distributional properties of a p(50) Be neutron beam using a continuously variable multi-leaf collimator are presented and compared with a 6 MV photon beam. The differences in physical dose delivery between these two radiation modalities are generally insignificant for radiation therapy, and stringent comparisons of neutron and photon treatments should therefore be possible. The flexibility in field shaping with the multi-leaf collimator opens new possibilities in the treatment of complex irregular target volumes. The collimator consists of 40 wedge-shaped leaves that are independently moved under computer control with their collimating surfaces always aligned with the effective radiation source to minimize the penumbra. The leaf collimator eliminates the need for handling of heavy insert collimators and beam blocks at the same time that it allows dynamic conformation therapy with neutrons.

  13. Technology assessment of multileaf collimation: a North American users survey.

    PubMed

    Klein, E E; Tepper, J; Sontag, M; Franklin, M; Ling, C; Kubo, D

    1999-06-01

    The American Association of Physicists in Medicine (AAPM) initiated an Assessment of Technology Subcommittee (ATS) to help the radiotherapy community evaluate emerging technologies. The ATS decided to first address multileaf collimation (MLC) by means of a North American users survey. The survey attempted to address issues such as MLC utility, efficacy, cost-effectiveness, and customer satisfaction. The survey was designed with 38 questions, with cross-tabulation set up to decipher a particular clinic's perception of MLC. The surveys were coded according to MLC types, which were narrowed to four: Elekta, Siemens, Varian 52-leaf, and Varian 80-leaf. A 40% return rate was desired. A 44% (108 of 250) return was achieved. On an MLC machine, 76.5% of photon patients are being treated with MLC. The main reasons for not using MLC were stair stepping, field size limitation, and physician objection. The most common sites in which MLC is being used are lung, pelvis, and prostate. The least used sites are head & neck and mantle fields. Of the facilities, 31% claimed an increase in number of patients being treated since MLC was installed, and 44% claimed an increase in the number of fields. Though the staffing for block cutting has decreased, therapist staffing has not. However, 91% of the facilities claimed a decreased workload for the therapists, despite the increase in daily treated patients and fields. Of the facilities that justified MLC purchase for more daily patients, 63% are actually treating more patients. Only 26% of the facilities that justified an MLC purchase for intensity-modulated radiotherapy (IMRT) are currently using it for that purpose. The satisfaction rating (1 = low to 5 = high) for department groups averaged 4.0. Therapists ranked MLC as 4.6. Our survey shows that most users have successfully introduced MLC into the clinic as a block replacement. Most have found MLC to be cost-effective and efficient. The use of MLC for IMRT has progressed slower, but

  14. Radiologic validation of a fast neutron multileaf collimator

    SciTech Connect

    Farr, J. B.; Maughan, R. L.; Yudelev, M.; Blosser, E.; Brandon, J.; Horste, T.; Forman, J. D.

    2007-09-15

    Teletherapy with high linear energy transfer radiations (LET), perhaps more than with low LET types, requires careful beam collimation to limit effects to normal structures. Intensity modulated techniques may also hold promise in this regard. Accordingly, a remote computer-controlled, high-resolution multileaf collimator (MLC) is placed into service at the Gershenson Radiation Oncology Center's fast neutron therapy center of the Karmanos Cancer Institute, Detroit, Michigan. Prior to clinical application the basic radiological properties of the fast neutron MLC are studied. Complicating the evaluation is the mixed neutron and gamma radiation field environment encountered with fast neutron beams. As a reference the MLC performance is compared to an existing multirod collimator (MRC) used at the facility for more than ten years. The MLC aggregate transmission is found to be about 4%, slightly outperforming the MRC. The measured gamma component for a closed collimator is 1.5 times higher for the MLC, compared with the MRC. The different materials used for attenuation, steel and tungsten, respectively account for the difference. The geometry for the MRC is double focused whereas that for the MLC is single focused. The resulting penumbrae agree between the focused axis of the MLC and both axes of the MRC. Penumbra differences between the focused and unfocused axes were not observable at small field sizes and a maximum of about 1 cm for a 25x25 cm{sup 2} field at 2.5 cm depth in water. For a 10x10 cm{sup 2} field the focused penumbra is 9 mm, and the unfocused is 12 mm. The many benefits of the fully automatic MLC over the semimanual MRC are considered to justify this compromise.

  15. Multileaf collimator characteristics and reliability requirements for IMRT Elekta system.

    PubMed

    Liu, Chihray; Simon, Thomas A; Fox, Christopher; Li, Jonathan; Palta, Jatinder R

    2008-01-01

    Understanding the characteristics of a multileaf collimator (MLC) system, modeling MLC in a treatment planning system, and maintaining the mechanical accuracy of the linear accelerator gantry head system are important factors in the safe implementation of an intensity-modulated radiotherapy program. We review the characteristics of an Elekta MLC system, discuss the necessary MLC modeling parameters for a treatment planning system, and provide a novel method to establish an MLC leaf position quality assurance program. To perform quality assurance on 40 pairs of individual MLC leaves is a time-consuming and difficult task. In this report, an effective routine MLC quality assurance method based on the field edge of a backup jaw as referenced in conjunction with a diode array as a radiation detector system is discussed. The sensitivity of this test for determining the relative leaf positions was observed to be better than 0.1 mm. The Elekta MLC leaf position accuracy measured with this system has been better than 0.3 mm.

  16. Miniature multileaf collimator as an alternative to traditional circular collimators for stereotactic radiosurgery and stereotactic radiotherapy.

    PubMed

    Urie, M M; Lo, Y C; Litofsky, S; FitzGerald, T J

    2001-01-01

    To evaluate the miniature multileaf collimator (MMLC) as an alternative to traditional circular collimators for radiosurgery. 'Circular' fields were created with the Radionics MMLC (leaf width 3.53 mm at isocenter). Beam data, including tissue maximum ratios, output factors, penumbrae and isodose distributions of these fields were measured. These were compared to the Radionics circular collimators traditionally used for radiosurgery. The MMLC data were input to the XKnife Treatment Planning System. Treatment plans were completed and evaluated using both the MMLC 'circular' fields and the circular collimators. MMLC fields using 3, 5, 7, 9, 11, and 13 leaves on each side of the Radionics MMLC were created to approximate circular fields. The TMRs are essentially identical to those of comparable-size circular collimators. Measured at isocenter at 5-cm depth for 6 MV, the 80-20% penumbra widths are comparable to circular collimators, but are increased by as much as 1 mm at the leaf intersections (steps) where scalloping occurs. Isodose distributions were matched to those of circular collimators with comparable 50% isodose widths. Treatment plans for the MMLC 'circular' fields with four arcs (totaling 360 degrees) are essentially identical to those of comparable circular collimators. Dose-volume histograms revealed clinically insignificant differences between the two in doses to the target, to the volume surrounding the target, and to adjacent critical normal tissues. There is very little discrepancy between the dose distribution calculated with the approximated MMLC fields and with those of simulated arcs with the actual MMLC fields. With the MMLC simulating circular fields, dose distributions may be obtained which are essentially identical to comparable-size circular collimators. The mechanical accuracy of the MMLC is as good as that of the circular collimators, and the leakage dose is less. The diameter of 'circular' fields is limited by the MMLC leaf width to 1 cm

  17. High-resolution field shaping utilizing a masked multileaf collimator.

    PubMed

    Williams, P C; Cooper, P

    2000-08-01

    Multileaf collimators (MLCs) have become an important tool in the modern radiotherapy department. However, the current limit of resolution (1 cm at isocentre) can be too coarse for acceptable shielding of all fields. A number of mini- and micro-MLCs have been developed, with thinner leaves to achieve approved resolution. Currently however, such devices are limited to modest field sizes and stereotactic applications. This paper proposes a new method of high-resolution beam collimation by use of a tertiary grid collimator situated below the conventional MLC. The width of each slit in the grid is a submultiple of the MLC width. A composite shaped field is thus built up from a series of subfields, with the main MLC defining the length of each strip within each subfield. Presented here are initial findings using a prototype device. The beam uniformity achievable with such a device was examined by measuring transmission profiles through the grid using a diode. Profiles thus measured were then copied and superposed to generate composite beams, from which the uniformity achievable could be assessed. With the average dose across the profile normalized to 100%, hot spots up to 5.0% and troughs of 3% were identified for a composite beam of 2 x 5.0 mm grids, as measured at Dmax for a 6 MV beam. For a beam composed from 4 x 2.5 mm grids, the maximum across the profile was 3.0% above the average, and the minimum 2.5% below. Actual composite profiles were also formed using the integrating properties of film, with the subfield indexing performed using an engineering positioning stage. The beam uniformity for these fields compared well with that achieved in theory using the diode measurements. Finally sine wave patterns were generated to demonstrate the potential improvements in field shaping and conformity using this device as opposed to the conventional MLC alone. The scalloping effect on the field edge commonly seen on MLC fields was appreciably reduced by use of 2 x 5.0 mm

  18. Pitfalls of tungsten multileaf collimator in proton beam therapy

    SciTech Connect

    Moskvin, Vadim; Cheng, Chee-Wai; Das, Indra J.

    2011-12-15

    Purpose: Particle beam therapy is associated with significant startup and operational cost. Multileaf collimator (MLC) provides an attractive option to improve the efficiency and reduce the treatment cost. A direct transfer of the MLC technology from external beam radiation therapy is intuitively straightforward to proton therapy. However, activation, neutron production, and the associated secondary cancer risk in proton beam should be an important consideration which is evaluated. Methods: Monte Carlo simulation with FLUKA particle transport code was applied in this study for a number of treatment models. The authors have performed a detailed study of the neutron generation, ambient dose equivalent [H*(10)], and activation of a typical tungsten MLC and compared with those obtained from a brass aperture used in a typical proton therapy system. Brass aperture and tungsten MLC were modeled by absorber blocks in this study, representing worst-case scenario of a fully closed collimator. Results: With a tungsten MLC, the secondary neutron dose to the patient is at least 1.5 times higher than that from a brass aperture. The H*(10) from a tungsten MLC at 10 cm downstream is about 22.3 mSv/Gy delivered to water phantom by noncollimated 200 MeV beam of 20 cm diameter compared to 14 mSv/Gy for the brass aperture. For a 30-fraction treatment course, the activity per unit volume in brass aperture reaches 5.3 x 10{sup 4} Bq cm{sup -3} at the end of the last treatment. The activity in brass decreases by a factor of 380 after 24 h, additional 6.2 times after 40 days of cooling, and is reduced to background level after 1 yr. Initial activity in tungsten after 30 days of treating 30 patients per day is about 3.4 times higher than in brass that decreases only by a factor of 2 after 40 days and accumulates to 1.2 x 10{sup 6} Bq cm{sup -3} after a full year of operation. The daily utilization of the MLC leads to buildup of activity with time. The overall activity continues to increase

  19. Leakage of the Siemens 160 MLC multileaf collimator on a dual energy linear accelerator.

    PubMed

    Klüter, Sebastian; Sroka-Perez, Gabriele; Schubert, Kai; Debus, Jürgen

    2011-01-21

    Multileaf collimators (MLCs) have been in clinical use for many years and meanwhile are commonly used to deliver intensity-modulated radiotherapy (IMRT) beams. For this purpose it is important to know their dosimetric properties precisely, one of them being inter- and intraleaf leakage. The Siemens 160 MLC features a single focus design with flat-sided and tilted leaves instead of tongue-and-groove. The leakage performance of the 160 MLC was investigated on a dual energy linear accelerator Siemens ARTISTE with 6 MV and 18 MV photon energies. While the intraleaf leakage amounted to nearly the same dose for 6 and for 18 MV, a much higher interleaf leakage for 6 MV was measured. It could be reduced by simply rotating the collimator, and also by changing the voltage applied to the beam steering coils. The leakage of the 160 MLC is shown to be sensitive to beam alignment. This is of special interest for dual energy accelerators, as the two focal spots of both energies, neither in position nor in shape, do not necessarily always coincide. As a consequence of that, a higher leakage can be expected for one out of two energies for the 160 MLC.

  20. NOTE Leakage of the Siemens 160 MLC multileaf collimator on a dual energy linear accelerator

    NASA Astrophysics Data System (ADS)

    Klüter, Sebastian; Sroka-Perez, Gabriele; Schubert, Kai; Debus, Jürgen

    2011-01-01

    Multileaf collimators (MLCs) have been in clinical use for many years and meanwhile are commonly used to deliver intensity-modulated radiotherapy (IMRT) beams. For this purpose it is important to know their dosimetric properties precisely, one of them being inter- and intraleaf leakage. The Siemens 160 MLC features a single focus design with flat-sided and tilted leaves instead of tongue-and-groove. The leakage performance of the 160 MLC was investigated on a dual energy linear accelerator Siemens ARTISTE with 6 MV and 18 MV photon energies. While the intraleaf leakage amounted to nearly the same dose for 6 and for 18 MV, a much higher interleaf leakage for 6 MV was measured. It could be reduced by simply rotating the collimator, and also by changing the voltage applied to the beam steering coils. The leakage of the 160 MLC is shown to be sensitive to beam alignment. This is of special interest for dual energy accelerators, as the two focal spots of both energies, neither in position nor in shape, do not necessarily always coincide. As a consequence of that, a higher leakage can be expected for one out of two energies for the 160 MLC.

  1. Leakage of the Siemens 160 MLC multileaf collimator on a dual energy linear accelerator

    NASA Astrophysics Data System (ADS)

    Klüter, Sebastian; Sroka-Perez, Gabriele; Schubert, Kai; Debus, Jürgen

    2011-01-01

    Multileaf collimators (MLCs) have been in clinical use for many years and meanwhile are commonly used to deliver intensity-modulated radiotherapy (IMRT) beams. For this purpose it is important to know their dosimetric properties precisely, one of them being inter- and intraleaf leakage. The Siemens 160 MLC features a single focus design with flat-sided and tilted leaves instead of tongue-and-groove. The leakage performance of the 160 MLC was investigated on a dual energy linear accelerator Siemens ARTISTE with 6 MV and 18 MV photon energies. While the intraleaf leakage amounted to nearly the same dose for 6 and for 18 MV, a much higher interleaf leakage for 6 MV was measured. It could be reduced by simply rotating the collimator, and also by changing the voltage applied to the beam steering coils. The leakage of the 160 MLC is shown to be sensitive to beam alignment. This is of special interest for dual energy accelerators, as the two focal spots of both energies, neither in position nor in shape, do not necessarily always coincide. As a consequence of that, a higher leakage can be expected for one out of two energies for the 160 MLC.

  2. Dosimetric characteristics of novalis Tx system with high definition multileaf collimator.

    PubMed

    Chang, Zheng; Wang, Zhiheng; Wu, Q Jackie; Yan, Hui; Bowsher, Jim; Zhang, Junan; Yin, Fang-Fang

    2008-10-01

    A new Novalis Tx system equipped with a high definition multileaf collimator (HDMLC) recently became available to perform both image-guided radiosurgery and conventional radiotherapy. It is capable of delivering a highly conformal radiation dose with three energy modes: 6 MV photon energy, 15 MV photon energy, and 6 MV photon energy in a stereotactic radiosurgery mode with 1000 MU/min dose rate. Dosimetric characteristics of the new Novalis Tx treatment unit with the HDMLC are systematically measured for commissioning. A high resolution diode detector and miniion-chamber detector are used to measure dosimetric data for a range of field sizes from 4 x 4 mm to 400 x 400 mm. The commissioned Novalis Tx system has passed the RPC stereotactic radiosurgery head phantom irradiation test. The Novalis Tx system not only expands its capabilities with three energy modes, but also achieves better beam conformity and sharer beam penumbra with HDMLC. Since there is little beam data information available for the new Novalis Tx system, we present in this work the dosimetric data of the new modality for reference and comparison.

  3. Measuring output factors of small fields formed by collimator jaws and multileaf collimator using plastic scintillation detectors

    SciTech Connect

    Klein, David M.; Tailor, Ramesh C.; Archambault, Louis; Wang, Lilie; Therriault-Proulx, Francois; Beddar, A. Sam

    2010-10-15

    Purpose: As the practice of using high-energy photon beams to create therapeutic radiation fields of subcentimeter dimensions (as in intensity-modulated radiotherapy or stereotactic radiosurgery) grows, so too does the need for accurate verification of beam output at these small fields in which standard practices of dose verification break down. This study investigates small-field output factors measured using a small plastic scintillation detector (PSD), as well as a 0.01 cm{sup 3} ionization chamber. Specifically, output factors were measured with both detectors using small fields that were defined by either the X-Y collimator jaws or the multileaf collimator (MLC). Methods: A PSD of 0.5 mm diameter and 2 mm length was irradiated with 6 and 18 MV linac beams. The PSD was positioned vertically at a source-to-axis distance of 100 cm, at 10 cm depth in a water phantom, and irradiated with fields ranging in size from 0.5x0.5 to 10x10 cm{sup 2}. The field sizes were defined either by the collimator jaws alone or by a MLC alone. The MLC fields were constructed in two ways: with the closed leaves (i.e., those leaves that were not opened to define the square field) meeting at either the field center line or at a 4 cm offset from the center line. Scintillation light was recorded using a CCD camera and an estimation of error in the median-filtered signals was made using the bootstrapping technique. Measurements were made using a CC01 ionization chamber under conditions identical to those used for the PSD. Results: Output factors measured by the PSD showed close agreement with those measured using the ionization chamber for field sizes of 2.0x2.0 cm{sup 2} and above. At smaller field sizes, the PSD obtained output factors as much as 15% higher than those found using the ionization chamber by 0.6x0.6 cm{sup 2} jaw-defined fields. Output factors measured with no offset of the closed MLC leaves were as much as 20% higher than those measured using a 4 cm leaf offset

  4. Measuring output factors of small fields formed by collimator jaws and multileaf collimator using plastic scintillation detectors

    PubMed Central

    Klein, David M.; Tailor, Ramesh C.; Archambault, Louis; Wang, Lilie; Therriault-Proulx, Francois; Beddar, A. Sam

    2010-01-01

    Purpose: As the practice of using high-energy photon beams to create therapeutic radiation fields of subcentimeter dimensions (as in intensity-modulated radiotherapy or stereotactic radiosurgery) grows, so too does the need for accurate verification of beam output at these small fields in which standard practices of dose verification break down. This study investigates small-field output factors measured using a small plastic scintillation detector (PSD), as well as a 0.01 cm3 ionization chamber. Specifically, output factors were measured with both detectors using small fields that were defined by either the X-Y collimator jaws or the multileaf collimator (MLC). Methods: A PSD of 0.5 mm diameter and 2 mm length was irradiated with 6 and 18 MV linac beams. The PSD was positioned vertically at a source-to-axis distance of 100 cm, at 10 cm depth in a water phantom, and irradiated with fields ranging in size from 0.5×0.5 to 10×10 cm2. The field sizes were defined either by the collimator jaws alone or by a MLC alone. The MLC fields were constructed in two ways: with the closed leaves (i.e., those leaves that were not opened to define the square field) meeting at either the field center line or at a 4 cm offset from the center line. Scintillation light was recorded using a CCD camera and an estimation of error in the median-filtered signals was made using the bootstrapping technique. Measurements were made using a CC01 ionization chamber under conditions identical to those used for the PSD. Results: Output factors measured by the PSD showed close agreement with those measured using the ionization chamber for field sizes of 2.0×2.0 cm2 and above. At smaller field sizes, the PSD obtained output factors as much as 15% higher than those found using the ionization chamber by 0.6×0.6 cm2 jaw-defined fields. Output factors measured with no offset of the closed MLC leaves were as much as 20% higher than those measured using a 4 cm leaf offset. Conclusions: The authors

  5. Testing of the stability of intensity modulated beams generated with dynamic multileaf collimation, applied to the MM50 racetrack microtron.

    PubMed

    Dirkx, M L; Heijmen, B J

    2000-12-01

    Recently, we have published a method for the calculation of required leaf trajectories to generate optimized intensity modulated x-ray beams by means of dynamic multileaf collimation [Phys. Med. Biol. 43, 1171-1184 (1998)]. For the MM50 Racetrack Microtron it has been demonstrated that the dosimetric accuracy of this method, in combination with the dose calculation algorithm of the Cadplan 3D treatment planning system, is adequate for a clinical application (within 2% or 0.2 cm). Prior to initiating patient treatment with dynamic multileaf collimation (DMLC), tests have been performed to investigate the stability of DMLC fields generated at the MM50, (i) in time, (ii) subject to gantry rotation and (iii) in case of treatment interrupts, e.g., caused by an error detected by the treatment machine. The stability of relative dose profiles, normalized to a reference point in a relatively flat part of the modulated beam profile, was assessed from measurements with an electronic portal imaging device (EPID), with a linear diode array attached to the collimator and with film. The dose in the reference point was monitored using an ionization chamber. Tests were performed for several intensity modulated fields using 10 and 25 MV photon beams. Based on film measurements for sweeping 0.1 cm leaf gaps it was concluded that in an 80 days period the variation in leaf positioning was within 0.05 cm, without requiring any recalibration. For a uniform 10x10 cm2 field, realized dynamically by a scanning 0.4x10 cm2 slit beam, a maximum variation in slit width of 0.01 cm was derived from ionization chamber measurements, both in time and for gantry rotation. For a clinical example, the dose in the reference point reproduced within 0.2% (1 SD) over a period of 100 days. Apart from regions with very large dose gradients, variations in the relative beam profiles measured with the EPID were generally less than 1% (1 SD). For different gantry angles the dose profiles also reproduced within 1

  6. Development of multileaf collimator- and compensator-based techniques for modulated electron radiotherapy

    NASA Astrophysics Data System (ADS)

    Tynan, Patricia Marie

    Modulated electron radiotherapy (MERT) is a new electron therapy technique that uses intensity- and/or energy-modulated electron beams to provide a highly conformal dose of radiation to the treatment volume with low levels of dose deposition outside the treatment volume. Several methods are under investigation for treatment of patients, including the use of photon multileaf collimator-modulated (pMLC-modulated) beams, add-on electron multileaf collimators, and carved bolus materials placed directly on the patient's skin. This project developed a new method of delivering MERT beams using patient-specific milled compensators mounted in the standard electron applicator of a linear accelerator, accomplished through four specific aims. Aim 1: Conduct a feasibility study regarding the application of pMLC- and compensator-based MERT techniques within the clinic. Aim 2: Develop a software system to design compensators for modulated electron radiotherapy. Using MATLAB, an automated process for extracting treatment volume location data from a patient's CT data set was created. This software provides data about the depth to which the compensator must be machined to provide a conformal dose to the tumor. Aim 3: Use the Monte Carlo codes BEAMnrc and DOSXYZnrc to commission electron beams of a Varian 23EX linear accelerator for subsequent use in MERT treatment planning. A 10 cm x 10 cm field was modeled for three different energies (9, 12, and 16 MeV) for a Varian 23EX linear accelerator. Excellent match of the models to physical data was achieved, with less than 2% difference in dose and less than 2 mm difference in the lateral dimensions for the beam profiles. Aim 4: Create and validate a compensator-based MERT treatment plan. Using the coordinate data provided by the program created in Aim 3, a treatment plan was developed using the Monte Carlo code MCSIM for a simulated treatment volume. The resulting plan was manually optimized, resulting in a final dosimetric distribution

  7. [Mechanical accuracy of a stereotactic irradiation system using a micro multi-leaf collimator].

    PubMed

    Tatsumi, Daisaku; Nakada, Ryosei; Tsutsumi, Shinichi; Sakamoto, Mariko; Inoue, Makoto; Ichida, Takao; Hosono, Masako

    2011-01-01

    Mechanical accuracy of a stereotactic irradiation system using a micro multi-leaf collimator (mMLC), Elekta DMLC, has been evaluated. Measurements were made to obtain transmission, leakage, penumbra, and positioning accuracy of the DMLC leaf for a 6 MV photon beam. Mechanical accuracy and long term stability of a linac isocenter was also evaluated. The resulting transmission, along a line perpendicular to the leaf movement, was 0.31±0.01%, and the leakage from the closed opposing leaf pairs was 0.39±0.01%. The measured penumbra, at a depth incurring maximum dose, was 2.37±0.16 mm toward the leaf end and 2.14±0.18 mm toward the leaf side for various field sizes. The leaf gap width error, of 0.10±0.08 mm, was obtained by analyzing picket fence test results. The maximum leaf positioning error, of 0.14±0.06 mm, was obtained by analyzing the log file for a various gantry angles during an arc delivery. The isocenter accuracy was within a radius of 1 mm, without any recalibration for two years. In conclusion, our stereotactic irradiation system using DMLC was capable of providing accurate stereotactic treatment.

  8. Comparison of the penumbra between focused and nondivergent blocks--implications for multileaf collimators.

    PubMed

    Biggs, P; Capalucci, J; Russell, M

    1991-01-01

    The penumbra from a 10-MV x-ray beam has been measured using various field-shaping blocks located in the normal blocking tray position and compared to the penumbra of the adjustable photon jaws of the machine. The results showed that the penumbra was substantially degraded by these blocks only for field sizes greater than 15 x 15 cm2 and at the depth of maximum dose, dmax. At depths of 11 cm or greater, there was a significant difference only for the same range of field sizes in the 80% to 50% dose region. There was no significant difference at these depths for either the 95%-50% or the 90%-50% dose regions. No significant difference was observed between the use of lead and tungsten blocks and also between lead blocks with a straight edge and those with either an 0.5-mm or a 1-mm step in the face. Since the width of the 95% dose relative to the 50% dose is of greatest interest clinically, straight-edged blocks are as effective as divergent blocks in most situations. These results imply that the design and complexity of a multileaf collimator can be greatly simplified from a double focusing device to one that is single focusing in the plane orthogonal to the leaves.

  9. Characterization of a dynamic multi-leaf collimator for stereotactic radiotherapy applications

    NASA Astrophysics Data System (ADS)

    Godwin, G. A.; Simpson, J. B.; Mugabe, K. V.

    2012-07-01

    The Apex® dynamic mini-multileaf collimator has recently been released by Elekta and attaches directly to the linear accelerator head. This paper details the work and results obtained in characterizing this mini-MLC for stereotactic usage within our department. A range of mechanical and dosimetric characteristics were investigated which included inter and intra leaf leakage, light/radiation field congruence, leaf position reproducibility, radiation penumbra, total scatter factors and mechanical rotational stability with the additional mini-MLC weight.

  10. Efficient Monte Carlo simulation of multileaf collimators using geometry-related variance-reduction techniques.

    PubMed

    Brualla, L; Salvat, F; Palanco-Zamora, R

    2009-07-07

    A technique for accelerating the simulation of multileaf collimators with Monte Carlo methods is presented. This technique, which will be referred to as the movable-skin method, is based on geometrical modifications that do not alter the physical shape of the leaves, but that affect the logical way in which the Monte Carlo code processes the geometry. Zones of the geometry from which secondary radiation can emerge are defined as skins and the radiation transport throughout these zones is simulated accurately, while transport in non-skin zones is modelled approximately. The skins method is general and can be applied to most of the radiation transport Monte Carlo codes used in radiotherapy. The code AUTOLINAC for the automatic generation of the geometry file and the physical parameters required in a simulation of a linac with the Monte Carlo code PENELOPE is also introduced. This code has a modularized library of all Varian Clinac machines with their multileaf collimators and electron applicators. AUTOLINAC automatically determines the position of skins and the parameter values employed for other variance-reduction techniques that are adequate for the simulation of a linac. Using the adaptive variance-reduction techniques presented here it is possible to simulate with PENELOPE an entire linac with a fully closed multileaf collimator in two hours. For this benchmark a single core of a 2.8 GHz processor was used and 2% statistical uncertainty (1sigma) of the absorbed dose in water was reached with a voxel size of 2 x 2 x 2 mm(3). Several configurations of the multileaf collimator were simulated and the results were found to be in excellent agreement with experimental measurements.

  11. Development and validation of a BEAMnrc component module for a miniature multileaf collimator.

    PubMed

    Doerner, E; Hartmann, G H

    2012-05-21

    A new component module (CM) named mini multileaf collimator (mMLC) was developed for the Monte Carlo code BEAMnrc. It models the geometry of the add-on miniature multileaf collimator ModuLeaf (MRC Systems GmbH, Heidelberg, Germany, now part of Siemens, Erlangen, Germany). The new CM is partly based on the existing CM called DYNVMLC. The development was performed using a modified EGSnrc platform which enables us to work in the Microsoft Visual Studio environment. In order to validate the new CM, the PRIMUS linac with 6 MV x-rays (Siemens OCS, Concord, CA, USA) equipped with the ModuLeaf mMLC was modelled. Validation was performed by two methods: (a) a ray-tracing method to check the correct geometry of the multileaf collimator (MLC) and (b) a comparison of calculated and measured results of the following dosimetrical parameters: output factors, dose profiles, field edge position penumbra, MLC interleaf leakage and transmission values. Excellent agreement was found for all parameters. It was, in particular, found that the relationship between leaf position and field edge depending on the shape of the leaf ends can be investigated with a higher accuracy by this new CM than by measurements demonstrating the usefulness of the new CM.

  12. Varying MLC end projection size: an effect of the double-focused Siemens multileaf collimator.

    PubMed

    Buckle, A H

    2006-04-21

    Siemens linacs use multileaf collimators (MLCs) that move in an arc such that the flat faces of the leaf ends are always in the same plane as the radiation focus. An effect of this is that the magnification of the leaf end projection at the isocentric plane normal to the collimator rotation axis varies with the drive position of the leaves. This effect is quantified theoretically and empirically verified. A method is introduced for assessing the importance of the effect for a particular MLC pattern. The significance of the effect is discussed.

  13. A new concept of multileaf collimator (the shuttling MLC)--an interpreter for high-efficiency IMRT.

    PubMed

    Webb, S

    2000-11-01

    This paper proposes a radically new concept for a multileaf collimator for a photon linear accelerator for delivering IMRT with high monitor-unit efficiency. The concept is to consider each M (rows) x N (columns) two-dimensional intensity-modulated beam (2D IMB) as a set of N/2 M (rows) x 2 (columns) areas of modulation. Each area is then delivered by a set of M shuttling attenuating elements (called here the shuttling MLC) with a very high monitor-unit efficiency. The elements shuttle between each of the two columns comprising the M x 2 area and the modulation is provided by the variation in dwell time of the elements. The principles of this shuttling multileaf collimator are discussed and examples illustrating its operation are given. The main achievement reported in this paper is the development and robust testing of an interpreter which describes the position-time course of movement of the elements as a function of monitor units. This interpreter fully accounts for leakage transmission through the elements. It completely avoids the across-the-rows tongue-and-groove underdose. A large number of ID and 2D IMBs have been subjected to this interpreter and it is shown that for random patterns of fluence the SMLC is more monitor-unit efficient than the Bortfeld-Boyer technique (the most efficient with a conventional MLC) when the modulation is highly structured.

  14. Development of a Multileaf Collimator for Proton Therapy

    DTIC Science & Technology

    2012-11-01

    dose as a function of collimator material and thickness. Daartz et al.14 used a Bonner sphere to measure an increase of up to two-fold in neutron ...Zn, and 3% Pb by weight). The relative neutron sensitivities, kU and kT, as a function of incident neutron energy up to 50 MeV have been computed...with known neutron energy spectra. However, since neutron sensitivities are also a function of chamber gas composition, wall material, and chamber

  15. Measurement of back-scattered radiation from micro multileaf collimator into the beam monitor chamber from a dual energy linear accelerator

    PubMed Central

    Muralidhar, K. R.; Murthy, P. Narayana; Sresty, N. V. N. M.; Dixit, Pramod Kumar; Kumar, Rajneesh; Raju, A. K.

    2007-01-01

    Measurements designed to find the collimator backscatter into the beam monitor chamber from Micro Multileaf collimator of 6 MV photon beams of the Siemens Primus linear accelerator were made with the help of dose rate feedback control. The photons and electrons backscattered from the upper and lower secondary collimator jaws give rise to a significant increase in the ion charge measured by monitor chamber. This increase varies between the different accelerators. The output measurements were carried out in air at the isocenter. The effect of collimator backscatter was investigated by measuring the pulse width, number of beam pulses per monitor unit, monitor unit rate and dose for different mMLC openings. These measurements were made with and without dose rate feedback control, i.e., with constant electron beam current in the accelerator. Monitor unit rate (MU/min) was almost constant for all field sizes. The maximum variation between the open and the closed feedback control circuits was 2.5%. There was no difference in pulse width and negligible difference in pulse frequency. Maximum value of backscattered radiation from the micro Multileaf collimator into the beam monitor chamber was found to be 0.5%. PMID:21157537

  16. Secondary neutron spectra from modern Varian, Siemens, and Elekta linacs with multileaf collimators.

    PubMed

    Howell, Rebecca M; Kry, Stephen F; Burgett, Eric; Hertel, Nolan E; Followill, David S

    2009-09-01

    Neutrons are a by-product of high-energy x-ray radiation therapy (threshold for [gamma,n] reactions in high-Z material -7 MeV). Neutron production varies depending on photon beam energy as well as on the manufacturer of the accelerator. Neutron production from modern linear accelerators (linacs) has not been extensively compared, particularly in terms of the differences in the strategies that various manufacturers have used to implement multileaf collimators (MLCs) into their linac designs. However, such information is necessary to determine neutron dose equivalents for different linacs and to calculate vault shielding requirements. The purpose of the current study, therefore, was to measure the neutron spectra from the most up-to-date linacs from three manufacturers: Varian 21EX operating at 15, 18, and 20 MV, Siemens ONCOR operating at 15 and 18 MV, and Elekta Precise operating at 15 and 18 MV. Neutron production was measured by means of gold foil activation in Bonner spheres. Based on the measurements, the authors determined neutron spectra and calculated the average energy, total neutron fluence, ambient dose equivalent, and neutron source strength. The shapes of the neutron spectra did not change significantly between accelerators or even as a function of treatment energy. However, the neutron fluence, and therefore the ambient dose equivalent, did vary, increasing with increasing treatment energy. For a given nominal treatment energy, these values were always highest for the Varian linac. The current study thus offers medical physicists extensive information about the neutron production of MLC-equipped linacs currently in operation and provides them information vital for accurate comparison and prediction of neutron dose equivalents and calculation of vault shielding requirements.

  17. Secondary neutron spectra from modern Varian, Siemens, and Elekta linacs with multileaf collimators

    PubMed Central

    Howell, Rebecca M.; Kry, Stephen F.; Burgett, Eric; Hertel, Nolan E.; Followill, David S.

    2009-01-01

    Neutrons are a by-product of high-energy x-ray radiation therapy (threshold for [γ,n] reactions in high-Z material ∼7 MeV). Neutron production varies depending on photon beam energy as well as on the manufacturer of the accelerator. Neutron production from modern linear accelerators (linacs) has not been extensively compared, particularly in terms of the differences in the strategies that various manufacturers have used to implement multileaf collimators (MLCs) into their linac designs. However, such information is necessary to determine neutron dose equivalents for different linacs and to calculate vault shielding requirements. The purpose of the current study, therefore, was to measure the neutron spectra from the most up-to-date linacs from three manufacturers: Varian 21EX operating at 15, 18, and 20 MV, Siemens ONCOR operating at 15 and 18 MV, and Elekta Precise operating at 15 and 18 MV. Neutron production was measured by means of gold foil activation in Bonner spheres. Based on the measurements, the authors determined neutron spectra and calculated the average energy, total neutron fluence, ambient dose equivalent, and neutron source strength. The shapes of the neutron spectra did not change significantly between accelerators or even as a function of treatment energy. However, the neutron fluence, and therefore the ambient dose equivalent, did vary, increasing with increasing treatment energy. For a given nominal treatment energy, these values were always highest for the Varian linac. The current study thus offers medical physicists extensive information about the neutron production of MLC-equipped linacs currently in operation and provides them information vital for accurate comparison and prediction of neutron dose equivalents and calculation of vault shielding requirements. PMID:19810475

  18. Qualitative analysis of irregular fields delivered with dual electron multileaf collimator: A Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Inyang, Samuel Okon; Chamberlain, Alan

    2016-03-01

    The use of a dual electron multileaf collimator (eMLC) to collimate therapeutic electron beam without the use of cutouts has been previously shown to be feasible. Further Monte Carlo simulations were performed in this study to verify the nature and appearance of the isodose distribution in water phantom of irregular electron beams delivered by the eMLC. Electron fields used in this study were selected to reflect those used in electron beam therapy. Results of this study show that the isodose distribution in a water phantom obtained from the simulation of irregular electron beams through the eMLC conforms to the pattern of the eMLC used in the delivery of the beam. It is therefore concluded that the dual eMLC could deliver isodose distributions reflecting the pattern of the eMLC field that was used in the delivery of the beam.

  19. Gamma knife, stereotactic linac radiosurgery, and micro multileaf collimator optimized treatment plan comparison

    NASA Astrophysics Data System (ADS)

    Kulik, Carine; Vermandel, Maximilien; Rousseau, Jean; Gibon, D.; Maouche, Salah

    2002-05-01

    The aim of conformal radiation therapy and of radiosurgery (Gamma Knife and Multi-beam radiosurgery) is to irradiate the pathological target volume with ionizing radiation while avoiding as well as possible the surrounding normal tissues. Recently, new micro multileaf collimator ((mu) MLC) devices are available for conformal therapy. A (mu) MLC is formed by narrow sliding leafs in such a manner that the irradiation field can be adjusted to the shape of the target. It is interesting to compare the different techniques to evaluate their effectiveness and their accuracy. This comparison involves 8 clinical cases. For each treatment modality, we compare indexes defined in the international literature by the Radiation Therapy Oncology Group (RTOG). This theoretical study shows (i) the interest of the use of intensity modulation in the case of conformal radiation therapy and (ii) the improvement of RTOG indexes with using the conformal radiotherapy although the volumes of irradiated normal tissue remains lower with the radiosurgery than those with the (mu) MLC. However the comparison between these three techniques for the brain tumors shows that in complex cases it is more effective to use the fractionated conformal therapy with intensity modulation instead of radiosurgery. It is already sure that the micro multileaf collimator holds an important place in conformal therapy.

  20. Compact multileaf collimator for conformal and intensity modulated fast neutron therapy: Electromechanical design and validation

    SciTech Connect

    Farr, J. B.; Maughan, R. L.; Yudelev, M.; Blosser, E.; Brandon, J.; Horste, T.; Forman, J. D.

    2006-09-15

    The electromechanical properties of a 120-leaf, high-resolution, computer-controlled, fast neutron multileaf collimator (MLC) are presented. The MLC replaces an aging, manually operated multirod collimator. The MLC leaves project 5 mm in the isocentric plane perpendicular to the beam axis. A taper is included on the leaves matching beam divergence along one axis. The 5-mm leaf projection width is chosen to give high-resolution conformality across the entire field. The maximum field size provided is 30x30 cm{sup 2}. To reduce the interleaf transmission a 0.254-mm blocking step is included. End-leaf steps totaling 0.762 mm are also provided allowing opposing leaves to close off within the primary radiation beam. The neutron MLC also includes individual 45 deg. and 60 deg. automated universal tungsten wedges. The automated high-resolution neutron collimation provides an increase in patient throughput capacity, enables a new modality, intensity modulated neutron therapy, and limits occupational radiation exposure by providing remote operation from a shielded console area.

  1. Using multileaf collimator interleaf leakage to extract absolute spatial information from electronic portal imaging device images.

    PubMed

    Gao, Zhanrong; Szanto, Janos; Gerig, Lee

    2005-12-15

    Electronic portal imaging devices (EPIDs) are potentially valuable tools for linear accelerator quality assurance and for measuring and analyzing geometric variations in radiation treatment delivery. Geometric analysis is more robust if referenced against an absolute position such as the isocenter (collimator axis of rotation), allowing the observer to discriminate between various setup errors and jaw or multileaf collimator (MLC) calibration errors. Unfortunately, mechanical instabilities in EPIDs make such analysis difficult. In the present work, we describe how MLC interleaf radiation leakage, hidden in the background of portal images, can be extracted and analyzed to find the field isocenter perpendicular to leaf travel direction. The signal from the interleaf radiation leakage is extracted to provide a precise and accurate determination of the isocenter location in the direction perpendicular to MLC leaf travel. In the direction of leaf travel, the minimization of residuals between planned and measured leaf positions is used to determine the isocenter. This method assumes that leaf positioning errors are randomly distributed. The validity of the method for determining the angular deviation between EPID image grid lines and collimator angle and for determining the known isocenter position is experimentally established.

  2. Compact multileaf collimator for conformal and intensity modulated fast neutron therapy: electromechanical design and validation.

    PubMed

    Farr, J B; Maughan, R L; Yudelev, M; Blosser, E; Brandon, J; Horste, T; Forman, J D

    2006-09-01

    The electromechanical properties of a 120-leaf, high-resolution, computer-controlled, fast neutron multileaf collimator (MLC) are presented. The MLC replaces an aging, manually operated multirod collimator. The MLC leaves project 5 mm in the isocentric plane perpendicular to the beam axis. A taper is included on the leaves matching beam divergence along one axis. The 5-mm leaf projection width is chosen to give high-resolution conformality across the entire field. The maximum field size provided is 30 x 30 cm2. To reduce the interleaf transmission a 0.254-mm blocking step is included. End-leaf steps totaling 0.762 mm are also provided allowing opposing leaves to close off within the primary radiation beam. The neutron MLC also includes individual 45 degrees and 60 degrees automated universal tungsten wedges. The automated high-resolution neutron collimation provides an increase in patient throughput capacity, enables a new modality, intensity modulated neutron therapy, and limits occupational radiation exposure by providing remote operation from a shielded console area.

  3. Collimator based tracking with an add-on multileaf collimator: Moduleaf

    NASA Astrophysics Data System (ADS)

    Böhler, A.; Weichenberger, H.; Gaisberger, C.; Sedlmayer, F.; Deutschmann, H.

    2015-04-01

    Radiotherapy is one of the most important methods used for the treatment of cancer. Irradiating a moving target is also one of the most challenging tasks to accomplish in modern radiotherapy. We have developed a tracking system by modifying an add-on collimator, the Siemens Moduleaf, for realtime applications in radiotherapy. As the add-on collimator works nearly completely independently of the linear accelerator (LinAc), no modifications to the latter were necessary. The adaptations to the Moduleaf were mainly software-based. In order to reduce the complexity of the system, outdated electronic parts were replaced with newer components where practical. Verification was performed by measuring the latency of the system as well as the impact on applied dose to a predefined target volume, moving in the leaf’s travel direction. Latency measurements in the software were accomplished by comparing the target and current positions of the leaves. For dose measurements, a Gafchromic EBT2 film was placed beneath the target 4D phantom, in between solid water plates and moved alongside with it. Comparing the dose distribution on the film with a moving target between ‘tracking disabled’ towards ‘tracking enabled’ functions resulted in penumbra widths of 23 mm to 4 mm for 0.1 Hz sinusoidal movements with an amplitude of 32 mm, respectively. The maximum speed was therefore 20 mm s-1. Latency was measured to be less than 50 ms for the signal runtimes. Based on the results, a tracking-capable add-on collimator seems to be a useful tool for reducing the margins for the treatment of small, slow-moving targets.

  4. SU-E-T-247: Multi-Leaf Collimator Model Adjustments Improve Small Field Dosimetry in VMAT Plans

    SciTech Connect

    Young, L; Yang, F

    2014-06-01

    Purpose: The Elekta beam modulator linac employs a 4-mm micro multileaf collimator (MLC) backed by a fixed jaw. Out-of-field dose discrepancies between treatment planning system (TPS) calculations and output water phantom measurements are caused by the 1-mm leaf gap required for all moving MLCs in a VMAT arc. In this study, MLC parameters are optimized to improve TPS out-of-field dose approximations. Methods: Static 2.4 cm square fields were created with a 1-mm leaf gap for MLCs that would normally park behind the jaw. Doses in the open field and leaf gap were measured with an A16 micro ion chamber and EDR2 film for comparison with corresponding point doses in the Pinnacle TPS. The MLC offset table and tip radius were adjusted until TPS point doses agreed with photon measurements. Improvements to the beam models were tested using static arcs consisting of square fields ranging from 1.6 to 14.0 cm, with 45° collimator rotation, and 1-mm leaf gap to replicate VMAT conditions. Gamma values for the 3-mm distance, 3% dose difference criteria were evaluated using standard QA procedures with a cylindrical detector array. Results: The best agreement in point doses within the leaf gap and open field was achieved by offsetting the default rounded leaf end table by 0.1 cm and adjusting the leaf tip radius to 13 cm. Improvements in TPS models for 6 and 10 MV photon beams were more significant for smaller field sizes 3.6 cm or less where the initial gamma factors progressively increased as field size decreased, i.e. for a 1.6cm field size, the Gamma increased from 56.1% to 98.8%. Conclusion: The MLC optimization techniques developed will achieve greater dosimetric accuracy in small field VMAT treatment plans for fixed jaw linear accelerators. Accurate predictions of dose to organs at risk may reduce adverse effects of radiotherapy.

  5. A reduction in the AAPM TG-36 reported peripheral dose distributions with tertiary multileaf collimation. American Association of Physicists in Medicine Task Group 36.

    PubMed

    Mutic, S; Klein, E E

    1999-07-01

    The American Association of Physicists in Medicine Task Group 36 (AAPM TG-36) data can be used to estimate peripheral dose (PD) distributions outside the primary radiation field. However, the report data apply to linear accelerators not equipped with tertiary multileaf collimators (MLCs). Peripheral dose distributions consist of internal scatter, collimation scatter, transmission through collimation, head leakage, and room scatter. Tertiary MLCs may significantly reduce the PD due to a reduction in collimation scatter, transmission through collimation, and head leakage. Measurements were performed on a multimodality linear accelerator, equipped with a tertiary MLC, to determine PD distributions as a function of energy, field size, distance from the primary radiation field edge, MLC position, and collimator orientation. Measurements were made using an ionization chamber embedded in a 20 x 40 x 120-cm3 water-equivalent plastic phantom with the secondary collimator and MLC settings of 10 x 10, 15 x 15, 20 x 20, 25 x 25 cm2, and with the MLC fully retracted. Data were taken along the longitudinal axis of the machine for 6 and 18 MV photons. Peripheral dose distributions were evaluated with the collimator set to 180 and 90 degrees. Rotation of the collimator allowed measurements parallel and orthogonal to the direction of motion of the MLC. For both photon energies, peripheral doses measured on a MLC machine were lower than the TG-36 data. When the collimator is rotated by 90 degrees, placing the lower jaws and the MLC leaves along the plane of interest, PD was reduced by as much as a factor of three compared with PDs measured with the MLC fully retracted and the collimator rotated to 180 degrees. PDs measured with the MLC fully retracted and collimator rotated to 180 degrees were comparable to the TG-36 data. Measured PDs were lower when the MLC was used to shape the field than when the MLC was fully retracted. A strategic orientation of the collimator with a tertiary

  6. Multibeam tomotherapy: A new treatment unit devised for multileaf collimation, intensity-modulated radiation therapy

    SciTech Connect

    Achterberg, Nils; Mueller, Reinhold G.

    2007-10-15

    A fully integrated system for treatment planning, application, and verification for automated multileaf collimator (MLC) based, intensity-modulated, image-guided, and adaptive radiation therapy (IMRT, IGRT and ART, respectively) is proposed. Patient comfort, which was the major development goal, will be achieved through a new unit design and short treatment times. Our device for photon beam therapy will consist of a new dual energy linac with five fixed treatment heads positioned evenly along one plane but one electron beam generator only. A minimum of moving parts increases technical reliability and reduces motion times to a minimum. Motion is allowed solely for the MLCs, the robotic patient table, and the small angle gantry rotation of {+-}36 deg. . Besides sophisticated electron beam guidance, this compact setup can be built using existing modules. The flattening-filter-free treatment heads are characterized by reduced beam-on time and contain apertures restricted in one dimension to the area of maximum primary fluence output. In the case of longer targets, this leads to a topographic intensity modulation, thanks to the combination of 'step and shoot' MLC delivery and discrete patient couch motion. Owing to the limited number of beam directions, this multislice cone beam serial tomotherapy is referred to as 'multibeam tomotherapy.' Every patient slice is irradiated by one treatment head at any given moment but for one subfield only. The electron beam is then guided to the next head ready for delivery, while the other heads are preparing their leaves for the next segment. The 'Multifocal MLC-positioning' algorithm was programmed to enable treatment planning and optimize treatment time. We developed an overlap strategy for the longitudinally adjacent fields of every beam direction, in doing so minimizing the field match problem and the effects of possible table step errors. Clinical case studies show for the same or better planning target volume coverage, better

  7. Multibeam tomotherapy: a new treatment unit devised for multileaf collimation, intensity-modulated radiation therapy.

    PubMed

    Achterberg, Nils; Müller, Reinhold G

    2007-10-01

    A fully integrated system for treatment planning, application, and verification for automated multileaf collimator (MLC) based, intensity-modulated, image-guided, and adaptive radiation therapy (IMRT, IGRT and ART, respectively) is proposed. Patient comfort, which was the major development goal, will be achieved through a new unit design and short treatment times. Our device for photon beam therapy will consist of a new dual energy linac with five fixed treatment heads positioned evenly along one plane but one electron beam generator only. A minimum of moving parts increases technical reliability and reduces motion times to a minimum. Motion is allowed solely for the MLCs, the robotic patient table, and the small angle gantry rotation of +/- 36 degrees. Besides sophisticated electron beam guidance, this compact setup can be built using existing modules. The flattening-filter-free treatment heads are characterized by reduced beam-on time and contain apertures restricted in one dimension to the area of maximum primary fluence output. In the case of longer targets, this leads to a topographic intensity modulation, thanks to the combination of "step and shoot" MLC delivery and discrete patient couch motion. Owing to the limited number of beam directions, this multislice cone beam serial tomotherapy is referred to as "multibeam tomotherapy." Every patient slice is irradiated by one treatment head at any given moment but for one subfield only. The electron beam is then guided to the next head ready for delivery, while the other heads are preparing their leaves for the next segment. The "Multifocal MLC-positioning" algorithm was programmed to enable treatment planning and optimize treatment time. We developed an overlap strategy for the longitudinally adjacent fields of every beam direction, in doing so minimizing the field match problem and the effects of possible table step errors. Clinical case studies show for the same or better planning target volume coverage, better

  8. SU-E-T-467: Implementation of Monte Carlo Dose Calculation for a Multileaf Collimator Equipped Robotic Radiotherapy System

    SciTech Connect

    Li, JS; Fan, J; Ma, C-M

    2015-06-15

    Purpose: To improve the treatment efficiency and capabilities for full-body treatment, a robotic radiosurgery system has equipped with a multileaf collimator (MLC) to extend its accuracy and precision to radiation therapy. To model the MLC and include it in the Monte Carlo patient dose calculation is the goal of this work. Methods: The radiation source and the MLC were carefully modeled to consider the effects of the source size, collimator scattering, leaf transmission and leaf end shape. A source model was built based on the output factors, percentage depth dose curves and lateral dose profiles measured in a water phantom. MLC leaf shape, leaf end design and leaf tilt for minimizing the interleaf leakage and their effects on beam fluence and energy spectrum were all considered in the calculation. Transmission/leakage was added to the fluence based on the transmission factors of the leaf and the leaf end. The transmitted photon energy was tuned to consider the beam hardening effects. The calculated results with the Monte Carlo implementation was compared with measurements in homogeneous water phantom and inhomogeneous phantoms with slab lung or bone material for 4 square fields and 9 irregularly shaped fields. Results: The calculated output factors are compared with the measured ones and the difference is within 1% for different field sizes. The calculated dose distributions in the phantoms show good agreement with measurements using diode detector and films. The dose difference is within 2% inside the field and the distance to agreement is within 2mm in the penumbra region. The gamma passing rate is more than 95% with 2%/2mm criteria for all the test cases. Conclusion: Implementation of Monte Carlo dose calculation for a MLC equipped robotic radiosurgery system is completed successfully. The accuracy of Monte Carlo dose calculation with MLC is clinically acceptable. This work was supported by Accuray Inc.

  9. Assessment of a new multileaf collimator concept using GEANT4 Monte Carlo simulations.

    PubMed

    Tacke, Martin B; Szymanowski, Hanitra; Oelfke, Uwe; Schulze, Carsten; Nuss, Susanne; Wehrwein, Eugen; Leidenberger, Stefan

    2006-04-01

    The aim of the work was to investigate in advance the dosimetric properties of a new multileaf collimator (MLC) concept with the help of Monte Carlo (MC) simulations prior to the production of a prototype. The geometrical design of the MLC was implemented in the MC code GEANT4. For the simulation of a 6 MV treatment beam, an experimentally validated phase space and a virtual spatial Gaussian-shaped model placed in the origin were used. For the simulation of the geometry in GEANT4, the jaws and the two leaf packages were implemented with the help of computer-aided design data. First, transmission values for different tungsten alloys were extracted using the simulation codes GEANT4 and BEAMnrc and compared to experimental measurements. In a second step, high-resolution simulations were performed to detect the leakage at depth of maximum dose. The 20%-80% penumbra along the travel direction of the leaves was determined using 10 x 10 cm2 fields shifted along the x- and y-axis. The simulated results were compared with measured data. The simulation of the transmission values for different tungsten alloys showed a good agreement with the experimental measurements (within 2.0%). This enabled an accurate estimation of the attenuation coefficient for the various leaf materials. Simulations with varying width of the spatial Gaussian distribution showed that the leakage and the penumbra depend very much on this parameter: for instance, for widths of 2 and 4 mm, the interleaf leakage is below 0.3% and 0.75%, respectively. The results for the leakage and the penumbra (4.7+/-0.5 mm) are in good agreement with the measurements. This study showed that GEANT4 is appropriate for the investigation of the dosimetric properties of a multileaf collimator. In particular, a quantification of the leakage, the penumbra, and the tongue-and-groove effect and an evaluation of the influence of the beam parameters such as the width of the Gaussian distribution was possible.

  10. Monte Carlo simulation of the dynamic micro-multileaf collimator of a LINAC Elekta Precise using PENELOPE.

    PubMed

    González, W; Lallena, A M; Alfonso, R

    2011-06-07

    Micro-multileaf collimators are devices that are added to LINAC heads for stereotactic radiosurgery. In this work, the performance of an Elekta Precise LINAC with a dynamic micro-multileaf collimator manufactured by 3D-line has been studied. Monte Carlo simulations based on PENELOPE code and measurements with three different detectors (PTW Semiflex 31010 chamber, PTW PinPoint 31016 chamber and PTW Diode 60008) have been carried out. Simulations were tuned by reproducing the experimental TPR(20, 10) quality index, providing a nice description of both the PDD curve and the transverse profiles at the two depths measured. The geometry of the micro-multileaf collimator was tested by calculating the transmission through it, and it was needed to significantly reduce the leaf separation indicated by the manufacturer to reproduce the experimental results. An approximate simulation in which the transport of the particles traversing the dynamic micro-multileaf collimator was described in a simplified way was analyzed, providing good agreement with the full simulations. With the MC model fixed, output factors for various field sizes were calculated and compared to the experimental ones, obtaining good agreement. Percentage depth doses (PDDs) and transverse profiles at two depths measured with the diode for small fields were well reproduced by the simulation, while the measurements performed with the PinPoint chamber showed differences in the PDDs, at large depths, and transverse profiles, at the penumbra. Monte Carlo simulations and Semiflex and diode measurements, performed for a 7.0 cm × 7.0 cm field, were in nice agreement, while those obtained with the PinPoint chamber showed differences that increased with the depth in water. At the phantom entrance, all measurements showed non-negligible differences that made Monte Carlo a good option to estimate the absorbed dose in this region.

  11. Monte Carlo simulation of the dynamic micro-multileaf collimator of a LINAC Elekta Precise using PENELOPE

    NASA Astrophysics Data System (ADS)

    González, W.; Lallena, A. M.; Alfonso, R.

    2011-06-01

    Micro-multileaf collimators are devices that are added to LINAC heads for stereotactic radiosurgery. In this work, the performance of an Elekta Precise LINAC with a dynamic micro-multileaf collimator manufactured by 3D-line has been studied. Monte Carlo simulations based on PENELOPE code and measurements with three different detectors (PTW Semiflex 31010 chamber, PTW PinPoint 31016 chamber and PTW Diode 60008) have been carried out. Simulations were tuned by reproducing the experimental TPR20, 10 quality index, providing a nice description of both the PDD curve and the transverse profiles at the two depths measured. The geometry of the micro-multileaf collimator was tested by calculating the transmission through it, and it was needed to significantly reduce the leaf separation indicated by the manufacturer to reproduce the experimental results. An approximate simulation in which the transport of the particles traversing the dynamic micro-multileaf collimator was described in a simplified way was analyzed, providing good agreement with the full simulations. With the MC model fixed, output factors for various field sizes were calculated and compared to the experimental ones, obtaining good agreement. Percentage depth doses (PDDs) and transverse profiles at two depths measured with the diode for small fields were well reproduced by the simulation, while the measurements performed with the PinPoint chamber showed differences in the PDDs, at large depths, and transverse profiles, at the penumbra. Monte Carlo simulations and Semiflex and diode measurements, performed for a 7.0 cm × 7.0 cm field, were in nice agreement, while those obtained with the PinPoint chamber showed differences that increased with the depth in water. At the phantom entrance, all measurements showed non-negligible differences that made Monte Carlo a good option to estimate the absorbed dose in this region.

  12. Sensitivity of 3D Dose Verification to Multileaf Collimator Misalignments in Stereotactic Body Radiation Therapy of Spinal Tumor.

    PubMed

    Xin-Ye, Ni; Ren, Lei; Yan, Hui; Yin, Fang-Fang

    2016-12-01

    This study aimed to detect the sensitivity of Delt 4 on ordinary field multileaf collimator misalignments, system misalignments, random misalignments, and misalignments caused by gravity of the multileaf collimator in stereotactic body radiation therapy. (1) Two field sizes, including 2.00 cm (X) × 6.00 cm (Y) and 7.00 cm (X) × 6.00 cm (Y), were set. The leaves of X1 and X2 in the multileaf collimator were simultaneously opened. (2) Three cases of stereotactic body radiation therapy of spinal tumor were used. The dose of the planning target volume was 1800 cGy with 3 fractions. The 4 types to be simulated included (1) the leaves of X1 and X2 in the multileaf collimator were simultaneously opened, (2) only X1 of the multileaf collimator and the unilateral leaf were opened, (3) the leaves of X1 and X2 in the multileaf collimator were randomly opened, and (4) gravity effect was simulated. The leaves of X1 and X2 in the multileaf collimator shifted to the same direction. The difference between the corresponding 3-dimensional dose distribution measured by Delt 4 and the dose distribution in the original plan made in the treatment planning system was analyzed with γ index criteria of 3.0 mm/3.0%, 2.5 mm/2.5%, 2.0 mm/2.0%, 2.5 mm/1.5%, and 1.0 mm/1.0%. (1) In the field size of 2.00 cm (X) × 6.00 cm (Y), the γ pass rate of the original was 100% with 2.5 mm/2.5% as the statistical standard. The pass rate decreased to 95.9% and 89.4% when the X1 and X2 directions of the multileaf collimator were opened within 0.3 and 0.5 mm, respectively. In the field size of 7.00 (X) cm × 6.00 (Y) cm with 1.5 mm/1.5% as the statistical standard, the pass rate of the original was 96.5%. After X1 and X2 of the multileaf collimator were opened within 0.3 mm, the pass rate decreased to lower than 95%. The pass rate was higher than 90% within the 3 mm opening. (2) For spinal tumor, the change in the planning target volume V18 under various modes calculated using treatment planning system

  13. Dosimetric impact of different multileaf collimators on prostate intensity modulated treatment planning

    PubMed Central

    Orlandini, Lucia Clara; Betti, Margherita; Fulcheri, Christian; Coppola, Marianna; Cionini, Luca

    2015-01-01

    Aim The main purpose of this study is to perform a dosimetric comparison on target volumes and organs at risks (OARs) between prostate intensity modulated treatment plans (IMRT) optimized with different multileaf collimators (MLCs). Background The use of MLCs with a small leaf width in the IMRT optimization may improve conformity around the tumor target whilst reducing the dose to normal tissues. Materials and methods Two linacs mounting MLCs with 5 and 10 mm leaf-width, respectively, implemented in Pinnacle3 treatment planning system were used for this work. Nineteen patients with prostate carcinoma undergoing a radiotherapy treatment were enrolled. Treatment planning with different setup arrangements (7 and 5 beams) were performed for each patient and each machine. Dose volume histograms (DVHs) cut-off points were used in the treatment planning comparison. Results Comparable planning target volume (PTV) coverage was obtained with 7- and 5-beam configuration (both with 5 and 10 mm MLC leaf-width). The comparison of bladder and rectum DVH cut-off points for the 5-beam arrangement shows that 52.6% of the plans optimized with a larger leaf-width did not satisfy at least one of the OARs’ constraints. This percentage is reduced to 10.5% for the smaller leaf-width. If a 7-beam arrangement is used the value of 52.6% decreases to 21.1% while the value of 10.5% remains unchanged. Conclusion MLCs collimators with different widths and number of leaves lead to a comparable prostate treatment planning if a proper adjustment is made of the number of gantry angles. PMID:26549993

  14. Verification of multileaf collimator leaf positions using an electronic portal imaging device.

    PubMed

    Samant, Sanjiv S; Zheng, Wei; Parra, Nestor Andres; Chandler, Jason; Gopal, Arun; Wu, Jian; Jain, Jinesh; Zhu, Yunping; Sontag, Marc

    2002-12-01

    An automated method is presented for determining individual leaf positions of the Siemens dual focus multileaf collimator (MLC) using the Siemens BEAMVIEW(PLUS) electronic portal imaging device (EPID). Leaf positions are computed with an error of 0.6 mm at one standard deviation (sigma) using separate computations of pixel dimensions, image distortion, and radiation center. The pixel dimensions are calculated by superimposing the film image of a graticule with the corresponding EPID image. A spatial correction is used to compensate for the optical distortions of the EPID, reducing the mean distortion from 3.5 pixels (uncorrected) per localized x-ray marker to 2 pixels (1 mm) for a rigid rotation and 1 pixel for a third degree polynomial warp. A correction for a nonuniform dosimetric response across the field of view of the EPID images is not necessary due to the sharp intensity gradients across leaf edges. The radiation center, calculated from the average of the geometric centers of a square field at 0 degrees and 180 degrees collimator angles, is independent of graticule placement error. Its measured location on the EPID image was stable to within 1 pixel based on 3 weeks of repeated extensions/retractions of the EPID. The MLC leaf positions determined from the EPID images agreed to within a pixel of the corresponding values measured using film and ionization chamber. Several edge detection algorithms were tested: contour, Sobel, Roberts, Prewitt, Laplace, morphological, and Canny. These agreed with each other to within < or = 1.2 pixels for the in-air EPID images. Using a test pattern, individual MLC leaves were found to be typically within 1 mm of the corresponding record-and-verify values, with a maximum difference of 1.8 mm, and standard deviations of <0.3 mm in the daily reproducibility. This method presents a fast, automatic, and accurate alternative to using film or a light field for the verification and calibration of the MLC.

  15. Variable Circular Collimator in Robotic Radiosurgery: A Time-Efficient Alternative to a Mini-Multileaf Collimator?

    SciTech Connect

    Water, Steven van de; Hoogeman, Mischa S.; Breedveld, Sebastiaan; Nuyttens, Joost J.M.E.; Schaart, Dennis R.; Heijmen, Ben J.M.

    2011-11-01

    Purpose: Compared with many small circular beams used in CyberKnife treatments, beam's eye view-shaped fields are generally more time-efficient for dose delivery. However, beam's eye view-shaping devices, such as a mini-multileaf collimator (mMLC), are not presently available for CyberKnife, although a variable-aperture collimator (Iris, 12 field diameters; 5-60 mm) is available. We investigated whether the Iris can mimic noncoplanar mMLC treatments using a limited set of principal beam orientations (nodes) to produce time-efficient treatment plans. Methods and Materials: The data from 10 lung cancer patients and the beam-orientation optimization algorithm 'Cycle' were used to generate stereotactic treatment plans (3 x 20 Gy) for a CyberKnife virtually equipped with a mMLC. Typically, 10-16 favorable beam orientations were selected from 117 available robot node positions using beam's eye view-shaped fields with uniform fluence. Second, intensity-modulated Iris plans were generated by inverse optimization of nonisocentric circular candidate beams targeted from the same nodes selected in the mMLC plans. The plans were evaluated using the mean lung dose, lung volume receiving {>=}20 Gy, conformality index, number of nodes, beams, and monitor units, and estimated treatment time. Results: The mMLC plans contained an average of 12 nodes and 11,690 monitor units. For a comparable mean lung dose, the Iris plans contained 12 nodes, 64 beams, and 21,990 monitor units. The estimated fraction duration was 12.2 min (range, 10.8-13.5) for the mMLC plans and 18.4 min (range, 12.9-28.5) for the Iris plans. In contrast to the mMLC plans, the treatment time for the Iris plans increased with an increasing target volume. The Iris plans were, on average, 40% longer than the corresponding mMLC plans for small targets (<80 cm{sup 3}) and {<=}121% longer for larger targets. For a comparable conformality index, similar results were obtained. Conclusion: For stereotactic lung irradiation

  16. Manual multi-leaf collimator for electron beam shaping--a feasibility study.

    PubMed

    Ravindran, B Paul; Singh, I Rabi Raja; Brindha, S; Sathyan, S

    2002-12-21

    In electron beam therapy, lead or low melting point alloy (LMA) sheet cutouts of sufficient thickness are commonly used to shape the beam. In order to avoid making cutouts for each patient, an attempt has been made to develop a manual multi-leaf collimator for electron beams (eMLC). The eMLC has been developed using LMA for a 15 x 15 cm2 applicator. Electron beam characteristics such as depth dose, beam profiles, surface dose, output factors and virtual source position with the eMLC have been studied and compared with those of an applicator electron beam. The interleaf leakage radiation has also been measured with film dosimetry. Depth dose values obtained using the eMLC were found to be identical to those with the applicator for depths larger than Dmax. However, a decrease in the size of the beam penumbra with the eMLC and increase in the values of surface dose, output factors and virtual source position with eMLC were observed. The leakage between the leaves was less than 5% and the leakage between the opposing leaves was 15%, which could be minimized further by careful positioning of the leaves. It is observed that it is feasible to use such a manual eMLC for patients and eliminate the fabrication of cutouts for each patient.

  17. Design and fabrication of the control part of a prototype multileaf collimator system.

    PubMed

    Hashemian, Abdolreza; Toossi, Mohammad Taghi Bahreyni; Nasseri, Shahrokh

    2014-10-01

    Multileaf collimator (MLC) is among the radiation field shaping systems used for conformal radiotherapy and intensity modulation radiation therapy techniques. The MLC system that has been designed and fabricated in this study includes 52 leaves, 52 stepper motors, 2 DC motors, 16 programmable logic controllers (PLCs) and one human machine interface (HMI). This system can be mounted on conventional linear accelerators (linac) as an add-on accessory. The 52 leaves are mounted on two carriages that are moved independently. The leaves sequence acquired from the image processing of computed tomography images is used to arrange leaves. This sequence is saved in a text file. The leaves are arranged by HMI and labVIEW. Using HMI it is possible to test the operation of PLCs and manually enter the numerical values of the leaves edges. An executable file is developed by labVIEW program, which is graphically user interfaced between the operator and the MLC control system. The projected width of each leaf on the isocenter accelerator (usually at 100 cm from the source) is 10 mm. The positioning accuracy of each leaf is approximately 1.4 mm.

  18. Postoperative modified stereotactic radiotherapy using a micro-multileaf collimator in patients with malignant glioma.

    PubMed

    Isaka, Toshihiko; Nishiyama, Kinji; Nakagawa, Hidemitsu; Suzuki, Tsuyoshi; Wada, Kouichi

    2002-06-01

    To achieve local control of malignant glioma, we designed a postoperative stereotactic radiotherapy using a micro-multileaf collimator (micro-MLC). The purpose of this study was to clarify the feasibility of this treatment. The treatment was performed in six patients who met the following eligibility criteria: (1) supratentorial tumor, (2) residual tumor volume < or = 40 cm3, and (3) Karnofsky performance status > or = 70. The three planning target volumes (PTVs), which consisted of restricted PTV (RPTV), intermediate PTV (IPTV), and extended PTV (EPTV), defined as the residual tumor plus a 1 cm, 2 cm, and 3 cm margins, respectively, and total dose delivery of 60-68 Gy, 52-60 Gy, and 44-52 Gy to the isocenters of RPTV, IPTV, and EPTV, respectively, in 4 Gy per fraction at five fractions per week, were established. The beam arrangement and the conformal blockade with a micro-MLC for the optimal treatment plan were designed. The treatment plans showed the high dose conformation to EPTV, the appropriate dose gradients in the three PTVs with the high dose homogeneity to RPTV, and the tolerated dose to critical structures. Following the plans, treatment was performed. The clinical findings more than 12 months after the treatment supported its possible use. We conclude that this treatment is feasible at least in selected patients.

  19. Monte Carlo simulation of a multi-leaf collimator design for telecobalt machine using BEAMnrc code.

    PubMed

    Ayyangar, Komanduri M; Kumar, M Dinesh; Narayan, Pradush; Jesuraj, Fenedit; Raju, M R

    2010-01-01

    This investigation aims to design a practical multi-leaf collimator (MLC) system for the cobalt teletherapy machine and check its radiation properties using the Monte Carlo (MC) method. The cobalt machine was modeled using the BEAMnrc Omega-Beam MC system, which could be freely downloaded from the website of the National Research Council (NRC), Canada. Comparison with standard depth dose data tables and the theoretically modeled beam showed good agreement within 2%. An MLC design with low melting point alloy (LMPA) was tested for leakage properties of leaves. The LMPA leaves with a width of 7 mm and height of 6 cm, with tongue and groove of size 2 mm wide by 4 cm height, produced only 4% extra leakage compared to 10 cm height tungsten leaves. With finite (60)Co source size, the interleaf leakage was insignificant. This analysis helped to design a prototype MLC as an accessory mount on a cobalt machine. The complete details of the simulation process and analysis of results are discussed.

  20. Monte Carlo modeling of a Novalis Tx Varian 6 MV with HD-120 multileaf collimator.

    PubMed

    Vazquez-Quino, Luis Alberto; Massingill, Brian; Shi, Chengyu; Gutierrez, Alonso; Esquivel, Carlos; Eng, Tony; Papanikolaou, Nikos; Stathakis, Sotirios

    2012-09-06

    A Monte Carlo model of the Novalis Tx linear accelerator equipped with high-definition multileaf collimator (HD-120 HD-MLC) was commissioned using ionization chamber measurements in water. All measurements in water were performed using a liquid filled ionization chamber. Film measurements were made using EDR2 film in solid water. Open rectangular fields defined by the jaws or the HD-MLC were used for comparison against measurements. Furthermore, inter- and intraleaf leakage calculated by the Monte Carlo model was compared against film measurements. The statistical uncertainty of the Monte Carlo calculations was less than 1% for all simulations. Results for all regular field sizes show an excellent agreement with commissioning data (percent depth-dose curves and profiles), well within 1% of difference in the relative dose and 1 mm distance to agreement. The computed leakage through HD-MLCs shows good agreement with film measurements. The Monte Carlo model developed in this study accurately represents the new Novalis Tx Varian linac with HD-MLC and can be used for reliable patient dose calculations.

  1. An independent system for real-time dynamic multileaf collimation trajectory verification using EPID

    NASA Astrophysics Data System (ADS)

    Fuangrod, Todsaporn; Woodruff, Henry C.; Rowshanfarzad, Pejman; O'Connor, Daryl J.; Middleton, Richard H.; Greer, Peter B.

    2014-01-01

    A new tool has been developed to verify the trajectory of dynamic multileaf collimators (MLCs) used in advanced radiotherapy techniques using only the information provided by the electronic portal imaging devices (EPID) measured image frames. The prescribed leaf positions are resampled to a higher resolution in a pre-processing stage to improve the verification precision. Measured MLC positions are extracted from the EPID frames using a template matching method. A cosine similarity metric is then applied to synchronise measured and planned leaf positions for comparison. Three additional comparison functions were incorporated to ensure robust synchronisation. The MLC leaf trajectory error detection was simulated for both intensity modulated radiation therapy (IMRT) (prostate) and volumetric modulated arc therapy (VMAT) (head-and-neck) deliveries with anthropomorphic phantoms in the beam. The overall accuracy for MLC positions automatically extracted from EPID image frames was approximately 0.5 mm. The MLC leaf trajectory verification system can detect leaf position errors during IMRT and VMAT with a tolerance of 3.5 mm within 1 s.

  2. Feasibility of replacing patient specific cutouts with a computer-controlled electron multileaf collimator

    NASA Astrophysics Data System (ADS)

    Eldib, Ahmed; Jin, Lihui; Li, Jinsheng; Ma, C.-M. Charlie

    2013-08-01

    A motorized electron multileaf collimator (eMLC) was developed as an add-on device to the Varian linac for delivery of advanced electron beam therapy. It has previously been shown that electron beams collimated by an eMLC have very similar penumbra to those collimated by applicators and cutouts. Thus, manufacturing patient specific cutouts would no longer be necessary, resulting in the reduction of time taken in the cutout fabrication process. Moreover, cutout construction involves handling of toxic materials and exposure to toxic fumes that are usually generated during the process, while the eMLC will be a pollution-free device. However, undulation of the isodose lines is expected due to the finite size of the eMLC. Hence, the provided planned target volume (PTV) shape will not exactly follow the beam's-eye-view of the PTV, but instead will make a stepped approximation to the PTV shape. This may be a problem when the field edge is close to a critical structure. Therefore, in this study the capability of the eMLC to achieve the same clinical outcome as an applicator/cutout combination was investigated based on real patient computed tomographies (CTs). An in-house Monte Carlo based treatment planning system was used for dose calculation using ten patient CTs. For each patient, two plans were generated; one with electron beams collimated using the applicator/cutout combination; and the other plan with beams collimated by the eMLC. Treatment plan quality was compared for each patient based on dose distribution and dose-volume histogram. In order to determine the optimal position of the leaves, the impact of the different leaf positioning strategies was investigated. All plans with both eMLC and cutouts were generated such that 100% of the target volume receives at least 90% of the prescribed dose. Then the percentage difference in dose between both delivery techniques was calculated for all the cases. The difference in the dose received by 10% of the volume of the

  3. Feasibility of replacing patient specific cutouts with a computer-controlled electron multileaf collimator.

    PubMed

    Eldib, Ahmed; Jin, Lihui; Li, Jinsheng; Ma, C-M Charlie

    2013-08-21

    A motorized electron multileaf collimator (eMLC) was developed as an add-on device to the Varian linac for delivery of advanced electron beam therapy. It has previously been shown that electron beams collimated by an eMLC have very similar penumbra to those collimated by applicators and cutouts. Thus, manufacturing patient specific cutouts would no longer be necessary, resulting in the reduction of time taken in the cutout fabrication process. Moreover, cutout construction involves handling of toxic materials and exposure to toxic fumes that are usually generated during the process, while the eMLC will be a pollution-free device. However, undulation of the isodose lines is expected due to the finite size of the eMLC. Hence, the provided planned target volume (PTV) shape will not exactly follow the beam's-eye-view of the PTV, but instead will make a stepped approximation to the PTV shape. This may be a problem when the field edge is close to a critical structure. Therefore, in this study the capability of the eMLC to achieve the same clinical outcome as an applicator/cutout combination was investigated based on real patient computed tomographies (CTs). An in-house Monte Carlo based treatment planning system was used for dose calculation using ten patient CTs. For each patient, two plans were generated; one with electron beams collimated using the applicator/cutout combination; and the other plan with beams collimated by the eMLC. Treatment plan quality was compared for each patient based on dose distribution and dose-volume histogram. In order to determine the optimal position of the leaves, the impact of the different leaf positioning strategies was investigated. All plans with both eMLC and cutouts were generated such that 100% of the target volume receives at least 90% of the prescribed dose. Then the percentage difference in dose between both delivery techniques was calculated for all the cases. The difference in the dose received by 10% of the volume of the

  4. Enhancement of electron-beam surface dose with an electron multi-leaf collimator (eMLC): a feasibility study.

    PubMed

    Vatanen, T; Traneus, E; Lahtinen, T

    2009-04-21

    Use of a water-equivalent bolus in electron-beam radiotherapy is sometimes impractical and non-hygienic. Therefore, the feasibility of applying adjacent narrow beams for producing high surface dose electron beams without a bolus was investigated. Depth dose curves and profiles in water were calculated and measured for 6 and 9 MeV electron-beam segments (width 0.3-1.5 cm, length 10 cm) for source-to-surface distances (SSD) 102 and 105 cm. Segment shaping was performed with an add-on electron multi-leaf collimator prototype attached to the Varian 2100 C/D linac. Dose calculations were performed with the Voxel Monte Carlo++ algorithm. Resulting dose distributions in typical clinical cases were compared with the bolus technique. With a composite segmental field with 1.0 cm wide segments the surface dose was over 90% of the depth dose maximum for both energies. The build-up area practically disappeared with a 0.5 cm wide single beam. This led to decrease in the therapeutic range for composite fields with segment widths smaller than 1.0 cm. The new technique yielded similar surface doses as the bolus technique. The photon contamination was 4% with a 9 x 10 cm(2) field (1.0 cm wide segments) compared to 1% for the respective open field with 9 MeV with a bolus. The calculated dose agreed within 2 mm and 3% of the measured dose in 93.7% and 85.2% of the voxels. Adjacent narrow eMLC beams with a 1.0 cm width are suitable to produce electron fields with high surface dose. Despite a slight nonuniformity in the surface profiles in the lateral part of the field at SSD 102 cm, surface dose and target coverage are comparable with the bolus technique.

