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Sample records for helical tomotherapy beams

  1. Shielding requirements in helical tomotherapy

    NASA Astrophysics Data System (ADS)

    Baechler, S.; Bochud, F. O.; Verellen, D.; Moeckli, R.

    2007-08-01

    Helical tomotherapy is a relatively new intensity-modulated radiation therapy (IMRT) treatment for which room shielding has to be reassessed for the following reasons. The beam-on-time needed to deliver a given target dose is increased and leads to a weekly workload of typically one order of magnitude higher than that for conventional radiation therapy. The special configuration of tomotherapy units does not allow the use of standard shielding calculation methods. A conventional linear accelerator must be shielded for primary, leakage and scatter photon radiations. For tomotherapy, primary radiation is no longer the main shielding issue since a beam stop is mounted on the gantry directly opposite the source. On the other hand, due to the longer irradiation time, the accelerator head leakage becomes a major concern. An analytical model based on geometric considerations has been developed to determine leakage radiation levels throughout the room for continuous gantry rotation. Compared to leakage radiation, scatter radiation is a minor contribution. Since tomotherapy units operate at a nominal energy of 6 MV, neutron production is negligible. This work proposes a synthetic and conservative model for calculating shielding requirements for the Hi-Art II TomoTherapy unit. Finally, the required concrete shielding thickness is given for different positions of interest.

  2. Shielding requirements in helical tomotherapy.

    PubMed

    Baechler, S; Bochud, F O; Verellen, D; Moeckli, R

    2007-08-21

    Helical tomotherapy is a relatively new intensity-modulated radiation therapy (IMRT) treatment for which room shielding has to be reassessed for the following reasons. The beam-on-time needed to deliver a given target dose is increased and leads to a weekly workload of typically one order of magnitude higher than that for conventional radiation therapy. The special configuration of tomotherapy units does not allow the use of standard shielding calculation methods. A conventional linear accelerator must be shielded for primary, leakage and scatter photon radiations. For tomotherapy, primary radiation is no longer the main shielding issue since a beam stop is mounted on the gantry directly opposite the source. On the other hand, due to the longer irradiation time, the accelerator head leakage becomes a major concern. An analytical model based on geometric considerations has been developed to determine leakage radiation levels throughout the room for continuous gantry rotation. Compared to leakage radiation, scatter radiation is a minor contribution. Since tomotherapy units operate at a nominal energy of 6 MV, neutron production is negligible. This work proposes a synthetic and conservative model for calculating shielding requirements for the Hi-Art II TomoTherapy unit. Finally, the required concrete shielding thickness is given for different positions of interest.

  3. Helical tomotherapy superficial dose measurements

    SciTech Connect

    Ramsey, Chester R.; Seibert, Rebecca M.; Robison, Benjamin; Mitchell, Martha

    2007-08-15

    Helical tomotherapy is a treatment technique that is delivered from a 6 MV fan beam that traces a helical path while the couch moves linearly into the bore. In order to increase the treatment delivery dose rate, helical tomotherapy systems do not have a flattening filter. As such, the dose distributions near the surface of the patient may be considerably different from other forms of intensity-modulated delivery. The purpose of this study was to measure the dose distributions near the surface for helical tomotherapy plans with a varying separation between the target volume and the surface of an anthropomorphic phantom. A hypothetical planning target volume (PTV) was defined on an anthropomorphic head phantom to simulate a 2.0 Gy per fraction IMRT parotid-sparing head and neck treatment of the upper neck nodes. A total of six target volumes were created with 0, 1, 2, 3, 4, and 5 mm of separation between the surface of the phantom and the outer edge of the PTV. Superficial doses were measured for each of the treatment deliveries using film placed in the head phantom and thermoluminescent dosimeters (TLDs) placed on the phantom's surface underneath an immobilization mask. In the 0 mm test case where the PTV extends to the phantom surface, the mean TLD dose was 1.73{+-}0.10 Gy (or 86.6{+-}5.1% of the prescribed dose). The measured superficial dose decreases to 1.23{+-}0.10 Gy (61.5{+-}5.1% of the prescribed dose) for a PTV-surface separation of 5 mm. The doses measured by the TLDs indicated that the tomotherapy treatment planning system overestimates superficial doses by 8.9{+-}3.2%. The radiographic film dose for the 0 mm test case was 1.73{+-}0.07 Gy, as compared to the calculated dose of 1.78{+-}0.05 Gy. Given the results of the TLD and film measurements, the superficial calculated doses are overestimated between 3% and 13%. Without the use of bolus, tumor volumes that extend to the surface may be underdosed. As such, it is recommended that bolus be added for these

  4. A Case Report on the Effect of Fan Beam Thickness in Helical Tomotherapy of Nasopharyngeal Carcinoma

    SciTech Connect

    Wu, W.C. Vincent; Mui, Wing Lun A.

    2011-04-01

    The fan beam thickness (FBT) in helical tomotherapy is defined by a pair of collimators parallel to the rotational orbit of the radiation beam and is fixed for a specific patient treatment. The aim of this case study is to evaluate the dosimetric influence of changing the FBT in the treatment of a nasopharyngeal carcinoma (NPC) patient. The subject was a T2N1M0 stage NPC patient. The planning target volumes (PTVs) of the primary nasopharyngeal tumor and the left and right cervical lymphatics were delineated along with the organs at risk (OARs) in the corresponding computed tomography slices. Three treatment plans with FBT of 1.0 cm, 2.5 cm, and 5.0 cm (FBT-10, FBT-25, and FBT-50) were generated separately based on similar dose constraints and planning parameters. The dosimetric results of the PTV and OARs were collected and compared among the 3 treatment plans. The differences in the dose parameters of the PTVs were small among the 3 plans. The FBT-10 plan demonstrated the most homogeneous PTV doses with the smallest homogeneity indices (HIs). The FBT-50 plan delivered the highest dose to the OARs and the FBT-10 plan delivered the lowest. The differences between the 2 plans were more significant in the spinal cord, optic chiasm, optic nerves, and lens. This case study demonstrated that the variation of FBT in tomotherapy affected the quality of the treatment plan mainly in the OAR doses, but not so much in the PTV. Increasing the FBT reduced the effectiveness in the sparing of OARs.

  5. Feasibility of Postmastectomy Treatment With Helical TomoTherapy

    SciTech Connect

    Ashenafi, Michael; Boyd, Robert A.; Lee, Tae K.; Lo, Kenneth K.

    2010-07-01

    Purpose: To investigate the potential of helical tomotherapy for postmastectomy radiation therapy. Methods and Materials: By use of the TomoTherapy Hi-Art II treatment-planning system (TomoTherapy Inc., Madison, WI), helical tomotherapy dose plans were developed for 5 patients and compared with the mixed-beam (electron-photon) plans with which they had been treated. The TomoTherapy plans were evaluated by use of dose-volume quantities, tumor control probability, normal tissue complication probability (NTCP), and secondary cancer complication probability (SCCP). Results: The TomoTherapy plans showed better dose homogeneity in the planning treatment volume containing the chest wall and internal mammary nodes (p = 0.001) and eliminated the need for abutting fields. For the normal tissues, the TomoTherapy plans showed a smaller fractional volume receiving 20Gy or greater for the ipsilateral lung (p = 0.05), no change in NTCP for postradiation pneumonitis, increased SCCP for each lung and both lungs together (p < 0.02), no change in the volume of the heart receiving more than 15Gy, no change in NTCP for excess cardiac mortality, and a larger mean dose and SCCP in the contralateral breast (p < 0.001). For nonspecific tissues, the volume receiving between 5Gy and 25Gy and SCCP were both larger for the TomoTherapy plans (p < 0.01). Total SCCP was larger for the TomoTherapy plans (p = 0.001). Conclusions: Overall, the TomoTherapy plans had comparable tumor control probability and NTCP to the mixed-beam plans and increased SCCP. The TomoTherapy plans showed significantly greater dose homogeneity in the chest wall, which offers the potential for improved cosmesis after treatment. These factors have resulted in TomoTherapy often being the treatment of choice for postmastectomy radiation therapy in our clinic.

  6. Quality assurance of a helical tomotherapy machine

    NASA Astrophysics Data System (ADS)

    Fenwick, J. D.; Tomé, W. A.; Jaradat, H. A.; Hui, S. K.; James, J. A.; Balog, J. P.; DeSouza, C. N.; Lucas, D. B.; Olivera, G. H.; Mackie, T. R.; Paliwal, B. R.

    2004-07-01

    Helical tomotherapy has been developed at the University of Wisconsin, and 'Hi-Art II' clinical machines are now commercially manufactured. At the core of each machine lies a ring-gantry-mounted short linear accelerator which generates x-rays that are collimated into a fan beam of intensity-modulated radiation by a binary multileaf, the modulation being variable with gantry angle. Patients are treated lying on a couch which is translated continuously through the bore of the machine as the gantry rotates. Highly conformal dose-distributions can be delivered using this technique, which is the therapy equivalent of spiral computed tomography. The approach requires synchrony of gantry rotation, couch translation, accelerator pulsing and the opening and closing of the leaves of the binary multileaf collimator used to modulate the radiation beam. In the course of clinically implementing helical tomotherapy, we have developed a quality assurance (QA) system for our machine. The system is analogous to that recommended for conventional clinical linear accelerator QA by AAPM Task Group 40 but contains some novel components, reflecting differences between the Hi-Art devices and conventional clinical accelerators. Here the design and dosimetric characteristics of Hi-Art machines are summarized and the QA system is set out along with experimental details of its implementation. Connections between this machine-based QA work, pre-treatment patient-specific delivery QA and fraction-by-fraction dose verification are discussed.