  5. Beam modeling and VMAT performance with the Agility 160-leaf multileaf collimator.

    PubMed

    Bedford, James L; Thomas, Michael D R; Smyth, Gregory

    2013-05-06

    The Agility multileaf collimator (Elekta AB, Stockholm, Sweden) has 160 leaves of projected width 0.5 cm at the isocenter, with maximum leaf speed 3.5 cms-1. These characteristics promise to facilitate fast and accurate delivery of radiotherapy, particularly volumetric-modulated arc therapy (VMAT). The aim of this study is therefore to create a beam model for the Pinnacle3 treatment planning system (Philips Radiation Oncology Systems, Fitchburg, WI), and to use this beam model to explore the performance of the Agility MLC in delivery of VMAT. A 6 MV beam model was created and verified by measuring doses under irregularly shaped fields. VMAT treatment plans for five typical head-and-neck patients were created using the beam model and delivered using both binned and continuously variable dose rate (CVDR). Results were compared with those for an MLCi unit without CVDR. The beam model has similar parameters to those of an MLCi model, with interleaf leakage of only 0.2%. The verification of irregular fields shows a mean agreement between measured and planned dose of 1.3% (planned dose higher). The Agility VMAT head-and-neck plans show equivalent plan quality and delivery accuracy to those for an MLCi unit, with 95% of verification measurements within 3% and 3 mm of planned dose. Mean delivery time is 133 s with the Agility head and CVDR, 171 s without CVDR, and 282 s with an MLCi unit. Pinnacle3 has therefore been shown to model the Agility MLC accurately, and to provide accurate VMAT treatment plans which can be delivered significantly faster with Agility than with an MLCi.

  6. SU-E-T-178: Clinical Feasibility of Multi-Leaf Collimator Based Dynamic Wedge

    SciTech Connect

    Jeong, C; Kwak, J; Ahn, S; Kim, J; Park, J; Yoon, S; Cho, B

    2015-06-15

    Purpose: A multi-leaf collimator (MLC) based dynamic wedge (MDW), which provide similar dose profile of physical wedge (PW) along x-jaw direction while significant monitor unit (MU) reduction, was developed and investigated for clinical use. Methods: A novel technique was used to create the wedge profile using MLC. A modification was applied to the DICOM-RT format file of the plan made with the PW to replace PW with MDW. The Varian enhanced dynamic wedge profile was used to produce MLC sequence, while the MU of the wedged field was recalculated using PW factor and fluence map. The profiles for all possible MDWs to substitute PWs were verified in 6/15 MV x-ray irradiations. New plans with MDWs were compared with the original plans in 5 rectal, 5 RT breast and 5 liver cases. Results: The wedge profile of the MDW fields were well matched with those of PWs inside the fields while less scatter than PW out of the fields. For plan comparisons of the clinical cases no significant dose discrepancy was observed between MDW plan and PW’s with the dose volume histograms. The maximum and mean doses in PTVs are agreed within 1.0%. The Result of OARs of MDW plans are slightly improved in the maximum doses (3.22 ∼ 150.4 cGy) and the mean doses (17.18 ∼ 85.52 cGy) on average for all cases while the prescribed doses are 45 Gy for rectal cases, 40 or 45 Gy for liver cases and 50 Gy for breast cases. The MUs of the fields which replace PW with MDW are reduced to 68% of those of PW. Conclusion: We developed a novel dynamic wedge technique with MLC that shows clinical advantage compared to PW.

  7. Mantle fields in the era of dynamic multileaf collimation: Field shaping and electronic tissue compensation

    SciTech Connect

    Davis, Quillin G.; Paulino, Arnold C. . E-mail: apaulino@tmh.tmc.edu; Miller, Robin M.S.; Ting, Joseph Y.

    2006-10-01

    Mantle field radiotherapy for Hodgkin's disease is complicated by significant dose gradient (up to 10-20%) across the large fields required. Many different strategies of tissue compensation have been investigated, including custom physical compensators to provide better dose distributions. We present a method using dynamic multileaf collimator (dMLC) fluence modulation to simultaneously shape the treatment field and give homogeneous dose at depth throughout the classic mantle field. Five patients were treated for early-stage Hodgkin's disease with a conventional anterior-posterior-posterior-anterior (AP-PA) mantle field. The patients were planned using the Varian Eclipse treatment planning system, version 6.1.3, and treated on a Varian 2300CD. An AP-PA dynamic MLC beam-shaped and dose-compensated plan was created for each, and compared with the conventional blocked plan. Nine dose points were calculated at midplane in each plan. Chamber measurements were taken to confirm accurate dMLC delivery of the planned doses. The mean dose per fraction, relative to a central axis dose of 1.8 Gy, was increased in the conventional plans compared with the dMLC plans in the right (R) neck, left (L) neck, R supraclavicular, L supraclavicular, and L axillary points. The mediastinum tended to be underdosed relative to central axis, with the mid-mediastinal and lower mediastinal points showing improved coverage with the dMLC plans. Measurements showed excellent agreement between planned doses and delivered doses, with less than 2% in-field variation. Dynamic MLC fluence modulation was used to effectively deliver a mantle field that is both shape- and electronically-dose-compensated with sliding window MLC. Homogeneity was significantly improved throughout the treatment field, and measurements confirmed accurate dose delivery using this technique.

  8. Electromagnetic-Guided Dynamic Multileaf Collimator Tracking Enables Motion Management for Intensity-Modulated Arc Therapy

    SciTech Connect

    Keall, Paul J.; Sawant, Amit; Cho, Byungchul; Ruan, Dan; Wu Junqing; Poulsen, Per; Petersen, Jay; Newell, Laurence J.; Cattell, Herbert; Korreman, Stine

    2011-01-01

    Purpose: Intensity-modulated arc therapy (IMAT) is attractive because of high-dose conformality and efficient delivery. However, managing intrafraction motion is challenging for IMAT. The purpose of this research was to develop and investigate electromagnetically guided dynamic multileaf collimator (DMLC) tracking as an enabling technology to treat moving targets during IMAT. Methods and Materials: A real-time three-dimensional DMLC-based target tracking system was developed and integrated with a linear accelerator. The DMLC tracking software inputs a real-time electromagnetically measured target position and the IMAT plan, and dynamically creates new leaf positions directed at the moving target. Low- and high-modulation IMAT plans were created for lung and prostate cancer cases. The IMAT plans were delivered to a three-axis motion platform programmed with measured patient motion. Dosimetric measurements were acquired by placing an ion chamber array on the moving platform. Measurements were acquired with tracking, without tracking (current clinical practice), and with the phantom in a static position (reference). Analysis of dose distribution differences from the static reference used a {gamma}-test. Results: On average, 1.6% of dose points for the lung plans and 1.2% of points for the prostate plans failed the 3-mm/3% {gamma}-test with tracking; without tracking, 34% and 14% (respectively) of points failed the {gamma}-test. The delivery time was the same with and without tracking. Conclusions: Electromagnetic-guided DMLC target tracking with IMAT has been investigated for the first time. Dose distributions to moving targets with DMLC tracking were significantly superior to those without tracking. There was no loss of treatment efficiency with DMLC tracking.

  9. A machine learning approach to the accurate prediction of multi-leaf collimator positional errors

    NASA Astrophysics Data System (ADS)

    Carlson, Joel N. K.; Park, Jong Min; Park, So-Yeon; In Park, Jong; Choi, Yunseok; Ye, Sung-Joon

    2016-03-01

    Discrepancies between planned and delivered movements of multi-leaf collimators (MLCs) are an important source of errors in dose distributions during radiotherapy. In this work we used machine learning techniques to train models to predict these discrepancies, assessed the accuracy of the model predictions, and examined the impact these errors have on quality assurance (QA) procedures and dosimetry. Predictive leaf motion parameters for the models were calculated from the plan files, such as leaf position and velocity, whether the leaf was moving towards or away from the isocenter of the MLC, and many others. Differences in positions between synchronized DICOM-RT planning files and DynaLog files reported during QA delivery were used as a target response for training of the models. The final model is capable of predicting MLC positions during delivery to a high degree of accuracy. For moving MLC leaves, predicted positions were shown to be significantly closer to delivered positions than were planned positions. By incorporating predicted positions into dose calculations in the TPS, increases were shown in gamma passing rates against measured dose distributions recorded during QA delivery. For instance, head and neck plans with 1%/2 mm gamma criteria had an average increase in passing rate of 4.17% (SD  =  1.54%). This indicates that the inclusion of predictions during dose calculation leads to a more realistic representation of plan delivery. To assess impact on the patient, dose volumetric histograms (DVH) using delivered positions were calculated for comparison with planned and predicted DVHs. In all cases, predicted dose volumetric parameters were in closer agreement to the delivered parameters than were the planned parameters, particularly for organs at risk on the periphery of the treatment area. By incorporating the predicted positions into the TPS, the treatment planner is given a more realistic view of the dose distribution as it will truly be

  10. The impact of a high-definition multileaf collimator for spine SBRT.

    PubMed

    Younge, Kelly C; Kuchta, John R; Mikell, Justin K; Rosen, Benjamin; Bredfeldt, Jeremy S; Matuszak, Martha M

    2017-09-27

    Advanced radiotherapy delivery systems designed for high-dose, high-precision treatments often come equipped with high-definition multi-leaf collimators (HD-MLC) aimed at more finely shaping radiation dose to the target. In this work, we study the effect of a high definition MLC on spine stereotactic body radiation therapy (SBRT) treatment plan quality and plan deliverability. Seventeen spine SBRT cases were planned with VMAT using a standard definition MLC (M120), HD-MLC, and HD-MLC with an added objective to reduce monitor units (MU). M120 plans were converted into plans deliverable on an HD-MLC using in-house software. Plan quality and plan deliverability as measured by portal dosimetry were compared among the three types of plans. Only minor differences were noted in plan quality between the M120 and HD-MLC plans. Plans generated with the HD-MLC tended to have better spinal cord sparing (3% reduction in maximum cord dose). HD-MLC plans on average had 12% more MU and 55% greater modulation complexity as defined by an in-house metric. HD-MLC plans also had significantly degraded deliverability. Of the VMAT arcs measured, 94% had lower gamma passing metrics when using the HD-MLC. Modest improvements in plan quality were noted when switching from M120 to HD-MLC at the expense of significantly less accurate deliverability in some cases. © 2017 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.

  11. Determining leaf trajectories for dynamic multileaf collimators with consideration of marker visibility: an algorithm study.

    PubMed

    Zhao, Bo; Dai, Jianrong

    2014-09-01

    The purpose of this study was to develop a leaf-setting algorithm for Dynamic Multileaf Collimator-Intensity-Modulated Radiation Therapy (DMLC-IMRT) for optimal marker visibility. Here, a leaf-setting algorithm (called a Delta algorithm) was developed with the objective of maximizing marker visibility so as to improve the tracking effectiveness of fiducial markers during treatment delivery. The initial leaf trajectories were generated using a typical leaf-setting algorithm, then the leaf trajectories were adjusted by Delta algorithm operations (analytical computations and a series of matrix calculations) to achieve the optimal solution. The performance of the Delta algorithm was evaluated with six test fields (with randomly generated intensity profiles) and 15 clinical fields from IMRT plans of three prostate cancer patients. Compared with the initial solution, the Delta algorithm kept the total delivered intensities (TDIs) constant (without increasing the beam delivery time), but improved marker visibility (the percentage ratio of marker visibility time to beam delivery time). For the artificial fields (with three markers), marker visibility increased from 68.00-72.00% for a small field (5 × 5), from 38.46-43.59% for a medium field (10 × 10), and from 28.57-37.14% for a large field (20 × 20). For the 15 clinical fields, marker visibility increased 6-30% for eight fields and > 50% for two fields but did not change for five fields. A Delta algorithm was proposed to maximize marker visibility for DMLC-IMRT without increasing beam delivery time, and this will provide theoretical fundamentals for future studies of 4D DMLC tracking radiotherapy. © The Author 2014. Published by Oxford University Press on behalf of The Japan Radiation Research Society and Japanese Society for Radiation Oncology.

  12. Characteristics and performance of the first commercial multileaf collimator for a robotic radiosurgery system

    SciTech Connect

    Fürweger, Christoph; Prins, Paulette; Coskan, Harun; Heijmen, Ben J. M.

    2016-05-15

    Purpose: The “InCise™ multileaf-collimator (MLC)” is the first commercial MLC to be mounted on a robotic SRS/SBRT platform (CyberKnife). The authors assessed characteristics and performance of this novel device in a preclinical five months test period. Methods: Commissioning beam data were acquired with unshielded diodes. EBT3 radiochromic films were employed for measurement of transmission, leaf/bank position accuracy (garden fence) before and after exercising the MLC, for end-to-end testing and further characterization of the beam. The robot workspace with MLC was assessed analytically by transformation to an Euler geometry (“plane,” “gantry,” and “collimator” angles) and by measuring pointing accuracy at each node. Stability over time was evaluated in picket fence and adapted Winston–Lutz tests (AQA). Results: Beam penumbrae (80%–20%, with 100% = 2 × dose at inflection point for field sizes ≥ 50 × 50 mm{sup 2}) were 2.2–3.7 mm for square fields in reference condition (source-axis-distance 800 mm, depth 15 mm) and depended on field size and off-axis position. Transmission and leakage did not exceed 0.5%. Accessible clinical workspace with MLC covered non-coplanar gantry angles of [−113°; +112°] and collimator angles of [−100°; +107°], with an average robot pointing accuracy of 0.12 ± 0.09 mm. For vertical beams, garden fence tests exhibited an average leaf positioning error of ≤0.2 mm, which increased by 0.25 and 0.30 mm (banks X1 and X2) with leaves traveling parallel to gravity. After execution of a leaf motion stress routine, garden fence tests showed slightly increased jaggedness and allowed to identify one malfunctioning leaf motor. Total system accuracy with MLC was 0.38 ± 0.05 mm in nine end-to-end tests. Picket fence and AQA tests displayed stable results over the test period. Conclusions: The InCise™ MLC for CyberKnife showed high accuracy and adequate characteristics for SRS/SBRT applications. MLC performance

  13. Monte Carlo simulation based study of a proposed multileaf collimator for a telecobalt machine

    SciTech Connect

    Sahani, G.; Dash Sharma, P. K.; Hussain, S. A.; Dutt Sharma, Sunil; Sharma, D. N.

    2013-02-15

    Purpose: The objective of the present work was to propose a design of a secondary multileaf collimator (MLC) for a telecobalt machine and optimize its design features through Monte Carlo simulation. Methods: The proposed MLC design consists of 72 leaves (36 leaf pairs) with additional jaws perpendicular to leaf motion having the capability of shaping a maximum square field size of 35 Multiplication-Sign 35 cm{sup 2}. The projected widths at isocenter of each of the central 34 leaf pairs and 2 peripheral leaf pairs are 10 and 5 mm, respectively. The ends of the leaves and the x-jaws were optimized to obtain acceptable values of dosimetric and leakage parameters. Monte Carlo N-Particle code was used for generating beam profiles and depth dose curves and estimating the leakage radiation through the MLC. A water phantom of dimension 50 Multiplication-Sign 50 Multiplication-Sign 40 cm{sup 3} with an array of voxels (4 Multiplication-Sign 0.3 Multiplication-Sign 0.6 cm{sup 3}= 0.72 cm{sup 3}) was used for the study of dosimetric and leakage characteristics of the MLC. Output files generated for beam profiles were exported to the PTW radiation field analyzer software through locally developed software for analysis of beam profiles in order to evaluate radiation field width, beam flatness, symmetry, and beam penumbra. Results: The optimized version of the MLC can define radiation fields of up to 35 Multiplication-Sign 35 cm{sup 2} within the prescribed tolerance values of 2 mm. The flatness and symmetry were found to be well within the acceptable tolerance value of 3%. The penumbra for a 10 Multiplication-Sign 10 cm{sup 2} field size is 10.7 mm which is less than the generally acceptable value of 12 mm for a telecobalt machine. The maximum and average radiation leakage through the MLC were found to be 0.74% and 0.41% which are well below the International Electrotechnical Commission recommended tolerance values of 2% and 0.75%, respectively. The maximum leakage through the

  14. Collimator-free photon tomography

    DOEpatents

    Dilmanian, F. Avraham; Barbour, Randall L.

    1998-10-06

    A method of uncollimated single photon emission computed tomography includes administering a radioisotope to a patient for producing gamma ray photons from a source inside the patient. Emissivity of the photons is measured externally of the patient with an uncollimated gamma camera at a plurality of measurement positions surrounding the patient for obtaining corresponding energy spectrums thereat. Photon emissivity at the plurality of measurement positions is predicted using an initial prediction of an image of the source. The predicted and measured photon emissivities are compared to obtain differences therebetween. Prediction and comparison is iterated by updating the image prediction until the differences are below a threshold for obtaining a final prediction of the source image.

  15. Collimator-free photon tomography

    DOEpatents

    Dilmanian, F.A.; Barbour, R.L.

    1998-10-06

    A method of uncollimated single photon emission computed tomography includes administering a radioisotope to a patient for producing gamma ray photons from a source inside the patient. Emissivity of the photons is measured externally of the patient with an uncollimated gamma camera at a plurality of measurement positions surrounding the patient for obtaining corresponding energy spectrums thereat. Photon emissivity at the plurality of measurement positions is predicted using an initial prediction of an image of the source. The predicted and measured photon emissivities are compared to obtain differences therebetween. Prediction and comparison is iterated by updating the image prediction until the differences are below a threshold for obtaining a final prediction of the source image. 6 figs.

  16. Physical and dosimetric characteristic of high-definition multileaf collimator (HDMLC) for SRS and IMRT.

    PubMed

    Sharma, Dayananda Shamurailatpam; Dongre, Prabhakar M; Mhatre, Vaibav; Heigrujam, Malhotra

    2011-04-14

    Physical and dosimetric characteristics of HDMLC were studied for SRS6, 6, and 10 MV X-rays from Novalis Tx. This in-built tertiary collimator consists of 60 pairs (32 × 0.25 cm; 26 × 0.5 cm and 2 × 0.7 cm) of leaves. Properties of HDMLC studied included alignment, readout and radiation field congruence, radiation penumbra, accuracy and reproducibility of leaf position and gap width, static and dynamic leaf shift, tongue-and-groove effect, leaf transmission and leakage, leaf travel speed, and delivery of dynamic conformal arc and IMRT. All tests were performed using a calibrated ionization chamber, film dosimetry and DynaLog file analysis. Alignment of leaves with isocenter plane was better than 0.03 cm at all gantry and collimator positions. The congruence of HDMLC readout and radiation field agreed to within ± 0.03 cm for filed sizes ranging from 1 × 1 to 20 × 20 cm2. Mean 80% to 20% penumbra width parallel (perpendicular) to leaf motion was 0.24 ± 0.05 (0.21 ± 0.02) cm, 0.37 ± 0.12 (0.29 ± 0.07) cm, and 0.51 ± 0.13 (0.43± 0.07) cm for SRS6, 6, and 10 MV X-rays, respectively. Circular field penumbra was comparable to corresponding square field. Average penumbra of 1 × 20 cm2 field was effectively constant over off-axis positions of up to 12 cm with mean value of 0.16 (± 0.01) cm at 1.5 cm depth and 0.38 (± 0.04) cm at 10 cm depth. Minimum and maximum effective penumbra along the straight diagonal edge of irregular fields increased from 0.3 and 0.32 cm at 70° steep angle to 0.35 and 0.56 cm at 20° steep angle. Modified Picket Fence test showed average FWHM of 0.18 cm and peak-to-peak distance of 1.99 cm for 0.1 cm band and 2 cm interband separation. Dynamic multileaf collimation (DMLC) output factor remained within ± 1% for 6 MV and ± 0.5% for 10 MV X-rays at all gantry positions, and was reproducible within ± 0.5% over a period of 14 months. The static leaf shift was 0.03 cm for all energies, while dynamic leaf shift was 0.044 cm for 10 MV and

  17. Efficient beaming of self-collimated light from photonic crystals.

    PubMed

    Park, Jong-Moon; Lee, Sun-Goo; Park, Hae Yong; Kim, Jae-Eun

    2008-12-08

    We propose a novel structure for achieving highly efficient beaming of self-collimated light from two-dimensional photonic crystals. The finite-difference time-domain simulations show that both enhanced transmission and highly directional emission of self-collimated beams from photonic crystals are achieved by using the bending and splitting of self-collimated beams in photonic crystals, and also by introducing an antireflection coating-like photonic crystal collimator to the exit surface of the structure. This structure is potentially important for highly efficient coupling of self-collimated beams from photonic crystals into conventional optical fibers and photonic crystal waveguides.

  18. Photonic crystal self-collimation sensor.

    PubMed

    Wang, Yufei; Wang, Hailing; Xue, Qikun; Zheng, Wanhua

    2012-05-21

    A novel refractive index sensor based on the two dimensional photonic crystal folded Michelson interferometer employing the self-collimation effect is proposed and its performances are theoretically investigated. Two sensing areas are included in the sensor. Simulation results indicate the branch area is suitable for the small index variety range and fine detection, whereas the reflector area prone to the large index change range and coarse detection. Because of no defect waveguides and no crosstalk of signal, the sensor is desirable to perform monolithic integrated, low-cost, label-free real-time parallel sensing. In addition, a flexible design of self-collimation sensors array is demonstrated.

  19. Super-collimation by axisymmetric photonic crystals

    SciTech Connect

    Purlys, V.; Gailevičius, D.; Peckus, M.; Gadonas, R.; Maigyte, L.; Staliunas, K.

    2014-06-02

    We propose and experimentally show the mechanism of beam super-collimation by axisymmetric photonic crystals, specifically by periodic (in propagation direction) structure of layers of concentric rings. The physical mechanism behind the effect is an inverse scattering cascade of diffracted wave components back into on- and near-axis angular field components, resulting in substantial enhancement of intensity of these components. We explore the super-collimation by numerical calculations and prove it experimentally. We demonstrate experimentally the axial field enhancement up to 7 times in terms of field intensity.

  20. 6 MV dosimetric characterization of the 160 MLC, the new Siemens multileaf collimator.

    PubMed

    Tacke, Martin B; Nill, Simeon; Häring, Peter; Oelfke, Uwe

    2008-05-01

    New technical developments constantly aim at improving the outcome of radiation therapy. With the use of a computer-controlled multileaf collimator (MLC), the quality of the treatment and the efficiency in patient throughput is significantly increased. New MLC designs aim to further enhance the advantages. In this article, we present the first detailed experimental investigation of the new 160 MLC, Siemens Medical Solutions. The assessment included the experimental investigation of typical MLC characteristics such as leakage, tongue-and-groove effect, penumbra, leaf speed, and leaf positioning accuracy with a 6 MV treatment beam. The leakage is remarkably low with an average of 0.37% due to a new design principle of slightly tilted leaves instead of the common tongue-and-groove design. But due to the tilt, the triangular tongue-and-groove effect occurs. Its magnitude of approximately 19% is similar to the dose defect measured for MLCs with the common tongue-and-groove design. The average longitudinal penumbra measured at depth d(max) = 15 mm with standard 100 x 100 mm2 fields is 4.1 +/- 0.5 mm for the central range and increases to 4.9 +/- 1.3 mm for the entire field range of 400 x 400 mm2. The increase is partly due to the single-focusing design and the large distance between the MLC and the isocenter enabling a large patient clearance. Regarding the leaf speed, different velocity tests were performed. The positions of the moving leaves were continuously recorded with the kilovoltage-imaging panel. The maximum leaf velocities measured were 42.9 +/- 0.6 mm/s. In addition, several typical intensity-modulated radiation therapy treatments were performed and the delivery times compared to the Siemens OPTIFOCUS MLC. An average decrease of 11% in delivery time was observed. The experimental results presented in this article indicate that the dosimetric characteristics of the 160 MLC are capable of improving the quality of dose delivery with respect to precision and dose

  1. Planning 4D intensity-modulated arc therapy for tumor tracking with a multileaf collimator

    NASA Astrophysics Data System (ADS)

    Niu, Ying; Betzel, Gregory T.; Yang, Xiaocheng; Gui, Minzhi; Parke, William C.; Yi, Byongyong; Yu, Cedric X.

    2017-02-01

    This study introduces a practical four-dimensional (4D) planning scheme of IMAT using 4D computed tomography (4D CT) for planning tumor tracking with dynamic multileaf beam collimation. We assume that patients can breathe regularly, i.e. the same way as during 4D CT with an unchanged period and amplitude, and that the start of 4D-IMAT delivery can be synchronized with a designated respiratory phase. Each control point of the IMAT-delivery process can be associated with an image set of 4D CT at a specified respiratory phase. Target is contoured at each respiratory phase without a motion-induced margin. A 3D-IMAT plan is first optimized on a reference-phase image set of 4D CT. Then, based on the projections of the planning target volume in the beam’s eye view at different respiratory phases, a 4D-IMAT plan is generated by transforming the segments of the optimized 3D plan by using a direct aperture deformation method. Compensation for both translational and deformable tumor motion is accomplished, and the smooth delivery of the transformed plan is ensured by forcing connectivity between adjacent angles (control points). It is envisioned that the resultant plans can be delivered accurately using the dose rate regulated tracking method which handles breathing irregularities (Yi et al 2008 Med. Phys. 35 3955–62).This planning process is straightforward and only adds a small step to current clinical 3D planning practice. Our 4D planning scheme was tested on three cases to evaluate dosimetric benefits. The created 4D-IMAT plans showed similar dose distributions as compared with the 3D-IMAT plans on a single static phase, indicating that our method is capable of eliminating the dosimetric effects of breathing induced target motion. Compared to the 3D-IMAT plans with large treatment margins encompassing respiratory motion, our 4D-IMAT plans reduced radiation doses to surrounding normal organs and tissues.

  2. Markerless EPID image guided dynamic multi-leaf collimator tracking for lung tumors

    NASA Astrophysics Data System (ADS)

    Rottmann, J.; Keall, P.; Berbeco, R.

    2013-06-01

    Compensation of target motion during the delivery of radiotherapy has the potential to improve treatment accuracy, dose conformity and sparing of healthy tissue. We implement an online image guided therapy system based on soft tissue localization (STiL) of the target from electronic portal images and treatment aperture adaptation with a dynamic multi-leaf collimator (DMLC). The treatment aperture is moved synchronously and in real time with the tumor during the entire breathing cycle. The system is implemented and tested on a Varian TX clinical linear accelerator featuring an AS-1000 electronic portal imaging device (EPID) acquiring images at a frame rate of 12.86 Hz throughout the treatment. A position update cycle for the treatment aperture consists of four steps: in the first step at time t = t0 a frame is grabbed, in the second step the frame is processed with the STiL algorithm to get the tumor position at t = t0, in a third step the tumor position at t = ti + δt is predicted to overcome system latencies and in the fourth step, the DMLC control software calculates the required leaf motions and applies them at time t = ti + δt. The prediction model is trained before the start of the treatment with data representing the tumor motion. We analyze the system latency with a dynamic chest phantom (4D motion phantom, Washington University). We estimate the average planar position deviation between target and treatment aperture in a clinical setting by driving the phantom with several lung tumor trajectories (recorded from fiducial tracking during radiotherapy delivery to the lung). DMLC tracking for lung stereotactic body radiation therapy without fiducial markers was successfully demonstrated. The inherent system latency is found to be δt = (230 ± 11) ms for a MV portal image acquisition frame rate of 12.86 Hz. The root mean square deviation between tumor and aperture position is smaller than 1 mm. We demonstrate the feasibility of real-time markerless DMLC

  3. Markerless EPID image guided dynamic multi-leaf collimator tracking for lung tumors

    PubMed Central

    Rottmann, J.; Keall, P.; Berbeco, R.

    2014-01-01

    Compensation of target motion during the delivery of radiotherapy has the potential to improve treatment accuracy, dose conformity and sparing of healthy tissue. We implement an online image guided therapy system based on soft tissue localization (STiL) of the target from electronic portal images and treatment aperture adaptation with a dynamic multi-leaf collimator (DMLC). The treatment aperture is moved synchronously and in real-time with the tumor during the entire breathing cycle. The system is implemented and tested on a Varian TX clinical linear accelerator featuring an AS-1000 electronic portal imaging device (EPID) acquiring images at a frame rate of 12.86 Hz throughout the treatment. A position update cycle for the treatment aperture consists of 4 steps: in the first step at time t = t0 a frame is grabbed, in the second step the frame is processed with the STiL algorithm to get the tumor position at t = t0, in a third step the tumor position at t = t + δt is predicted to overcome system latencies and in the fourth step, the DMLC control software calculates the required leaf motions and applies them at time t = t + δt. The prediction model is trained before the start of the treatment with data representing the tumor motion. We analyze the system latency with a dynamic chest phantom (4D motion phantom, Washington University). We estimate the average planar position deviation between target and treatment aperture in a clinical setting by driving the phantom with several lung tumor trajectories (recorded from fiducial tracking during radiotherapy delivery to the lung). DMLC tracking for lung SBRT without fiducial markers was successfully demonstrated. The inherent system latency is found to be δt = (230 ± 11) ms for a MV portal image acquisition frame rate of 12.86 Hz. The root mean square deviation between tumor and aperture position is smaller than 1 mm. We demonstrate the feasibility of real-time markerless DMLC tracking with a standard LINAC

  4. Dosimetric comparison between 3DCRT and IMRT using different multileaf collimators in the treatment of brain tumors.

    PubMed

    Ding, Meisong; Newman, Francis; Chen, Changhu; Stuhr, Kelly; Gaspar, Laurie E

    2009-01-01

    We investigated the differences between 3-dimensional conformal radiotherapy (3DCRT) and intensity modulated radiotherapy (IMRT), and the impact of collimator leaf-width on IMRT plans for the treatment of nonspherical brain tumors. Eight patients treated by 3DCRT with Novalis were selected. We developed 3 IMRT plans with different multileaf collimators (Novalis m3, Varian MLC-120, and Varian MLC-80) with the same treatment margins, number of beams, and gantry positions as in the 3DCRT treatment plans. Treatment planning utilized the BrainLAB treatment planning system. For each patient, the dose constraints and optimization parameters remained identical for all plans. The heterogeneity index, the percentage target coverage, critical structures, and normal tissue volumes receiving 50% of the prescription dose were calculated to compare the dosimetric difference. Equivalent uniform dose (EUD) and tumor control probability (TCP) were also introduced to evaluate the radiobiological effect for different plans. We found that IMRT significantly improved the target dose homogeneity compared to the 3DCRT. However, IMRT showed the same radiobiological effect as 3DCRT. For the brain tumors adjacent to (or partially overlapping with) critical structures, IMRT dramatically spared the volume of the critical structures to be irradiated. In IMRT plans, the smaller collimator leaf width could reduce the volume of critical structures irradiated to the 50% level for those partially overlapping with the brain tumors. For relatively large and spherical brain tumors, the smaller collimator leaf widths give no significant benefit.

  5. SU-E-T-411: Dosimetric Comparison Between Two Multileaf Collimator Systems for Stereotactic Radiosurgery and Radiotherapy.

    PubMed

    Asnaashari, K; Chow, J; Heydarian, M

    2012-06-01

    This aim of this study is to compare the dosimetric parameters of two multileaf collimator (MLC) systems: (1) the beam modulator (BM), which is the MLC commercial name for Elekta 'Synergy S' linear accelerator; and (2) Radionics micro-MLC (MMLC). Dosimetric parameters of percentage depth dose (PDD), in-plane and cross-plane beam profile, penumbra, MLC leakage and transmission for a 6 MV photon beam with different field sizes and depths were measured using ionization chamber, film, solid water phantom and water tank. At the same time, the BM and MMLC were modeled using the BEAMnrc code and the above dosimetric parameters were calculated using Monte Carlo simulations. Energy fluence spectra for the two MLC were determined using the BEAMnrc and BEAMDP. We found that dosimetric parameters (PDD, beam profile, energy fluence spectra, leakage and transmission) of the two MLC were similar, except for penumbra. The leaf-side and leaf-end 20%-80% penumbras at 10 cm depth for a 10×10 cm(2) field were 4.8 and 5.1 mm for the MMLC and 5.3 mm and 6.3 mm for the BM, respectively. The maximum percentage of the leakage for the BM and MMLC are 1.3% and 1.2%, while the average percentage of leakage for the BM and MMLC are 0.9% and 1%. Based on their dosimetric characteristics for stereotactic radiosurgery and radiotherapy, it can be concluded that both the BM and MMLC can be used effectively, though the latter showed slightly sharper dose penumbra especially in the leaf-end direction. However, the BM has the advantages of producing considerably larger field at isocenter and having a greater isocenter clearance compared to the MMLC. The dosimetric data in this study should help radiotherapy staff to appreciate dependence of dosimetry on the MLC design and configuration for stereotactic radiosurgery and radiotherapy. Actual or potential conflicts of interest do not exist. © 2012 American Association of Physicists in Medicine.

  6. Multileaf collimator performance monitoring and improvement using semiautomated quality control testing and statistical process control

    SciTech Connect

    Létourneau, Daniel McNiven, Andrea; Keller, Harald; Wang, An; Amin, Md Nurul; Pearce, Jim; Norrlinger, Bernhard; Jaffray, David A.

    2014-12-15

    Purpose: High-quality radiation therapy using highly conformal dose distributions and image-guided techniques requires optimum machine delivery performance. In this work, a monitoring system for multileaf collimator (MLC) performance, integrating semiautomated MLC quality control (QC) tests and statistical process control tools, was developed. The MLC performance monitoring system was used for almost a year on two commercially available MLC models. Control charts were used to establish MLC performance and assess test frequency required to achieve a given level of performance. MLC-related interlocks and servicing events were recorded during the monitoring period and were investigated as indicators of MLC performance variations. Methods: The QC test developed as part of the MLC performance monitoring system uses 2D megavoltage images (acquired using an electronic portal imaging device) of 23 fields to determine the location of the leaves with respect to the radiation isocenter. The precision of the MLC performance monitoring QC test and the MLC itself was assessed by detecting the MLC leaf positions on 127 megavoltage images of a static field. After initial calibration, the MLC performance monitoring QC test was performed 3–4 times/week over a period of 10–11 months to monitor positional accuracy of individual leaves for two different MLC models. Analysis of test results was performed using individuals control charts per leaf with control limits computed based on the measurements as well as two sets of specifications of ±0.5 and ±1 mm. Out-of-specification and out-of-control leaves were automatically flagged by the monitoring system and reviewed monthly by physicists. MLC-related interlocks reported by the linear accelerator and servicing events were recorded to help identify potential causes of nonrandom MLC leaf positioning variations. Results: The precision of the MLC performance monitoring QC test and the MLC itself was within ±0.22 mm for most MLC leaves

  7. Toward the development of intrafraction tumor deformation tracking using a dynamic multi-leaf collimator

    SciTech Connect

    Ge, Yuanyuan; O’Brien, Ricky T.; Shieh, Chun-Chien; Keall, Paul J.; Booth, Jeremy T.

    2014-06-15

    Purpose: Intrafraction deformation limits targeting accuracy in radiotherapy. Studies show tumor deformation of over 10 mm for both single tumor deformation and system deformation (due to differential motion between primary tumors and involved lymph nodes). Such deformation cannot be adapted to with current radiotherapy methods. The objective of this study was to develop and experimentally investigate the ability of a dynamic multi-leaf collimator (DMLC) tracking system to account for tumor deformation. Methods: To compensate for tumor deformation, the DMLC tracking strategy is to warp the planned beam aperture directly to conform to the new tumor shape based on real time tumor deformation input. Two deformable phantoms that correspond to a single tumor and a tumor system were developed. The planar deformations derived from the phantom images in beam's eye view were used to guide the aperture warping. An in-house deformable image registration software was developed to automatically trigger the registration once new target image was acquired and send the computed deformation to the DMLC tracking software. Because the registration speed is not fast enough to implement the experiment in real-time manner, the phantom deformation only proceeded to the next position until registration of the current deformation position was completed. The deformation tracking accuracy was evaluated by a geometric target coverage metric defined as the sum of the area incorrectly outside and inside the ideal aperture. The individual contributions from the deformable registration algorithm and the finite leaf width to the tracking uncertainty were analyzed. Clinical proof-of-principle experiment of deformation tracking using previously acquired MR images of a lung cancer patient was implemented to represent the MRI-Linac environment. Intensity-modulated radiation therapy (IMRT) treatment delivered with enabled deformation tracking was simulated and demonstrated. Results: The first

  8. Toward the development of intrafraction tumor deformation tracking using a dynamic multi-leaf collimator.

    PubMed

    Ge, Yuanyuan; O'Brien, Ricky T; Shieh, Chun-Chien; Booth, Jeremy T; Keall, Paul J

    2014-06-01

    Intrafraction deformation limits targeting accuracy in radiotherapy. Studies show tumor deformation of over 10 mm for both single tumor deformation and system deformation (due to differential motion between primary tumors and involved lymph nodes). Such deformation cannot be adapted to with current radiotherapy methods. The objective of this study was to develop and experimentally investigate the ability of a dynamic multi-leaf collimator (DMLC) tracking system to account for tumor deformation. To compensate for tumor deformation, the DMLC tracking strategy is to warp the planned beam aperture directly to conform to the new tumor shape based on real time tumor deformation input. Two deformable phantoms that correspond to a single tumor and a tumor system were developed. The planar deformations derived from the phantom images in beam's eye view were used to guide the aperture warping. An in-house deformable image registration software was developed to automatically trigger the registration once new target image was acquired and send the computed deformation to the DMLC tracking software. Because the registration speed is not fast enough to implement the experiment in real-time manner, the phantom deformation only proceeded to the next position until registration of the current deformation position was completed. The deformation tracking accuracy was evaluated by a geometric target coverage metric defined as the sum of the area incorrectly outside and inside the ideal aperture. The individual contributions from the deformable registration algorithm and the finite leaf width to the tracking uncertainty were analyzed. Clinical proof-of-principle experiment of deformation tracking using previously acquired MR images of a lung cancer patient was implemented to represent the MRI-Linac environment. Intensity-modulated radiation therapy (IMRT) treatment delivered with enabled deformation tracking was simulated and demonstrated. The first experimental investigation of

  9. Toward the development of intrafraction tumor deformation tracking using a dynamic multi-leaf collimator

    PubMed Central

    Ge, Yuanyuan; O’Brien, Ricky T.; Shieh, Chun-Chien; Booth, Jeremy T.; Keall, Paul J.

    2014-01-01

    Purpose: Intrafraction deformation limits targeting accuracy in radiotherapy. Studies show tumor deformation of over 10 mm for both single tumor deformation and system deformation (due to differential motion between primary tumors and involved lymph nodes). Such deformation cannot be adapted to with current radiotherapy methods. The objective of this study was to develop and experimentally investigate the ability of a dynamic multi-leaf collimator (DMLC) tracking system to account for tumor deformation. Methods: To compensate for tumor deformation, the DMLC tracking strategy is to warp the planned beam aperture directly to conform to the new tumor shape based on real time tumor deformation input. Two deformable phantoms that correspond to a single tumor and a tumor system were developed. The planar deformations derived from the phantom images in beam's eye view were used to guide the aperture warping. An in-house deformable image registration software was developed to automatically trigger the registration once new target image was acquired and send the computed deformation to the DMLC tracking software. Because the registration speed is not fast enough to implement the experiment in real-time manner, the phantom deformation only proceeded to the next position until registration of the current deformation position was completed. The deformation tracking accuracy was evaluated by a geometric target coverage metric defined as the sum of the area incorrectly outside and inside the ideal aperture. The individual contributions from the deformable registration algorithm and the finite leaf width to the tracking uncertainty were analyzed. Clinical proof-of-principle experiment of deformation tracking using previously acquired MR images of a lung cancer patient was implemented to represent the MRI-Linac environment. Intensity-modulated radiation therapy (IMRT) treatment delivered with enabled deformation tracking was simulated and demonstrated. Results: The first

  10. Assessment of the acceptability of the Elekta multileaf collimator (MLC) within the Corvus planning system for static and dynamic delivery of intensity modulated beams (IMBs).

    PubMed

    Linthout, Nadine; Verellen, Dirk; Van Acker, Swana; Van de Vondel, Iwein; Coppens, Luc; Storme, Guy

    2002-04-01

    The sliding window technique used for static and dynamic segmentation of intensity modulated beams is evaluated. Dynamic delivery is preferred since the resulting distributions correspond better with the calculated distributions, the treatment beam is used more efficiently and the delivery is less sensitive to small variations in the accuracy of the multileaf collimator (MLC).

  11. Neutron dosimetry in organs of an adult human phantom using linacs with multileaf collimator in radiotherapy treatments

    SciTech Connect

    Martinez-Ovalle, S. A.; Barquero, R.; Gomez-Ros, J. M.; Lallena, A. M.

    2012-05-15

    Purpose: To calculate absorbed doses due to neutrons in 87 organs/tissues for anthropomorphic phantoms, irradiated in position supine (head first into the gantry) with orientations anteroposterior (AP) and right-left (RLAT) with a 18 MV accelerator. Conversion factors from monitor units to {mu}Gy per neutron in organs, equivalent doses in organs/tissues, and effective doses, which permit to quantify stochastic risks, are estimated. Methods: MAX06 and FAX06 phantoms were modeled with MCNPX and irradiated with a 18 MV Varian Clinac 2100C/D accelerator whose geometry included a multileaf collimator. Two actual fields of a pelvic treatment were simulated using electron-photon-neutron coupled transport. Absorbed doses due to neutrons were estimated from kerma. Equivalent doses were estimated using the radiation weighting factor corresponding to an average incident neutron energy 0.47 MeV. Statistical uncertainties associated to absorbed doses, as calculated by MCNPX, were also obtained. Results: Largest doses were absorbed in shallowest (with respect to the neutron pathway) organs. In {mu}GyMU{sup -1}, values of 2.66 (for penis) and 2.33 (for testes) were found in MAX06, and 1.68 (for breasts), 1.05 (for lenses of eyes), and 0.94 (for sublingual salivary glands) in FAX06, in AP orientation. In RLAT, the largest doses were found for bone tissues (leg) just at the entrance of the beam in the body (right side in our case). Values, in {mu}GyMU{sup -1}, of 1.09 in upper leg bone right spongiosa, for MAX06, and 0.63 in mandible spongiosa, for FAX06, were found. Except for gonads, liver, and stomach wall, equivalent doses found for FAX06 were, in both orientations, higher than for MAX06. Equivalent doses in AP are higher than in RLAT for all organs/tissues other than brain and liver. Effective doses of 12.6 and 4.1 {mu}SvMU{sup -1} were found for AP and RLAT, respectively. The organs/tissues with larger relative contributions to the effective dose were testes and breasts, in

  12. Neutron dosimetry in organs of an adult human phantom using linacs with multileaf collimator in radiotherapy treatments.

    PubMed

    Martinez-Ovalle, S A; Barquero, R; Gomez-Ros, J M; Lallena, A M

    2012-05-01

    To calculate absorbed doses due to neutrons in 87 organs/tissues for anthropomorphic phantoms, irradiated in position supine (head first into the gantry) with orientations anteroposterior (AP) and right-left (RLAT) with a 18 MV accelerator. Conversion factors from monitor units to μGy per neutron in organs, equivalent doses in organs/tissues, and effective doses, which permit to quantify stochastic risks, are estimated. MAX06 and FAX06 phantoms were modeled with MCNPX and irradiated with a 18 MV Varian Clinac 2100C/D accelerator whose geometry included a multileaf collimator. Two actual fields of a pelvic treatment were simulated using electron-photon-neutron coupled transport. Absorbed doses due to neutrons were estimated from kerma. Equivalent doses were estimated using the radiation weighting factor corresponding to an average incident neutron energy 0.47 MeV. Statistical uncertainties associated to absorbed doses, as calculated by MCNPX, were also obtained. Largest doses were absorbed in shallowest (with respect to the neutron pathway) organs. In μGyMU(-1), values of 2.66 (for penis) and 2.33 (for testes) were found in MAX06, and 1.68 (for breasts), 1.05 (for lenses of eyes), and 0.94 (for sublingual salivary glands) in FAX06, in AP orientation. In RLAT, the largest doses were found for bone tissues (leg) just at the entrance of the beam in the body (right side in our case). Values, in μGyMU(-1), of 1.09 in upper leg bone right spongiosa, for MAX06, and 0.63 in mandible spongiosa, for FAX06, were found. Except for gonads, liver, and stomach wall, equivalent doses found for FAX06 were, in both orientations, higher than for MAX06. Equivalent doses in AP are higher than in RLAT for all organs/tissues other than brain and liver. Effective doses of 12.6 and 4.1 μSvMU(-1) were found for AP and RLAT, respectively. The organs/tissues with larger relative contributions to the effective dose were testes and breasts, in AP, and breasts and red marrow, in RLAT

  13. Method for selecting minimum width of leaf in multileaf adjustable collimator while inhibiting passage of particle beams of radiation through sawtooth joints between collimator leaves

    DOEpatents

    Ludewigt, Bernhard; Bercovitz, John; Nyman, Mark; Chu, William

    1995-01-01

    A method is disclosed for selecting the minimum width of individual leaves of a multileaf adjustable collimator having sawtooth top and bottom surfaces between adjacent leaves of a first stack of leaves and sawtooth end edges which are capable of intermeshing with the corresponding sawtooth end edges of leaves in a second stack of leaves of the collimator. The minimum width of individual leaves in the collimator, each having a sawtooth configuration in the surface facing another leaf in the same stack and a sawtooth end edge, is selected to comprise the sum of the penetration depth or range of the particular type of radiation comprising the beam in the particular material used for forming the leaf; plus the total path length across all the air gaps in the area of the joint at the edges between two leaves defined between lines drawn across the peaks of adjacent sawtooth edges; plus at least one half of the length or period of a single sawtooth. To accomplish this, in accordance with the method of the invention, the penetration depth of the particular type of radiation in the particular material to be used for the collimator leaf is first measured. Then the distance or gap between adjoining or abutting leaves is selected, and the ratio of this distance to the height of the sawteeth is selected. Finally the number of air gaps through which the radiation will pass between sawteeth is determined by selecting the number of sawteeth to be formed in the joint. The measurement and/or selection of these parameters will permit one to determine the minimum width of the leaf which is required to prevent passage of the beam through the sawtooth joint.

  14. Dosimetric and radiobiological comparison of CyberKnife M6™ InCise multileaf collimator over IRIS™ variable collimator in prostate stereotactic body radiation therapy

    PubMed Central

    Kathriarachchi, Vindu; Shang, Charles; Evans, Grant; Leventouri, Theodora; Kalantzis, Georgios

    2016-01-01

    The impetus behind our study was to establish a quantitative comparison between the IRIS collimator and the InCise multileaf collimator (MLC) (Accuray Inc. Synnyvale, CA) for prostate stereotactic body radiation therapy (SBRT). Treatment plans for ten prostate cancer patients were performed on MultiPlan™ 5.1.2 treatment planning system utilizing MLC and IRIS for 36.25 Gy in five fractions. To reduce the magnitude of variations between cases, the planning tumor volume (PTV) was defined and outlined for treating prostate gland only, assuming no seminal vesicle or ex-capsule involvement. Evaluation indices of each plan include PTV coverage, conformity index (CI), Paddick's new CI, homogeneity index, and gradient index. Organ at risk (OAR) dose sparing was analyzed by the bladder wall Dmax and V37Gy, rectum Dmax and V36Gy. The radiobiological response was evaluated by tumor control probability and normal tissue complication probability based on equivalent uniform dose. The dose delivery efficiency was evaluated on the basis of planned monitor units (MUs) and the reported treatment time per fraction. Statistical significance was tested using the Wilcoxon signed rank test. The studies indicated that CyberKnife M6™ IRIS and InCise™ MLC produce equivalent SBRT prostate treatment plans in terms of dosimetry, radiobiology, and OAR sparing, except that the MLC plans offer improvement of the dose fall-off gradient by 29% over IRIS. The main advantage of replacing the IRIS collimator with MLC is the improved efficiency, determined from the reduction of MUs by 42%, and a 36% faster delivery time. PMID:27217626

  15. Dosimetric and radiobiological comparison of CyberKnife M6™ InCise multileaf collimator over IRIS™ variable collimator in prostate stereotactic body radiation therapy.

    PubMed

    Kathriarachchi, Vindu; Shang, Charles; Evans, Grant; Leventouri, Theodora; Kalantzis, Georgios

    2016-01-01

    The impetus behind our study was to establish a quantitative comparison between the IRIS collimator and the InCise multileaf collimator (MLC) (Accuray Inc. Synnyvale, CA) for prostate stereotactic body radiation therapy (SBRT). Treatment plans for ten prostate cancer patients were performed on MultiPlan™ 5.1.2 treatment planning system utilizing MLC and IRIS for 36.25 Gy in five fractions. To reduce the magnitude of variations between cases, the planning tumor volume (PTV) was defined and outlined for treating prostate gland only, assuming no seminal vesicle or ex-capsule involvement. Evaluation indices of each plan include PTV coverage, conformity index (CI), Paddick's new CI, homogeneity index, and gradient index. Organ at risk (OAR) dose sparing was analyzed by the bladder wall Dmax and V37Gy, rectum Dmax and V36Gy. The radiobiological response was evaluated by tumor control probability and normal tissue complication probability based on equivalent uniform dose. The dose delivery efficiency was evaluated on the basis of planned monitor units (MUs) and the reported treatment time per fraction. Statistical significance was tested using the Wilcoxon signed rank test. The studies indicated that CyberKnife M6™ IRIS and InCise™ MLC produce equivalent SBRT prostate treatment plans in terms of dosimetry, radiobiology, and OAR sparing, except that the MLC plans offer improvement of the dose fall-off gradient by 29% over IRIS. The main advantage of replacing the IRIS collimator with MLC is the improved efficiency, determined from the reduction of MUs by 42%, and a 36% faster delivery time.

  16. Multileaf Collimator Tracking Improves Dose Delivery for Prostate Cancer Radiation Therapy: Results of the First Clinical Trial

    SciTech Connect

    Colvill, Emma; Booth, Jeremy T.; O'Brien, Ricky T.; Eade, Thomas N.; Kneebone, Andrew B.; Poulsen, Per R.; Keall, Paul J.

    2015-08-01

    Purpose: To test the hypothesis that multileaf collimator (MLC) tracking improves the consistency between the planned and delivered dose compared with the dose without MLC tracking, in the setting of a prostate cancer volumetric modulated arc therapy trial. Methods and Materials: Multileaf collimator tracking was implemented for 15 patients in a prostate cancer radiation therapy trial; in total, 513 treatment fractions were delivered. During each treatment fraction, the prostate trajectory and treatment MLC positions were collected. These data were used as input for dose reconstruction (multiple isocenter shift method) to calculate the treated dose (with MLC tracking) and the dose that would have been delivered had MLC tracking not been applied (without MLC tracking). The percentage difference from planned for target and normal tissue dose-volume points were calculated. The hypothesis was tested for each dose-volume value via analysis of variance using the F test. Results: Of the 513 fractions delivered, 475 (93%) were suitable for analysis. The mean difference and standard deviation between the planned and treated MLC tracking doses and the planned and without-MLC tracking doses for all 475 fractions were, respectively, PTV D{sub 99%} −0.8% ± 1.1% versus −2.1% ± 2.7%; CTV D{sub 99%} −0.6% ± 0.8% versus −0.6% ± 1.1%; rectum V{sub 65%} 1.6% ± 7.9% versus −1.2% ± 18%; and bladder V{sub 65%} 0.5% ± 4.4% versus −0.0% ± 9.2% (P<.001 for all dose-volume results). Conclusion: This study shows that MLC tracking improves the consistency between the planned and delivered doses compared with the modeled doses without MLC tracking. The implications of this finding are potentially improved patient outcomes, as well as more reliable dose-volume data for radiobiological parameter determination.

  17. The treatment planning of segmental, conformal stereotactic radiosurgery utilizing a standard multileaf collimator.

    PubMed

    Archer, P G; Balter, J M; Ross, D A; Hayman, J A; Sandler, H M

    1999-01-01

    Over a period of approximately 3 years, our institution has implemented and refined a system of Stereotactic Radiosurgery (SRS) which utilizes the standard multi leaf collimator (MLC) of the Scanditronix MM50 Racetrack Microtron and treats in an arrangement of segmental "pseudo-arcs." This system employs a commercial BRW based stereotactic frame which is mounted to the treatment table. With the exception of the table-mounted frame hardware there have been no modifications to the treatment machine to accommodate these treatments. By use of standard evaluation parameters (e.g., treatment time, planning time, dose conformance and dose heterogeneity ratios) this system compares quite favorably with reported data from institutions treating SRS with either a GammaKnife or a standard linear accelerator with tertiary collimators.

  18. Comparison of stereotactic plans for brain tumors with two different multileaf collimating systems.

    PubMed

    Marrazzo, Livia; Zani, Margherita; Pallotta, Stefania; Greto, Daniela; Scoccianti, Silvia; Talamonti, Cinzia; Biti, Giampaolo; Bucciolini, Marta

    2014-01-06

    Linac-based stereotactic radiosurgery (SRS) has been widely used for treating small intracranial lesions. This technique allows conforming the dose distribution to the planning target volume (PTV), providing a steep dose gradient with the surrounding normal tissues. This is realized through dedicated collimation systems. The present study aims to compare SRS plans with two collimating systems: the beam modulator (BM) of the Elekta Synergy linac and the DirexGroup micromultileaf collimator (μMLC). Seventeen patients (25 PTVs) were planned both with BM and μMLC (mounted on an Elekta Precise linac) using the Odyssey (PerMedics) treatment planning system (TPS). Plans were compared in terms of dose-volume histograms (DVH), minimum dose to the PTV, conformity index (CI), and homogeneity index (HI), as defined by the TPS, and doses to relevant organs at risk (OAR). The mean difference between the μMLC and the BM plans in minimum PTV dose was 5.7% ± 4.2% in favor of the μMLC plans. No statistically significant difference was found between the distributions of the CI values for the two planning modalities (p = 0.54), while the difference between the distributions of the HI values was statistically significant (p = 0.018). For both BM and μMLC plans, no differences were observed in CI and HI, depending on lesion size and shape. The PTV homogeneity achieved by BM plans was 15.1% ± 6.8% compared to 10.4% ± 6.6% with μMLC. Higher maximum and mean doses to OAR were observed in the BM plans; however, for both plans, dose constraints were respected. The comparison between the two collimating systems showed no substantial differences in terms of PTV coverage or OAR sparing. The improvements obtained by using μMLC are relatively small, and both systems turned out to be adequate for SRS treatments.

  19. Rounded leaf end effect of multileaf collimator on penumbra width and radiation field offset: an analytical and numerical study

    PubMed Central

    Zhou, Dong; Zhang, Hui; Ye, Peiqing

    2015-01-01

    Background Penumbra characteristics play a significant role in dose delivery accuracy for radiation therapy. For treatment planning, penumbra width and radiation field offset strongly influence target dose conformity and organ at risk sparing. Methods In this study, we present an analytical and numerical approach for evaluation of the rounded leaf end effect on penumbra characteristics. Based on the rule of half-value layer, algorithms for leaf position calculation and radiation field offset correction were developed, which were advantageous particularly in dealing with large radius leaf end. Computer simulation was performed based on the Monte Carlo codes of EGSnrc/BEAMnrc, with groups of leaf end radii and source sizes. Data processing technique of curve fitting was employed for deriving penumbra width and radiation field offset. Results Results showed that penumbra width increased with source size. Penumbra width curves for large radius leaf end were U-shaped. This observation was probably related to the fact that radiation beams penetrated through the proximal and distal leaf sides. In contrast, source size had negligible impact on radiation field offset. Radiation field offsets were found to be constant both for analytical method and numerical simulation. However, the overall resulting values of radiation field offset obtained by analytical method were slightly smaller compared with Monte Carlo simulation. Conclusions The method we proposed could provide insight into the investigation of rounded leaf end effects on penumbra characteristics. Penumbra width and radiation field offset calibration should be carefully performed to commission multileaf collimator for intensity modulated radiotherapy. PMID:26401137

  20. Technical and dosimetric considerations in multi-isocenter intensity modulated radiotherapy for nasopharyngeal carcinoma with small multileaf collimator.

    PubMed

    Xiance, Jin; Shixiu, Wu; Jianyi, Yu; Jinling, Yi

    2009-01-01

    Multileaf collimator (MLC)-assisted intensity modulated radiotherapy (IMRT) has greatly improved the target coverage and avoidance of organs at risk (OAR) for the treatment of nasopharyngeal carcinoma; however, its implementation is also constrained by the features of the MLC. Nasopharyngeal carcinoma tends to have a large gross target volume (GTV) and clinical target volume (CTV) due to its biological characteristics. More than one isocenter may be needed when small MLCs (i.e., BrainLAB M3, whose largest field is 10 x 10 cm(2)) are used to treat the nasopharyngeal carcinoma. The BrainLAB IMRT system was used to evaluate the effectiveness of a multi-isocenter IMRT plan for treating nasopharyngeal cancers. Dose coverage of GTVs and CTVs were compared among IMRT plans with 1, 2 and 3 isocenters, as were dose objectives for OARs including brainstem, cord, and parotids. The dosimetric variation and the delivery time were also measured with a phantom. IMRT plans with more than 1 isocenter achieved a better dose coverage, homogeneity, and conformity on GTVs and CTVs; however, with risk of higher doses given to OARs. In most cases, one can generate satisfactory IMRT plans using the 2-isocenter IMRT planning strategy. Two-isocenter planning strategy may be a suitable compromise when more isocenters are needed.

  1. Technical and Dosimetric Considerations in Multi-Isocenter Intensity Modulated Radiotherapy for Nasopharyngeal carcinoma with Small Multileaf Collimator

    SciTech Connect

    Jin Xiance Wu Shixiu; Yu Jianyi; Yi Jinling

    2009-04-01

    Multileaf collimator (MLC)-assisted intensity modulated radiotherapy (IMRT) has greatly improved the target coverage and avoidance of organs at risk (OAR) for the treatment of nasopharyngeal carcinoma; however, its implementation is also constrained by the features of the MLC. Nasopharyngeal carcinoma tends to have a large gross target volume (GTV) and clinical target volume (CTV) due to its biological characteristics. More than one isocenter may be needed when small MLCs (i.e., BrainLAB M3, whose largest field is 10 x 10 cm{sup 2}) are used to treat the nasopharyngeal carcinoma. The BrainLAB IMRT system was used to evaluate the effectiveness of a multi-isocenter IMRT plan for treating nasopharyngeal cancers. Dose coverage of GTVs and CTVs were compared among IMRT plans with 1, 2 and 3 isocenters, as were dose objectives for OARs including brainstem, cord, and parotids. The dosimetric variation and the delivery time were also measured with a phantom. IMRT plans with more than 1 isocenter achieved a better dose coverage, homogeneity, and conformity on GTVs and CTVs; however, with risk of higher doses given to OARs. In most cases, one can generate satisfactory IMRT plans using the 2-isocenter IMRT planning strategy. Two-isocenter planning strategy may be a suitable compromise when more isocenters are needed.

  2. Determining leaf trajectories for dynamic multileaf collimators with consideration of marker visibility: an algorithm study

    PubMed Central

    Zhao, Bo; Dai, Jianrong

    2014-01-01

    The purpose of this study was to develop a leaf-setting algorithm for Dynamic Multileaf Collimator–Intensity-Modulated Radiation Therapy (DMLC–IMRT) for optimal marker visibility. Here, a leaf-setting algorithm (called a Delta algorithm) was developed with the objective of maximizing marker visibility so as to improve the tracking effectiveness of fiducial markers during treatment delivery. The initial leaf trajectories were generated using a typical leaf-setting algorithm, then the leaf trajectories were adjusted by Delta algorithm operations (analytical computations and a series of matrix calculations) to achieve the optimal solution. The performance of the Delta algorithm was evaluated with six test fields (with randomly generated intensity profiles) and 15 clinical fields from IMRT plans of three prostate cancer patients. Compared with the initial solution, the Delta algorithm kept the total delivered intensities (TDIs) constant (without increasing the beam delivery time), but improved marker visibility (the percentage ratio of marker visibility time to beam delivery time). For the artificial fields (with three markers), marker visibility increased from 68.00–72.00% for a small field (5 × 5), from 38.46–43.59% for a medium field (10 × 10), and from 28.57–37.14% for a large field (20 × 20). For the 15 clinical fields, marker visibility increased 6–30% for eight fields and > 50% for two fields but did not change for five fields. A Delta algorithm was proposed to maximize marker visibility for DMLC–IMRT without increasing beam delivery time, and this will provide theoretical fundamentals for future studies of 4D DMLC tracking radiotherapy. PMID:24914104

  3. Formation of collimated beams behind the woodpile photonic crystal

    SciTech Connect

    Trull, J.; Maigyte, L.; Cojocaru, C.; Mizeikis, V.; Malinauskas, M.; Rutkauskas, M.; Peckus, M.; Sirutkaitis, V.; Juodkazis, S.; Staliunas, K.

    2011-09-15

    We experimentally observe formation of narrow laser beams behind the woodpile photonic crystal, when the beam remains well collimated in free propagation behind the crystal. We show that the collimation depends on the input laser beam's focusing conditions, and we interpret theoretically the observed effect by calculating the spatial dispersion of propagation eigenmodes and by numerical simulation of paraxial propagation model.

  4. Stereotactic IMRT for prostate cancer: dosimetric impact of multileaf collimator leaf width in the treatment of prostate cancer with IMRT.

    PubMed

    Wang, L; Movsas, B; Jacob, R; Fourkal, E; Chen, L; Price, R; Feigenberg, S; Konski, A; Pollack, A; Ma, C

    2004-01-01

    The focus of this work is the dosimetric impact of multileaf collimator (MLC) leaf width on the treatment of prostate cancer with intensity-modulated radiation therapy (IMRT). Ten patients with prostate cancer were planned for IMRT delivery using two different MLC leaf widths--4mm and 10mm--representing the Radionics micro-multileaf collimator (mMLC) and Siemens MLC, respectively. Treatment planning was performed on the XKnifeRT2 treatment-planning system (Radionics, Burlington, MA). All beams and optimization parameters were identical for the mMLC and MLC plans. All the plans were normalized to ensure that 95% of the planning target volume (PTV) received 100% of the prescribed dose. The differences in dose distribution between the two different plans were assessed by dose-volume histogram (DVH) analysis of the target and critical organs. We specifically compared the volume of rectum receiving 40 Gy (V40), 50 Gy (V50), 60 Gy (V60), the dose received by 17% and 35% of rectum (D17 and D35), and the maximum dose to 1 cm3 of the rectum for a prescription dose of 74 Gy. For the urinary bladder, the dose received by 25% of bladder (D25), V40, and the maximum dose to 1 cm3 of the organ were recorded. For PTV we compared the maximum dose to the "hottest" 1 cm3 (Dmax1 cm3) and the dose to 99% of the PTV (D99). The dose inhomogeneity in the target, defined as the ratio of the difference in Dmax1 cm3 and D99 to the prescribed dose, was also compared between the two plans. In all cases studied, significant reductions in the volume of rectum receiving doses less than 65 Gy were seen using the mMLC. The average decrease in the volume of the rectum receiving 40 Gy, 50 Gy, and 60 Gy using the mMLC plans was 40.2%, 33.4%, and 17.7%, respectively, with p < 0.0001 for V40 and V50 and p < 0.012 for V60. The mean dose reductions for D17 and D35 for the rectum using the mMLC were 20.4% (p < 0.0001) and 18.3% (p < 0.0002), respectively. There were consistent reductions in all dose

  5. SU-E-T-214: Intensity Modulated Proton Therapy (IMPT) Based On Passively Scattered Protons and Multi-Leaf Collimation: Prototype TPS and Dosimetry Study

    SciTech Connect

    Sanchez-Parcerisa, D; Carabe-Fernandez, A

    2014-06-01

    Purpose. Intensity-modulated proton therapy is usually implemented with multi-field optimization of pencil-beam scanning (PBS) proton fields. However, at the view of the experience with photon-IMRT, proton facilities equipped with double-scattering (DS) delivery and multi-leaf collimation (MLC) could produce highly conformal dose distributions (and possibly eliminate the need for patient-specific compensators) with a clever use of their MLC field shaping, provided that an optimal inverse TPS is developed. Methods. A prototype TPS was developed in MATLAB. The dose calculation process was based on a fluence-dose algorithm on an adaptive divergent grid. A database of dose kernels was precalculated in order to allow for fast variations of the field range and modulation during optimization. The inverse planning process was based on the adaptive simulated annealing approach, with direct aperture optimization of the MLC leaves. A dosimetry study was performed on a phantom formed by three concentrical semicylinders separated by 5 mm, of which the inner-most and outer-most were regarded as organs at risk (OARs), and the middle one as the PTV. We chose a concave target (which is not treatable with conventional DS fields) to show the potential of our technique. The optimizer was configured to minimize the mean dose to the OARs while keeping a good coverage of the target. Results. The plan produced by the prototype TPS achieved a conformity index of 1.34, with the mean doses to the OARs below 78% of the prescribed dose. This Result is hardly achievable with traditional conformal DS technique with compensators, and it compares to what can be obtained with PBS. Conclusion. It is certainly feasible to produce IMPT fields with MLC passive scattering fields. With a fully developed treatment planning system, the produced plans can be superior to traditional DS plans in terms of plan conformity and dose to organs at risk.

  6. Investigation of the feasibility of a simple method for verifying the motion of a binary multileaf collimator synchronized with the rotation of the gantry for helical tomotherapy.

    PubMed

    Hashimoto, Masatoshi; Uematsu, Masahiro; Ito, Makiko; Hama, Yukihiro; Inomata, Takayuki; Fujii, Masahiro; Nishio, Teiji; Nakamura, Naoki; Nakagawa, Keiichi

    2012-01-05

    In this paper, we suggest a new method for verifying the motion of a binary multileaf collimator (MLC) in helical tomotherapy. For this we used a combination of a cylindrical scintillator and a general-purpose camcorder. The camcorder records the light from the scintillator following photon irradiation, which we use to track the motion of the binary MLC. The purpose of this study is to demonstrate the feasibility of this method as a binary MLC quality assurance (QA) tool. First, the verification was performed using a simple binary MLC pattern with a constant leaf open time; secondly, verification using the binary MLC pattern used in a clinical setting was also performed. Sinograms of simple binary MLC patterns, in which leaves that were open were detected as "open" from the measured light, define the sensitivity which, in this case, was 1.000. On the other hand, the specificity, which gives the fraction of closed leaves detected as "closed", was 0.919. The leaf open error identified by our method was -1.3 ± 7.5%. The 68.6% of observed leaves were performed within ± 3% relative error. The leaf open error was expressed by the relative errors calculated on the sinogram. In the clinical binary MLC pattern, the sensitivity and specificity were 0.994 and 0.997, respectively. The measurement could be performed with -3.4 ± 8.0% leaf open error. The 77.5% of observed leaves were performed within ± 3% relative error. With this method, we can easily verify the motion of the binary MLC, and the measurement unit developed was found to be an effective QA tool.

  7. SU-E-I-49: The Evaluation of Usability of Multileaf Collimator for Diagnostic Radiation in Cephalometric Exposure

    SciTech Connect

    Han, S; Kim, K; Jung, H; Kim, M; Ji, Y; Park, S; Choi, S

    2014-06-01

    Purpose: This study evaluated usability of Multileaf collimator (MLC) for diagnostic radiation in cephalometric exposure using optical stimulated luminance dosimeters (OSLDs) Methods: The MLC material was made alloy tool steel (SKD-11) and the density of it is 7.89g/m3 that is similar to it of steel (Fe, 7.85 g/m3) and the MLC was attached to general radiography unit (Rex-650R, Listem Inc, Korea) for cephalometric exposure. The OSLDs that used were nanoDotTM Dosimeter (Landauer Inc, Glenwood, USA) and we read out OSLDs with micro star system (Landauer Inc, Glenwood, USA). The Optical annealing system contained fluorescent lamps (Osram lumilux, 24 W, 280 ∼780 nm). To measure absorbed dose using OSLDs, was carried out dosimetric characteristics of OSLDs. Based on these, we evaluated dose reduction of critical organ (Eyes, Thyroids) with MLC in cephalometric exposure Results: The dosimetric characteristics were following that batch homogeneity was 1.21% and reproducibility was 0.96% of the coefficient of variation The linearity was that the correlation of between dose and count was fitted by linear function (dose,mGy = 0.00029 × Count, R2 =0.997). The range of angular dependence was from −3.6% to 3.7% variation when each degree was normalized by zero degree. The organ dose of Rt. eye, Lt eye, thyroids were 77.8 μGy, 337.0 μGy, 323.1μGy, respectively in open field and the dose reduction of organ dose was 10.6%(8.3μGy), 12.4 %(42 μGy), 87.1%(281.4μGy) with MLC Conclusion: We certified dose reduction of organ dose in cephalometric exposure. The dose reduction of Eye was 11% because of reduction of field size and it of thyroids was 87% by primary beam shielding.

  8. Impact of Multileaf Collimator Configuration Parameters on the Dosimetric Accuracy of 6-MV Intensity-Modulated Radiation Therapy Treatment Plans.

    PubMed

    Petersen, Nick; Perrin, David; Newhauser, Wayne; Zhang, Rui

    2017-01-01

    The purpose of this study was to evaluate the impact of selected configuration parameters that govern multileaf collimator (MLC) transmission and rounded leaf offset in a commercial treatment planning system (TPS) (Pinnacle(3), Philips Medical Systems, Andover, MA, USA) on the accuracy of intensity-modulated radiation therapy (IMRT) dose calculation. The MLC leaf transmission factor was modified based on measurements made with ionization chambers. The table of parameters containing rounded-leaf-end offset values was modified by measuring the radiation field edge as a function of leaf bank position with an ionization chamber in a scanning water-tank dosimetry system and comparing the locations to those predicted by the TPS. The modified parameter values were validated by performing IMRT quality assurance (QA) measurements on 19 gantry-static IMRT plans. Planar dose measurements were performed with radiographic film and a diode array (MapCHECK2) and compared to TPS calculated dose distributions using default and modified configuration parameters. Based on measurements, the leaf transmission factor was changed from a default value of 0.001 to 0.005. Surprisingly, this modification resulted in a small but statistically significant worsening of IMRT QA gamma-index passing rate, which revealed that the overall dosimetric accuracy of the TPS depends on multiple configuration parameters in a manner that is coupled and not intuitive because of the commissioning protocol used in our clinic. The rounded leaf offset table had little room for improvement, with the average difference between the default and modified offset values being -0.2 ± 0.7 mm. While our results depend on the current clinical protocols, treatment unit and TPS used, the methodology used in this study is generally applicable. Different clinics could potentially obtain different results and improve their dosimetric accuracy using our approach.

  9. Determining the optimal dosimetric leaf gap setting for rounded leaf-end multileaf collimator systems by simple test fields.

    PubMed

    Yao, Weiguang; Farr, Jonathan B

    2015-07-08

    Individual QA for IMRT/VMAT plans is required by protocols. Sometimes plans cannot pass the institute's QA criteria. For the Eclipse treatment planning system (TPS) with rounded leaf-end multileaf collimator (MLC), one practical way to improve the agreement of planned and delivered doses is to tune the value of dosimetric leaf gap (DLG) in the TPS from the measured DLG. We propose that this step may be necessary due to the complexity of the MLC system, including dosimetry of small fields and the tongue-and-groove (T&G) effects, and report our use of test fields to obtain linac-specific optimal DLGs in TPSs. More than 20 original patient plans were reoptimized with the linac-specific optimal DLG value. We examined the distribution of gaps and T&G extensions in typical patient plans and the effect of using the optimal DLG on the distribution. The QA pass rate of patient plans using the optimal DLG was investigated. The dose-volume histograms (DVHs) of targets and organs at risk were checked. We tested three MLC systems (Varian millennium 120 MLC, high-definition 120 MLC, and Siemens 160 MLC) installed in four Varian linear accelerators (linacs) (TrueBEAM STx, Trilogy, Clinac 2300 iX, and Clinac 21 EX) and 1 Siemens linac (Artiste). With an optimal DLG, the individual QA for all those patient plans passed the institute's criteria (95% in DTA test or gamma test with 3%/3 mm/10%), even though most of these plans had failed to pass QA when using original DLGs optimized from typical patient plans or from the optimization process (automodeler) of Pinnacle TPS. Using either our optimal DLG or one optimized from typical patient plans or from the Pinnacle optimization process yielded similar DVHs.

  10. [Detailed analysis of multi-leaf collimator movement during radiation delivery using an in-house-developed program].

    PubMed

    Adachi, Yumiko; Hayashi, Naoki; Kato, Hideki; Ehara, Isao; Yada, Ryuichi; Matsunaga, Takuma; Muraki, Yuta

    2013-10-01

    Multi-leaf collimators (MLCs) are used to modulate intensity during intensity modulated radiation therapy (IMRT). Evaluation of MLC movement in IMRT is important, since the accuracy of MLC movements affects the dose distribution. This evaluation is conventionally performed using an attached Dynalog File Viewer (DFV). However, due to its being an overall evaluation, it is not possible to discover significant errors. In this study, we developed software that permits easy analysis of MLC movements that can be used to retrospectively evaluate MLC movement during irradiation. We also evaluated the usefulness of our in-house program and confirmed its potential for use in clinical scenarios. We created a program that can read MLC logfiles using Visual Basic 6.0 and visualize the temporal changes and movements of the MLC. To evaluate our in-house program's efficacy in analyzing dynamic MLC-QA (quality assurance), we compared the numerical results yielded by our in-house program and the DFV. The results showed that our in-house program was able to reveal errors below the error root mean square (RMS) values obtained using the DFV. Using irregular surface compensator (ISC) irradiation conditions in a clinical context, we compared our in-house program with the DFV and, using RMS analysis, identified cases that showed excessive error. Our in-house program can also be used to investigate whether unacceptable errors are present, as well as their cause, when using the MLC, as it allows easy real-time observation and evaluation of MLC movements. An additional benefit is that collecting the MLC logfile during actual treatment also allows it to be evaluated retrospectively after continuous MLC operation.

  11. Determination of maximum leaf velocity and acceleration of a dynamic multileaf collimator: implications for 4D radiotherapy.

    PubMed

    Wijesooriya, K; Bartee, C; Siebers, J V; Vedam, S S; Keall, P J

    2005-04-01

    The dynamic multileaf collimator (MLC) can be used for four-dimensional (4D), or tumor tracking radiotherapy. However, the leaf velocity and acceleration limitations become a crucial factor as the MLC leaves need to respond in near real time to the incoming respiration signal. The aims of this paper are to measure maximum leaf velocity, acceleration, and deceleration to obtain the mechanical response times for the MLC, and determine whether the MLC is suitable for 4D radiotherapy. MLC leaf sequence files, requiring the leaves to reach maximum acceleration and velocity during motion, were written. The leaf positions were recorded every 50 ms, from which the maximum leaf velocity, acceleration, and deceleration were derived. The dependence on the velocity and acceleration of the following variables were studied: leaf banks, inner and outer leaves, MLC-MLC variations, gravity, friction, and the stability of measurements over time. Measurement results show that the two leaf banks of a MLC behave similarly, while the inner and outer leaves have significantly different maximum leaf velocities. The MLC-MLC variations and the dependence of gravity on maximum leaf velocity are statistically significant. The average maximum leaf velocity at the isocenter plane of the MLC ranged from 3.3 to 3.9 cm/s. The acceleration and deceleration at the isocenter plane of the MLC ranged from 50 to 69 cm/s2 and 46 to 52 cm/s2, respectively. Interleaf friction had a negligible effect on the results, and the MLC parameters remained stable with time. Equations of motion were derived to determine the ability of the MLC response to fluoroscopymeasured diaphragm motion. Given the present MLC mechanical characteristics, 4D radiotherapy is feasible for up to 97% of respiratory motion. For the largest respiratory motion velocities observed, beam delivery should be temporarily stopped (beam hold).