  7. Reducing the probability of radiation-induced hepatic toxicity by changing the treatment modality from helical tomotherapy to fixed-beam intensity-modulated radiotherapy

    PubMed Central

    Song, Jin Ho; Son, Seok Hyun; Kay, Chul Seung; Jang, Hong Seok

    2015-01-01

    Purpose To estimate and compare the risk of radiation-induced hepatic toxicity (RIHT) in helical tomotherapy and fixed-beam intensity-modulated radiotherapy (IMRT) for the treatment of hepatocellular carcinoma (HCC). Materials and Methods Twenty patients with unresectable HCC treated with tomotherapy were selected. We performed tomotherapy re-planning to reduce the non-target normal liver volume receiving a dose of more than 15 Gy (NTNL-V15Gy), and we created a fixed-beam IMRT plan (FB-P). We compared the dosimetric results as well as the estimated probability of RIHT among the tomotherapy initial plan (T-IP), the tomotherapy re-plan (T-RP), and the FB-P. Results Comparing the T-RP and FB-P, the homogeneity index was 0.11 better with the T-RP. However, the mean NTNL-V15Gy was 6.3% lower with the FB-P. These differences result in a decline in the probability of RIHT from 0.216 in the T-RP to 0.115 in the FB-P. In patients whose NTNL-V15Gy was higher than 43.2% with the T-RP, the probability of RIHT markedly reduced from 0.533 to 0.274. Conclusions By changing the treatment modality from tomotherapy to fixed-beam IMRT, we could reduce the liver dose and the probability of RIHT without scarifying the target coverage, especially in patients whose liver dose is high. PMID:26376679

  8. Helical tomotherapy quality assurance with ArcCHECK

    SciTech Connect

    Chapman, David; Barnett, Rob; Yartsev, Slav

    2014-07-01

    To design a quality assurance (QA) procedure for helical tomotherapy that measures multiple beam parameters with 1 delivery and uses a rotating gantry to simulate treatment conditions. The customized QA procedure was preprogrammed on the tomotherapy operator station. The dosimetry measurements were performed using an ArcCHECK diode array and an A1SL ion chamber inserted in the central holder. The ArcCHECK was positioned 10 cm above the isocenter so that the 21-cm diameter detector array could measure the 40-cm wide tomotherapy beam. During the implementation of the new QA procedure, separate comparative measurements were made using ion chambers in both liquid and solid water, the tomotherapy onboard detector array, and a MapCHECK diode array for a period of 10 weeks. There was good agreement (within 1.3%) for the beam output and cone ratio obtained with the new procedure and the routine QA measurements. The measured beam energy was comparable (0.3%) to solid water measurement during the 10-week evaluation period, excluding 2 of the 10 measurements with unusually high background. The symmetry reading was similarly compromised for those 2 weeks, and on the other weeks, it deviated from the solid water reading by ∼2.5%. The ArcCHECK phantom presents a suitable alternative for performing helical tomotherapy QA, provided the background is collected properly. The proposed weekly procedure using ArcCHECK and water phantom makes the QA process more efficient.

  9. Utility of Megavoltage Fan-Beam CT for Treatment Planning in a Head-And-Neck Cancer Patient with Extensive Dental Fillings Undergoing Helical Tomotherapy

    SciTech Connect

    Yang, Claus; Liu Tianxiao; Jennelle, Richard L.; Ryu, Janice K.; Vijayakumar, Srinivasan; Purdy, James A.; Chen, Allen M.

    2010-07-01

    The purpose of this study was to demonstrate the potential utility of megavoltage fan-beam computed tomography (MV-FBCT) for treatment planning in a patient undergoing helical tomotherapy for nasopharyngeal carcinoma in the presence of extensive dental artifact. A 28-year-old female with locally advanced nasopharyngeal carcinoma presented for radiation therapy. Due to the extensiveness of the dental artifact present in the oral cavity kV-CT scan acquired at simulation, which made treatment planning impossible on tomotherapy planning system, MV-FBCT imaging was obtained using the HI-ART tomotherapy treatment machine, with the patient in the treatment position, and this information was registered with her original kV-CT scan for the purposes of structure delineation, dose calculation, and treatment planning. To validate the feasibility of the MV-FBCT-generated treatment plan, an electron density CT phantom (model 465, Gammex Inc., Middleton, WI) was scanned using MV-FBCT to obtain CT number to density table. Additionally, both a 'cheese' phantom (which came with the tomotherapy treatment machine) with 2 inserted ion chambers and a generic phantom called Quasar phantom (Modus Medical Devices Inc., London, ON, Canada) with one inserted chamber were used to confirm dosimetric accuracy. The MV-FBCT could be used to clearly visualize anatomy in the region of the dental artifact and provide sufficient soft-tissue contrast to assist in the delineation of normal tissue structures and fat planes. With the elimination of the dental artifact, the MV-FBCT images allowed more accurate dose calculation by the tomotherapy system. It was confirmed that the phantom material density was determined correctly by the tomotherapy MV-FBCT number to density table. The ion chamber measurements agreed with the calculations from the MV-FBCT generated phantom plan within 2%. MV-FBCT may be useful in radiation treatment planning for nasopharyngeal cancer patients in the setting of extensive

  10. Helical Tomotherapy for Parotid Gland Tumors

    SciTech Connect

    Lee, Tae Kyu; Rosen, Isaac I.; Gibbons, John P.; Fields, Robert S.; Hogstrom, Kenneth R.

    2008-03-01

    Purpose: To investigate helical tomotherapy (HT) intensity-modulated radiotherapy (IMRT) as a postoperative treatment for parotid gland tumors. Methods and Materials: Helical tomotherapy plans were developed for 4 patients previously treated with segmental multileaf collimator (SMLC) IMRT. A primary planning target volume (PTV64) and two secondary PTVs (PTV60, PTV54) were defined. The clinical goals from the SMLC plans were applied as closely as possible to the HT planning. The SMLC plans included bolus, whereas HT plans did not. Results: In general, the HT plans showed better target coverage and target dose homogeneity. The minimum doses to the desired coverage volume were greater, on average, in the HT plans for all the targets. Minimum PTV doses were larger, on average, in the HT plans by 4.6 Gy (p = 0.03), 4.8 Gy (p = 0.06), and 4.9 Gy (p = 0.06) for PTV64, PTV60, and PTV54, respectively. Maximum PTV doses were smaller, on average, by 2.9 Gy (p = 0.23), 3.2 Gy (p = 0.02), and 3.6 Gy (p = 0.03) for PTV64, PTV60, and PTV54, respectively. Average dose homogeneity index was statistically smaller in the HT plans, and conformity index was larger for PTV64 in 3 patients. Tumor control probabilities were higher for 3 of the 4 patients. Sparing of normal structures was comparable for the two techniques. There were no significant differences between the normal tissue complication probabilities for the HT and SMLC plans. Conclusions: Helical tomotherapy treatment plans were comparable to or slightly better than SMLC plans. Helical tomotherapy is an effective alternative to SMLC IMRT for treatment of parotid tumors.

  11. Rotational output and beam quality evaluations for helical tomotherapy with use of a third-party quality assurance tool.

    PubMed

    Shimizu, Hidetoshi; Sasaki, Koji; Iwata, Manabu; Kawai, Minoru; Nakashima, Kuniyasu; Kubota, Takashi; Osaki, Hikaru; Nakayama, Masashi; Yoshimoto, Manabu; Kodaira, Takeshi

    2016-01-01

    Our aim was to determine whether a third-party quality assurance (QA) tool was suitable for the measurement of rotational output and beam quality in place of on-board detector signals. A Rotational Therapy Phantom 507 (507 Phantom) was used as a QA tool. The rotational output constancy (ROC507) and the beam quality index ([Formula: see text]) were evaluated by analysis of signals from an ion chamber inserted into the 507 Phantom. On-board detector signals were obtained for comparisons with the data from the 507 Phantom. The rotational output (ROC(detector)) and beam quality (corrected cone ratio; CCR) were determined by analysis of on-board detector signals that were generated by irradiation. The tissue phantom ratio at depth 20 and 10 cm (TPR20, 10) was measured with a Farmer-type ionization chamber inserted in a plastic-slab phantom. For rotational output measurement, the correlation coefficient between ROC507 and ROC(detector) values was 0.68 (p < 0.001). ROC507 and ROC(detector) values showed a reduced coefficient of variation after magnetron replacement, which was done during the measurement period. In addition, ROC507 values were reduced significantly along with ROC(detector) values after target replacement (p < 0.001). Regarding the beam quality index, [Formula: see text] showed a change similar to CCR and an increase similar to TPR20, 10 after magnetron/target replacement. This QA tool could check for daily rotational output and detect changes in rotational output and beam quality caused by magnetron or target failure as well as when on-board detector signals were used. Without needing a tomotherapy quality assurance license, we could effectively and quantitatively estimate the rotational output and beam quality at a low cost.

  12. Optimization of helical tomotherapy treatment plans for prostate cancer

    NASA Astrophysics Data System (ADS)

    Grigorov, G.; Kron, T.; Wong, E.; Chen, J.; Sollazzo, J.; Rodrigues, G.

    2003-07-01

    Helical tomotherapy (HT) is a novel treatment approach where the ring gantry irradiation geometry of a helical CT scanner is combined with an intensity-modulated megavoltage x-ray fan beam. An inverse treatment planning system (TomoTherapy Inc., Madison) was used to optimize the treatment plans for ten randomly selected prostate patients. Five different sets of margins (2, 5, 7.5 and 10 mm uniform 3D margins and a non-uniform margin of 5 to 10 mm) were employed for the prostate (GTV2) and seminal vesicles (GTV1). The dose distribution was evaluated in targets, rectum, bladder and femoral heads. HT plans are characterized by a rapid dose fall off around the target in all directions resulting in low doses (less than 30% of the dose at ICRU reference point) to the femurs in all cases. Up to a margin of 5 mm for target structures, it was always possible to satisfy the requirements for dose delivery set by RTOG protocol P-0126. Using a 'class solution', HT plans require minimal operator interaction and result in excellent sparing of normal structures in prostate radiotherapy.

  13. Can We Spare the Pancreas and Other Abdominal Organs at Risk? A Comparison of Conformal Radiotherapy, Helical Tomotherapy and Proton Beam Therapy in Pediatric Irradiation

    PubMed Central

    Jouglar, Emmanuel; Wagner, Antoine; Delpon, Grégory; Campion, Loïc; Meingan, Philippe; Bernier, Valérie; Demoor-Goldschmidt, Charlotte; Mahé, Marc-André; Lacornerie, Thomas; Supiot, Stéphane

    2016-01-01

    Objectives Late abdominal irradiation toxicity during childhood included renal damage, hepatic toxicity and secondary diabetes mellitus. We compared the potential of conformal radiotherapy (CRT), helical tomotherapy (HT) and proton beam therapy (PBT) to spare the abdominal organs at risk (pancreas, kidneys and liver- OAR) in children undergoing abdominal irradiation. Methods We selected children with abdominal tumors who received more than 10 Gy to the abdomen. Treatment plans were calculated in order to keep the dose to abdominal OAR as low as possible while maintaining the same planned target volume (PTV) coverage. Dosimetric values were compared using the Wilcoxon signed-rank test. Results The dose distribution of 20 clinical cases with a median age of 8 years (range 1–14) were calculated with different doses to the PTV: 5 medulloblastomas (36 Gy), 3 left-sided and 2 right-sided nephroblastomas (14.4 Gy to the tumor + 10.8 Gy boost to para-aortic lymphnodes), 1 left-sided and 4 right-sided or midline neuroblastomas (21 Gy) and 5 Hodgkin lymphomas (19.8 Gy to the para-aortic lymphnodes and spleen). HT significantly reduced the mean dose to the whole pancreas (WP), the pancreatic tail (PT) and to the ipsilateral kidney compared to CRT. PBT reduced the mean dose to the WP and PT compared to both CRT and HT especially in midline and right-sided tumors. PBT decreased the mean dose to the ispilateral kidney but also to the contralateral kidney and the liver compared to CRT. Low dose to normal tissue was similar or increased with HT whereas integral dose and the volume of normal tissue receiving at least 5 and 10 Gy were reduced with PBT compared to CRT and HT. Conclusion In children undergoing abdominal irradiation therapy, proton beam therapy reduces the dose to abdominal OAR while sparing normal tissue by limiting low dose irradiation. PMID:27764132

  14. Standard and Nonstandard Craniospinal Radiotherapy Using Helical TomoTherapy

    SciTech Connect

    Parker, William; Brodeur, Marylene; Roberge, David; Freeman, Carolyn

    2010-07-01

    Purpose: To show the advantages of planning and delivering craniospinal radiotherapy with helical TomoTherapy (TomoTherapy Inc., Madison, WI) by presenting 4 cases treated at our institution. Methods and Materials: We first present a standard case of craniospinal irradiation in a patient with recurrent myxopapillary ependymoma (MPE) and follow this with 2 cases requiring differential dosing to multiple target volumes. One of these, a patient with recurrent medulloblastoma, required a lower dose to be delivered to the posterior fossa because the patient had been previously irradiated to the full dose, and the other required concurrent boosts to leptomeningeal metastases as part of his treatment for newly diagnosed MPE. The final case presented is a patient with pronounced scoliosis who required spinal irradiation for recurrent MPE. Results: The four cases presented were planned and treated successfully with Helical Tomotherapy. Conclusions: Helical TomoTherapy delivers continuous arc-based intensity-modulated radiotherapy that gives high conformality and excellent dose homogeneity for the target volumes. Increased healthy tissue sparing is achieved at higher doses albeit at the expense of larger volumes of tissue receiving lower doses. Helical TomoTherapy allows for differential dosing of multiple targets, resulting in very elegant dose distributions. Daily megavoltage computed tomography imaging allows for precision of patient positioning, permitting a reduction in planning margins and increased healthy tissue sparing in comparison with standard techniques.

  15. An absolute dose determination of helical tomotherapy accelerator, TomoTherapy High-Art II

    SciTech Connect

    Bailat, Claude J.; Buchillier, Thierry; Pachoud, Marc; Moeckli, Raphaeel; Bochud, Francois O.

    2009-09-15

    Purpose: A helical tomotherapy accelerator presents a dosimetric challenge because, to this day, there is no internationally accepted protocol for the determination of the absolute dose. Because of this reality, we investigated the different alternatives for characterizing and measuring the absolute dose of such an accelerator. We tested several dosimetric techniques with various metrological traceabilities as well as using a number of phantoms in static and helical modes. Methods: Firstly, the relationship between the reading of ionization chambers and the absorbed dose is dependent on the beam quality value of the photon beam. For high energy photons, the beam quality is specified by the tissue phantom ratio (TPR{sub 20,10}) and it is therefore necessary to know the TPR{sub 20,10} to calculate the dose delivered by a given accelerator. This parameter is obtained through the ratio of the absorbed dose at 20 and 10 cm depths in water and was measured in the particular conditions of the tomotherapy accelerator. Afterward, measurements were performed using the ionization chamber (model A1SL) delivered as a reference instrument by the vendor. This chamber is traceable in absorbed dose to water in a Co-60 beam to a water calorimeter of the American metrology institute (NIST). Similarly, in Switzerland, each radiotherapy department is directly traceable to the Swiss metrology institute (METAS) in absorbed dose to water based on a water calorimeter. For our research, this traceability was obtained by using an ionization chamber traceable to METAS (model NE 2611A), which is the secondary standard of our institute. Furthermore, in order to have another fully independent measurement method, we determined the dose using alanine dosimeters provided by and traceable to the British metrology institute (NPL); they are calibrated in absorbed dose to water using a graphite calorimeter. And finally, we wanted to take into account the type of chamber routinely used in clinical

  16. Spatially fractionated radiotherapy (GRID) using helical tomotherapy.

    PubMed

    Zhang, Xin; Penagaricano, Jose; Yan, Yulong; Liang, Xiaoying; Morrill, Steven; Griffin, Robert J; Corry, Peter; Ratanatharathorn, Vaneerat

    2016-01-08

    Spatially fractionated radiotherapy (GRID) was designed to treat large tumors while sparing skin, and it is usually delivered with a linear accelerator using a commercially available block or multileaf collimator (LINAC-GRID). For deep-seated (skin to tumor distance (> 8 cm)) tumors, it is always a challenge to achieve adequate tumor dose coverage. A novel method to perform GRID treatment using helical tomotherapy (HT-GRID) was developed at our institution. Our approach allows treating patients by generating a patient-specific virtual GRID block (software-generated) and using IMRT technique to optimize the treatment plan. Here, we report our initial clinical experience using HT-GRID, and dosimetric comparison results between HT-GRID and LINAC-GRID. This study evaluates 10 previously treated patients who had deep-seated bulky tumors with complex geometries. Five of these patients were treated with HT-GRID and replanned with LINAC-GRID for comparison. Similarly, five other patients were treated with LINAC-GRID and replanned with HT-GRID for comparison. The prescription was set such that the maximum dose to the GTV is 20 Gy in a single fraction. Dosimetric parameters compared included: mean GTV dose (DGTV mean), GTV dose inhomogeneity (valley-to-peak dose ratio (VPR)), normal tissue doses (DNmean), and other organs-at-risk (OARs) doses. In addition, equivalent uniform doses (EUD) for both GTV and normal tissue were evaluated. In summary, HT-GRID technique is patient-specific, and allows adjustment of the GRID pattern to match different tumor sizes and shapes when they are deep-seated and cannot be adequately treated with LINAC-GRID. HT-GRID delivers a higher DGTV mean, EUD, and VPR compared to LINAC-GRID. HT-GRID delivers a higher DNmean and lower EUD for normal tissue compared to LINAC-GRID. HT-GRID plans also have more options for tumors with complex anatomical relationships between the GTV and the avoidance OARs (abutment or close proximity).

  17. Dosimetric verification of helical tomotherapy for total scalp irradiation

    SciTech Connect

    Hardcastle, Nicholas; Soisson, Emilie; Metcalfe, Peter; Rosenfeld, Anatoly B.; Tome, Wolfgang A.

    2008-11-15

    Total scalp irradiation is a treatment technique used for a variety of superficial malignancies. Helical tomotherapy is an effective technique used for total scalp irradiation. Recent published work has shown the TomoTherapy planning system to overestimate the superficial dose. In this study, the superficial doses for a helical tomotherapy total scalp irradiation have been measured on an anthropomorphic phantom using radiochromic and radiographic film as well as a new skin dosimeter, the MOSkin. The superficial dose was found to be accurately calculated by the TomoTherapy planning system. This is in contrast to recent reports, probably due to a combination of the smaller dose grid resolution used in planning and this particular treatment primarily consisting of beamlets tangential to the scalp. The superficial dose was found to increase from 33.6 to 41.2 Gy and 36.0 to 42.0 Gy over the first 2 mm depth in the phantom in selected regions of the PTV, measured with radiochromic film. The prescription dose was 40 Gy. The superficial dose was at the prescription dose or higher in some regions due to the bolus effect of the thermoplastic head mask and the head rest used to aid treatment setup. It is suggested that to achieve the prescription dose at the surface ({<=}2 mm depth) bolus or a custom thermoplastic helmet is used.

  18. Stereotactic Image-Guided Intensity Modulated Radiotherapy Using the HI-ART II Helical Tomotherapy System

    SciTech Connect

    Holmes, Timothy W. Hudes, Richard; Dziuba, Sylwester; Kazi, Abdul; Hall, Mark; Dawson, Dana

    2008-07-01

    The highly integrated adaptive radiation therapy (HI-ART II) helical tomotherapy unit is a new radiotherapy machine designed to achieve highly precise and accurate treatments at all body sites. The precision and accuracy of the HI-ART II is similar to that provided by stereotactic radiosurgery systems, hence the historical distinction between external beam radiotherapy and stereotactic procedures based on differing precision requirements is removed for this device. The objectives of this work are: (1) to describe stereotactic helical tomotherapy processes (SRS, SBRT); (2) to show that the precision and accuracy of the HI-ART meet the requirements defined for SRS and SBRT; and (3) to describe the clinical implementation of a stereotactic image-guided intensity modulated radiation therapy (IG-IMRT) system that incorporates optical motion management.