  12. Determination of maximum leaf velocity and acceleration of a dynamic multileaf collimator: Implications for 4D radiotherapy

    SciTech Connect

    Wijesooriya, K.; Bartee, C.; Siebers, J.V.; Vedam, S.S.; Keall, P.J.

    2005-04-01

    The dynamic multileaf collimator (MLC) can be used for four-dimensional (4D), or tumor tracking radiotherapy. However, the leaf velocity and acceleration limitations become a crucial factor as the MLC leaves need to respond in near real time to the incoming respiration signal. The aims of this paper are to measure maximum leaf velocity, acceleration, and deceleration to obtain the mechanical response times for the MLC, and determine whether the MLC is suitable for 4D radiotherapy. MLC leaf sequence files, requiring the leaves to reach maximum acceleration and velocity during motion, were written. The leaf positions were recorded every 50 ms, from which the maximum leaf velocity, acceleration, and deceleration were derived. The dependence on the velocity and acceleration of the following variables were studied: leaf banks, inner and outer leaves, MLC-MLC variations, gravity, friction, and the stability of measurements over time. Measurement results show that the two leaf banks of a MLC behave similarly, while the inner and outer leaves have significantly different maximum leaf velocities. The MLC-MLC variations and the dependence of gravity on maximum leaf velocity are statistically significant. The average maximum leaf velocity at the isocenter plane of the MLC ranged from 3.3 to 3.9 cm/s. The acceleration and deceleration at the isocenter plane of the MLC ranged from 50 to 69 cm/s{sup 2} and 46 to 52 cm/s{sup 2}, respectively. Interleaf friction had a negligible effect on the results, and the MLC parameters remained stable with time. Equations of motion were derived to determine the ability of the MLC response to fluoroscopy-measured diaphragm motion. Given the present MLC mechanical characteristics, 4D radiotherapy is feasible for up to 97% of respiratory motion. For the largest respiratory motion velocities observed, beam delivery should be temporarily stopped (beam hold)

  13. Evaluation of dosimetric effect caused by slowing with multi-leaf collimator (MLC) leaves for volumetric modulated arc therapy (VMAT).

    PubMed

    Xu, Zhengzheng; Wang, Iris Z; Kumaraswamy, Lalith K; Podgorsak, Matthew B

    2016-03-01

    This study is to report 1) the sensitivity of intensity modulated radiation therapy (IMRT) QA method for clinical volumetric modulated arc therapy (VMAT) plans with multi-leaf collimator (MLC) leaf errors that will not trigger MLC interlock during beam delivery; 2) the effect of non-beam-hold MLC leaf errors on the quality of VMAT plan dose delivery. Eleven VMAT plans were selected and modified using an in-house developed software. For each control point of a VMAT arc, MLC leaves with the highest speed (1.87-1.95 cm/s) were set to move at the maximal allowable speed (2.3 cm/s), which resulted in a leaf position difference of less than 2 mm. The modified plans were considered as 'standard' plans, and the original plans were treated as the 'slowing MLC' plans for simulating 'standard' plans with leaves moving at relatively lower speed. The measurement of each 'slowing MLC' plan using MapCHECK®2 was compared with calculated planar dose of the 'standard' plan with respect to absolute dose Van Dyk distance-to-agreement (DTA) comparisons using 3%/3 mm and 2%/2 mm criteria. All 'slowing MLC' plans passed the 90% pass rate threshold using 3%/3 mm criteria while one brain and three anal VMAT cases were below 90% with 2%/2 mm criteria. For ten out of eleven cases, DVH comparisons between 'standard' and 'slowing MLC' plans demonstrated minimal dosimetric changes in targets and organs-at-risk. For highly modulated VMAT plans, pass rate threshold (90%) using 3%/3mm criteria is not sensitive in detecting MLC leaf errors that will not trigger the MLC leaf interlock. However, the consequential effects of non-beam hold MLC errors on target and OAR doses are negligible, which supports the reliability of current patient-specific IMRT quality assurance (QA) method for VMAT plans.

  14. Dosimetric impact assessment using a general algorithm in geant4 simulations for a complex-shaped multileaf collimator.

    PubMed

    Perales, Á; Cortés-Giraldo, M A; Miras, H; Arráns, R; Gallardo, M I

    2017-09-01

    We have developed an inhouse algorithm for the multileaf collimator (MLC) geometry model construction with an appropriate accuracy for dosimetric tests. Our purpose is to build a complex type of MLC and analyze the influence of the modeling parameters on the dose calculation. Using radiochromic films as detector the following tests were done: (I) Density test field: to compare measured and calculated dose distributions in order to determine the tungsten alloy physical density value. (II) Leaf ends test field: to verify the penumbra shape sensitivity against the discretization level set to simulate the curved leaf ends. (III) MLC-closed field: to obtain the value of the air gap between opposite leaves for a closed configuration which completes the modeling of the MLC leakage radiation. (IV) Picket-fence field: to fit the leaf tilt angle with respect of the divergent ray emerging from the source. For a 18.5g/cm(3) density value we have obtained a maximum, minimum and mean leakage values of 0.43%, 0.36% and 0.38%, similar to the experimental ones. The best discretization level in the leaf ends field shows a 5.51mm FWHM, very close to the measured value (5.49mm). An air gap of 370μm has been used in the simulation for the separation between opposite leaves. Using a 0.44° tilt angle, we found the same pattern as the experimental values. Our code can reproduce complex MLC designs with a submilimetric dosimetric accuracy which implies the necessary background for dose calculation of high clinical interest small fields. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

  15. Development, physical properties and clinical applicability of a mechanical Multileaf Collimator for the use in Cobalt-60 radiotherapy.

    PubMed

    Langhans, Marco; Echner, Gernot; Runz, Armin; Baumann, Martin; Xu, Mark; Ueltzhöffer, Stefan; Häring, Peter; Schlegel, Wolfgang

    2015-04-21

    According to the Directory of Radiotherapy Centres (DIRAC) there are 2348 Cobalt-60 (Co-60) teletherapy units worldwide, most of them in low and middle income countries, compared to 11046 clinical accelerators. To improve teletherapy with Co-60, a mechanical Multi-Leaf Collimator (MLC) was developed, working with pneumatic pressure and thus independent of electricity supply. Instead of tungsten, brass was used as leaf material to make the mechanical MLC more affordable. The physical properties and clinical applicability of this mechanical MLC are presented here. The leakage strongly depends on the fieldsize of the therapy unit due to scatter effects. The maximum transmission through the leaves measured 2.5 cm from the end-to-end gap, within a field size of 20 cm × 30 cm defined by jaws of the therapy unit at 80 cm SAD, amounts 4.2%, normalized to an open 10 cm × 10 cm field, created by the mechanical MLC. Within a precollimated field size of 12.5 cm × 12.5 cm, the end-to-end leakage is 6.5% normalized to an open 10 cm × 10 cm field as well. This characteristic is clinically acceptable considering the criteria for non-IMRT MLCs of the International Electrotechnical Commission (IEC 60601-2-1). The penumbra for a 10 cm × 10 cm field was measured to be 9.14 mm in plane and 8.38 mm cross plane. The clinical applicability of the designed mechanical MLC was affirmed by measurements relating to all relevant clinical properties such as penumbra, leakage, output factors and field widths. Hence this novel device presents an apt way forward to make radiotherapy with conformal fields possible in low-infrastructure environments, using gantry based Co-60 therapy units.

  16. Multileaf collimator leaf position verification and analysis for adaptive radiation therapy using a video-optical method

    NASA Astrophysics Data System (ADS)

    Sethna, Sohrab B.

    External beam radiation therapy is commonly used to eliminate and control cancerous tumors. High-energy beams are shaped to match the patient's specific tumor volume, whereby maximizing radiation dose to malignant cells and limiting dose to normal tissue. A multileaf collimator (MLC) consisting of multiple pairs of tungsten leaves is used to conform the radiation beam to the desired treatment field. Advanced treatment methods utilize dynamic MLC settings to conform to multiple treatment fields and provide intensity modulated radiation therapy (IMRT). Future methods would further increase conformity by actively tracking tumor motion caused by patient cardiac and respiratory motion. Leaf position quality assurance for a dynamic MLC is critical as variation between the planned and actual leaf positions could induce significant errors in radiation dose. The goal of this research project is to prototype a video-optical quality assurance system for MLC leaf positions. The system captures light-field images of MLC leaf sequences during dynamic therapy. Image acquisition and analysis software was developed to determine leaf edge positions. The mean absolute difference between QA prototype predicted and caliper measured leaf positions was found to be 0.6 mm with an uncertainty of +/- 0.3 mm. Maximum errors in predicted positions were below 1.0 mm for static fields. The prototype served as a proof of concept for quality assurance of future tumor tracking methods. Specifically, a lung tumor phantom was created to mimic a lung tumor's motion from respiration. The lung tumor video images were superimposed on MLC field video images for visualization and analysis. The toolbox is capable of displaying leaf position, leaf velocity, tumor position, and determining errors between planned and actual treatment fields for dynamic radiation therapy.

  17. Development, physical properties and clinical applicability of a mechanical Multileaf Collimator for the use in Cobalt-60 radiotherapy

    NASA Astrophysics Data System (ADS)

    Langhans, Marco; Echner, Gernot; Runz, Armin; Baumann, Martin; Xu, Mark; Ueltzhöffer, Stefan; Häring, Peter; Schlegel, Wolfgang

    2015-04-01

    According to the Directory of Radiotherapy Centres (DIRAC) there are 2348 Cobalt-60 (Co-60) teletherapy units worldwide, most of them in low and middle income countries, compared to 11046 clinical accelerators. To improve teletherapy with Co-60, a mechanical Multi-Leaf Collimator (MLC) was developed, working with pneumatic pressure and thus independent of electricity supply. Instead of tungsten, brass was used as leaf material to make the mechanical MLC more affordable. The physical properties and clinical applicability of this mechanical MLC are presented here. The leakage strongly depends on the fieldsize of the therapy unit due to scatter effects. The maximum transmission through the leaves measured 2.5 cm from the end-to-end gap, within a field size of 20 cm × 30 cm defined by jaws of the therapy unit at 80 cm SAD, amounts 4.2%, normalized to an open 10 cm × 10 cm field, created by the mechanical MLC. Within a precollimated field size of 12.5 cm × 12.5 cm, the end-to-end leakage is 6.5% normalized to an open 10 cm × 10 cm field as well. This characteristic is clinically acceptable considering the criteria for non-IMRT MLCs of the International Electrotechnical Commission (IEC 60601-2-1). The penumbra for a 10 cm × 10 cm field was measured to be 9.14 mm in plane and 8.38 mm cross plane. The clinical applicability of the designed mechanical MLC was affirmed by measurements relating to all relevant clinical properties such as penumbra, leakage, output factors and field widths. Hence this novel device presents an apt way forward to make radiotherapy with conformal fields possible in low-infrastructure environments, using gantry based Co-60 therapy units.

  18. SU-E-T-610: Comparison of Treatment Times Between the MLCi and Agility Multileaf Collimators

    SciTech Connect

    Ramsey, C; Bowling, J

    2014-06-01

    Purpose: The Agility is a new 160-leaf MLC developed by Elekta for use in their Infinity and Versa HD linacs. As compared to the MLCi, the Agility increased the maximum leaf speed from 2 cm/s to 3.5 cm/s, and the maximum primary collimator speed from 1.5 cm/s to 9.0 cm/s. The purpose of this study was to determine if the Agility MLC resulted in improved plan quality and/or shorter treatment times. Methods: An Elekta Infinity that was originally equipped with a 80 leaf MLCi was upgraded to an 160 leaf Agility. Treatment plan quality was evaluated using the Pinnacle planning system with SmartArc. Optimization was performed once for the MLCi and once for the Agility beam models using the same optimization parameters and the same number of iterations. Patient treatment times were measured for all IMRT, VMAT, and SBRT patients treated on the Infinity with the MLCi and Agility MLCs. Treatment times were extracted from the EMR and measured from when the patient first walked into the treatment room until exiting the treatment room. Results: 11,380 delivery times were measured for patients treated with the MLCi, and 1,827 measurements have been made for the Agility MLC. The average treatment times were 19.1 minutes for the MLCi and 20.8 minutes for the Agility. Using a t-test analysis, there was no difference between the two groups (t = 0.22). The dose differences between patients planned with the MLCi and the Agility MLC were minimal. For example, the dose difference for the PTV, GTV, and cord for a head and neck patient planned using Pinnacle were effectively equivalent. However, the dose to the parotid glands was slightly worse with the Agility MLC. Conclusion: There was no statistical difference in treatment time, or any significant dosimetric difference between the Agility MLC and the MLCi.

  19. Electromagnetic real-time tumor position monitoring and dynamic multileaf collimator tracking using a Siemens 160 MLC: geometric and dosimetric accuracy of an integrated system.

    PubMed

    Krauss, Andreas; Nill, Simeon; Tacke, Martin; Oelfke, Uwe

    2011-02-01

    Dynamic multileaf collimator tracking represents a promising method for high-precision radiotherapy to moving tumors. In the present study, we report on the integration of electromagnetic real-time tumor position monitoring into a multileaf collimator-based tracking system. The integrated system was characterized in terms of its geometric and radiologic accuracy. The former was assessed from portal images acquired during radiation delivery to a phantom in tracking mode. The tracking errors were calculated from the positions of the tracking field and of the phantom as extracted from the portal images. Radiologic accuracy was evaluated from film dosimetry performed for conformal and intensity-modulated radiotherapy applied to different phantoms moving on sinusoidal trajectories. A static radiation delivery to the nonmoving target served as a reference for the delivery to the moving phantom with and without tracking applied. Submillimeter tracking accuracy was observed for two-dimensional target motion despite the relatively large system latency of 500 ms. Film dosimetry yielded almost complete recovery of a circular dose distribution with tracking in two dimensions applied: 2%/2 mm gamma-failure rates could be reduced from 59.7% to 3.3%. For single-beam intensity-modulated radiotherapy delivery, accuracy was limited by the finite leaf width. A 2%/2 mm gamma-failure rate of 15.6% remained with tracking applied. The integrated system we have presented marks a major step toward the clinical implementation of high-precision dynamic multileaf collimator tracking. However, several challenges such as irregular motion traces or a thorough quality assurance still need to be addressed. Copyright © 2011 Elsevier Inc. All rights reserved.

  20. Real-Time Target Position Estimation Using Stereoscopic Kilovoltage/Megavoltage Imaging and External Respiratory Monitoring for Dynamic Multileaf Collimator Tracking

    SciTech Connect

    Cho, Byungchul; Poulsen, Per Rugaard; Sawant, Amit; Ruan, Dan; Keall, Paul J.

    2011-01-01

    Purpose: To develop a real-time target position estimation method using stereoscopic kilovoltage (kV)/megavoltage (MV) imaging and external respiratory monitoring, and to investigate the performance of a dynamic multileaf collimator tracking system using this method. Methods and Materials: The real-time three-dimensional internal target position estimation was established by creating a time-varying correlation model that connected the external respiratory signals with the internal target motion measured intermittently using kV/MV imaging. The method was integrated into a dynamic multileaf collimator tracking system. Tracking experiments were performed for 10 thoracic/abdominal traces. A three-dimensional motion platform carrying a gold marker and a separate one-dimensional motion platform were used to reproduce the target and external respiratory motion, respectively. The target positions were detected by kV (1 Hz) and MV (5.2 Hz) imaging, and external respiratory motion was captured by an optical system (30 Hz). The beam-target alignment error was quantified as the positional difference between the target and circular beam center on the MV images acquired during tracking. The correlation model error was quantified by comparing a model estimate and measured target positions. Results: The root-mean-square errors in the beam-target alignment that had ranged from 3.1 to 7.6 mm without tracking were reduced to <1.5 mm with tracking, except during the model building period (6 s). The root-mean-square error in the correlation model was submillimeters in all directions. Conclusion: A novel real-time target position estimation method was developed and integrated into a dynamic multileaf collimator tracking system and demonstrated an average submillimeter geometric accuracy after initializing the internal/external correlation model. The method used hardware tools available on linear accelerators and therefore shows promise for clinical implementation.

  1. Electromagnetic Real-Time Tumor Position Monitoring and Dynamic Multileaf Collimator Tracking Using a Siemens 160 MLC: Geometric and Dosimetric Accuracy of an Integrated System

    SciTech Connect

    Krauss, Andreas; Nill, Simeon; Tacke, Martin; Oelfke, Uwe

    2011-02-01

    Purpose: Dynamic multileaf collimator tracking represents a promising method for high-precision radiotherapy to moving tumors. In the present study, we report on the integration of electromagnetic real-time tumor position monitoring into a multileaf collimator-based tracking system. Methods and Materials: The integrated system was characterized in terms of its geometric and radiologic accuracy. The former was assessed from portal images acquired during radiation delivery to a phantom in tracking mode. The tracking errors were calculated from the positions of the tracking field and of the phantom as extracted from the portal images. Radiologic accuracy was evaluated from film dosimetry performed for conformal and intensity-modulated radiotherapy applied to different phantoms moving on sinusoidal trajectories. A static radiation delivery to the nonmoving target served as a reference for the delivery to the moving phantom with and without tracking applied. Results: Submillimeter tracking accuracy was observed for two-dimensional target motion despite the relatively large system latency of 500 ms. Film dosimetry yielded almost complete recovery of a circular dose distribution with tracking in two dimensions applied: 2%/2 mm gamma-failure rates could be reduced from 59.7% to 3.3%. For single-beam intensity-modulated radiotherapy delivery, accuracy was limited by the finite leaf width. A 2%/2 mm gamma-failure rate of 15.6% remained with tracking applied. Conclusion: The integrated system we have presented marks a major step toward the clinical implementation of high-precision dynamic multileaf collimator tracking. However, several challenges such as irregular motion traces or a thorough quality assurance still need to be addressed.

  2. Dosimetric comparison of different multileaf collimator leaves in treatment planning of intensity-modulated radiotherapy for cervical cancer

    SciTech Connect

    Wang, Shichao; Ai, Ping; Xie, Li; Xu, Qingfeng; Bai, Sen; Lu, You; Li, Ping; Chen, Nianyong

    2013-01-01

    To study the effect of multileaf collimator (MLC) leaf widths (standard MLC [sMLC] width of 10 mm and micro-MLC [mMLC] width of 4 mm) on intensity-modulated radiotherapy (IMRT) for cervical cancer. Between January 2010 and August 2010, a retrospective analysis was conducted on 12 patients with cervical cancer. The treatment plans for all patients were generated with the same machine setup parameters and optimization methods in a treatment planning system (TPS) based on 2 commercial Elekta MLC devices. The dose distribution for the planning tumor volume (PTV), the dose sparing for organs at risk (OARs), the monitor units (MUs), and the number of IMRT segments were evaluated. For the delivery efficiency, the MUs were significantly higher in the sMLC-IMRT plan than in the mMLC-IMRT plan (802 ± 56.9 vs 702 ± 56.7; p < 0.05). The number of segments in the plans were 58.75 ± 1.8 and 59 ± 1.04 (p > 0.05). For the planning quality, the conformity index (CI) between the 2 paired IMRT plans with the mMLC and the sMLC did not differ significantly (average: 0.817 ± 0.024 vs 0.810 ± 0.028; p > 0.05). The differences of the homogeneity index (HI) between the 2 paired plans were statistically significant (average: 1.122 ± 0.010 vs 1.132 ± 0.014; p < 0.01). For OARs, the rectum, bladder, small intestine, and bony pelvis were evaluated in terms of V{sub 10}, V{sub 20}, V{sub 30}, and V{sub 40}, percentage of contoured OAR volumes receiving 10, 20, 30, and 40 Gy, respectively, and the mean dose (D{sub mean}) received. The IMRT plans with the mMLC protected the OARs better than the plans with the sMLC. There were significant differences (p < 0.05) in evaluated parameters between the 2 paired IMRT plans, except for V{sub 30} and V{sub 40} of the rectum and V{sub 10}, V{sub 20}, V{sub 40}, and D{sub mean} of the bladder. IMRT plans with the mMLC showed advantages over the plans with the sMLC in dose homogeneity for targets, dose sparing of OARs, and fewer MUs in cervical cancer.

  3. SU-E-T-646: Quality Assurance of Truebeam Multi-Leaf Collimator Using a MLC QA Phantom

    SciTech Connect

    Zhang, J; Lu, J; Hong, D

    2015-06-15

    Purpose: To perform a routine quality assurance procedure for Truebeam multi-leaf collimator (MLC) using MLC QA phantom, verify the stability and reliability of MLC during the treatment. Methods: MLC QA phantom is a specialized phantom for MLC quality assurance (QA), and contains five radio-opaque spheres that are embedded in an “L” shape. The phantom was placed isocentrically on the Truebeam treatment couch for the tests. A quality assurance plan was setted up in the Eclipse v10.0, the fields that need to be delivered in order to acquire the necessary images, the MLC shapes can then be obtained by the images. The images acquired by the electronic portal imaging device (EPID), and imported into the PIPSpro software for the analysis. The tests were delivered twelve weeks (once a week) to verify consistency of the delivery, and the images are acquired in the same manner each time. Results: For the Leaf position test, the average position error was 0.23mm±0.02mm (range: 0.18mm∼0.25mm). The Leaf width was measured at the isocenter, the average error was 0.06mm±0.02mm (range: 0.02mm∼0.08mm) for the Leaf width test. Multi-Port test showed the dynamic leaf shift error, the average error was 0.28mm±0.03mm (range: 0.2mm∼0.35mm). For the leaf transmission test, the average inter-leaf leakage value was 1.0%±0.17% (range: 0.8%∼1.3%) and the average inter-bank leakage value was 32.6%±2.1% (range: 30.2%∼36.1%). Conclusion: By the test of 12 weeks, the MLC system of the Truebeam is running in a good condition and the MLC system can be steadily and reliably carried out during the treatment. The MLC QA phantom is a useful test tool for the MLC QA.

  4. Evaluation of dosimetric effect caused by slowing with multi-leaf collimator (MLC) leaves for volumetric modulated arc therapy (VMAT)

    PubMed Central

    Wang, Iris Z.; Kumaraswamy, Lalith K.; Podgorsak, Matthew B.

    2016-01-01

    Background This study is to report 1) the sensitivity of intensity modulated radiation therapy (IMRT) QA method for clinical volumetric modulated arc therapy (VMAT) plans with multi-leaf collimator (MLC) leaf errors that will not trigger MLC interlock during beam delivery; 2) the effect of non-beam-hold MLC leaf errors on the quality of VMAT plan dose delivery. Materials and methods. Eleven VMAT plans were selected and modified using an in-house developed software. For each control point of a VMAT arc, MLC leaves with the highest speed (1.87-1.95 cm/s) were set to move at the maximal allowable speed (2.3 cm/s), which resulted in a leaf position difference of less than 2 mm. The modified plans were considered as ‘standard’ plans, and the original plans were treated as the ‘slowing MLC’ plans for simulating ‘standard’ plans with leaves moving at relatively lower speed. The measurement of each ‘slowing MLC’ plan using MapCHECK®2 was compared with calculated planar dose of the ‘standard’ plan with respect to absolute dose Van Dyk distance-to-agreement (DTA) comparisons using 3%/3 mm and 2%/2 mm criteria. Results All ‘slowing MLC’ plans passed the 90% pass rate threshold using 3%/3 mm criteria while one brain and three anal VMAT cases were below 90% with 2%/2 mm criteria. For ten out of eleven cases, DVH comparisons between ‘standard’ and ‘slowing MLC’ plans demonstrated minimal dosimetric changes in targets and organs-at-risk. Conclusions For highly modulated VMAT plans, pass rate threshold (90%) using 3%/3mm criteria is not sensitive in detecting MLC leaf errors that will not trigger the MLC leaf interlock. However, the consequential effects of non-beam hold MLC errors on target and OAR doses are negligible, which supports the reliability of current patient-specific IMRT quality assurance (QA) method for VMAT plans. PMID:27069458

  5. Performance evaluation of a high-speed multileaf collimator in real-time IMRT delivery to moving targets.

    PubMed

    Li, Fang; Ye, Peiqing; Zhang, Hui

    2016-03-01

    Multileaf collimator (MLC) tracking can be used for motion management. However, on account of mechanical constraints, it is a crucial challenge for conventional MLCs (3-4 cm/s in leaf speed) to track fast targets, especially moving in 2D in the beam's eye view (BEV). Our group has recently developed a "high-speed" MLC (HS-MLC) prototype with a maximum leaf speed of 40 cm/s, which makes it possible to track the vast majority of moving targets without violation of mechanical constraints. The major innovation of the HS-MLC design is that it employs linear motors instead of rotary motors to drive leaves. This paper mainly aims to evaluate the performance of the HS-MLC in real-time intensity-modulated radiation therapy delivery to targets moving in 2D in the BEV. A 2D real-time tracking algorithm was proposed first based on a previous superimposing leaf sequencing method. Then, simulations were performed to evaluate the delivery performance including fluence accuracy, efficiency, delivery time, and number of monitor units under various settings of limiting coefficient and dose rate for four clinical fluence maps and two target speeds. The comparisons between the HS-MLC with a "medium-speed" MLC (MS-MLC, 10 cm/s) and a "low-speed" MLC (LS-MLC, 5 cm/s) were also made. For validation, experiments were carried out on the HS-MLC prototype in the lab environment. A camera-based measurement system was set up to detect actual leaf trajectories. Simulation results indicate that a limiting coefficient of 0.5 and a dose rate of 400 MU/min are "optimal" in the sense of getting best compromise between delivery time and number of monitor units. Under the optimal parameters, the HS-MLC achieved 100% in efficiency, 18.1 s in delivery time, and 121.2 MU in number of monitor units on average for the "fast" target speed, compared to 94%, 20.6 s, and 129.9 MU with the MS-MLC, and to 53%, 40.2 s, and 141.1 MU with the LS-MLC. The benefits of increased leaf speed were demonstrated. The

  6. SU-E-T-766: Treatment Planning Comparison Study On Two Different Multileaf Collimators Delivered with Volumetric Modulated Arc Therapy

    SciTech Connect

    Zhang, R; Xiaomei, F; Bai, W; Zhang, X; Gao, Y

    2015-06-15

    Purpose: To compare and evaluate the performance of two different multileaf collimators(MLCi2 and Agility) delivery with volumetric modulated arc therapy techniques. Methods: Treatment plans were graded four (Low, Moderate, Moderate-High and High complexity) accorrding to the complexity. This includes 1 Low complexity(brain metastasis), 2 Moderate complexity(Lung and Liver), 1 Moderate-High complexity(prostate) and 1 High complexity ( head and neck) cases. Total dose of 60 Gy was given for all the plans. All cases were desigined two VMAT plans, one with MLCi2(group A) and the other with Agility(group B). All plans were done on Elekta VMAT with Monaco treatment planning system. All plans were generated with 6 MV X-rays for both Plan A and Plan B. Plans were evaluated based on the ability to meet the dose volume histogram, radiation conformity index, estimated radiation delivery time, dose homogeneity index(HI) and monitor units(MU) needed to deliver the prescribed dose. Results: Plans of group B achieved the best HI (HI = 1.05 Vs. 1.06) at the Low complexity cases while plans of group A were slightly better at the high complexity cases (HI = 1.12 Vs. 1.14). Faster VMAT plan delivery with Agility than with MLCi2 as plan complexity increased (Low complexity:52s Vs.52s, Moderate complexity:58s Vs. 55s, Moderate-High complexity: 171s Vs.152s, High complexity : 326s Vs. 202s ), especially for the most complex paradigms delivered time can be decresed 38%. No Significant changes were observed between the group B and group A plans in terms of the healthy tissue mean dose and MU. Both plans respected the planning objective for all organs at risk. Conclusion: The study concludes that VMAT plans with the novel Agility MLC can significant decrease the delivering time at the high complexity cases, while a slight compromise in the dose homogeneity index should be noted. This work was supported by The Medical Science Foundation of The health department of Hebei Province (No

  7. Robotic radiosurgery versus micro-multileaf collimator: a dosimetric comparison for large or critically located arteriovenous malformations

    PubMed Central

    2013-01-01

    Background Stereotactic irradiation of large or critically located arteriovenous malformations (AVMs) is a special challenge for clinicians and radiation physicists. To date, no comprehensive comparison of two linac-based radiosurgery systems used for hypofractionated radiotherapy of large AVMs was published. The aim of the study was to compare dose distributions between CyberKnife (CK) system and linac with a micro-multileaf collimator (L-mMLC) in high-grade or critically located cerebral AVMs. Methods Two sets of plans made for 15 different patients with at least 95% target coverage were selected for comparisons. Conformity (CI), homogeneity (HI) and gradient score (GSI) indices, conformity index proposed by Lomax (CIL), conformation number (CN), quality of coverage (Q), volumes of brain receiving 12,10,8,6,4, and 2 Gy, minimum and maximum doses for critical structures in both treatment planning systems (TPS) were compared. Finally, the number of monitor units needed to deliver the prescribed dose was compared. Results The mean minimum doses in the target volume were 93.3% (CK) and 90.7% (L-mMLC),p=n.s, maximum: 119.7 and 110%, respectively (p=0.004). The mean CI was 1.46 and 1.86, HI: 1.2, and 1.11, CIL 0.7, and 0.6, CN: 0.68 and 0.58 for CK and mMLC, respectively (p<0.05). The values of GSI and Q were not significantly different. The volumes of the brain receiving low doses (4 Gy and 2 Gy) were significantly lower in the CK system. The number of monitor units necessary to deliver the prescribed dose was significantly greater in case of the CK system. Conclusions Better conformity can favor the CK system for treatment of large AVMs at the cost of higher maximum doses and worse homogeneity. L-mMLC is superior when shorter treatment time is required. Neither system can assure satisfying dose gradients outside large targets surrounded by numerous critical structures. PMID:23968165

  8. SU-E-T-348: Verification MU Calculation for Conformal Radiotherapy with Multileaf Collimator Using Report AAPM TG 114

    SciTech Connect

    Adrada, A; Tello, Z; Medina, L; Garrigo, E; Venencia, D

    2014-06-01

    Purpose: The purpose of this work was to develop and validate an open source independent MU dose calculation software for 3D conformal radiotherapy with multileaf high and low resolution according to the report of AAPM TG 11 Methods: Treatment plans were done using Iplan v4.5 BrainLAB TPS. A 6MV photon beam produced by Primus and Novalis linear accelerators equipped with an Optifocus MLC and HDMLC, respectively. TPS dose calculation algorithms were pencil beam and Monte Carlo. 1082 treatments plans were selected for the study. The algorithm was written in free and open source CodeBlocks C++ platform. Treatment plans were imported by the software using RTP format. Equivalent size field is obtained from the positions of the leaves; the effective depth of calculation can be introduced by TPS's dosimetry report or automatically calculated starting from SSD. The inverse square law is calculated by the 3D coordinates of the isocenter and normalization point of the treatment plan. The dosimetric parameters TPR, Sc, Sp and WF are linearly interpolated. Results: 1082 plans of both machines were analyzed. The average uncertainty between the TPS and the independent calculation was −0.43% ± 2.42% [−7.90%, 7.50%]. Specifically for the Primus the variation obtained was −0.85% ± 2.53% and for the Novalis 0.00% ± 2.23%. Data show that 94.8% of the cases the uncertainty was less than or equal to 5%, while 98.9% is less than or equal to 6%. Conclusion: The developed software is appropriate for use in calculation of UM. This software can be obtained upon request.

  9. Real-time verification of multileaf collimator-driven radiotherapy using a novel optical attenuation-based fluence monitor.

    PubMed

    Goulet, Mathieu; Gingras, Luc; Beaulieu, Luc

    2011-03-01

    Multileaf collimator (MLC)-driven conformal radiotherapy modalities [e.g., such as intensity-modulated radiotherapy (IMRT), intensity-modulated arc therapy, and stereotactic body radiotherapy] are more subject to delivery errors and dose calculation inaccuracies than standard modalities. Fluence monitoring during treatment delivery could reduce such errors by allowing an independent interface to quantify and assess measured difference between the delivered and planned treatment administration. We developed an optical attenuation-based detector to monitor fluence for the on-line quality control of radiotherapy delivery. The purpose of the current study was to develop the theoretical background of the invention and to evaluate the detector's performance both statistically and in clinical situations. We aligned 60 27-cm scintillating fibers coupled to a photodetector via clear optical fibers in the direction of motion of each of the 60 leaf pairs of a 120 leaves Millenium MLC on a Varian Clinac iX. We developed a theoretical model to predict the intensity of light collected on each side of the scintillating fibers when placed under radiation fields of varying sizes, intensities, and positions. The model showed that both the central position of the radiation field on the fiber (x(c)) and the integral fluence passing through the fiber (phi(int)) could be assessed independently in a single measurement. We evaluated the performance of the prototype by (1) measuring the intrinsic variation of the measured values of x(c) and phi(int), (2) measuring the impact on the measured values of x(c) and phi(int) of random leaf positioning errors introduced into IMRT fields, and (3) comparing the predicted values of x(c) and phi(int) calculated with the treatment planning software to the measured values of x(c) and phi(int) in order to assess the predictive effectiveness of the developed theoretical model. We observed a very low intrinsic dispersion, dominated by Poisson statistics

  10. Real-time verification of multileaf collimator-driven radiotherapy using a novel optical attenuation-based fluence monitor

    SciTech Connect

    Goulet, Mathieu; Gingras, Luc; Beaulieu, Luc

    2011-03-15

    Purpose: Multileaf collimator (MLC)-driven conformal radiotherapy modalities [e.g., such as intensity-modulated radiotherapy (IMRT), intensity-modulated arc therapy, and stereotactic body radiotherapy] are more subject to delivery errors and dose calculation inaccuracies than standard modalities. Fluence monitoring during treatment delivery could reduce such errors by allowing an independent interface to quantify and assess measured difference between the delivered and planned treatment administration. We developed an optical attenuation-based detector to monitor fluence for the on-line quality control of radiotherapy delivery. The purpose of the current study was to develop the theoretical background of the invention and to evaluate the detector's performance both statistically and in clinical situations. Methods: We aligned 60 27-cm scintillating fibers coupled to a photodetector via clear optical fibers in the direction of motion of each of the 60 leaf pairs of a 120 leaves Millenium MLC on a Varian Clinac iX. We developed a theoretical model to predict the intensity of light collected on each side of the scintillating fibers when placed under radiation fields of varying sizes, intensities, and positions. The model showed that both the central position of the radiation field on the fiber (x{sub c}) and the integral fluence passing through the fiber ({Phi}{sub int}) could be assessed independently in a single measurement. We evaluated the performance of the prototype by (1) measuring the intrinsic variation of the measured values of x{sub c} and {Phi}{sub int}, (2) measuring the impact on the measured values of x{sub c} and {Phi}{sub int} of random leaf positioning errors introduced into IMRT fields, and (3) comparing the predicted values of x{sub c} and {Phi}{sub int} calculated with the treatment planning software to the measured values of x{sub c} and {Phi}{sub int} in order to assess the predictive effectiveness of the developed theoretical model. Results: We

  11. Dosimetric effects of multileaf collimator leaf width on intensity-modulated radiotherapy for head and neck cancer

    SciTech Connect

    Hong, Chae-Seon; Ju, Sang Gyu Kim, Minkyu; Kim, Jin Man; Han, Youngyih; Ahn, Yong Chan; Choi, Doo Ho; Park, Hee Chul; Kim, Jung-in; Nam, Heerim; Suh, Tae-Suk

    2014-02-15

    Purpose: The authors evaluated the effects of multileaf collimator (MLC) leaf width (2.5 vs. 5 mm) on dosimetric parameters and delivery efficiencies of intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) for head and neck (H and N) cancers. Methods: The authors employed two types of mock phantoms: large-sized head and neck (LH and N) and small-sized C-shape (C-shape) phantoms. Step-and-shoot IMRT (S and S-IMRT) and VMAT treatment plans were designed with 2.5- and 5.0-mm MLC for both C-shape and LH and N phantoms. Their dosimetric characteristics were compared in terms of the conformity index (CI) and homogeneity index (HI) for the planning target volume (PTV), the dose to organs at risk (OARs), and the dose-spillage volume. To analyze the effects of the field and arc numbers, 9-field IMRT (9F-IMRT) and 13-field IMRT (13F-IMRT) plans were established for S and S-IMRT. For VMAT, single arc (VMAT{sub 1}) and double arc (VMAT{sub 2}) plans were established. For all plans, dosimetric verification was performed using the phantom to examine the relationship between dosimetric errors and the two leaf widths. Delivery efficiency of the two MLCs was compared in terms of beam delivery times, monitor units (MUs) per fraction, and the number of segments for each plan. Results: 2.5-mm MLC showed better dosimetric characteristics in S and S-IMRT and VMAT for C-shape, providing better CI for PTV and lower spinal cord dose and high and intermediate dose-spillage volume as compared with the 5-mm MLC (p < 0.05). However, no significant dosimetric benefits were provided by the 2.5-mm MLC for LH and N (p > 0.05). Further, beam delivery efficiency was not observed to be significantly associated with leaf width for either C-shape or LH and N. However, MUs per fraction were significantly reduced for the 2.5-mm MLC for the LH and N. In dosimetric error analysis, absolute dose evaluations had errors of less than 3%, while the Gamma passing rate was

  12. Dosimetric effects of multileaf collimator leaf width on intensity-modulated radiotherapy for head and neck cancer.

    PubMed

    Hong, Chae-Seon; Ju, Sang Gyu; Kim, Minkyu; Kim, Jung-In; Kim, Jin Man; Suh, Tae-Suk; Han, Youngyih; Ahn, Yong Chan; Choi, Doo Ho; Nam, Heerim; Park, Hee Chul

    2014-02-01

    The authors evaluated the effects of multileaf collimator (MLC) leaf width (2.5 vs. 5 mm) on dosimetric parameters and delivery efficiencies of intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) for head and neck (H&N) cancers. The authors employed two types of mock phantoms: large-sized head and neck (LH&N) and small-sized C-shape (C-shape) phantoms. Step-and-shoot IMRT (S&S_IMRT) and VMAT treatment plans were designed with 2.5- and 5.0-mm MLC for both C-shape and LH&N phantoms. Their dosimetric characteristics were compared in terms of the conformity index (CI) and homogeneity index (HI) for the planning target volume (PTV), the dose to organs at risk (OARs), and the dose-spillage volume. To analyze the effects of the field and arc numbers, 9-field IMRT (9F-IMRT) and 13-field IMRT (13F-IMRT) plans were established for S&S_IMRT. For VMAT, single arc (VMAT1) and double arc (VMAT2) plans were established. For all plans, dosimetric verification was performed using the phantom to examine the relationship between dosimetric errors and the two leaf widths. Delivery efficiency of the two MLCs was compared in terms of beam delivery times, monitor units (MUs) per fraction, and the number of segments for each plan. 2.5-mm MLC showed better dosimetric characteristics in S&S_IMRT and VMAT for C-shape, providing better CI for PTV and lower spinal cord dose and high and intermediate dose-spillage volume as compared with the 5-mm MLC (p < 0.05). However, no significant dosimetric benefits were provided by the 2.5-mm MLC for LH&N (p > 0.05). Further, beam delivery efficiency was not observed to be significantly associated with leaf width for either C-shape or LH&N. However, MUs per fraction were significantly reduced for the 2.5-mm MLC for the LH&N. In dosimetric error analysis, absolute dose evaluations had errors of less than 3%, while the Gamma passing rate was greater than 95% according to the 3%/3 mm criteria. There were no significant

  13. Dose verification of intensity-modulated arc therapy using an ERGO++ treatment planning system and Elekta internal multileaf collimators for prostate cancer treatment.

    PubMed

    Yoda, K; Nakagawa, K; Shiraishi, K; Okano, Y; Ohtomo, K; Pellegrini, R G

    2009-04-01

    Dose verification of intensity-modulated arc therapy using an ERGO++ treatment planning system and Elekta internal multileaf collimators is described. Prostate intensity-modulated arc therapy was planned using the arc modulation optimization algorithm inverse planning module of ERGO++. After transferring the plan to Elekta Synergy's controller (Elekta Ltd, Crawley, UK), the isocentre dose was measured and compared with a calculated dose using a pinpoint chamber and a water phantom in a cylindrical acrylic enclosure. Subsequently, an EDR2 film was placed inside a multilayer plastic phantom, and total dose distributions were measured in three axial planes as well as in the coronal and sagittal planes to compare the actual dose with the calculated dose. The dose discrepancy at the isocentre was 1.7%. The calculated gamma indices were less than 1 over 90% of the three axial planes, as well as in the coronal and sagittal planes, having a dose greater than 50% of the maximum target dose.

  14. Changes to dose in the build-up region when using multi-leaf collimators in place of lead blocks supported on an accessory tray.

    PubMed

    Adams, E J; Hounsell, A R

    1995-12-01

    Doses in the build-up region have been compared for regular fields with and without a perspex accessory tray and for two irregular fields defined by either a Philips multi-leaf collimator (MLC) or lead blocks. The results show an increase in doses within the build-up region, by up to a factor of two, primarily due to the presence of the accessory tray. Fields shaped with the MLC exhibited build-up characteristics similar to those in unblocked fields and hence there will be systematic changes to the build-up dose when treatments are transferred from lead blocking techniques to those using an MLC mounted within the treatment head.

  15. Broadband super-collimation with low-symmetric photonic crystal

    NASA Astrophysics Data System (ADS)

    Giden, Ibrahim H.; Turduev, Mirbek; Kurt, Hamza

    2013-05-01

    We investigate dispersive properties of two dimensional photonic crystal (PC) called star-shaped PC (STAR-PC) in order to succeed super-collimation over a broad bandwidth. Both time- and frequency-domain numerical methods are conducted. Due to introduced low-symmetry in the primitive cell, flat contours are observed at the fifth band for transverse magnetic mode. The proposed structure supports a super-collimation effect over a broad wavelength range between 1443 nm and 1701 nm with a bandwidth of Δω = 16.42%. The intrinsic characteristic of STAR-PC provides in-plane beam propagation with a limited diffraction length of 120a, where a is the lattice constant. By means of STAR-PC, one may realize super-collimation based single-mode optical devices with a low insertion loss, reduced dispersion and wide bandwidth.

  16. Self-collimation-based photonic crystal notch filters

    NASA Astrophysics Data System (ADS)

    Lee, Sun-Goo; Kim, Kap-Joong; Kim, Seong-Han; Kee, Chul-Sik

    2017-05-01

    We introduce a design concept of an optical notch filter (NF) utilizing two perfectly reflecting mirrors and a beam splitter. Based on the new design concept, a photonic crystal (PC)-NF based on the self-collimation phenomenon in a two-dimensional PC is proposed and studied through finite-difference time-domain simulations and experimental measurements in a microwave region. The transmission properties of the self-collimation-based PC-NF were demonstrated to be controlled by adjusting the values of parameters such as the radius of rods in the line-defect beam splitter, distance between the two perfectly reflecting mirrors, and radius of rods on the outermost surface of the perfectly reflecting mirrors. Our results indicate that the proposed design concept could provide a new approach to manipulate light propagation, and the PC-NF could increase the applicability of the self-collimation phenomenon in a PC.

  17. Minimum requirements for commissioning and long-term quality assurance of Elekta multi-leaf collimator for volumetric modulated arc therapy.

    PubMed

    Tatsumi, Daisaku; Nakada, Ryosei; Yomoda, Akane; Ishii, Kentaro; Tsutsumi, Shinichi; Inoue, Makoto; Ichida, Takao; Hosono, Masako N; Miki, Yukio

    2013-01-01

    We have proposed minimum requirements for commissioning and long-term quality assurance (QA) of an Elekta multi-leaf collimator (MLC) for volumetric modulated arc therapy (VMAT). The MLC leaf position accuracy during VMAT delivery was evaluated with the use of three different QA test plans: (1) a leaf gap-width test between opposing leaves by measurement of the isocenter dose during constant-gap sliding-window delivery with varied dose rates, MLC leaf speeds, and gantry angles; (2) a leaf position test by picket-fence delivery with and without gantry rotation; and (3) a leaf-bank symmetry test by measurement of the field geometry with different collimator angles at a fixed gantry position. All the QA test plans were created using an ERGO++ treatment-planning system. The leaf gap-width deviation was within 0.2 mm, the leaf position deviation was within 0.5 mm, and the leaf-bank symmetry error was within 0.5 mm under all the test conditions. MLC leaf position accuracy and long-term stability were confirmed by the proposed procedures.

  18. SU-E-T-515: Field-In-Field Compensation Technique Using Multi-Leaf Collimator to Deliver Total Body Irradiation (TBI) Dose

    SciTech Connect

    Lakeman, T; Wang, IZ

    2014-06-01

    Purpose: Total body irradiation (TBI) uses large parallel-opposed radiation fields to suppress the patient's immune system and eradicate the residual cancer cells in preparation of recipient for bone marrow transplant. The manual placement of lead compensators has been used conventionally to compensate for the varying thickness through the entire body in large-field TBI. The goal of this study is to pursue utilizing the modern field-in-field (FIF) technique with the multi-leaf collimator (MLC) to more accurately and efficiently deliver dose to patients in need of TBI. Method: Treatment plans utilizing the FIF technique to deliver a total body dose were created retrospectively for patients for whom CT data had been previously acquired. Treatment fields include one pair of opposed open large fields (collimator=45°) with a specific weighting and a succession of smaller fields (collimator=90°) each with their own weighting. The smaller fields are shaped by moving MLC to block the sections of the patient which have already received close to 100% of the prescribed dose. The weighting factors for each of these fields were calculated using the attenuation coefficient of the initial lead compensators and the separation of the patient in different positions in the axial plane. Results: Dose-volume histograms (DVH) were calculated for evaluating the FIF compensation technique. The maximum body doses calculated from the DVH were reduced from the non-compensated 179.3% to 148.2% in the FIF plans, indicating a more uniform dose with the FIF compensation. All calculated monitor units were well within clinically acceptable limits and exceeded those of the original lead compensation plan by less than 50 MU (only ~1.1% increase). Conclusion: MLC FIF technique for TBI will not significantly increase the beam on time while it can substantially reduce the compensator setup time and the potential risk of errors in manually placing lead compensators.

  19. Megavoltage Image-Based Dynamic Multileaf Collimator Tracking of a NiTi Stent in Porcine Lungs on a Linear Accelerator

    SciTech Connect

    Poulsen, Per R.; Carl, Jesper; Nielsen, Jane; Nielsen, Martin S.; Thomsen, Jakob B.; Jensen, Henrik K.; Kjaergaard, Benedict; Zepernick, Peter R.; Worm, Esben; Fledelius, Walther; Cho, Byungchul; Sawant, Amit; Ruan, Dan; Keall, Paul J.

    2012-02-01

    Purpose: To investigate the accuracy and potential limitations of MV image-based dynamic multileaf collimator (DMLC) tracking in a porcine model on a linear accelerator. Methods and Materials: A thermo-expandable NiTi stent designed for kilovoltage (kV) X-ray visualization of lung lesions was inserted into the bronchia of three anaesthetized Goettingen minipigs. A four-dimensional computed tomography scan was used for planning a five-field conformal treatment with circular multileaf collimator (MLC) apertures. A 22.5 Gy single fraction treatment was delivered to the pigs. The peak-to-peak stent motion was 3 to 8 mm, with breathing periods of 1.2 to 4 s. Before treatment, X-ray images were used for image-guided setup based on the stent. During treatment delivery, continuous megavoltage (MV) portal images were acquired at 7.5 Hz. The stent was segmented in the images and used for continuous adaptation of the MLC aperture. Offline, the tracking error in beam's eye view of the treatment beam was calculated for each MV image as the difference between the MLC aperture center and the segmented stent position. The standard deviations of the systematic error {Sigma} and the random error {sigma} were determined and compared with the would-be errors for a nontracking treatment with pretreatment image-guided setup. Results: Reliable stent segmentation was obtained for 11 of 15 fields. Segmentation failures occurred when image contrast was dominated by overlapping anatomical structures (ribs, diaphragm) rather than by the stent, which was designed for kV rather than MV X-ray visibility. For the 11 fields with reliable segmentation, {Sigma} was 0.5 mm/0.4 mm in the two imager directions, whereas {sigma} was 0.5 mm/1.1 mm. Without tracking, {Sigma} and {sigma} would have been 1.7 mm/1.4 mm and 0.8 mm/1.4 mm, respectively. Conclusion: For the first time, in vivo DMLC tracking has been demonstrated on a linear accelerator showing the potential for improved targeting accuracy. The

  20. Self-collimation-based photonic crystal Mach-Zehnder demultiplexer

    NASA Astrophysics Data System (ADS)

    Lee, Sun-Goo; Jung, Soo-Yong; Lee, Jongjin; Park, Jong-Moon; Kee, Chul-Sik

    2016-09-01

    A photonic crystal Mach-Zehnder demultiplexer (PC-MZDmux) with four output ports based on the self-collimation phenomenon in a two-dimensional (2D) PC is proposed and numerically studied using finite-difference time-domain simulations. The PC-MZDmux is composed of three Mach-Zehnder interferometers (MZIs) and each MZI consists of two 50:50 beam splitters and two perfect mirrors. Employed as the design parameters to achieve the demultiplexing functionality are the radius of phase control rods (PCRs) in the mirrors and the distance between the beam spitter and the mirror in the three MZIs. From spatial electric field distributions and transmission spectra, it is demonstrated that an incident self-collimated beam with four different frequencies can be demultiplexed to four output ports of the PC-MZDmux with proper design parameters. Our results indicate that this device design may constitute an efficient approach to light propagation manipulation and increase the application range of self-collimated beams.

  1. SU-E-T-600: Utilizing Collimator Rotation to Increase Maximum Treatable Target Dimensions Using an Elekta Synergy-S with Beam Modulator Multileaf Collimator.

    PubMed

    Rhodes, C; Campbell, S; Shields, W; Fabien, J; Colussi, V; Wessels, B

    2012-06-01

    To determine if a rotated collimator on an Elekta Synergy-S with Beam Modulator MLC (BMx) allows for dosimetrically acceptable treatment of targets exceeding the length of the maximum field size (21×16cm). The BMx is a high-resolution MLC with 4mm leaves but is of limited clinical use on patient target volumes exceeding 20cm in length. Rotation of the collimator utilizes the Pythagorean geometry to extend treatment length. This potentially increases the length of the PTV that be conformally treated. Rods of 21-23cm length were contoured in water with the Pinnacle treatment planning system. The width of the rods varies from 1 -5cm. Four isocentric treatment plans were generated for each target: four-field conformal, 7-field IMRT, single-arc VMAT, and a modified double-arc VMAT (MDAV), with the collimator angled at 55°. The MDAV method consists of two opposing 180° arcs with the collimator turned 55° in opposite directions. A successful plan is defined as 99% of the target volume being covered by a minimum of 95% of the prescribed dose. Conformality is determined as a ratio of the volume exposed to prescribed isodose and target volume. Targets of length 21cm, 22cm, and 23 cm are able to be treated with widths of 4cm, 5 cm, and 4cm respectively. The MDAV method achieves these results on all trials. The VMAT method achieves these results for the 21cm and 23cm long target. The IMRT Method achieves these results for the 21cm long target. With the exception of the 1cm wide targets, the average conformality is approximately 2.5. Changing the collimator angle of the BMx Elekta-S machine allows for a 3cm length increase of targets up to 5cm. Further work will assess clinical suitability of these findings for treatment of head and neck tumors and spinal masses. © 2012 American Association of Physicists in Medicine.

  2. Commissioning and quality assurance for intensity modulated radiotherapy with dynamic multileaf collimator: experience of the Pontificia Universidad Católica de Chile.

    PubMed

    Venencia, Carlos Daniel; Besa, Pelayo

    2004-01-01

    The objective of this paper is to present our experience in the commissioning and quality assurance (QA) for intensity modulated radiotherapy (IMRT) using dynamic multileaf collimator (dMLC), sliding window technique. Using Varian equipment solution, the connectivity and operation between all IMRT chain components was checked. Then the following test were done: stability of leaf positioning and leaf speed, sensitivity to treatment interruptions (acceleration and deceleration), evaluation of standard field patterns, stability of dMLC output, segmental dose accuracy check, average leaf transmission, dosimetric leaf separation, effects of lateral disequilibrium between adjacent leaves in dose profiles and multiple carriage field verification. Standard patterns were generated for verification: uniform field, pyramid, hole, wedge, peaks and chair. Weekly QA Protocol include: sweeping gap output, Garden Fence Test (narrow bands, 2 mm wide, of exposure spaced at 2-cm intervals) and segmental dose accuracy check. Monthly QA include: sweeping gap output at multiple gantry and collimator angle, sweeping gap output off-axis, Picket Fence Test (eight consecutive movements of a 5-cm wide rectangular field spaced at 5-cm intervals), stability of leaf speed and leaf motor current test (PWM test). Patient QA procedure consists of an absolute dose measurement for all treatments fields in the treatment condition, analysis of actual leaf position versus planned leaf position (dynalog files) for each treatment field, film relative dose determination for each field, film relative dose determination for the plan (all treatment fields) in two axial planes and patient positioning verification with orthogonal films. The tests performed showed acceptable result. After more than one year of IMRT treatment the routine QA machine checks confirm the precision and stability of the IMRT system.

  3. Electronic compensation using multileaf collimation for involved field radiation to the neck and mediastinum in non-Hodgkin's lymphoma and Hodgkin's lymphoma

    SciTech Connect

    MacDonald, Shelly; Bernard, Shelley; Balogh, Alex; Spencer, David; Sawchuk, Stephen . E-mail: stephen.sawchuk@swedish.org

    2005-06-30

    An efficient procedure is required for the preparation, planning, and delivery of radiation therapy for involved field radiation to the neck and mediastinum. This technique must reduce tissue complications while maintaining dose uniformity. An elegant intensity-modulated radiation therapy (IMRT) treatment that is forward planned has been developed. Both static fields and static subfields shaped by multileaf collimators (MLCs) and asymmetric jaws are used. Patients receiving involved field radiation to the neck and mediastinum are planned in 3 dimensions (3D), where 3D dose compensation is provided using subfields consisting of MLC or asymmetric jaws instead of physical compensators or wedges. Forward planning is performed, usually generating 2 pairs of parallel-opposed fields, with at least 1 of them consisting of subfields to eliminate elevated dose regions. Efficiency in the preparation, planning, and delivery of treatment has been achieved for more than 10 patients. Verification of treatment setup, target anatomy, and MLC configuration is quick when using an electronic portal imaging device. Thermoluminescent dosimeters (TLDs) have verified point-dose uniformity noticeably to {+-} 5%. An efficient technique using forward planning for simple IMRT consisting of static MLC and asymmetric jaws has been developed.

  4. Clinical effect of multileaf collimator width on the incidence of late rectal bleeding after high-dose intensity-modulated radiotherapy for localized prostate carcinoma.

    PubMed

    Inokuchi, Haruo; Mizowaki, Takashi; Norihisa, Yoshiki; Takayama, Kenji; Ikeda, Itaru; Nakamura, Kiyonao; Nakamura, Mitsuhiro; Hiraoka, Masahiro

    2016-02-01

    Several studies have confirmed a dosimetric advantage associated with use of a smaller leaf in intensity-modulated radiation therapy (IMRT). However, no studies have identified any clinical benefits. We investigated the effect of a smaller multileaf collimator (MLC) width on the onset of late rectal bleeding after high-dose prostate IMRT. Two hundred and five prostate cancer patients were treated with a total dose of 78 Gy in 39 fractions by use of a dynamic MLC technique; however, two different MLC were used: a 10-mm-wide device and a 5-mm-wide device. Gastrointestinal toxicity and several clinical factors were assessed. The 5-year actuarial risk of grade 2 or higher rectal bleeding was 6.9 % for the 10-mm-wide group (n = 132) and 1.8 % for the 5-mm-wide group (n = 73) (p = 0.04). The median estimated rectal doses for the two groups were 55.1 and 50.6 Gy (p < 0.001), respectively. Univariate analysis showed that acute toxicity, rectal V30-60, median rectal dose, normal tissue complication probability (NTCP), and MLC type were significant predictive factors for late rectal toxicity. In multivariate analysis, acute toxicity and NTCP remained significant. In our planning approach for prostate IMRT, a decrease in MLC width from 10 to 5 mm contributed to further rectal dose reduction, which was the most important predictor of late rectal toxicity.

  5. The influence of field size on stopping-power ratios in- and out-of-field: quantitative data for the BrainLAB m3 micro-multileaf collimator.

    PubMed

    Taylor, Michael; Kairn, Tanya; Kron, Tomas; Dunn, Leon; Johnston, Peter N; Franich, Rick D

    2012-11-08

    The objective of this work is to quantify the systematic errors introduced by the common assumption of invariant secondary electron spectra with changing field sizes, as relevant to stereotactic radiotherapy and other treatment modes incorporating small beam segments delivered with a linac-based stereotactic unit. The EGSnrc/BEAMnrc Monte Carlo radiation transport code was used to construct a dosimetrically-matched model of a Varian 600C linear accelerator with mounted BrainLAB micro-multileaf collimator. Stopping-power ratios were calculated for field sizes ranging from 6 × 6 mm2 up to the maximum (98 × 98 mm2), and differences between these and the reference field were computed. Quantitative stopping power data for the BrainLAB micro-multileaf collimator has been compiled. Field size dependent differences to reference conditions increase with decreasing field size and increasing depth, but remain a fraction of a percent for all field sizes studied. However, for dosimetry outside the primary field, errors induced by the assumption of invariant electron spectra can be greater than 1%, increasing with field size. It is also shown that simplification of the Spencer-Attix formulation by ignoring secondary electrons below the cutoff kinetic energy applied to the integration results in underestimation of stopping-power ratios of about 0.3% (and is independent of field size and depth). This work is the first to quantify stopping powers from a BrainLAB micro-multileaf collimator. Many earlier studies model simplified beams, ignoring collimator scatter, which is shown to significantly influence the spectrum. Importantly, we have confirmed that the assumption of unchanging electron spectra with varying field sizes is justifiable when performing (typical) in-field dosimetry of stereotactic fields. Clinicians and physicists undertaking precise out-of-field measurements for the purposes of risk estimation, ought to be aware that the more pronounced spectral variation results

  6. Bending self-collimated one-way light by using gyromagnetic photonic crystals

    SciTech Connect

    Li, Qing-Bo; Li, Zhen; Wu, Rui-xin

    2015-12-14

    We theoretically demonstrate that electromagnetic waves can self-collimate and propagate unidirectionally in photonic crystals fabricated using semicylindrical ferrite rods in magnetized states. The parity and time-reversal symmetries of such photonic crystals are broken, resulting in a self-collimated one-way body wave within the photonic crystals. By applying the bias magnetic field in a complex configuration, the self-collimated one-way wave beam can be bent into arbitrary trajectories within the photonic crystal, providing an avenue for controlling wave beams.

  7. Integration of real-time internal electromagnetic position monitoring coupled with dynamic multileaf collimator tracking: an intensity-modulated radiation therapy feasibility study.

    PubMed

    Smith, Ryan L; Sawant, Amit; Santanam, Lakshmi; Venkat, Raghu B; Newell, Laurence J; Cho, Byung-Chul; Poulsen, Per; Catell, Herbert; Keall, Paul J; Parikh, Parag J

    2009-07-01

    Continuous tumor position measurement coupled with a tumor tracking system would result in a highly accurate radiation therapy system. Previous internal position monitoring systems have been limited by fluoroscopic radiation dose and low delivery efficiency. We aimed to incorporate a continuous, electromagnetic, three-dimensional position tracking system (Calypso 4D Localization System) with a dynamic multileaf collimator (DMLC)-based dose delivery system. A research version of the Calypso System provided real-time position of three Beacon transponders. These real-time three-dimensional positions were sent to research MLC controller with a motion-tracking algorithm that changed the planned leaf sequence. Electromagnetic transponders were embedded in a solid water film phantom that moved with patient lung trajectories while being irradiated with two different plans: a step-and-shoot intensity-modulated radiation therapy (S-IMRT) field and a dynamic IMRT (D-IMRT) field. Dosimetric results were recorded under three conditions: no intervention, DMLC tracking, and a spatial gating system. Dosimetric accuracy was comparable for gating and DMLC tracking. Failure rates for gating/DMLC tracking are as follows: +/-3 cGy 10.9/ 7.5% for S-IMRT, 3.3/7.2% for D-IMRT; gamma (3mm/3%) 0.2/1.2% for S-IMRT, 0.2/0.2% for D-IMRT. DMLC tracking proved to be as efficient as standard delivery, with a two- to fivefold efficiency increase over gating. Real-time target position information was successfully integrated into a DMLC effector system to modify dose delivery. Experimental results show both comparable dosimetric accuracy as well as improved efficiency compared with spatial gating.

  8. Implementation of a New Method for Dynamic Multileaf Collimator Tracking of Prostate Motion in Arc Radiotherapy Using a Single KV Imager

    SciTech Connect

    Poulsen, Per Rugaard; Cho, Byungchul; Sawant, Amit; Keall, Paul J.

    2010-03-01

    Purpose: To implement a method for real-time prostate motion estimation with a single kV imager during arc radiotherapy and to integrate it with dynamic multileaf collimator (DMLC) target tracking. Methods and Materials: An arc field with a circular aperture and 358 deg. gantry rotation was delivered to a motion phantom with a fiducial marker under continuous kV X-ray imaging at 5 Hz, perpendicular to the treatment beam. A pretreatment gantry rotation of 120 deg. in 20 sec with continuous imaging preceded the treatment. During treatment, each kV image was first used together with all previous images to estimate the three-dimensional (3D) target probability density function and then used together with this probability density function to estimate the 3D target position. The MLC aperture was then adapted to the estimated 3D target position. Tracking was performed with five patient-measured prostate trajectories that represented characteristic prostate motion patterns. Two data sets were recorded during tracking: (1) the estimated 3D target positions, for off-line comparison with the actual phantom motion; and (2) continuous portal images, for independent off-line calculation of the 2D tracking error as the positional difference between the marker and the MLC aperture center in each portal image. All experiments were also made with 1- Hz kV imaging. Results: The mean 3D root-mean-square error of the trajectory estimation was 0.6 mm. The mean root-mean-square tracking error was 0.7 mm, both parallel and perpendicular to the MLC. The accuracy degraded slightly for 1- Hz imaging. Conclusions: Single-imager DMLC prostate tracking that allows arbitrary beam modulation during arc radiotherapy was implemented. It has submillimeter accuracy for most prostate motion types.

  9. SU-E-T-424: Dosimetric Verification of Modulated Electron Radiation Therapy Delivered Using An Electron Specific Multileaf Collimator for Treatment of Scalp Cases

    SciTech Connect

    Eldib, A; Jin, L; Martin, J; Li, J; Chibani, O; Galloway, T; Ma, C; Mora, G

    2014-06-01

    Purpose: Modulated electron radiotherapy (MERT) has the potential to achieve better treatment outcome for shallow tumors such as those of breast and scalp. In a separate study with scalp lesions, MERT was compared to volumetric modulated arc therapy. Our results showed a reduction in the dose reaching the brain with MERT. However dose calculation accuracy and delivery efficiency challenges remain. Thus in the current study we proceed to add more cases to demonstrate MERT beneficial outcome and its delivery accuracy using an electron specific multileaf collimator (eMLC). Methods: We have used the MCBEAM code for treatment head simulation and for generating phase space files to be used as radiation source input for our Monte Carlo based treatment planning system (MC TPS). MCPLAN code is used for calculation of patient specific dose deposition coefficient and for final MERT plan dose calculation. An in-house developed optimization code is used for the optimization process. MERT plans were generated for real patients and head and neck phantom. Film was used for dosimetric verification. The film was cut following the contour of the curved phantom surface and then sealed with black masking tape. In the measurement, the sealed film packet was sandwiched between two adjacent slabs of the head and neck phantom. The measured 2D dose distribution was then compared with calculations. Results: The eMLC allows effective treatment of scalps with multi-lesions spreading around the patient head, which was usually difficult to plan or very time consuming with conventional applicators. MERT continues to show better reduction in the brain dose. The dosimetric measurements showed slight discrepancy, which was attributed to the film setup. Conclusion: MERT can improve treatment plan quality for patients with scalp cancers. Our in-house MC TPS is capable of performing treatment planning and accurate dose calculation for MERT using the eMLC.

  10. Influence of multi-leaf collimator leaf width in radiosurgery via volumetric modulated arc therapy and 3D dynamic conformal arc therapy.

    PubMed

    Serna, Alfredo; Puchades, Vicente; Mata, Fernando; Ramos, David; Alcaraz, Miguel

    2015-05-01

    To study the influence of Multileaf Collimator (MLC) leaf width in radiosurgery treatment planning for Volumetric Modulated Arc Therapy (VMAT) and 3D Dynamic Conformal Arc Therapy (3D-DCA). 16 patients with solitary brain metastases treated with radiosurgery via the non-coplanar VMAT were replanned for the 3D-DCA. For each planning technique two MLC leaf width sizes were utilized, i.e. 5 mm and 2.5 mm. These treatment plans were compared using dosimetric indices (conformity, gradient and mean dose for brain tissue) and the normal tissue complication probability (NTCP). An improvement in planning quality for VMAT was observed versus 3D-DCA for any MLC leaf width, mainly with regards to dose conformity and to a lesser extent regards dose gradient. No significant difference was observed for any of both techniques using smaller leaf width. However, dose gradient was improved in favor of the 2.5 mm MLC for either of both techniques (15% VMAT and 10% 3D-DCA); being noticeable for lesions smaller than 10cm(3). Nonetheless, the NTCP index was not significantly affected by variations in the dose gradient index. This, our present study, suggests that the use of an MLC leaf width of 2.5 mm via the noncoplanar VMAT and 3D-DCA techniques provides improvement in terms of dose gradient for small volumes, over those results obtained with an MLC leaf width of 5 mm. The 3D-DCA does also benefit from MLC leaf widths of a smaller size, mainly in terms of conformity. Copyright © 2015 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

  11. Development and verification of a time delivery model for prostate intensity modulated radiotherapy using a Siemens(®) Artiste™ 160 Multi-leaf Collimator Linac.

    PubMed

    Fourie, Nicola; Ali, Omer A; Rae, William I D

    2017-03-01

    Time delivery models thus far proposed for prediction of radiotherapy delivery times are not applicable to all makes of Linac. Our purpose was to develop a time delivery model, which would also be applicable for a Siemens(®) ARTISTE™ 160 Multi-leaf Collimator (MLC) linear accelerator (Linac) and validate the model using prostate Intensity Modulated Radiation Therapy (IMRT) treatment plans. To our knowledge, a time delivery model has not yet been proposed for a Siemens(®) ARTISTE™ 160 MLC Linac. We used the principles of the time delivery model created for a Varian(®) Linac and added the radio frequency (RF) wave component, and the MLC delay time to the MLC travel time component. Machine input parameters were confirmed using a WIN(®) stopwatch. We tested our derived model by selecting ten random 15 MV prostate IMRT treatment plans from our clinic. The delivery time was measured three times, once per day on three different days. The calculated and measured times were compared by means of correlation. The time delivery ranged between 314 and 480 s. The largest percentage difference was 3.3% (16 s) and the smallest 0.2% (1 s); the mean percentage difference was 1.9%. MLC delay and MLC speed, representing segment delivery, had the greatest uncertainties. From the successfully verified time delivery model created, it is concluded that the inter-segmental component of the process is most time-consuming. In order to decrease delivery time it is proposed that the total segments of a treatment plan be decreased.

  12. Multileaf collimator tongue-and-groove effect on depth and off-axis doses: A comparison of treatment planning data with measurements and Monte Carlo calculations

    SciTech Connect

    Kim, Hee Jung; Kim, Siyong; Park, Yang-Kyun; Kim, Jung-in; Park, Jong Min; Ye, Sung-Joon

    2015-01-01

    To investigate how accurately treatment planning systems (TPSs) account for the tongue-and-groove (TG) effect, Monte Carlo (MC) simulations and radiochromic film (RCF) measurements were performed for comparison with TPS results. Two commercial TPSs computed the TG effect for Varian Millennium 120 multileaf collimator (MLC). The TG effect on off-axis dose profile at 3 depths of solid water was estimated as the maximum depth and the full width at half maximum (FWHM) of the dose dip at an interleaf position. When compared with the off-axis dose of open field, the maximum depth of the dose dip for MC and RCF ranged from 10.1% to 20.6%; the maximum depth of the dose dip gradually decreased by up to 8.7% with increasing depths of 1.5 to 10 cm and also by up to 4.1% with increasing off-axis distances of 0 to 13 cm. However, TPS results showed at most a 2.7% decrease for the same depth range and a negligible variation for the same off-axis distances. The FWHM of the dose dip was approximately 0.19 cm for MC and 0.17 cm for RCF, but 0.30 cm for Eclipse TPS and 0.45 cm for Pinnacle TPS. Accordingly, the integrated value of TG dose dip for TPS was larger than that for MC and RCF and almost invariant along the depths and off-axis distances. We concluded that the TG dependence on depth and off-axis doses shown in the MC and RCF results could not be appropriately modeled by the TPS versions in this study.

  13. Impacts of multileaf collimators leaf width on intensity-modulated radiotherapy planning for nasopharyngeal carcinoma: analysis of two commercial elekta devices.

    PubMed

    Wang, Shichao; Gong, Youling; Xu, Qingfeng; Bai, Sen; Lu, You; Jiang, Qingfeng; Chen, Nianyong

    2011-01-01

    We compared the impacts of multileaf collimator (MLC) widths (standard MLC width of 10 mm [SMLC] and micro-MLC width of 4 mm [MMLC]) on intensity-modulated radiotherapy (IMRT) planning for nasopharyngeal carcinoma (NPC). Ten patients with NPC were recruited in this study. In each patient's case, plans were generated with the same machine setup parameter and optimizing methods in a treatment planning system according to 2 commercial Elekta MLC devices. All of the parameters were collected from dose-volume histograms of paired plans and evaluated. The average conformity index (CI) and homogeneous index (HI) for the planning gross target volume in IMRT plans with MMLC were 0.790 ± 0.036 and 1.062 ± 0.011, respectively. Data in plans with SMLC were 0.754 ± 0.038 and 1.070 ± 0.010, respectively. The differences were statistically significant (p < 0.05). Compared with CI and HI for planning target volume in paired plans, data with MMLC obviously were better than those with SMLC (CI: 0.858 ± 0.026 vs. 0.850 ± 0.021, p < 0.05; and HI: 1.185 ± 0.011 vs. 1.195 ± 0.011, p < 0.05). However, there was no statistical significance between evaluated parameters (Dmean, Dmax, D₅, gEUD, or NTCP) for organs at risk (OARs) in the 2 paired IMRT plans. According to these two kinds of Elekta MLC devices, IMRT plans with the MMLC have significant advantages in dose coverage for the targets, with more efficiency in treatment for NPC but fail to improve dose sparing of the OARs.

  14. Impacts of Multileaf Collimators Leaf Width on Intensity-Modulated Radiotherapy Planning for Nasopharyngeal Carcinoma: Analysis of Two Commercial Elekta Devices

    SciTech Connect

    Wang Shichao; Gong Youling; Xu Qingfeng; Bai Sen; Lu You; Jiang Qingfeng; Chen Nianyong

    2011-07-01

    We compared the impacts of multileaf collimator (MLC) widths (standard MLC width of 10 mm [SMLC] and micro-MLC width of 4 mm [MMLC]) on intensity-modulated radiotherapy (IMRT) planning for nasopharyngeal carcinoma (NPC). Ten patients with NPC were recruited in this study. In each patient's case, plans were generated with the same machine setup parameter and optimizing methods in a treatment planning system according to 2 commercial Elekta MLC devices. All of the parameters were collected from dose-volume histograms of paired plans and evaluated. The average conformity index (CI) and homogeneous index (HI) for the planning gross target volume in IMRT plans with MMLC were 0.790 {+-} 0.036 and 1.062 {+-} 0.011, respectively. Data in plans with SMLC were 0.754 {+-} 0.038 and 1.070 {+-} 0.010, respectively. The differences were statistically significant (p < 0.05). Compared with CI and HI for planning target volume in paired plans, data with MMLC obviously were better than those with SMLC (CI: 0.858 {+-} 0.026 vs. 0.850 {+-} 0.021, p < 0.05; and HI: 1.185 {+-} 0.011 vs. 1.195 {+-} 0.011, p < 0.05). However, there was no statistical significance between evaluated parameters (Dmean, Dmax, D{sub 5}, gEUD, or NTCP) for organs at risk (OARs) in the 2 paired IMRT plans. According to these two kinds of Elekta MLC devices, IMRT plans with the MMLC have significant advantages in dose coverage for the targets, with more efficiency in treatment for NPC but fail to improve dose sparing of the OARs.

  15. Impact of the number of control points has on isodose distributions in a dynamic multileaf collimator intensity-modulated radiation therapy delivery

    SciTech Connect

    Goraj, Andrew; Boer, Steven F. de

    2012-01-01

    Intensity-modulated radiation therapy (IMRT) is a powerful technique in planning the delivery of dose. The most common IMRT delivery requires the use of moving multileaf collimators (MLCs) to deliver the requested fluence pattern. A dynamic delivery IMRT field file will contain several control points that are defined MLC shapes at a marked fraction of the delivered monitor units. The size of this file and the fidelity of the deliverable fluence are proportional to the number of control points defined. This study investigates the effect of reducing the number of control points has on the resultant dose distribution quality in complex IMRT in efforts to reduce transfer times, loading times, check sum times and file storage. Analysis was performed with 6 head and neck patients on an Eclipse version 8.5 treatment planning system (Varian, Palo Alto, CA). To ensure the quality of all treatments, Eclipse defines a minimum of 64 and a maximum of 320 control points per subfield (Eclipse Algorithms Reference guide). All 6 patients' plans were calculated with fixed 64, 166, and 320 control points using the sliding window technique. In addition, each plan was calculated in variable mode (Normal mode) in which the planning system determined the required number of control points. Each of the 4 plans for each patient was renormalized to provide the same mean planning target volume (PTV) 70 dose. Dose values for critical and target structures were examined for each patient. When examining the minimum, maximum, and mean doses to all target structures, it was noted that the greatest reduction in target dose coverage caused by reduced number of control points was 0.5%, which occurred for the minimum dose to the PTV56 structure in one plan.' Dose analysis for critical structures showed no clinically significant increase in dose when compared with the 320 control point plan.

  16. Integration of Real-Time Internal Electromagnetic Position Monitoring Coupled With Dynamic Multileaf Collimator Tracking: An Intensity-Modulated Radiation Therapy Feasibility Study

    SciTech Connect

    Smith, Ryan L.; Sawant, Amit PhD.; Santanam, Lakshmi PhD.; Venkat, Raghu B.; Newell, Laurence J.; Cho, Byung-chul; Poulsen, Per; Catell, Herbert; Keall, Paul J.; Parikh, Parag J.

    2009-07-01

    Purpose: Continuous tumor position measurement coupled with a tumor tracking system would result in a highly accurate radiation therapy system. Previous internal position monitoring systems have been limited by fluoroscopic radiation dose and low delivery efficiency. We aimed to incorporate a continuous, electromagnetic, three-dimensional position tracking system (Calypso 4D Localization System) with a dynamic multileaf collimator (DMLC)-based dose delivery system. Methods and Materials: A research version of the Calypso System provided real-time position of three Beacon transponders. These real-time three-dimensional positions were sent to research MLC controller with a motion-tracking algorithm that changed the planned leaf sequence. Electromagnetic transponders were embedded in a solid water film phantom that moved with patient lung trajectories while being irradiated with two different plans: a step-and-shoot intensity-modulated radiation therapy (S-IMRT) field and a dynamic IMRT (D-IMRT) field. Dosimetric results were recorded under three conditions: no intervention, DMLC tracking, and a spatial gating system. Results: Dosimetric accuracy was comparable for gating and DMLC tracking. Failure rates for gating/DMLC tracking are as follows: {+-}3 cGy 10.9/ 7.5% for S-IMRT, 3.3/7.2% for D-IMRT; gamma (3mm/3%) 0.2/1.2% for S-IMRT, 0.2/0.2% for D-IMRT. DMLC tracking proved to be as efficient as standard delivery, with a two- to fivefold efficiency increase over gating. Conclusions: Real-time target position information was successfully integrated into a DMLC effector system to modify dose delivery. Experimental results show both comparable dosimetric accuracy as well as improved efficiency compared with spatial gating.

  17. Dosimetric impact of multileaf collimator leaf width according to sophisticated grade of technique in the IMRT and VMAT planning for pituitary adenoma lesion

    PubMed Central

    Chae, Soo-Min; Lee, Ki Woong; Son, Seok Hyun

    2016-01-01

    We analyzed the difference in the dosimetric effect between 5-mm and 2.5-mm multileaf collimator (MLC) leaf width according to the sophisticated grades of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT). Nineteen patients with pituitary adenomas were selected for this study. The treatment plans were performed according to the size of the MLC (5-mm and 2.5-mm MLC), the type of technique (IMRT and VMAT), and the sophisticated grades of each technique (5-field, 9-field, 13-field, 17-field technique in IMRT and 1-arc and 2-arc techniques in VMAT). The downsizing effects of MLC leaf width were analyzed using target volume coverage (TVC), conformity index (CI), dose gradient index (GI), and normal tissue difference 70% isodose line and 50% isodose line. Upon replacing the 5-mm MLC with the 2.5-mm MLC, TVC and CI improved by 1.30% and 1.36%, respectively, in total plans. The TVC and CI improved by 1.68% and 1.67% in IMRT, respectively, and by 0.54% and 0.72% in VMAT, respectively. TVC improved by 2.53%, 1.82%, 1.34%, and 0.94%, and CI also improved by 2.70%, 1.81%, 1.24%, and 0.94%, in 5-field, 9-field, 13-field, and 17-field IMRT, respectively. TVC improved by 0.66% and 0.43%, and CI also improved by 0.93%, and 0.52% in 1-arc and 2-arc VMAT, respectively. Regarding the target coverage, there were dosimetric benefits of a smaller MLC leaf width. However, the downsizing effect of the MLC leaf width decreased with the use of a more precise RT technique and a more sophisticated grade of the same technique. PMID:27806336

  18. Advances in Pinhole and Multi-Pinhole Collimators for Single Photon Emission Computed Tomography Imaging

    PubMed Central

    Islamian, Jalil Pirayesh; Azazrm, AhmadReza; Mahmoudian, Babak; Gharapapagh, Esmail

    2015-01-01

    The collimator in single photon emission computed tomography (SPECT), is an important part of the imaging chain. One of the most important collimators that used in research, preclinical study, small animal, and organ imaging is the pinhole collimator. Pinhole collimator can improve the tradeoff between sensitivity and resolution in comparison with conventional parallel-hole collimator and facilities diagnosis. However, a major problem with pinhole collimator is a small field of view (FOV). Multi-pinhole collimator has been investigated in order to increase the sensitivity and FOV with a preserved spatial resolution. The geometry of pinhole and multi-pinhole collimators is a critical factor in the image quality and plays a key role in SPECT imaging. The issue of the material and geometry for pinhole and multi-pinhole collimators have been a controversial and much disputed subject within the field of SPECT imaging. On the other hand, recent developments in collimator optimization have heightened the need for appropriate reconstruction algorithms for pinhole SPECT imaging. Therefore, iterative reconstruction algorithms were introduced to minimize the undesirable effect on image quality. Current researches have focused on geometry and configuration of pinhole and multi-pinhole collimation rather than reconstruction algorithm. The lofthole and multi-lofthole collimator are samples of novel designs. The purpose of this paper is to provide a review on recent researches in the pinhole and multi-pinhole collimators for SPECT imaging. PMID:25709537

  19. Advances in pinhole and multi-pinhole collimators for single photon emission computed tomography imaging.

    PubMed

    Islamian, Jalil Pirayesh; Azazrm, AhmadReza; Mahmoudian, Babak; Gharapapagh, Esmail

    2015-01-01

    The collimator in single photon emission computed tomography (SPECT), is an important part of the imaging chain. One of the most important collimators that used in research, preclinical study, small animal, and organ imaging is the pinhole collimator. Pinhole collimator can improve the tradeoff between sensitivity and resolution in comparison with conventional parallel-hole collimator and facilities diagnosis. However, a major problem with pinhole collimator is a small field of view (FOV). Multi-pinhole collimator has been investigated in order to increase the sensitivity and FOV with a preserved spatial resolution. The geometry of pinhole and multi-pinhole collimators is a critical factor in the image quality and plays a key role in SPECT imaging. The issue of the material and geometry for pinhole and multi-pinhole collimators have been a controversial and much disputed subject within the field of SPECT imaging. On the other hand, recent developments in collimator optimization have heightened the need for appropriate reconstruction algorithms for pinhole SPECT imaging. Therefore, iterative reconstruction algorithms were introduced to minimize the undesirable effect on image quality. Current researches have focused on geometry and configuration of pinhole and multi-pinhole collimation rather than reconstruction algorithm. The lofthole and multi-lofthole collimator are samples of novel designs. The purpose of this paper is to provide a review on recent researches in the pinhole and multi-pinhole collimators for SPECT imaging.

  20. Photonic drop splitters based on silicon photonic crystal cascaded self-collimation ring resonators

    NASA Astrophysics Data System (ADS)

    Lin, Yuan-Yuan; Chen, Xi-Yao; Jiang, Jun-Zhen; Fu, Ping; Chen, Biao; Yang, Li-Hui; Liu, Jing-Ping; Lin, Bao-Cheng

    2014-10-01

    In this paper, the 1×5 optical splitters (OSs) based on 2D rod-type silicon photonic crystal embed cascaded self-collimation (SC) ring resonators (CSCRR) was proposed. The 1×5 OSs consist of eight beam splitters, which are formed by varying the radii of the rod. With self-collimation effect, we can manipulate the light's propagation in the OSs. Here we consider TM modes. Utilizing multiple-beam interference theory, the theoretical transmission spectra at different outputs were analysed. These transmission spectra can help us to set the radii of eight slitters properly, for we can control the light coming out from five ports with the light-intensity ratio we need. Meanwhile these outputs' transmission spectra were investigated by the finite-difference time-domain (FDTD) method. The simulative results have an agreement with the theoretical prediction. The 1×5 OSs will have practical applications in photonic integrated circuits.

  1. Tracking 'differential organ motion' with a 'breathing' multileaf collimator: magnitude of problem assessed using 4D CT data and a motion-compensation strategy

    NASA Astrophysics Data System (ADS)

    McClelland, J. R.; Webb, S.; McQuaid, D.; Binnie, D. M.; Hawkes, D. J.

    2007-08-01

    Intrafraction tumour (e.g. lung) motion due to breathing can, in principle, be compensated for by applying identical breathing motions to the leaves of a multileaf collimator (MLC) as intensity-modulated radiation therapy is delivered by the dynamic MLC (DMLC) technique. A difficulty arising, however, is that irradiated voxels, which are in line with a bixel at one breathing phase (at which the treatment plan has been made), may move such that they cease to be in line with that breathing bixel at another phase. This is the phenomenon of differential voxel motion and existing tracking solutions have ignored this very real problem. There is absolutely no tracking solution to the problem of compensating for differential voxel motion. However, there is a strategy that can be applied in which the leaf breathing is determined to minimize the geometrical mismatch in a least-squares sense in irradiating differentially-moving voxels. A 1D formulation in very restricted circumstances is already in the literature and has been applied to some model breathing situations which can be studied analytically. These are, however, highly artificial. This paper presents the general 2D formulation of the problem including allowing different importance factors to be applied to planning target volume and organ at risk (or most generally) each voxel. The strategy also extends the literature strategy to the situation where the number of voxels connecting to a bixel is a variable. Additionally the phenomenon of 'cross-leaf-track/channel' voxel motion is formally addressed. The general equations are presented and analytic results are given for some 1D, artificially contrived, motions based on the Lujan equations of breathing motion. Further to this, 3D clinical voxel motion data have been extracted from 4D CT measurements to both assess the magnitude of the problem of 2D motion perpendicular to the beam-delivery axis in clinical practice and also to find the 2D optimum breathing-leaf strategy

  2. SU-E-T-331: Dosimetric Impact of Multileaf Collimator Leaf Width On Stereotactic Radiosurgery (SRS) RapidArc Treatment Plans for Single and Multiple Brain Metastases

    SciTech Connect

    Hossain, S; Keeling, V; Ahmad, S; Algan, O

    2015-06-15

    Purpose: To determine the effects of multileaf collimator (MLC) leaf width on normal-brain-tissue doses and dose conformity of SRS RapidArc treatment plans for brain tumors. Methods: Ten patients with 24 intracranial tumors (seven with 1–2 and three with 4–6 lesions) were planned using RapidArc for both Varian Millennium 120 MLC (5 mm leaf width) and high definition (HD) MLC (2.5 mm leaf width). Between 2 and 8 arcs were used with two full coplanar arcs and the rest non-coplanar half arcs. 6 MV beams were used and plans were optimized with a high priority to the Normal Tissue Objective (to achieve dose conformity and sharp dose fall-off) and normal brain tissue. Calculation was done using AAA on a 1 mm grid size. The prescription dose ranged from 14–22 Gy. Plans were normalized such that 99% of the target received the prescription dose. Identical beam geometries, optimizations, calculations, and normalizations were used for both plans. Paddick Conformity Index (PCI), V4, V8 and V12 Gy for normal brain tissue and Integral Dose were used for analysis. Results: In all cases, HD MLC plans performed better in sparing normal brain tissue, achieving a higher PCI with a lower Integral Dose. The average PCI for all 24 targets was 0.75±0.23 and 0.70±0.23 (p ≤0.0015) for HD MLC and Millennium MLC plans, respectively. The average ratio of normal brain doses for Millennium MLC to HD MLC plans was 1.30±0.16, 1.27±0.15, and 1.31±0.18 for the V4, V8, and V12, respectively. The differences in normal brain dose for all criteria were statistically significant with p-value < 0.02. On average Millennium MLC plans had a 16% higher integral dose than HD MLC plans. Conclusion: Significantly better dose conformity with reduced volume of normal brain tissue and integral dose was achieved with HD MLC plans compared to Millennium MLC plans.

  3. SU-E-T-428: Dosimetric Impact of Multileaf Collimator Leaf Width On Single and multiple Isocenter Stereotactic IMRT Treatment Plans for multiple Brain Tumors

    SciTech Connect

    Giem, J; Algan, O; Ahmad, S; Ali, I; Young, J; Hossain, S

    2014-06-01

    Purpose: To assess the impacts that multileaf collimator (MLC) leaf width has on the dose conformity and normal brain tissue doses of single and multiple isocenter stereotactic IMRT (SRT) plans for multiple intracranial tumors. Methods: Fourteen patients with 2–3 targets were studied retrospectively. Patients treated with multiple isocenter treatment plans using 9 to 12 non-coplanar beams per lesion underwent repeat planning using single isocenter and 10 to 12 non-coplanar beams with 2.5mm, 3mm and 5mm MLC leaf widths. Brainlab iPlan treatment planning system for delivery with the 2.5mm MLC served as reference. Identical contour sets and dose-volume constraints were applied. The prescribed dose to each target was 25 Gy to be delivered over 5 fractions with a minimum of 99% dose to cover ≥ 95% of the target volume. Results: The lesions and normal brains ranged in size from 0.11 to 51.67cc (median, 2.75cc) and 1090 to 1641cc (median, 1401cc), respectively. The Paddick conformity index for single and multiple isocenter (2.5mm vs. 3mm and 5mm MLCs) was (0.79±0.08 vs. 0.79±0.07 and 0.77±0.08) and (0.79±0.09 vs. 0.77±0.09 and 0.76±0.08), respectively. The average normal brain volumes receiving 15 Gy for single and multiple isocenter (2.5mm vs. 3mm and 5mm MLCs) were (3.65% vs. 3.95% and 4.09%) and (2.89% vs. 2.91% and 2.92%), respectively. Conclusion: The average dose conformity observed for the different leaf width for single and multiple isocenter plans were similar, throughout. However, the average normal brain volumes receiving 2.5 to 15 Gy were consistently lower for the 2.5mm MLC leaf width, especially for single isocenter plans. The clinical consequences of these integral normal brain tissue doses are still unknown, but employing the use of the 2.5mm MLC option is desirable at sparing normal brain tissue for both single and multiple isocenter cases.

  4. Tracking 'differential organ motion' with a 'breathing' multileaf collimator: magnitude of problem assessed using 4D CT data and a motion-compensation strategy.

    PubMed

    McClelland, J R; Webb, S; McQuaid, D; Binnie, D M; Hawkes, D J

    2007-08-21

    Intrafraction tumour (e.g. lung) motion due to breathing can, in principle, be compensated for by applying identical breathing motions to the leaves of a multileaf collimator (MLC) as intensity-modulated radiation therapy is delivered by the dynamic MLC (DMLC) technique. A difficulty arising, however, is that irradiated voxels, which are in line with a bixel at one breathing phase (at which the treatment plan has been made), may move such that they cease to be in line with that breathing bixel at another phase. This is the phenomenon of differential voxel motion and existing tracking solutions have ignored this very real problem. There is absolutely no tracking solution to the problem of compensating for differential voxel motion. However, there is a strategy that can be applied in which the leaf breathing is determined to minimize the geometrical mismatch in a least-squares sense in irradiating differentially-moving voxels. A 1D formulation in very restricted circumstances is already in the literature and has been applied to some model breathing situations which can be studied analytically. These are, however, highly artificial. This paper presents the general 2D formulation of the problem including allowing different importance factors to be applied to planning target volume and organ at risk (or most generally) each voxel. The strategy also extends the literature strategy to the situation where the number of voxels connecting to a bixel is a variable. Additionally the phenomenon of 'cross-leaf-track/channel' voxel motion is formally addressed. The general equations are presented and analytic results are given for some 1D, artificially contrived, motions based on the Lujan equations of breathing motion. Further to this, 3D clinical voxel motion data have been extracted from 4D CT measurements to both assess the magnitude of the problem of 2D motion perpendicular to the beam-delivery axis in clinical practice and also to find the 2D optimum breathing-leaf strategy

  5. Feasibility of using Geant4 Monte Carlo simulation for IMRT dose calculations for the Novalis Tx with a HD-120 multi-leaf collimator

    NASA Astrophysics Data System (ADS)

    Jung, Hyunuk; Shin, Jungsuk; Chung, Kwangzoo; Han, Youngyih; Kim, Jinsung; Choi, Doo Ho

    2015-05-01

    The aim of this study was to develop an independent dose verification system by using a Monte Carlo (MC) calculation method for intensity modulated radiation therapy (IMRT) conducted by using a Varian Novalis Tx (Varian Medical Systems, Palo Alto, CA, USA) equipped with a highdefinition multi-leaf collimator (HD-120 MLC). The Geant4 framework was used to implement a dose calculation system that accurately predicted the delivered dose. For this purpose, the Novalis Tx Linac head was modeled according to the specifications acquired from the manufacturer. Subsequently, MC simulations were performed by varying the mean energy, energy spread, and electron spot radius to determine optimum values of irradiation with 6-MV X-ray beams by using the Novalis Tx system. Computed percentage depth dose curves (PDDs) and lateral profiles were compared to the measurements obtained by using an ionization chamber (CC13). To validate the IMRT simulation by using the MC model we developed, we calculated a simple IMRT field and compared the result with the EBT3 film measurements in a water-equivalent solid phantom. Clinical cases, such as prostate cancer treatment plans, were then selected, and MC simulations were performed. The accuracy of the simulation was assessed against the EBT3 film measurements by using a gamma-index criterion. The optimal MC model parameters to specify the beam characteristics were a 6.8-MeV mean energy, a 0.5-MeV energy spread, and a 3-mm electron radius. The accuracy of these parameters was determined by comparison of MC simulations with measurements. The PDDs and the lateral profiles of the MC simulation deviated from the measurements by 1% and 2%, respectively, on average. The computed simple MLC fields agreed with the EBT3 measurements with a 95% passing rate with 3%/3-mm gamma-index criterion. Additionally, in applying our model to clinical IMRT plans, we found that the MC calculations and the EBT3 measurements agreed well with a passing rate of greater

  6. Cardiac single-photon emission-computed tomography using combinedcone-beam/fan-beam collimation

    SciTech Connect

    Gullberg, Grant T.; Zeng, Gengsheng L.

    2004-12-03

    The objective of this work is to increase system sensitivity in cardiac single-photon emission-computed tomography (SPECT) studies without increasing patient imaging time. For imaging the heart, convergent collimation offers the potential of increased sensitivity over that of parallel-hole collimation. However, if a cone-beam collimated gamma camera is rotated in a planar orbit, the projection data obtained are not complete. Two cone-beam collimators and one fan-beam collimator are used with a three-detector SPECT system. The combined cone-beam/fan-beam collimation provides a complete set of data for image reconstruction. The imaging geometry is evaluated using data acquired from phantom and patient studies. For the Jaszazck cardiac torso phantom experiment, the combined cone-beam/fan-beam collimation provided 1.7 times greater sensitivity than standard parallel-hole collimation (low-energy high-resolution collimators). Also, phantom and patient comparison studies showed improved image quality. The combined cone-beam/fan-beam imaging geometry with appropriate weighting of the two data sets provides improved system sensitivity while measuring sufficient data for artifact free cardiac images.

  7. Electronic tissue compensation achieved with both dynamic and static multileaf collimator in eclipse treatment planning system for Clinac 6 EX and 2100 CD Varian linear accelerators: Feasibility and dosimetric study

    PubMed Central

    Kinhikar, Rajesh A.; Sharma, Pramod K.; Patkar, Sachin; Tambe, Chandrashekhar M.; Deshpande, Deepak D.

    2007-01-01

    Dynamic multileaf collimator (DMLC) and static multileaf collimator (SMLC), along with three-dimensional treatment planning system (3-D TPS), open the possibility of tissue compensation. A method using electronic tissue compensator (ETC) has been implemented in Eclipse 3-D TPS (V 7.3, Varian Medical Systems, Palo Alto, USA) at our center. The ETC was tested for head and neck conformal radiotherapy planning. The purpose of this study was to verify the feasibility of DMLC and SMLC in head and neck field irradiation for delivering homogeneous dose in the midplane at a pre-defined depth. In addition, emphasis was given to the dosimetric aspects in commissioning ETC in Eclipse. A Head and Neck Phantom (The Phantom Laboratory, USA) was used for the dosimetric verification. Planning was carried out for both DMLC and SMLC ETC plans. The dose calculated at central axis by eclipse with DMLC and SMLC was noted. This was compared with the doses measured on machine with ion chamber and thermoluminescence dosimetry (TLD). The calculated isodose curves and profiles were compared with the measured ones. The dose profiles along the two major axes from Eclipse were also compared with the profiles obtained from Amorphous Silicon (AS500) Electronic portal imaging device (EPID) on Clinac 6 EX machine. In uniform dose regions, measured dose values agreed with the calculated doses within 3%. Agreement between calculated and measured isodoses in the dose gradient zone was within 3 mm. The isodose curves and the profiles were found to be in good agreement with the measured curves and profiles. The measured and the calculated dose profiles along the two major axes were flat for both DMLC and SMLC. The dosimetric verification of ETC for both the linacs demonstrated the feasibility and the accuracy of the ETC treatment modality for achieving uniform dose distributions. Therefore, ETC can be used as a tool in head and neck treatment planning optimization for improved dose uniformity. PMID

  8. SU-E-T-88: Acceptance Testing and Commissioning Measurements of a Newly Released InCiseâ„¢ Multileaf Collimator for CyberKnife M6â„¢ System

    SciTech Connect

    Huq, M Saiful; Ozhasoglu, C; Jang, S; Hwang, M; Heron, D; Lalonde, R

    2015-06-15

    Purpose: Accuray recently released a new collimator, the InCise™ Multileaf Collimator (MLC), for clinical use with the CyberKnife M6™ System. This work reports the results of acceptance testing and commissioning measurements for this collimator. Methods: The MLC consists of 41 pairs of 2.5 mm wide leaves projecting a clinical maximum field size of 110 mm x 97.5 mm at 800 mm SAD. The leaves are made of tungsten, 90 mm in height and tilted by 0.5 degree. The manufacturer stated leaf positioning accuracy and reproducibility are 0.5 mm and 0.4 mm respectively at 800 mm SAD. The leaf over-travel is 100% with full interdigitation capability. Acceptance testing included, but are not limited to, the verification of the specifications of various parameters described above, leakage measurements and end-to-end tests. Dosimetric measurements included, but not limited to, measurements of output factors, open beam profiles, tissue-phantom ratios, beam flatness and symmetry, and patient specific QA. Results: All measurements were well within the manufacturer specifications. The values of output factors ranged from 0.804 (smallest field size of 7.6 mm x 7.5 mm) to 1.018 (largest field size of 110.0 mm x 97.5 mm). End-to-end test results for the various tracking modes are: Skull (0.27mm), fiducial (0.16mm), Xsight Spine (0.4mm), Xsight Lung (0.93 mm) and Synchrony (0.43mm). Measured maximum and average leakage was 0.37% and 0.3%, respectively. Patient-specific QA measurements with chamber were all within 5% absolute dose agreement, and film measurements all passed 2%/2mm gamma evaluation for more than 95% of measurement points. Conclusion: The presented results are the first set of data reported on the InCise™ MLC. The MLC proved to be very reliable and is currently in clinical use.

  9. Small animal imaging by single photon emission using pinhole and coded aperture collimation

    SciTech Connect

    Garibaldi, F.; Accorsi, R.; Cinti, M.N.; Colilli, S.; Cusanno, F.; De Vincentis, G.; Fortuna, A.; Girolami, B.; Giuliani, F.; Gricia, M.; Lanza, R.; Loizzo, A.; Loizzo, S.; Lucentini, M.; Majewski, S.; Santavenere, F.; Pani, R.; Pellegrini, R.; Signore, A.; Scopinaro, F.

    2005-06-01

    The aim of this paper is to investigate the basic properties and limits of the small animal imaging systems based on single photon detectors. The detectors for radio imaging of small animals are challenging because of the very high spatial resolution needed, possibly coupled with high efficiency to allow dynamic studies. These performances are hardly attainable with single photon technique because of the collimator that limits both spatial resolution and sensitivity. In this paper we describe a simple desktop detector based on pixellated NaI(Tl) scintillator array coupled with a pinhole collimator and a PSPMT, the Hamamatsu R2486. The limits of such systems as well as the way to overcome them will be shown. In fact better light sampling at the anode level would allow better pixel identification for higher number of pixel that is one of the parameters defining the image quality. Also the spatial resolution would improve. The performances of such layout are compared with others using PSPMTs differing from R2486 for the light sampling at the anode level and different areas. We show how a further step, namely the substitution of the pinhole collimator with a coded aperture, will allow a great improvement in system sensitivity while maintaining very good spatial resolution, possibly submillimetric. Calculations and simulations show that sensitivity would improve by a factor of 50.

  10. The 1 × 4 Optical Splitters Based on Silicon Photonic Crystal Self-Collimation Ring Resonators

    NASA Astrophysics Data System (ADS)

    Zhuang, Dong-Xia; Chen, Xi-Yao; Li, Jun-Jun; Qiang, Ze-Xuan; Jiang, Jun-Zhen; Chen, Zhi-Yong; Qiu, Yi-Shen; Li, Hui

    2012-12-01

    We report 1 × 4 optical splitters (OSs) with different splitting ratios based on either rod-type or hole-type silicon photonic crystal self-collimation ring resonators (SCRRs). The four beam splitters of the OSs are formed by changing the radii of silicon rods or air holes. The light beam propagating along the SCRR can be controlled by the self-collimation effect. The transmission spectra at the through and drop ports are investigated by using the finite-difference time-domain (FDTD) method. The simulated results agree well with the theoretical calculation. For 1550-nm dropping wavelength, the free spectral ranges for rod-type and hole-type configurations are 28.8nm and 32.5nm, respectively, which almost cover the whole optical communication C-band window. The dimensions of these structures are only about 10 μm × 10 μm.

  11. Study of scattered photons from the collimator system of Leksell Gamma Knife using the EGS4 Monte Carlo Code

    SciTech Connect

    Cheung, Joel Y.C.; Yu, K.N.

    2006-01-15

    In the algorithm of Leksell GAMMAPLAN (the treatment planning software of Leksell Gamma Knife), scattered photons from the collimator system are presumed to have negligible effects on the Gamma Knife dosimetry. In this study, we used the EGS4 Monte Carlo (MC) technique to study the scattered photons coming out of the single beam channel of Leksell Gamma Knife. The PRESTA (Parameter Reduced Electron-Step Transport Algorithm) version of the EGS4 (Electron Gamma Shower version 4) MC computer code was employed. We simulated the single beam channel of Leksell Gamma Knife with the full geometry. Primary photons were sampled from within the {sup 60}Co source and radiated isotropically in a solid angle of 4{pi}. The percentages of scattered photons within all photons reaching the phantom space using different collimators were calculated with an average value of 15%. However, this significant amount of scattered photons contributes negligible effects to single beam dose profiles for different collimators. Output spectra were calculated for the four different collimators. To increase the efficiency of simulation by decreasing the semiaperture angle of the beam channel or the solid angle of the initial directions of primary photons will underestimate the scattered component of the photon fluence. The generated backscattered photons from within the {sup 60}Co source and the beam channel also contribute to the output spectra.

  12. A versatile optical junction using photonic band-gap guidance and self collimation

    SciTech Connect

    Gupta, Man Mohan; Medhekar, Sarang

    2014-09-29

    We show that it is possible to design two photonic crystal (PC) structures such that an optical beam of desired wavelength gets guided within the line defect of the first structure (photonic band gap guidance) and the same beam gets guided in the second structure by self-collimation. Using two dimensional simulation of a design made of the combination of these two structures, we propose an optical junction that allows for crossing of two optical signals of same wavelength and same polarization with very low crosstalk. Moreover, the junction can be operated at number of frequencies in a wide range. Crossing of multiple beams with very low cross talk is also possible. The proposed junction should be important in future integrated photonic circuits.

  13. Design of photonic crystal Fizeau interferometer using self-collimation effect

    NASA Astrophysics Data System (ADS)

    Wang, Jun; Yuan, Xiao

    2016-10-01

    A Fizeau interferometer based on the self-collimation effect of two-dimensional air-cylinder photonic crystal is discussed theoretically. The Fizeau interferometer includes one total reflection photonic crystal mirrors and two splitters. Compared with non-common optical path interferometer (e.g. Michelson and Sagnac), Fizeau is a type of common optical path interferometer, therefore the machining errors of optical paths lead to little influence on the interference signals. The equi-frequency contours are calculated by using the plane-wave expansion method, and interference properties are investigated by using the finite-difference time-domain method. The curves of the interference signals at output port are determined by the optical path difference of the interferometer. The peaks of the curves are sensitive to the refraction index changes in the optical path, which make it possible to be applied in future high-density photonic integrated circuits, such as air-sensors.

  14. SU-E-T-604: Penumbra Characteristics of a New InCiseâ„¢ Multileaf Collimator of CyberKnife M6â„¢ System

    SciTech Connect

    Hwang, M; Jang, S; Ozhasoglu, C; Lalonde, R; Heron, D; Huq, M

    2015-06-15

    Purpose: The InCise™ Multileaf Collimator (MLC) of CyberKnife M6™ System has been released recently. The purpose of this study was to explore the dosimetric characteristics of the new MLC. In particular, the penumbra characteristics of MLC fields at varying locations are evaluated. Methods: EBT3-based film measurements were performed with varying MLC fields ranging from 7.5 mm to 27.5 mm. Seventeen regions of interests (ROIs) were identified for irradiation. These are regions located at the central area (denoted as reference field), at the left/right edge areas of reference open field, at an intermediate location between central and edge area. Single beam treatment plans were designed by using the MultiPlan and was delivered using the Blue Phantom. Gafchromic films were irradiated at 1.5 cm depth in the Blue Phantom and analyzed using the Film Pro software. Variation of maximum dose, penumbra of MLC-defined fields, and symmetry/flatness were calculated as a function of locations of MLC fields. Results: The InCise™ MLC System showed relatively consistent dose distribution and penumbra size with varying locations of MLC fields. The measured maximum dose varied within 5 % at different locations compared to that at the central location and agreed with the calculated data well within 2%. The measured penumbrae were in the range of 2.9 mm and 3.7 mm and were relatively consistent regardless of locations. However, dose profiles in the out-of-field and in-field regions varied with locations and field sizes. Strong variation was seen for all fields located at 55 mm away from the central field. The MLC leakage map showed that the leakage is dependent on position. Conclusion: The size of penumbra and normalized maximum dose for MLC-defined fields were consistent in different regions of MLC. However, dose profiles in the out-field region varied with locations and field sizes.

  15. Use of peripheral dose data from uniform dynamic multileaf collimation fields to estimate out-of-field organ dose in patients treated employing sliding window intensity-modulated radiotherapy

    NASA Astrophysics Data System (ADS)

    Dayananda Sharma, Shamurailatpam; Upreti, Ritu Raj; Dattatray Deshpande, Deepak

    2006-06-01

    Peripheral doses (PD) from uniform dynamic multileaf collimation (DMLC) fields were measured for 6 MV x-rays on a Varian linear accelerator using a 0.6 cc ionization chamber inserted at 5 cm depth into a 35 × 35 × 105 cm3 plastic water phantom. PD measurements were also carried out under identical conditions for seven patients treated for head and neck and cervical cancer employing sliding window intensity-modulated radiotherapy (IMRT). The measured PD from these patient-specific intensity-modulated beams (IMBs) were compared with the corresponding data from uniform DMLC fields having similar jaws setting. The measured PD per monitor unit (PD/MU) decreases almost exponentially with out-of-field distance for all uniform DMLC and static fields. For the same strip field width of 1.2 cm, uniform DMLC fields with a larger size of 14 × 22 cm2 deliver an average of 3.51 (SD = 0.51) times higher PD/MU at all out-of-field distances compared to 6 × 6 cm2. Similar to uniform DMLC fields, PD/MU measured from different patient-specific IMBs was found to decrease almost exponentially with out-of-field distance and increase with increase in field dimension. PD per MU from uniform DMLC fields and patient-specific IMBs having similar jaws setting shows good agreement (±7%) except at the most proximal distance, where a variation of more than 10% (maximum 15%) was observed. Our study shows that PD data generated from uniform DMLC fields can be used as baseline data to estimate out-of-field critical organ or whole-body dose in patients treated employing sliding window IMRT if an appropriate correction factor for field dimension is applied. The whole-body dose information can be used to estimate the possible increase in risk of fatal secondary malignancy in patients treated employing sliding window IMRT.

  16. Feasibility of single-isocenter, multi-arc non-coplanar volumetric modulated arc therapy for multiple brain tumors using a linear accelerator with a 160-leaf multileaf collimator: a phantom study.

    PubMed

    Iwai, Yoshio; Ozawa, Shuichi; Ageishi, Tatsuya; Pellegrini, Roberto; Yoda, Kiyoshi

    2014-09-01

    The feasibility of single isocenter, multi-arc non-coplanar volumetric modulated arc therapy (VMAT) for multiple brain tumors was studied using an Elekta Synergy linear accelerator with an Agility multileaf collimator and a Monaco treatment planning system. Two VMAT radiosurgery plans consisting of a full arc and three half arcs were created with a prescribed dose of 20 Gy in a single fraction. After dose delivery to a phantom, ionization chambers and radiochromic films were used for dose measurement. The first VMAT radiosurgery plan had nine targets inside the phantom, and the doses were measured by the chambers at two different points and by the films on three sagittal and three coronal planes. The differences between the calculated dose and the dose measured by a Farmer ionization chamber and a pinpoint ionization chamber were <1.00% and <2.30%, respectively, and the average pass rates of gamma indices among the six planes under each of 3%/3 mm and 2%/2 mm criteria were 98.6% and 92.6%, respectively. The second VMAT radiosurgery plan was based on a clinical 14 brain metastases. Differences between calculated and film-measured doses were evaluated on two sagittal planes. The average pass rates of the gamma indices on the planes under each of 3%/3 mm and 2%/2 mm criteria were 97.8% and 88.8%, respectively. It was confirmed that single-isocenter, non-coplanar multi-arc VMAT radiosurgery for multiple brain metastases was feasible using Elekta Synergy with Agility and Monaco treatment planning systems. It was further shown that film dosimetry was accurately performed for a dose of up to nearly 25 Gy. © The Author 2014. Published by Oxford University Press on behalf of The Japan Radiation Research Society and Japanese Society for Radiation Oncology.

  17. Feasibility of single-isocenter, multi-arc non-coplanar volumetric modulated arc therapy for multiple brain tumors using a linear accelerator with a 160-leaf multileaf collimator: a phantom study

    PubMed Central

    Iwai, Yoshio; Ozawa, Shuichi; Ageishi, Tatsuya; Pellegrini, Roberto; Yoda, Kiyoshi

    2014-01-01

    The feasibility of single isocenter, multi-arc non-coplanar volumetric modulated arc therapy (VMAT) for multiple brain tumors was studied using an Elekta Synergy linear accelerator with an Agility multileaf collimator and a Monaco treatment planning system. Two VMAT radiosurgery plans consisting of a full arc and three half arcs were created with a prescribed dose of 20 Gy in a single fraction. After dose delivery to a phantom, ionization chambers and radiochromic films were used for dose measurement. The first VMAT radiosurgery plan had nine targets inside the phantom, and the doses were measured by the chambers at two different points and by the films on three sagittal and three coronal planes. The differences between the calculated dose and the dose measured by a Farmer ionization chamber and a pinpoint ionization chamber were <1.00% and <2.30%, respectively, and the average pass rates of gamma indices among the six planes under each of 3%/3 mm and 2%/2 mm criteria were 98.6% and 92.6%, respectively. The second VMAT radiosurgery plan was based on a clinical 14 brain metastases. Differences between calculated and film-measured doses were evaluated on two sagittal planes. The average pass rates of the gamma indices on the planes under each of 3%/3 mm and 2%/2 mm criteria were 97.8% and 88.8%, respectively. It was confirmed that single-isocenter, non-coplanar multi-arc VMAT radiosurgery for multiple brain metastases was feasible using Elekta Synergy with Agility and Monaco treatment planning systems. It was further shown that film dosimetry was accurately performed for a dose of up to nearly 25 Gy. PMID:24944266

  18. New multileaf collimator with a leaf width of 5 mm improves plan quality compared to 10 mm in step-and-shoot IMRT of HNC using integrated boost procedure.

    PubMed

    Zwicker, Felix; Hauswald, Henrik; Nill, Simeon; Rhein, Bernhard; Thieke, Christian; Roeder, Falk; Timke, Carmen; Zabel-du Bois, Angelika; Debus, Jürgen; Huber, Peter E

    2010-06-01

    To investigate whether a new multileaf collimator with a leaf width of 5 mm (MLC-5) over the entire field size of 40 x 40 cm(2) improves plan quality compared to a leaf width of 10 mm (MLC-10) in intensity-modulated radiotherapy (IMRT) with integrated boost for head and neck cancer. A plan comparison was performed for ten patients with head and neck cancer. For each patient, seven plans were calculated: one plan with MLC-10 and nine beams, four plans with MLC-5 and nine beams (with different intensity levels and two-dimensional median filter sizes [2D-MFS]), and one seven-beam plan with MLC-5 and MLC-10, respectively. Isocenter, beam angles and planning constraints were not changed. Mean values of common plan parameters over all ten patients were estimated, and plan groups of MLC-5 and MLC-10 with nine and seven beams were compared. The use of MLC-5 led to a significantly higher conformity index and an improvement of the 90% coverage of PTV1 (planning target volume) and PTV2 compared with MLC-10. This was noted in the nine- and seven-beam plans. Within the nine-beam group with MLC-5, a reduction of the segment number by up to 25% at reduced intensity levels and for increased 2D-MFS did not markedly worsen plan quality. Interestingly, a seven-beam IMRT with MLC-5 was inferior to a nine-beam IMRT with MLC-5, but superior to a nine-beam IMRT with MLC-10. The use of an MLC-5 has significant advantages over an MLC-10 with respect to target coverage and protection of normal tissues in step-and-shoot IMRT of head and neck cancer.

  19. Self-collimation-based photonic crystal Mach-Zehnder add-drop filters

    NASA Astrophysics Data System (ADS)

    Lee, Sun-Goo; Park, Jong-Moon; Kee, Chul-Sik; Lee, Jongjin

    2016-02-01

    Photonic crystal Mach-Zehnder add-drop filters (PC-MZADFs) based on the self-collimation phenomenon in a two-dimensional (2D) PC are proposed and numerically studied using finite-difference time-domain (FDTD) simulations. Each PC-MZADF is composed of a symmetric Mach-Zehnder interferometer (MZI) with an identical filter in each of its two different optical paths. Zizag-box resonators (ZBRs) and Fano resonators (FRs) are employed as the optical filters in rod-type and hole-type PCs, respectively. It is shown that self-collimated beams with the ZBR and FR resonant frequencies can be dropped or added using multiple-beam interference. We also show that the resonant frequencies of the resonators can be adjusted by varying the radii of their rods or holes. Our results indicate that this device design may constitute an efficient approach to light propagation manipulation and increase the application range of self-collimated beams.

  20. Asymmetric Mach-Zehnder filter based on self-collimation phenomenon in two-dimensional photonic crystals.

    PubMed

    Kim, Teun-Teun; Lee, Sun-Goo; Park, Hae Yong; Kim, Jae-Eun; Kee, Chul-Sik

    2010-03-15

    A two-dimensional photonic crystal asymmetric Mach-Zehnder filter (AMZF) based on the self-collimation effect is studied by numerical simulations and experimental measurements in microwave region. A self-collimated beam is effectively controlled by employing line-defect beam splitters and mirrors. The measured transmission spectra at the two output ports of the AMZF sinusoidally oscillate with the phase difference of pi in the self-collimation frequency range. Position of the transmission peaks and dips can be controlled by varying the size of the defect rod of perfect mirrors, and therefore this AMZF can be used as a tunable power filter.

  1. Photon and electron collimator effects on electron output and abutting segments in energy modulated electron therapy

    SciTech Connect

    Olofsson, Lennart; Karlsson, Magnus G.; Karlsson, Mikael

    2005-10-15

    In energy modulated electron therapy a large fraction of the segments will be arranged as abutting segments where inhomogeneities in segment matching regions must be kept as small as possible. Furthermore, the output variation between different segments should be minimized and must in all cases be well predicted. For electron therapy with add-on collimators, both the electron MLC (eMLC) and the photon MLC (xMLC) contribute to these effects when an xMLC tracking technique is utilized to reduce the x-ray induced leakage. Two add-on electron collimator geometries have been analyzed using Monte Carlo simulations: One isocentric eMLC geometry with an isocentric clearance of 35 cm and air or helium in the treatment head, and one conventional proximity geometry with a clearance of 5 cm and air in the treatment head. The electron fluence output for 22.5 MeV electrons is not significantly affected by the xMLC if the shielding margins are larger than 2-3 cm. For small field sizes and 9.6 MeV electrons, the isocentric design with helium in the treatment head or shielding margins larger than 3 cm is needed to avoid a reduced electron output. Dose inhomogeneity in the matching region of electron segments is, in general, small when collimator positions are adjusted to account for divergence in the field. The effect of xMLC tracking on the electron output can be made negligible while still obtaining a substantially reduced x-ray leakage contribution. Collimator scattering effects do not interfere significantly when abutting beam techniques are properly applied.

  2. Design and performance of a compact collimator on GM/CA-CAT at the Advanced Photon Source

    NASA Astrophysics Data System (ADS)

    Xu, S.; Fischetti, R. F.

    2007-09-01

    A new macromolecular crystallographic facility developed by The General Medicine and Cancer Institutes Collaborative Access Team (GM/CA-CAT) at the Advanced Photon Source (APS) is a part of the Biosciences Division (BIO), Argonne National Laboratory (ANL). The facility consists of three beamlines: two lines based on the first "hard" dual canted undulators and one bending magnet beamline [1]. Several compact collimator systems have been developed for the purpose of background reduction in macromolecular crystallography experiments. The apparatus consists of a tube collimator, pinhole and kinematics mount. This paper will present a series of compact collimator designs and crystallographic applications based on experimental requirements [2]. We also describe the magnet-based kinematic mounting structures [3] developed as a collimator holder.

  3. SU-E-T-225: Correction Matrix for PinPoint Ionization Chamber for Dosimetric Measurements in the Newly Released Incise™ Multileaf Collimator Shaped Small Field for CyberKnife M6™ Machine

    SciTech Connect

    Zhang, Y; Li, T; Heron, D; Huq, M

    2015-06-15

    Purpose: For small field dosimetry, such as measurements of output factors for cones or MLC-shaped irregular small fields, ion chambers often Result in an underestimation of the dose, due to both the volume averaging effect and the lack of lateral charged particle equilibrium. This work presents a mathematical model for correction matrix for a PTW PinPoint ionization chamber for dosimetric measurements made in the newly released Incise™ Multileaf collimator fields of the CyberKnife M6™ machine. Methods: A correction matrix for a PTW 0.015cc PinPoint ionization chamber was developed by modeling its 3D dose response in twelve cone-shaped circular fields created using the 5mm, 7.5mm, 10mm, 12.5mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 50mm, 60mm cones in a CyberKnife M6™ machine. For each field size, hundreds of readings were recorded for every 2mm chamber shift in the horizontal plane. The contribution of each dose pixel to a measurement point depended on the radial distance and the angle to the chamber axis. These readings were then compared with the theoretical dose as obtained with Monte Carlo calculation. A penalized least-square optimization algorithm was developed to generate the correction matrix. After the parameter fitting, the mathematical model was validated for MLC-shaped irregular fields. Results: The optimization algorithm used for parameter fitting was stable and the resulted response factors were smooth in spatial domain. After correction with the mathematical model, the chamber reading matched with the calculation for all the tested fields to within 2%. Conclusion: A novel mathematical model has been developed for PinPoint chamber for dosimetric measurements in small MLC-shaped irregular fields. The correction matrix is dependent on detector, treatment unit and the geometry of setup. The model can be applied to non-standard composite fields and provides an access to IMRT point dose validation.

  4. Conformal Stereotactic Radiosurgery With Multileaf Collimation.

    DTIC Science & Technology

    1992-01-01

    Radiation Therapy, I.A.D. Bruin- vis, P.H. van der Giessen, H.J. van Kleffens, F.W. Wittk~ mper (Editors), Elsevier Science Publishers B.V., Holland (1987...BRW stereotaxic system," The Use of Computers in Radiation Therapy, I.A.D. Bruinvis, P.H. van der Giessen, H.J. van Kleffens, F.W. Wittk~ mper (Editors...I.A.D. Bruinvis, P.H. van der Giessen, H.J. van Kleffens, F.W. Wittk& mper (Editors), Elsevier Science Publishers B.V., Holland (1987) Sta88 G

  5. Monte Carlo simulation of small electron fields collimated by the integrated photon MLC

    NASA Astrophysics Data System (ADS)

    Mihaljevic, Josip; Soukup, Martin; Dohm, Oliver; Alber, Markus

    2011-02-01

    In this study, a Monte Carlo (MC)-based beam model for an ELEKTA linear accelerator was established. The beam model is based on the EGSnrc Monte Carlo code, whereby electron beams with nominal energies of 10, 12 and 15 MeV were considered. For collimation of the electron beam, only the integrated photon multi-leaf-collimators (MLCs) were used. No additional secondary or tertiary add-ons like applicators, cutouts or dedicated electron MLCs were included. The source parameters of the initial electron beam were derived semi-automatically from measurements of depth-dose curves and lateral profiles in a water phantom. A routine to determine the initial electron energy spectra was developed which fits a Gaussian spectrum to the most prominent features of depth-dose curves. The comparisons of calculated and measured depth-dose curves demonstrated agreement within 1%/1 mm. The source divergence angle of initial electrons was fitted to lateral dose profiles beyond the range of electrons, where the imparted dose is mainly due to bremsstrahlung produced in the scattering foils. For accurate modelling of narrow beam segments, the influence of air density on dose calculation was studied. The air density for simulations was adjusted to local values (433 m above sea level) and compared with the standard air supplied by the ICRU data set. The results indicate that the air density is an influential parameter for dose calculations. Furthermore, the default value of the BEAMnrc parameter 'skin depth' for the boundary crossing algorithm was found to be inadequate for the modelling of small electron fields. A higher value for this parameter eliminated discrepancies in too broad dose profiles and an increased dose along the central axis. The beam model was validated with measurements, whereby an agreement mostly within 3%/3 mm was found.

  6. A 1 × 4 optical splitter for TE modes based on a silicon photonic crystal self-collimation ring resonator

    NASA Astrophysics Data System (ADS)

    Zhong, Yuangang; Chen, Xiyao; Qiang, Zexuan; Lin, Guimin; Jiang, Junzhen; Qiu, Yishen; Li, Hui

    2013-09-01

    A 1 × 4 optical splitter (OS) is proposed for TE modes based on a self-collimation (SC) effect ring resonator (SCRR) in an air-hole type silicon photonic crystal. A 1 × 4 OS consists of four beam splitters formed by varying the radii of the air holes. Utilizing multiple-beam interference theory, the theoretical transmission spectra at each port in the OS were analyzed. By forming four splitters in a SCRR properly, self-collimation light can come out from four ports with the light-intensity ratio we set. OSs were investigated using the two-dimensional finite-difference time-domain (FDTD) simulation technique. The simulation results have good agreement with the theoretical prediction. Because of its small dimensions, whole silicon material, and air-hole type, this structure may have an important role in photonic integrated circuits.

  7. UCD-SPI: Un-Collimated Detector Single-Photon Imaging System for Small Animal and Plant Imaging

    NASA Astrophysics Data System (ADS)

    Walker, Katherine Leigh

    Medical imaging systems using single gamma-ray emitting radioisotopes implement collimators in order to form images. However, a tradeoff in sensitivity is inherent in the use of collimators, and modern preclinical single-photon emission computed tomography (SPECT) systems detect a very small fraction of emitted gamma-rays (<0.3%). We have built a collimator-less system, which can reach sensitivity of 40% for 99mTc imaging, while still producing images of sufficient spatial resolution for certain applications in "thin" objects such as mice, small plants, and well plates used for in vitro experiments. This flexible geometry un-collimated detector single-photon imaging (UCD-SPI) system consists of two large (5 cm x 10 cm), thin (3 mm and 5 mm), closely spaced, pixelated scintillation detectors of either NaI(Tl), CsI(Na), or BGO. The detectors are read out by two adjacent Hamamatsu H8500 multichannel photomultiplier tubes. The detector heads enable the interchange of scintillation detectors of different materials and thicknesses to optimize performance for a wide range of gamma-ray energies and imaging subjects. The detectors are horizontally oriented for animal imaging, and for plant imaging the system is rotated on its side to orient the detectors vertically. While this un-collimated detector system is unable to approach the sub-mm spatial resolution obtained by the most advanced preclinical pinhole SPECT systems, the high sensitivity could enable significant and new use in molecular imaging applications which do not require good spatial resolution- for example, screening applications for drug development (small animals), for material transport and sequestration studies for phytoremediation (plants), or for counting radiolabeled cells in vitro (well plates).

  8. Development of a pixelated GSO gamma camera system with tungsten parallel hole collimator for single photon imaging

    SciTech Connect

    Yamamoto, S.; Watabe, H.; Kanai, Y.; Shimosegawa, E.; Hatazawa, J.

    2012-02-15

    Purpose: In small animal imaging using a single photon emitting radionuclide, a high resolution gamma camera is required. Recently, position sensitive photomultiplier tubes (PSPMTs) with high quantum efficiency have been developed. By combining these with nonhygroscopic scintillators with a relatively low light output, a high resolution gamma camera can become useful for low energy gamma photons. Therefore, the authors developed a gamma camera by combining a pixelated Ce-doped Gd{sub 2}SiO{sub 5} (GSO) block with a high quantum efficiency PSPMT. Methods: GSO was selected for the scintillator, because it is not hygroscopic and does not contain any natural radioactivity. An array of 1.9 mm x 1.9 mm x 7 mm individual GSO crystal elements was constructed. These GSOs were combined with a 0.1-mm thick reflector to form a 22 x 22 matrix and optically coupled to a high quantum efficiency PSPMT (H8500C-100 MOD8). The GSO gamma camera was encased in a tungsten gamma-ray shield with tungsten pixelated parallel hole collimator, and the basic performance was measured for Co-57 gamma photons (122 keV). Results: In a two-dimensional position histogram, all pixels were clearly resolved. The energy resolution was {approx}15% FWHM. With the 20-mm thick tungsten pixelated collimator, the spatial resolution was 4.4-mm FWHM 40 mm from the collimator surface, and the sensitivity was {approx}0.05%. Phantom and small animal images were successfully obtained with our developed gamma camera. Conclusions: These results confirmed that the developed pixelated GSO gamma camera has potential as an effective instrument for low energy gamma photon imaging.

  9. Complete photonic band gaps and tunable self-collimation in the two-dimensional plasma photonic crystals with a new structure

    SciTech Connect

    Zhang, Hai-Feng; Ding, Guo-Wen; Li, Hai-Ming; Liu, Shao-Bin

    2015-02-15

    In this paper, the properties of complete photonic band gaps (CPBGs) and tunable self-collimation in two-dimensional plasma photonic crystals (2D PPCs) with a new structure in square lattices, whose dielectric fillers (GaAs) are inserted into homogeneous and nomagnetized plasma background are theoretically investigated by a modified plane wave expansion (PWE) method with a novel technique. The novel PWE method can be utilized to compute the dispersion curves of 2D PPCs with arbitrary-shaped cross section in any lattices. As a comparison, CPBGs of PPCs for four different configurations are numerically calculated. The computed results show that the proposed design has the advantages of achieving the larger CPBGs compared to the other three configurations. The influences of geometric parameters of filled unit cell and plasma frequency on the properties of CPBGs are studied in detail. The calculated results demonstrate that CPBGs of the proposed 2D PPCs can be easily engineered by changing those parameters, and the larger CPBGs also can be obtained by optimization. The self-collimation in such 2D PPCs also is discussed in theory under TM wave. The theoretical simulations reveal that the self-collimation phenomena can be found in the TM bands, and both the frequency range of self-collimation and the equifrequency surface contours can be tuned by the parameters as mentioned above. It means that the frequency range and direction of electromagnetic wave can be manipulated by designing, as it propagates in the proposed PPCs without diffraction. Those results can hold promise for designing the tunable applications based on the proposed PPCs.

  10. Un-collimated single-photon imaging system for high-sensitivity small animal and plant imaging

    SciTech Connect

    Walker, Katherine L.; Judenhofer, Martin S.; Cherry, Simon R.; Mitchell, Gregory S.

    2014-12-12

    In preclinical single-photon emission computed tomography (SPECT) system development the primary objective has been to improve spatial resolution by using novel parallel-hole or multi-pinhole collimator geometries. Furthermore, such high-resolution systems have relatively poor sensitivity (typically 0.01% to 0.1%). In contrast, a system that does not use collimators can achieve very high-sensitivity. Here we present a high-sensitivity un-collimated detector single-photon imaging (UCD-SPI) system for the imaging of both small animals and plants. This scanner consists of two thin, closely spaced, pixelated scintillator detectors that use NaI(Tl), CsI(Na), or BGO. The performance of the system has been characterized by measuring sensitivity, spatial resolution, linearity, detection limits, and uniformity. With 99mTc (140 keV) at the center of the field of view (20 mm scintillator separation), the sensitivity was measured to be 31.8% using the NaI(Tl) detectors and 40.2% with CsI(Na). The best spatial resolution (FWHM when the image formed as the geometric mean of the two detector heads, 20 mm scintillator separation) was 19.0 mm for NaI(Tl) and 11.9 mm for CsI(Na) at 140 keV, and 19.5 mm for BGO at 1116 keV, which is somewhat degraded compared to the cm-scale resolution obtained with only one detector head and a close source. The quantitative accuracy of the system’s linearity is better than 2% with detection down to activity levels of 100 nCi. Two in vivo animal studies (a renal scan using 99mTc MAG-3 and a thyroid scan with 123I) and one plant study (a 99mTcO4- xylem transport study) highlight the unique capabilities of this UCD-SPI system. From the renal scan, we observe approximately a one thousand-fold increase in sensitivity compared to the Siemens Inveon SPECT/CT scanner. In conclusion, UCD-SPI is useful for many imaging tasks that do not require excellent spatial resolution, such as high

  11. Un-collimated single-photon imaging system for high-sensitivity small animal and plant imaging

    DOE PAGES

    Walker, Katherine L.; Judenhofer, Martin S.; Cherry, Simon R.; ...

    2014-12-12

    In preclinical single-photon emission computed tomography (SPECT) system development the primary objective has been to improve spatial resolution by using novel parallel-hole or multi-pinhole collimator geometries. Furthermore, such high-resolution systems have relatively poor sensitivity (typically 0.01% to 0.1%). In contrast, a system that does not use collimators can achieve very high-sensitivity. Here we present a high-sensitivity un-collimated detector single-photon imaging (UCD-SPI) system for the imaging of both small animals and plants. This scanner consists of two thin, closely spaced, pixelated scintillator detectors that use NaI(Tl), CsI(Na), or BGO. The performance of the system has been characterized by measuring sensitivity, spatialmore » resolution, linearity, detection limits, and uniformity. With 99mTc (140 keV) at the center of the field of view (20 mm scintillator separation), the sensitivity was measured to be 31.8% using the NaI(Tl) detectors and 40.2% with CsI(Na). The best spatial resolution (FWHM when the image formed as the geometric mean of the two detector heads, 20 mm scintillator separation) was 19.0 mm for NaI(Tl) and 11.9 mm for CsI(Na) at 140 keV, and 19.5 mm for BGO at 1116 keV, which is somewhat degraded compared to the cm-scale resolution obtained with only one detector head and a close source. The quantitative accuracy of the system’s linearity is better than 2% with detection down to activity levels of 100 nCi. Two in vivo animal studies (a renal scan using 99mTc MAG-3 and a thyroid scan with 123I) and one plant study (a 99mTcO4- xylem transport study) highlight the unique capabilities of this UCD-SPI system. From the renal scan, we observe approximately a one thousand-fold increase in sensitivity compared to the Siemens Inveon SPECT/CT scanner. In conclusion, UCD-SPI is useful for many imaging tasks that do not require excellent spatial resolution, such as high-throughput screening applications, simple radiotracer uptake

  12. Un-collimated single-photon imaging system for high-sensitivity small animal and plant imaging

    NASA Astrophysics Data System (ADS)

    Walker, Katherine L.; Judenhofer, Martin S.; Cherry, Simon R.; Mitchell, Gregory S.

    2015-01-01

    In preclinical single-photon emission computed tomography (SPECT) system development the primary objective has been to improve spatial resolution by using novel parallel-hole or multi-pinhole collimator geometries. However, such high-resolution systems have relatively poor sensitivity (typically 0.01-0.1%). In contrast, a system that does not use collimators can achieve very high-sensitivity. Here we present a high-sensitivity un-collimated detector single-photon imaging (UCD-SPI) system for the imaging of both small animals and plants. This scanner consists of two thin, closely spaced, pixelated scintillator detectors that use NaI(Tl), CsI(Na), or BGO. The performance of the system has been characterized by measuring sensitivity, spatial resolution, linearity, detection limits, and uniformity. With 99mTc (140 keV) at the center of the field of view (20 mm scintillator separation), the sensitivity was measured to be 31.8% using the NaI(Tl) detectors and 40.2% with CsI(Na). The best spatial resolution (FWHM when the image formed as the geometric mean of the two detector heads, 20 mm scintillator separation) was 19.0 mm for NaI(Tl) and 11.9 mm for CsI(Na) at 140 keV, and 19.5 mm for BGO at 1116 keV, which is somewhat degraded compared to the cm-scale resolution obtained with only one detector head and a close source. The quantitative accuracy of the system’s linearity is better than 2% with detection down to activity levels of 100 nCi. Two in vivo animal studies (a renal scan using 99mTc MAG-3 and a thyroid scan with 123I) and one plant study (a 99mTcO4- xylem transport study) highlight the unique capabilities of this UCD-SPI system. From the renal scan, we observe approximately a one thousand-fold increase in sensitivity compared to the Siemens Inveon SPECT/CT scanner. UCD-SPI is useful for many imaging tasks that do not require excellent spatial resolution, such as high-throughput screening applications, simple radiotracer uptake studies in tumor

  13. A CCD based approach to collimated photon counting imaging for micro-SPECT/CT.

    PubMed

    Eaker, Diane R; Dzyubak, Bogdan; Jorgensen, Steven M; Ritman, Erik L

    2009-01-01

    Analog summation methods of x-ray imaging have nonlinearity in signal readout and dynamic range limitations. To minimize these limitations, a photon counting CCD-based gamma camera imaging system has been developed and evaluated.

  14. 1×5 optical splitter for TE modes in air-hole photonic crystal based on self-collimation effect

    NASA Astrophysics Data System (ADS)

    Chen, Weijuan; Lin, Yuanyuan; Lin, Guimin; Fu, Ping; Liu, Chengkun; Qiu, Yishen; Li, Hui; Chen, Xiyao

    2016-11-01

    We propose a novel 1×5 optical splitter (OS) for TE modes based on self-collimation effect in an air-hole silicon photonic crystal. The OS consists of two cascaded resonators which is formed with eight beam splitters. The theoretical transmission spectra of the OS is derived with multiple-beam interference theory. From our analysis of transmission spectra, it is found that the transmission spectra at five drop ports will reach the maximum values while the transmission spectra at two through ports reach zero for resonant frequencies. By scanning the radius of a beam splitter, the relationship between the radius and the reflectivity is obtained. Therefore, by changing the radii of the air-hole in eight beam splitters, we can manipulate the output light-intensity ratio at five drop ports to meet requirement. Theoretically, when reflectivity of beam splitters R1=2/11, R2=8/11, R3=5/8, R4=2/5, R5=7/12, R6 =6/7, R7=1/2, R8 =2/3, the light intensity ratio at five drop ports is 1:1:1:1:1. When R1=2/7, R2=6/7, R3=1/2, R4=2/3, R5=1/7, R6=6/7, R7=2/3, R8 =1/4, the light intensity ratio at five drop ports is 2:2:1:2:3. By means of finite-difference time-domain (FDTD) simulations, the numerical transmission spectra of OS can be figured out. The simulation results are consistent with the theoretical results. Considering micro processing technology of silicon materials is already available, this OS can be used in the photonic integrated circuits because of its small size, whole-silicon material and low insertion loss.

  15. Focusing, collimation and flux throughput at the IMCA-CAT bending-magnet beamline at the Advanced Photon Source

    SciTech Connect

    Koshelev, Irina; Huang, Rong; Graber, Timothy; Meron, Mati; Muir, J. Lewis; Lavender, William; Battaile, Kevin; Mulichak, Anne M.; Keefe, Lisa J.

    2009-09-02

    The IMCA-CAT bending-magnet beamline was upgraded with a collimating mirror in order to achieve the energy resolution required to conduct high-quality multi- and single-wavelength anomalous diffraction (MAD/SAD) experiments without sacrificing beamline flux throughput. Following the upgrade, the bending-magnet beamline achieves a flux of 8 x 10{sup 11} photons s{sup -1} at 1 {angstrom} wavelength, at a beamline aperture of 1.5 mrad (horizontal) x 86 {mu}rad (vertical), with energy resolution (limited mostly by the intrinsic resolution of the monochromator optics) {delta}E/E = 1.5 x 10{sup -4} (at 10 kV). The beamline operates in a dynamic range of 7.5-17.5 keV and delivers to the sample focused beam of size (FWHM) 240 {micro}m (horizontally) x 160 {micro}m (vertically). The performance of the 17-BM beamline optics and its deviation from ideally shaped optics is evaluated in the context of the requirements imposed by the needs of protein crystallography experiments. An assessment of flux losses is given in relation to the (geometric) properties of major beamline components.

  16. Monte Carlo simulation of the photoneutron field in linac radiotherapy treatments with different collimation systems

    NASA Astrophysics Data System (ADS)

    Zanini, A.; Durisi, E.; Fasolo, F.; Ongaro, C.; Visca, L.; Nastasi, U.; Burn, K. W.; Scielzo, G.; Adler, J. O.; Annand, J. R. M.; Rosner, G.

    2004-02-01

    Bremsstrahlung photon beams produced by linac accelerators are currently the most commonly used method of radiotherapy for tumour treatments. When the photon energy exceeds 10 MeV the patient receives an undesired dose due to photoneutron production in the accelerator head. In the last few decades, new sophisticated techniques such as multileaf collimators have been used for a better definition of the target volume. In this case it is crucial to evaluate the photoneutron dose produced after giant dipole resonance (GDR) excitation of the high Z materials (mainly tungsten and lead) constituting the collimator leaves in view of the optimization of the radiotherapy treatment. A Monte Carlo approach has been used to calculate the photoneutron dose arising from the GDR reaction during radiotherapy with energetic photon beams. The simulation has been performed using the code MCNP4B-GN which is based on MCNP4B, but includes a new routine GAMMAN to model photoneutron production. Results for the facility at IRCC (Istituto per la Ricerca e la Cura del Cancro) Candiolo (Turin), which is based on 18 MV x-rays from a Varian Clinac 2300 C/D, are presented for a variety of different collimator configurations.

  17. Monte Carlo simulation of the photoneutron field in linac radiotherapy treatments with different collimation systems.

    PubMed

    Zanini, A; Durisi, E; Fasolo, F; Ongaro, C; Visca, L; Nastasi, U; Burn, K W; Scielzo, G; Adler, J O; Annand, J R M; Rosner, G

    2004-02-21

    Bremsstrahlung photon beams produced by linac accelerators are currently the most commonly used method of radiotherapy for tumour treatments. When the photon energy exceeds 10 MeV the patient receives an undesired dose due to photoneutron production in the accelerator head. In the last few decades, new sophisticated techniques such as multileaf collimators have been used for a better definition of the target volume. In this case it is crucial to evaluate the photoneutron dose produced after giant dipole resonance (GDR) excitation of the high Z materials (mainly tungsten and lead) constituting the collimator leaves in view of the optimization of the radiotherapy treatment. A Monte Carlo approach has been used to calculate the photoneutron dose arising from the GDR reaction during radiotherapy with energetic photon beams. The simulation has been performed using the code MCNP4B-GN which is based on MCNP4B, but includes a new routine GAMMAN to model photoneutron production. Results for the facility at IRCC (Istituto per la Ricerca e la Cura del Cancro) Candiolo (Turin), which is based on 18 MV x-rays from a Varian Clinac 2300 C/D, are presented for a variety of different collimator configurations.

  18. Measurements of Output Factors For Small Photon Fields Up to 10 cm x 10 cm

    NASA Astrophysics Data System (ADS)

    Bacala, Angelina

    Field output factors (OF) for photon beams from a 6 MV medical accelerator were measured using five different detectors in a scanning water phantom. The measurements were taken for square field sizes of integral widths ranging from 1 cm to 10 cm for two reference source-to-surface distances (SSD) and depths in water. For the diode detectors, square field widths as small as 2.5 mm were also studied. The photon beams were collimated by using either the jaws or the multileaf collimators. Measured OFs are found to depend upon the field size, SSD, depth and also upon the type of beam collimation, size and type of detector used. For field sizes larger than 3 cm x 3 cm, the OF measurements agree to within 1% or less. The largest variation in OF occurs for jawsshaped field of size 1 cm x 1cm, where a difference of more than 18% is observed.

  19. Realization of all-optical three-person voting function based on self-collimation with the two-dimensional photonic crystals

    NASA Astrophysics Data System (ADS)

    Jiang, Yu-Chi; Liu, Shao-Bin

    2016-01-01

    In the paper, a simple structure of three-person voting circuit is proposed and based on self-collimation effect with the two-dimensional photonic crystals. The electric field intensity of the proposed structure is deduced according to optical interference theory. The results show that the simple structure with two-dimensional photonic crystals can realize the three-person voting either from the optical interference theory or simulation, meanwhile, the light contrast ratio between the output logic signal "1" and "0" can reach as high as 19 dB. When compared with three-person voting designed with digital electronic technology, the size of the proposed design in this paper is more smaller, which is valuable in photonic device integration and compactness.

  20. Fast IMRT with narrow high energy scanned photon beams.

    PubMed

    Andreassen, Björn; Strååt, Sara Janek; Holmberg, Rickard; Näfstadius, Peder; Brahme, Anders

    2011-08-01

    Since the first publications on intensity modulated radiation therapy (IMRT) in the early 1980s almost all efforts have been focused on fairly time consuming dynamic or segmental multileaf collimation. With narrow fast scanned photon beams, the flexibility and accuracy in beam shaping increases, not least in combination with fast penumbra trimming multileaf collimators. Previously, experiments have been performed with full range targets, generating a broad bremsstrahlung beam, in combination with multileaf collimators or material compensators. In the present publication, the first measurements with fast narrow high energy (50 MV) scanned photon beams are presented indicating an interesting performance increase even though some of the hardware used were suboptimal. Inverse therapy planning was used to calculate optimal scanning patterns to generate dose distributions with interesting properties for fast IMRT. To fully utilize the dose distributional advantages with scanned beams, it is necessary to use narrow high energy beams from a thin bremsstrahlung target and a powerful purging magnet capable of deflecting the transmitted electron beam away from the generated photons onto a dedicated electron collector. During the present measurements the scanning system, purging magnet, and electron collimator in the treatment head of the MM50 racetrack accelerator was used with 3-6 mm thick bremsstrahlung targets of beryllium. The dose distributions were measured with diodes in water and with EDR2 film in PMMA. Monte Carlo simulations with GEANT4 were used to study the influence of the electrons transmitted through the target on the photon pencil beam kernel. The full width at half-maximum (FWHM) of the scanned photon beam was 34 mm measured at isocenter, below 9.5 cm of water, 1 m from the 3 mm Be bremsstrahlung target. To generate a homogeneous dose distribution in a 10 x 10 cm2 field, the authors used a spot matrix of 100 equal intensity beam spots resulting in a

  1. Development of a Multileaf Collimator for Proton Radiotherapy

    DTIC Science & Technology

    2012-06-01

    quadratic. Previously we relied on IBA spec for spot size at isocenter , measurements of the beam emittance at another facility, and the idea that the...beam would be focused at isocenter to determine the 3 parameters of the quadratic. It turns out that the beam is not focused exactly at isocenter , but

  2. Development of a Multileaf Collimator for Proton Radiotherapy

    DTIC Science & Technology

    2011-06-01

    compensator absent. The simulation can now read the drill positions and remaining Plexiglas thicknesses of the compensator from a DICOM file, and create the...simulation reads in the row and column spacing and row offset of the drill positions from a DICOM file and creates a rectangular prism with the...geometry based on the dicom CT datafiles in the path ct/datafiles/. The geometry is properly oriented in the beamline based on the isocenter, gantry

  3. Development of a Multileaf Collimator for Proton Radiotherapy

    DTIC Science & Technology

    2007-06-01

    in early 2008. 3. Development of phantom for motion studies: (FY 2007-2008). Because of the delay in signing the contract for the facility this...Measurement of dose distributions in static and moving phantoms : (FY 2008-2010). 9. Joint Military/Civilian Proton Therapy Center telemedicine system...cm2 were assessed. A 40 × 40 × 40 cm3 water phantom abutted the downstream face of the MLC. Energy deposits within the phantom were recorded in 1 × 1

  4. Development of a Multileaf Collimator for Proton Radiotherapy

    DTIC Science & Technology

    2006-06-01

    Philadelphia (CHOP). The accomplishments during the past year of the project are described in this report. (1) We developed software to read in DICOM -RT...achievements: (1) Adaptation of the GEANT4 code to read in DICOM -RT data so structures and beams could be transferred between a treatment planning system and...progress a. Importing Dicom -RT CT Image Sets into Geant4 Environment Introduction CT Images consist of a voxelized region of the patient chosen at

  5. Development of a Multileaf Collimator for Proton Radiotherapy

    DTIC Science & Technology

    2010-06-01

    beam and re-optimizing the beam current modulation files based on the measurements that are now available from our beams. More recently, we have...treatment plans in our simulation, we needed to create a phantom that could be composed of multiple materials based on the components of a patient’s body...ability to read in and use MLC leaf positions from Eclipse treatment plans and to be able to construct patient-specific range compensators based on the

  6. Development of a Multileaf Collimator for Proton Radiotherapy

    DTIC Science & Technology

    2005-06-01

    40 0 50 100 150 200 250 300 x (ram) Fig. 3: Energy deposition in water by a 200 MeV pencil proton beam ( top ) and by a 6 cm x 6 cm field of the same...iit I S B Figure 12: TOP - Theta and Phi distribution for all particles in the MLC and water...distributions in addition to the number of secondaries produced. Figure 18 ( top ) shows the energy deposited in water by a 250 MeV 5 x 5 cm2 proton beam. The

  7. SU-E-T-175: Evaluation of the Relative Output Ratio for Collimator Jaw and MLC Defined Small Static 6MV Photon Fields

    SciTech Connect

    Cho, G; Thwaites, D

    2014-06-01

    Purpose: To evaluate relative output ratio of collimator jaw and MLC defined small photon fields. Methods: Relative output ratios were measured using Gafchromic EBT3 film for a 6 MV photon beam on a Novalis Tx with HD120 MLC. Beam collimation was achieved by the jaws for 1.0 cm and 3.0 cm and MLC defined square field sizes between 0.5 cm and 1.0 cm with varying jaw settings between 2.0 and 4.0 cm. Film pieces were exposed to 4 Gy. Experiments were repeated with each session consisting of five consecutive exposures for the given MLC and/or jaw collimation and with the MLC and the jaws reset for each exposure. Films were scanned using EPSON 10000XL flatbed scanner approximately 24 hours after exposure in 48 bit RGB format at 150 dpi. Film calibration data were corrected for daily linac output variations. Doses were evaluated using the green channel with square ROI sizes of 0.1 – 0.6 cm. Converted doses were normalised for output ratio calculation using the 3.0 cm field as a machine specific reference field size. Mean output ratio and coefficient of variation (CV) were calculated for each experimental session. Results: For the Novalis 6 MV photon beam the output ratios between 0.719 and 0.872 have been measured for the jaw/MLC combinations tested. For a jaw setting of 4.0 cm field, the mean CV of the output ratios increased from 0.77% to 1.48% with decreasing MLC field size from 1.0 cm to 0.5 cm. For a nominal MLC 1.0 cm field, the CV increased to 1.00% from 0.77% with reducing jaw field size from 4.0 cm to 2.0 cm. Conclusion: The relative output ratio and the associated CV were dependent on the collimator jaw and MLC settings. The field size dependent CV showed similar trends to those reported in the literature.

  8. Collimation study for LCLS

    DOE PAGES

    Marin, E.; Raubenhaimer, T.; Welch, J.; ...

    2017-06-13

    In this study we investigate the power deposition along the undulator section of the SLAC Linac Coherent Light Source (LCLS) due to the primary e¯ -beam but also due to potential secondary particles. The expected beam distribution after the LCLS injector is deliberately broadened as an approximated representation of the beam halo. Secondary particles, as e+, e¯ and photons, are generated as a result of tracking the intercepted beam through a dense material. This process is carried out by means of GEANT-4, which has been convoluted into our main tracking engine, LUCRETIA. Simulations show no losses along the undulator sectionmore » when assuming the nominal primary beam and collimator gaps. However when opening the gaps of collimators located at the first collimator section, by 25%, the fattened beam is partially intercepted by the second collimator section, which is aligned to the undulators. Secondary particles, mostly photons generated at the second collimator section, deposit their energy along the undulator section, at a rate of the order of a milliwatt.« less

  9. Collimation study for LCLS

    NASA Astrophysics Data System (ADS)

    Marin, E.; Raubenhaimer, T.; Welch, J.; White, G.

    2017-09-01

    In this paper we investigate the power deposition along the undulator section of the SLAC Linac Coherent Light Source (LCLS) due to the primary e--beam but also due to potential secondary particles. The expected beam distribution after the LCLS injector is deliberately broadened as an approximated representation of the beam halo. Secondary particles, as e+, e- and photons, are generated as a result of tracking the intercepted beam through a dense material. This process is carried out by means of GEANT-4, which has been convoluted into our main tracking engine, LUCRETIA. Simulations show no losses along the undulator section when assuming the nominal primary beam and collimator gaps. However when opening the gaps of collimators located at the first collimator section, by 25%, the fattened beam is partially intercepted by the second collimator section, which is aligned to the undulators. Secondary particles, mostly photons generated at the second collimator section, deposit their energy along the undulator section, at a rate of the order of a milliwatt.

  10. SU-E-J-104: Single Photon Image From PET with Insertable SPECT Collimator for Boron Neutron Capture Therapy: A Feasibility Study

    SciTech Connect

    Jung, J; Yoon, D; Suh, T

    2014-06-01

    Purpose: The aim of our proposed system is to confirm the feasibility of extraction of two types of images from one positron emission tomography (PET) module with an insertable collimator for brain tumor treatment during the BNCT. Methods: Data from the PET module, neutron source, and collimator was entered in the Monte Carlo n-particle extended (MCNPX) source code. The coincidence events were first compiled on the PET detector, and then, the events of the prompt gamma ray were collected after neutron emission by using a single photon emission computed tomography (SPECT) collimator on the PET. The obtaining of full width at half maximum (FWHM) values from the energy spectrum was performed to collect effective events for reconstructed image. In order to evaluate the images easily, five boron regions in a brain phantom were used. The image profiles were extracted from the region of interest (ROI) of a phantom. The image was reconstructed using the ordered subsets expectation maximization (OSEM) reconstruction algorithm. The image profiles and the receiver operating characteristic (ROC) curve were compiled for quantitative analysis from the two kinds of reconstructed image. Results: The prompt gamma ray energy peak of 478 keV appeared in the energy spectrum with a FWHM of 41 keV (6.4%). On the basis of the ROC curve in Region A to Region E, the differences in the area under the curve (AUC) of the PET and SPECT images were found to be 10.2%, 11.7%, 8.2% (center, Region C), 12.6%, and 10.5%, respectively. Conclusion: We attempted to acquire the PET and SPECT images simultaneously using only PET without an additional isotope. Single photon images were acquired using an insertable collimator on a PET detector. This research was supported by the Leading Foreign Research Institute Recruitment Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, Information and Communication Technologies (ICT) and Future Planning (MSIP)(Grant No

  11. Multiprism collimator

    NASA Technical Reports Server (NTRS)

    Minott, P. O. (Inventor)

    1982-01-01

    A special purpose optical collimator system which generates multiple collimated light beams with precisely related angular separation of the beams, is comprised of a stack of relatively flat plate-like refracted prisms in the form of wedges. Each prism has a specified angular deviation, mounted on top of one another in a fixture which holds the wedges so that they are adapted to operate at minimum angular deviation and thus are relatively insensitive to rotational and angular charges. A collimated sources of monochromatic light, generated for example by a helium-neon laser and a collimated beam expander, provides a common incident beam to the wedges whereupon a number equally spaced emergent beams are provided.

  12. Light propagation characteristics in photonic crystal fibers with α-power profiles of air hole diameter distributions and their application to fiber collimator

    NASA Astrophysics Data System (ADS)

    Yokota, Hirohisa; Higuchi, Keiichi; Imai, Yoh

    2016-08-01

    Light propagation characteristics in photonic crystal fibers (PCFs) with α-power profiles of air hole diameter distributions were theoretically investigated. It was clarified that the intensity peak of the beam propagating in the PCF with Gaussian beam excitation varied periodically with little power attenuation. It was found that the envelope of the periodic intensity variation depended on α. We theoretically demonstrated that the PCF with the α-power profile of the air hole diameter distribution could be applied to a collimator for a conventional PCF with uniform air holes in Gaussian beam excitation to reduce coupling loss, where a PCF of appropriate length with the α-power air hole diameter distribution was spliced to a conventional PCF. It was also found that the coupling efficiency was higher for a larger α.

  13. Photon beam description in PEREGRINE for Monte Carlo dose calculations

    SciTech Connect

    Cox, L. J., LLNL

    1997-03-04

    Goal of PEREGRINE is to provide capability for accurate, fast Monte Carlo calculation of radiation therapy dose distributions for routine clinical use and for research into efficacy of improved dose calculation. An accurate, efficient method of describing and sampling radiation sources is needed, and a simple, flexible solution is provided. The teletherapy source package for PEREGRINE, coupled with state-of-the-art Monte Carlo simulations of treatment heads, makes it possible to describe any teletherapy photon beam to the precision needed for highly accurate Monte Carlo dose calculations in complex clinical configurations that use standard patient modifiers such as collimator jaws, wedges, blocks, and/or multi-leaf collimators. Generic beam descriptions for a class of treatment machines can readily be adjusted to yield dose calculation to match specific clinical sites.