  19. Dynamic Jaws and Dynamic Couch in Helical Tomotherapy

    SciTech Connect

    Sterzing, Florian; Uhl, Matthias; Hauswald, Henrik; Schubert, Kai; Sroka-Perez, Gabriele; Chen Yu; Lu Weiguo; Mackie, Rock; Debus, Juergen; Herfarth, Klaus; Oliveira, Gustavo

    2010-03-15

    Purpose: To investigate the next generation of helical tomotherapy delivery with dynamic jaw and dynamic couch movements. Methods and Materials: The new technique of dynamic jaw and dynamic couch movements is described, and a comparative planning study is performed. Ten nasopharyngeal cancer patients with skull base infiltration were chosen for this comparison of longitudinal dose profiles using regular tomotherapy delivery, running-start-stop treatment, and dynamic jaw and dynamic couch delivery. A multifocal simultaneous integrated boost concept was used (70.4Gy to the primary tumor and involved lymph nodes; 57.4Gy to the bilateral cervical lymphatic drainage pathways, 32 fractions). Target coverage, conformity, homogeneity, sparing of organs at risk, integral dose, and radiation delivery time were evaluated. Results: Mean parotid dose for all different deliveries was between 24.8 and 26.1Gy, without significant differences. The mean integral dose was lowered by 6.3% by using the dynamic technique, in comparison with a 2.5-cm-field width for regular delivery and 16.7% with 5-cm-field width for regular delivery. Dynamic jaw and couch movements reduced the calculated radiation time by 66% of the time required with regular 2.5-cm-field width delivery (199 sec vs. 595 sec, p < 0.001). Conclusions: The current delivery mode of helical tomotherapy produces dose distributions with conformal avoidance of parotid glands, brain stem, and spinal cord. The new technology with dynamic jaw and couch movements improves the plan quality by reducing the dose penumbra and thereby reducing the integral dose. In addition, radiation time is reduced by 66% of the regular delivery time.

  20. Helical tomotherapy for duodenal adenocarcinoma in an elderly patient: A case report

    PubMed Central

    Lancellotta, Valentina; Russo, Giuseppe; Lupattelli, Marco; Iacco, Martina; Perrucci, Elisabetta; Zucchetti, Claudio; Falcinelli, Lorenzo; Aristei, Cynthia

    2017-01-01

    To evaluate the efficacy and feasibility of external beam radiotherapy (EBRT) for duodenal adenocarcinoma in an 84-year-old female who underwent EBRT (2.2 Gy/d for a total dose of 46.2 Gy) using helical tomotherapy (HT). Toxicity was evaluated on the National Cancer Institute’s common toxicity criteria (CTCAE 3.0). The patient completed the treatment without G3-G4 toxicity. After 22-mo follow-up, she is alive and well, in complete remission with no late side effects. HT seems to be feasible and effective for duodenal adenocarcinoma in old to very old patients. PMID:28255431

  1. Helical tomotherapy with dynamic running-start-stop delivery compared to conventional tomotherapy delivery

    SciTech Connect

    Rong, Yi; Chen, Yu; Lu, Weiguo; Shang, Lu; Zuo, Li; Chen, Quan

    2014-05-15

    Purpose: Despite superior target dose uniformity, helical tomotherapy{sup ®} (HT) may involve a trade-off between longitudinal dose conformity and beam-on time (BOT), due to the limitation of only three available jaw sizes with the conventional HT (1.0, 2.5, and 5.0 cm). The recently introduced dynamic running-start-stop (RSS) delivery allows smaller jaw opening at the superior and inferior ends of the target when a sharp penumbra is needed. This study compared the dosimetric performance of RSS delivery with the fixed jaw HT delivery. Methods: Twenty patient cases were selected and deidentified prior to treatment planning, including 16 common clinical cases (brain, head and neck (HN), lung, and prostate) and four special cases of whole brain with hippocampus avoidance (WBHA) that require a high degree of dose modulation. HT plans were generated for common clinical cases using the fixed 2.5 cm jaw width (HT2.5) and WBHA cases using 1.0 cm (HT1.0). The jaw widths for RSS were preset with a larger size (RSS5.0 vs HT2.5 and RSS2.5 vs HT1.0). Both delivery techniques were planned based on identical contours, prescriptions, and planning objectives. Dose indices for targets and critical organs were compared using dose-volume histograms, BOT, and monitor units. Results: The average BOT was reduced from 4.8 min with HT2.5 to 2.5 min with RSS5.0. Target dose homogeneity with RSS5.0 was shown comparable to HT2.5 for common clinical sites. Superior normal tissue sparing was observed in RSS5.0 for optic nerves and optic chiasm in brain and HN cases. RSS5.0 demonstrated improved dose sparing for cord and esophagus in lung cases, as well as penile bulb in prostate cases. The mean body dose was comparable for both techniques. For the WBHA cases, the target homogeneity was significantly degraded in RSS2.5 without distinct dose sparing for hippocampus, compared to HT1.0. Conclusions: Compared to the fixed jaw HT delivery, RSS combined with a larger jaw width provides faster

  2. Verification of Calculated Skin Doses in Postmastectomy Helical Tomotherapy

    SciTech Connect

    Ito, Shima; Parker, Brent C.; Levine, Renee; Sanders, Mary Ella; Fontenot, Jonas; Gibbons, John; Hogstrom, Kenneth

    2011-10-01

    Purpose: To verify the accuracy of calculated skin doses in helical tomotherapy for postmastectomy radiation therapy (PMRT). Methods and Materials: In vivo thermoluminescent dosimeters (TLDs) were used to measure the skin dose at multiple points in each of 14 patients throughout the course of treatment on a TomoTherapy Hi.Art II system, for a total of 420 TLD measurements. Five patients were evaluated near the location of the mastectomy scar, whereas 9 patients were evaluated throughout the treatment volume. The measured dose at each location was compared with calculations from the treatment planning system. Results: The mean difference and standard error of the mean difference between measurement and calculation for the scar measurements was -1.8% {+-} 0.2% (standard deviation [SD], 4.3%; range, -11.1% to 10.6%). The mean difference and standard error of the mean difference between measurement and calculation for measurements throughout the treatment volume was -3.0% {+-} 0.4% (SD, 4.7%; range, -18.4% to 12.6%). The mean difference and standard error of the mean difference between measurement and calculation for all measurements was -2.1% {+-} 0.2% (standard deviation, 4.5%: range, -18.4% to 12.6%). The mean difference between measured and calculated TLD doses was statistically significant at two standard deviations of the mean, but was not clinically significant (i.e., was <5%). However, 23% of the measured TLD doses differed from the calculated TLD doses by more than 5%. Conclusions: The mean of the measured TLD doses agreed with TomoTherapy calculated TLD doses within our clinical criterion of 5%.

  3. Comparison study of the partial-breast irradiation techniques: Dosimetric analysis of three-dimensional conformal radiation therapy, electron beam therapy, and helical tomotherapy depending on various tumor locations

    SciTech Connect

    Kim, Min-Joo; Park, So-Hyun; Son, Seok-Hyun; Cheon, Keum-Seong; Choi, Byung-Ock; Suh, Tae-Suk

    2013-10-01

    The partial-breast irradiation (PBI) technique, an alternative to whole-breast irradiation, is a beam delivery method that uses a limited range of treatment volume. The present study was designed to determine the optimal PBI treatment modalities for 8 different tumor locations. Treatment planning was performed on computed tomography (CT) data sets of 6 patients who had received lumpectomy treatments. Tumor locations were classified into 8 subsections according to breast quadrant and depth. Three-dimensional conformal radiation therapy (3D-CRT), electron beam therapy (ET), and helical tomotherapy (H-TOMO) were utilized to evaluate the dosimetric effect for each tumor location. Conformation number (CN), radical dose homogeneity index (rDHI), and dose delivered to healthy tissue were estimated. The Kruskal-Wallis, Mann-Whitney U, and Bonferroni tests were used for statistical analysis. The ET approach showed good sparing effects and acceptable target coverage for the lower inner quadrant—superficial (LIQ-S) and lower inner quadrant—deep (LIQ-D) locations. The H-TOMO method was the least effective technique as no evaluation index achieved superiority for all tumor locations except CN. The ET method is advisable for treating LIQ-S and LIQ-D tumors, as opposed to 3D-CRT or H-TOMO, because of acceptable target coverage and much lower dose applied to surrounding tissue.

  4. Comparison study of the partial-breast irradiation techniques: dosimetric analysis of three-dimensional conformal radiation therapy, electron beam therapy, and helical tomotherapy depending on various tumor locations.

    PubMed

    Kim, Min-Joo; Park, So-Hyun; Son, Seok-Hyun; Cheon, Keum-Seong; Choi, Byung-Ock; Suh, Tae-Suk

    2013-01-01

    The partial-breast irradiation (PBI) technique, an alternative to whole-breast irradiation, is a beam delivery method that uses a limited range of treatment volume. The present study was designed to determine the optimal PBI treatment modalities for 8 different tumor locations. Treatment planning was performed on computed tomography (CT) data sets of 6 patients who had received lumpectomy treatments. Tumor locations were classified into 8 subsections according to breast quadrant and depth. Three-dimensional conformal radiation therapy (3D-CRT), electron beam therapy (ET), and helical tomotherapy (H-TOMO) were utilized to evaluate the dosimetric effect for each tumor location. Conformation number (CN), radical dose homogeneity index (rDHI), and dose delivered to healthy tissue were estimated. The Kruskal-Wallis, Mann-Whitney U, and Bonferroni tests were used for statistical analysis. The ET approach showed good sparing effects and acceptable target coverage for the lower inner quadrant-superficial (LIQ-S) and lower inner quadrant-deep (LIQ-D) locations. The H-TOMO method was the least effective technique as no evaluation index achieved superiority for all tumor locations except CN. The ET method is advisable for treating LIQ-S and LIQ-D tumors, as opposed to 3D-CRT or H-TOMO, because of acceptable target coverage and much lower dose applied to surrounding tissue.

  5. Dosimetric comparisons of helical tomotherapy treatment plans and step-and-shoot intensity-modulated radiosurgery treatment plans in intracranial stereotactic radiosurgery

    SciTech Connect

    Han Chunhui . E-mail: chan@coh.org; Liu An; Schultheiss, Timothy E.; Pezner, Richard D.; Chen Yijen; Wong, Jeffrey Y.C.

    2006-06-01

    Purpose: To evaluate dose conformity, dose homogeneity, and dose gradient in helical tomotherapy treatment plans for stereotactic radiosurgery, and compare results with step-and-shoot intensity-modulated radiosurgery (IMRS) treatment plans. Methods and Materials: Sixteen patients were selected with a mean tumor size of 14.65 {+-} 11.2 cm{sup 3}. Original step-and-shoot IMRS treatment plans used coplanar fields because of the constraint of the beam stopper. Retrospective step-and-shoot IMRS plans were generated using noncoplanar fields. Helical tomotherapy treatment plans were generated using the tomotherapy planning station. Dose conformity index, dose gradient score index, and homogeneity index were used in plan intercomparisons. Results: Noncoplanar IMRS plans increased dose conformity and dose gradient, but not dose homogeneity, compared with coplanar IMRS plans. Tomotherapy plans increased dose conformity and dose gradient, yet increased dose heterogeneity compared with noncoplanar IMRS plans. The average dose conformity index values were 1.53 {+-} 0.38, 1.35 {+-} 0.15, and 1.26 {+-} 0.10 in coplanar IMRS, noncoplanar IMRS, and tomotherapy plans, respectively. The average dose homogeneity index values were 1.15 {+-} 0.05, 1.13 {+-} 0.04, and 1.18 {+-} 0.09 in coplanar IMRS, noncoplanar IMRS, and tomotherapy plans, respectively. The mean dose gradient score index values were 1.37 {+-} 19.08, 22.32 {+-} 19.20, and 43.28 {+-} 13.78 in coplanar IMRS, noncoplanar IMRS, and tomotherapy plans, respectively. The mean treatment time in tomotherapy was 42 {+-} 16 min. Conclusions: We were able to achieve better dose conformity and dose gradient in tomotherapy plans compared with step-and-shoot IMRS plans for intracranial stereotactic radiosurgery. However, tomotherapy treatment time was significantly larger than that in step-and-shoot IMRS.

  6. Postmastectomy radiotherapy with integrated scar boost using helical tomotherapy

    SciTech Connect

    Rong Yi; Yadav, Poonam; Welsh, James S.; Fahner, Tasha; Paliwal, Bhudatt

    2012-10-01

    The purpose of this study was to evaluate helical tomotherapy dosimetry in postmastectomy patients undergoing treatment for chest wall and positive nodal regions with simultaneous integrated boost (SIB) in the scar region using strip bolus. Six postmastectomy patients were scanned with a 5-mm-thick strip bolus covering the scar planning target volume (PTV) plus 2-cm margin. For all 6 cases, the chest wall received a total cumulative dose of 49.3-50.4 Gy with daily fraction size of 1.7-2.0 Gy. Total dose to the scar PTV was prescribed to 58.0-60.2 Gy at 2.0-2.5 Gy per fraction. The supraclavicular PTV and mammary nodal PTV received 1.7-1.9 dose per fraction. Two plans (with and without bolus) were generated for all 6 cases. To generate no-bolus plans, strip bolus was contoured and overrode to air density before planning. The setup reproducibility and delivered dose accuracy were evaluated for all 6 cases. Dose-volume histograms were used to evaluate dose-volume coverage of targets and critical structures. We observed reduced air cavities with the strip bolus setup compared with what we normally see with the full bolus. The thermoluminescence dosimeters (TLD) in vivo dosimetry confirmed accurate dose delivery beneath the bolus. The verification plans performed on the first day megavoltage computed tomography (MVCT) image verified that the daily setup and overall dose delivery was within 2% accuracy compared with the planned dose. The hotspot of the scar PTV in no-bolus plans was 111.4% of the prescribed dose averaged over 6 cases compared with 106.6% with strip bolus. With a strip bolus only covering the postmastectomy scar region, we observed increased dose uniformity to the scar PTV, higher setup reproducibility, and accurate dose delivered beneath the bolus. This study demonstrates the feasibility of using a strip bolus over the scar using tomotherapy for SIB dosimetry in postmastectomy treatments.

  7. The use of a commercial QA device for daily output check of a helical tomotherapy unit

    SciTech Connect

    Alaei, Parham; Hui, Susanta K.; Higgins, Patrick D.; Gerbi, Bruce J.

    2006-10-15

    Helical tomotherapy radiation therapy units, due to their particular design and differences from a traditional linear accelerator, require different procedures by which to perform routine quality assurance (QA). One of the principal QA tasks that should be performed daily on any radiation therapy equipment is the output constancy check. The daily output check on a Hi-Art TomoTherapy unit is commonly performed utilizing ionization chambers placed inside a solid water phantom. This provides a good check of output at one point, but does not give any information on either energy or symmetry of the beam, unless more than one point is measured. This also has the added disadvantage that it has to be done by the physics staff. To address these issues, and to simplify the process, such that it can be performed by radiation therapists, we investigated the use of a commercially available daily QA device to perform this task. The use of this device simplifies the task of daily output constancy checks and eliminates the need for continued physics involvement. This device can also be used to monitor the constancy of beam energy and cone profile and can potentially be used to detect gross errors in the couch movement or laser alignment.

  8. Hypofractionated breast and chest wall irradiation using simultaneous in-field boost IMRT delivered via helical tomotherapy.

    PubMed

    Rong, Y; Fahner, T; Welsh, J S

    2008-12-01

    Although helical tomotherapy has been described as a means of administering accelerated partial breast irradiation, its practicality in routine whole breast irradiation as part of breast conserving therapy or chest wall irradiation has been questioned. In this technical note we describe our method of whole breast or chest wall irradiation using helical tomotherapy based image-guided, hypofractionated, simultaneous in-field boost intensity modulated radiation therapy. We have observed that excellent dose-distributions can be achieved with helical tomotherapy through a careful selection of treatment planning parameters. Dose homogeneity to the whole breast and simultaneously targeted lumpectomy region appears superior to conventional "tangents" with minimal hot or cold spots. Dose-volume histogram analysis documents effective reduction of high dose to critical sensitive structures (heart and lung) although a greater volume of these non-target organs receives low dose compared to what is typical with tangential beams. Treatment planning is efficient and is usually completed within one to two hours, although physician contouring requires more time and attention than non-IMRT approaches. Pretreatment megavoltage CT (MVCT) imaging has proved invaluable in aiding set-up and engenders greater confidence that the planned IMRT dose distributions are truly being delivered. In some situations, MVCT can provide visual feedback when a seroma or overall breast volume has changed significantly since simulation, thereby identifying cases where replanning might be prudent. Treatment is brief, typically completed in 6 to 9 minutes. Initial clinical application has confirmed the feasibility and practicality of helical tomotherapy as an efficient means of administering radiation therapy for routine breast-conserving therapy and post-mastectomy chest wall irradiation. A simultaneous in-field boost technique reduces the length of the overall course by about a week thereby adding

  9. Novel Application of Helical Tomotherapy in Whole Skull Palliative Radiotherapy

    SciTech Connect

    Rodrigues, George Yartsev, Slav; Coad, Terry; Bauman, Glenn

    2008-01-01

    Helical tomotherapy (HT) is a radiation planning/delivery platform that combines inversely planned IMRT with on-board megavoltage imaging. A unique HT radiotherapy whole skull brain sparing technique is described in a patient with metastatic prostate cancer. An inverse HT plan and an accompanying back-up conventional lateral 6-MV parallel opposed pair (POP) plan with corresponding isodose distributions and dose-volume histograms (DVH) were created and assessed prior to initiation of therapy. Plans conforming to the planning treatment volume (PTV) with significant sparing of brain, optic nerve, and eye were created. Dose heterogeneity to the PTV target was slightly higher in the HT plan compared to the back-up POP plan. Conformal sparing of brain, optic nerve, and eye was achieved by the HT plan. Similar lens and brain stem/spinal cord doses were seen with both plans. Prospective clinical evaluation with relevant end points (quality of life, symptom relief) are required to confirm the potential benefits of highly conformal therapies applied to palliative situations such as this case.

  10. Dosimetric effects of rotational output variation and x-ray target degradation on helical tomotherapy plans.

    PubMed

    Staton, Robert J; Langen, Katja M; Kupelian, Patrick A; Meeks, Sanford L

    2009-07-01

    In this study, two potential sources of IMRT delivery error have been identified for helical tomotherapy delivery using the HiART system (TomoTherapy, Inc., Madison, WI): Rotational output variation and target degradation. The HiArt system is known to have output variation, typically about +/- 2%, due to the absence of a dose servo system. On the HiArt system, x-ray target replacement is required approximately every 10-12 months due to target degradation. Near the end of target life, the target thins and causes a decrease in the beam energy and a softening of the beam profile at the lateral edges of the beam. The purpose of this study is to evaluate the dosimetric effects of rotational output variation and target degradation by modeling their effects and incorporating them into recalculated treatment plans for three clinical scenarios: Head and neck, partial breast, and prostate. Models were created to emulate both potential sources of error. For output variation, a model was created using a sine function to match the amplitude (+/- 2%), frequency, and phase of the measured rotational output variation data. A second model with a hypothetical variation of +/- 7% was also created to represent the largest variation that could exist without violating the allowable dose window in the delivery system. A measured beam profile near the end of target life was used to create a modified beam profile model for the target degradation. These models were then incorporated into the treatment plan by modifying the leaf opening times in the delivery sinogram. A new beam model was also created to mimic the change in beam energy seen near the end of target life. The plans were then calculated using a research version of the PLANNED ADAPTIVE treatment planning software from TomoTherapy, Inc. Three plans were evaluated in this study: Head and neck, partial breast, and prostate. The D50 of organs at risk, the D95 for planning target volumes (PTVs), and the local dose difference were used