  14. Advantages of mini-multileaf in stereotactic radiotherapy

    PubMed Central

    Kurup, P. G. G.; Murali, V.; Sankar, A.

    2007-01-01

    Over the past few decades, cones of different diameter (12.5 mm to 40 mm) were used for treatment of intracranial lesions. These give very focused dose delivery to the target with minimum dose to outside normal brain tissues. This study is intended to compare the older method of arc-based stereotactic treatments using cones with the new mini-multileaf collimator (mMLC). Treatment plans are made for various sites of intracranial lesions with the cones and mMLC. In case of nonspherical lesions, more than one isocenter is used to get an optimum dose distribution with cones, while a single isocenter is sufficient with mMLC. Treatment plans are compared for irregular lesions using cones with multiple isocenters and mMLC. It is observed that conformity index and dose heterogeneity are better for mMLC based treatments. PMID:21217913

  15. Electron contamination in clinical high energy photon beams.

    PubMed

    Sjögren, R; Karlsson, M

    1996-11-01

    The electron contamination in photon beams has been investigated by means of contaminating lepton depth doses and dose profiles in different geometries with two 20 MV beams. Different components of this contamination have been investigated separately by systematically adding contamination to a "clean" reference field. At 20 MV, the air generated electrons were found to be almost negligible compared to the electrons originating from the accelerator head when measurements were performed in standard fields at SSDs between 80 and 120 cm. The total electron part of the depth dose curve was then almost the same, i.e., independent of SSD, when the collimator opening was held fixed. However, when different accessories such as a shaping block and different attenuating plates were located in the beam path below the collimators, a large SSD dependence of the electron contamination was noticed. A comparison was also made between two machines, one equipped with a multileaf collimator, with similar beam qualities at 20 MV. These measurements indicate that the interior view of the treatment head seen by the detector (mainly the flattening filter, monitor chamber, or other electron generating material) influences the magnitude of the electron contamination. When the collimator opening is decreased the electron contamination will also decrease as parts of the electron source will be shielded by the collimator blocks.

  16. SU-E-T-132: Assess the Shielding of Secondary Neutrons From Patient Collimator in Proton Therapy Considering Secondary Photons Generated in the Shielding Process with Monte Carlo Simulation

    SciTech Connect

    Yamanaka, M; Takashina, M; Kurosu, K; Koizumi, M; Moskvin, V; Das, I

    2015-06-15

    Purpose: In this study we present Monte Carlo based evaluation of the shielding effect for secondary neutrons from patient collimator, and secondary photons emitted in the process of neutron shielding by combination of moderator and boron-10 placed around patient collimator. Methods: The PHITS Monte Carlo Simulation radiation transport code was used to simulate the proton beam (Ep = 64 to 93 MeV) from a proton therapy facility. In this study, moderators (water, polyethylene and paraffin) and boron (pure {sup 10}B) were placed around patient collimator in this order. The rate of moderator and boron thicknesses was changed fixing the total thickness at 3cm. The secondary neutron and photons doses were evaluated as the ambient dose equivalent per absorbed dose [H*(10)/D]. Results: The secondary neutrons are shielded more effectively by combination moderators and boron. The most effective combination of shielding neutrons is the polyethylene of 2.4 cm thick and the boron of 0.6 cm thick and the maximum reduction rate is 47.3 %. The H*(10)/D of secondary photons in the control case is less than that of neutrons by two orders of magnitude and the maximum increase of secondary photons is 1.0 µSv/Gy with the polyethylene of 2.8 cm thick and the boron of 0.2 cm thick. Conclusion: The combination of moderators and boron is beneficial for shielding secondary neutrons. Both the secondary photons of control and those emitted in the shielding neutrons are very lower than the secondary neutrons and photon has low RBE in comparison with neutron. Therefore the secondary photons can be ignored in the shielding neutrons.This work was supported by JSPS Core-to-Core Program (No.23003). This work was supported by JSPS Core-to-Core Program (No.23003)

  17. Optimization of helical acquisition parameters to preserve uniformity of mouse whole body using multipinhole collimator in single-photon emission computed tomography

    NASA Astrophysics Data System (ADS)

    Ukon, Naoyuki; Kubo, Naoki; Ishikawa, Masayori; Zhao, Songji; Tamaki, Nagara; Kuge, Yuji

    Focusing on whole-body uniformity in small-animal single-photon emission computed tomography (SPECT), we examined the optimal helical acquisition parameters using five-pinhole collimators for mouse imaging. SPECT images of an 80-mm-long cylindrical phantom with 99mTc solution were acquired using an Inveon multimodality imaging platform. The bed travels used in this study were 0, 30, 60, 90 and 120 mm, and the numbers of revolutions traversed during the SPECT scan were 1.0, 2.0, 3.0, 4.0, 5.0 and 7.0, respectively. Artifacts that degrade uniformity in reconstructed images were conspicuous when the bed travel was smaller than the object length. Regarding the distal-to-center ratio (DCR) of SPECT values in the object's axial direction, the DCR nearest to the ideal ratio of 1.00 was 1.02 in the optimal uniformity with 4.0 revolutions and a bed travel of 120 mm. Moreover, the helical acquisition using these parameters suppressed the formation of artifacts. We proposed the optimal parameters in whole-body helical SPECT; the bed travel was sufficiently larger than the object length; the 4.0 or more revolutions were required for a pitch of approximately 30 mm/revolution. The optimal acquisition parameters in SPECT to preserve uniformity would contribute to the accurate quantification of whole-body biodistribution.

  18. Apparatus and method for variable angle slant hole collimator

    DOEpatents

    Lee, Seung Joon; Kross, Brian J.; McKisson, John E.

    2017-07-18

    A variable angle slant hole (VASH) collimator for providing collimation of high energy photons such as gamma rays during radiological imaging of humans. The VASH collimator includes a stack of multiple collimator leaves and a means of quickly aligning each leaf to provide various projection angles. Rather than rotate the detector around the subject, the VASH collimator enables the detector to remain stationary while the projection angle of the collimator is varied for tomographic acquisition. High collimator efficiency is achieved by maintaining the leaves in accurate alignment through the various projection angles. Individual leaves include unique angled cuts to maintain a precise target collimation angle. Matching wedge blocks driven by two actuators with twin-lead screws accurately position each leaf in the stack resulting in the precise target collimation angle. A computer interface with the actuators enables precise control of the projection angle of the collimator.

  19. Measuring the wobble of radiation field centers during gantry rotation and collimator movement on a linear accelerator.

    PubMed

    Du, Weiliang; Gao, Song

    2011-08-01

    The isocenter accuracy of a linear accelerator is often assessed with star-shot films. This approach is limited in its ability to quantify three dimensional wobble of radiation field centers (RFCs). The authors report a Winston-Lutz based method to measure the 3D wobble of RFCs during gantry rotation, collimator rotation, and collimator field size change. A stationary ball-bearing phantom was imaged using multileaf collimator-shaped radiation fields at various gantry angles, collimator angles, and field sizes. The center of the ball-bearing served as a reference point, to which all RFCs were localized using a computer algorithm with sub-pixel accuracy. Then, the gantry rotation isocenter and the collimator rotation axis were derived from the coordinates of these RFCs. Finally, the deviation or wobble of the individual RFC from the derived isocenter or rotation axis was quantified. The results showed that the RFCs were stable as the field size of the multileaf collimator was varied. The wobble of RFCs depended on the gantry angle and the collimator angle and was reproducible, indicating that the mechanical imperfections of the linac were mostly systematic and quantifiable. It was found that the 3D wobble of RFCs during gantry rotation was reduced after compensating for a constant misalignment of the multileaf collimator. The 3D wobble of RFCs can be measured with submillimeter precision using the proposed method. This method provides a useful tool for checking and adjusting the radiation isocenter tightness of a linac.

  20. Measuring the wobble of radiation field centers during gantry rotation and collimator movement on a linear accelerator

    SciTech Connect

    Du, Weiliang; Gao, Song

    2011-08-15

    Purpose: The isocenter accuracy of a linear accelerator is often assessed with star-shot films. This approach is limited in its ability to quantify three dimensional wobble of radiation field centers (RFCs). The authors report a Winston-Lutz based method to measure the 3D wobble of RFCs during gantry rotation, collimator rotation, and collimator field size change. Methods: A stationary ball-bearing phantom was imaged using multileaf collimator-shaped radiation fields at various gantry angles, collimator angles, and field sizes. The center of the ball-bearing served as a reference point, to which all RFCs were localized using a computer algorithm with subpixel accuracy. Then, the gantry rotation isocenter and the collimator rotation axis were derived from the coordinates of these RFCs. Finally, the deviation or wobble of the individual RFC from the derived isocenter or rotation axis was quantified. Results: The results showed that the RFCs were stable as the field size of the multileaf collimator was varied. The wobble of RFCs depended on the gantry angle and the collimator angle and was reproducible, indicating that the mechanical imperfections of the linac were mostly systematic and quantifiable. It was found that the 3D wobble of RFCs during gantry rotation was reduced after compensating for a constant misalignment of the multileaf collimator. Conclusions: The 3D wobble of RFCs can be measured with submillimeter precision using the proposed method. This method provides a useful tool for checking and adjusting the radiation isocenter tightness of a linac.

  1. Radiation leakage dose from Elekta electron collimation system.

    PubMed

    Pitcher, Garrett M; Hogstrom, Kenneth R; Carver, Robert L

    2016-09-08

    This study provided baseline data required for a greater project, whose objective was to design a new Elekta electron collimation system having significantly lighter electron applicators with equally low out-of field leakage dose. Specifically, off-axis dose profiles for the electron collimation system of our uniquely configured Elekta Infinity accelerator with the MLCi2 treatment head were measured and calculated for two primary purposes: 1) to evaluate and document the out-of-field leakage dose in the patient plane and 2) to validate the dose distributions calculated using a BEAMnrc Monte Carlo (MC) model for out-of-field dose profiles. Off-axis dose profiles were measured in a water phantom at 100 cm SSD for 1 and 2 cm depths along the in-plane, cross-plane, and both diagonal axes using a cylindrical ionization chamber with the 10 × 10 and 20 × 20 cm2 applicators and 7, 13, and 20 MeV beams. Dose distributions were calculated using a previously developed BEAMnrc MC model of the Elekta Infinity accelerator for the same beam energies and applicator sizes and compared with measurements. Measured results showed that the in-field beam flatness met our acceptance criteria (± 3% on major and ±4% on diagonal axes) and that out-of-field mean and maximum percent leakage doses in the patient plane met acceptance criteria as specified by the International Electrotechnical Commission (IEC). Cross-plane out-of-field dose profiles showed greater leakage dose than in-plane profiles, attributed to the curved edges of the upper X-ray jaws and multileaf collimator. Mean leakage doses increased with beam energy, being 0.93% and 0.85% of maximum central axis dose for the 10 × 10 and 20 × 20 cm2 applicators, respectively, at 20 MeV. MC calculations predicted the measured dose to within 0.1% in most profiles outside the radiation field; however, excluding model-ing of nontrimmer applicator components led to calculations exceeding measured data by as much as 0.2% for some regions

  2. The use of intensity-modulated radiation therapy photon beams for improving the dose uniformity of electron beams shaped with MLC

    SciTech Connect

    Mosalaei, Homeira; Karnas, Scott; Shah, Sheel; Van Doodewaard, Sharon; Foster, Tim; Chen, Jeff

    2012-04-01

    Electrons are ideal for treating shallow tumors and sparing adjacent normal tissue. Conventionally, electron beams are collimated by cut-outs that are time-consuming to make and difficult to adapt to tumor shape throughout the course of treatment. We propose that electron cut-outs can be replaced using photon multileaf collimator (MLC). Two major problems of this approach are that the scattering of electrons causes penumbra widening because of a large air gap, and available commercial treatment planning systems (TPSs) do not support MLC-collimated electron beams. In this study, these difficulties were overcome by (1) modeling electron beams collimated by photon MLC for a commercial TPS, and (2) developing a technique to reduce electron beam penumbra by adding low-energy intensity-modulated radiation therapy (IMRT) photons (4 MV). We used blocks to simulate MLC shielding in the TPS. Inverse planning was used to optimize boost photon beams. This technique was applied to a parotid and a central nervous system (CNS) clinical case. Combined photon and electron plans were compared with conventional plans and verified using ion chamber, film, and a 2D diode array. Our studies showed that the beam penumbra for mixed beams with 90 cm source to surface distance (SSD) is comparable with electron applicators and cut-outs at 100 cm SSD. Our mixed-beam technique yielded more uniform dose to the planning target volume and lower doses to various organs at risk for both parotid and CNS clinical cases. The plans were verified with measurements, with more than 95% points passing the gamma criteria of 5% in dose difference and 5 mm for distance to agreement. In conclusion, the study has demonstrated the feasibility and potential advantage of using photon MLC to collimate electron beams with boost photon IMRT fields.

  3. Design of a wire-mesh collimator for gamma cameras.

    PubMed

    Saripan, M Iqbal; Petrou, Maria; Wells, Kevin

    2007-09-01

    This paper presents a model of a wire-mesh collimator for a gamma camera that produces images of comparable quality as those produced with the conventional multihole collimator, but has about half the weight of the multihole collimator. The gamma camera and the collimator are simulated using the MCNPX code. Two final configurations of the wire-mesh collimator are proposed, and their performance is compared with other wire-mesh collimators and with the multihole collimator, using a point source, a planar square source, and two point sources, all in water. In all cases, photons with energy 140 keV are simulated. In addition, we use the simulation of a realistic phantom of a hot tumor in a warm background to assess the performance of our collimator in conjunction with an extended source.

  4. Efficient photon beam dose calculations using DOSXYZnrc with BEAMnrc.

    PubMed

    Kawrakow, I; Walters, B R B

    2006-08-01

    This study examines the efficiencies of doses calculated using DOSXYZnrc for 18 MV (10 X 10 cm2 field size) and 6 MV (10 X 10 cm2 and 20 X 20 cm2 field sizes) photon beams simulated using BEAMnrc. Both phase-space sources and full BEAMnrc simulation sources are used in the DOSXYZnrc calculations. BEAMnrc simulation sources consist of a BEAMnrc accelerator simulation compiled as a shared library and run by the user code (DOSXYZnrc in this case) to generate source particles. Their main advantage is in eliminating the need to store intermediate phase-space files. In addition, the efficiency improvements due to photon splitting and particle recycling in the DOSXYZnrc simulation are examined. It is found that photon splitting increases dose calculation efficiency by a factor of up to 6.5, depending on beam energy, field size, voxel size, and the type of secondary collimation used in the BEAMnrc simulation (multileaf collimator vs photon jaws). The optimum efficiency with photon splitting is approximately 55% higher than that with particle recycling, indicating that, while most of the gain is due to time saved by reusing source particle data, there is significant gain due to the uniform distribution of interaction sites and faster DOSXYZnrc simulation time when photon splitting is employed. Use of optimized directional bremsstrahlung splitting in the BEAMnrc simulation sources increases the efficiency of photon beam simulations sufficiently that the peak efficiencies (i.e., with optimum setting of the photon splitting number) of DOSXYZnrc simulations using these sources are only 3-13% lower than those with phase-space file sources. This points towards eliminating the need for storing intermediate phase-space files.

  5. Radiological considerations for POE-1 photon shutters, collimators and beam stops of the Biomedical Imaging and Therapy beamline at the Canadian Light Source

    NASA Astrophysics Data System (ADS)

    Asai, Juhachi; Wysokinski, Tomasz W.; Smith, Sheldon; Chapman, Dean

    2008-01-01

    A study of radiation levels due to primary and secondary gas bremsstrahlung is carried out for the BioMedical Imaging and Therapy (BMIT) beamline at the Canadian Light Source (CLS). The BMIT beamline, being built at present, is a major research and diagnostic tool for X-ray imaging and X-ray radiation therapy for animals and humans. For the BMIT beamline to be as flexible as possible, a movable tungsten collimator is designed. This can move vertically and assumes two positions; up and down. The BMIT beamline is, thus, able to perform two modes of operation: one white beam, the other monochromatic. Gas bremsstrahlung produced in the vacuum chamber propagates with synchrotron radiation and may enter the imaging or therapy hutch. In this study, the dose behind the collimator is investigated in each mode by assessing the energy deposition in a water phantom that surrounds the entire copper shutter-tungsten collimator unit. When estimating the dose, particular attention is given to the opening area of the collimator, since this passage leads to the imaging or therapy hutch. Also examined are the doses when a tungsten safety shutter is closed.

  6. A column generation approach for evaluating delivery efficiencies of collimator technologies in IMRT treatment planning

    NASA Astrophysics Data System (ADS)

    Gören, M.; Taşkın, Z. C.

    2015-03-01

    Collimator systems used in Intensity Modulated Radiation Therapy can form different geometric aperture shapes depending on their physical capabilities. We compare the efficiency of using regular, rotating and dual multileaf collimator (MLC) systems under different combinations of consecutiveness, interdigitation and rectangular constraints. We also create a virtual freeform collimator, which can form any possible segment shape by opening or closing each bixel independently, to provide a basis for comparison. We formulate the problem of minimizing beam-on time as a large-scale linear programming problem. To deal with its dimensionality, we propose a column generation approach. We demonstrate the efficacy of our approach on a set of clinical problem instances. Our results indicate that the dual MLC under consecutiveness constraint yields very similar beam-on time to a virtual freeform collimator. Our approach also provides a ranking between other collimator technologies in terms of their delivery efficiencies.

  7. Effect of the collimator angle on dosimetric verification of volumetric modulated arc therapy

    NASA Astrophysics Data System (ADS)

    Kim, Yong Ho; Park, Ha Ryung; Kim, Won Taek; Kim, Dong Won; Ki, Yongkan; Lee, Juhye; Bae, Jinsuk; Park, Dahl; Jeon, Hosang; Nam, Ji Ho

    2015-07-01

    The collimator is usually rotated when planning volumetric modulated arc therapy (VMAT) due to the leakage of radiation between the multi-leaf collimator (MLC) leaves. We studied the effect of the collimator angle on the results of dosimetric verification of VMAT plans for head and neck patients. We studied VMAT plans for 10 head and neck patients. We made two sets of VMAT plans for each patient. Each set was composed of 10 plans with collimator angles of 0, 5, 10, 15, 20, 25, 30, 35, 40, 45 degrees. Plans in the first set were optimized individually, and plans in the second set shared the 30-degree collimator-angle optimization. The two sets of plans were verified by using the 2-dimensional ion chamber array MatriXX (IBA Dosimetry, Germany). The comparisons between the calculation and the measurements were made by using a γ-index analysis. The γ-index (2%/2 mm) and (3%/3 mm) passing rates had negative correlations with the collimator angle. The maximum difference between γ-index (3%/3 mm) passing rates of different collimator angles for each patient ranged from 1.46% to 5.60% with an average of 3.67%. There were significant differences (maximum 5.6%) in the passing rates for different collimator angles. The results suggested that the accuracy of the delivered dose depended on the collimator angle. These findings are informative when choosing a collimator angle for VMAT plans.

  8. Retinoblastoma external beam photon irradiation with a special ‘D’-shaped collimator: a comparison between measurements, Monte Carlo simulation and a treatment planning system calculation

    NASA Astrophysics Data System (ADS)

    Brualla, L.; Mayorga, P. A.; Flühs, A.; Lallena, A. M.; Sempau, J.; Sauerwein, W.

    2012-11-01

    Retinoblastoma is the most common eye tumour in childhood. According to the available long-term data, the best outcome regarding tumour control and visual function has been reached by external beam radiotherapy. The benefits of the treatment are, however, jeopardized by a high incidence of radiation-induced secondary malignancies and the fact that irradiated bones grow asymmetrically. In order to better exploit the advantages of external beam radiotherapy, it is necessary to improve current techniques by reducing the irradiated volume and minimizing the dose to the facial bones. To this end, dose measurements and simulated data in a water phantom are essential. A Varian Clinac 2100 C/D operating at 6 MV is used in conjunction with a dedicated collimator for the retinoblastoma treatment. This collimator conforms a ‘D’-shaped off-axis field whose irradiated area can be either 5.2 or 3.1 cm2. Depth dose distributions and lateral profiles were experimentally measured. Experimental results were compared with Monte Carlo simulations’ run with the penelope code and with calculations performed with the analytical anisotropic algorithm implemented in the Eclipse treatment planning system using the gamma test. penelope simulations agree reasonably well with the experimental data with discrepancies in the dose profiles less than 3 mm of distance to agreement and 3% of dose. Discrepancies between the results found with the analytical anisotropic algorithm and the experimental data reach 3 mm and 6%. Although the discrepancies between the results obtained with the analytical anisotropic algorithm and the experimental data are notable, it is possible to consider this algorithm for routine treatment planning of retinoblastoma patients, provided the limitations of the algorithm are known and taken into account by the medical physicist and the clinician. Monte Carlo simulation is essential for knowing these limitations. Monte Carlo simulation is required for optimizing the

  9. Fabrication of collimators for gamma-ray imaging.

    SciTech Connect

    Makarova, O. V.; Yang, G.; Tang, C.-M.; Mancini, D. C.; Divan, R.; Yaeger, J.; Experimental Facilities Division; Creatv Micro Tech, Inc.

    2004-01-01

    Collimators capable of higher resolution and optimized for greater sensitivity can significantly improve the imaging quality of gamma-cameras for single-photon-emission computed tomography of small animals. We are applying deep x-ray lithography and gold electroforming techniques to fabricate high-resolution collimators with continuous, smooth, and thin septa. Negative SU-8 photoresist was used for mold fabrication. To be efficient, collimators for gamma-cameras designed to image 140 keV gamma-rays should be over 1.5 cm tall. The height of the collimator can be achieved by stacking the appropriate number of layers.

  10. A parallel-cone collimator for high-energy SPECT.

    PubMed

    Beijst, Casper; Elschot, Mattijs; Viergever, Max A; de Jong, Hugo W A M

    2015-03-01

    In SPECT using high-energy photon-emitting isotopes, such as (131)I, parallel-hole collimators with thick septa are required to limit septal penetration, at the cost of sensitivity and resolution. This study investigated a parallel-hole collimator with cone-shaped holes, which was designed to limit collimator penetration while preserving resolution and sensitivity. The objective was to demonstrate that a single-slice prototype of the parallel-cone (PC) collimator was capable of improving the image quality of high-energy SPECT. The image quality of the PC collimator was quantitatively compared with that of clinically used low-energy high-resolution (LEHR; for (99m)Tc) and high-energy general-purpose (HEGP; for (131)I and (18)F) parallel-hole collimators. First, Monte Carlo simulations of single and double point sources were performed to assess sensitivity and resolution by comparing point-spread functions (PSFs). Second, a prototype PC collimator was used in an experimental phantom study to assess and compare contrast recovery coefficients and image noise. Monte Carlo simulations showed reduced broadening of the PSF due to collimator penetration for the PC collimator as compared with the HEGP collimator (e.g., 0.9 vs. 1.4 cm in full width at half maximum for (131)I). Simulated double point sources placed 2 cm apart were separately detectable for the PC collimator, whereas this was not the case for (131)I and (18)F at distances from the collimator face of 10 cm or more for the HEGP collimator. The sensitivity, measured over the simulated profiles as the total amount of counts per decay, was found to be higher for the LEHR and HEGP collimators than for the PC collimator (e.g., 3.1 × 10(-5) vs. 2.9 × 10(-5) counts per decay for (131)I). However, at equal noise level, phantom measurements showed that contrast recovery coefficients were similar for the PC and LEHR collimators for (99m)Tc but that the PC collimator significantly improved the contrast recovery

  11. T type collimator

    SciTech Connect

    LaVallie, E.; Smith, G.; Sorenson, D.; Volk, J.

    1989-01-01

    The Research Division has developed a pin-hole collimator capable of attenuating the 800 GeV proton beam by a factor of ten to one hundred. A bid package has been let for the first prototype and has been sent out. The other four collimators will be ordered in the spring of 1989. 3 refs., 2 figs., 3 tabs.

  12. CRYSTAL COLLIMATION AT RHIC.

    SciTech Connect

    FLILLER,R.P.,III.DREES,A.GASSNER,D.HAMMONS,L.MCINTYRE,G.PEGGS,S.TRBOJEVIC,D.BIRYUKOV,V.CHESNOKOV,Y.TEREKHOV,V.

    2003-06-19

    Crystal Channeling occurs when an ion enters a crystal with a small angle with respect to the crystal planes. The electrostatic interaction between the incoming ion and the lattice causes the ion to follow the crystal planes. By mechanically bending a crystal, it is possible to use a crystal to deflect ions. One novel use of a bent crystal is to use it to channel beam halo particles into a collimator downstream. By deflecting the halo particles into a collimator with a crystal it may be possible to improve collimation efficiency as compared to a single collimator. A bent crystal is installed in the yellow ring of the Relativistic Heavy Ion Collider (RHIC). In this paper we discuss our experience with the crystal collimator, and compare our results to previous data, simulation, and theoretical prediction.

  13. NLC Collimation Study Update: Performance with Tail Folding Octupoles (LCC-0118)

    SciTech Connect

    Drozhdin, A

    2004-03-16

    This note describes an update to the study of linear collider collimation system performance performed by the collimation task force and presented in [1, 2, 3]. In particular, the performance of the NLC collimation system with the addition of ''tail-folding'' octupoles is described. These octupoles allow the betatron collimation gaps to be opened by more than a factor of three. We present the optimized gap settings, the location of additional photon masks, and the resulting synchrotron-radiation collimation efficiency. The studies confirm that the tail-folding octupoles are efficient, give additional flexibility, and enhance the collimation system performance.

  14. Radiation collimator and systems incorporating same

    DOEpatents

    Norman, Daren R [Idaho Falls, ID; Yoon, Woo Y [Idaho Falls, ID; Jones, James L [Idaho Falls, ID; Haskell, Kevin J [Idaho Falls, ID; Bennett, Brion D [Idaho Falls, ID; Tschaggeny, Charles W [Woods Cross, UT; Jones, Warren F [Idaho Falls, ID

    2011-09-13

    A collimator including a housing having disposed therein a shield element surrounding a converter core in which a photon beam is generated from electrons emanating from a linear accelerator. A beam channeler longitudinally adjacent the shield element has a beam aperture therethrough coaxially aligned with, and of the same diameter as, an exit bore of the converter core. A larger entry bore in the converter core is coaxial with, and longitudinally separated from, the exit bore thereof. Systems incorporating the collimator are also disclosed.

  15. An energy-optimized collimator design for a CZT-based SPECT camera

    PubMed Central

    Weng, Fenghua; Bagchi, Srijeeta; Zan, Yunlong; Huang, Qiu; Seo, Youngho

    2015-01-01

    In single photon emission computed tomography, it is a challenging task to maintain reasonable performance using only one specific collimator for radio-tracers over a broad spectrum of diagnostic photon energies, since photon scatter and penetration in a collimator differ with the photon energy. Frequent collimator exchanges are inevitable in daily clinical SPECT imaging, which hinders throughput while subjecting the camera to operational errors and damage. Our objective is to design a collimator, which independent of the photon energy performs reasonably well for commonly used radiotracers with low- to medium-energy levels of gamma emissions. Using the Geant4 simulation toolkit, we simulated and evaluated a parallel-hole collimator mounted to a CZT detector. With the pixel-geometry-matching collimation, the pitch of the collimator hole was fixed to match the pixel size of the CZT detector throughout this work. Four variables, hole shape, hole length, hole radius/width and the source-to-collimator distance were carefully studied. Scatter and penetration of the collimator, sensitivity and spatial resolution of the system were assessed for four radionuclides including 57Co, 99mTc, 123I and 111In, with respect to the aforementioned four variables. An optimal collimator was then decided upon such that it maximized the total relative sensitivity (TRS) for the four considered radionuclides while other performance parameters, such as scatter, penetration and spatial resolution, were benchmarked to prevalent commercial scanners and collimators. Digital phantom studies were also performed to validate the system with the optimal square-hole collimator (23 mm hole length, 1.28 mm hole width, 0.32 mm septal thickness) in terms of contrast, contrast-to-noise ratio and recovery ratio. This study demonstrates promise of our proposed energy-optimized collimator to be used in a CZT-based gamma camera, with comparable or even better imaging performance versus commercial collimators

  16. An energy-optimized collimator design for a CZT-based SPECT camera

    NASA Astrophysics Data System (ADS)

    Weng, Fenghua; Bagchi, Srijeeta; Zan, Yunlong; Huang, Qiu; Seo, Youngho

    2016-01-01

    In single photon emission computed tomography, it is a challenging task to maintain reasonable performance using only one specific collimator for radiotracers over a broad spectrum of diagnostic photon energies, since photon scatter and penetration in a collimator differ with the photon energy. Frequent collimator exchanges are inevitable in daily clinical SPECT imaging, which hinders throughput while subjecting the camera to operational errors and damage. Our objective is to design a collimator, which is independent of the photon energy, performs reasonably well for commonly used radiotracers with low- to medium-energy levels of gamma emissions. Using the Geant4 simulation toolkit, we simulated and evaluated a parallel-hole collimator mounted to a CZT detector. With the pixel-geometry-matching collimation, the pitch of the collimator hole was fixed to match the pixel size of the CZT detector throughout this work. Four variables, hole shape, hole length, hole radius/width and the source-to-collimator distance were carefully studied. Scatter and penetration of the collimator, sensitivity and spatial resolution of the system were assessed for four radionuclides including 57Co, 99mTc, 123I and 111In, with respect to the aforementioned four variables. An optimal collimator was then decided upon such that it maximized the total relative sensitivity (TRS) for the four considered radionuclides while other performance parameters, such as scatter, penetration and spatial resolution, were benchmarked to prevalent commercial scanners and collimators. Digital phantom studies were also performed to validate the system with the optimal square-hole collimator (23 mm hole length, 1.28 mm hole width, and 0.32 mm septal thickness) in terms of contrast, contrast-to-noise ratio and recovery ratio. This study demonstrates promise of our proposed energy-optimized collimator to be used in a CZT-based gamma camera, with comparable or even better imaging performance versus commercial

  17. Dosimetry and evaluating the effect of treatment parameters on the leakage of multi leaf collimators in ONCOR linear accelerators

    PubMed Central

    Jabbari, Keyvan; Akbari, Muhaddeseh; Tavakoli, Mohamad Bagher; Amouheidari, Alireza

    2016-01-01

    Background: One of the standard equipment in medical linear accelerators is multi-leaf collimators (MLCs); which is used as a replacement for lead shielding. MLC's advantages are a reduction of the treatment time, the simplicity of treatment, and better dose distribution. The main disadvantage of MLC is the radiation leakages from the edges and between the leaves. The purpose of this study was to determine the effect of various treatment parameters in the magnitude of MLC leakage in linear accelerators. Materials and Methods: This project was performed with ONCOR Siemens linear accelerators. The amount of radiation leakage was determined by film dosimetry method. The films were Kodak-extended dose range-2, and the beams were 6 MV and 18 MV photons. In another part of the experiment, the fluctuation of the leakage was measured at various depths and fields. Results: The amount of leakage was generally up to 1.5 ± 0.2% for both energies. The results showed that the level of the leakage and the amount of dose fluctuation depends on the field size and depth of measurement. The amount of the leakage fluctuations in all energies was decreased with increasing of field size. The variation of the leakage versus field size was similar to the inverse of scattering collimator factor. Conclusions: The amount of leakage was more for 18 MV compare to 6 MV The percentage of the leakage for both energies is less than the 5% value which is recommended by protocols. The fluctuation of the MLC leakage reduced by increasing the field size and depth. PMID:28217631

  18. Conformity of LINAC-Based Stereotactic Radiosurgery Using Dynamic Conformal Arcs and Micro-Multileaf Collimator

    SciTech Connect

    Hazard, Lisa J. Wang, Brian; Skidmore, Thomas B.; Chern, Shyh-Shi; Salter, Bill J.; Jensen, Randy L.; Shrieve, Dennis C.

    2009-02-01

    Purpose: To assess the conformity of dynamic conformal arc linear accelerator-based stereotactic radiosurgery and to describe a standardized method of isodose surface (IDS) selection. Methods and Materials: In 174 targets, the conformity index (CI) at the prescription IDS used for treatment was calculated as CI = (PIV/PVTV)/(PVTV/TV), where TV is the target volume, PIV (prescription isodose volume) is the total volume encompassed by the prescription IDS, and PVTV is the TV encompassed by the IDS. In addition, a 'standardized' prescription IDS (sIDS) was chosen according to the following criteria: 95% of the TV was encompassed by the PIV and 99% of TV was covered by 95% of the prescription dose. The CIs at the sIDS were also calculated. Results: The median CI at the prescription IDS and sIDS was 1.63 and 1.47, respectively (p < 0.001). In 132 of 174 cases, the volume of normal tissue in the PIV was reduced by the prescription to the sIDS compared with the prescription IDS, in 20 cases it remained unchanged, and in 22 cases it was increased. Conclusion: The CIs obtained with linear accelerator-based stereotactic radiosurgery are comparable to those previously reported for gamma knife stereotactic radiosurgery. Using a uniform method to select the sIDS, adequate target coverage was usually achievable with prescription to an IDS greater than that chosen by the treating physician (prescription IDS), providing sparing of normal tissue. Thus, the sIDS might aid physicians in identifying a prescription IDS that balances coverage and conformity.

  19. Electromagnetic guided couch and multileaf collimator tracking on a TrueBeam accelerator

    SciTech Connect

    Hansen, Rune; Ravkilde, Thomas; Worm, Esben Schjødt; Toftegaard, Jakob; Grau, Cai; Poulsen, Per Rugaard; Macek, Kristijan

    2016-05-15

    Purpose: Couch and MLC tracking are two promising methods for real-time motion compensation during radiation therapy. So far, couch and MLC tracking experiments have mainly been performed by different research groups, and no direct comparison of couch and MLC tracking of volumetric modulated arc therapy (VMAT) plans has been published. The Varian TrueBeam 2.0 accelerator includes a prototype tracking system with selectable couch or MLC compensation. This study provides a direct comparison of the two tracking types with an otherwise identical setup. Methods: Several experiments were performed to characterize the geometric and dosimetric performance of electromagnetic guided couch and MLC tracking on a TrueBeam accelerator equipped with a Millennium MLC. The tracking system latency was determined without motion prediction as the time lag between sinusoidal target motion and the compensating motion of the couch or MLC as recorded by continuous MV portal imaging. The geometric and dosimetric tracking accuracies were measured in tracking experiments with motion phantoms that reproduced four prostate and four lung tumor trajectories. The geometric tracking error in beam’s eye view was determined as the distance between an embedded gold marker and a circular MLC aperture in continuous MV images. The dosimetric tracking error was quantified as the measured 2%/2 mm gamma failure rate of a low and a high modulation VMAT plan delivered with the eight motion trajectories using a static dose distribution as reference. Results: The MLC tracking latency was approximately 146 ms for all sinusoidal period lengths while the couch tracking latency increased from 187 to 246 ms with decreasing period length due to limitations in the couch acceleration. The mean root-mean-square geometric error was 0.80 mm (couch tracking), 0.52 mm (MLC tracking), and 2.75 mm (no tracking) parallel to the MLC leaves and 0.66 mm (couch), 1.14 mm (MLC), and 2.41 mm (no tracking) perpendicular to the leaves. The motion-induced gamma failure rate was in mean 0.1% (couch tracking), 8.1% (MLC tracking), and 30.4% (no tracking) for prostate motion and 2.9% (couch), 2.4% (MLC), and 41.2% (no tracking) for lung tumor motion. The residual tracking errors were mainly caused by inadequate adaptation to fast lung tumor motion for couch tracking and to prostate motion perpendicular to the MLC leaves for MLC tracking. Conclusions: Couch and MLC tracking markedly improved the geometric and dosimetric accuracies of VMAT delivery. However, the two tracking types have different strengths and weaknesses. While couch tracking can correct perfectly for slowly moving targets such as the prostate, MLC tracking may have considerably larger dose errors for persistent target shift perpendicular to the MLC leaves. Advantages of MLC tracking include faster dynamics with better adaptation to fast moving targets, the avoidance of moving the patient, and the potential to track target rotations and deformations.

  20. Electromagnetic guided couch and multileaf collimator tracking on a TrueBeam accelerator.

    PubMed

    Hansen, Rune; Ravkilde, Thomas; Worm, Esben Schjødt; Toftegaard, Jakob; Grau, Cai; Macek, Kristijan; Poulsen, Per Rugaard

    2016-05-01

    Couch and MLC tracking are two promising methods for real-time motion compensation during radiation therapy. So far, couch and MLC tracking experiments have mainly been performed by different research groups, and no direct comparison of couch and MLC tracking of volumetric modulated arc therapy (VMAT) plans has been published. The Varian TrueBeam 2.0 accelerator includes a prototype tracking system with selectable couch or MLC compensation. This study provides a direct comparison of the two tracking types with an otherwise identical setup. Several experiments were performed to characterize the geometric and dosimetric performance of electromagnetic guided couch and MLC tracking on a TrueBeam accelerator equipped with a Millennium MLC. The tracking system latency was determined without motion prediction as the time lag between sinusoidal target motion and the compensating motion of the couch or MLC as recorded by continuous MV portal imaging. The geometric and dosimetric tracking accuracies were measured in tracking experiments with motion phantoms that reproduced four prostate and four lung tumor trajectories. The geometric tracking error in beam's eye view was determined as the distance between an embedded gold marker and a circular MLC aperture in continuous MV images. The dosimetric tracking error was quantified as the measured 2%/2 mm gamma failure rate of a low and a high modulation VMAT plan delivered with the eight motion trajectories using a static dose distribution as reference. The MLC tracking latency was approximately 146 ms for all sinusoidal period lengths while the couch tracking latency increased from 187 to 246 ms with decreasing period length due to limitations in the couch acceleration. The mean root-mean-square geometric error was 0.80 mm (couch tracking), 0.52 mm (MLC tracking), and 2.75 mm (no tracking) parallel to the MLC leaves and 0.66 mm (couch), 1.14 mm (MLC), and 2.41 mm (no tracking) perpendicular to the leaves. The motion-induced gamma failure rate was in mean 0.1% (couch tracking), 8.1% (MLC tracking), and 30.4% (no tracking) for prostate motion and 2.9% (couch), 2.4% (MLC), and 41.2% (no tracking) for lung tumor motion. The residual tracking errors were mainly caused by inadequate adaptation to fast lung tumor motion for couch tracking and to prostate motion perpendicular to the MLC leaves for MLC tracking. Couch and MLC tracking markedly improved the geometric and dosimetric accuracies of VMAT delivery. However, the two tracking types have different strengths and weaknesses. While couch tracking can correct perfectly for slowly moving targets such as the prostate, MLC tracking may have considerably larger dose errors for persistent target shift perpendicular to the MLC leaves. Advantages of MLC tracking include faster dynamics with better adaptation to fast moving targets, the avoidance of moving the patient, and the potential to track target rotations and deformations.

  1. Multileaf collimator tracking integrated with a novel x-ray imaging system and external surrogate monitoring

    NASA Astrophysics Data System (ADS)

    Krauss, Andreas; Fast, Martin F.; Nill, Simeon; Oelfke, Uwe

    2012-04-01

    We have previously developed a tumour tracking system, which adapts the aperture of a Siemens 160 MLC to electromagnetically monitored target motion. In this study, we exploit the use of a novel linac-mounted kilovoltage x-ray imaging system for MLC tracking. The unique in-line geometry of the imaging system allows the detection of target motion perpendicular to the treatment beam (i.e. the directions usually featuring steep dose gradients). We utilized the imaging system either alone or in combination with an external surrogate monitoring system. We equipped a Siemens ARTISTE linac with two flat panel detectors, one directly underneath the linac head for motion monitoring and the other underneath the patient couch for geometric tracking accuracy assessments. A programmable phantom with an embedded metal marker reproduced three patient breathing traces. For MLC tracking based on x-ray imaging alone, marker position was detected at a frame rate of 7.1 Hz. For the combined external and internal motion monitoring system, a total of only 85 x-ray images were acquired prior to or in between the delivery of ten segments of an IMRT beam. External motion was monitored with a potentiometer. A correlation model between external and internal motion was established. The real-time component of the MLC tracking procedure then relied solely on the correlation model estimations of internal motion based on the external signal. Geometric tracking accuracies were 0.6 mm (1.1 mm) and 1.8 mm (1.6 mm) in directions perpendicular and parallel to the leaf travel direction for the x-ray-only (the combined external and internal) motion monitoring system in spite of a total system latency of ˜0.62 s (˜0.51 s). Dosimetric accuracy for a highly modulated IMRT beam-assessed through radiographic film dosimetry-improved substantially when tracking was applied, but depended strongly on the respective geometric tracking accuracy. In conclusion, we have for the first time integrated MLC tracking with x-ray imaging in the in-line geometry and demonstrated highly accurate respiratory motion tracking.

  2. Results of multifield conformal radiation therapy of nonsmall-cell lung carcinoma using multileaf collimation beams.

    PubMed

    Bahri, S; Flickinger, J C; Kalend, A M; Deutsch, M; Belani, C P; Sciurba, F C; Luketich, J D; Greenberger, J S

    1999-01-01

    A five-field conformal technique with three-dimensional radiation therapy treatment planning (3-DRTP) has been shown to permit better definition of the target volume for lung cancer, while minimizing the normal tissue volume receiving greater than 50% of the target dose. In an initial study to confirm the safety of conventional doses, we used the five-field conformal 3-DRTP technique. We then used the technique in a second study, enhancing the therapeutic index in a series of 42 patients, as well as to evaluate feasibility, survival outcome, and treatment toxicity. Forty-two consecutive patients with nonsmall-cell lung carcinoma (NSCLC) were evaluated during the years 1993-1997. The median age was 60 years (range 34-80). The median radiation therapy (RT) dose to the gross tumor volume was 6,300 cGy (range 5,000-6,840 cGy) delivered over 6 to 6.5 weeks in 180-275 cGy daily fractions, 5 days per week. There were three patients who received a split course treatment of 5,500 cGy in 20 fractions, delivering 275 cGy daily with a 2-week break built into the treatment course after 10 fractions. The stages of disease were II in 2%, IIIA in 40%, IIIB in 42.9%, and recurrent disease in 14.3% of the patients. The mean tumor volume was 324.14 cc (range 88.3-773.7 cc); 57.1% of the patients received combined chemoradiotherapy, while the others were treated with radiation therapy alone. Of the 42 patients, 7 were excluded from the final analysis because of diagnosis of distant metastasis during treatment. Two of the patients had their histology reinterpreted as being other than NSCLC, 2 patients did not complete RT at the time of analysis, and 1 patient voluntarily discontinued treatment because of progressive deterioration. Median follow-up was 11.2 months (range 3-32.5 months). Survival for patients with Stage III disease was 70.2% at 1 year and 51.5% at 2 years, with median survival not yet reached. Local control for the entire series was 23.3+/-11.4% at 2 years. However, for Stage III patients, local control was 50% at 1 year and 30% at 2 years. Patients who received concurrent chemotherapy had significantly improved survival (P = 0.002) and local control (P = 0.004), compared with RT alone. Late esophageal toxicity of > or =Grade 3 occurred in 14.1+/-9.3% of patients (3 of 20) receiving combined chemoradiotherapy, but in none of the 15 patients treated with RT alone. Pulmonary toxicity limited to Grades 1-2 occurred in 6.8% of the patients, and none developed > or =Grade 3 pulmonary toxicity. Patients with locally advanced NSCLC, who commonly have tumor volumes in excess of 200 cc, presenta challenge for adequate dose delivery without significant toxicity. Our five-field conformal 3-DRTP technique, which incorporates treatment planning by dose/volume histogram (DVH) was associated with minimal toxicity and may facilitate dose escalation to the gross tumor.

  3. Multileaf collimator tracking integrated with a novel x-ray imaging system and external surrogate monitoring.

    PubMed

    Krauss, Andreas; Fast, Martin F; Nill, Simeon; Oelfke, Uwe

    2012-04-21

    We have previously developed a tumour tracking system, which adapts the aperture of a Siemens 160 MLC to electromagnetically monitored target motion. In this study, we exploit the use of a novel linac-mounted kilovoltage x-ray imaging system for MLC tracking. The unique in-line geometry of the imaging system allows the detection of target motion perpendicular to the treatment beam (i.e. the directions usually featuring steep dose gradients). We utilized the imaging system either alone or in combination with an external surrogate monitoring system. We equipped a Siemens ARTISTE linac with two flat panel detectors, one directly underneath the linac head for motion monitoring and the other underneath the patient couch for geometric tracking accuracy assessments. A programmable phantom with an embedded metal marker reproduced three patient breathing traces. For MLC tracking based on x-ray imaging alone, marker position was detected at a frame rate of 7.1 Hz. For the combined external and internal motion monitoring system, a total of only 85 x-ray images were acquired prior to or in between the delivery of ten segments of an IMRT beam. External motion was monitored with a potentiometer. A correlation model between external and internal motion was established. The real-time component of the MLC tracking procedure then relied solely on the correlation model estimations of internal motion based on the external signal. Geometric tracking accuracies were 0.6 mm (1.1 mm) and 1.8 mm (1.6 mm) in directions perpendicular and parallel to the leaf travel direction for the x-ray-only (the combined external and internal) motion monitoring system in spite of a total system latency of ~0.62 s (~0.51 s). Dosimetric accuracy for a highly modulated IMRT beam--assessed through radiographic film dosimetry--improved substantially when tracking was applied, but depended strongly on the respective geometric tracking accuracy. In conclusion, we have for the first time integrated MLC tracking with x-ray imaging in the in-line geometry and demonstrated highly accurate respiratory motion tracking.

  4. Combined modulated electron and photon beams planned by a Monte-Carlo-based optimization procedure for accelerated partial breast irradiation.

    PubMed

    Palma, Bianey Atriana; Sánchez, Ana Ureba; Salguero, Francisco Javier; Arráns, Rafael; Sánchez, Carlos Míguez; Zurita, Amadeo Walls; Hermida, María Isabel Romero; Leal, Antonio

    2012-03-07

    The purpose of this study was to present a Monte-Carlo (MC)-based optimization procedure to improve conventional treatment plans for accelerated partial breast irradiation (APBI) using modulated electron beams alone or combined with modulated photon beams, to be delivered by a single collimation device, i.e. a photon multi-leaf collimator (xMLC) already installed in a standard hospital. Five left-sided breast cases were retrospectively planned using modulated photon and/or electron beams with an in-house treatment planning system (TPS), called CARMEN, and based on MC simulations. For comparison, the same cases were also planned by a PINNACLE TPS using conventional inverse intensity modulated radiation therapy (IMRT). Normal tissue complication probability for pericarditis, pneumonitis and breast fibrosis was calculated. CARMEN plans showed similar acceptable planning target volume (PTV) coverage as conventional IMRT plans with 90% of PTV volume covered by the prescribed dose (D(p)). Heart and ipsilateral lung receiving 5% D(p) and 15% D(p), respectively, was 3.2-3.6 times lower for CARMEN plans. Ipsilateral breast receiving 50% D(p) and 100% D(p) was an average of 1.4-1.7 times lower for CARMEN plans. Skin and whole body low-dose volume was also reduced. Modulated photon and/or electron beams planned by the CARMEN TPS improve APBI treatments by increasing normal tissue sparing maintaining the same PTV coverage achieved by other techniques. The use of the xMLC, already installed in the linac, to collimate photon and electron beams favors the clinical implementation of APBI with the highest efficiency.

  5. Random array grid collimator

    DOEpatents

    Fenimore, E.E.

    1980-08-22

    A hexagonally shaped quasi-random no-two-holes touching grid collimator. The quasi-random array grid collimator eliminates contamination from small angle off-axis rays by using a no-two-holes-touching pattern which simultaneously provides for a self-supporting array increasng throughput by elimination of a substrate. The presentation invention also provides maximum throughput using hexagonally shaped holes in a hexagonal lattice pattern for diffraction limited applications. Mosaicking is also disclosed for reducing fabrication effort.

  6. Target, purging magnet and electron collector design for scanned high-energy photon beams

    NASA Astrophysics Data System (ADS)

    Svensson, Roger; Åsell, Mats; Näfstadius, Peder; Brahme, Anders

    1998-05-01

    A new method for producing very narrow and intense 50 MV bremsstrahlung beams with a half-width as low as 35 mm at a distance of 1 m from the target is presented. Such a beam is well suited for intensity modulation using scanned photon beams. An algorithm has been developed to minimize the width of the bremsstrahlung beam generated in a multilayer target by varying the individual layer thicknesses and atomic numbers under given constraints on the total target thickness and the mean energy of the transmitted electrons. Under such constraints the narrowest possible bremsstrahlung beam is obtained with a target composed of layers of monotonically increasing atomic number starting with the lowest possible value at the entrance side where the electrons impinge. It is also shown that the narrowest photon beam profile is associated with the highest possible forward photon yield. To be able to use the optimized target clinically it is desirable to be able to collect and stop all the electrons that are transmitted through the target. The electrons are most efficiently collected if they are kept close together, i.e. by minimizing the multiple scatter of the electrons and consequently the half-width of the generated bremsstrahlung beam. This is achieved by a thin low-atomic-number target. A dedicated electron stopper has been developed and integrated with the purging magnet. When the electron stopper is combined with a purging magnet, a primary photon collimator and a multileaf collimator, almost all of the transmitted electrons and their associated bremsstrahlung contamination can effectively be collected. The narrow photon beams from thin low-atomic-number targets have the additional advantage of producing the hardest and most penetrative photon spectrum possible, which is ideal for treating large deep-seated tumours.

  7. Target, purging magnet and electron collector design for scanned high-energy photon beams.

    PubMed

    Svensson, R; Asell, M; Näfstadius, P; Brahme, A

    1998-05-01

    A new method for producing very narrow and intense 50 MV bremsstrahlung beams with a half-width as low as 35 mm at a distance of 1 m from the target is presented. Such a beam is well suited for intensity modulation using scanned photon beams. An algorithm has been developed to minimize the width of the bremsstrahlung beam generated in a multilayer target by varying the individual layer thicknesses and atomic numbers under given constraints on the total target thickness and the mean energy of the transmitted electrons. Under such constraints the narrowest possible bremsstrahlung beam is obtained with a target composed of layers of monotonically increasing atomic number starting with the lowest possible value at the entrance side where the electrons impinge. It is also shown that the narrowest photon beam profile is associated with the highest possible forward photon yield. To be able to use the optimized target clinically it is desirable to be able to collect and stop all the electrons that are transmitted through the target. The electrons are most efficiently collected if they are kept close together, i.e. by minimizing the multiple scatter of the electrons and consequently the half-width of the generated bremsstrahlung beam. This is achieved by a thin low-atomic-number target. A dedicated electron stopper has been developed and integrated with the purging magnet. When the electron stopper is combined with a purging magnet, a primary photon collimator and a multileaf collimator, almost all of the transmitted electrons and their associated bremsstrahlung contamination can effectively be collected. The narrow photon beams from thin low-atomic-number targets have the additional advantage of producing the hardest and most penetrative photon spectrum possible, which is ideal for treating large deep-seated tumours.

  8. Simultaneous optimization of photons and electrons for mixed beam radiotherapy

    NASA Astrophysics Data System (ADS)

    Mueller, S.; Fix, M. K.; Joosten, A.; Henzen, D.; Frei, D.; Volken, W.; Kueng, R.; Aebersold, D. M.; Stampanoni, M. F. M.; Manser, P.

    2017-07-01

    The aim of this work is to develop and investigate an inverse treatment planning process (TPP) for mixed beam radiotherapy (MBRT) capable of performing simultaneous optimization of photon and electron apertures. A simulated annealing based direct aperture optimization (DAO) is implemented to perform simultaneous optimization of photon and electron apertures, both shaped with the photon multileaf collimator (pMLC). Validated beam models are used as input for Monte Carlo dose calculations. Consideration of photon pMLC transmission during DAO and a weight re-optimization of the apertures after deliverable dose calculation are utilized to efficiently reduce the differences between optimized and deliverable dose distributions. The TPP for MBRT is evaluated for an academic situation with a superficial and an enlarged PTV in the depth, a left chest wall case including the internal mammary chain and a squamous cell carcinoma case. Deliverable dose distributions of MBRT plans are compared to those of modulated electron radiotherapy (MERT), photon IMRT and if available to those of clinical VMAT plans. The generated MBRT plans dosimetrically outperform the MERT, photon IMRT and VMAT plans for all investigated situations. For the clinical cases of the left chest wall and the squamous cell carcinoma, the MBRT plans cover the PTV similarly or more homogeneously than the VMAT plans, while OARs are spared considerably better with average reductions of the mean dose to parallel OARs and D 2% to serial OARs by 54% and 26%, respectively. Moreover, the low dose bath expressed as V 10% to normal tissue is substantially reduced by up to 45% compared to the VMAT plans. A TPP for MBRT including simultaneous optimization is successfully implemented and the dosimetric superiority of MBRT plans over MERT, photon IMRT and VMAT plans is demonstrated for academic and clinical situations including superficial targets with and without deep-seated part.

  9. Gamma Imaging using Rotational Modulation Collimation

    DTIC Science & Technology

    2014-01-01

    Gamma imaging techniques 2 2.1 Compton imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.2 Pinhole or parallel-hole collimation...imaging techniques that are of relevance to national security applications. 2.1 Compton imaging Compton scattering is a specific interaction...Overlaying multiple trajectory cones over many gamma photon interactions reveals the source position, and this forms the basis for the technique of Compton

  10. Optimization of convergent collimators for pixelated SPECT systems

    SciTech Connect

    Capote, Ricardo M.; Matela, Nuno; Conceicao, Raquel C.; Almeida, Pedro

    2013-06-15

    Purpose: The optimization of the collimator design is essential to obtain the best possible sensitivity in single photon emission computed tomography imaging. The aim of this work is to present a methodology for maximizing the sensitivity of convergent collimators, specifically designed to match the pitch of pixelated detectors, for a fixed spatial resolution value and to present some initial results using this approach. Methods: Given the matched constraint, the optimal collimator design cannot be simply found by allowing the highest level of septal penetration and spatial resolution consistent with the imposed restrictions, as it is done for the optimization of conventional collimators. Therefore, an algorithm that interactively calculates the collimator dimensions, with the maximum sensitivity, which respect the imposed restrictions was developed and used to optimize cone and fan beam collimators with tapered square-shaped holes for low (60-300 keV) and high energy radiation (300-511 keV). The optimal collimator dimensions were locally calculated based on the premise that each hole and septa of the convergent collimator should locally resemble an appropriate optimal matched parallel collimator. Results: The optimal collimator dimensions, calculated for subcentimeter resolutions (3 and 7.5 mm), common pixel sizes (1.6, 2.1, and 2.5 mm), and acceptable septal penetration at 140 keV, were approximately constant throughout the collimator, despite their different hole incidence angles. By using these input parameters and a less strict septal penetration value of 5%, the optimal collimator dimensions and the corresponding mass per detector area were calculated for 511 keV. It is shown that a low value of focal distance leads to improvements in the average sensitivity at a fixed source-collimator distance and resolution. The optimal cone beam performance outperformed that of other optimal collimation geometries (fan and parallel beam) in imaging objects close to the

  11. Motion-frozen Imaging by Gated Myocardial Perfusion Single Photon Emission Computed Tomography Using Multi-focus Fan Beam Collimator in Thallium-201 Study.

    PubMed

    Takahashi, Kaito; Takeuchi, Takashi; Hosokai, Yoshiyuki; Odagiri, Hayato; Saito, Haruo

    This study aimed to evaluate the statistical noise of motion-frozen (MF) image generated by gated myocardial perfusion single photon emission computed tomography (SPECT) imaging using IQ · SPECT and to determine the optimal acquisition and reconstruction parameters for MF image using IQ · SPECT. A movement cardiac phantom and static cardiac phantom were used to acquire the MF images. The acquisition times used were different in 8 and 16 frames per R-R interval, and varying reconstruction parameters (subset and iteration) were used. We determined the %CV value, contrast, and normalized mean square error (NMSE) to evaluate the image quality. The %CV value for a MF image with IQ · SPECT was lower than that for a conventional non-gated myocardial perfusion SPECT (MPS) image with low energy high resolution (LEHR). With regard to the acquisition parameters, the contrast did not change when the acquisition time was increased in 8 and 16 frames per R-R interval. NMSE converged in 56 beats/view in 8 frames per R-R interval. With regard to the reconstruction parameters, the contrast and the %CV value of the anterior and septal wall converged in update 40. The minimum NMSE in subsets 1, 2, and 3 were almost similar. Uniformity in the MF image with IQ · SPECT was higher than that in the conventional image. The results of this MF image with IQ · SPECT study suggest that the optimal acquisition parameter should be 56 beats/view in 8 frames per R-R interval, and the optimal reconstruction parameters should be subset 3 and iteration 14.

  12. Determination of optimal collimation parameters for a rotating slat collimator system: a system matrix method using ML-EM

    NASA Astrophysics Data System (ADS)

    Boisson, F.; Bekaert, V.; Brasse, D.

    2016-03-01

    Nowadays, Single Photon imaging has become an essential part of molecular imaging and nuclear medicine. Whether to establish a diagnosis or in the therapeutic monitoring, this modality presents performance that continues to improve. For over 50 years, several collimators have been proposed. Mainly governed by collimation parameters, the resolution-sensitivity trade-off is the factor determining the collimator the most suitable for an intended study. One alternative to the common approaches is the rotating slat collimator (RSC). In the present study, we are aiming at developing a preclinical system equipped with a RSC dedicated to mice and rats imaging, which requires both high sensitivity and spatial resolution. We investigated the resolution-sensitivity trade-offs obtained by varying different collimation parameters: (i) the slats height (H), and (ii) the gap between two consecutive slats (g), considering different intrinsic spatial resolutions. One system matrix was generated for each set of collimation parameters (H,g). Spatial resolutions, Signal-to-Noise Ratio (SNR) and sensitivity obtained for all the set of collimation parameters (H,g) were measured in the 2D projections reconstructed with ML-EM. According to our results, 20 mm high slats and a 1 mm gap were chosen as a good RSC candidate for a preclinical detection module. This collimator will ensure a sensitivity greater than 0.2% and a system spatial resolution below 1 mm, considering an intrinsic spatial resolution below 0.8 mm.

  13. Process for manufacturing slit collimators

    NASA Technical Reports Server (NTRS)

    Romanenko, V. P.; Yemelyanov, A. A.; Churbakov, K. I.

    1974-01-01

    Peculiarities are described of the manufacturing process and the control of elements of slit collimators, the structural design of the required equipment and the process or assembling the collimators.

  14. Multipinhole collimator with 20 apertures for a brain SPECT application

    SciTech Connect

    Lee, Tzu-Cheng; Ellin, Justin R.; Shrestha, Uttam; Seo, Youngho; Huang, Qiu; Gullberg, Grant T.

    2014-11-01

    Purpose: Several new technologies for single photon emission computed tomography (SPECT) instrumentation with parallel-hole collimation have been proposed to improve detector sensitivity and signal collection efficiency. Benefits from improved signal efficiency include shorter acquisition times and lower dose requirements. In this paper, the authors show a possibility of over an order of magnitude enhancement in photon detection efficiency (from 7.6 × 10{sup −5} to 1.6 × 10{sup −3}) for dopamine transporter (DaT) imaging of the striatum over the conventional SPECT parallel-hole collimators by use of custom-designed 20 multipinhole (20-MPH) collimators with apertures of 0.75 cm diameter. Methods: Quantifying specific binding ratio (SBR) of {sup 123}I-ioflupane or {sup 123}I-iometopane’s signal at the striatal region is a common brain imaging method to confirm the diagnosis of the Parkinson’s disease. The authors performed imaging of a striatal phantom filled with aqueous solution of I-123 and compared camera recovery ratios of SBR acquired between low-energy high-resolution (LEHR) parallel-hole collimators and 20-MPH collimators. Results: With only two-thirds of total acquisition time (20 min against 30 min), a comparable camera recovery ratio of SBR was achieved using 20-MPH collimators in comparison to that from the LEHR collimator study. Conclusions: Their systematic analyses showed that the 20-MPH collimator could be a promising alternative for the DaT SPECT imaging for brain over the traditional LEHR collimator, which could give both shorter scan time and improved diagnostic accuracy.

  15. Enhanced PET resolution by combining pinhole collimation and coincidence detection

    NASA Astrophysics Data System (ADS)

    DiFilippo, Frank P.

    2015-10-01

    Spatial resolution of clinical PET scanners is limited by detector design and photon non-colinearity. Although dedicated small animal PET scanners using specialized high-resolution detectors have been developed, enhancing the spatial resolution of clinical PET scanners is of interest as a more available alternative. Multi-pinhole 511 keV SPECT is capable of high spatial resolution but requires heavily shielded collimators to avoid significant background counts. A practical approach with clinical PET detectors is to combine multi-pinhole collimation with coincidence detection. In this new hybrid modality, there are three locations associated with each event, namely those of the two detected photons and the pinhole aperture. These three locations over-determine the line of response and provide redundant information that is superior to coincidence detection or pinhole collimation alone. Multi-pinhole collimation provides high resolution and avoids non-colinearity error but is subject to collimator penetration and artifacts from overlapping projections. However the coincidence information, though at lower resolution, is valuable for determining whether the photon passed near a pinhole within the cone acceptance angle and for identifying through which pinhole the photon passed. This information allows most photons penetrating through the collimator to be rejected and avoids overlapping projections. With much improved event rejection, a collimator with minimal shielding may be used, and a lightweight add-on collimator for high resolution imaging is feasible for use with a clinical PET scanner. Monte Carlo simulations were performed of a 18F hot rods phantom and a 54-pinhole unfocused whole-body mouse collimator with a clinical PET scanner. Based on coincidence information and pinhole geometry, events were accepted or rejected, and pinhole-specific crystal-map projections were generated. Tomographic images then were reconstructed using a conventional pinhole SPECT

  16. NOMOS Peacock IMRT utilizing the Beak post collimation device.

    PubMed

    Salter, B J

    2001-01-01

    Intensity-modulated radiation therapy (IMRT), an exciting recent development in the field of radiation therapy, is widely anticipated by many to make possible significant improvements in the quality of radiation treatments delivered to patients. The NOMOS Peacock method of delivery, often referred to as serial tomotherapy because of its "slice-wise" treatment of a tumor, has been used since 1994 to treat some 8000+ patients worldwide. This slice-wise method of treatment is known to produce extremely conformal dose distributions due to its ability to specifically match the dose distribution on each slice to the shape of the target volume on that same slice. Based on the belief of this institution, and the NOMOS Corporation, that an increase in the number of treatment slices into which the target is segmented would lead directly to an improvement in three-dimensional (3D) dose conformality, a joint effort was undertaken to develop a new MIMIC collimator treatment mode. Inherent to the original design of the NOMOS MIMIC binary multileaf collimator were 2 treatment modes: a 2-cm mode with a slice thickness of approximately 1.7 cm and a 1-cm mode with a slice thickness of approximately 0.85 cm. As a result of this collaborative effort, a new MIMIC treatment mode has been developed. The method employs a slit collimator, post-collimation device known as the BEAK, enabling the treatment mode referred to as Beak Mode. The device imposes a distal redefinition of the slice thickness, or length, by effectively blocking the full retraction of the MIMIC vanes. The end result is a newly available slice thickness of approximately 4 mm, which is shown in this work to yield significant improvements in dose conformality for 2 representative patients. The comparative analysis of these 2 patient plans includes, in addition to a comparison of isodose distributions, an evaluation of dose-volume histogram (DVH) information, and a comparison of indices of conformality (CI) and homogeneity

  17. Verification of the accuracy of a photon dose-calculation algorithm.

    PubMed

    Gifford, Kent A; Followill, David S; Liu, H Helen; Starkschall, George

    2002-01-01

    An extensive set of measured data was developed for the purpose of verifying the accuracy of a photon dose-calculation algorithm. Dose distributions from a linear accelerator were measured using an ion chamber in a water phantom and thermoluminescent dosimeters in a heterogeneous anthropomorphic phantom. Test cases included square fields, rectangular fields, fields having different source-to-surface distances, wedged fields, irregular fields, obliquely incident fields, asymmetrically collimated fields with wedges, multileaf collimator-shaped fields, and two heterogeneous density cases. The data set was used to validate the photon dose-calculation algorithm in a commercial radiation treatment planning system. The treatment planning system calculated photon doses to within the American Association of Physicists in Medicine (AAPM) Task Group 53 (TG-53) criteria for 99% of points in the buildup region, 90% of points in the inner region, 88% of points in the outer region, and 93% of points in the penumbra. For the heterogeneous phantoms, calculations agreed with actual measurements to within +/-3%. The monitor unit tests revealed that the 18-MV open square fields, oblique incidence, oblique incidence with wedge, and mantle field test cases did not meet the TG-53 criteria but were within +/-2.5% of measurements. It was concluded that (i) the photon dose calculation algorithm used by the treatment planning system did not meet the TG-53 criteria 100% of the time; (ii) some of the TG-53 criteria may need to be modified, and (iii) the generally stated goal of accuracy in dose delivery of within 5% cannot be met in all situations using this beam model in the treatment planning system.

  18. VIRUS instrument collimator assembly

    NASA Astrophysics Data System (ADS)

    Marshall, Jennifer L.; DePoy, Darren L.; Prochaska, Travis; Allen, Richard D.; Williams, Patrick; Rheault, Jean-Philippe; Li, Ting; Nagasawa, Daniel Q.; Akers, Christopher; Baker, David; Boster, Emily; Campbell, Caitlin; Cook, Erika; Elder, Alison; Gary, Alex; Glover, Joseph; James, Michael; Martin, Emily; Meador, Will; Mondrik, Nicholas; Rodriguez-Patino, Marisela; Villanueva, Steven; Hill, Gary J.; Tuttle, Sarah; Vattiat, Brian; Lee, Hanshin; Chonis, Taylor S.; Dalton, Gavin B.; Tacon, Mike

    2014-07-01

    The Visual Integral-Field Replicable Unit Spectrograph (VIRUS) instrument is a baseline array 150 identical fiber fed optical spectrographs designed to support observations for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). The collimator subassemblies of the instrument have been assembled in a production line and are now complete. Here we review the design choices and assembly practices used to produce a suite of identical low-cost spectrographs in a timely fashion using primarily unskilled labor.

  19. Gamma ray collimator

    NASA Technical Reports Server (NTRS)

    Casanova, Edgar J. (Inventor)

    1991-01-01

    A gamma ray collimator including a housing having first and second sections is disclosed. The first section encloses a first section of depleted uranium which is disposed for receiving and supporting a radiation emitting component such as cobalt 60. The second section encloses a depleted uranium member which is provided with a conical cut out focusing portion disposed in communication with the radiation emitting element for focusing the emitted radiation to the target.

  20. Gamma ray collimator

    NASA Technical Reports Server (NTRS)

    Casanova, Edgar J. (Inventor)

    1993-01-01

    A gamma ray collimator including a housing having first and second sections. The first section encloses a first section of depleted uranium which is disposed for receiving and supporting a radiation emitting component such as cobalt 60. The second section encloses a depleted uranium member which is provided with a conical cut-out focusing portion disposed in communication with the radiation emitting element for focusing the emitted radiation to the target.

  1. A Feasibility Study of Using Hybrid Collimation for Nuclear Environment.

    PubMed

    Meng, L J; Wehe, D K

    2003-08-01

    This paper presents a feasibility of a gamma ray imager using combined electronic and mechanical collimation methods. This detector is based on the use of a multiple pinhole collimator, a position sensitive scintillation detector with Anger logic readout. A pixelated semiconductor detector, located between the collimator and the scintillation detector, is used as a scattering detector. For gamma rays scattered in the first detector and then stopped in the second detector, an image can also be built up based on the joint probability of their passing through the collimator and falling into a broadened conical surface, defined by the detected Compton scattering event. Since these events have a much smaller angular uncertainty, they provide more information content per photon compared with using solely the mechanical or electronic collimation. Therefore, the overall image quality can be improved. This feasibility study adapted a theoretical approach, based on analysing the resolution-variance trade-off in images reconstructed using Maximum a priori (MAP) algorithm. The effect of factors such as the detector configuration, Doppler broadening and collimator configuration are studied. The results showed that the combined collimation leads to a significant improvement in image quality at energy range below 300keV. However, due to the mask penetration, the performance of such a detector configuration is worse than a standard Compton camera at above this energy.

  2. A Feasibility Study of Using Hybrid Collimation for Nuclear Environment

    PubMed Central

    Meng, L J; Wehe, D. K.

    2016-01-01

    This paper presents a feasibility of a gamma ray imager using combined electronic and mechanical collimation methods. This detector is based on the use of a multiple pinhole collimator, a position sensitive scintillation detector with Anger logic readout. A pixelated semiconductor detector, located between the collimator and the scintillation detector, is used as a scattering detector. For gamma rays scattered in the first detector and then stopped in the second detector, an image can also be built up based on the joint probability of their passing through the collimator and falling into a broadened conical surface, defined by the detected Compton scattering event. Since these events have a much smaller angular uncertainty, they provide more information content per photon compared with using solely the mechanical or electronic collimation. Therefore, the overall image quality can be improved. This feasibility study adapted a theoretical approach, based on analysing the resolution-variance trade-off in images reconstructed using Maximum a priori (MAP) algorithm. The effect of factors such as the detector configuration, Doppler broadening and collimator configuration are studied. The results showed that the combined collimation leads to a significant improvement in image quality at energy range below 300keV. However, due to the mask penetration, the performance of such a detector configuration is worse than a standard Compton camera at above this energy. PMID:28260807

  3. Dosimetric properties of a flattening filter-free 6-MV photon beam: a Monte Carlo study.

    PubMed

    Mesbahi, Asghar; Mehnati, Parinaz; Keshtkar, Ahmad; Farajollahi, Alireza

    2007-08-01

    The dosimetric features of an unflattened 6-MV photon beam of an Elekta SL-25 linac was calculated by the Monte Carlo (MC) method. The head of the Elekta SL-25 linac was simulated using the MCNP4C MC code. The accuracy of the model was evaluated using measured dosimetric features, including depth dose values and dose profiles in a water phantom. The flattening filter was then removed, and beam dosimetric properties were calculated by the MC method and compared with those of the flattened photon beam. Our results showed a significant (twofold) increase in the dose rate for all field sizes. Also, the photon beam spectra for an unflattened beam were softer, which led to a steeper reduction in depth doses. The decrease in the out-of-field dose and increase in the contamination electrons and a buildup region dose were the other consequences of removing the flattening filter. Our study revealed that, for recent radiotherapy techniques, the use of multileaf collimators for beam shaping removing the flattening filter could offer some advantages, including an increased dose rate and decreased out-of-field dose.

  4. Choreographing Couch and Collimator in Volumetric Modulated Arc Therapy

    SciTech Connect

    Yang Yingli; Zhang Pengpeng; Happersett, Laura; Xiong Jianping; Yang Jie; Chan, Maria; Beal, Kathryn; Mageras, Gig; Hunt, Margie

    2011-07-15

    Purpose: To design and optimize trajectory-based, noncoplanar subarcs for volumetric modulated arc therapy (VMAT) deliverable on both Varian TrueBEAM system and traditional accelerators; and to investigate their potential advantages for treating central nervous system (CNS) tumors. Methods and Materials: To guide the computerized selection of beam trajectories consisting of simultaneous couch, gantry, and collimator motion, a score function was implemented to estimate the geometric overlap between targets and organs at risk for each couch/gantry angle combination. An initial set of beam orientations is obtained as a function of couch and gantry angle, according to a minimum search of the score function excluding zones of collision. This set is grouped into multiple continuous and extended subarcs subject to mechanical limitations using a hierarchical clustering algorithm. After determination of couch/gantry trajectories, a principal component analysis finds the collimator angle at each beam orientation that minimizes residual target-organ at risk overlaps. An in-house VMAT optimization algorithm determines the optimal multileaf collimator position and monitor units for control points within each subarc. A retrospective study of 10 CNS patients compares the proposed method of VMAT trajectory with dynamic gantry, leaves, couch, and collimator motion (Tra-VMAT); a standard noncoplanar VMAT with no couch/collimator motion within subarcs (Std-VMAT); and noncoplanar intensity-modulated radiotherapy (IMRT) plans that were clinically used. Results: Tra-VMAT provided improved target dose conformality and lowered maximum dose to brainstem, optic nerves, and chiasm by 7.7%, 1.1%, 2.3%, and 1.7%, respectively, compared with Std-VMAT. Tra-VMAT provided higher planning target volume minimum dose and reduced maximum dose to chiasm, optic nerves, and cochlea by 6.2%, 1.3%, 6.3%, and 8.4%, respectively, and reduced cochlea mean dose by 8.7%, compared with IMRT. Tra-VMAT averaged

  5. Experimentally simulating quantum walks with self-collimated light

    PubMed Central

    Qi, F.; Wang, Y. F.; Ma, Q. Y.; Zheng, W. H.

    2016-01-01

    In self-collimated photonic crystal, periodically arranged air holes of sub-wavelength scale provide flattened equi-frequency curves perpendicular to the ΓM direction, which allow light or photons propagating in a quasi-uniform medium without diffraction. Here we for the first time experimentally simulate four-step single-photon discrete time quantum walks with classical light in such a photonic crystal chip fabricated on silicon-on-insulator. Similarities between theoretical expectations and experimental results are higher than 0.98. The functional area is compact and can be extended to construct more complicated linear quantum circuits. PMID:27353428

  6. A Study of Optical Collimators.

    DTIC Science & Technology

    1980-04-01

    d’opgration d’un collimateur optique sur see performances. On stattache principalement A l’influence du diamitre du filtre spatial, du diamitre du...INTRODUCTION A collimator is basically a laser beam expander and spatial noise filter. It is composed of a microscope objective, a pinhole for noise...interchangeable pinholes and microscope objectives. The third, a Tropel 280-50 collimator, did not permit such flexibility. These collimators were used to

  7. Analytical derivation of the point spread function for pinhole collimators.

    PubMed

    Bal, Girish; Acton, Paul D

    2006-10-07

    The point spread function (PSF) of a pinhole collimator plays an important role in determining the resolution and characterizing the sensitivity of the accepted photons from a given point in the image space. The focus of this paper is to derive an analytical expression for the PSF of two different types of focusing pinhole collimators that are based on (1) right-circular double cones and (2) oblique-circular double cones. Conventionally, focusing pinhole collimators used in multi-pinhole SPECT were designed using right-circular double cones, as they were easier to fabricate. In this work, a novel focusing collimator consisting of oblique-circular double cones was designed and its properties were studied in detail with respect to right-circular double-cone based collimators. The main advantage of determining the PSF is the fact that they can be used to accurately model the PSF during the reconstruction, thereby improving the resolution of the reconstructed image. The PSF of the focusing collimators based on oblique-circular cones were found to be almost shift invariant for low and medium energy photons (below 200 keV). This property is very advantageous as algorithms such as slice-by-slice reconstruction can be used for resolution recovery thereby drastically reducing the reconstruction time. However, the PSF of focusing oblique-circular double cones (FOCDC) for higher energy photons were found to be asymmetric and hence need to be modelled more accurately during the reconstruction. On the other hand, the PSF for the right-circular cone based collimators were found to be asymmetric for all energy levels. However, due to the smaller acceptance angle used, the number of penetration photons was found to be far less than that observed for oblique-circular cones. This results in a smaller PSF making right-circular cone based collimators preferable for high-resolution small animal imaging, especially where very small pinhole diameters are used. The analytically derived

  8. Commissioning of mini-multi-leaf-collimator (MMLC) for stereotactic radiosurgery and radiotherapy.

    PubMed

    Mardirossian, George; Urie, Marcia; Fitzgerald, Thomas J; Mayr, Nina; Montebello, Joseph; Lo, Yuan-Chynan

    2003-01-01

    Commissioning of a Radionics miniature multi-leaf collimator (MMLC) for stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) is reported. With single isocenter and multi static fields, the MMLC can provide better conformity of dose distributions to the target and/or irregularly shaped target volumes than standard arc (circular) field beams with multiple isocenters. Advantages offered by the MMLC over traditional LINAC based SRS and SRT includes greatly improved dose homogeneity to the target, reduced patient positioning time and reduced treatment time. In this work, the MMLC is attached to a Varian 2300 C/D with Varian 80-leaf multi-leaf collimator. The MMLC has 62 leaves, each measured to a width of 3.53 mm at isocenter, with fields range from 1x1 cm to less than 10 × 12 cm. Beam parameters required by the Radionics treatment planning system (XPlan version 2) for evaluating the dose include tissue maximum ratio (TMR), scatter factors (SF), off-axis ratios (OAR), output factors, penumbra function (P) and transmission factors (TF) are performed in this work. Beam data are acquired with a small stereotactic diode, standard ion chambers and radiographic films. Measured profiles of dose distribution are compared to those calculated by the software and absolute dosimetry is performed.