  11. Craniospinal irradiation using helical tomotherapy for central nervous system tumors.

    PubMed

    Schiopu, Sanziana R I; Habl, Gregor; Häfner, Matthias; Katayama, Sonja; Herfarth, Klaus; Debus, Juergen; Sterzing, Florian

    2017-01-17

    The aim of this study was to describe early and late toxicity, survival and local control in 45 patients with primary brain tumors treated with helical tomotherapy craniospinal irradiation (HT-CSI). From 2006 to 2014, 45 patients with central nervous system malignancies were treated with HT-CSI. The most common tumors were medulloblastoma in 20 patients, ependymoma in 10 patients, intracranial germinoma (ICG) in 7 patients, and primitive neuroectodermal tumor in 4 patients. Hematological toxicity during treatment included leukopenia Grades 1-4 (6.7%, 33.3%, 37.8% and 17.8%, respectively), anemia Grades 1-4 (44.4%, 22.2%, 22.2% and 0%, respectively) and thrombocytopenia Grades 1-4 (51.1%, 15.6%, 15.6% and 6.7%, respectively). The most common acute toxicities were nausea, vomiting, fatigue, loss of appetite, alopecia and neurotoxicity. No Grade 3 or higher late toxicity occurred. The overall 3- and 5-year survival rates were 80% and 70%, respectively. Survival for the main tumor entities included 3- and 5-year survival rates of 80% and 70%, respectively, for patients with medulloblastoma, 70% for both in patients with ependymoma, and 100% for both in patients with ICG. Relapse occurred in 11 patients (24.4%): 10 with local and 1 with multifocal relapse. One patient experienced a secondary cancer. M-status and the results of the re-evaluation at the end of treatment were significantly related to survival. Survival after HT-CSI was in line with the existing literature, and acute treatment-induced toxicity resolved quickly. Compared with conventional radiotherapy, HT offers benefits such as avoiding gaps and junctions, sparing organs, and better and more homogeneous dose distribution and coverage of the target volume.

  12. Intensity-Modulated Proton Therapy Versus Helical Tomotherapy in Nasopharynx Cancer: Planning Comparison and NTCP Evaluation

    SciTech Connect

    Widesott, Lamberto Pierelli, Alessio; Fiorino, Claudio; Dell'Oca, Italo; Broggi, Sara; Cattaneo, Giovanni Mauro; Di Muzio, Nadia; Fazio, Ferruccio; Calandrino, Riccardo; Schwarz, Marco

    2008-10-01

    Purpose: To compare intensity-modulated proton therapy (IMPT) and helical tomotherapy (HT) treatment plans for nasopharynx cancer using a simultaneous integrated boost approach. Methods and Materials: The data from 6 patients who had previously been treated with HT were used. A three-beam IMPT technique was optimized in the Hyperion treatment planning system, simulating a 'beam scanning' technique. HT was planned using the tomotherapy treatment planning system. Both techniques were optimized to simultaneously deliver 66 Gy in 30 fractions to planning target volume (PTV1; GTV and enlarged nodes) and 54 Gy to PTV2 subclinical, electively treated nodes. Normal tissue complication probability calculation was performed for the parotids and larynx. Results: Very similar PTVs coverage and homogeneity of the target dose distribution for IMPT and HT were found. The conformity index was significantly lower for protons than for photons (1.19 vs. 1.42, respectively). The mean dose to the ipsilateral and contralateral parotid glands decreased by 6.4 Gy and 5.6 Gy, respectively, with IMPT. The volume of mucosa and esophagus receiving {>=}20 Gy and {>=}30 Gy with IMPT was significantly lower than with HT. The average volume of larynx receiving {>=}50 Gy was significantly lower with HT, while for thyroid, it was comparable. The volume receiving {>=}30, {>=}20, and {>=}10 Gy in total body volume decreased with IMPT by 14.5%, 19.4%, and 23.1%, respectively. The normal tissue complication probability for the parotid glands was significantly lower with IMPT for all sets of parameters; however, we also estimated an almost full recovery of the contralateral parotid with HT. The normal tissue complication probability for the larynx was not significantly different between the two irradiation techniques. Conclusion: Excellent target coverage, homogeneity within the PTVs, and sparing of the organs at risk were reached with both modalities. IMPT allows for better sparing of most organs at

  13. Total marrow irradiation using Helical TomoTherapy

    NASA Astrophysics Data System (ADS)

    Garcia-Fernandez, Lourdes Maria

    Clinical dose response data of human tumours are limited or restricted to a radiation dose range determined by the level of toxicity to the normal tissues. This is the case for the most common disseminated plasma cell neoplasm, multiple myeloma, where the maximum dose deliverable to the entire bony skeleton using a standard total body irradiation (TBI) technique is limited to about 12 Gy. This study is part of scientific background of a phase I/II dose escalation clinical trial for multiple myeloma using image-guided intensity modulated radiotherapy (IG-IMRT) to deliver high dose to the entire volume of bone marrow with Helical TomoTherapy (HT). This relatively new technology can deliver highly conformal dose distributions to complex target shapes while reducing the dose to critical normal tissues. In this study tools for comparing and predicting the effectiveness of different approaches to total marrow irradiation (TMI) using HT were provided. The expected dose response for plasma cell neoplasms was computed and a radiobiological evaluation of different treatment cohorts in a dose escalating study was performed. Normal tissue complication probability (NTCP) and tumour control probability (TCP) models were applied to an actual TMI treatment plan for a patient and the implications of using different longitudinal field widths were assessed. The optimum dose was ˜39 Gy for which a predicted tumour control of 95% (+/-3%) was obtained, with a predicted 3% (0, 8%) occurrence of radiation pneumonitis. Tissue sparing was seen by using smaller field widths only in the organs of the head. This suggests it would be beneficial to use the small fields in the head only since using small fields for the whole treatment would lead to long treatment times. In TMI it may be necessary to junction two longitudinally adjacent treatment volumes to form a contiguous planning target volume PTV. For instance, this is the case when a different SUP-INF spatial resolution is required or when

  14. Investigation of dose homogeneity for loose helical tomotherapy delivery in the context of breath-hold radiation therapy

    NASA Astrophysics Data System (ADS)

    Kim, Bryan; Kron, Tomas; Battista, Jerry; Van Dyk, Jake

    2005-05-01

    Loose helical delivery is a potential solution to account for respiration-driven tumour motion in helical tomotherapy (HT). In this approach, a treatment is divided into a set of interlaced 'loose' helices commencing at different gantry angles. Each loose helix covers the entire target length in one gantry rotation during a single breath-hold. The dosimetric characteristics of loose helical delivery were investigated by delivering a 6 MV photon beam in a HT-like manner. Multiple scenarios of conventional 'tight' HT and loose helical deliveries were modelled in treatment planning software, and carried out experimentally with Kodak EDR2 film. The advantage of loose helical delivery lies in its ability to produce a more homogeneous dose distribution by eliminating the 'thread' effect—an inherent characteristic of HT, which results in dose modulations away from the axis of gantry rotation. However, loose helical delivery was also subjected to undesirable dose modulations in the direction of couch motion (termed 'beating' effect), when the ratio between the number of beam projections per gantry rotation (n) and pitch factor (p) was a non-integer. The magnitude of dose modulations decreased with an increasing n/p ratio. The results suggest that for the current HT unit (n = 51), dose modulations could be kept under 5% by selecting a pitch factor smaller than 7. A pitch factor of this magnitude should be able to treat a target up to 30 cm in length. Loose helical delivery should increase the total session time only by a factor of 2, while the planning time should stay the same since the total number of beam projections remains unchanged. Considering its dosimetric advantage and clinical practicality, loose helical delivery is a promising solution for the future HT treatments of respiration-driven targets.

  15. Helical Tomotherapy-Based STAT RT: Dosimetric Evaluation for Clinical Implementation of a Rapid Radiation Palliation Program

    SciTech Connect

    McIntosh, Alyson; Dunlap, Neal; Sheng, Ke; Geezey, Constance; Turner, Benton; Blackhall, Leslie; Weiss, Geoffrey; Lappinen, Eric; Larner, James M.; Read, Paul W.

    2010-01-01

    Helical tomotherapy-based STAT radiation therapy (RT) uses an efficient software algorithm for rapid intensity-modulated treatment planning, enabling conformal radiation treatment plans to be generated on megavoltage computed tomography (MVCT) scans for CT simulation, treatment planning, and treatment delivery in one session. We compared helical tomotherapy-based STAT RT dosimetry with standard linac-based 3D conformal plans and standard helical tomotherapy-based intensity-modulated radiation therapy (IMRT) dosimetry for palliative treatments of whole brain, a central obstructive lung mass, multilevel spine disease, and a hip metastasis. Specifically, we compared the conformality, homogeneity, and dose with regional organs at risk (OARs) for each plan as an initial step in the clinical implementation of a STAT RT rapid radiation palliation program. Hypothetical planning target volumes (PTVs) were contoured on an anthropomorphic phantom in the lung, spine, brain, and hip. Treatment plans were created using three planning techniques: 3D conformal on Pinnacle{sup 3}, helical tomotherapy, and helical tomotherapy-based STAT RT. Plan homogeneity, conformality, and dose to OARs were analyzed and compared. STAT RT and tomotherapy improved conformality indices for spine and lung plans (CI spine = 1.21, 1.17; CI lung = 1.20, 1.07, respectively) in comparison with standard palliative anteroposterior/posteroanterior (AP/PA) treatment plans (CI spine = 7.01, CI lung = 7.30), with better sparing of heart, esophagus, and spinal cord. For palliative whole-brain radiotherapy, STAT RT and tomotherapy reduced maximum and mean doses to the orbits and lens (maximum/mean lens dose: STAT RT = 2.94/2.65 Gy, tomotherapy = 3.13/2.80 Gy, Lateral opposed fields = 7.02/3.65 Gy), with an increased dose to the scalp (mean scalp dose: STAT RT = 16.19 Gy, tomotherapy = 15.61 Gy, lateral opposed fields = 14.01 Gy). For bony metastatic hip lesions, conformality with both tomotherapy techniques (CI

  16. Pediatric Craniospinal Axis Irradiation With Helical Tomotherapy: Patient Outcome and Lack of Acute Pulmonary Toxicity

    SciTech Connect

    Penagaricano, Jose; Moros, Eduardo; Corry, Peter; Saylors, Robert; Ratanatharathorn, Vaneerat

    2009-11-15

    Purpose: To present the patient outcomes and risk of symptomatic acute radiation pneumonitis (ARP) in 18 pediatric patients treated with helical tomotherapy to their craniospinal axis for a variety of neoplasms. Methods and Materials: A total of 18 patients received craniospinal axis irradiation with helical tomotherapy. The median age was 12 years (range, 2.5-21). The follow-up range was 3-48 months (median, 16.5). Of the 18 patients, 15 received chemotherapy in the neoadjuvant, adjuvant, or concomitant setting. Chemotherapy was tailored to the particular histologic diagnosis; 10 of 18 patients underwent surgical removal of the gross primary tumor. The patients were followed and evaluated for ARP starting at 3-6 months after completion of craniospinal axis irradiation. ARP was graded using the Common Toxicity Criteria, version 3. Results: At the last follow-up visit, 14, 2, and 2 patients were alive without disease, alive with disease, and dead of disease, respectively. The cause-specific survival rate was 89% (16 of 18), disease-free survival rate was 78% (14 of 18), and overall survival rate was 89% (16 of 18). No patient had treatment failure at the cribriform plate. No patient developed symptoms of ARP. Conclusion: Craniospinal axis irradiation using helical tomotherapy yielded encouraging patient outcomes and acute toxicity profiles. Although large volumes of the lung received low radiation doses, no patient developed symptoms of ARP during the follow-up period.

  17. Surface dose for five telecobalt machines, 6MV photon beam from four linear accelerators and a Hi-Art Tomotherapy.

    PubMed

    Kinhikar, Rajesh A

    2008-10-01

    The purpose of this study was to estimate the surface dose for five telecobalt machines (four from Best Theratronics Limited, Canada, one from Panacea Medical Technologies, India), 6 MV photon beam (static) from four linear accelerators (three Varian linear accelerators and one Siemens) and Hi-Art Tomotherapy unit. The surface dose was measured with Thermoluminescent dosimeters in phantom slabs. For Tomotherapy 6 MV beam the surface dose was estimated as 32% while it was 35%, 33%, and 36% for Clinac 6EX, Clinac 2100CD, and Clinac 2100C linear accelerators, respectively. Similarly, the surface dose for 6 MV photon beam from Primus linear accelerator was estimated as 35%. Surface doses from telecobalt machines Equinox-80, Elite-80, Th-780C, Th-780, and Bhabhatron-II was found to be 30%, 29.1%, 27.8%, 29.3%, and 29.9% for 10 cm x 10 field size, respectively. Measured surface dose from all four linear accelerators were in good agreement with that of the Tomotherapy. The surface dose measurements were useful for Tomotherapy to predict the superficial dose during helical IMRT treatments.

  18. Analysis of peripheral doses for base of tongue treatment by linear accelerator and helical TomoTherapy IMRT.

    PubMed

    Bennett, Brian Richard; Lamba, Michael A S; Elson, Howard R

    2010-06-21

    The purpose of this study was to compare the peripheral doses to various organs from a typical head and neck intensity-modulated radiation therapy (IMRT) treatment delivered by linear accelerator (linac) and helical TomoTherapy. Multiple human CT data sets were used to segment critical structures and organs at risk, fused and adjusted to an anthropomorphic phantom. Eighteen contours were designated for thermoluminescent dosimeter (TLD) placement. Following the RTOG IMRT Protocol 0522, treatment of the primary tumor and involved nodes (PTV70) and subclinical disease sites (PTV56) was planned utilizing IMRT to 70Gy and 56 Gy. Clinically acceptable treatment plans were produced for linac and TomoTherapy treatments. TLDs were placed and each treatment plan was delivered to the anthropomorphic phantom four times. Within 2.5 cm (one helical TomoTherapy field width) superior and inferior to the field edges, normal tissue doses were on average 45% lower using linear accelerator. Beyond 2.5 cm, the helical TomoTherapy normal tissue dose was an average of 52% lower. The majority of points proved to be statistically different using the Student's t-test with p > 0.05. Using one method of calculation, probability of a secondary malignancy was 5.88% for the linear accelerator and 4.08% for helical TomoTherapy. Helical TomoTherapy delivers more dose than a linac immediately above and below the treatment field, contributing to the higher peripheral doses adjacent to the field. At distances beyond one field width (where leakage is dominant), helical TomoTherapy doses are lower than linear accelerator doses.

  19. Performance characterization of megavoltage computed tomography imaging on a helical tomotherapy unit

    SciTech Connect

    Meeks, Sanford L.; Harmon, Joseph F. Jr.; Langen, Katja M.; Willoughby, Twyla R.; Wagner, Thomas H.; Kupelian, Patrick A.

    2005-08-15

    Helical tomotherapy is an innovative means of delivering IGRT and IMRT using a device that combines features of a linear accelerator and a helical computed tomography (CT) scanner. The HI-ART II can generate CT images from the same megavoltage x-ray beam it uses for treatment. These megavoltage CT (MVCT) images offer verification of the patient position prior to and potentially during radiation therapy. Since the unit uses the actual treatment beam as the x-ray source for image acquisition, no surrogate telemetry systems are required to register image space to treatment space. The disadvantage to using the treatment beam for imaging, however, is that the physics of radiation interactions in the megavoltage energy range may force compromises between the dose delivered and the image quality in comparison to diagnostic CT scanners. The performance of the system is therefore characterized in terms of objective measures of noise, uniformity, contrast, and spatial resolution as a function of the dose delivered by the MVCT beam. The uniformity and spatial resolutions of MVCT images generated by the HI-ART II are comparable to that of diagnostic CT images. Furthermore, the MVCT scan contrast is linear with respect to the electron density of material imaged. MVCT images do not have the same performance characteristics as state-of-the art diagnostic CT scanners when one objectively examines noise and low-contrast resolution. These inferior results may be explained, at least partially, by the low doses delivered by our unit; the dose is 1.1 cGy in a 20 cm diameter cylindrical phantom. In spite of the poorer low-contrast resolution, these relatively low-dose MVCT scans provide sufficient contrast to delineate many soft-tissue structures. Hence, these images are useful not only for verifying the patient's position at the time of therapy, but they are also sufficient for delineating many anatomic structures. In conjunction with the ability to recalculate radiotherapy doses on

  20. Comparison of Elekta VMAT with helical tomotherapy and fixed field IMRT: Plan quality, delivery efficiency and accuracy

    SciTech Connect

    Rao Min; Yang Wensha; Chen Fan; Sheng Ke; Ye Jinsong; Mehta, Vivek; Shepard, David; Cao Daliang

    2010-03-15

    Purpose: Helical tomotherapy (HT) and volumetric modulated arc therapy (VMAT) are arc-based approaches to IMRT delivery. The objective of this study is to compare VMAT to both HT and fixed field IMRT in terms of plan quality, delivery efficiency, and accuracy. Methods: Eighteen cases including six prostate, six head-and-neck, and six lung cases were selected for this study. IMRT plans were developed using direct machine parameter optimization in the Pinnacle{sup 3} treatment planning system. HT plans were developed using a Hi-Art II planning station. VMAT plans were generated using both the Pinnacle{sup 3} SmartArc IMRT module and a home-grown arc sequencing algorithm. VMAT and HT plans were delivered using Elekta's PreciseBeam VMAT linac control system (Elekta AB, Stockholm, Sweden) and a TomoTherapy Hi-Art II system (TomoTherapy Inc., Madison, WI), respectively. Treatment plan quality assurance (QA) for VMAT was performed using the IBA MatriXX system while an ion chamber and films were used for HT plan QA. Results: The results demonstrate that both VMAT and HT are capable of providing more uniform target doses and improved normal tissue sparing as compared with fixed field IMRT. In terms of delivery efficiency, VMAT plan deliveries on average took 2.2 min for prostate and lung cases and 4.6 min for head-and-neck cases. These values increased to 4.7 and 7.0 min for HT plans. Conclusions: Both VMAT and HT plans can be delivered accurately based on their own QA standards. Overall, VMAT was able to provide approximately a 40% reduction in treatment time while maintaining comparable plan quality to that of HT.

  1. SU-E-P-37: Helical Tomotherapy to LINAC Plan Conversion Utilizing RayStation Fallback Planning

    SciTech Connect

    Zhang, X; Penagaricano, J; Liang, X; Morrill, S; Corry, P; Griffin, R; Paudel, N; Ratanatharathorn, V

    2015-06-15

    Purpose: RayStation Fallback (RSF) plan was developed to switch patient’s treatment from Helical Tomotherapy (HT) to Varian TrueBeam. Helical Tomotherapy plans were compared with the corresponding RSF plans by looking at the following dosimetric parameters: PTV coverage (Dmean and D95), Paddick conformity index (CI), uniformity index (UI=(D98-D2)/Drx) and organ-at-risk (OAR) doses. Methods: Five patients with five tumor sites including larynx, head and neck, esophagus, lung, and prostate previously treated with HT were re-planned using RSF treatment planning station(TPS) to best match the HT treatment plans. IMRT technique with nine fields 6 MV X-ray beams and a static multi-leaf collimator (MLC) were used for RSF plans without any additional attempt to further optimize the RSF plans. Results: A physician evaluated and confirmed the clinical acceptability of the RSF plans. Both HT and RSF plans gave comparable PTV coverage with a maximum percentage difference for D95 of 0.7%. HT plans had a better CIs ranging from 2%–15% higher conformity compared to RSF plans. HT plans also had better UIs for all tumor sites except the esophagus. The UIs were 1.6% to 8.9% lower for HT plans compared to RSF plans. Both HT and RSF plans gave comparable and acceptable OAR doses. However, the integral dose was 1%–15% higher for HT plans compared to RSF plans. Conclusion: RSF plans were simple and fast to generate. In the study cases of 5 various tumor sites, RSF efficiently created clinically acceptable plans without further optimization. However, further optimization for any IMRT plan can be done if clinically warranted. The absolute differences in CI and UI were small between RSF and HT plans.