  9. A dosimetric characterization of a novel linear accelerator collimator

    SciTech Connect

    Thompson, C. M.; Weston, S. J. Cosgrove, V. C.; Thwaites, D. I.

    2014-03-15

    Purpose: The aim of this work is to characterize a new linear accelerator collimator which contains a single pair of sculpted diaphragms mounted orthogonally to a 160 leaf multileaf collimator (MLC). The diaphragms have “thick” regions providing full attenuation and “thin” regions where attenuation is provided by both the leaves and the diaphragm. The leaves are mounted on a dynamic leaf guide allowing rapid leaf motion and leaf travel over 350 mm. Methods: Dosimetric characterization, including assessment of leaf transmission, leaf tip transmission, penumbral width, was performed in a plotting tank. Head scatter factor was measured using a mini-phantom and the effect of leaf guide position on output was assessed using a water phantom. The tongue and groove effect was assessed using multiple exposures on radiochromic film. Leaf reproducibility was assessed from portal images of multiple abutting fields. Results: The maximum transmission through the multileaf collimator is 0.44% at 6 MV and 0.52% at 10 MV. This reduced to 0.22% and 0.27%, respectively, when the beam passes through the dynamic leaf guide in addition to the MLC. The maximum transmission through the thick part of the diaphragm is 0.32% and 0.36% at 6 and 10 MV. The combination of leaf and diaphragm transmission ranges from 0.08% to 0.010% at 6 MV and 0.10% to 0.14% depending on whether the shielding is through the thick or thin part of the diaphragm. The off-axis intertip transmission for a zero leaf gap is 2.2% at 6 and 10 MV. The leaf tip penumbra for a 100 × 100 mm field ranges from 5.4 to 4.3 mm at 6 and 10 MV across the full range of leaf motion when measured in the AB direction, which reduces to 4.0–3.4 mm at 6 MV and 4.5–3.8 mm at 10 MV when measured in the GT direction. For a 50 × 50 mm field, the diaphragm penumbra ranges from 4.3 to 3.7 mm at 6 MV and 4.5 to 4.1 mm at 10 MV in the AB direction and 3.7 to 3.2 mm at 6 MV and 4.2 to 3.7 mm when measured in the GT direction. The

  10. Collimation optics for high power blue laser diodes

    NASA Astrophysics Data System (ADS)

    Huber, M.; Forrer, H.; Wuest, P.; Moser, H.; Forrer, M.

    2017-02-01

    Similar to the well-established high power laser diodes in the infrared wavelength range, the laser diodes in the blue wavelength range require tailored optics for beam shaping, to make the light usable for a variety of applications. High power laser diode arrays or single emitters require fast and slow axis optical collimation for further transport or photonics applications using high power laser radiation. With increasing requirements in higher brightness for slow axis collimation different engineering solutions exist. By using novel production technologies, e.g. precision molding, approaches that were considered too expensive for mass production become available to broad application fields. Here we report about the benefits of molded refractive, freeform slow axis collimation optics and compare them to the ubiquitous standard circular cylindrical, as well as acircular cylindrical slow axis collimation optics. By using refractive free form slow axis collimation optics it is possible to achieve significantly better brightness compared to circular cylindrical or acircular cylindrical slow axis collimation optics.

  11. A collimator optimization method for quantitative imaging: application to Y-90 bremsstrahlung SPECT.

    PubMed

    Rong, Xing; Frey, Eric C

    2013-08-01

    Post-therapy quantitative 90Y bremsstrahlung single photon emission computed tomography (SPECT) has shown great potential to provide reliable activity estimates, which are essential for dose verification. Typically 90Y imaging is performed with high- or medium-energy collimators. However, the energy spectrum of 90Y bremsstrahlung photons is substantially different than typical for these collimators. In addition, dosimetry requires quantitative images, and collimators are not typically optimized for such tasks. Optimizing a collimator for 90Y imaging is both novel and potentially important. Conventional optimization methods are not appropriate for 90Y bremsstrahlung photons, which have a continuous and broad energy distribution. In this work, the authors developed a parallel-hole collimator optimization method for quantitative tasks that is particularly applicable to radionuclides with complex emission energy spectra. The authors applied the proposed method to develop an optimal collimator for quantitative 90Y bremsstrahlung SPECT in the context of microsphere radioembolization. To account for the effects of the collimator on both the bias and the variance of the activity estimates, the authors used the root mean squared error (RMSE) of the volume of interest activity estimates as the figure of merit (FOM). In the FOM, the bias due to the null space of the image formation process was taken in account. The RMSE was weighted by the inverse mass to reflect the application to dosimetry; for a different application, more relevant weighting could easily be adopted. The authors proposed a parameterization for the collimator that facilitates the incorporation of the important factors (geometric sensitivity, geometric resolution, and septal penetration fraction) determining collimator performance, while keeping the number of free parameters describing the collimator small (i.e., two parameters). To make the optimization results for quantitative 90Y bremsstrahlung SPECT more

  12. Use of flattening filter-free photon beams in treating medulloblastoma: a dosimetric evaluation.

    PubMed

    Anchineyan, Pichandi; Mani, Ganesh K; Amalraj, Jerrin; Karthik, Balaji; Anbumani, Surega

    2014-01-01

    Aim. To evaluate the dosimetric benefits of flattening filter-free (FFF) photon beams in intensity modulated radiation therapy (IMRT) and Rapid Arc (RA) over conventional CSI methods. Methods and Materials. Five patients treated with IMRT using static multileaf collimators (MLC) were randomly selected for this retrospective study. Dynamic MLC IMRT, RA, and conformal therapy (3DCRT) were iterated with the same CT data sets with and without flattening filter photons. Total dose prescribed was 28.80 Gy in 16 fractions. Dosimetric parameters such as D max⁡, D min⁡, D mean, V 95%, V 107%, DHI, and CI for PTV and D max⁡, D mean, V 80%, V 50%, V 30%, and V 10% for OARs were extracted from DVHs. Beam on time (BOT) for various plans was also compared. Results. FFF RA therapy (6F_RA) resulted in highly homogeneous and conformal doses throughout the craniospinal axis. 3DCRT resulted in the highest V 107% (SD) 46.97 ± 28.6, whereas flattening filter (FF) and FFF dynamic IMRT had a minimum V 107%. 6F_RA and 6F_DMLC resulted in lesser doses to thyroid, eyes, esophagus, liver, lungs, and kidneys. Conclusion. FFF IMRT and FFF RA for CSI have definite dosimetric advantages over 3DCRT technique in terms of target coverage and OAR sparing. Use of FFF in IMRT resulted in 50% reduction in BOT, thereby increasing the treatment efficiency.

  13. Use of Flattening Filter-Free Photon Beams in Treating Medulloblastoma: A Dosimetric Evaluation

    PubMed Central

    Anchineyan, Pichandi; Mani, Ganesh K.; Amalraj, Jerrin; Karthik, Balaji; Anbumani, Surega

    2014-01-01

    Aim. To evaluate the dosimetric benefits of flattening filter-free (FFF) photon beams in intensity modulated radiation therapy (IMRT) and Rapid Arc (RA) over conventional CSI methods. Methods and Materials. Five patients treated with IMRT using static multileaf collimators (MLC) were randomly selected for this retrospective study. Dynamic MLC IMRT, RA, and conformal therapy (3DCRT) were iterated with the same CT data sets with and without flattening filter photons. Total dose prescribed was 28.80 Gy in 16 fractions. Dosimetric parameters such as D max⁡, D min⁡, D mean, V 95%, V 107%, DHI, and CI for PTV and D max⁡, D mean, V 80%, V 50%, V 30%, and V 10% for OARs were extracted from DVHs. Beam on time (BOT) for various plans was also compared. Results. FFF RA therapy (6F_RA) resulted in highly homogeneous and conformal doses throughout the craniospinal axis. 3DCRT resulted in the highest V 107% (SD) 46.97 ± 28.6, whereas flattening filter (FF) and FFF dynamic IMRT had a minimum V 107%. 6F_RA and 6F_DMLC resulted in lesser doses to thyroid, eyes, esophagus, liver, lungs, and kidneys. Conclusion. FFF IMRT and FFF RA for CSI have definite dosimetric advantages over 3DCRT technique in terms of target coverage and OAR sparing. Use of FFF in IMRT resulted in 50% reduction in BOT, thereby increasing the treatment efficiency. PMID:24579052

  14. High energy collimating fine grids

    NASA Technical Reports Server (NTRS)

    Arrieta, Victor M.; Tuffias, Robert H.; Laferla, Raffaele

    1995-01-01

    The objective of this project was to demonstrate the fabrication of extremely tight tolerance collimating grids using a high-Z material, specifically tungsten. The approach taken was to fabricate grids by a replication method involving the coating of a silicon grid substrate with tungsten by chemical vapor deposition (CVD). A negative of the desired grid structure was fabricated in silicon using highly wafering techniques developed for the semiconductor industry and capable of producing the required tolerances. Using diamond wafering blades, a network of accurately spaced slots was machined into a single-crystal silicon surface. These slots were then filled with tungsten by CVD, via the hydrogen reduction of tungsten hexafluoride. Following tungsten deposition, the silicon negative was etched away to leave the tungsten collimating grid structure. The project was divided into five tasks: (1) identify materials of construction for the replica and final collimating grid structures; (2) identify and implement a micromachining technique for manufacturing the negative collimator replicas (performed by NASA/JPL); (3) develop a CVD technique and processing parameters suitable for the complete tungsten densification of the collimator replicas; (4) develop a chemical etching technique for the removal of the collimator replicas after the tungsten deposition process; and (5) fabricate and deliver tungsten collimating grid specimens.

  15. High energy collimating fine grids

    NASA Astrophysics Data System (ADS)

    Arrieta, Victor M.; Tuffias, Robert H.; Laferla, Raffaele

    1995-02-01

    The objective of this project was to demonstrate the fabrication of extremely tight tolerance collimating grids using a high-Z material, specifically tungsten. The approach taken was to fabricate grids by a replication method involving the coating of a silicon grid substrate with tungsten by chemical vapor deposition (CVD). A negative of the desired grid structure was fabricated in silicon using highly wafering techniques developed for the semiconductor industry and capable of producing the required tolerances. Using diamond wafering blades, a network of accurately spaced slots was machined into a single-crystal silicon surface. These slots were then filled with tungsten by CVD, via the hydrogen reduction of tungsten hexafluoride. Following tungsten deposition, the silicon negative was etched away to leave the tungsten collimating grid structure. The project was divided into five tasks: (1) identify materials of construction for the replica and final collimating grid structures; (2) identify and implement a micromachining technique for manufacturing the negative collimator replicas (performed by NASA/JPL); (3) develop a CVD technique and processing parameters suitable for the complete tungsten densification of the collimator replicas; (4) develop a chemical etching technique for the removal of the collimator replicas after the tungsten deposition process; and (5) fabricate and deliver tungsten collimating grid specimens.

  16. Feasibility of a simple method of hybrid collimation for megavoltage grid therapy

    SciTech Connect

    Almendral, Pedro; Mancha, Pedro J.; Roberto, Daniel

    2013-05-15

    Purpose: Megavoltage grid therapy is currently delivered with step-and-shoot multisegment techniques or using a high attenuation block with divergent holes. However, the commercial availability of grid blocks is limited, their construction is difficult, and step-and-shoot techniques require longer treatment times and are not practical with some multileaf collimators. This work studies the feasibility of a hybrid collimation system for grid therapy that does not require multiple segments and can be easily implemented with widely available technical means. Methods: The authors have developed a system to generate a grid of beamlets by the simultaneous use of two perpendicular sets of equally spaced leaves that project stripe patterns in orthogonal directions. One of them is generated with the multileaf collimator integrated in the accelerator and the other with an in-house made collimator constructed with a low melting point alloy commonly available at radiation oncology departments. The characteristics of the grid fields for 6 and 18 MV have been studied with a shielded diode, an unshielded diode, and radiochromic film. Results: The grid obtained with the hybrid collimation is similar to some of the grids used clinically with respect to the beamlet size (about 1 cm) and the percentage of open beam (1/4 of the total field). The grid fields are less penetrating than the open fields of the same energy. Depending on the depth and the direction of the profiles (diagonal or along the principal axes), the measured valley-to-peak dose ratios range from 5% to 16% for 6 MV and from 9% to 20% for 18 MV. All the detectors yield similar results in the measurement of profiles and percent depth dose, but the shielded diode seems to overestimate the output factors. Conclusions: The combination of two stripe pattern collimators in orthogonal directions is a feasible method to obtain two-dimensional arrays of beamlets and has potential usefulness as an efficient way to deliver grid

  17. Is 5 mm MMLC suitable for VMAT-based lung SBRT? A dosimetric comparison with 2.5 mm HDMLC using RTOG-0813 treatment planning criteria for both conventional and high-dose flattening filter-free photon beams.

    PubMed

    Subramanian, Shanmuga V; Subramani, Vellaiyan; Thirumalai Swamy, Shanmugam; Gandhi, Arun; Chilukuri, Srinivas; Kathirvel, Murugesan

    2015-07-08

    The aim of this study is to assess the suitability of 5 mm millennium multileaf collimator (MMLC) for volumetric-modulated arc therapy (VMAT)-based lung stereotactic body radiotherapy (SBRT). Thirty lung SBRT patient treatment plans along with their planning target volumes (ranging from 2.01 cc to 150.11 cc) were transferred to an inhomogeneous lung phantom and retrospectively planned using VMAT technique, along with the high definition multileaf collimator (HDMLC) and MMLC systems. The plans were evaluated using Radiation Therapy Oncology Group (RTOG-0813) treatment planning criteria for target coverage, normal tissue sparing, and treatment efficiency for both the MMLC and HDMLC systems using flat and flattening filter-free (FFF) photon beams. Irrespective of the target volumes, both the MLC systems were able to satisfy the RTOG-0813 treatment planning criteria without having any major deviation. Dose conformity was marginally better with HDMLC. The average conformity index (CI) value was found to be 1.069 ± 0.034 and 1.075 ± 0.0380 for HDMLC and MMLC plans, respectively. For the 6 MV FFF beams, the plan was slightly more conformal, with the average CI values of 1.063 ± 0.029 and 1.073 ± 0.033 for the HDMLC and MMLC plans, respectively. The high dose spillage was the maximum for 2 cc volume set (3% for HDMLC and 3.1% for MMLC). In the case of low dose spillage, both the MLCs were within the protocol of no deviation, except for the 2 cc volume set. The results from this study revealed that VMAT-based lung SBRT using 5 mm MMLC satisfies the RTOG-0813 treatment planning criteria for the studied target size and shapes.

  18. Wakefields in SLAC linac collimators

    DOE PAGES

    Novokhatski, A.; Decker, F. -J.; Smith, H.; ...

    2014-12-02

    When a beam travels near collimator jaws, it gets an energy loss and a transverse kick due to the backreaction of the beam field diffracted from the jaws. The effect becomes very important for an intense short bunch when a tight collimation of the background beam halo is required. In the Linac Coherent Light Source at SLAC a collimation system is used to protect the undulators from radiation due to particles in the beam halo. The halo is most likely formed from gun dark current or dark current in some of the accelerating sections. However, collimators are also responsible formore » the generation of wake fields. The wake field effect from the collimators not only brings an additional energy jitter and change in the trajectory of the beam, but it also rotates the beam on the phase plane, which consequently leads to a degradation of the performance of the Free Electron Laser at the Linac Coherent Light Source. In this paper, we describe a model of the wake field radiation in the SLAC linac collimators. We use the results of a numerical simulation to illustrate the model. Based on the model, we derive simple formulas for the bunch energy loss and the average kick. We also present results from experimental measurements that confirm our model.« less

  19. SU-E-T-11: A Dosimetric Comparison of Robotic Prostatic Radiosugery Using Multi- Leaf Collimation Vs Circular Collimators

    SciTech Connect

    Feng, J; Yang, J; Lamond, J; Lavere, N; Laciano, R; Ding, W; Arrigo, S; Brady, L

    2014-06-01

    Purpose: The study compared the dosimetry plans of Stereotatic Body Radiotherapy (SBRT) prostate cancer patients using the M6 Cyberknife with Multi-leaf Collimation (MLC) compared with the plans using G4 Cyberknife with circular collimators. Methods: Eight previously treated prostate cancer patients' SBRT plans using circular collimators, designed with Multiplan v3.5.3, were used as a benchmark. The CT, contours and the optimization scripts were imported into Multiplan v5.0 system and replanned with MLC. The same planning objectives were used: more than 95% of PTV received 36.25Gy, 90% of prostate received 40Gy and maximum dose <45Gy, in five fractions. For organs at risk, less than 1cc of rectum received 36Gy and less than 10cc of bladder received 37Gy. Plans were evaluated on parameters derived from dose volume. The beam number, MU and delivery time were recorded to compare the treatment efficiency. Results: The mean CTV volume was 41.3cc (27.5∼57.6cc) and mean PTV volume was 76.77cc (59.1∼99.7cc). The mean PTV coverage was comparable between MLC (98.87%) and cone (98.74%). MLC plans had a slightly more favorable homogeneity index (1.22) and conformity index (1.17), than the cone (1.24 and 1.15). The mean rectum volume of 36 Gy (0.52cc) of MLC plans was slightly larger than cone (0.38cc) and the mean bladder volume of 37 Gy was smaller in MLC (1.82cc) than in cone plans (3.09cc). The mean number of nodes and beams were 65.9 and 80.5 in MLC vs 65.9 and 203.6 in cone. The mean MUs were significantly less for MLC plans (24,228MUs) than cone (32,347MUs). The total delivery time (which included 5 minutes for setup) was less, 29.6min (26∼32min) for MLC vs 45min (35∼55min) for cone. Conclusion: While the differences in the dosimetry between the MLC and circular collimator plans were rather minor, the MLC plans were much more efficient and required significantly less treatment time.

  20. Simulation of the 6 MV Elekta Synergy Platform linac photon beam using Geant4 Application for Tomographic Emission

    PubMed Central

    Didi, Samir; Moussa, Abdelilah; Yahya, Tayalati; Mustafa, Zerfaoui

    2015-01-01

    The present work validates the Geant4 Application for Tomographic Emission Monte Carlo software for the simulation of a 6 MV photon beam given by Elekta Synergy Platform medical linear accelerator treatment head. The simulation includes the major components of the linear accelerator (LINAC) with multi-leaf collimator and a homogeneous water phantom. Calculations were performed for the photon beam with several treatment field sizes ranging from 5 cm × 5 cm to 30 cm × 30 cm at 100 cm distance from the source. The simulation was successfully validated by comparison with experimental distributions. Good agreement between simulations and measurements was observed, with dose differences of about 0.02% and 2.5% for depth doses and lateral dose profiles, respectively. This agreement was also emphasized by the Kolmogorov–Smirnov goodness-of-fit test and by the gamma-index comparisons where more than 99% of the points for all simulations fulfill the quality assurance criteria of 2 mm/2%. PMID:26500399

  1. Simulation of the 6 MV Elekta Synergy Platform linac photon beam using Geant4 Application for Tomographic Emission.

    PubMed

    Didi, Samir; Moussa, Abdelilah; Yahya, Tayalati; Mustafa, Zerfaoui

    2015-01-01

    The present work validates the Geant4 Application for Tomographic Emission Monte Carlo software for the simulation of a 6 MV photon beam given by Elekta Synergy Platform medical linear accelerator treatment head. The simulation includes the major components of the linear accelerator (LINAC) with multi-leaf collimator and a homogeneous water phantom. Calculations were performed for the photon beam with several treatment field sizes ranging from 5 cm × 5 cm to 30 cm × 30 cm at 100 cm distance from the source. The simulation was successfully validated by comparison with experimental distributions. Good agreement between simulations and measurements was observed, with dose differences of about 0.02% and 2.5% for depth doses and lateral dose profiles, respectively. This agreement was also emphasized by the Kolmogorov-Smirnov goodness-of-fit test and by the gamma-index comparisons where more than 99% of the points for all simulations fulfill the quality assurance criteria of 2 mm/2%.

  2. Binocular collimation vs conditional alignment

    NASA Astrophysics Data System (ADS)

    Cook, William J.

    2012-10-01

    As binocular enthusiasts share their passion, topics related to collimation abound. Typically, we find how observers, armed only with a jeweler's screwdriver, can "perfectly collimate" his or her binocular, make it "spot on," or other verbiage of similar connotation. Unfortunately, what most are addressing is a form of pseudo-collimation I have referred to since the mid-1970s as "Conditional Alignment." Ignoring the importance of the mechanical axis (hinge) in the alignment process, this "condition," while having the potential to make alignment serviceable, or even outstanding—within a small range of IPD (Interpupillary Distance) settings relative to the user's spatial accommodation (the ability to accept small errors in parallelism of the optical axes)—may take the instrument farther from the 3-axis collimation conscientious manufacturers seek to implement. Becoming more optically savvy—and especially with so many mechanically inferior binoculars entering the marketplace— the consumer contemplating self-repair and alignment has a need to understand the difference between clinical, 3-axis "collimation" (meaning both optical axes are parallel with the axis of the hinge) and "conditional alignment," as differentiated in this paper. Furthermore, I believe there has been a long-standing need for the term "Conditional Alignment," or some equivalent, to be accepted as part of the vernacular of those who use binoculars extensively, whether for professional or recreational activities. Achieving that acceptance is the aim of this paper.

  3. Fermilab Recycler Collimation System Design

    SciTech Connect

    Brown, B. C.; Adamson, P.; Ainsworth, R.; Capista, D.; Hazelwood, K.; Kourbanis, I.; Mokhov, N. V.; Morris, D. K.; Murphy, M.; Sidorov, V.; Stern, E.; Tropin, I.; Yang, M-J.

    2016-10-04

    To provide 700 kW proton beams for neutrino production in the NuMI facility, we employ slip stacking in the Recycler with transfer to the Main Injector for recapture and acceleration. Slip stacking with 12 Booster batches per 1.33 sec cycle of the Main Injector has been implemented and briefly tested while extensive operation with 8 batches and 10 batches per MI cycle has been demonstrated. Operation in this mode since 2013 shows that loss localization is an essential component for long term operation. Beam loss in the Recycler will be localized in a collimation region with design capability for absorbing up to 2 kW of lost protons in a pair of 20-Ton collimators (absorbers). This system will employ a two stage collimation with a thin molybdenum scattering foil to define the bottom edge of both the injected and decelerated-for-slipping beams. Optimization and engineering design of the collimator components and radiation shielding are based on comprehensive MARS15 simulations predicting high collimation efficiency as well as tolerable levels of prompt and residual radiation. The system installation during the Fermilab 2016 facility shutdown will permit commissioning in the subsequent operating period.

  4. Optimization of the rounded leaf offset table in modeling the multileaf collimator leaf edge in a commercial treatment planning system.

    PubMed

    Rice, John R

    2014-11-08

    An editable rounded leaf offset (RLO) table is provided in the Pinnacle3 treatment planning software. Default tables are provided for major linear accelerator manu- facturers, but it is not clear how the default table values should be adjusted by the user to optimize agreement between the calculated leaf tip value and the actual measured value. Since we wish for the calculated MLC-defined field edge to closely match the actual delivered field edge, optimal RLO table values are crucial. This is especially true for IMRT fields containing a large number of segments, since any errors would add together. A method based on the calculated MLC-defined field edge was developed for optimizing and modifying the default RLO table values. Modified RLO tables were developed and evaluated for both dosimetric and light field-based MLC leaf calibrations. It was shown, using a Picket Fence type test, that the optimized RLO table better modeled the calculated leaf tip than the Pinnacle3 default table. This was demonstrated for both an Elekta Synergy 80-leaf and a Varian 120-leaf MLC. 

  5. Surface dose investigation of the flattening filter-free photon beams.

    PubMed

    Wang, Yuenan; Khan, Mohammad K; Ting, Joseph Y; Easterling, Stephen B

    2012-06-01

    Flattening filter-free (FFF) x-rays can provide more efficient use of photons and a significant increase of dose rate compared with conventional flattened x-rays, features that are especially beneficial for stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT). The available data on the entrance doses of the FFF photon beams remain limited. The purpose of this study was to investigate the entrance dose of FFF photons in the buildup region and to compare it with that of conventional flattened photons. A Varian TrueBeam linear accelerator has been in full clinical operation with 6-MV and 10-MV FFF and flattened x-ray photons. Entrance dose at the surface was measured using a parallel plate ionization chamber in a solid water phantom with buildup depth = 0~15 mm for 6X and 0~25 mm for 10X. Different field size (FS) patterns were created in the Eclipse Treatment Planning System by multileaf collimator (MLC) rather than jaws (FS = 2 × 2, 3 × 3, 4 × 4, 6 × 6, and 10 × 10 cm(2) by MLC and jaw size = 2.2 × 2.2, 3.2 × 3.2, 4.2 × 4.2, 6 × 6, and 10 × 10 cm(2)). The smallest FS was about four times larger than the ion chamber dimension. All buildup dose measurements were normalized to FS = 10 × 10 cm(2) at the depth of dose maximum (dmax). Good repeatability was demonstrated and surface dose increased linearly with FS for both flattened and FFF photons. The entrance dose of the FFF photons was modestly larger than that of the corresponding flattened photons for both 6X and 10X for different FS ranging from 2 × 2 cm(2) to 10 × 10 cm(2). The FFF photons have a higher entrance dose than that of the corresponding flattened photons for FS smaller than 10 × 10 cm(2). However, the difference is not substantial and may be clinically insignificant. Published by Elsevier Inc.

  6. Surface Dose Investigation of the Flattening Filter-Free Photon Beams

    SciTech Connect

    Wang Yuenan; Khan, Mohammad K.; Ting, Joseph Y.; Easterling, Stephen B.

    2012-06-01

    Purpose: Flattening filter-free (FFF) x-rays can provide more efficient use of photons and a significant increase of dose rate compared with conventional flattened x-rays, features that are especially beneficial for stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT). The available data on the entrance doses of the FFF photon beams remain limited. The purpose of this study was to investigate the entrance dose of FFF photons in the buildup region and to compare it with that of conventional flattened photons. Methods and Materials: A Varian TrueBeam linear accelerator has been in full clinical operation with 6-MV and 10-MV FFF and flattened x-ray photons. Entrance dose at the surface was measured using a parallel plate ionization chamber in a solid water phantom with buildup depth = 0{approx}15 mm for 6X and 0{approx}25 mm for 10X. Different field size (FS) patterns were created in the Eclipse Treatment Planning System by multileaf collimator (MLC) rather than jaws (FS = 2 Multiplication-Sign 2, 3 Multiplication-Sign 3, 4 Multiplication-Sign 4, 6 Multiplication-Sign 6, and 10 Multiplication-Sign 10 cm{sup 2} by MLC and jaw size = 2.2 Multiplication-Sign 2.2, 3.2 Multiplication-Sign 3.2, 4.2 Multiplication-Sign 4.2, 6 Multiplication-Sign 6, and 10 Multiplication-Sign 10 cm{sup 2}). The smallest FS was about four times larger than the ion chamber dimension. All buildup dose measurements were normalized to FS = 10 Multiplication-Sign 10 cm{sup 2} at the depth of dose maximum (dmax). Results: Good repeatability was demonstrated and surface dose increased linearly with FS for both flattened and FFF photons. The entrance dose of the FFF photons was modestly larger than that of the corresponding flattened photons for both 6X and 10X for different FS ranging from 2 Multiplication-Sign 2 cm{sup 2} to 10 Multiplication-Sign 10 cm{sup 2}. Conclusions: The FFF photons have a higher entrance dose than that of the corresponding flattened photons for FS

  7. Multileaf shielding design against neutrons produced by medical linear accelerators.

    PubMed

    Rebello, W F; Silva, A X; Facure, A

    2008-01-01

    This work aims at presenting a study using Monte Carlo simulation of a Multileaf Shielding (MLS) System designed to be used for the protection of patients who undergo radiotherapy treatment, against undesired exposure to neutrons produced in the components of the medical linear accelerator heads. The choice of radiotherapy equipment as the subject of study fell on the Varian Clinac 2,100/2,300 with MLC-120 operating at 18 MeV. The general purpose Monte Carlo N-Particle radiation transport code, MCNP5, was used in the computer simulation in order to determine the ambient dose equivalent, H (10), on several points on the patient's plane, with the equipment operation with and without the MLS. The results of the simulations showed a significant neutron dose reduction after the inclusion of the proposed shielding.

  8. Emission tomography with a large-hole collimator (CACAO): a possible new way to improve radionuclide imaging.

    PubMed

    Jeanguillaume, Christian; Quartuccio, Marc; Begot, Stéphane; Douiri, Abdellah; Franck, Didier; Ricolfi, Frédéric; Ballongue, Paul; Tencé, Marcel

    2002-01-01

    This work aims to improve the quality of scintigraphy. It evaluates the use of a large-hole collimator, the Computer Aided Collimation Gamma Camera Project (CACAO), in SPECT. Acquisition data from the same object were simulated for CACAO and for a conventional collimator. Better signal-to-noise ratios were found for CACAO images, whatever the number of emitted photons. This work demonstrates that high-resolution images may be obtained with large-hole collimators. The combination of CACAO and pixilated detectors may further improve radionuclide imaging.

  9. Radiation beam collimation system and method

    SciTech Connect

    Schmidt, Oliver A.; Ramanathan, Mohan

    2015-08-18

    The invention provides a method for collimating a radiation beam, the method comprising subjecting the beam to a collimator that yaws and pitches, either separately or simultaneously relative to the incident angle of the beam. Also provided is a system for collimating radiation beams, the system comprising a collimator body, and a stage for pitching and yawing the body. A feature of the invention is that a single, compact mask body defines one or a plurality of collimators having no moving surfaces relative to each other, whereby the entire mask body is moved about a point in space to provide various collimator opening dimensions to oncoming radiation beams.

  10. Effect of MLC leaf position, collimator rotation angle, and gantry rotation angle errors on intensity-modulated radiotherapy plans for nasopharyngeal carcinoma

    SciTech Connect

    Bai, Sen; Li, Guangjun; Wang, Maojie; Jiang, Qinfeng; Zhang, Yingjie; Wei, Yuquan

    2013-07-01

    The purpose of this study was to investigate the effect of multileaf collimator (MLC) leaf position, collimator rotation angle, and accelerator gantry rotation angle errors on intensity-modulated radiotherapy plans for nasopharyngeal carcinoma. To compare dosimetric differences between the simulating plans and the clinical plans with evaluation parameters, 6 patients with nasopharyngeal carcinoma were selected for simulation of systematic and random MLC leaf position errors, collimator rotation angle errors, and accelerator gantry rotation angle errors. There was a high sensitivity to dose distribution for systematic MLC leaf position errors in response to field size. When the systematic MLC position errors were 0.5, 1, and 2 mm, respectively, the maximum values of the mean dose deviation, observed in parotid glands, were 4.63%, 8.69%, and 18.32%, respectively. The dosimetric effect was comparatively small for systematic MLC shift errors. For random MLC errors up to 2 mm and collimator and gantry rotation angle errors up to 0.5°, the dosimetric effect was negligible. We suggest that quality control be regularly conducted for MLC leaves, so as to ensure that systematic MLC leaf position errors are within 0.5 mm. Because the dosimetric effect of 0.5° collimator and gantry rotation angle errors is negligible, it can be concluded that setting a proper threshold for allowed errors of collimator and gantry rotation angle may increase treatment efficacy and reduce treatment time.

  11. Review of SPECT collimator selection, optimization, and fabrication for clinical and preclinical imaging

    SciTech Connect

    Van Audenhaege, Karen Van Holen, Roel; Vandenberghe, Stefaan; Vanhove, Christian; Moore, Stephen C.

    2015-08-15

    In single photon emission computed tomography, the choice of the collimator has a major impact on the sensitivity and resolution of the system. Traditional parallel-hole and fan-beam collimators used in clinical practice, for example, have a relatively poor sensitivity and subcentimeter spatial resolution, while in small-animal imaging, pinhole collimators are used to obtain submillimeter resolution and multiple pinholes are often combined to increase sensitivity. This paper reviews methods for production, sensitivity maximization, and task-based optimization of collimation for both clinical and preclinical imaging applications. New opportunities for improved collimation are now arising primarily because of (i) new collimator-production techniques and (ii) detectors with improved intrinsic spatial resolution that have recently become available. These new technologies are expected to impact the design of collimators in the future. The authors also discuss concepts like septal penetration, high-resolution applications, multiplexing, sampling completeness, and adaptive systems, and the authors conclude with an example of an optimization study for a parallel-hole, fan-beam, cone-beam, and multiple-pinhole collimator for different applications.

  12. Review of SPECT collimator selection, optimization, and fabrication for clinical and preclinical imaging

    PubMed Central

    Van Audenhaege, Karen; Van Holen, Roel; Vandenberghe, Stefaan; Vanhove, Christian; Metzler, Scott D.; Moore, Stephen C.

    2015-01-01

    In single photon emission computed tomography, the choice of the collimator has a major impact on the sensitivity and resolution of the system. Traditional parallel-hole and fan-beam collimators used in clinical practice, for example, have a relatively poor sensitivity and subcentimeter spatial resolution, while in small-animal imaging, pinhole collimators are used to obtain submillimeter resolution and multiple pinholes are often combined to increase sensitivity. This paper reviews methods for production, sensitivity maximization, and task-based optimization of collimation for both clinical and preclinical imaging applications. New opportunities for improved collimation are now arising primarily because of (i) new collimator-production techniques and (ii) detectors with improved intrinsic spatial resolution that have recently become available. These new technologies are expected to impact the design of collimators in the future. The authors also discuss concepts like septal penetration, high-resolution applications, multiplexing, sampling completeness, and adaptive systems, and the authors conclude with an example of an optimization study for a parallel-hole, fan-beam, cone-beam, and multiple-pinhole collimator for different applications. PMID:26233207

  13. Image reconstruction algorithm for a spinning strip CZT SPECT camera with a parallel slat collimator and small pixels

    SciTech Connect

    Zeng, Gengsheng L.; Gagnon, Daniel

    2004-12-01

    This paper discusses the use of small pixels in a spinning CdZnTe single photon emission computed tomography (SPECT) camera that is mounted with a parallel slat collimator. In a conventional slat collimation configuration, there is a detector pixel between two adjacent collimator slats. In our design, the pixel size is halved. That is, there are two smaller pixels to replace a regular pixel between two adjacent slats while the collimator remains unchanged. It has an advantage over our older design that uses tilted slats. In order to acquire a complete data set the tilted-slat collimator must spin 360 deg. at each SPECT view while the proposed design requires only 180 deg. at each SPECT view. Computer simulations and phantom experiments have been carried out to investigate the performance of the small-pixel configuration. It is observed that this design has the potential to increase the spatial resolution of the detector while keeping photon counts the same.

  14. A feasibility study of Dynamic Phantom scanner for quality assurance of photon beam profiles at various gantry angles.

    PubMed

    Zhang, Yunkai; Hsi, Wen C; Chu, James C H; Bernard, Damian B; Abrams, Ross A

    2005-01-01

    The effect of gantry rotation on beam profiles of photon and electron beams is an important issue in quality assurance for radiotherapy. To address variations in the profiles of photon and electron beams at different gantry angles, a Dynamic Phantom scanner composed of a 20 x 12 x 6 cm3 scanning Lucite block was designed as a cross-beam-profile scanner. To our knowledge, differences between scanned profiles acquired at different gantry angles with a small size Lucite block and those acquired a full-size (60 x 60 x 50 cm3) water phantom have not been previously investigated. We therefore performed a feasibility study for a first prototype Dynamic Phantom scanner without a gantry attachment mount. Radiation beams from a Varian LINAC 21EX and 2100C were used. Photon beams (6 MV and 18 MV) were shaped by either collimator jaws or a Varian 120 Multileaf (MLC) collimator, and electron beams (6 MeV, 12 MeV, and 20 MeV) were shaped by a treatment cone. To investigate the effect on profiles by using a Lucite block, a quantitative comparison of scanned profiles with the Dynamic Phantom and a full-size water phantom was first performed at a 0 degrees gantry angle for both photon and electron beams. For photon beam profiles defined by jaws at 1.0 cm and 5.0 cm depths of Lucite (i.e., at 1.1 cm and 5.7 cm depth of water), a good agreement (less than 1% variation) inside the field edge was observed between profiles scanned with the Dynamic Phantom and with a water phantom. The use of Lucite in the Dynamic Phantom resulted in reduced penumbra width (about 0.5 mm out of 5 mm to 8mm) and reduced (1% to 2%) scatter dose beyond the field edges for both 6 MV and 18 MV beams, compared with the water phantom scanner. For profiles of the MLC-shaped 6 MV photon beam, a similar agreement was observed. For profiles of electron beams scanned at 2.9 cm depth of Lucite (i.e., at 3.3 cm depth of water), larger disagreements in profiles (3% to 4%) and penumbra width (3 mm to 4 mm out of 12 mm

  15. Proton Collimators for Fusion Reactors

    NASA Technical Reports Server (NTRS)

    Miley, George H.; Momota, Hiromu

    2003-01-01

    Proton collimators have been proposed for incorporation into inertial-electrostatic-confinement (IEC) fusion reactors. Such reactors have been envisioned as thrusters and sources of electric power for spacecraft and as sources of energetic protons in commercial ion-beam applications.

  16. Optimizing Collimator Margins for Isotoxically Dose-Escalated Conformal Radiation Therapy of Non-Small Cell Lung Cancer

    SciTech Connect

    Warren, Samantha; Panettieri, Vanessa; Panakis, Niki; Bates, Nicholas; Lester, Jason F.; Jain, Pooja; Landau, David B.; Nahum, Alan E.; Mayles, W. Philip M.; Fenwick, John D.

    2014-04-01

    Purpose: Isotoxic dose escalation schedules such as IDEAL-CRT [isotoxic dose escalation and acceleration in lung cancer chemoradiation therapy] (ISRCTN12155469) individualize doses prescribed to lung tumors, generating a fixed modeled risk of radiation pneumonitis. Because the beam penumbra is broadened in lung, the choice of collimator margin is an important element of the optimization of isotoxic conformal radiation therapy for lung cancer. Methods and Materials: Twelve patients with stage I-III non-small cell lung cancer (NSCLC) were replanned retrospectively using a range of collimator margins. For each plan, the prescribed dose was calculated according to the IDEAL-CRT isotoxic prescription method, and the absolute dose (D{sub 99}) delivered to 99% of the planning target volume (PTV) was determined. Results: Reducing the multileaf collimator margin from the widely used 7 mm to a value of 2 mm produced gains of 2.1 to 15.6 Gy in absolute PTV D{sub 99}, with a mean gain ± 1 standard error of the mean of 6.2 ± 1.1 Gy (2-sided P<.001). Conclusions: For NSCLC patients treated with conformal radiation therapy and an isotoxic dose prescription, absolute doses in the PTV may be increased by using smaller collimator margins, reductions in relative coverage being offset by increases in prescribed dose.

  17. Collimator with attachment mechanism and system

    DOEpatents

    Kross, Brian J [Yorktown, VA; McKisson, John [Hampton, VA; Stolin, Aleksandr [Morgantown, WV; Weisenberger, Andrew G [Yorktown, VA; Zorn, Carl [Yorktown, VA

    2012-07-10

    A self-aligning collimator for a radiation imaging device that is secured and aligned through the use of a plurality of small magnets. The collimator allows for the rapid exchange, removal, or addition of collimators for the radiation imaging device without the need for tools. The accompanying method discloses the use of magnets and accompanying magnetic fields to align and secure collimators in a radiation imaging assembly.

  18. Carbon nanotube collimator fabrication and application

    DOEpatents

    Chow, Lee; Chai, Guangyu; Schenkel, Thomas

    2010-07-06

    Apparatus, methods, systems and devices for fabricating individual CNT collimators. Micron size fiber coated CNT samples are synthesized with chemical vapor deposition method and then the individual CNT collimators are fabricated with focused ion beam technique. Unfocused electron beams are successfully propagated through the CNT collimators. The CNT nano-collimators are used for applications including single ion implantation and in high-energy physics, and allow rapid, reliable testing of the transmission of CNT arrays for transport of molecules.

  19. Mechanical and Thermal Prototype Testing for a Rotatable Collimator for the LHC Phase II Collimation Upgrade

    SciTech Connect

    Smith, Jeffrey Claiborne; Doyle, Eric; Keller, Lewis; Lundgren, Steven; Markiewicz, Thomas Walter; /SLAC

    2010-08-26

    The Phase II upgrade to the LHC collimation system calls for complementing the robust Phase I graphite collimators with high Z, low impedance Phase II collimators. The design for the collimation upgrade has not been finalized. One option is to use metallic rotatable collimators and testing of this design will be discussed here. The Phase II collimators must be robust in various operating conditions and accident scenarios. A prototype collimator jaw has been tested for both mechanical and thermal compliance with the design goals. Thermal expansion bench-top tests are compared to ANSYS simulation results.

  20. Technical Report: Evaluation of peripheral dose for flattening filter free photon beams.

    PubMed

    Covington, E L; Ritter, T A; Moran, J M; Owrangi, A M; Prisciandaro, J I

    2016-08-01

    To develop a comprehensive peripheral dose (PD) dataset for the two unflattened beams of nominal energy 6 and 10 MV for use in clinical care. Measurements were made in a 40 × 120 × 20 cm(3) (width × length × depth) stack of solid water using an ionization chamber at varying depths (dmax, 5, and 10 cm), field sizes (3 × 3 to 30 × 30 cm(2)), and distances from the field edge (5-40 cm). The effects of the multileaf collimator (MLC) and collimator rotation were also evaluated for a 10 × 10 cm(2) field. Using the same phantom geometry, the accuracy of the analytic anisotropic algorithm (AAA) and Acuros dose calculation algorithm was assessed and compared to the measured values. The PDs for both the 6 flattening filter free (FFF) and 10 FFF photon beams were found to decrease with increasing distance from the radiation field edge and the decreasing field size. The measured PD was observed to be higher for the 6 FFF than for the 10 FFF for all field sizes and depths. The impact of collimator rotation was not found to be clinically significant when used in conjunction with MLCs. AAA and Acuros algorithms both underestimated the PD with average errors of -13.6% and -7.8%, respectively, for all field sizes and depths at distances of 5 and 10 cm from the field edge, but the average error was found to increase to nearly -69% at greater distances. Given the known inaccuracies of peripheral dose calculations, this comprehensive dataset can be used to estimate the out-of-field dose to regions of interest such as organs at risk, electronic implantable devices, and a fetus. While the impact of collimator rotation was not found to significantly decrease PD when used in conjunction with MLCs, results are expected to be machine model and beam energy dependent. It is not recommended to use a treatment planning system to estimate PD due to the underestimation of the out-of-field dose and the inability to calculate dose at extended distances due to the limits of the dose

  1. Technical Report: Evaluation of peripheral dose for flattening filter free photon beams

    PubMed Central

    Covington, E. L.; Ritter, T. A.; Moran, J. M.; Owrangi, A. M.; Prisciandaro, J. I.

    2016-01-01

    Purpose: To develop a comprehensive peripheral dose (PD) dataset for the two unflattened beams of nominal energy 6 and 10 MV for use in clinical care. Methods: Measurements were made in a 40 × 120 × 20 cm3 (width × length × depth) stack of solid water using an ionization chamber at varying depths (dmax, 5, and 10 cm), field sizes (3 × 3 to 30 × 30 cm2), and distances from the field edge (5–40 cm). The effects of the multileaf collimator (MLC) and collimator rotation were also evaluated for a 10 × 10 cm2 field. Using the same phantom geometry, the accuracy of the analytic anisotropic algorithm (AAA) and Acuros dose calculation algorithm was assessed and compared to the measured values. Results: The PDs for both the 6 flattening filter free (FFF) and 10 FFF photon beams were found to decrease with increasing distance from the radiation field edge and the decreasing field size. The measured PD was observed to be higher for the 6 FFF than for the 10 FFF for all field sizes and depths. The impact of collimator rotation was not found to be clinically significant when used in conjunction with MLCs. AAA and Acuros algorithms both underestimated the PD with average errors of −13.6% and −7.8%, respectively, for all field sizes and depths at distances of 5 and 10 cm from the field edge, but the average error was found to increase to nearly −69% at greater distances. Conclusions: Given the known inaccuracies of peripheral dose calculations, this comprehensive dataset can be used to estimate the out-of-field dose to regions of interest such as organs at risk, electronic implantable devices, and a fetus. While the impact of collimator rotation was not found to significantly decrease PD when used in conjunction with MLCs, results are expected to be machine model and beam energy dependent. It is not recommended to use a treatment planning system to estimate PD due to the underestimation of the out-of-field dose and the inability to calculate dose at extended

  2. Optimizing Pinhole and Parallel Hole Collimation for Scintimammography With Compact Pixellated Detectors

    SciTech Connect

    Mark F. Smith; Stan Majewski; Andrew G. Weisenberger

    2002-11-01

    The relative resolution and sensitivity advantages of pinhole and parallel hole collimators for planar scintimammography with compact, pixellated gamma detectors were investigated using analytic models. Collimator design was studied as follows. A desired object resolution was specified for a pixellated detector with a given crystal size and intrinsic spatial resolution and for a given object-to- collimator distance. Using analytic formulas, pinhole and parallel hole collimator parameters were calculated that satisfy this object resolution with optimal geometric sensitivity. Analyses were performed for 15 cm x 20 cm field of view detectors with crystal elements 1.0, 2.0 and 3.0 mm on a side and 140 keV incident photons. The sensitivity for a given object resolution was greater for pinhole collimation at smaller distances, as expected. The object distance at which the pinhole and parallel hole sensitivity curves cross each other is important. The crossover distances increased with larger crystal size for a constant object resolution and increased as the desired object resolution decreases for a constant crystal size. For example, for 4 mm object resolution and a pinhole collimator with focal length 13 cm, these distances were 5.5 cm, 6.5 cm and 8 cm for the 1 mm, 2 mm and 3 mm crystal detectors, respectively. The results suggest a strategy of parallel hole collimation for whole breast imaging and pinhole collimation for imaging focal uptake. This could be accomplished with a dual detector system with a different collimator type on each head or a single head system equipped with two collimators and a rapid switching mechanism.

  3. Monitor unit calculations for external photon and electron beams: Report of the AAPM Therapy Physics Committee Task Group No. 71

    SciTech Connect

    Gibbons, John P.; Antolak, John A.; Followill, David S.; Huq, M. Saiful; Klein, Eric E.; Lam, Kwok L.; Palta, Jatinder R.; Roback, Donald M.; Reid, Mark; Khan, Faiz M.

    2014-03-15

    A protocol is presented for the calculation of monitor units (MU) for photon and electron beams, delivered with and without beam modifiers, for constant source-surface distance (SSD) and source-axis distance (SAD) setups. This protocol was written by Task Group 71 of the Therapy Physics Committee of the American Association of Physicists in Medicine (AAPM) and has been formally approved by the AAPM for clinical use. The protocol defines the nomenclature for the dosimetric quantities used in these calculations, along with instructions for their determination and measurement. Calculations are made using the dose per MU under normalization conditions, D{sub 0}{sup ′}, that is determined for each user's photon and electron beams. For electron beams, the depth of normalization is taken to be the depth of maximum dose along the central axis for the same field incident on a water phantom at the same SSD, where D{sub 0}{sup ′} = 1 cGy/MU. For photon beams, this task group recommends that a normalization depth of 10 cm be selected, where an energy-dependent D{sub 0}{sup ′} ≤ 1 cGy/MU is required. This recommendation differs from the more common approach of a normalization depth of d{sub m}, with D{sub 0}{sup ′} = 1 cGy/MU, although both systems are acceptable within the current protocol. For photon beams, the formalism includes the use of blocked fields, physical or dynamic wedges, and (static) multileaf collimation. No formalism is provided for intensity modulated radiation therapy calculations, although some general considerations and a review of current calculation techniques are included. For electron beams, the formalism provides for calculations at the standard and extended SSDs using either an effective SSD or an air-gap correction factor. Example tables and problems are included to illustrate the basic concepts within the presented formalism.

  4. Monitor unit calculations for external photon and electron beams: Report of the AAPM Therapy Physics Committee Task Group No. 71.

    PubMed

    Gibbons, John P; Antolak, John A; Followill, David S; Huq, M Saiful; Klein, Eric E; Lam, Kwok L; Palta, Jatinder R; Roback, Donald M; Reid, Mark; Khan, Faiz M

    2014-03-01

    A protocol is presented for the calculation of monitor units (MU) for photon and electron beams, delivered with and without beam modifiers, for constant source-surface distance (SSD) and source-axis distance (SAD) setups. This protocol was written by Task Group 71 of the Therapy Physics Committee of the American Association of Physicists in Medicine (AAPM) and has been formally approved by the AAPM for clinical use. The protocol defines the nomenclature for the dosimetric quantities used in these calculations, along with instructions for their determination and measurement. Calculations are made using the dose per MU under normalization conditions, D'0, that is determined for each user's photon and electron beams. For electron beams, the depth of normalization is taken to be the depth of maximum dose along the central axis for the same field incident on a water phantom at the same SSD, where D'0 = 1 cGy/MU. For photon beams, this task group recommends that a normalization depth of 10 cm be selected, where an energy-dependent D'0 ≤ 1 cGy/MU is required. This recommendation differs from the more common approach of a normalization depth of dm, with D'0 = 1 cGy/MU, although both systems are acceptable within the current protocol. For photon beams, the formalism includes the use of blocked fields, physical or dynamic wedges, and (static) multileaf collimation. No formalism is provided for intensity modulated radiation therapy calculations, although some general considerations and a review of current calculation techniques are included. For electron beams, the formalism provides for calculations at the standard and extended SSDs using either an effective SSD or an air-gap correction factor. Example tables and problems are included to illustrate the basic concepts within the presented formalism.

  5. Optimization of the CLIC Baseline Collimation System

    SciTech Connect

    Resta-Lopez, Javier; Angal-Kalinin, Deepa; Fernandez-Hernando, Juan; Jackson, Frank; Dalena, Barbara; Schulte, Daniel; Tomas, Rogelio; Seryi, Andrei; /SLAC

    2012-07-06

    Important efforts have recently been dedicated to the improvement of the design of the baseline collimation system of the Compact Linear Collider (CLIC). Different aspects of the design have been optimized: the transverse collimation depths have been recalculated in order to reduce the collimator wakefield effects while maintaining a good efficiency in cleaning the undesired beam halo; the geometric design of the spoilers have also been reviewed to minimize wakefields; in addition, the optics design have been polished to improve the collimation efficiency. This paper describes the current status of the CLIC collimation system after this optimization.

  6. Fabricating High-Resolution X-Ray Collimators

    NASA Technical Reports Server (NTRS)

    Appleby, Michael; Atkinson, James E.; Fraser, Iain; Klinger, Jill

    2008-01-01

    A process and method for fabricating multi-grid, high-resolution rotating modulation collimators for arcsecond and sub-arcsecond x-ray and gamma-ray imaging involves photochemical machining and precision stack lamination. The special fixturing and etching techniques that have been developed are used for the fabrication of multiple high-resolution grids on a single array substrate. This technology has application in solar and astrophysics and in a number of medical imaging applications including mammography, computed tomography (CT), single photon emission computed tomography (SPECT), and gamma cameras used in nuclear medicine. This collimator improvement can also be used in non-destructive testing, hydrodynamic weapons testing, and microbeam radiation therapy.

  7. Multiple pinhole collimator based X-ray luminescence computed tomography

    PubMed Central

    Zhang, Wei; Zhu, Dianwen; Lun, Michael; Li, Changqing

    2016-01-01

    X-ray luminescence computed tomography (XLCT) is an emerging hybrid imaging modality, which is able to improve the spatial resolution of optical imaging to hundreds of micrometers for deep targets by using superfine X-ray pencil beams. However, due to the low X-ray photon utilization efficiency in a single pinhole collimator based XLCT, it takes a long time to acquire measurement data. Herein, we propose a multiple pinhole collimator based XLCT, in which multiple X-ray beams are generated to scan a sample at multiple positions simultaneously. Compared with the single pinhole based XLCT, the multiple X-ray beam scanning method requires much less measurement time. Numerical simulations and phantom experiments have been performed to demonstrate the feasibility of the multiple X-ray beam scanning method. In one numerical simulation, we used four X-ray beams to scan a cylindrical object with 6 deeply embedded targets. With measurements from 6 angular projections, all 6 targets have been reconstructed successfully. In the phantom experiment, we generated two X-ray pencil beams with a collimator manufactured in-house. Two capillary targets with 0.6 mm edge-to-edge distance embedded in a cylindrical phantom have been reconstructed successfully. With the two beam scanning, we reduced the data acquisition time by 50%. From the reconstructed XLCT images, we found that the Dice similarity of targets is 85.11% and the distance error between two targets is less than 3%. We have measured the radiation dose during XLCT scan and found that the radiation dose, 1.475 mSv, is in the range of a typical CT scan. We have measured the changes of the collimated X-ray beam size and intensity at different distances from the collimator. We have also studied the effects of beam size and intensity in the reconstruction of XLCT. PMID:27446686

  8. Multiple pinhole collimator based X-ray luminescence computed tomography.

    PubMed

    Zhang, Wei; Zhu, Dianwen; Lun, Michael; Li, Changqing

    2016-07-01

    X-ray luminescence computed tomography (XLCT) is an emerging hybrid imaging modality, which is able to improve the spatial resolution of optical imaging to hundreds of micrometers for deep targets by using superfine X-ray pencil beams. However, due to the low X-ray photon utilization efficiency in a single pinhole collimator based XLCT, it takes a long time to acquire measurement data. Herein, we propose a multiple pinhole collimator based XLCT, in which multiple X-ray beams are generated to scan a sample at multiple positions simultaneously. Compared with the single pinhole based XLCT, the multiple X-ray beam scanning method requires much less measurement time. Numerical simulations and phantom experiments have been performed to demonstrate the feasibility of the multiple X-ray beam scanning method. In one numerical simulation, we used four X-ray beams to scan a cylindrical object with 6 deeply embedded targets. With measurements from 6 angular projections, all 6 targets have been reconstructed successfully. In the phantom experiment, we generated two X-ray pencil beams with a collimator manufactured in-house. Two capillary targets with 0.6 mm edge-to-edge distance embedded in a cylindrical phantom have been reconstructed successfully. With the two beam scanning, we reduced the data acquisition time by 50%. From the reconstructed XLCT images, we found that the Dice similarity of targets is 85.11% and the distance error between two targets is less than 3%. We have measured the radiation dose during XLCT scan and found that the radiation dose, 1.475 mSv, is in the range of a typical CT scan. We have measured the changes of the collimated X-ray beam size and intensity at different distances from the collimator. We have also studied the effects of beam size and intensity in the reconstruction of XLCT.

  9. A photon thermal diode.

    PubMed

    Chen, Zhen; Wong, Carlaton; Lubner, Sean; Yee, Shannon; Miller, John; Jang, Wanyoung; Hardin, Corey; Fong, Anthony; Garay, Javier E; Dames, Chris

    2014-11-17

    A thermal diode is a two-terminal nonlinear device that rectifies energy carriers (for example, photons, phonons and electrons) in the thermal domain, the heat transfer analogue to the familiar electrical diode. Effective thermal rectifiers could have an impact on diverse applications ranging from heat engines to refrigeration, thermal regulation of buildings and thermal logic. However, experimental demonstrations have lagged far behind theoretical proposals. Here we present the first experimental results for a photon thermal diode. The device is based on asymmetric scattering of ballistic energy carriers by pyramidal reflectors. Recent theoretical work has predicted that this ballistic mechanism also requires a nonlinearity in order to yield asymmetric thermal transport, a requirement of all thermal diodes arising from the second Law of Thermodynamics, and realized here using an 'inelastic thermal collimator' element. Experiments confirm both effects: with pyramids and collimator the thermal rectification is 10.9 ± 0.8%, while without the collimator no rectification is detectable (<0.3%).

  10. Evaluation of uncertainty predictions and dose output for model-based dose calculations for megavoltage photon beams

    SciTech Connect

    Olofsson, Joergen; Nyholm, Tufve; Georg, Dietmar; Ahnesjoe, Anders; Karlsson, Mikael

    2006-07-15

    In many radiotherapy clinics an independent verification of the number of monitor units (MU) used to deliver the prescribed dose to the target volume is performed prior to the treatment start. Traditionally this has been done by using methods mainly based on empirical factors which, at least to some extent, try to separate the influence from input parameters such as field size, depth, distance, etc. The growing complexity of modern treatment techniques does however make this approach increasingly difficult, both in terms of practical application and in terms of the reliability of the results. In the present work the performance of a model-based approach, describing the influence from different input parameters through actual modeling of the physical effects, has been investigated in detail. The investigated model is based on two components related to megavoltage photon beams; one describing the exiting energy fluence per delivered MU, and a second component describing the dose deposition through a pencil kernel algorithm solely based on a measured beam quality index. Together with the output calculations, the basis of a method aiming to predict the inherent calculation uncertainties in individual treatment setups has been developed. This has all emerged from the intention of creating a clinical dose/MU verification tool that requires an absolute minimum of commissioned input data. This evaluation was focused on irregular field shapes and performed through comparison with output factors measured at 5, 10, and 20 cm depth in ten multileaf collimated fields on four different linear accelerators with varying multileaf collimator designs. The measurements were performed both in air and in water and the results of the two components of the model were evaluated separately and combined. When compared with the corresponding measurements the resulting deviations in the calculated output factors were in most cases smaller than 1% and in all cases smaller than 1.7%. The

  11. [Characterization of the response of hexagonal parallel-hole collimators of scintillation cameras].

    PubMed

    de Lagrevol, R; Gantet, P; Esquerré, J P; Danet, B; Guiraud, R

    1996-05-01

    This paper presents a formulation of the frequency response of hexagonal parallel-hole collimator scintillation cameras. To describe this response, we propose an equation determined semi-empirically from a great number of simulations. The utility of the equation is that it enables the simple calculation of the response from collimator characteristics by taking into account the collimator's hexagonal structure. Because the equation does not assume translation invariance, the results can be directly compared with experimental measurements obtained with a point source. It is particularly interesting for collimators with large holes, like the medium-resolution ones used for high-energy radiation. Quality control and physical performance measurements are thus facilitated for this kind of collimator. Also, we present a new parameter that gives a quantitative assessment of the importance of partition penetration. This parameter is measured directly from the collimator frequency response. It has been studied by simulation, taking into account gamma photon attenuation in collimator partitions. The experimental measurements that have been made are in accord with the proposed equations.

  12. Performance of collimators used for tomographic imaging of I-123 contaminated with I-124

    SciTech Connect

    Polak, J.F.; English, R.J.; Holman, B.L.

    1983-11-01

    Iodine-123 prepared from the /sup 124/Te(p,2n)/sup 123/I reaction is contaminated with between 3% to 5% I-124 when imaging is performed. The effects of such a mixture were evaluated for medium-energy and low energy general-purpose collimators on a commerically available ratating gamma camera equipped to perform tomography. The planar sensitivity for I-123 was less for the general- purpose collimator, varying between 0.84 and 0.85 in water relative to that measured for the medium energy-collimator. Counts due to scattering or septal penetration of I-124 photons were greater for the general-purpose collimator (36%) than for the medium-energy collimator (15%). Evaluation of the higher-frequency components of the modulation transfer functions confirmed that the low-energy general-purpose collimator is expected to offer significantly more contrast information at frequencies above 0.21 cycles/cm. This is expected to contribute to image quality when studies are performed with collimators of similar design.

  13. Brain SPECT with short focal-length cone-beam collimation

    SciTech Connect

    Park, Mi-Ae; Moore, Stephen C.; Kijewski, Marie Foley

    2005-07-15

    Single-photon emission-computed tomography (SPECT) imaging of deep brain structures is compromised by loss of photons due to attenuation. We have previously shown that a centrally peaked collimator sensitivity function can compensate for this phenomenon, increasing sensitivity over most of the brain. For dual-head instruments, parallel-hole collimators cannot provide variable sensitivity without simultaneously degrading spatial resolution near the center of the brain; this suggests the use of converging collimators. We have designed collimator pairs for dual-head SPECT systems to increase sensitivity, particularly in the center of the brain, and compared the new collimation approach to existing approaches on the basis of performance in estimating activity concentration of small structures at various locations in the brain. The collimator pairs we evaluated included a cone-beam collimator, for increased sensitivity, and a fan-beam collimator, for data sufficiency. We calculated projections of an ellipsoidal uniform background, with 0.9-cm-radius spherical lesions at several locations in the background. From these, we determined ideal signal-to-noise ratios (SNR{sub CRB}) for estimation of activity concentration within the spheres, based on the Cramer-Rao lower bound on variance. We also reconstructed, by an ordered-subset expectation-maximization (OS-EM) procedure, images of this phantom, as well as of the Zubal brain phantom, to allow visual assessment and to ensure that they were free of artifacts. The best of the collimator pairs evaluated comprised a cone-beam collimator with 20 cm focal length, for which the focal point is inside the brain, and a fan-beam collimator with 40 cm focal length. This pair yielded increased SNR{sub CRB}, compared to the parallel-parallel pair, throughout the imaging volume. The factor by which SNR{sub CRB} increased ranged from 1.1 at the most axially extreme location to 3.5 at the center. The gains in SNR{sub CRB} were relatively

  14. Design of a Rotatable Copper Collimator for the LHC Phase II Collimation Upgrade

    SciTech Connect

    Smith, Jeffrey Claiborne; Doyle, Eric; Keller, Lewis; Lundgren, Steven; Markiewicz, Thomas Walter; Lari, Luisella; /LPHE, Lausanne

    2010-02-15

    The Phase II upgrade to the LHC collimation system calls for complementing the robust Phase I graphite collimators with high Z, low impedance Phase II collimators. The design for the collimation upgrade has not been finalized. One option is to use metallic rotatable collimators and this design will be discussed here. The Phase II collimators must be robust in various operating conditions and accident scenarios. Design issues include: (1) Collimator jaw deflection and sagitta due to heating must be small when operated in the steady state condition, (2) Collimator jaws must withstand transitory periods of high beam impaction with no permanent damage, (3) Jaws must recover from accident scenario where up to 8 full intensity beam pulses impact on the jaw surface and (4) The beam impedance contribution due to the collimators must be small to minimize coherent beam instabilities.

  15. Effect of collimator and couch angle change on breast IMRT dose distributions.

    PubMed

    Yang, Jie; Ma, Charlie; Wang, Lu; Chen, Lili; Li, Jinsheng

    2009-09-30

    Intensity modulated tangential photon beams for breast cancer treatment can improve the dose uniformity significantly throughout the whole breast and reduce the dose to the lung and the heart comparing with the conventional technique. Before the first treatment, patient setup may require a change on the collimator angle and/or the couch angle based on the chest wall coverage according to the port films. The objective of this work is to investigate the effects of the collimator and the couch angle change on the dose distribution for breast cancer treatment using intensity modulated tangential photon beams, and thus to determine the clinical acceptable range of the angle change for routine treatment. Ten breast cases treated with intensity modulated tangential photon beams were analyzed in this study. Patient-specific CT data and the RTP files obtained from our home-grown Monte Carlo based breast IMRT treatment planning system were used for IMRT dose re-calculation with collimator or couch angle changes. The isodose distributions and DVHs were compared with the original plans and the effects of the collimator and couch angle change to breast IMRT dose distributions were evaluated. Our results show that a 4-degree change in the collimator angle or the couch angle did not affect the dose distribution significantly and it is acceptable in the clinic for patient treatment.

  16. Photonics and Optoelectronics

    DTIC Science & Technology

    2013-03-07

    Distribution Outline/Agenda • Nanophotonics: plasmonics, nanostructures, metasurfaces etc • Integrated Nanophotonics & Silicon Photonics...Highlights Nanophotonics Nanophotonics: metasurfaces , nanostructures, plasmonics etc • Shalaev – Broadband Light Bending with Plasmonic...solitons, slot waveguide, “ Metasurface ” collimator etc " World Changing Ideas 2012” Electronic Tattoos, sciencemag , J. Rogers UICU P

  17. 503MHz repetition rate femtosecond Yb: fiber ring laser with an integrated WDM collimator.

    PubMed

    Wang, Aimin; Yang, Hongyu; Zhang, Zhigang

    2011-12-05

    We demonstrate 503MHz fundamental high repetition rate operation in a ring cavity passively mode-locked Yb:fiber laser incorporating a novel wavelength-division-multiplexing collimator and a piece of all-solid photonic bandgap fiber. The Yb doped fiber was directly fabricated as one fiber pigtail into the functional collimator, greatly shortening the cavity length and facilitating the splicing operation. A 5cm long photonic bandgap fiber with abnormal dispersion at the lasing wavelength (centered at 1030nm) decreases the net dispersion for shorter output pulses. The spectral bandwidth of the pulse was 34nm. The direct output pulse was measured to be 156fs and the dechirped pulse was about 76fs. With this innovative Yb:fiber pigtailed WDM collimator, the ring cavity laser has the potential to work at a repetition rate up to GHz.

  18. Measurements of backscattered radiation from Therac-20 collimator and trimmer jaws into beam monitor chamber.

    PubMed

    Kubo, H; Lo, K K

    1989-01-01

    The field size dependent photon output is known to be influenced by the existence of backscattered radiation (BSR) generated in the collimator or trimmer jaws of a linear accelerator. This paper describes the results of measurements made to study the existence of such backscatter by simulating the geometry of the treatment head of a Therac-20 linear accelerator. The machine's monitor chamber, flattening filter, and collimator jaws were simulated by another real monitor chamber, a 1-cm thick lead sheet and 2.5-cm thick low-melting-point alloy divergent blocks, respectively. BSR from the simulated collimator jaws (SCJ) was measured with the simulated monitor chamber (SMC) as a function of the openings of the SCJ and as a function of distance between SMC and SCJ. The present results demonstrate the presence of BSR in an 18-MV photon beam from a Therac-20 linear accelerator.

  19. Measurements of backscattered radiation from Therac-20 collimator and trimmer jaws into beam monitor chamber

    SciTech Connect

    Kubo, H.; Lo, K.K.

    1989-03-01

    The field size dependent photon output is known to be influenced by the existence of backscattered radiation (BSR) generated in the collimator or trimmer jaws of a linear accelerator. This paper describes the results of measurements made to study the existence of such backscatter by simulating the geometry of the treatment head of a Therac-20 linear accelerator. The machine's monitor chamber, flattening filter, and collimator jaws were simulated by another real monitor chamber, a 1-cm thick lead sheet and 2.5-cm thick low-melting-point alloy divergent blocks, respectively. BSR from the simulated collimator jaws (SCJ) was measured with the simulated monitor chamber (SMC) as a function of the openings of the SCJ and as a function of distance between SMC and SCJ. The present results demonstrate the presence of BSR in an 18-MV photon beam from a Therac-20 linear accelerator.

  20. WE-AB-BRB-10: Filmless QA of CyberKnife MLC-Collimated and Iris-Collimated Fields

    SciTech Connect

    Gersh, J

    2015-06-15

    Purpose: Current methods of CK field shape QA is based on the use of radiochromic film. Though accurate results can be attained, these methods are prone to error, time consuming, and expensive. The techniques described herein perform similar QA using the FOIL Detector (Field, Output, and Image Localization). A key feature of this in-house QA solution, and central to this study, is an aSi flat-panel detector which provides the user with the means to perform accurate, immediate, and quantitative field analysis. Methods: The FOIL detector is automatically aligned in the CK beam using fiducial markers implanted within the detector case. Once the system is aligned, a treatment plan is delivered which irradiates the flat-panel imager using the field being tested. The current study tests each of the clinically-used fields shaped using the Iris variable-aperture collimation system using a plan which takes 6 minutes to deliver. The user is immediately provided with field diameter and beam profile, as well as a comparison to baseline values. Additionally, the detector is used to acquire and analyze leaf positions of the InCise multi-leaf collimation system. Results: Using a 6-minute plan consisting of 11 beams of 25MU-per-beam, the FOIL detector provided the user with a quantitative analysis of all clinically-used field shapes. The FOIL detector was also able to clearly resolve field edge junctions in a picket fence test, including slight over-travel of individual leaves as well as inter-leaf leakage. Conclusion: The FOIL system provided comparable field diameter and profile data when compared to methods using film; providing results much faster and with 5% of the MU used for film. When used with the MLC system, the FOIL detector provided the means for immediate quantification of the performance of the system through analysis of leaf positions in a picket fence test field. Author is the President/Owner of Spectrum Medical Physics, LLC, a company which maintains contracts

  1. Design and performance evaluation of a 20-aperture multipinhole collimator for myocardial perfusion imaging applications

    NASA Astrophysics Data System (ADS)

    Bowen, Jason D.; Huang, Qiu; Ellin, Justin R.; Lee, Tzu-Cheng; Shrestha, Uttam; Gullberg, Grant T.; Seo, Youngho

    2013-10-01

    Single photon emission computed tomography (SPECT) myocardial perfusion imaging remains a critical tool in the diagnosis of coronary artery disease. However, after more than three decades of use, photon detection efficiency remains poor and unchanged. This is due to the continued reliance on parallel-hole collimators first introduced in 1964. These collimators possess poor geometric efficiency. Here we present the performance evaluation results of a newly designed multipinhole collimator with 20 pinhole apertures (PH20) for commercial SPECT systems. Computer simulations and numerical observer studies were used to assess the noise, bias and diagnostic imaging performance of a PH20 collimator in comparison with those of a low energy high resolution (LEHR) parallel-hole collimator. Ray-driven projector/backprojector pairs were used to model SPECT imaging acquisitions, including simulation of noiseless projection data and performing MLEM/OSEM image reconstructions. Poisson noise was added to noiseless projections for realistic projection data. Noise and bias performance were investigated for five mathematical cardiac and torso (MCAT) phantom anatomies imaged at two gantry orbit positions (19.5 and 25.0 cm). PH20 and LEHR images were reconstructed with 300 MLEM iterations and 30 OSEM iterations (ten subsets), respectively. Diagnostic imaging performance was assessed by a receiver operating characteristic (ROC) analysis performed on a single MCAT phantom; however, in this case PH20 images were reconstructed with 75 pixel-based OSEM iterations (four subsets). Four PH20 projection views from two positions of a dual-head camera acquisition and 60 LEHR projections were simulated for all studies. At uniformly-imposed resolution of 12.5 mm, significant improvements in SNR and diagnostic sensitivity (represented by the area under the ROC curve, or AUC) were realized when PH20 collimators are substituted for LEHR parallel-hole collimators. SNR improves by factors of 1

  2. Linac Coherent Light Source Electron Beam Collimation

    SciTech Connect

    Wu, J.; Dowell, D.; Emma, P.; Limborg-Deprey, C.; Schmerge, J.F.; /SLAC

    2007-04-27

    This paper describes the design and simulation of the electron beam collimation system in the Linac Coherent Light Source (LCLS). Dark current is expected from the gun and some of the accelerating cavities. Particle tracking of the expected dark current through the entire LCLS linac, from gun through FEL undulator, is used to estimate final particle extent in the undulator as well as expected beam loss at each collimator or aperture restriction. A table of collimators and aperture restrictions is listed along with halo particle loss results, which includes an estimate of average continuous beam power lost. In addition, the transverse wakefield alignment tolerances are calculated for each collimator.

  3. Simulated Design Strategies for SPECT Collimators to Reduce the Eddy Currents Induced by MRI Gradient Fields

    NASA Astrophysics Data System (ADS)

    Samoudi, Amine M.; Van Audenhaege, Karen; Vermeeren, Günter; Verhoyen, Gregory; Martens, Luc; Van Holen, Roel; Joseph, Wout

    2015-10-01

    Combining single photon emission computed tomography (SPECT) with magnetic resonance imaging (MRI) requires the insertion of highly conductive SPECT collimators inside the MRI scanner, resulting in an induced eddy current disturbing the combined system. We reduced the eddy currents due to the insert of a novel tungsten collimator inside transverse and longitudinal gradient coils. The collimator was produced with metal additive manufacturing, that is part of a microSPECT insert for a preclinical SPECT/MRI scanner. We characterized the induced magnetic field due to the gradient field and adapted the collimators to reduce the induced eddy currents. We modeled the x-, y-, and z-gradient coil and the different collimator designs and simulated them with FEKO, a three-dimensional method of moments / finite element methods (MoM/FEM) full-wave simulation tool. We used a time analysis approach to generate the pulsed magnetic field gradient. Simulation results show that the maximum induced field can be reduced by 50.82% in the final design bringing the maximum induced magnetic field to less than 2% of the applied gradient for all the gradient coils. The numerical model was validated with measurements and was proposed as a tool for studying the effect of a SPECT collimator within the MRI gradient coils.

  4. Two-level multi-pinhole collimator for SPECT imaging using a small-field-of-view gamma camera

    NASA Astrophysics Data System (ADS)

    Bae, Jaekeon; Bae, Seungbin; Lee, Soo-young; Lee, Kisung; Kim, Yongkwon; Joung, Jinhun; Kim, MinHo; Kim, Kyeong Min

    2017-01-01

    The aim of this study was to develop a high-throughput imaging method for single-photon emission computed tomography. We developed a target-oriented multi-pinhole collimator and limitedangle method for scanning small organs such as the thyroid. To maximize the resolution and the sensitivity of the collimator, we designed a two-level multi-pinhole collimator whose levels were optimized for concave body contours. One level had a center hole whereas the other had surrounding holes. The limited-angle scanning method was employed to obtain tomographic images by using the collimator located near the body contour of the target, and a corresponding image reconstruction algorithm was implemented. A small-field-of-view gamma camera was used to achieve a smaller footprint. The design of the collimator also considered the dimensions of used gamma camera. Evaluation studies were conducted using the Geant4 application for tomographic emission. The results showed the resolution of the proposed collimator to be more than twice that of the previously designed multi-pinhole collimator while maintaining the same efficiency. Given that the designed collimator can be changed by simply replacing the center hole, the suggested imaging method is suitable for studying not only the thyroid but also any organ whose diameter is less than 90 mm.

  5. Objective comparison of lesion detectability in low and medium-energy collimator iodine-123 mIBG images using a channelized Hotelling observer

    NASA Astrophysics Data System (ADS)

    Gregory, Rebecca A.; Murray, Iain; Gear, Jonathan; Aldridge, Matthew D.; Levine, Daniel; Fowkes, Lucy; Waddington, Wendy A.; Chua, Sue; Flux, Glenn

    2017-01-01

    Iodine-123 mIBG imaging is widely regarded as a gold standard for diagnostic studies of neuroblastoma and adult neuroendocrine cancer although the optimal collimator for tumour imaging remains undetermined. Low-energy (LE) high-resolution (HR) collimators provide superior spatial resolution. However due to septal penetration of high-energy photons these provide poorer contrast than medium-energy (ME) general-purpose (GP) collimators. LEGP collimators improve count sensitivity. The aim of this study was to objectively compare the lesion detection efficiency of each collimator to determine the optimal collimator for diagnostic imaging. The septal penetration and sensitivity of each collimator was assessed. Planar images of the patient abdomen were simulated with static scans of a Liqui-Phil™ anthropomorphic phantom with lesion-shaped inserts, acquired with LE and ME collimators on 3 different manufacturers’ gamma camera systems (Skylight (Philips), Intevo (Siemens) and Discovery (GE)). Two-hundred normal and 200 single-lesion abnormal images were created for each collimator. A channelized Hotelling observer (CHO) was developed and validated to score the images for the likelihood of an abnormality. The areas under receiver-operator characteristic (ROC) curves, Az, created from the scores were used to quantify lesion detectability. The CHO ROC curves for the LEHR collimators were inferior to the GP curves for all cameras. The LEHR collimators resulted in statistically significantly smaller Azs (p  <  0.05), of on average 0.891  ±  0.004, than for the MEGP collimators, 0.933  ±  0.004. In conclusion, the reduced background provided by MEGP collimators improved 123I mIBG image lesion detectability over LEHR collimators that provided better spatial resolution.

  6. Ion source with improved primary arc collimation

    DOEpatents

    Dagenhart, W.K.

    1983-12-16

    An improved negative ion source is provided in which a self-biasing, molybdenum collimator is used to define the primary electron stream arc discharge from a filament operated at a negative potential. The collimator is located between the anode and the filament. It is electrically connected to the anode by means of an appropriate size resistor such that the collimator is biased at essentially the filament voltage during operation. Initially, the full arc voltage appears across the filament to collimator until the arc discharge strikes. Then the collimator biases itself to essentially filament potential due to current flow through the resistor thus defining the primary electron stream without intercepting any appreciable arc power. The collimator aperture is slightly smaller than the anode aperture to shield the anode from the arc power which, in the past, has caused overheating and erosion of the anode collimator during extended time pulsed-beam operation of the source. With the self-biasing collimator of this invention, the ion source may be operated from short pulse periods to steady-state without destroying the anode.

  7. Ion source with improved primary arc collimation

    DOEpatents

    Dagenhart, William K.

    1985-01-01

    An improved negative ion source is provided in which a self-biasing, molybdenum collimator is used to define the primary electron stream arc discharge from a filament operated at a negative potential. The collimator is located between the anode and the filament. It is electrically connected to the anode by means of an appropriate size resistor such that the collimator is biased at essentially the filament voltage during operation. Initially, the full arc voltage appears across the filament to collimator until the arc discharge strikes. Then the collimator biases itself to essentially filament potential due to current flow through the resistor thus defining the primary electron stream without intercepting any appreciable arc power. The collimator aperture is slightly smaller than the anode aperture to shield the anode from the arc power, thereby preventing the exposure of the anode to the full arc power which, in the past, has caused overheating and erosion of the anode collimator during extended time pulsed-beam operation of the source. With the self-biasing collimator of this invention, the ion source may be operated from short pulse periods to steady-state without destroying the anode.

  8. Dual-prism interferometer for collimation testing

    SciTech Connect

    Hii, King Ung; Kwek, Kuan Hiang

    2009-01-10

    An air-wedge lateral-shear interferometer using two prisms is presented. With a variable shear, the interferometer is suitable for testing collimation of a wide range of beam sizes down to a few millimeters in diameter. No antireflection coatings are necessary. Collimation for a light source with short coherent length is also demonstrated.

  9. Collimator design for the NSNS accumulator ring

    SciTech Connect

    Ludewig, H.; Schmidt, E.; Aronson, A.; Walker, J.; Todosow, M.; Mughabghab, S.

    1997-10-01

    Collimators are used to remove halo or off-momentum particles from the main proton beam. Off-momentum particles are removed by situating collimators in high dispersion areas of the beam. In addition to removing halo particles collimators will also act as shielding for the remainder of the accelerator structures. Thus, collimators reduce uncontrolled losses around the ring and reduce activation of the accelerator components. Requirements and performance goals for the collimator are summarized. In order to meet these goals a self-shielding collimator configuration will be designed. An arrangement consisting of a layered structure will be considered. The initial layers (in the direction of the proton beam) are transparent to protons, and become progressively less transparent (blacker) with depth into the collimator. In addition, a high density (iron) shield will be added around this structure, particularly in the backward direction, to attenuate any reflected protons. The protons are stopped in the approximate center of the collimator, and thus the bulk of the secondary particles will also be generated there. Since these secondary particles are primarily produced isotropically their leakage path length will be maximized in this manner (high probability of capture or attenuation). In the case of neutrons a black layer is included at each end in order to further minimize their leakage in the direction of the beam. This design will therefore minimize the activation of surrounding accelerator components.

  10. Construction and Bench Testing of a Rotatable Collimator for the LHC Collimation Upgrade

    SciTech Connect

    Smith, Jeffrey Claiborne; Keller, Lewis; Lundgren, Steven; Markiewicz, Thomas; /SLAC

    2010-08-26

    The Phase II upgrade to the LHC collimation system calls for complementing the 30 high robust Phase I graphite secondary collimators with 30 high Z Phase II collimators. The Phase II collimators must be robust in various operating conditions and accident scenarios. This paper reports on the final construction and testing of the prototype collimator to be installed in the SPS (Super Proton Synchrotron) at CERN. Bench-top measurements will demonstrate that the device is fully operational and has the mechanical and vacuum characteristics acceptable for installation in the SPS.

  11. The PEP-II Movable Collimators

    SciTech Connect

    DeBarger, S.; Metcalfe, S.; Ng, C.; Porter, T.G.; Seeman, J.; Sullivan, M.; Wienands, U.; /SLAC

    2006-03-13

    Three movable collimators have been manufactured for installation in the PEP-II LER and HER beamlines upstream of BaBar to improve backgrounds in BaBar by a factor of 2. Each collimator has a pair of horizontally opposed, water cooled jaws with RF finger seals all around the edge of the jaws, these seals are the only sliding parts inside the vacuum chamber. Each jaw travels independently through a distance of 16.5 mm (LER) or 21mm (HER) and is supported above the collimator from motorized slideways with position feedback. The larger HER collimator has a titanium sublimation pump incorporated into the underside of the collimator, pumping through RF screens in the bottom of the chamber. Water cooled fixed ramps protect the leading and trailing edges of the jaws.

  12. Prototype Testing for a Copper Rotatable Collimator for the LHC Collimation Upgrade

    SciTech Connect

    Smith, Jeffrey Claiborne; Anzalone, Gene; Doyle, Eric; Keller, Lewis; Lundgren, Steven; Markiewicz, Thomas Walter; Rogers, Reggie; /SLAC

    2009-01-20

    The Phase II upgrade to the LHC collimation system calls for complementing the robust Phase I graphite collimators with high Z Phase II collimators. The design for the collimation upgrade has not been finalized. One option is to use metallic rotatable collimators and testing of this design will be discussed here. The Phase II collimators must be robust in various operating conditions and accident scenarios. A prototype collimator jaw referred to as RC0 has been tested for both mechanical and thermal compliance with the design goals. Thermal expansion bench-top tests are compared to ANSYS simulation results. The prototype has also been tested in vacuum bake-out to confirm compliance with the LHC vacuum spec. CMM equipment has been used to verify the flatness of the jaw surface after heat tests and bake-out.

  13. Geometrical Wake of a Smooth Flat Collimator

    SciTech Connect

    Stupakov, G.V.; /SLAC

    2011-09-09

    A transverse geometrical wake generated by a beam passing through a smooth flat collimator with a gradually varying gap between the upper and lower walls is considered. Based on generalization of the approach recently developed for a smooth circular taper we reduce the electromagnetic problem of the impedance calculation to the solution of two much simpler static problems - a magnetostatic and an electrostatic ones. The solution shows that in the limit of not very large frequencies, the impedance increases with the ratio h/d where h is the width and d is the distance between the collimating jaws. Numerical results are presented for the NLC Post Linac collimator.

  14. CODEX sounding rocket wire grid collimator design

    NASA Astrophysics Data System (ADS)

    Shipley, Ann; Zeiger, Ben; Rogers, Thomas

    2011-05-01

    CODEX is a sounding rocket payload designed to operate in the soft x-ray (0.1-1.0 kV) regime. The instrument has a 3.25 degree square field of view that uses a one meter long wire grid collimator to create a beam that converges to a line in the focal plane. Wire grid collimator performance is directly correlated to the geometric accuracy of actual grid features and their relative locations. Utilizing a strategic combination of manufacturing and assembly techniques, this design is engineered for precision within the confines of a typical rocket budget. Expected resilience of the collimator under flight conditions is predicted by mechanical analysis.

  15. Optical cone beam tomography of Cherenkov-mediated signals for fast 3D dosimetry of x-ray photon beams in water

    SciTech Connect

    Glaser, Adam K. E-mail: Brian.W.Pogue@dartmouth.edu; Andreozzi, Jacqueline M.; Zhang, Rongxiao; Pogue, Brian W. E-mail: Brian.W.Pogue@dartmouth.edu; Gladstone, David J.

    2015-07-15

    Purpose: To test the use of a three-dimensional (3D) optical cone beam computed tomography reconstruction algorithm, for estimation of the imparted 3D dose distribution from megavoltage photon beams in a water tank for quality assurance, by imaging the induced Cherenkov-excited fluorescence (CEF). Methods: An intensified charge-coupled device coupled to a standard nontelecentric camera lens was used to tomographically acquire two-dimensional (2D) projection images of CEF from a complex multileaf collimator (MLC) shaped 6 MV linear accelerator x-ray photon beam operating at a dose rate of 600 MU/min. The resulting projections were used to reconstruct the 3D CEF light distribution, a potential surrogate of imparted dose, using a Feldkamp–Davis–Kress cone beam back reconstruction algorithm. Finally, the reconstructed light distributions were compared to the expected dose values from one-dimensional diode scans, 2D film measurements, and the 3D distribution generated from the clinical Varian ECLIPSE treatment planning system using a gamma index analysis. A Monte Carlo derived correction was applied to the Cherenkov reconstructions to account for beam hardening artifacts. Results: 3D light volumes were successfully reconstructed over a 400 × 400 × 350 mm{sup 3} volume at a resolution of 1 mm. The Cherenkov reconstructions showed agreement with all comparative methods and were also able to recover both inter- and intra-MLC leaf leakage. Based upon a 3%/3 mm criterion, the experimental Cherenkov light measurements showed an 83%–99% pass fraction depending on the chosen threshold dose. Conclusions: The results from this study demonstrate the use of optical cone beam computed tomography using CEF for the profiling of the imparted dose distribution from large area megavoltage photon beams in water.

  16. Optical cone beam tomography of Cherenkov-mediated signals for fast 3D dosimetry of x-ray photon beams in water.

    PubMed

    Glaser, Adam K; Andreozzi, Jacqueline M; Zhang, Rongxiao; Pogue, Brian W; Gladstone, David J

    2015-07-01

    To test the use of a three-dimensional (3D) optical cone beam computed tomography reconstruction algorithm, for estimation of the imparted 3D dose distribution from megavoltage photon beams in a water tank for quality assurance, by imaging the induced Cherenkov-excited fluorescence (CEF). An intensified charge-coupled device coupled to a standard nontelecentric camera lens was used to tomographically acquire two-dimensional (2D) projection images of CEF from a complex multileaf collimator (MLC) shaped 6 MV linear accelerator x-ray photon beam operating at a dose rate of 600 MU/min. The resulting projections were used to reconstruct the 3D CEF light distribution, a potential surrogate of imparted dose, using a Feldkamp-Davis-Kress cone beam back reconstruction algorithm. Finally, the reconstructed light distributions were compared to the expected dose values from one-dimensional diode scans, 2D film measurements, and the 3D distribution generated from the clinical Varian ECLIPSE treatment planning system using a gamma index analysis. A Monte Carlo derived correction was applied to the Cherenkov reconstructions to account for beam hardening artifacts. 3D light volumes were successfully reconstructed over a 400 × 400 × 350 mm(3) volume at a resolution of 1 mm. The Cherenkov reconstructions showed agreement with all comparative methods and were also able to recover both inter- and intra-MLC leaf leakage. Based upon a 3%/3 mm criterion, the experimental Cherenkov light measurements showed an 83%-99% pass fraction depending on the chosen threshold dose. The results from this study demonstrate the use of optical cone beam computed tomography using CEF for the profiling of the imparted dose distribution from large area megavoltage photon beams in water.

  17. Optical cone beam tomography of Cherenkov-mediated signals for fast 3D dosimetry of x-ray photon beams in water

    PubMed Central

    Glaser, Adam K.; Andreozzi, Jacqueline M.; Zhang, Rongxiao; Pogue, Brian W.; Gladstone, David J.

    2015-01-01

    Purpose: To test the use of a three-dimensional (3D) optical cone beam computed tomography reconstruction algorithm, for estimation of the imparted 3D dose distribution from megavoltage photon beams in a water tank for quality assurance, by imaging the induced Cherenkov-excited fluorescence (CEF). Methods: An intensified charge-coupled device coupled to a standard nontelecentric camera lens was used to tomographically acquire two-dimensional (2D) projection images of CEF from a complex multileaf collimator (MLC) shaped 6 MV linear accelerator x-ray photon beam operating at a dose rate of 600 MU/min. The resulting projections were used to reconstruct the 3D CEF light distribution, a potential surrogate of imparted dose, using a Feldkamp–Davis–Kress cone beam back reconstruction algorithm. Finally, the reconstructed light distributions were compared to the expected dose values from one-dimensional diode scans, 2D film measurements, and the 3D distribution generated from the clinical Varian ECLIPSE treatment planning system using a gamma index analysis. A Monte Carlo derived correction was applied to the Cherenkov reconstructions to account for beam hardening artifacts. Results: 3D light volumes were successfully reconstructed over a 400 × 400 × 350 mm3 volume at a resolution of 1 mm. The Cherenkov reconstructions showed agreement with all comparative methods and were also able to recover both inter- and intra-MLC leaf leakage. Based upon a 3%/3 mm criterion, the experimental Cherenkov light measurements showed an 83%–99% pass fraction depending on the chosen threshold dose. Conclusions: The results from this study demonstrate the use of optical cone beam computed tomography using CEF for the profiling of the imparted dose distribution from large area megavoltage photon beams in water. PMID:26133613

  18. Design Studies of a CZT-based Detector Combined with a Pixel-Geometry-Matching Collimator for SPECT Imaging.

    PubMed

    Weng, Fenghua; Bagchi, Srijeeta; Huang, Qiu; Seo, Youngho

    2013-10-01

    Single Photon Emission Computed Tomography (SPECT) suffers limited efficiency due to the need for collimators. Collimator properties largely decide the data statistics and image quality. Various materials and configurations of collimators have been investigated in many years. The main thrust of our study is to evaluate the design of pixel-geometry-matching collimators to investigate their potential performances using Geant4 Monte Carlo simulations. Here, a pixel-geometry-matching collimator is defined as a collimator which is divided into the same number of pixels as the detector's and the center of each pixel in the collimator is a one-to-one correspondence to that in the detector. The detector is made of Cadmium Zinc Telluride (CZT), which is one of the most promising materials for applications to detect hard X-rays and γ-rays due to its ability to obtain good energy resolution and high light output at room temperature. For our current project, we have designed a large-area, CZT-based gamma camera (20.192 cm×20.192 cm) with a small pixel pitch (1.60 mm). The detector is pixelated and hence the intrinsic resolution can be as small as the size of the pixel. Materials of collimator, collimator hole geometry, detection efficiency, and spatial resolution of the CZT detector combined with the pixel-matching collimator were calculated and analyzed under different conditions. From the simulation studies, we found that such a camera using rectangular holes has promising imaging characteristics in terms of spatial resolution, detection efficiency, and energy resolution.

  19. Design Studies of a CZT-based Detector Combined with a Pixel-Geometry-Matching Collimator for SPECT Imaging

    PubMed Central

    Weng, Fenghua; Bagchi, Srijeeta; Huang, Qiu; Seo, Youngho

    2014-01-01

    Single Photon Emission Computed Tomography (SPECT) suffers limited efficiency due to the need for collimators. Collimator properties largely decide the data statistics and image quality. Various materials and configurations of collimators have been investigated in many years. The main thrust of our study is to evaluate the design of pixel-geometry-matching collimators to investigate their potential performances using Geant4 Monte Carlo simulations. Here, a pixel-geometry-matching collimator is defined as a collimator which is divided into the same number of pixels as the detector’s and the center of each pixel in the collimator is a one-to-one correspondence to that in the detector. The detector is made of Cadmium Zinc Telluride (CZT), which is one of the most promising materials for applications to detect hard X-rays and γ-rays due to its ability to obtain good energy resolution and high light output at room temperature. For our current project, we have designed a large-area, CZT-based gamma camera (20.192 cm×20.192 cm) with a small pixel pitch (1.60 mm). The detector is pixelated and hence the intrinsic resolution can be as small as the size of the pixel. Materials of collimator, collimator hole geometry, detection efficiency, and spatial resolution of the CZT detector combined with the pixel-matching collimator were calculated and analyzed under different conditions. From the simulation studies, we found that such a camera using rectangular holes has promising imaging characteristics in terms of spatial resolution, detection efficiency, and energy resolution. PMID:25378898

  20. Internal scatter, the unavoidable major component of the peripheral dose in photon-beam radiotherapy.

    PubMed

    Chofor, Ndimofor; Harder, Dietrich; Willborn, Kay C; Poppe, Björn

    2012-03-21

    In clinical photon beams, the dose outside the geometrical field limits is produced by photons originating from (i) head leakage, (ii) scattering at the beam collimators and the flattening filter (head scatter) and (iii) scattering from the directly irradiated region of the patient or phantom (internal scatter). While the first two components can be modified, e.g. by reinforcement of shielding components or by re-modeling the filter system, internal scatter remains an unavoidable contributor to the peripheral dose. Its relative magnitude compared to the other components, its numerical variation with beam energy, field size and off-axis distance as well as its spectral distribution are evaluated in this study. We applied a detailed Monte Carlo (MC) model of our 6/15 MV Siemens Primus linear accelerator beam head, provided with ideal head leakage shielding conditions (multi-leaf collimator without gaps) to assess the head scatter contribution. Experimental values obtained under real shielding conditions were used to evaluate the head leakage contribution. It was found that the MC-computed internal scatter doses agree with the results of our previous measurements, that internal scatter is the major contributor to the peripheral dose in the near periphery while head leakage prevails in the far periphery, and that the lateral decline of the internal scatter dose can be represented by the sum of two exponentials, with an asymptotic tenth value of 18 to 19 cm. Internal scatter peripheral doses from various elementary beams are additive, so that their sum increases approximately in proportion with field size. The ratio between normalized internal scatter doses at 6 and 15 MV is approximately 2:1. The energy fluence spectra of the internal scatter component at all points of interest outside the field have peaks near 500 keV. The fact that the energy-shifted internal scatter constitutes the major contributor to the dose in the near periphery has a general bearing for

  1. Internal scatter, the unavoidable major component of the peripheral dose in photon-beam radiotherapy

    NASA Astrophysics Data System (ADS)

    Chofor, Ndimofor; Harder, Dietrich; Willborn, Kay C.; Poppe, Björn

    2012-03-01

    In clinical photon beams, the dose outside the geometrical field limits is produced by photons originating from (i) head leakage, (ii) scattering at the beam collimators and the flattening filter (head scatter) and (iii) scattering from the directly irradiated region of the patient or phantom (internal scatter). While the first two components can be modified, e.g. by reinforcement of shielding components or by re-modeling the filter system, internal scatter remains an unavoidable contributor to the peripheral dose. Its relative magnitude compared to the other components, its numerical variation with beam energy, field size and off-axis distance as well as its spectral distribution are evaluated in this study. We applied a detailed Monte Carlo (MC) model of our 6/15 MV Siemens Primus linear accelerator beam head, provided with ideal head leakage shielding conditions (multi-leaf collimator without gaps) to assess the head scatter contribution. Experimental values obtained under real shielding conditions were used to evaluate the head leakage contribution. It was found that the MC-computed internal scatter doses agree with the results of our previous measurements, that internal scatter is the major contributor to the peripheral dose in the near periphery while head leakage prevails in the far periphery, and that the lateral decline of the internal scatter dose can be represented by the sum of two exponentials, with an asymptotic tenth value of 18 to 19 cm. Internal scatter peripheral doses from various elementary beams are additive, so that their sum increases approximately in proportion with field size. The ratio between normalized internal scatter doses at 6 and 15 MV is approximately 2:1. The energy fluence spectra of the internal scatter component at all points of interest outside the field have peaks near 500 keV. The fact that the energy-shifted internal scatter constitutes the major contributor to the dose in the near periphery has a general bearing for

  2. Acoustic logic gates and Boolean operation based on self-collimating acoustic beams

    SciTech Connect

    Zhang, Ting; Xu, Jian-yi; Cheng, Ying Liu, Xiao-jun; Guo, Jian-zhong

    2015-03-16

    The reveal of self-collimation effect in two-dimensional (2D) photonic or acoustic crystals has opened up possibilities for signal manipulation. In this paper, we have proposed acoustic logic gates based on the linear interference of self-collimated beams in 2D sonic crystals (SCs) with line-defects. The line defects on the diagonal of the 2D square SCs are actually functioning as a 3 dB splitter. By adjusting the phase difference between two input signals, the basic Boolean logic functions such as XOR, OR, AND, and NOT are achieved both theoretically and experimentally. Due to the non-diffracting property of self-collimation beams, more complex Boolean logic and algorithms such as NAND, NOR, and XNOR can be realized by cascading the basic logic gates. The achievement of acoustic logic gates and Boolean operation provides a promising approach for acoustic signal computing and manipulations.

  3. Acoustic logic gates and Boolean operation based on self-collimating acoustic beams

    NASA Astrophysics Data System (ADS)

    Zhang, Ting; Cheng, Ying; Guo, Jian-zhong; Xu, Jian-yi; Liu, Xiao-jun

    2015-03-01

    The reveal of self-collimation effect in two-dimensional (2D) photonic or acoustic crystals has opened up possibilities for signal manipulation. In this paper, we have proposed acoustic logic gates based on the linear interference of self-collimated beams in 2D sonic crystals (SCs) with line-defects. The line defects on the diagonal of the 2D square SCs are actually functioning as a 3 dB splitter. By adjusting the phase difference between two input signals, the basic Boolean logic functions such as XOR, OR, AND, and NOT are achieved both theoretically and experimentally. Due to the non-diffracting property of self-collimation beams, more complex Boolean logic and algorithms such as NAND, NOR, and XNOR can be realized by cascading the basic logic gates. The achievement of acoustic logic gates and Boolean operation provides a promising approach for acoustic signal computing and manipulations.

  4. Meteoroid fragments dynamics: Collimation effect

    NASA Astrophysics Data System (ADS)

    Barri, N. G.

    2010-02-01

    There is significant evidence that some fraction of meteoric bodies is destroyed in the atmosphere. The evolution of the fragment cloud depends on a large number of factors, amound them: the meteoroid’s altitude and velocity at the moment of greakup, fragment sizes and properties of a body material. The interaction of shock waves forming in front of the fragments may lead to both an increase and decrease of the midsection area of the fragment cloud (Artem’eva & Shuvalov, 1996; Laurence et al., 2007). In this work, we consider the interaction of the fragments in a supersonic flow. The configuration properties of two spherical bodies of different radii are considered. Via numerical simulations, we calculate the pressure distribution in the flow around the two bodies for different relative positions. We construct the functions of the coefficients of transverse and drag forces from the angle between the central line of the two bodies and the flow direction for different distances between the two fragments. We find the conditions for the collimation effect, i.e., fragment involving into the wake of the leading (usually, the largest) fragment. We systematize the simulation results for drag and transverse forces and infer the basic aerodynamic properties of the meteoroid fragments.

  5. Advanced Collimator Systems for the NLC

    SciTech Connect

    Frisch, Josef C

    2000-08-23

    The Next Linear Collider accelerator will include a large (kilometer scale) and complex collimation system. Its size and complexity could be reduced if the collimator jaws were made immune to damage from the electron beam. The authors describe two collimation systems currently under development. Construction of a prototype system, which uses wheels that can be moved to a new position after damage, is underway. The second system, currently in the R+D phase, will use rotors that are continuously reformed from a bath of liquid metal as the collimation surface. This second system should allow operation at beam intensities that damage the jaws on every pulse. They describe results of tests on both systems.

  6. Advanced Collimator Prototype Results for the NLC

    SciTech Connect

    Frisch, Josef C

    2000-06-05

    The Next Linear Collider accelerator will include a large (kilometer scale) and complex collimation system. The size and complexity of this system could be reduced if the collimator jaws could be made immune to damage from the electron beam. The authors describe two collimation systems currently under development. Construction of a prototype system which uses wheels that can be moved to a new position after damage is underway. The second system, currently in the R+D phase, uses rotors which are continuously reformed from a bath of liquid metal as the collimation surface. This second system allows operation at beam intensities which damage the jaws on every pulse. They describe results of tests on both systems.

  7. Variable aperture collimator for high energy radiation

    DOEpatents

    Hill, Ronald A.

    1984-05-22

    An apparatus is disclosed providing a variable aperture energy beam collimator. A plurality of beam opaque blocks are in sliding interface edge contact to form a variable aperture. The blocks may be offset at the apex angle to provide a non-equilateral aperture. A plurality of collimator block assemblies may be employed for providing a channel defining a collimated beam. Adjacent assemblies are inverted front-to-back with respect to one another for preventing noncollimated energy from emerging from the apparatus. An adjustment mechanism comprises a cable attached to at least one block and a hand wheel mechanism for operating the cable. The blocks are supported by guide rods engaging slide brackets on the blocks. The guide rods are pivotally connected at each end to intermediate actuators supported on rotatable shafts to change the shape of the aperture. A divergent collimated beam may be obtained by adjusting the apertures of adjacent stages to be unequal.

  8. Quasi-random array imaging collimator

    DOEpatents

    Fenimore, E.E.

    1980-08-20

    A hexagonally shaped quasi-random no-two-holes-touching imaging collimator. The quasi-random array imaging collimator eliminates contamination from small angle off-axis rays by using a no-two-holes-touching pattern which simultaneously provides for a self-supporting array increasing throughput by elimination of a substrate. The present invention also provides maximum throughput using hexagonally shaped holes in a hexagonal lattice pattern for diffraction limited applications. Mosaicking is also disclosed for reducing fabrication effort.

  9. Crystal collimator systems for high energy frontier

    NASA Astrophysics Data System (ADS)

    Sytov, A. I.; Tikhomirov, V. V.; Lobko, A. S.

    2017-07-01

    Crystalline collimators can potentially considerably improve the cleaning performance of the presently used collimator systems using amorphous collimators. A crystal-based collimation scheme which relies on the channeling particle deflection in bent crystals has been proposed and extensively studied both theoretically and experimentally. However, since the efficiency of particle capture into the channeling regime does not exceed ninety percent, this collimation scheme partly suffers from the same leakage problems as the schemes using amorphous collimators. To improve further the cleaning efficiency of the crystal-based collimation system to meet the requirements of the FCC, we suggest here a double crystal-based collimation scheme, to which the second crystal is introduced to enhance the deflection of the particles escaping the capture to the channeling regime in its first crystal. The application of the effect of multiple volume reflection in one bent crystal and of the same in a sequence of crystals is simulated and compared for different crystal numbers and materials at the energy of 50 TeV. To enhance also the efficiency of use of the first crystal of the suggested double crystal-based scheme, we propose: the method of increase of the probability of particle capture into the channeling regime at the first crystal passage by means of fabrication of a crystal cut and the method of the amplification of nonchanneled particle deflection through the multiple volume reflection in one bent crystal, accompanying the particle channeling by a skew plane. We simulate both of these methods for the 50 TeV FCC energy.

  10. Review of freeform TIR collimator design methods

    NASA Astrophysics Data System (ADS)

    Talpur, Taimoor; Herkommer, Alois

    2016-04-01

    Total internal reflection (TIR) collimators are essential illumination components providing high efficiency and uniformity in a compact geometry. Various illumination design methods have been developed for designing such collimators, including tailoring methods, design via optimization, the mapping and feedback method, and the simultaneous multiple surface (SMS) method. This paper provides an overview of the different methods and compares the performance of the methods along with their advantages and their limitations.

  11. Solid Collection Efforts: Ta Collimator Evaluation

    SciTech Connect

    Gostic, J M

    2011-11-21

    Ta collimator sets that were part of the gated x-ray detector diagnostic (GXD) at NIF were analyzed for debris distribution and damage in 2011. These disks (ranging in thickness from 250 to 750 {mu}m) were fielded approximately 10 cm from target chamber center (TCC) on various symcap, THD and re-emit shots. The nose cone holder and forward Ta collimator (facing target chamber center, TCC) from all shots show evidence of surface melt. Non-destructive analysis techniques such as optical microscopy, surface profilometry, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray fluorescence (XRF) were used to determine debris composition and degree of deformation associated with each Ta disk. Molten debris from the stainless steel nose cone contaminated the surface of the collimators along with other debris associated with the target assembly (Al, Si, Cu, Au and In). Surface elemental analysis of the forward collimator Ta disks indicates that Au hohlraum debris is less concentrated on these samples versus those fielded 50 cm from TCC in the wedge range filter (WRF) assembly. It is possible that the Au is distributed below or within the stainless steel melt layer covering the disk, as most of the foreign debris is captured in the melted coating. The other disks (fielded directly behind the forward collimator in a sandwiched configuration) have visible forms of deformation and warping. The degree of warping increases as the shock wave penetrates the assembly with the most damage sustained on the back collimator. In terms of developing a solid collection capability, the collimator analyses suggests that close proximity may cause more interference with capsule debris collection and more damage to the surface of the collector diagnostic. The analyses of the Ta collimators were presented to the Target and Laser Interaction Sphere (TaLIS) group; a representative presentation is attached to this document.

  12. Comparison of Carbon and Hi-Z Primary Collimators for the LHC Phase II Collimation System

    SciTech Connect

    Keller, Lewis; Markiewicz, Thomas; Smith, Jeffrey; Assmann, Ralph; Bracco, Chiara; Weiler, Thomas; /Karlsruhe, Inst. Technol.

    2011-10-31

    A current issue with the LHC collimation system is single-diffractive, off-energy protons from the primary collimators that pass completely through the secondary collimation system and are absorbed immediately downbeam in the cold magnets of the dispersion suppressor section. Simulations suggest that the high impact rate could result in quenching of these magnets. We have studied replacing the 60 cm primary graphite collimators, which remove halo mainly by inelastic strong interactions, with 5.25 mm tungsten, which remove halo mainly by multiple coulomb scattering and thereby reduce the rate of single-diffractive interactions that cause losses in the dispersion suppressor.

  13. Design and performance of a small-animal imaging system using synthetic collimation

    NASA Astrophysics Data System (ADS)

    Havelin, R. J.; Miller, B. W.; Barrett, H. H.; Furenlid, L. R.; Murphy, J. M.; Dwyer, R. M.; Foley, M. J.

    2013-05-01

    This work outlines the design and construction of a single-photon emission computed tomography imaging system based on the concept of synthetic collimation. A focused multi-pinhole collimator is constructed using rapid-prototyping and casting techniques. The collimator projects the centre of the field of view (FOV) through 46 pinholes when the detector is adjacent to the collimator, with the number reducing towards the edge of the FOV. The detector is then moved further from the collimator to increase the magnification of the system. The object distance remains constant, and each new detector distance is a new system configuration. The level of overlap of the pinhole projections increases as the system magnification increases, but the number of projections subtended by the detector is reduced. There is no rotation in the system; a single tomographic angle is used in each system configuration. Image reconstruction is performed using maximum-likelihood expectation-maximization and an experimentally measured system matrix. The system matrix is measured for each configuration on a coarse grid, using a point source. The pinholes are individually identified and tracked, and a Gaussian fit is made to each projection. The coefficients of these fits are used to interpolate the system matrix. The system is validated experimentally with a hot-rod phantom. The Fourier crosstalk matrix is also measured to provide an estimate of the average spatial resolution along each axis over the entire FOV. The 3D synthetic-collimator image is formed by estimating the activity distribution within the FOV and summing the activities in the voxels along the axis perpendicular to the collimator face.

  14. Comparison of inhomogeneity correction algorithms in small photon fields.

    PubMed

    Jones, Andrew O; Das, Indra J

    2005-03-01

    Algorithms such as convolution superposition, Batho, and equivalent pathlength which were originally developed and validated for conventional treatments under conditions of electronic equilibrium using relatively large fields greater than 5 x 5 cm2 are routinely employed for inhomogeneity corrections. Modern day treatments using intensity modulated radiation therapy employ small beamlets characterized by the resolution of the multileaf collimator. These beamlets, in general, do not provide electronic equilibrium even in a homogeneous medium, and these effects are exaggerated in media with inhomogenieties. Monte Carlo simulations are becoming a tool of choice in understanding the dosimetry of small photon fields as they encounter low density media. In this study, depth dose data from the Monte Carlo simulations are compared to the results of the convolution superposition, Batho, and equivalent pathlength algorithms. The central axis dose within the low-density inhomogeneity as calculated by Monte Carlo simulation and convolution superposition decreases for small field sizes whereas it increases using the Batho and equivalent pathlength algorithms. The dose perturbation factor (DPF) is defined as the ratio of dose to a point within the inhomogeneity to the same point in a homogeneous phantom. The dose correction factor is defined as the ratio of dose calculated by an algorithm at a point to the Monte Carlo derived dose at the same point, respectively. DPF is noted to be significant for small fields and low density for all algorithms. Comparisons of the algorithms with Monte Carlo simulations is reflected in the DCF, which is close to 1.0 for the convolution-superposition algorithm. The Batho and equivalent pathlength algorithms differ significantly from Monte Carlo simulation for most field sizes and densities. Convolution superposition shows better agreement with Monte Carlo data versus the Batho or equivalent pathlength corrections. As the field size increases the

  15. Wake fields in SLAC Linac Collimators

    SciTech Connect

    Novokhatski, Alexander; Decker, F. -J.; Smith, H.; Sullivan, M.

    2014-12-02

    When a beam travels near collimator jaws, it gets an energy loss and a transverse kick due to the backreaction of the beam field diffracted from the jaws. The effect becomes very important for an intense short bunch when a tight collimation of the background beam halo is required. In the Linac Coherent Light Source at SLAC a collimation system is used to protect the undulators from radiation due to particles in the beam halo. The halo is most likely formed from gun dark current or dark current in some of the accelerating sections. However, collimators are also responsible for the generation of wake fields. The wake field effect from the collimators not only brings an additional energy jitter and change in the trajectory of the beam, but it also rotates the beam on the phase plane, which consequently leads to a degradation of the performance of the Free Electron Laser at the Linac Coherent Light Source. In this paper, we describe a model of the wake field radiation in the SLAC linac collimators. We use the results of a numerical simulation to illustrate the model. Based on the model, we derive simple formulas for the bunch energy loss and the average kick. In addition, we also present results from experimental measurements that confirm our model.

  16. Collimator selection and I-124 contamination determination for I-123 imaging studies

    SciTech Connect

    Madsen, M.T.; Patel, J.; Thakur, M.L.; Park, C.H.

    1984-01-01

    The use of I-123 as an imaging agent is increasing. Because of the high energy photons from contaminant I-124 compromise the quality of I-123 images, it is important to determine the amount of I-124 and to carefully evaluate the imaging system. The authors have developed an automatic method which yields an accurate, precise and rapid means of assessing I-124 contamination. The fraction of I-124 is determined by comparing counts in the 604 keV peak to the counts in the I-123 159 keV peak from spectra acquired on a computer based multichannel analyzer linked to a Ge(Li) detector. The acquisition, peak selection and calculation are performed under program control. The optimal collimation was determined from computer acquired line source images of I-123 positioned above the gamma camera in the presence of scattering material. The system resolution was evaluated for a low energy general purpose collimator (hole size: 2.5mm, septa: 0.3mm, length: 41mm) and a medium energy collimator (2mm, 0.8mm, 25mm). The general purpose collimator has the best performance when I-124 levels are low (less than 3%) or when high contrast objects are imaged with good statistics. The medium energy collimator yields the best results when contamination exceeds 3% and the objects lack high frequency components or when the image is noisy.

  17. Evaluation of the geometric, scatter, and septal penetration components in fan-beam collimators using Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    Cot, A.; Sempau, J.; Pareto, D.; Bullich, S.; Pavia, J.; Calvino, F.; Ros, D.

    2002-02-01

    The quantitative analysis of single-photon emission computed tomography data requires an accurate determination of the collimator point spread function (PSF). The aim of this paper is to characterize fan-beam collimators' PSFs by using Monte Carlo simulation. Given a particular collimator configuration, a detailed hexagonal hole array was generated and information describing its geometry was stored in a lookup table. When a photon crossed the collimator front plane, a hole array was placed around its impact position using this table. Each photon was then tracked up to the detector surface by using the Monte Carlo code PENELOPE and its associated geometry handling routines. Particle counters were defined that score the probability of impact on the detector as a function of the final photon position. Four sets of counters were employed so as to differentiate contributions to the geometric, septal penetration, coherent (Rayleigh), and incoherent (Compton) scatter components. Furthermore, sensitivity quantification was calculated for different source locations. Monte Carlo results were compared with sensitivity values obtained experimentally, and good agreement was found. Our results show that for /sup 99m/Tc imaging, the geometric component represents about 95% of the fan-beam PSF, whereas the incoherent scattering component is negligible.

  18. Upgrade scenario for the RHIC collimation system

    SciTech Connect

    Robert-Demolaize, G.; Drees, A.

    2012-01-19

    The RHIC collimation system is used to reduce background levels in both STAR and PHENIX detectors. With a push for higher luminosity in the near future, it becomes critical to check if and how the level of performance of the collimators can be improved. The following reviews a proposal for additional collimators placed further downstream of the current system and designed to intercept the tertiary halo coming out of the IR8 insertion before it can reach the triplet quadrupoles in either STAR or PHENIX. Simulations have been peformed to quantify the efficiency of additional collimator jaws in RHIC. Each figure presented in this article clearly shows that the additional mask collimators provide the expected reduction in losses around the machine, and especially to the incoming triplet to the STAR experiment (IP6), for the Yellow beam as much as for the Blue beam. Looking at compiled statistics for all three working point cases studied, proton losses around the machine are reduced by roughly one order of magnitude: at most a factor 30 for magnet losses, and at most a factor 40 for losses in spaces between magnets.

  19. A SPECT imager with synthetic collimation

    NASA Astrophysics Data System (ADS)

    Havelin, Ronan J.; Miller, Brian W.; Barrett, Harrison H.; Furenlid, Lars R.; Murphy, J. M.; Foley, Mark J.

    2013-09-01

    This work outlines the development of a multi-pinhole SPECT system designed to produce a synthetic-collimator image of a small field of view. The focused multi-pinhole collimator was constructed using rapid-prototyping and casting techniques. The collimator projects the field of view through forty-six pinholes when the detector is adjacent to the collimator. The detector is then moved further from the collimator to increase the magnification of the system. The amount of pinhole-projection overlap increases with the system magnification. There is no rotation in the system; a single tomographic angle is used in each system configuration. The maximum-likelihood expectation-maximization (MLEM) algorithm is implemented on graphics processing units to reconstruct the object in the field of view. Iterative reconstruction algorithms, such as MLEM, require an accurate model of the system response. For each system magnification, a sparsely-sampled system response is measured by translating a point source through a grid encompassing the field of view. The pinhole projections are individually identified and associated with their respective apertures. A 2D elliptical Gaussian model is applied to the pinhole projections on the detector. These coefficients are associated with the object-space location of the point source, and a finely-sampled system matrix is interpolated. Simulations with a hot-rod phantom demonstrate the efficacy of combining low-resolution non-multiplexed data with high-resolution multiplexed data to produce high-resolution reconstructions.

  20. Grazing function g and collimation angular acceptance

    SciTech Connect

    Peggs, S.G.; Previtali, V.

    2009-11-02

    The grazing function g is introduced - a synchrobetatron optical quantity that is analogous (and closely connected) to the Twiss and dispersion functions {beta}, {alpha}, {eta}, and {eta}'. It parametrizes the rate of change of total angle with respect to synchrotron amplitude for grazing particles, which just touch the surface of an aperture when their synchrotron and betatron oscillations are simultaneously (in time) at their extreme displacements. The grazing function can be important at collimators with limited acceptance angles. For example, it is important in both modes of crystal collimation operation - in channeling and in volume reflection. The grazing function is independent of the collimator type - crystal or amorphous - but can depend strongly on its azimuthal location. The rigorous synchrobetatron condition g = 0 is solved, by invoking the close connection between the grazing function and the slope of the normalized dispersion. Propagation of the grazing function is described, through drifts, dipoles, and quadrupoles. Analytic expressions are developed for g in perfectly matched periodic FODO cells, and in the presence of {beta} or {eta} error waves. These analytic approximations are shown to be, in general, in good agreement with realistic numerical examples. The grazing function is shown to scale linearly with FODO cell bend angle, but to be independent of FODO cell length. The ideal value is g = 0 at the collimator, but finite nonzero values are acceptable. Practically achievable grazing functions are described and evaluated, for both amorphous and crystal primary collimators, at RHIC, the SPS (UA9), the Tevatron (T-980), and the LHC.

  1. Performance of a novel collimator for high-sensitivity brain SPECT

    SciTech Connect

    El Fakhri, Georges; Ouyang Jinsong; Zimmerman, Robert E.; Fischman, Alan J.; Kijewski, Marie Foley

    2006-01-15

    We assessed improvements in performance in detection and estimation tasks due to a novel brain single photon computed tomography collimator. Data were acquired on the CeraSPECT{sup TM} scanner using both new and standard collimators. The new variable focusing collimator SensOgrade{sup TM} samples the projections unequally, with central regions more heavily represented, to compensate for attenuation of counts from central brain structures. Furthermore, it utilizes more of the cylindrical crystal surface. Two phantom studies were performed. The first phantom was a 21-cm-diameter cylindrical background containing nine spheres ranging from 0.5 to 5 cm{sup 3} in volume. {sup 99m}Tc sphere to background activity ratio was 10:1. Twenty-nine 10-min datasets were acquired with each collimator. The second phantom was the Radiology Support Devices (Long Beach, CA) striatal phantom with striatal-background ratios of 10:1 on the left and 5:1 on the right. Twenty-nine 4-min datasets were acquired with each collimator. Perfusion imaging using {sup 99m}Tc-HMPAO was also performed in three healthy volunteers using both collimators under identical simulations. Projections were reconstructed by filtered backprojection with an unwindowed ramp filter. The nonprewhitening matched filter signal-to-noise ratio (NPW-SNR) was computed as a surrogate for human performance in detecting spherical lesions. Sphere activity concentration, radius, and location coordinates were simultaneously estimated by fitting images to an assumed model using an iterative nonlinear algorithm. Resolution recovery was implicit in the estimation procedure, as the point spread function was incorporated into the model. NPW-SNR for sphere detection was 1.5 to 2 times greater with the new collimator; for the striatal phantom the improvement in SNR was 54%. The SNR for estimating sphere activity concentration improved by 46 to 89 % for spheres located more than 5 cm from the phantom center. Images acquired with the

  2. Performance of a novel collimator for high-sensitivity brain SPECT.

    PubMed

    El Fakhri, Georges; Ouyang, Jinsong; Zimmerman, Robert E; Fischman, Alan J; Kijewski, Marie Foley

    2006-01-01

    We assessed improvements in performance in detection and estimation tasks due to a novel brain single photon computed tomography collimator. Data were acquired on the CeraSPECT scanner using both new and standard collimators. The new variable focusing collimator SensOgrade samples the projections unequally, with central regions more heavily represented, to compensate for attenuation of counts from central brain structures. Furthermore, it utilizes more of the cylindrical crystal surface. Two phantom studies were performed. The first phantom was a 21-cm-diameter cylindrical background containing nine spheres ranging from 0.5 to 5 cm3 in volume. 99mTc sphere to background activity ratio was 10:1. Twenty-nine 10-min datasets were acquired with each collimator. The second phantom was the Radiology Support Devices (Long Beach, CA) striatal phantom with striatal-background ratios of 10:1 on the left and 5:1 on the right. Twenty-nine 4-min datasets were acquired with each collimator. Perfusion imaging using 99mTc-HMPAO was also performed in three healthy volunteers using both collimators under identical simulations. Projections were reconstructed by filtered backprojection with an unwindowed ramp filter. The nonprewhitening matched filter signal-to-noise ratio (NPW-SNR) was computed as a surrogate for human performance in detecting spherical lesions. Sphere activity concentration, radius, and location coordinates were simultaneously estimated by fitting images to an assumed model using an iterative nonlinear algorithm. Resolution recovery was implicit in the estimation procedure, as the point spread function was incorporated into the model. NPW-SNR for sphere detection was 1.5 to 2 times greater with the new collimator; for the striatal phantom the improvement in SNR was 54%. The SNR for estimating sphere activity concentration improved by 46 to 89% for spheres located more than 5 cm from the phantom center. Images acquired with the standard collimator were too noisy in

  3. Collimation Studies with Hollow Electron Beams

    SciTech Connect

    Stancari, G.; Annala, G.; Johnson, T.R.; Saewert, G.W.; Shiltsev, V.; Still, D.A.; Valishev, A.; /Fermilab

    2011-08-01

    Recent experimental studies at the Fermilab Tevatron collider have shown that magnetically confined hollow electron beams can act as a new kind of collimator for high-intensity beams in storage rings. In a hollow electron beam collimator, electrons enclose the circulating beam. Their electric charge kicks halo particles transversely. If their distribution is axially symmetric, the beam core is unaffected. This device is complementary to conventional two-stage collimation systems: the electron beam can be placed arbitrarily close to the circulating beam; and particle removal is smooth, so that the device is a diffusion enhancer rather than a hard aperture limitation. The concept was tested in the Tevatron collider using a hollow electron gun installed in one of the existing electron lenses. We describe some of the technical aspects of hollow-beam scraping and the results of recent measurements.

  4. Channeling collimation studies at the Fermilab Tevatron

    SciTech Connect

    Carrigan, Richard A.; Drozhdin, Alexandr I.; Fliller, Raymond P., III; Mokhov, Nikolai V.; Shiltsev, Vladimir D.; Still, Dean A.; /Fermilab

    2006-08-01

    Bent crystal channeling has promising advantages for accelerator beam collimation at high energy hadron facilities such as the LHC. This significance has been amplified by several surprising developments including multi-pass channeling and the observation of enhanced deflections over the entire arc of a bent crystal. The second effect has been observed both at RHIC and recently at the Tevatron. Results are reported showing channeling collimation of the circulating proton beam halo at the Tevatron. Parenthetically, this study is the highest energy proton channeling experiment ever carried out. The study is continuing.

  5. Cardiac imaging using a four-segment slant-hole collimator

    SciTech Connect

    Bal, G.; DiBella, E.V.R.; Gullberg, G.T.; Zeng, G.L.

    2005-09-27

    The main objective of this paper is to evaluate four segmentslant-hole (FSSH) SPECT for cardiac imaging. FSSH is a slant-holecollimator that is divided into four segments and arranged such that thephotons from the volume of interest (VOI)are projected four times forevery location of the detector. These multiple projections help toimprove the sensitivity of the photons from the VOI by a factor4(cos(sigma))3, where is the slant angle of the collimator. Anotheradvantage of FSSH SPECT is a reduction in the total scan time, since agantry rotation of pi-2sigma is sufficient to satisfy Orlov's condition.That means, for a slant angle of 30 degrees, a gantry rotation of 120degrees is sufficient to satisfy Orlov's condition and obtain a completedataset. In this paper, we evaluate and compare the reconstructed imagesobtained using an FSSH collimator, for a gantry rotation of 180 degreesand 120 degrees, with those obtained from a parallel-hole (PH) SPECTsystem using a 180 degree acquisition. The reconstructed images from thethree imaging geometries were compared in terms of average image noise,contrast, and percentage error, for seven different clinical count levelsand for multiple noise realizations in each case. The increase insensitivity of the FSSH system was found to translate into a proportionaldecrease in statistical noise for voxels in the VOI of the reconstructedimages. Finally, a physical phantom study was performed using a prototypeFSSH collimator. Our findings show that FSSH collimators have thepotential of being the collimator of choice for cardiac SPECT imaging.Though we explore the potential of FSSH collimators for cardiac imagingin this paper, the concept can be extended for imaging other organs suchas the breasts, kidney, and brain.

  6. Collimating Montel mirror as part of a multi-crystal analyzer system for resonant inelastic x-ray scattering

    SciTech Connect

    Kim, Jungho; Shi, Xianbo; Casa, Diego; Qian, Jun; Huang, XianRong; Gog, Thomas

    2016-07-01

    Advances in resonant inelastic x-ray scattering (RIXS) have come in lockstep with improvements in energy resolution. Currently, the best energy resolution at the Ir-L3 edge stands at ~25 meV, which is achieved using a diced Si spherical analyzer. An angular dispersion analyzer system using multiple flat crystals provides a promising way to achieve higher energy resolution, namely 10 meV or better, thereby overcoming the intrinsic energy resolution limit of diced spherical crystal analyzers. One essential component for a practical use of such multi-crystal systems is the xray collimation optics. In this work, a laterally graded, parabolic collimation Montel mirror was designed with larger than 10 mrad acceptance, collimating the x-ray beam to smaller than 100 μrad divergence at the Ir-L3 absorption energy. The x-ray collimation performance was investigated at beamline 27-ID of the Advanced Photon Source, using incident photons from a Diamond (111) monochromator illuminating a controlled 40 mrad divergence scattering source of 5 μm diameter. A flat Si (111) crystal served as the analyzer. It is found from experimental data and ray-tracing simulations, combined with metrology results, that the manufactured Montel mirror satisfies the required specifications of angular acceptance and collimated x-ray divergence for a high resolution RIXS spectrometer at the Ir-L3 edge.

  7. Monte Carlo simulation of a collimation system for low-energy beamline of ELI-NP Gamma Beam System

    NASA Astrophysics Data System (ADS)

    Cardarelli, P.; Gambaccini, M.; Marziani, M.; Bagli, E.; Petrillo, V.; Bacci, A.; Curatolo, C.; Drebot, I.; Vaccarezza, C.

    2015-07-01

    ELI-nuclear physics (NP) Gamma Beam System (GBS) is an intense and monochromatic gamma beam source based on inverse Compton interaction, currently being built in Bucharest, Romania. The gamma beam produced, with energy ranging from 0.2 to 20 MeV, energy bandwidth 0.5% and flux of about 108photons/s, will be devoted to investigate a broad range of applications such as nuclear physics, astrophysics, material science and life sciences. The radiation produced by an inverse Compton interaction is not intrinsically monochromatic. In fact, the energy of the photons produced is related to the emission angle, therefore the energy bandwidth can be modified adjusting the collimation of the gamma beam. In order to define the optimal layout and evaluate the performance of a collimation system for the ELI-NP-GBS low-energy beamline (0.2-3.5 MeV), a detailed Monte Carlo simulation activity has been carried out. The simulation, using Geant4 and MCNPX codes, included the transport of the gamma beam from the interaction point to the experimental area passing through vacuum pipes, vacuum chambers, collimation system and relative shielding. The effectiveness of the collimation system, in obtaining the required energy distribution and avoiding the contamination due to secondary radiation production, was evaluated. Also, the background radiation generated by collimation and the shielding layout have been studied.

  8. Measuring Collimator Infrared (IR) Spectral Transmission

    DTIC Science & Technology

    2016-05-01

    looking down a collimator and a standalone large surface blackbody. They were both focused and had the same total atmospheric path length between...3 3. Setup of SR5000 With Atmospheric Paths Equal at 4 m...standalone large surface blackbody. The total atmospheric path length between source and sensor were the same, yet discrepancies were noticed

  9. Multiple wavelength light collimator and monitor

    NASA Technical Reports Server (NTRS)

    Gore, Warren J. (Inventor)

    2011-01-01

    An optical system for receiving and collimating light and for transporting and processing light received in each of N wavelength ranges, including near-ultraviolet, visible, near-infrared and mid-infrared wavelengths, to determine a fraction of light received, and associated dark current, in each wavelength range in each of a sequence of time intervals.

  10. BPM Design and Impedance Considerations for a Rotatable Collimator for the LHC Collimation Upgrade

    SciTech Connect

    Smith, Jeffrey Claiborne; Keller, Lewis; Lundgren, Steven; Markiewicz, Thomas; Young, Andrew; /SLAC

    2010-08-26

    The Phase II upgrade to the LHC collimation system calls for complementing the 30 high robust Phase I graphite secondary collimators with 30 high Z Phase II collimators. This paper reports on BPM and impedance considerations and measurements of the integrated BPMs in the prototype rotatable collimator to be installed in the Super Proton Synchrotron (SPS) at CERN. The BPMs are necessary to align the jaws with the beam. Without careful design the beam impedance can result in unacceptable heating of the chamber wall or beam instabilities. The impedance measurements involve utilizing both a single displaced wire and two wires excited in opposite phase to disentangle the driving and detuning transverse impedances. Trapped mode resonances and longitudinal impedance are to also be measured and compared with simulations. These measurements, when completed, will demonstrate the device is fully operational and has the impedance characteristics and BPM performance acceptable for installation in the SPS.

  11. A collimation system for ELI-NP Gamma Beam System - design and simulation of performance

    NASA Astrophysics Data System (ADS)

    Paternò, G.; Cardarelli, P.; Marziani, M.; Bagli, E.; Evangelisti, F.; Andreotti, M.; Gambaccini, M.; Petrillo, V.; Drebot, I.; Bacci, A.; Vaccarezza, C.; Palumbo, L.; Variola, A.

    2017-07-01

    The purpose of this study was to evaluate the performance and refine the design of the collimation system for the gamma radiation source (GBS) currently being realised at ELI-NP facility. The gamma beam, produced by inverse Compton scattering, will provide a tunable average energy in the range between 0.2 and 20 MeV, an energy bandwidth 0.5% and a flux of about 108 photons/s. As a result of the inverse Compton interaction, the energy of the emitted radiation is related to the emission angle, it is maximum in the backscattering direction and decreases as the angle increase [1,2]. Therefore, the required energy bandwidth can be obtained only by developing a specific collimation system of the gamma beam, i.e. filtering out the radiation emitted at larger angles. The angular acceptance of the collimation for ELI-NP-GBS must be continuously adjustable in a range from about 700 to 60 μrad, to obtain the required parameters in the entire energy range. The solution identified is a stack of adjustable slits, arranged with a relative rotation around the beam axis to obtain an hole with an approximately circular shape. In this contribution, the final collimation design and its performance evaluated by carrying out a series of detailed Geant4 simulations both of the high-energy and the low-energy beamline are presented.

  12. Technical Report: Reference photon dosimetry data for Varian accelerators based on IROC-Houston site visit data

    PubMed Central

    Kerns, James R.; Followill, David S.; Lowenstein, Jessica; Molineu, Andrea; Alvarez, Paola; Taylor, Paige A.; Stingo, Francesco C.; Kry, Stephen F.

    2016-01-01

    Purpose: Accurate data regarding linear accelerator (Linac) radiation characteristics are important for treatment planning system modeling as well as regular quality assurance of the machine. The Imaging and Radiation Oncology Core-Houston (IROC-H) has measured the dosimetric characteristics of numerous machines through their on-site dosimetry review protocols. Photon data are presented and can be used as a secondary check of acquired values, as a means to verify commissioning a new machine, or in preparation for an IROC-H site visit. Methods: Photon data from IROC-H on-site reviews from 2000 to 2014 were compiled and analyzed. Specifically, data from approximately 500 Varian machines were analyzed. Each dataset consisted of point measurements of several dosimetric parameters at various locations in a water phantom to assess the percentage depth dose, jaw output factors, multileaf collimator small field output factors, off-axis factors, and wedge factors. The data were analyzed by energy and parameter, with similarly performing machine models being assimilated into classes. Common statistical metrics are presented for each machine class. Measurement data were compared against other reference data where applicable. Results: Distributions of the parameter data were shown to be robust and derive from a student’s t distribution. Based on statistical and clinical criteria, all machine models were able to be classified into two or three classes for each energy, except for 6 MV for which there were eight classes. Quantitative analysis of the measurements for 6, 10, 15, and 18 MV photon beams is presented for each parameter; supplementary material has also been made available which contains further statistical information. Conclusions: IROC-H has collected numerous data on Varian Linacs and the results of photon measurements from the past 15 years are presented. The data can be used as a comparison check of a physicist’s acquired values. Acquired values that are well

  13. Technical Report: Reference photon dosimetry data for Varian accelerators based on IROC-Houston site visit data.

    PubMed

    Kerns, James R; Followill, David S; Lowenstein, Jessica; Molineu, Andrea; Alvarez, Paola; Taylor, Paige A; Stingo, Francesco C; Kry, Stephen F

    2016-05-01

    Accurate data regarding linear accelerator (Linac) radiation characteristics are important for treatment planning system modeling as well as regular quality assurance of the machine. The Imaging and Radiation Oncology Core-Houston (IROC-H) has measured the dosimetric characteristics of numerous machines through their on-site dosimetry review protocols. Photon data are presented and can be used as a secondary check of acquired values, as a means to verify commissioning a new machine, or in preparation for an IROC-H site visit. Photon data from IROC-H on-site reviews from 2000 to 2014 were compiled and analyzed. Specifically, data from approximately 500 Varian machines were analyzed. Each dataset consisted of point measurements of several dosimetric parameters at various locations in a water phantom to assess the percentage depth dose, jaw output factors, multileaf collimator small field output factors, off-axis factors, and wedge factors. The data were analyzed by energy and parameter, with similarly performing machine models being assimilated into classes. Common statistical metrics are presented for each machine class. Measurement data were compared against other reference data where applicable. Distributions of the parameter data were shown to be robust and derive from a student's t distribution. Based on statistical and clinical criteria, all machine models were able to be classified into two or three classes for each energy, except for 6 MV for which there were eight classes. Quantitative analysis of the measurements for 6, 10, 15, and 18 MV photon beams is presented for each parameter; supplementary material has also been made available which contains further statistical information. IROC-H has collected numerous data on Varian Linacs and the results of photon measurements from the past 15 years are presented. The data can be used as a comparison check of a physicist's acquired values. Acquired values that are well outside the expected distribution should be

  14. Technical Report: Reference photon dosimetry data for Varian accelerators based on IROC-Houston site visit data

    SciTech Connect

    Kerns, James R.; Followill, David S.; Kry, Stephen F.; Lowenstein, Jessica; Molineu, Andrea; Alvarez, Paola; Taylor, Paige A.; Stingo, Francesco C.

    2016-05-15

    Purpose: Accurate data regarding linear accelerator (Linac) radiation characteristics are important for treatment planning system modeling as well as regular quality assurance of the machine. The Imaging and Radiation Oncology Core-Houston (IROC-H) has measured the dosimetric characteristics of numerous machines through their on-site dosimetry review protocols. Photon data are presented and can be used as a secondary check of acquired values, as a means to verify commissioning a new machine, or in preparation for an IROC-H site visit. Methods: Photon data from IROC-H on-site reviews from 2000 to 2014 were compiled and analyzed. Specifically, data from approximately 500 Varian machines were analyzed. Each dataset consisted of point measurements of several dosimetric parameters at various locations in a water phantom to assess the percentage depth dose, jaw output factors, multileaf collimator small field output factors, off-axis factors, and wedge factors. The data were analyzed by energy and parameter, with similarly performing machine models being assimilated into classes. Common statistical metrics are presented for each machine class. Measurement data were compared against other reference data where applicable. Results: Distributions of the parameter data were shown to be robust and derive from a student’s t distribution. Based on statistical and clinical criteria, all machine models were able to be classified into two or three classes for each energy, except for 6 MV for which there were eight classes. Quantitative analysis of the measurements for 6, 10, 15, and 18 MV photon beams is presented for each parameter; supplementary material has also been made available which contains further statistical information. Conclusions: IROC-H has collected numerous data on Varian Linacs and the results of photon measurements from the past 15 years are presented. The data can be used as a comparison check of a physicist’s acquired values. Acquired values that are well

  15. Can Collimated Extraterrestrial Signals be Intercepted?

    NASA Astrophysics Data System (ADS)

    Forgan, D. H.

    2014-06-01

    The Optical Search for Extraterrestrial Intelligence (OSETI) attempts to detect collimated, narrow-band pulses of electromagnetic radiation. These pulses may either consist of signals intentionally directed at the Earth, or signals between two star systems with a vector that unintentionally intersects the Solar System, allowing Earth to intercept the communication. But should we expect to be able to intercept these unintentional signals? And what constraints can we place upon the frequency of intelligent civilisations if we do? We carry out Monte Carlo Realisation simulations of interstellar communications between civilisations in the Galactic Habitable Zone (GHZ) using collimated beams. We measure the frequency with which beams between two stars are intercepted by a third. The interception rate increases linearly with the fraction of communicating civilisations, and as the cube of the beam opening angle, which is somewhat stronger than theoretical expectations, which we argue is due to the geometry of the GHZ. We find that for an annular GHZ containing 10,000 civilisations, intersections are unlikely unless the beams are relatively uncollimated. These results indicate that optical SETI is more likely to find signals deliberately directed at the Earth than accidentally intercepting collimated communications. Equally, civilisations wishing to establish a network of communicating species may use weakly collimated beams to build up the network through interception, if they are willing to pay a cost penalty that is lower than that meted by fully isotropic beacons. Future SETI searches should consider the possibility that communicating civilisations will attempt to strike a balance between optimising costs and encouraging contact between civilisations, and look for weakly collimated pulses as well as narrow-beam pulses directed deliberately at the Earth.

  16. Comparison of pinhole collimator materials based on sensitivity equivalence.

    PubMed

    Bom, Victor; Goorden, Marlies; Beekman, Freek

    2011-06-07

    Pinhole SPECT often provides an excellent resolution sensitivity trade-off for radionuclide imaging compared to SPECT with parallel holes, particularly when imaging small experimental animals like rodents. High absorption pinhole materials are often chosen because of their low edge penetration and therefore good system resolution. Capturing more photons in the edges however results in decreased system sensitivity if the pinhole diameter remains the same, which may partly undo the beneficial effect on the resolution. In the search for an optimal trade-off we have compared pinhole projection data and reconstructed images of different materials with pinhole aperture diameters adjusted to obtain equal sensitivity. Monte Carlo calculations modeling the transmission, penetration and scattering of gamma radiation in single pinholes of uranium, gold, tungsten and lead were performed for a range of pinhole opening angles, diameters and gamma ray energies. In addition, reconstructed images of a hot rod phantom were determined for a multipinhole SPECT system and for a system that can image the 511 keV annihilation photons of positron emitting tracers with clustered pinholes. Our results indicate that, under the condition of equal sensitivity, tungsten and for SPECT also lead pinholes perform just as well as gold and uranium ones, indicating that a significant cost reduction can be achieved in pinhole collimator manufacturing while the use of rare or impractical materials can be avoided.

  17. SU-E-T-534: Dosimetric Effect of Multileaf Collimator Leaf Width On Volumetric Modulated Arc Stereotactic Radiotherapy for Spine Tumors

    SciTech Connect

    Amoush, A; Djemil, T; Subedi, L; Huang, L; Xia, P

    2014-06-01

    Purpose: To study the dosimetric impact of MLC leaf width in patients treated with Volumetric Modulated Arc Therapy (VMAT) for spine Stereotactic Body radiation Therapy (SBRT). Methods: Twelve spine SBRT patients were retrospectively selected for this study. The patients were treated with IMRT following the RTOG-0631 of spine metastasis. The prescription dose was 16 Gy in one fraction to 90% of the target volume (V16 > 90%). The maximum spinal cord dose of 14 Gy and 10% of the cord receiving < 10 Gy (V10) were set as dose constraints. For purpose of this study, three dual arc VMAT plans were created for each patient using three different MLC leaf widths: 2.5 mm, 4mm, and 5mm. The compliance to RTOG 0631, conformal index (CI), dose gradient index (DGI), and number of monitor units (MUs) were compared. Results: The average V16 of the target was 91.91±1.36%, 93.73±2.38%, and 92.25±2.49% for 2.5 mm, 4 mm, and 5 mm leaf widths, respectively (p=0.39). Accordingly, the average CI was 1.36±0.39, 1.36±0.34, and 1.41±0.3 (0.96), respectively. The average DGI was 0.24 ± 0.05, 0.22 ± 0.05, and 0.23 ± 0.04, respectively (p=0.86). The average spinal cord maximum dose was 12.10 ± 0.88 Gy, 12.52 ± 1.15 Gy, and 12.05 ± 1.12 (p=0.75) and V10 was 2.69 ± 1.71 cc, 5.43 ± 2.16 cc, and 3.71 ± 2.34 cc (p=0.15) for 2.5 mm, 4 mm, and 5 mm leaf widths, respectively. According, the average number of MUs was 4255 ± 431 MU, 5049 ± 1036 MU, and 4231 ± 580 MU respectively (p=0.17). Conclusion: The use of 2.5 mm, 4 mm, and 5 mm MLCs achieved similar VMAT plan quality as recommended by RTOG-0631. The dosimetric parameters were also comparable for the three MLCs.

  18. A dosimetric comparison of real-time adaptive and non-adaptive radiotherapy: A multi-institutional study encompassing robotic, gimbaled, multileaf collimator and couch tracking

    PubMed Central

    Colvill, Emma; Booth, Jeremy; Nill, Simeon; Fast, Martin; Bedford, James; Oelfke, Uwe; Nakamura, Mitsuhiro; Poulsen, Per; Worm, Esben; Hansen, Rune; Ravkilde, Thomas; Scherman Rydhög, Jonas; Pommer, Tobias; Munck af Rosenschold, Per; Lang, Stephanie; Guckenberger, Matthias; Groh, Christian; Herrmann, Christian; Verellen, Dirk; Poels, Kenneth; Wang, Lei; Hadsell, Michael; Sothmann, Thilo; Blanck, Oliver; Keall, Paul

    2016-01-01

    Purpose A study of real-time adaptive radiotherapy systems was performed to test the hypothesis that, across delivery systems and institutions, the dosimetric accuracy is improved with adaptive treatments over non-adaptive radiotherapy in the presence of patient-measured tumor motion. Methods and materials Ten institutions with robotic(2), gimbaled(2), MLC(4) or couch tracking(2) used common materials including CT and structure sets, motion traces and planning protocols to create a lung and a prostate plan. For each motion trace, the plan was delivered twice to a moving dosimeter; with and without real-time adaptation. Each measurement was compared to a static measurement and the percentage of failed points for γ-tests recorded. Results For all lung traces all measurement sets show improved dose accuracy with a mean 2%/2 mm γ-fail rate of 1.6% with adaptation and 15.2% without adaptation (p < 0.001). For all prostate the mean 2%/2 mm γ-fail rate was 1.4% with adaptation and 17.3% without adaptation (p < 0.001). The difference between the four systems was small with an average 2%/2 mm γ-fail rate of <3% for all systems with adaptation for lung and prostate. Conclusions The investigated systems all accounted for realistic tumor motion accurately and performed to a similar high standard, with real-time adaptation significantly outperforming non-adaptive delivery methods. PMID:27016171

  19. Monte Carlo modeling of HD120 multileaf collimator on Varian TrueBeam linear accelerator for verification of 6X and 6X FFF VMAT SABR treatment plans.

    PubMed

    Bergman, Alanah M; Gete, Ermias; Duzenli, Cheryl; Teke, Tony

    2014-05-08

    A Monte Carlo (MC) validation of the vendor-supplied Varian TrueBeam 6 MV flattened (6X) phase-space file and the first implementation of the Siebers-Keall MC MLC model as applied to the HD120 MLC (for 6X flat and 6X flattening filter-free (6X FFF) beams) are described. The MC model is validated in the context of VMAT patient-specific quality assurance. The Monte Carlo commissioning process involves: 1) validating the calculated open-field percentage depth doses (PDDs), profiles, and output factors (OF), 2) adapting the Siebers-Keall MLC model to match the new HD120-MLC geometry and material composition, 3) determining the absolute dose conversion factor for the MC calculation, and 4) validating this entire linac/MLC in the context of dose calculation verification for clinical VMAT plans. MC PDDs for the 6X beams agree with the measured data to within 2.0% for field sizes ranging from 2 × 2 to 40 × 40 cm2. Measured and MC profiles show agreement in the 50% field width and the 80%-20% penumbra region to within 1.3 mm for all square field sizes. MC OFs for the 2 to 40 cm2 square fields agree with measurement to within 1.6%. Verification of VMAT SABR lung, liver, and vertebra plans demonstrate that measured and MC ion chamber doses agree within 0.6% for the 6X beam and within 2.0% for the 6X FFF beam. A 3D gamma factor analysis demonstrates that for the 6X beam, > 99% of voxels meet the pass criteria (3%/3 mm). For the 6X FFF beam, > 94% of voxels meet this criteria. The TrueBeam accelerator delivering 6X and 6X FFF beams with the HD120 MLC can be modeled in Monte Carlo to provide an independent 3D dose calculation for clinical VMAT plans. This quality assurance tool has been used clinically to verify over 140 6X and 16 6X FFF TrueBeam treatment plans.

  20. Faking ordinary photons by displaced dark photon decays

    NASA Astrophysics Data System (ADS)

    Tsai, Yuhsin; Wang, Lian-Tao; Zhao, Yue

    2017-01-01

    A light metastable dark photon decaying into a collimated electron/positron pair can fake a photon, either converted or unconverted, at the LHC. The detailed object identification relies on the specifics of the detector and strategies for the reconstruction. We study the fake rate based on the ATLAS (CMS) detector geometry and show that it can be O(1) with a generic choice of parameters. Especially, the probability of being registered as a photon is angular dependent. Such detector effects can induce bias to measurements on certain properties of new physics. In this paper, we consider the scenario where dark photons in final states are from a heavy resonance decay. Consequently, the detector effects can dramatically affect the results when determining the spin of a resonance. Further, if the decay products from the heavy resonance are one photon and one dark photon, which has a large probability to fake a diphoton event, the resonance is allowed to be a vector. Because of the difference in detectors, the cross sections measured in ATLAS and CMS do not necessarily match. Furthermore, if the diphoton signal is given by the dark photons, the standard model Z γ and Z Z final states do not necessarily come with the γ γ channel, which is a unique signature in our scenario. The issue studied here is relevant also for any future new physics searches with photon(s) in the final state. We discuss possible ways of distinguishing dark photon decay and a real photon in the future.

  1. Transverse Wakefields from Tapered Collimators: Measurements and Analysis

    SciTech Connect

    Tenenbaum, Peter G

    2001-07-27

    We report on a series of measurements of the transverse wakefield from tapered collimators. The collimators were designed to principally present a geometric impedance to the beam, and to minimize impedances from resistivity or surface features; in addition, the geometries of the collimators were selected to permit examination of the scaling behavior of the wakefield due to collimator taper angle and minimum gap size. We present the measured near-center wakefields of the collimators, as well as the effect of bunch-length variation. The measurements are compared to analytic models and MAFIA simulations.

  2. PERFORMANCE OF AND UPGRADES TO THE SNS COLLIMATOR SYSTEMS

    SciTech Connect

    Plum, Michael A; Abdou, Ashraf A; Jacobs, Lorelei L; Janney, Jim G; Geoghegan, Patrick J; McTeer, Stephen Mark; Popova, Irina; Ferguson, Phillip D; Zhukov, Alexander P

    2009-01-01

    As the Spallation Neutron Source (SNS) beam power is increased, the collimator systems are becoming correspondingly more important. The High Energy Beam Transport (HEBT) transverse collimators are now routinely used during neutron production. We are in the process of redesigning the HEBT momentum collimation system due to problems with gas production from radiolysis. The Ring collimators are designed for two-stage operation but to date they are mainly used in one-stage mode. In this paper we will discuss the status, the operational performance, and upgrades to the collimation systems.

  3. Performance of a Lanthanum Bromide Detector and a New Conception Collimator for Radiopharmaceuticals Molecular Imaging in Oncology

    SciTech Connect

    Pani, Roberto; Pellegrini, Rosanna; Bennati, Paolo; Cinti, Maria Nerina; Scafe, Raffaele; De Vincentis, Giuseppe; Navarria, Francesco; Moschini, Giuliano; Rossi, Paolo; Cencelli, Valentino Orsolini; De Notaristefani, Francesco

    2009-03-10

    We have realized and tested a new-design compact gamma camera for high resolution SPET (Single Photon Emission Tomography), and small animals' radio-pharmaceutical molecular imaging. The camera is based on a 'continuous' Lanthanum tri-Bromide crystal, and a new Low Energy (LE) collimator. The crystal is interfaced to a 2x2 array of Hamamatsu-H8500 position sensitive photo-multipliers. The lead collimator features parallel hexagonal 1.0 mm holes, 18 mm length, 0.2 mm septa and 10x10 cm{sup 2} detection area. It was newly designed to fully exploit the high spatial resolution a Lanthanum crystal may provide. To better evaluate its role, we have compared our camera to three other systems with similar crystals and photomultipliers, but employing traditional collimators, either pinhole or parallel. The new camera seems to be complementary to pinhole systems and shows a very attractive trade-off between spatial resolution and detection area.

  4. Light Collimator and Monitor for a Spectroradiometer

    NASA Technical Reports Server (NTRS)

    Gore, Warren

    2008-01-01

    A system that comprises optical and electronic subsystems has been developed as an infrastructure for a spectroradiometer that measures time-dependent spectral radiance of the daylight sky, in a narrow field of view (having angular width of the order of 1 ) centered on the zenith, in several spectral bands in the wavelength range from 0.3 to 2.2 m. This system is used in conjunction with two commercially available monolithic spectrometers: a silicon-based one for wavelengths from 0.3 to 1.1 m and a gallium arsenide-based one for wavelengths from 1.05 to 2.2 m (see figure). The role of this system is to collect the light from the affected region of the sky, collimate the light, deliver the collimated light to the monolithic spectrometers, and process the electronic outputs of the spectrometers

  5. Fungal testing of diode laser collimators

    NASA Astrophysics Data System (ADS)

    de Lourdes Quinta, Maria; Freitas, Jose C. A.; Rodrigues, Fernando C.; Silva, Jeronimo A.

    1991-03-01

    The utilization of laser systems in adverse environment conditions imposes several project restrictions. In our application, the design of laser collimators was developed according not only with the specified optical, mechanical and electronic parameters, but also, taking into account the specific environment characteristics in which the equipment was to be used, namely, climate, physical elements and biological agents. The utilization of several kinds of materials, like silicone, rubber, PVC, nitro-cellulose lacquers and oil varnishes, may facilitate the attack by fungi and in some special cases by bacteria in humid environments. In this paper the behavior of laser collimators after a severe essay with optimal conditions of humidity and temperature appropriated to growth of fungi is described.

  6. Imaging the sun in hard X-rays - Spatial and rotating modulation collimators

    NASA Technical Reports Server (NTRS)

    Campbell, Jonathan W.; Davis, John M.; Emslie, A. G.

    1991-01-01

    Several approaches to imaging hard X-rays emitted from solar flares have been proposed or are planned for the nineties including the spatial modulation collimator (SMC) and the rotating modulation collimator (RMC). A survey of current solar flare theoretical literature indicates the desirability of spatial resolutions down to 1 arcsecond, field of views greater than the full solar disk (i.e., 32 arcminutes), and temporal resolutions down to 1 second. Although the sun typically provides relatively high flux levels, the requirement for 1 second temporal resolution raises the question as to the viability of Fourier telescopes subject to the aforementioned constraints. A basic photon counting, Monte Carlo 'end-to-end' model telescope was employed using the Astronomical Image Processing System (AIPS) for image reconstruction. The resulting solar flare hard X-ray images compared against typical observations indicated that both telescopes show promise for the future.

  7. Imaging the sun in hard X-rays - Spatial and rotating modulation collimators

    NASA Technical Reports Server (NTRS)

    Campbell, Jonathan W.; Davis, John M.; Emslie, A. G.

    1991-01-01

    Several approaches to imaging hard X-rays emitted from solar flares have been proposed or are planned for the nineties including the spatial modulation collimator (SMC) and the rotating modulation collimator (RMC). A survey of current solar flare theoretical literature indicates the desirability of spatial resolutions down to 1 arcsecond, field of views greater than the full solar disk (i.e., 32 arcminutes), and temporal resolutions down to 1 second. Although the sun typically provides relatively high flux levels, the requirement for 1 second temporal resolution raises the question as to the viability of Fourier telescopes subject to the aforementioned constraints. A basic photon counting, Monte Carlo 'end-to-end' model telescope was employed using the Astronomical Image Processing System (AIPS) for image reconstruction. The resulting solar flare hard X-ray images compared against typical observations indicated that both telescopes show promise for the future.

  8. TH-C-BRD-03: Determining the Optimal Collimator Position for Collimated Pencil Beam Scanning Proton Therapy

    SciTech Connect

    Wang, D; Smith, B; Hill, P; Gelover, E; Flynn, R; Hyer, D

    2014-06-15

    Purpose: There has been a growing interest in applying collimation to pencil beam scanning (PBS) proton therapy in order to sharpen the lateral dose falloff out of the target, especially at low energies. Currently, there is not a method to optimally determine the collimation position or margin around the target. A uniform margin would not be ideal due to the fact that an incoming symmetric pencil beam, after being intercepted by a collimator near the target boundary, will become asymmetric and experience a lateral shift away from its original spot location, leaving the target insufficiently covered. We demonstrate a method that optimally determines the collimator position on a per-spot basis, in order to maximize target dose while minimizing normal tissue dose. Methods: A library of collimated pencil beams were obtained through Monte Carlo simulation with a collimator placed at varying distances from the central axis of an incoming symmetrical pencil beam of 118 MeV and 5 mm sigma-in-air. Two-dimensional treatment plans were then created using this library of collimated pencil beams. For each spot position in a treatment plan, the collimator position was optimally determined in such a way that the resultant pencil beam maximized the ratio of in-target dose and out-of-target dose. For comparison, un-collimated treatment plans were also computed. Results: The spot-by-spot optimally determined collimator positions allowed the reduction of normal tissue dose while maintaining the same target coverage as un-collimated PBS. Quantitatively, the mean dose outside of the target was reduced by approximately 40% as compared to the plan without collimation. Conclusion: The proposed method determines the optimal collimator position for each spot in collimated PBS proton therapy. The use of a collimator will improve PBS dose distributions achievable today and will continue to be the subject of future investigations.

  9. Outflow Collimation in Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Noriega-Crespo, A.; Frank, A.

    1993-05-01

    Recent results of long-slit spectroscopy of the forbidden lines of the outflow in the young star DG Tau [7] suggest that its wind is well collimated very close to it, leading to the formation of its jet. The analysis of the width of stellar jets, on the other hand, seems to indicate that the collimation of the jets takes place at larger scales [5]. In other to understand this discrepancy, we are studying by means of a two dimensional hydrodynamical code [1][3], the collimation driven by the interaction of the stellar wind with the surrounding density structure left by the star formation process [8][9]. We have found in our adiabatic outflow simulations (using physical parameters similar to those for the HH 34 bipolar stellar jet [2]) that a spherical wind is well collimated near the source resembling a de Laval Nozzle [4][6]. ANC research is supported by NSF grant AST-91-14888. \\ References [1] Frank, A. 1992, PhD Thesis, University of Washington. [2] Heathcote, S. & Reipurth, B. 1992, AJ 104, 2193. [3] Icke, V., 1988 A&A 202, 177. [4] Konigl, A. 1982, ApJ 261, 115. [5] Mundt, R., Ray, T.P., & Raga, A.C. 1991, A&A 252, 740. [6] Raga A.C., & Canto, J. 1989, ApJ 344, 404. [7] Solf, J., & Bohm, K.H. 1993, ApJL (in press). [8] Terebey, S., Shu, F.H., & Cassen, P. 1984, ApJ 286, 529. [9] Yorke, H.W., Bodenheimer, P., & Laughlin, G. 1993, ApJ (in press).

  10. Coronal Jet Collimation by Nonlinear Induced Flows

    NASA Astrophysics Data System (ADS)

    Vasheghani Farahani, S.; Hejazi, S. M.

    2017-08-01

    Our objective is to study the collimation of solar jets by nonlinear forces corresponding to torsional Alfvén waves together with external forces. We consider a straight, initially non-rotating, untwisted magnetic cylinder embedded in a plasma with a straight magnetic field, where a shear between the internal and external flows exists. By implementing magnetohydrodynamic theory and taking into account the second-order thin flux tube approximation, the balance between the internal nonlinear forces is visualized. The nonlinear differential equation containing the ponderomotive, magnetic tension, and centrifugal forces in the presence of the shear flow is obtained. The solution presents the scale of influence of the propagating torsional Alfvén wave on compressive perturbations. Explicit expressions for the compressive perturbations caused by the forces connected to the torsional Alfvén wave show that, in the presence of a shear flow, the magnetic tension and centrifugal forces do not cancel each other’s effects as they did in its absence. This shear flow plays in favor of the magnetic tension force, resulting in a more efficient collimation. Regarding the ponderomotive force, the shear flow has no effect. The phase relations highlight the interplay of the shear flow and the plasma-β. As the shear flow and plasma-β increase, compressive perturbation amplitudes emerge. We conclude that the jet collimation due to the torsional Alfvén wave highly depends on the location of the jet. The shear flow tightens the collimation as the jet elevates up to the solar corona.

  11. Electron lenses for particle collimation in LHC

    SciTech Connect

    Shiltsev, v.; /Fermilab

    2007-12-01

    Electron Lenses built and installed in Tevatron have proven themselves as safe and very reliable instruments which can be effectively used in hadron collider operation for a number of applications, including compensation of beam-beam effects [1], DC beam removal from abort gaps [2], as a diagnostic tool. In this presentation we - following original proposal [3] - consider in more detail a possibility of using electron lenses with hollow electron beam for ion and proton collimation in LHC.

  12. Characterization of a SPECT pinhole collimator for optimal detector usage (the lofthole)

    NASA Astrophysics Data System (ADS)

    Deprez, Karel; Pato, Lara R. V.; Vandenberghe, Stefaan; Van Holen, Roel

    2013-02-01

    In single-photon emission computed tomography (SPECT), multi-pinhole collimation is often employed nowadays. Most multi-pinhole collimators avoid overlap (multiplexing) of the projections on the detector. This can be done by using additional shielding or by spacing the pinholes far enough apart. Using additional shielding has the drawback that it increases weight, design complexity and cost. Spacing the pinholes far enough apart results in sub-optimal detector usage, the valuable detector area is not entirely used. This is due to the circular projections of pinholes on the detector; these ellipses can not be tiled with high detector coverage. To overcome this we designed a new pinhole geometry, the lofthole, that has a rectangular projection on the detector. The lofthole has a circular aperture and a rectangular entrance/exit opening. Sensitivity formulae have been derived for pinholes and loftholes. These formulae take the penumbra effect into account; the proposed formulae do not take penetration into account. The derived formulae are valid for geometries where the field-of-view and the sensitivity of the aperture are solely limited by the exit window. A flood map measurement was performed to compare the rectangular projection of a lofthole with the circular projection of a pinhole. Finally, measurements were done to compare the amount of penetration of pinholes with the amount of penetration of a lofthole. A square lofthole collimator has less penetration than a knife-edge pinhole collimator that irradiates the same rectangular detector area with full coverage. A multi-lofthole collimator allows high detector coverage without using additional shielding. An additional advantage is the lower amount of penetration.

  13. Longitudinal wakefield for an axisymmetric collimator

    SciTech Connect

    Blednykh A.; Krinsky, S.

    2012-05-25

    We consider the longitudinal point-charge wakefield, w(s), for an axisymmetric collimator having inner radius b, outer radius d, inner length g, and taper length L. The taper angle {alpha} is defined by tan {alpha} = (d-b)/L. Using the electromagnetic simulation code ECHO, we explore the dependence of the wakefield on a collimator's geometric parameters over a wide range of profiles: from small-angle tapers to step-function transitions. The point-charge wakefield is determined using an approximation introduced by Podobedov and Stupakov. We have found it useful to exhibit the wakefield as a function of the scaled variable s/d{alpha}. For small taper angles, our results illustrate the satisfaction of the longitudinal scaling found by Stupakov, Bane, and Zagorodnov; and for larger taper angles, the breaking of this longitudinal scaling is clearly depicted. The use of the scaled variable s/d{alpha} turns out to be especially well suited to describing the wakefield for a collimator with step-function profile ({alpha} = {pi}/2).

  14. Collimation of Fast Wide-Field Telescopes

    NASA Astrophysics Data System (ADS)

    McLeod, Brian A.

    1996-02-01

    In this paper, I present a simple technique for collimating the secondary mirror of fast focal ratio wide-field Cassegrain telescopes. This technique minimizes both coma and astigmatism across the field. Because astigmatism is nearly zero on-axis even in a misaligned system, it is necessary to make measurements off-axis. This technique is useful on telescopes corrected for off-axis coma such as Ritchey-Cretien designs and classical Cassegrains with refractive correctors. Proper alignment for astigmatism is especially important in the latter type of telescope where there is no astigmatism across the field in a properly aligned system. The tools required for collimation are a camera that can examine images at several locations at the edge of the field and a secondary mirror that can be controlled in five axes. Also presented are analytic expressions for the amount of field-dependent astigmatism due to miscollimation. The technique is robust enough to collimate telescopes with fixed astigmatism in the telescope primary. (SECTION: Astronomical Instrumentation)

  15. LED collimation using high-index glass

    NASA Astrophysics Data System (ADS)

    Biertümpfel, Ralf; Reichel, Steffen

    2011-10-01

    LEDs emit light over a broad range of angles. Additionally, a narrow collimation of LED light is difficult because of the broad emission area of the LED. In order to implement an efficient beam shaping with small optics we propose to use a glass lens design with a refractive index (nd) greater than 1.7. Our design is characterized by a very small size and a high efficiency. This enables us to design optical arrays with an extremely high packing density of LEDs. Additional advantages are the high temperature resistance, the climate resistance and the stability against solarization. For many applications the footprint of the light beam should not only be collimated but also formed into a specific shape. Design results for a rectangular or oval beam shaping using high refractive index glass are presented. The designs collimate the broad emitted LED light and are optimized to incorporate also the manufacturability of the lens. Our proposed lens designs can easily be manufactured by modern pressing techniques, thus, these solutions are suitable for mass production.

  16. A Maximum NEC Criterion for Compton Collimation to Accurately Identify True Coincidences in PET

    PubMed Central

    Chinn, Garry; Levin, Craig S.

    2013-01-01

    In this work, we propose a new method to increase the accuracy of identifying true coincidence events for positron emission tomography (PET). This approach requires 3-D detectors with the ability to position each photon interaction in multi-interaction photon events. When multiple interactions occur in the detector, the incident direction of the photon can be estimated using the Compton scatter kinematics (Compton Collimation). If the difference between the estimated incident direction of the photon relative to a second, coincident photon lies within a certain angular range around colinearity, the line of response between the two photons is identified as a true coincidence and used for image reconstruction. We present an algorithm for choosing the incident photon direction window threshold that maximizes the noise equivalent counts of the PET system. For simulated data, the direction window removed 56%–67% of random coincidences while retaining > 94% of true coincidences from image reconstruction as well as accurately extracted 70% of true coincidences from multiple coincidences. PMID:21317079

  17. Bulletlike light pulses in photonic crystals

    NASA Astrophysics Data System (ADS)

    Zhou, Chuanhong; Gong, Qian; Yao, Peijun; Zhao, Deyin; Jiang, Xunya

    2008-08-01

    We report the bulletlike propagation of light pulse in a particularly designed two-dimensional (2D) photonic crystal. Unlike traditional light bullet supported by nonlinear materials, this bulletlike propagation is achieved only by 2D photonic crystal, where the diffraction and the group velocity dispersion of a light pulse are eliminated naturally by combining two distinct properties of photonic crystal, i.e., self-collimation and zero group velocity dispersion. Moreover, we studied the influence of third order dispersion on the propagation of light bullet and found that it can be greatly suppressed by an improved structure of photonic crystal.

  18. Design of a Tri-PET collimator for high-resolution whole-body mouse imaging.

    PubMed

    DiFilippo, Frank P

    2017-08-01

    Tri-PET refers to high-resolution 511-keV emission tomography using a multipinhole collimator in conjunction with lower resolution PET detectors operating in coincidence mode. Tri-PET is unique in that three spatial locations are associated with each event (two detector coordinates and one pinhole location). Spatial resolution and sensitivity are similar to that of 511-keV SPECT and are governed mainly by the collimator design. However because of a third spatial location in Tri-PET, the line-of-response is overdetermined. This feature permits new opportunities in data processing which impact collimator design. In particular, multiplexing can be avoided since the coincidence data identify the pinhole through which the photon passed. In this paper, the principles of Tri-PET collimator design are reviewed and then applied to the case of high-resolution imaging of a small animal in a clinical PET scanner. The design of a 148-pinhole collimator for whole-body imaging of a mouse is presented. Two pinhole designs were investigated: knife-edge pinholes with 1.1 mm aperture and novel hyperboloidal pinholes with 1.2 mm aperture, both having 18° cone angle. The pinhole configuration is unfocused, covering a whole-body mouse field of view with nearly uniform sensitivity. Computer simulations were performed of a micro hot rods phantom imaged with this collimator in a clinical PET scanner. Sensitivity was estimated by simulating a point source centered on-axis at locations spanning a 70-mm axial range, similar to the NEMA NU-4 standard for whole-body mouse imaging. Reconstructed images of the hot rods phantom demonstrated the ability to resolve 1.1 mm structures with the knife-edge pinholes and 1.0 mm structures with the hyperboloidal pinholes. Sensitivity was found to be 0.093% and 0.054% for the knife-edge and hyperboloidal pinholes, respectively. With a properly designed multipinhole collimator, high-resolution and acceptable sensitivity are achievable with Tri-PET using

  19. Source holder collimator for encapsulating radioactive material and collimating the emanations from the material

    DOEpatents

    Laurer, G.R.

    1974-01-22

    This invention provides a transportable device capable of detecting normal levels of a trace element, such as lead in a doughnutshaped blood sample by x-ray fluorescence with a minimum of sample preparation in a relatively short analyzing time. In one embodiment, the blood is molded into a doughnut-shaped sample around an annular array of low-energy radioactive material that is at the center of the doughnut-shaped sample but encapsulated in a collimator, the latter shielding a detector that is close to the sample and facing the same so that the detector receives secondary emissions from the sample while the collimator collimates ths primary emissions from the radioactive material to direct these emissions toward the sample around 360 deg and away from the detector. (Official Gazette)

  20. Development of collimator insert for linac based stereotactic irradiation.

    PubMed

    Singh, I R; Brindha, S; Ravindran, B P; John, S; Rajshekhar, V; Rangad, F V; Roul, R K

    1999-10-01

    The aim of this study is to develop collimator inserts of various sizes which are either not commercially available or are expensive to import. The dosimetry parameters such as tissue maximum ratio (TMR), off-axis ratio (OAR) and output factor of the developed collimator insert are compared with that of the commercial collimator insert (Radionics). In order to check the suitability of the collimator insert developed locally for clinical use and to standardize the method of development, a collimator insert of 15 mm identical to the one supplied by Radionics is developed with low-melting alloy (Cerrobend). Moreover for the clinical use of the developed collimator insert, certain acceptance tests are performed which include a collimator concentricity test, beam size check and radiation leakage test. The dose verification is carried out with a thermoluminescent dosimeter (7LiF rods) and an FBX chemical dosimeter in a human-head-shaped Perspex phantom filled with water. The variation between the calculated and measured dose is found to be within +2.4% for 7LiF rods and -2.0% for the FBX chemical dosimeter thus ensuring the suitability of the developed collimator insert for clinical use. This has encouraged us to standardize the method adapted to develop the collimator insert and to develop collimator inserts of different field sizes.

  1. SU-F-BRB-12: A Novel Haar Wavelet Based Approach to Deliver Non-Coplanar Intensity Modulated Radiotherapy Using Sparse Orthogonal Collimators

    SciTech Connect

    Nguyen, D; Ruan, D; Low, D; Sheng, K; O’Connor, D; Boucher, S

    2015-06-15

    Purpose: Existing efforts to replace complex multileaf collimator (MLC) by simple jaws for intensity modulated radiation therapy (IMRT) resulted in unacceptable compromise in plan quality and delivery efficiency. We introduce a novel fluence map segmentation method based on compressed sensing for plan delivery using a simplified sparse orthogonal collimator (SOC) on the 4π non-coplanar radiotherapy platform. Methods: 4π plans with varying prescription doses were first created by automatically selecting and optimizing 20 non-coplanar beams for 2 GBM, 2 head & neck, and 2 lung patients. To create deliverable 4π plans using SOC, which are two pairs of orthogonal collimators with 1 to 4 leaves in each collimator bank, a Haar Fluence Optimization (HFO) method was used to regulate the number of Haar wavelet coefficients while maximizing the dose fidelity to the ideal prescription. The plans were directly stratified utilizing the optimized Haar wavelet rectangular basis. A matching number of deliverable segments were stratified for the MLC-based plans. Results: Compared to the MLC-based 4π plans, the SOC-based 4π plans increased the average PTV dose homogeneity from 0.811 to 0.913. PTV D98 and D99 were improved by 3.53% and 5.60% of the corresponding prescription doses. The average mean and maximal OAR doses slightly increased by 0.57% and 2.57% of the prescription doses. The average number of segments ranged between 5 and 30 per beam. The collimator travel time to create the segments decreased with increasing leaf numbers in the SOC. The two and four leaf designs were 1.71 and 1.93 times more efficient, on average, than the single leaf design. Conclusion: The innovative dose domain optimization based on compressed sensing enables uncompromised 4π non-coplanar IMRT dose delivery using simple rectangular segments that are deliverable using a sparse orthogonal collimator, which only requires 8 to 16 leaves yet is unlimited in modulation resolution. This work is

  2. Hybrid algorithm for simulating the collimated transmittance of homogeneous stratified turbid media

    PubMed Central

    Cruzado, Beatriz Morales; Atencio, José Alberto Delgado; Vázquez y Montiel, Sergio; Gómez, Erick Sarmiento

    2015-01-01

    In this work we describe the development of a program that simulates the propagation of photons through refractive and reflecting optical components such as lenses, mirrors and stops that includes a biological tissue sample as the main issue to be investigated in order to get a simulated value of light distribution, in particular, of the unscattered light. The analysis of the photons that travel through the sample is based on the program Monte Carlo Multi-Layered with some modifications that consider a Gaussian beam as initial source of light. Position, directional cosines and weight of photons exiting the turbid media are used to propagate them through an optical system. As a mean of validation of the program, we selected a typical optical system for measurement of collimated transmittance. Therefore, several tests were carried out to find the optical system that gives the theoretical collimated transmittance at different values of the optical properties of the turbid media. Along this validation, the optimal experimental configuration is found. Using this results, a comparison between the simulated optimal configuration and the experimental set-up was done, by using a colloidal suspension as a turbid media. PMID:26137375

  3. Hybrid algorithm for simulating the collimated transmittance of homogeneous stratified turbid media.

    PubMed

    Cruzado, Beatriz Morales; Atencio, José Alberto Delgado; Vázquez Y Montiel, Sergio; Gómez, Erick Sarmiento

    2015-05-01

    In this work we describe the development of a program that simulates the propagation of photons through refractive and reflecting optical components such as lenses, mirrors and stops that includes a biological tissue sample as the main issue to be investigated in order to get a simulated value of light distribution, in particular, of the unscattered light. The analysis of the photons that travel through the sample is based on the program Monte Carlo Multi-Layered with some modifications that consider a Gaussian beam as initial source of light. Position, directional cosines and weight of photons exiting the turbid media are used to propagate them through an optical system. As a mean of validation of the program, we selected a typical optical system for measurement of collimated transmittance. Therefore, several tests were carried out to find the optical system that gives the theoretical collimated transmittance at different values of the optical properties of the turbid media. Along this validation, the optimal experimental configuration is found. Using this results, a comparison between the simulated optimal configuration and the experimental set-up was done, by using a colloidal suspension as a turbid media.

  4. A virtual photon source model of an Elekta linear accelerator with integrated mini MLC for Monte Carlo based IMRT dose calculation.

    PubMed

    Sikora, M; Dohm, O; Alber, M

    2007-08-07

    A dedicated, efficient Monte Carlo (MC) accelerator head model for intensity modulated stereotactic radiosurgery treatment planning is needed to afford a highly accurate simulation of tiny IMRT fields. A virtual source model (VSM) of a mini multi-leaf collimator (MLC) (the Elekta Beam Modulator (EBM)) is presented, allowing efficient generation of particles even for small fields. The VSM of the EBM is based on a previously published virtual photon energy fluence model (VEF) (Fippel et al 2003 Med. Phys. 30 301) commissioned with large field measurements in air and in water. The original commissioning procedure of the VEF, based on large field measurements only, leads to inaccuracies for small fields. In order to improve the VSM, it was necessary to change the VEF model by developing (1) a method to determine the primary photon source diameter, relevant for output factor calculations, (2) a model of the influence of the flattening filter on the secondary photon spectrum and (3) a more realistic primary photon spectrum. The VSM model is used to generate the source phase space data above the mini-MLC. Later the particles are transmitted through the mini-MLC by a passive filter function which significantly speeds up the time of generation of the phase space data after the mini-MLC, used for calculation of the dose distribution in the patient. The improved VSM model was commissioned for 6 and 15 MV beams. The results of MC simulation are in very good agreement with measurements. Less than 2% of local difference between the MC simulation and the diamond detector measurement of the output factors in water was achieved. The X, Y and Z profiles measured in water with an ion chamber (V = 0.125 cm(3)) and a diamond detector were used to validate the models. An overall agreement of 2%/2 mm for high dose regions and 3%/2 mm in low dose regions between measurement and MC simulation for field sizes from 0.8 x 0.8 cm(2) to 16 x 21 cm(2) was achieved. An IMRT plan film verification

  5. Sentinel node detection in patients with breast cancer: low-energy all-purpose collimator or medium-energy collimator?

    PubMed

    Lemstra, C; Broersma, M; Poot, L; Jager, P L

    2004-10-01

    Sentinel node detection in patients with breast cancer is routinely performed in our department. Images frequently show star-shaped activity at the site of injection caused by septum penetration. These star-shaped artifacts could possibly impair visualization of nearby sentinel nodes. The aim of this study was to determine whether sentinel node detection in patients with breast cancer can be improved using a medium-energy all-purpose (ME) collimator instead of a low-energy all-purpose (LEAP) collimator. For this purpose, 15 patients were studied and a phantom study was performed. The LEAP collimator was used for a dynamic study immediately after injection, and both the LEAP and the ME collimators were used for static studies. A total of 20 sentinel nodes were found with both collimators. All sentinel nodes were found in the axilla. To separate sentinel nodes from the injection site, the ME collimator gave the best results in 4 of 15 patients, but only within the first hour after injection. To separate 2 nearby sentinel nodes from each other, the LEAP collimator gave the best results in 3 of 15 patients. Our conclusion is that the LEAP collimator gave better results than the ME collimator as a result of the better resolution and the higher sensitivity. Use of the ME collimator did not improve sentinel node detection.

  6. The Effect of Parallel-hole Collimator Material on Image and Functional Parameters in SPECT Imaging: A SIMIND Monte Carlo Study.

    PubMed

    Azarm, Ahmadreza; Islamian, Jalil Pirayesh; Mahmoudian, Babak; Gharepapagh, Esmaeil

    2015-01-01

    The collimator in single-photon emission computed tomography (SPECT) is a critical component of the imaging system and plays an impressive role in the imaging quality. In this study, the effect of the collimator material on the radioisotopic image and its functional parameters was studied. The simulating medical imaging nuclear detectors (SIMIND) Monte Carlo program was used to simulate a Siemens E.CAM SPECT (Siemens Medical Solutions, Erlangen, Germany) system equipped with a low-energy high-resolution (LEHR) collimator. The simulation and experimental data from the SPECT imaging modality using (99m)Tc were obtained on a point source and Jaszczak phantom. Seventeen high atomic number materials were considered as LEHR collimator materials. In order to determine the effect of the collimator material on the image and functional parameters, the energy resolution, spatial resolution, contrast, and collimator characteristics parameters such as septal penetration and scatter-to-primary ratio were investigated. Energy spectra profiles, full width at half maximums (FWHMs) (mm) of the point spread function (PSF) curves, system sensitivity, and contrast of cold spheres of the Jaszczak phantom for the simulated and experiment systems have acceptability superimposed. The results of FWHM and energy resolution for the 17 collimators showed that the collimator made of 98% lead and 2% antimony could provide the best FWHM and energy resolution, 7.68 mm and 9.87%, respectively. The LEHR collimator with 98% lead and 2% antimony offers the best resolution and contrast when compared to other high atomic number metals and alloys.

  7. The Effect of Parallel-hole Collimator Material on Image and Functional Parameters in SPECT Imaging: A SIMIND Monte Carlo Study

    PubMed Central

    Azarm, Ahmadreza; Islamian, Jalil Pirayesh; Mahmoudian, Babak; Gharepapagh, Esmaeil

    2015-01-01

    The collimator in single-photon emission computed tomography (SPECT) is a critical component of the imaging system and plays an impressive role in the imaging quality. In this study, the effect of the collimator material on the radioisotopic image and its functional parameters was studied. The simulating medical imaging nuclear detectors (SIMIND) Monte Carlo program was used to simulate a Siemens E.CAM SPECT (Siemens Medical Solutions, Erlangen, Germany) system equipped with a low-energy high-resolution (LEHR) collimator. The simulation and experimental data from the SPECT imaging modality using 99mTc were obtained on a point source and Jaszczak phantom. Seventeen high atomic number materials were considered as LEHR collimator materials. In order to determine the effect of the collimator material on the image and functional parameters, the energy resolution, spatial resolution, contrast, and collimator characteristics parameters such as septal penetration and scatter-to-primary ratio were investigated. Energy spectra profiles, full width at half maximums (FWHMs) (mm) of the point spread function (PSF) curves, system sensitivity, and contrast of cold spheres of the Jaszczak phantom for the simulated and experiment systems have acceptability superimposed. The results of FWHM and energy resolution for the 17 collimators showed that the collimator made of 98% lead and 2% antimony could provide the best FWHM and energy resolution, 7.68 mm and 9.87%, respectively. The LEHR collimator with 98% lead and 2% antimony offers the best resolution and contrast when compared to other high atomic number metals and alloys. PMID:26420985

  8. Performance evaluation of high-resolution square parallel-hole collimators with a CZT room temperature pixelated semiconductor SPECT system: a Monte Carlo simulation study

    NASA Astrophysics Data System (ADS)

    Lee, Y.; Kang, W.

    2015-07-01

    The pixelated semiconductor based on cadmium zinc telluride (CZT) is a promising imaging device that provides many benefits compared with conventional scintillation detectors. By using a high-resolution square parallel-hole collimator with a pixelated semiconductor detector, we were able to improve both sensitivity and spatial resolution. Here, we present a simulation of a CZT pixleated semiconductor single-photon emission computed tomography (SPECT) system with a high-resolution square parallel-hole collimator using various geometric designs of 0.5, 1.0, 1.5, and 2.0 mm X-axis hole size. We performed a simulation study of the eValuator-2500 (eV Microelectronics Inc., Saxonburg, PA, U.S.A.) CZT pixelated semiconductor detector using a Geant4 Application for Tomographic Emission (GATE). To evaluate the performances of these systems, the sensitivity and spatial resolution was evaluated. Moreover, to evaluate the overall performance of the imaging system, a hot-rod phantom was designed. Our results showed that the average sensitivity of the 2.0 mm collimator X-axis hole size was 1.34, 1.95, and 3.92 times higher than that of the 1.5, 1.0, and 0.5 mm collimator X-axis hole size, respectively. Also, the average spatial resolution of the 0.5 mm collimator X-axis hole size was 28.69, 44.65, and 55.73% better than that of the 1.0, 1.5, and 2.0 mm collimator X-axis hole size, respectively. We discuss the high-resolution square parallel-hole collimator of various collimator geometric designs and our evaluations. In conclusion, we have successfully designed a high-resolution square parallel-hole collimator with a CZT pixelated semiconductor SPECT system.

  9. Treatment planning systems for external whole brain radiation therapy: With and without MLC (multi leaf collimator) optimization

    NASA Astrophysics Data System (ADS)

    Budiyono, T.; Budi, W. S.; Hidayanto, E.

    2016-03-01

    Radiation therapy for brain malignancy is done by giving a dose of radiation to a whole volume of the brain (WBRT) followed by a booster at the primary tumor with more advanced techniques. Two external radiation fields given from the right and left side. Because the shape of the head, there will be an unavoidable hotspot radiation dose of greater than 107%. This study aims to optimize planning of radiation therapy using field in field multi-leaf collimator technique. A study of 15 WBRT samples with CT slices is done by adding some segments of radiation in each field of radiation and delivering appropriate dose weighting using a TPS precise plan Elekta R 2.15. Results showed that this optimization a more homogeneous radiation on CTV target volume, lower dose in healthy tissue, and reduced hotspots in CTV target volume. Comparison results of field in field multi segmented MLC technique with standard conventional technique for WBRT are: higher average minimum dose (77.25% ± 0:47%) vs (60% ± 3:35%); lower average maximum dose (110.27% ± 0.26%) vs (114.53% ± 1.56%); lower hotspot volume (5.71% vs 27.43%); and lower dose on eye lenses (right eye: 9.52% vs 18.20%); (left eye: 8.60% vs 16.53%).

  10. Numerical Calculations of Short-Range Wakefields of Collimators

    SciTech Connect

    Ng, Cho-Kuen

    2001-12-07

    The performance of future linear colliders are limited by the effect of short-range collimator wakefields on the beam. The beam quality is sensitive to the positioning of collimators at the end of the linac. The determination of collimator wakefields has been difficult, largely because of the scarcity of measurement data, and of the limitation of applicability of analytical results to realistic structures. In this paper, numerical methods using codes such as MAFIA are used to determine a series of tapered collimators with rectangular apertures that have been built for studies at SLAC. We will study the dependences of the wakefield on the collimator taper angle, the collimator gap as well as the bunch length. Calculations are also compared with measurements.

  11. Numerical Calculations of Short-Range Wakefields of Collimators

    NASA Astrophysics Data System (ADS)

    Ng, C. K.

    2001-12-01

    The performance of future linear colliders are limited by the effect of short-range collimator wakefields on the beam. The beam quality is sensitive to the positioning of collimators at the end of the linac. The determination of collimator wakefields has been difficult, largely because of the scarcity of measurement data, and of the limitation of applicability of analytical results to realistic structures. In this paper, numerical methods using codes such as MAFIA are used to determine a series of tapered collimators with rectangular apertures that have been built for studies at SLAC (Stanford Linear Accelerator Center). We will study the dependences of the wakefield on the collimator taper angle, the collimator gap as well as the bunch length. Calculations are also compared with measurements.

  12. Collimator application for microchannel plate image intensifier resolution improvement

    DOEpatents

    Thomas, Stanley W.

    1996-02-27

    A collimator is included in a microchannel plate image intensifier (MCPI). Collimators can be useful in improving resolution of MCPIs by eliminating the scattered electron problem and by limiting the transverse energy of electrons reaching the screen. Due to its optical absorption, a collimator will also increase the extinction ratio of an intensifier by approximately an order of magnitude. Additionally, the smooth surface of the collimator will permit a higher focusing field to be employed in the MCP-to-collimator region than is currently permitted in the MCP-to-screen region by the relatively rough and fragile aluminum layer covering the screen. Coating the MCP and collimator surfaces with aluminum oxide appears to permit additional significant increases in the field strength, resulting in better resolution.

  13. Collimator application for microchannel plate image intensifier resolution improvement

    DOEpatents

    Thomas, S.W.

    1996-02-27

    A collimator is included in a microchannel plate image intensifier (MCPI). Collimators can be useful in improving resolution of MCPIs by eliminating the scattered electron problem and by limiting the transverse energy of electrons reaching the screen. Due to its optical absorption, a collimator will also increase the extinction ratio of an intensifier by approximately an order of magnitude. Additionally, the smooth surface of the collimator will permit a higher focusing field to be employed in the MCP-to-collimator region than is currently permitted in the MCP-to-screen region by the relatively rough and fragile aluminum layer covering the screen. Coating the MCP and collimator surfaces with aluminum oxide appears to permit additional significant increases in the field strength, resulting in better resolution. 2 figs.

  14. Collimator and energy window optimization for ⁹⁰Y bremsstrahlung SPECT imaging: A SIMIND Monte Carlo study.

    PubMed

    Roshan, Hoda Rezaei; Mahmoudian, Babak; Gharepapagh, Esmaeil; Azarm, Ahmadreza; Islamian, Jalil Pirayesh

    2016-02-01

    Treatment efficacy of radioembolization using Yttrium-90 ((90)Y) microspheres is assessed by the (90)Y bremsstrahlung single photon emission computed tomography (SPECT) imaging following radioembolization. The radioisotopic image has the potential of providing reliable activity map of (90)Y microspheres distribution. One of the main reasons of the poor image quality in (90)Y bremsstrahlung SPECT imaging is the continuous and broad energy spectrum of the related bremsstrahlung photons. Furthermore, collimator geometry plays an impressive role in the spatial resolution, sensitivity and image contrast. Due to the relatively poor quality of the (90)Y bremsstrahlung SPECT images, we intend to optimize the medium-energy (ME) parallel-hole collimator and energy window. The Siemens e.cam gamma camera equipped with a ME collimator and a voxelized phantom was simulated by the SImulating Medical Imaging Nuclear Detectors (SIMIND) program. We used the SIMIND Monte Carlo program to generate the (90)Y bremsstrahlung SPECT projection of the digital Jaszczak phantom. The phantom consist of the six hot spheres ranging from 9.5 to 31.8mm in diameter, which are used to evaluate the image contrast. In order to assess the effect of the energy window on the image contrast, three energy windows ranging from 60 to 160 KeV, 160 to 400 KeV, and 60 to 400 KeV were set on a (90)Y bremsstrahlung spectrum. As well, the effect of the hole diameter of a ME collimator on the image contrast and bremsstrahlung spectrum were investigated. For the fixed collimator and septa thickness values (3.28 cm and 1.14 mm, respectively), a hole diameter range (2.35-3.3mm) was chosen based on the appropriate balance between the spatial resolution and sensitivity. The optimal energy window for (90)Y bremsstrahlung SPECT imaging was extended energy window from 60 to 400 KeV. Besides, The optimal value of the hole diameter of ME collimator was obtained 3.3mm. Geometry of the ME parallel-hole collimator and energy

  15. Ballistic imaging of biological media with collimated illumination and focal plane detection.

    PubMed

    Brezner, Barak; Cahen, Sarah; Glasser, Ziv; Sternklar, Shmuel; Granot, Er'el

    2015-07-01

    A simple, affordable method for imaging through biological tissue is investigated. The method consists of (1) imaging with a wavelength that has a relatively small scattering coefficient (1310 nm in this case) and (2) collimated illumination together with (3) focal plane detection to enhance the detection of the ballistic photons relative to the diffusive light. We demonstrate ballistic detection of an object immersed in a 1-cm-thick cuvette filled with 4% Intralipid, which is equivalent to ∼1 to 2 cm of skin tissue. With the same technology, a ballistic image of a 1-mm-wide object in 10-mm-thick chicken breast is also presented.

  16. Ballistic imaging of biological media with collimated illumination and focal plane detection

    NASA Astrophysics Data System (ADS)

    Brezner, Barak; Cahen, Sarah; Glasser, Ziv; Sternklar, Shmuel; Granot, Er'el

    2015-07-01

    A simple, affordable method for imaging through biological tissue is investigated. The method consists of (1) imaging with a wavelength that has a relatively small scattering coefficient (1310 nm in this case) and (2) collimated illumination together with (3) focal plane detection to enhance the detection of the ballistic photons relative to the diffusive light. We demonstrate ballistic detection of an object immersed in a 1-cm-thick cuvette filled with 4% Intralipid, which is equivalent to ˜1 to 2 cm of skin tissue. With the same technology, a ballistic image of a 1-mm-wide object in 10-mm-thick chicken breast is also presented.

  17. CZT strip detectors for imaging and spectroscopy: collimated beam and ASIC readout experiments.

    NASA Astrophysics Data System (ADS)

    Kurczynski, P.; Krizmanic, J. F.; Stahle, C. M.; Parsons, A.; Palmer, D. M.; Bartlett, L. M.; Barthelmy, S. D.; Birsa, F.; Gehrels, N.; Odom, J.; Hanchak, C.; Shu, P.; Teegarden, B. J.; Tueller, J.; Barbier, L. M.

    The authors report the status of ongoing investigations into Cadmium Zinc Telluride (CZT) strip detectors for application in hard X-ray astronomy. They have instrumented a nine strip by nine strip region of a two sided strip detector. In order to measure the position resolution of the detectors, they have implemented a collimated beam that concentrates radiation to a spot size less than the strip width of the detector. The detectors exhibited excellent strip uniformity in terms of photon count rate and spectroscopic information.

  18. PEP-II New High Power Low Impedance Movable Collimator

    SciTech Connect

    Matter, Regina S.

    2000-09-20

    A new class of collimators has been designed and built for the PEP-II collider which has opposing movable jaws. These collimators are designed to reduce backgrounds in the BaBar detector. They can support several kW of synchrotron radiation power striking the jaws or the impedance matching ramps. There are no longitudinal nor transverse higher-order-modes. The jaws and collimator body are made of Glidcop.

  19. Mechanical approach to the neutrons spectra collimation and detection

    SciTech Connect

    Sadeghi, H.; Roshan, M. V.

    2014-11-15

    Neutrons spectra from most of known sources require being collimated for numerous applications; among them one is the Neutron Activation Analysis. High energy neutrons are collimated through a mechanical procedure as one of the most promising methods. The output energy of the neutron beam depends on the velocity of the rotating Polyethylene disks. The collimated neutrons are then measured by an innovative detection technique with high accuracy.

  20. Some basic considerations of measurements involving collimated direct sunlight

    NASA Technical Reports Server (NTRS)

    Chai, A. T.

    1976-01-01

    The geometry of collimators for devices or instruments dealing with terrestrial direct sunlight is discussed. Effects of the opening angle and slope angle of a collimator on the measurements are investigated with regard to variations of turbidity and air mass. Based on this investigation, geometric dimensions for collimators and certain realistic terrestrial reference conditions are recommended for the purpose of solar cell calibration in terrestrial applications.

  1. Diffraction effects on angular response of X-ray collimators

    NASA Technical Reports Server (NTRS)

    Blake, R. L.; Barrus, D. M.; Fenimore, E.

    1976-01-01

    Angular responses have been measured for X-ray collimators with half-widths ranging from minutes of arc down to 10 arcsec. In the seconds-of-arc range, diffraction peaks at off-axis angles can masquerade as side lobes of the collimator angular response. Measurements and qualitative physical arguments lead to a rule of thumb for collimator design; namely, the angle of first minimum in the Fraunhofer single-slit diffraction pattern should be less than one-fourth of the collimator geometrical full-width at half-maximum intensity.

  2. Research of TIR LED collimation system based on freeform

    NASA Astrophysics Data System (ADS)

    Zhao, Hui-fu

    2016-03-01

    In order to collect a wide angle range light to receive the collimating beam of a small divergence angle, a highly efficient, compact, TIR collimating system has been designed and optimized. The collimating system adopts a hybrid structure with TIR style. First, calculate the initial structure of the collimating system according to Snell's law and equal focal length principle. Then optimize the initial structure using Lighttools optical design software. Finally, the best LED collimating system has been successfully designed. According to the results of the design, the semi-diameter of the TIR collimating system is 20mm, the diameter is 25mm. The collimating angle is 1.5°. With the light absorption loss of the material and reflection loss of the interface have already been fully considered,the light energy utilization rate is as high as 89.5%. The initial structure of TIR-type LED collimator is designed by Snell's law and equal focal length principle, and then it is optimized by the Lighttools optical design software, so that light energy utilization ratio and uniformity of illumination in the target surface are improved. In addition, TIR-type collimating system, which is small and easy to use, not only has a high light energy utilization ratio but also a compact structure.

  3. Dosimetric characterization of a bi-directional micromultileaf collimator for stereotactic applications.

    PubMed

    Bucciolini, M; Russo, S; Banci Buonamici, F; Pini, S; Silli, P

    2002-07-01

    A 6 MV photon beam from Linac SL75-5 has been collimated with a new micromultileaf device that is able to shape the field in the two orthogonal directions with four banks of leaves. This is the first clinical installation of the collimator and in this paper the dosimetric characterization of the system is reported. The dosimetric parameters required by the treatment planning system used for the dose calculation in the patient are: tissue maximum ratios, output factors, transmission and leakage of the leaves, penumbra values. Ionization chambers, silicon diode, radiographic films, and LiF thermoluminescent dosimeters have been employed for measurements of absolute dose and beam dosimetric data. Measurements with different dosimeters supply results in reasonable agreement among them and consistent with data available in literature for other models of micromultileaf collimator; that permits the use of the measured parameters for clinical applications. The discrepancies between results obtained with the different detectors (around 2%) for the analyzed parameters can be considered an indication of the accuracy that can be reached by current stereotactic dosimetry.

  4. A variable-collimation display system

    NASA Astrophysics Data System (ADS)

    Batchko, Robert; Robinson, Sam; Schmidt, Jack; Graniela, Benito

    2014-03-01

    Two important human depth cues are accommodation and vergence. Normally, the eyes accommodate and converge or diverge in tandem; changes in viewing distance cause the eyes to simultaneously adjust both focus and orientation. However, ambiguity between accommodation and vergence cues is a well-known limitation in many stereoscopic display technologies. This limitation also arises in state-of-the-art full-flight simulator displays. In current full-flight simulators, the out-the-window (OTW) display (i.e., the front cockpit window display) employs a fixed collimated display technology which allows the pilot and copilot to perceive the OTW training scene without angular errors or distortions; however, accommodation and vergence cues are limited to fixed ranges (e.g., ~ 20 m). While this approach works well for long-range, the ambiguity of depth cues at shorter range hinders the pilot's ability to gauge distances in critical maneuvers such as vertical take-off and landing (VTOL). This is the first in a series of papers on a novel, variable-collimation display (VCD) technology that is being developed under NAVY SBIR Topic N121-041 funding. The proposed VCD will integrate with rotary-wing and vertical take-off and landing simulators and provide accurate accommodation and vergence cues for distances ranging from approximately 3 m outside the chin window to ~ 20 m. A display that offers dynamic accommodation and vergence could improve pilot safety and training, and impact other applications presently limited by lack of these depth cues.

  5. Leaky wave lenses for spoof plasmon collimation.

    PubMed

    Panaretos, Anastasios H; Werner, Douglas H

    2016-06-27

    We theoretically demonstrate the feasibility of collimating radiating spoof plasmons using a leaky wave lens approach. Spoof plasmons are surface waves excited along reactance surfaces realized through metallic corrugations. By employing a periodic perturbation to the geometric profile of this type of reactance surface, it becomes feasible to convert the excited spoof plasmons into free-space radiating leaky wave modes. It is demonstrated that by structurally modifying such a corrugated surface through the introduction of a non-uniform sinusoidally modulated reactance profile, then a tapered wavenumber, with a real part less than that of free space, can be established along the surface. In this way the radiating properties of the structure (amplitude and phase) can be locally controlled thereby creating a radiating effect similar to that of a non-uniform current distribution. By properly engineering the space dependent wavenumber along the corrugated surface, different regions of the structure will emit spoof plasmon energy at different angles with varying intensity. The combined effect is the emission of an electromagnetic wave exhibiting a converging wave-front that eventually collimates spoof plasmon energy at some desired focal point.

  6. A photon thermal diode

    PubMed Central

    Chen, Zhen; Wong, Carlaton; Lubner, Sean; Yee, Shannon; Miller, John; Jang, Wanyoung; Hardin, Corey; Fong, Anthony; Garay, Javier E.; Dames, Chris

    2014-01-01

    A thermal diode is a two-terminal nonlinear device that rectifies energy carriers (for example, photons, phonons and electrons) in the thermal domain, the heat transfer analogue to the familiar electrical diode. Effective thermal rectifiers could have an impact on diverse applications ranging from heat engines to refrigeration, thermal regulation of buildings and thermal logic. However, experimental demonstrations have lagged far behind theoretical proposals. Here we present the first experimental results for a photon thermal diode. The device is based on asymmetric scattering of ballistic energy carriers by pyramidal reflectors. Recent theoretical work has predicted that this ballistic mechanism also requires a nonlinearity in order to yield asymmetric thermal transport, a requirement of all thermal diodes arising from the second Law of Thermodynamics, and realized here using an ‘inelastic thermal collimator’ element. Experiments confirm both effects: with pyramids and collimator the thermal rectification is 10.9±0.8%, while without the collimator no rectification is detectable (<0.3%). PMID:25399761

  7. Analytic derivation of pinhole collimation sensitivity for a general source model using spherical harmonics.

    PubMed

    Li, Yu-Sheng; Oldendick, James E; Chang, Wei

    2010-05-07

    Pinhole collimators are widely used for single photon emission computed tomography (SPECT) imaging of small organs and animals. There has also been renewed interest in using pinhole arrays for clinical cardiac SPECT imaging to achieve high sensitivity and complete data sampling. Overall sensitivity of a pinhole array is critical in determining a system's performance. Conventionally, a point source model has been used to evaluate the sensitivity and optimize the system design. This model is simple but far from realistic. This work addresses the use of more realistic source models to assess the sensitivity performance of pinhole collimation. We have derived an analytical formula for pinhole collimation sensitivity with a general source distribution model using spherical harmonics. As special cases of this general model, we provided the pinhole sensitivity formulae for line, disk and sphere sources. These results show that the point source model is just the zeroth-order approximation of the other source models. The point source model overestimates or underestimates the sensitivity relative to the more realistic model. The sphere source model yields the same sensitivity as a point source located at the center of the sphere when attenuation is not taken into account. In the presence of attenuation, the average path length of emitted gamma rays is 3/4 of the radius of the sphere source. The calculated sensitivities based on these formulae show good agreement with separate Monte Carlo simulations in simple cases. The general and special sensitivity formulae derived here can be useful for the design and optimization of SPECT systems that utilize pinhole collimators.

  8. Photon-photon collisions

    SciTech Connect

    Burke, D.L.

    1982-10-01

    Studies of photon-photon collisions are reviewed with particular emphasis on new results reported to this conference. These include results on light meson spectroscopy and deep inelastic e..gamma.. scattering. Considerable work has now been accumulated on resonance production by ..gamma gamma.. collisions. Preliminary high statistics studies of the photon structure function F/sub 2//sup ..gamma../(x,Q/sup 2/) are given and comments are made on the problems that remain to be solved.

  9. Evaluation of collimation and imaging configuration in scintimammography

    SciTech Connect

    Tsui, B.M.W.; Frey, E.C.; Wessell, D.E.

    1996-12-31

    Conventional scintimammography (SM) with {sup 99m}Tc sestamibi has been limited to taking a single lateral view of the breast using a parallel-hole high resolution (LEHR) collimator. The collimator is placed close to the breast for best possible spatial resolution. However, the collimator geometry precludes imaging the breast from other views. We evaluated using a pinhole collimator instead of a LEHR collimator in SM for improved spatial resolution and detection efficiency, and to allow additional imaging views. Results from theoretical calculations indicated that pinhole collimators could be designed with higher spatial resolution and detection efficiency than LEHR when imaging small to medium size breasts. The geometrical shape of the pinhole collimator allows imaging of the breasts from both the lateral and craniocaudal views. The dual-view images allow better determination of the location of the tumors within the breast and improved detection of tumors located in the medial region of the breast. A breast model that simulates the shape and composition of the breast and breast tumors with different sizes and locations was added to an existing 3D mathematical cardiac-torso (MCAT) phantom. A cylindrically shaped phantom with 10 cm diameter and spherical inserts with different sizes and {sup 99m}Tc sestamibi uptakes with respect to the background provide physical models of breast with tumors. Simulation studies using the breast and MCAT phantoms and experimental studies using the cylindrical phantom confirmed the utility of the pinhole collimator in SM for improved breast tumor detection.

  10. Collimator design for a multipinhole brain SPECT insert for MRI.

    PubMed

    Van Audenhaege, Karen; Van Holen, Roel; Vanhove, Christian; Vandenberghe, Stefaan

    2015-11-01

    Brain single photon emission computed tomography (SPECT) imaging is an important clinical tool, with unique tracers for studying neurological diseases. Nowadays, most commercial SPECT systems are combined with x-ray computed tomography (CT) in so-called SPECT/CT systems to obtain an anatomical background for the functional information. However, while CT images have a high spatial resolution, they have a low soft-tissue contrast, which is an important disadvantage for brain imaging. Magnetic resonance imaging (MRI), on the other hand, has a very high soft-tissue contrast and does not involve extra ionizing radiation. Therefore, the authors designed a brain SPECT insert that can operate inside a clinical MRI. The authors designed and simulated a compact stationary multipinhole SPECT insert based on digital silicon photomultiplier detector modules, which have shown to be MR-compatible and have an excellent intrinsic resolution (0.5 mm) when combined with a monolithic 2 mm thick LYSO crystal. First, the authors optimized the different parameters of the SPECT system to maximize sensitivity for a given target resolution of 7.2 mm in the center of the field-of-view, given the spatial constraints of the MR system. Second, the authors performed noiseless simulations of two multipinhole configurations to evaluate sampling and reconstructed resolution. Finally, the authors performed Monte Carlo simulations and compared the SPECT insert with a clinical system with ultrahigh-resolution (UHR) fan beam collimators, based on contrast-to-noise ratio and a visual comparison of a Hoffman phantom with a 9 mm cold lesion. The optimization resulted in a stationary multipinhole system with a collimator radius of 150.2 mm and a detector radius of 172.67 mm, which corresponds to four rings of 34 diSPM detector modules. This allows the authors to include eight rings of 24 pinholes, which results in a system volume sensitivity of 395 cps/MBq. Noiseless simulations show sufficient axial

  11. Collimator design for a multipinhole brain SPECT insert for MRI

    SciTech Connect

    Van Audenhaege, Karen; Van Holen, Roel; Vanhove, Christian; Vandenberghe, Stefaan

    2015-11-15

    Purpose: Brain single photon emission computed tomography (SPECT) imaging is an important clinical tool, with unique tracers for studying neurological diseases. Nowadays, most commercial SPECT systems are combined with x-ray computed tomography (CT) in so-called SPECT/CT systems to obtain an anatomical background for the functional information. However, while CT images have a high spatial resolution, they have a low soft-tissue contrast, which is an important disadvantage for brain imaging. Magnetic resonance imaging (MRI), on the other hand, has a very high soft-tissue contrast and does not involve extra ionizing radiation. Therefore, the authors designed a brain SPECT insert that can operate inside a clinical MRI. Methods: The authors designed and simulated a compact stationary multipinhole SPECT insert based on digital silicon photomultiplier detector modules, which have shown to be MR-compatible and have an excellent intrinsic resolution (0.5 mm) when combined with a monolithic 2 mm thick LYSO crystal. First, the authors optimized the different parameters of the SPECT system to maximize sensitivity for a given target resolution of 7.2 mm in the center of the field-of-view, given the spatial constraints of the MR system. Second, the authors performed noiseless simulations of two multipinhole configurations to evaluate sampling and reconstructed resolution. Finally, the authors performed Monte Carlo simulations and compared the SPECT insert with a clinical system with ultrahigh-resolution (UHR) fan beam collimators, based on contrast-to-noise ratio and a visual comparison of a Hoffman phantom with a 9 mm cold lesion. Results: The optimization resulted in a stationary multipinhole system with a collimator radius of 150.2 mm and a detector radius of 172.67 mm, which corresponds to four rings of 34 diSPM detector modules. This allows the authors to include eight rings of 24 pinholes, which results in a system volume sensitivity of 395 cps/MBq. Noiseless simulations

  12. Self-collimation Mach-Zehnder interferometer based polarization-independent beam splitter

    NASA Astrophysics Data System (ADS)

    Lin, Guimin; Chen, Xiyao; Fu, Ping

    2016-12-01

    A polarization-independent beam splitter (PIBS) based on self-collimation Mach-Zehnder interferometer (SMZI) in a hole-type silicon photonic crystal (PC) is proposed and numerically demonstrated. Utilizing polarization dependence of the transmission spectra of the SMZI and polarization transmission matching method, the SMZI can work as a PIBS by selecting appropriate path length difference in the structure. For a certain operating frequency, the PIBS has the same splitting ratio for both transverse-electric mode and transverse-magnetic mode. In this paper, the PIBS with splitting ratios of 1∶1 and 1∶2 is designed and numerically demonstrated, respectively. For the operating wavelength of 1550 nm, the sizes of the PIBS are only 19.7 μm×19.7 μm. With its small dimensions, simple structure, and silicon-based material, this PIBS may have practical applications in photonic-integrated circuits.

  13. Radiation collimation in a thick crystalline undulator

    NASA Astrophysics Data System (ADS)

    Wistisen, Tobias Nyholm; Uggerhøj, Ulrik Ingerslev; Hansen, John Lundsgaard; Lauth, Werner; Klag, Pascal

    2017-05-01

    With the recent experimental confirmation of the existence of energetic radiation from a Small Amplitude, Small Period (SASP) crystalline undulator [T.N. Wistisen, K.K. Andersen, S. Yilmaz, R. Mikkelsen, J. Lundsgaard Hansen, U.I. Uggerhøj, W. Lauth, H. Backe, Phys. Rev. Lett. 112, 254801 (2014)], the field of specially manufactured crystals, from which specific radiation characteristics can be obtained, has evolved substantially. In this paper we confirm the existence of the crystalline undulator radiation, using electrons of energies of 855 GeV from the MAinzer MIcrotron (MAMI) in a crystal that is approximately 10 times thicker than the previous one. Furthermore, we have measured a significant increase in enhancement, in good agreement with calculations, of the undulator peak by collimation to angles smaller than the natural opening angle of the radiation emission process, 1 /γ. Contribution to the Topical Issue: "Dynamics of Systems at the Nanoscale", edited by Andrey Solov'yov and Andrei Korol.

  14. Self-collimated unstable resonator semiconductor laser

    NASA Technical Reports Server (NTRS)

    Lang, Robert J. (Inventor)

    1993-01-01

    Self-collimation of the output is achieved in an unstable resonator semiconductor laser by providing a large concave mirror M sub 1 and a small convex mirror M sub 2 on opposite surfaces of a semiconductor body of a material having an effective index of refraction denoted by n, where the respective mirror radii R sub 1, R sub 2 and beam radii r sub 1, r sub 2 are chosen to satisfy a condition (R sub 2)/(1 + r sub 1) = (n - 1)/n, with a value of geometric magnification 1 less than or equal to M less than or equal to (n + 1)/(n - 1) where r sub 1 and r sub 2 are the radii of counterpropagating beams at respective mirrors of radii R sub 1 and R sub 2.

  15. Cometary Jet Collimation Without Physical Confinement

    NASA Astrophysics Data System (ADS)

    Steckloff, J. K.; Melosh, H. J.

    2012-12-01

    Recent high-resolution images of comet nuclei reveal that gases and dust expelled by the comet are organized into narrow jets. Contemporary models postulate that these jets collimate when the expanding gases and dust pass through a physical aperture or nozzle. However, recent high-resolution spacecraft observations fail to detect such apertures on cometary surfaces. Furthermore, these models do not explain why cometary jets appear to be directed normal to the local gravitational potential, and/or appear to originate on the faces of scarps. Additionally, observations of comet nuclei by visiting spacecraft have observed that jet activity is tied to the diurnal rotation of the comet. This suggests that jet emissions are powered by the sun, and therefore must emanate from close to the surface of the comet due to a thermal skin depth on the order of ~10 cm. Here we describe a simplified computer model of jets emanating from Comet Tempel 1. Our novel mechanism is based on the occurrence of fluidized flows, which have gained observational support from the Deep Impact and Stardust-NExT flyby missions We approximate the vents of the comet as a region of smooth terrain on the order of ~10 m in width. We assume that each element of the active area is emitting gas molecules with the same spatial distribution function, and integrate over the active area in order to calculate the gas drag force due to the vent. We consider two angular emission profiles (isotropic and lambertian), and assume plane-strain geometry. The vent surfaces were modeled at various angles with respect to the gravitational potential. To approximate scarps, we modeled a non-venting region located above the vent and at the same angle as the vent. The size of this non-venting region was allowed to vary. We assumed that the scarp face, which is composed of the vent and non-venting regions, eroded uniformly. Particles of a constant size are placed randomly on the surface of the vent, and their positions in time

  16. Ion beam collimating grid to reduce added defects

    DOEpatents

    Lindquist, Walter B.; Kearney, Patrick A.

    2003-01-01

    A collimating grid for an ion source located after the exit grid. The collimating grid collimates the ion beamlets and disallows beam spread and limits the beam divergence during transients and steady state operation. The additional exit or collimating grid prevents beam divergence during turn-on and turn-off and prevents ions from hitting the periphery of the target where there is re-deposited material or from missing the target and hitting the wall of the vessel where there is deposited material, thereby preventing defects from being deposited on a substrate to be coated. Thus, the addition of a collimating grid to an ion source ensures that the ion beam will hit and be confined to a specific target area.

  17. Preliminary Exploratory Study of Different Phase II Collimators

    SciTech Connect

    Lari, L.; Assmann, R.W.; Bertarelli, A.; Bracco, C.; Brugger, M.; Cerutti, F.; Dallocchio, A.; Ferrari, A.; Mauri, M.; Roesler, S.; Sarchiapone, L.; Vlachoudis, Vasilis; Doyle, J.E.; Keller, L.; Lundgren, S.A.; Markiewicz, Thomas W.; Smith, J.C.; Lari, L.; /LPHE, Lausanne

    2011-11-02

    The Large Hadron Collider (LHC) collimation system is installed and commissioned in different phases, following the natural evolution of the LHC performance. To improve cleaning efficiency towards the end of the low beta squeeze at 7TeV, and in stable physics conditions, it is foreseen to complement the 30 highly robust Phase I secondary collimators with low impedance Phase II collimators. At this stage, their design is not yet finalized. Possible options include metallic collimators, graphite jaws with a movable metallic foil, or collimators with metallic rotating jaws. As part of the evaluation of the different designs, the FLUKA Monte Carlo code is extensively used for calculating energy deposition and studying material damage and activation. This report outlines the simulation approach and defines the critical quantities involved.

  18. Proton Collimator for Fusion Energy Extraction

    NASA Astrophysics Data System (ADS)

    Momota, Hiromu; Miley, George

    2001-10-01

    A proton collimator concept is under study for use with various fusion devices such as an inertial confinement fusion (IEC) reactor. G. H. Miley, et al., IEEE Trans. on Plasma Science, 25 (1997), 733. It consists essentially of a pair of coils anti-parallel to an external magnetic channel. Spacing of the coils is equal to the coil radius, forming a "Helmholtz Coil". To eliminate the attractive force between pair coils, a stabilization coil is installed anti-parallel to pair coils. The resulting magnetic configuration is cylindrically symmetric. Currents on each coil are chosen to chancel the magnetic field at the center, forming a hexa-pole magnetic configuration. With the zero-field region near the plasma center, an inertial confinement fusion (ICF) reactor or the IEC could be operated without interference. Isotropic fusion protons, as well as leaking fuel components, from D-D or D-He3 fusion will be collimated by the outer magnetic field. This stream can then be lead to a traveling wave direct energy converter, TWDEC, H. Momota, et al., Fusion Technology, 21 (1992), 2307-2323. or to a thruster for space propulsion. H. Momota, et al., AIAA Joint Propulsion Conf., Huntsville Al. Bombardment of particles on structural devices can largely be avoided by optimizing current ratios on the pair and stabilization coils. Another property of this design is that it scatters charged particles into random directions near the center, providing a separation of low-energy leaking unburned fuel components from energetic fusion products. Such separation is essential for use with a TWDEC or for a space thruster to avoid unwanted waste of costly fuel components. A quantitative discussion of these features will be presented.

  19. Estimation of photoneutron yield in linear accelerator with different collimation systems by Geant4 and MCNPX simulation codes.

    PubMed

    Kim, Yoon Sang; Khazaei, Zeinab; Ko, Junho; Afarideh, Hossein; Ghergherehchi, Mitra

    2016-04-07

    At present, the bremsstrahlung photon beams produced by linear accelerators are the most commonly employed method of radiotherapy for tumor treatments. A photoneutron source based on three different energies (6, 10 and 15 MeV) of a linac electron beam was designed by means of Geant4 and Monte Carlo N-Particle eXtended (MCNPX) simulation codes. To obtain maximum neutron yield, two arrangements for the photo neutron convertor were studied: (a) without a collimator, and (b) placement of the convertor after the collimator. The maximum photon intensities in tungsten were 0.73, 1.24 and 2.07 photon/e at 6, 10 and 15 MeV, respectively. There was no considerable increase in the photon fluence spectra from 6 to 15 MeV at the optimum thickness between 0.8 mm and 2 mm of tungsten. The optimum dimensions of the collimator were determined to be a length of 140 mm with an aperture of 5 mm  ×  70 mm for iron in a slit shape. According to the neutron yield, the best thickness obtained for the studied materials was 30 mm. The number of neutrons generated in BeO achieved the maximum value at 6 MeV, unlike that in Be, where the highest number of neutrons was observed at 15 MeV. Statistical uncertainty in all simulations was less than 0.3% and 0.05% for MCNPX and the standard electromagnetic (EM) physics packages of Geant4, respectively. Differences among spectra in various regions are due to various cross-section and stopping power data and different simulations of the physics processes.

  20. Photon-photon collisions

    SciTech Connect

    Brodsky, S.J.

    1988-07-01

    Highlights of the VIIIth International Workshop on Photon-Photon Collisions are reviewed. New experimental and theoretical results were reported in virtually every area of ..gamma gamma.. physics, particularly in exotic resonance production and tests of quantum chromodynamics where asymptotic freedom and factorization theorems provide predictions for both inclusive and exclusive ..gamma gamma.. reactions at high momentum transfer. 73 refs., 12 figs.

  1. Dispersion in photonic crystals

    NASA Astrophysics Data System (ADS)

    Witzens, Jeremy

    2005-11-01

    Investigations on the dispersive properties of photonic crystals, modified scattering in ring-resonators, monolithic integration of vertical-cavity surface-emitting lasers and advanced data processing techniques for the finite-difference time-domain method are presented. Photonic crystals are periodic mesoscopic arrays of scatterers that modify the propagation properties of electromagnetic waves in a similar way as "natural" crystals modify the properties of electrons in solid-state physics. In this thesis photonic crystals are implemented as planar photonic crystals, i.e., optically thin semiconductor films with periodic arrays of holes etched into them, with a hole-to-hole spacing of the order of the wavelength of light in the dielectric media. Photonic crystals can feature forbidden frequency ranges (the band-gaps) in which light cannot propagate. Even though most work on photonic crystals has focused on these band-gaps for application such as confinement and guiding of light, this thesis focuses on the allowed frequency regions (the photonic bands) and investigates how the propagation of light is modified by the crystal lattice. In particular the guiding of light in bulk photonic crystals in the absence of lattice defects (the self-collimation effect) and the angular steering of light in photonic crystals (the superprism effect) are investigated. The latter is used to design a planar lightwave circuit for frequency domain demultiplexion. Difficulties such as efficient insertion of light into the crystal are resolved and previously predicted limitations on the resolution are circumvented. The demultiplexer is also fabricated and characterized. Monolithic integration of vertical-cavity surface-emitting lasers by means of resonantly enhanced grating couplers is investigated. The grating coupler is designed to bend light through a ninety-degree angle and is characterized with the finite-difference time-domain method. The vertical-cavity surface-emitting lasers are

  2. A four mirror anastigmat collimator design for optical payload calibration

    NASA Astrophysics Data System (ADS)

    Rolt, Stephen; Calcines, Ariadna; Lomanowski, Bart A.; Bramall, David G.

    2016-07-01

    We present here a four mirror anastigmatic optical collimator design intended for the calibration of an earth observation satellite instrument. Specifically, the collimator is to be applied to the ground based calibration of the Sentinel-4/UVN instrument. This imaging spectrometer instrument itself is expected to be deployed in 2019 in a geostationary orbit and will make spatially resolved spectroscopic measurements of atmospheric contaminants. The collimator is to be deployed during the ground based calibration only and does not form part of the instrument itself. The purpose of the collimator is to provide collimated light within the two instrument passbands in the UV-VIS (305 - 500 nm) and the NIR (750 - 775 nm). Moreover, that collimated light will be derived from a variety of slit like objects located at the input focal (object) plane of the collimator which is uniformly illuminated by a number of light sources. The collimator must relay these objects with exceptionally high fidelity. To this end, the wavefront error of the collimator should be less than 30 nm rms across the collimator field of view. This field is determined by the largest object which is a large rectangular slit, 4.4° x 0.25°. Other important considerations affecting the optical design are the requirements for input telecentricity and the size (85 mm) and location (2500 mm `back focal distance') of the exit pupil. The design of the instrument against these basic requirements is discussed in detail. In addition an analysis of the straylight and tolerancing is presented in detail.

  3. High-sensitivity brain SPECT system using cadmium telluride (CdTe) semiconductor detector and 4-pixel matched collimator.

    PubMed

    Suzuki, Atsuro; Takeuchi, Wataru; Ishitsu, Takafumi; Tsuchiya, Katsutoshi; Morimoto, Yuichi; Ueno, Yuichiro; Kobashi, Keiji; Kubo, Naoki; Shiga, Tohru; Tamaki, Nagara

    2013-11-07

    For high-sensitivity brain imaging, we have developed a two-head single-photon emission computed tomography (SPECT) system using a CdTe semiconductor detector and 4-pixel matched collimator (4-PMC). The term, '4-PMC' indicates that the collimator hole size is matched to a 2 × 2 array of detector pixels. By contrast, a 1-pixel matched collimator (1-PMC) is defined as a collimator whose hole size is matched to one detector pixel. The performance of the higher-sensitivity 4-PMC was experimentally compared with that of the 1-PMC. The sensitivities of the 1-PMC and 4-PMC were 70 cps/MBq/head and 220 cps/MBq/head, respectively. The SPECT system using the 4-PMC provides superior image resolution in cold and hot rods phantom with the same activity and scan time to that of the 1-PMC. In addition, with half the usual scan time the 4-PMC provides comparable image quality to that of the 1-PMC. Furthermore, (99m)Tc-ECD brain perfusion images of healthy volunteers obtained using the 4-PMC demonstrated acceptable image quality for clinical diagnosis. In conclusion, our CdTe SPECT system equipped with the higher-sensitivity 4-PMC can provide better spatial resolution than the 1-PMC either in half the imaging time with the same administered activity, or alternatively, in the same imaging time with half the activity.

  4. High-sensitivity brain SPECT system using cadmium telluride (CdTe) semiconductor detector and 4-pixel matched collimator

    NASA Astrophysics Data System (ADS)

    Suzuki, Atsuro; Takeuchi, Wataru; Ishitsu, Takafumi; Tsuchiya, Katsutoshi; Morimoto, Yuichi; Ueno, Yuichiro; Kobashi, Keiji; Kubo, Naoki; Shiga, Tohru; Tamaki, Nagara

    2013-11-01

    For high-sensitivity brain imaging, we have developed a two-head single-photon emission computed tomography (SPECT) system using a CdTe semiconductor detector and 4-pixel matched collimator (4-PMC). The term, ‘4-PMC’ indicates that the collimator hole size is matched to a 2 × 2 array of detector pixels. By contrast, a 1-pixel matched collimator (1-PMC) is defined as a collimator whose hole size is matched to one detector pixel. The performance of the higher-sensitivity 4-PMC was experimentally compared with that of the 1-PMC. The sensitivities of the 1-PMC and 4-PMC were 70 cps/MBq/head and 220 cps/MBq/head, respectively. The SPECT system using the 4-PMC provides superior image resolution in cold and hot rods phantom with the same activity and scan time to that of the 1-PMC. In addition, with half the usual scan time the 4-PMC provides comparable image quality to that of the 1-PMC. Furthermore, 99mTc-ECD brain perfusion images of healthy volunteers obtained using the 4-PMC demonstrated acceptable image quality for clinical diagnosis. In conclusion, our CdTe SPECT system equipped with the higher-sensitivity 4-PMC can provide better spatial resolution than the 1-PMC either in half the imaging time with the same administered activity, or alternatively, in the same imaging time with half the activity.

  5. Collimator Magnet with Functionally Defined Profile for Ion Implantation

    SciTech Connect

    Nicolaescu, Dan; Gotoh, Yasuhito; Sakai, Shigeki; Ishikawa, Junzo

    2011-01-07

    Advanced implantation systems used for semiconductor processing should have high precision of ion beam collimation (+/-0.1 deg and better) and wide beam aperture (400 mm and more). Typical arrangements of ion implantation systems include beam scanning (BSM) and collimator magnets (CM). Standard collimator magnets have limited precision of beam collimation due to magnetic poles that have piecewise circular profile. This study proposes a novel ''constant sum angle collimator magnet''(CSACM) with non-circular magnetic pole profile. Angles of incidence {alpha}{sub i} and exit {alpha}{sub e} are defined as angles between ion trajectory and local normal to CM input/output magnetic pole edge. Profile of the CSACM is defined as having constant algebraic sum {alpha}{sub i}+{alpha}{sub e} = const for every ion trajectory of the scanned beam, in addition to ''usual'' beam collimation. An iterative procedure allows improve CSACM taking into account magnetic fringe field effects. Simulation results prove that CSACM assures precise beam collimation in two orthogonal planes. Circular approximations for CSACM magnetic poles are proposed. The model may be further developed for global design of the ion beam line (BSM+CM) and for taking into account space-charge effects.

  6. Effect of detector collimator and sample thickness on 0.662 MeV multiply Compton-scattered gamma rays.

    PubMed

    Singh, Manpreet; Singh, Gurvinderjit; Sandhu, B S; Singh, Bhajan

    2006-03-01

    The simultaneous effect of detector collimator and sample thickness on 0.662 MeV multiply Compton-scattered gamma photons was studied experimentally. An intense collimated beam, obtained from 6-Ci (137)Cs source, is allowed to impinge on cylindrical aluminium samples of varying diameter and the scattered photons are detected by a 51 mm x 51 mm NaI(Tl) scintillation detector placed at 90 degrees to the incident beam. The full energy peak corresponding to singly scattered events is reconstructed analytically. The thickness at which the multiply scattered events saturate is determined for different detector collimators. The parameters like signal-to-noise ratio and multiply scatter fraction (MSF) have also been deduced and support the work carried out by Shengli et al. [2000. EGS4 simulation of Compton scattering for nondestructive testing. KEK proceedings 200-20, Tsukuba, Japan, pp. 216-223] and Barnea et al. [1995. A study of multiple scattering background in Compton scatter imaging. NDT & E International 28, 155-162] based upon Monte Carlo calculations.

  7. The HEAO-1 Scanning Modulation Collimator

    NASA Astrophysics Data System (ADS)

    Schwartz, Daniel A.

    2013-01-01

    My niche on this panel seems to be the High Energy Astronomy Observatory-1 Scanning Modulation Collimator experiment. Our chair, Hale Bradt, and the late Herb Gursky each proposed a different version modulation collimator, which was condensed by NASA via "forced marriage," to the SMC. I worked as Project Scientist under Herb, later inheriting the PI role. The MIT Project Scientist, the late Rodger Doxsey, and I were told "this is your experiment," and "we are a seamless team regardless of institution." Rodger and I were young enough to believe this, and we made it happen (and not always with the best results vis a vis higher internal management). I was never interested in astronomy, and allegedly am still not. Why do an astro-metrical job of measuring and reporting the coordinates of X-ray sources? In fact we participated widely in the identification of the sources with astronomical object, and making each paper a discussion of the physics of the emission. An enjoyable way to learn some astronomy. The stated purpose of the Gursky/Bradt experiment was to enable optical identifications so that more detailed study could be done. I remember meeting with John Whelan to discuss his collaboration in making the optical identifications. He said he only wanted to study sources after they were identified. For many milliseconds I became very angry - "who is going to to the work to MAKE those identifications," but luckily before speaking I realized how satisfying it was that astronomers indeed wanted to study X-ray sources in other wavebands. The second biggest excitement in the HEAO-1 program was the "glitches" that appeared in the gyro data during final functional testing. This took some high-powered politics by all the PI's to convince MSFC to delay for 4 months, replacing the "funny" unit with one from HEAO-2 (Einstein) and later refurbishing that unit. Third biggest excitement was when a computer failed and final checkout during countdown at the Cape was done by looking at

  8. Design and simulation of a full-ring multi-lofthole collimator for brain SPECT

    NASA Astrophysics Data System (ADS)

    Van Audenhaege, Karen; Vandenberghe, Stefaan; Deprez, Karel; Vandeghinste, Bert; Van Holen, Roel

    2013-09-01

    Currently, clinical brain single photon emission computed tomography (SPECT) is mostly performed using rotating dual-head gamma cameras equipped with low-energy-high-resolution parallel-beam collimators (LEHR PAR). The resolution of these systems is rather poor (8-10 mm) and the rotation of the heavy gamma cameras can introduce misalignment errors. Therefore, we designed a static full-ring multi-lofthole brain SPECT insert for an existing ring of LaBr3 (5% Ce) detectors. The novelty of the design is found in the shutter mechanism that makes the system very flexible and eliminates the need for rotating parts. A stationary SPECT insert is not only more robust, it is also easier to integrate in a magnetic resonance imaging system (MRI) for simultaneous SPECT-MRI. The target spatial resolution of our design is 6 mm. In this study we used analytical calculations to optimize the collimator for an existing ring of LaBr3 (5% Ce) detectors. We fixed the target spatial resolution at 6 mm in the center of the field-of-view and maximized the volume sensitivity by changing the collimator radius, the aperture and the number of loftholes. Based on these optimal parameters we simulated phantom data and evaluated the image quality of our multi-lofthole system. We simulated a noiseless uniform and Defrise phantom to assess artifacts and sampling completeness and a noiseless hot-rod phantom to assess the reconstructed spatial resolution. We visually evaluated a simulated noisy Hoffman phantom with two lesions. Then, we evaluated the non-prewhitening matched filter signal-to-noise ratio (NPW-SNR) in two lesion detectability phantoms: one with hot lesions and one with cold lesions. Finally, a contrast-to-noise (CNR) study was performed on a phantom with both hot and cold lesions of different sizes (6-16 mm). All results were compared to a LEHR PAR system. The optimization resulted in a final collimator design with a volume sensitivity of 1.55 × 10-4 cps Bq-1, which is 2.5 times lower

  9. Design and simulation of a full-ring multi-lofthole collimator for brain SPECT.

    PubMed

    Van Audenhaege, Karen; Vandenberghe, Stefaan; Deprez, Karel; Vandeghinste, Bert; Van Holen, Roel

    2013-09-21

    Currently, clinical brain single photon emission computed tomography (SPECT) is mostly performed using rotating dual-head gamma cameras equipped with low-energy-high-resolution parallel-beam collimators (LEHR PAR). The resolution of these systems is rather poor (8-10 mm) and the rotation of the heavy gamma cameras can introduce misalignment errors. Therefore, we designed a static full-ring multi-lofthole brain SPECT insert for an existing ring of LaBr3 (5% Ce) detectors. The novelty of the design is found in the shutter mechanism that makes the system very flexible and eliminates the need for rotating parts. A stationary SPECT insert is not only more robust, it is also easier to integrate in a magnetic resonance imaging system (MRI) for simultaneous SPECT-MRI. The target spatial resolution of our design is 6 mm. In this study we used analytical calculations to optimize the collimator for an existing ring of LaBr3 (5% Ce) detectors. We fixed the target spatial resolution at 6 mm in the center of the field-of-view and maximized the volume sensitivity by changing the collimator radius, the aperture and the number of loftholes. Based on these optimal parameters we simulated phantom data and evaluated the image quality of our multi-lofthole system. We simulated a noiseless uniform and Defrise phantom to assess artifacts and sampling completeness and a noiseless hot-rod phantom to assess the reconstructed spatial resolution. We visually evaluated a simulated noisy Hoffman phantom with two lesions. Then, we evaluated the non-prewhitening matched filter signal-to-noise ratio (NPW-SNR) in two lesion detectability phantoms: one with hot lesions and one with cold lesions. Finally, a contrast-to-noise (CNR) study was performed on a phantom with both hot and cold lesions of different sizes (6-16 mm). All results were compared to a LEHR PAR system. The optimization resulted in a final collimator design with a volume sensitivity of 1.55 × 10(-4) cps Bq(-1), which is 2.5

  10. Development of hollow electron beams for proton and ion collimation

    SciTech Connect

    Stancari, G.; Drozhdin, A.I.; Kuznetsov, G.; Shiltsev, V.; Still, D.A.; Valishev, A.; Vorobiev, L.G.; Assmann, R.; Kabantsev, A.; /UC, San Diego

    2010-06-01

    Magnetically confined hollow electron beams for controlled halo removal in high-energy colliders such as the Tevatron or the LHC may extend traditional collimation systems beyond the intensity limits imposed by tolerable material damage. They may also improve collimation performance by suppressing loss spikes due to beam jitter and by increasing capture efficiency. A hollow electron gun was designed and built. Its performance and stability were measured at the Fermilab test stand. The gun will be installed in one of the existing Tevatron electron lenses for preliminary tests of the hollow-beam collimator concept, addressing critical issues such as alignment and instabilities of the overlapping proton and electron beams.

  11. SECONDARY ELECTRON PRODUCTION AT THE SNS STORAGE RING COLLIMATOR.

    SciTech Connect

    ZHANG,S.Y.

    1999-03-29

    Secondary electron (SE) production is briefly reviewed. If the collimator of the SNS storage ring allows proton beam scraping to take place, the electron yield might be quite large. At the AGS Booster, by steering the Au{sup 31+} ion beam into the electrostatic inflector, beam scraping effect on SE production is studied. The results of this experiment can be translated into the situation of proton beam scraping at the SNS collimator. It seems sufficient to support a new look of the SNS ring collimator design.

  12. High resolution collimator system for X-ray detector

    DOEpatents

    Eberhard, Jeffrey W.; Cain, Dallas E.

    1987-01-01

    High resolution in an X-ray computerized tomography (CT) inspection system is achieved by using a collimator