  2. Image-guided total marrow and total lymphatic irradiation using helical tomotherapy

    SciTech Connect

    Schultheiss, Timothy E. . E-mail: Schultheiss@coh.org; Wong, Jeffrey; Liu, An; Olivera, Gustavo; Somlo, George

    2007-03-15

    Purpose: To develop a treatment technique to spare normal tissue and allow dose escalation in total body irradiation (TBI). We have developed intensity-modulated radiotherapy techniques for the total marrow irradiation (TMI), total lymphatic irradiation, or total bone marrow plus lymphatic irradiation using helical tomotherapy. Methods and Materials: For TBI, we typically use 12 Gy in 10 fractions delivered at an extended source-to-surface distance (SSD). Using helical tomotherapy, it is possible to deliver equally effective doses to the bone marrow and lymphatics while sparing normal organs to a significant degree. In the TMI patients, whole body skeletal bone, including the ribs and sternum, comprise the treatment target. In the total lymphatic irradiation, the target is expanded to include the spleen and major lymph node areas. Sanctuary sites for disease (brain and testes) are included when clinically indicated. Spared organs include the lungs, esophagus, parotid glands, eyes, oral cavity, liver, kidneys, stomach, small and large intestine, bladder, and ovaries. Results: With TBI, all normal organs received the TBI dose; with TMI, total lymphatic irradiation, and total bone marrow plus lymphatic irradiation, the visceral organs are spared. For the first 6 patients treated with TMI, the median dose to organs at risk averaged 51% lower than would be achieved with TBI. By putting greater weight on the avoidance of specific organs, greater sparing was possible. Conclusion: Sparing of normal tissues and dose escalation is possible using helical tomotherapy. Late effects such as radiation pneumonitis, veno-occlusive disease, cataracts, neurocognitive effects, and the development of second tumors should be diminished in severity and frequency according to the dose reduction realized for the organs at risk.

  3. Early Clinical Experience and Outcome of Helical Tomotherapy for Multiple Metastatic Lesions

    SciTech Connect

    Lee, Ik Jae; Seong, Jinsil; Lee, Chang Geol; Kim, Yong Bae; Keum, Ki Chang; Suh, Chang Ok; Kim, Gwi Eon; Cho, Jaeho

    2009-04-01

    Purpose: To evaluate the feasibility of synchronous treatment of multiple metastatic lesions by helical tomotherapy. Methods and Materials: Forty-two patients with multiple metastatic lesions were treated by helical tomotherapy from April 2006 to February 2007. Among these patients, 21 had metastatic bone disease. Subjective pain response was assessed using the visual analogue scales, and morbidity was evaluated by Common Terminology Criteria for Adverse Events v3.0. The correlation between the percentage of red bone marrow in the radiation field and the severity of leukocytopenia was analyzed. Results: The median age was 57 years. Radiation dose to the gross tumor volume was 30-84 Gy, with a median fractional size of 3 Gy. Mean treatment time was 16 min and 1 sec. Treatment time and fraction size were modified because of poor performance status or hematologic toxicity in two patients. With regard to palliative effects for bone metastasis, 16 patients (76.2%) experienced positive pain relief. Four patients had Grade III leukocytopenia, and three had Grade IV leukocytopenia. In the multivariate logistic regression, red marrow percentage was the independent risk factor most associated with Grade III/IV leukocytopenia (p = 0.014). The tolerance cutoff point of red bone marrow was 26.8%, with a sensitivity and specificity of 85.7% and 85.7%, respectively. Conclusions: Helical tomotherapy was effective for symptom palliation and was feasible for patients with multiple metastatic diseases. The volume of red bone marrow, as well as performance status, must be taken into account to determine optimal treatment.

  4. Concurrent Chemoradiotherapy With Helical Tomotherapy for Oropharyngeal Cancer: A Preliminary Result

    SciTech Connect

    Shueng, Pei-Wei; Wu, Le-Jung; Chen, Shiou-Yi

    2010-07-01

    Purpose: To review the experience with and evaluate the treatment plan for helical tomotherapy for the treatment of oropharyngeal cancer. Methods and Materials: Between November 1, 2006 and January 31, 2009, 10 histologically confirmed oropharyngeal cancer patients were enrolled. All patients received definitive concurrent chemoradiation with helical tomotherapy. The prescription dose to the gross tumor planning target volume, the high-risk subclinical area, and the low-risk subclinical area was 70Gy, 63Gy, and 56Gy, respectively. During radiotherapy, all patients were treated with cisplatin, 30mg/m{sup 2}, plus 5-fluorouracil (425mg/m{sup 2})/leucovorin (30mg/m{sup 2}) intravenously weekly. Toxicity of treatment was scored according to the Common Terminology Criteria for Adverse Events, version 3.0. Several parameters, including maximal or median dose to critical organs, uniformity index, and conformal index, were evaluated from dose-volume histograms. Results: The mean survival was 18 months (range, 7-22 months). The actuarial overall survival, disease-free survival, locoregional control, and distant metastasis-free rates at 18 months were 67%, 70%, 80%, and 100%, respectively. The average for uniformity index and conformal index was 1.05 and 1.26, respectively. The mean of median dose for right side and left side parotid glands was 23.5 and 23.9Gy, respectively. No Grade 3 toxicity for dermatitis and body weight loss and only one instance of Grade 3 mucositis were noted. Conclusion: Helical tomotherapy achieved encouraging clinical outcomes in patients with oropharyngeal carcinoma. Treatment toxicity was acceptable, even in the setting of concurrent chemotherapy. Long-term follow-up is needed to confirm these preliminary findings.

  5. SU-E-T-761: TOMOMC, A Monte Carlo-Based Planning VerificationTool for Helical Tomotherapy

    SciTech Connect

    Chibani, O; Ma, C

    2015-06-15

    Purpose: Present a new Monte Carlo code (TOMOMC) to calculate 3D dose distributions for patients undergoing helical tomotherapy treatments. TOMOMC performs CT-based dose calculations using the actual dynamic variables of the machine (couch motion, gantry rotation, and MLC sequences). Methods: TOMOMC is based on the GEPTS (Gama Electron and Positron Transport System) general-purpose Monte Carlo system (Chibani and Li, Med. Phys. 29, 2002, 835). First, beam models for the Hi-Art Tomotherpy machine were developed for the different beam widths (1, 2.5 and 5 cm). The beam model accounts for the exact geometry and composition of the different components of the linac head (target, primary collimator, jaws and MLCs). The beams models were benchmarked by comparing calculated Pdds and lateral/transversal dose profiles with ionization chamber measurements in water. See figures 1–3. The MLC model was tuned in such a way that tongue and groove effect, inter-leaf and intra-leaf transmission are modeled correctly. See figure 4. Results: By simulating the exact patient anatomy and the actual treatment delivery conditions (couch motion, gantry rotation and MLC sinogram), TOMOMC is able to calculate the 3D patient dose distribution which is in principal more accurate than the one from the treatment planning system (TPS) since it relies on the Monte Carlo method (gold standard). Dose volume parameters based on the Monte Carlo dose distribution can also be compared to those produced by the TPS. Attached figures show isodose lines for a H&N patient calculated by TOMOMC (transverse and sagittal views). Analysis of differences between TOMOMC and TPS is an ongoing work for different anatomic sites. Conclusion: A new Monte Carlo code (TOMOMC) was developed for Tomotherapy patient-specific QA. The next step in this project is implementing GPU computing to speed up Monte Carlo simulation and make Monte Carlo-based treatment verification a practical solution.

  6. A novel method to correct for pitch and yaw patient setup errors in helical tomotherapy

    SciTech Connect

    Boswell, Sarah A.; Jeraj, Robert; Ruchala, Kenneth J.; Olivera, Gustavo H.; Jaradat, Hazim A.; James, Joshua A.; Gutierrez, Alonso; Pearson, Dave; Frank, Gary; Mackie, T. Rock

    2005-06-15

    An accurate means of determining and correcting for daily patient setup errors is important to the cancer outcome in radiotherapy. While many tools have been developed to detect setup errors, difficulty may arise in accurately adjusting the patient to account for the rotational error components. A novel, automated method to correct for rotational patient setup errors in helical tomotherapy is proposed for a treatment couch that is restricted to motion along translational axes. In tomotherapy, only a narrow superior/inferior section of the target receives a dose at any instant, thus rotations in the sagittal and coronal planes may be approximately corrected for by very slow continuous couch motion in a direction perpendicular to the scanning direction. Results from proof-of-principle tests indicate that the method improves the accuracy of treatment delivery, especially for long and narrow targets. Rotational corrections about an axis perpendicular to the transverse plane continue to be implemented easily in tomotherapy by adjustment of the initial gantry angle.

  7. Independent quality assurance of a helical tomotherapy machine using the dose magnifying glass

    SciTech Connect

    Wong, J. H. D.; Hardcastle, N.; Tome, W. A.; and others

    2011-04-15

    Purpose: Helical tomotherapy is a complex delivery technique, integrating CT image guidance and intensity modulated radiotherapy in a single system. The integration of the CT detector ring on the gantry not only allows patient position verification but is also often used to perform various QA procedures. This convenience lacks the rigor of a machine-independent QA process. Methods: In this article, a Si strip detector, known as the Dose Magnifying Glass (DMG), was used to perform machine-independent QA measurements of the multileaf collimator alignment, leaf open time threshold, and leaf fluence output factor (LFOF). Results: The DMG measurements showed good agreements with EDR2 film for the MLC alignment test while the CT detector agrees well with DMG measurements for leaf open time threshold and LFOF measurements. The leaf open time threshold was found to be approximately 20 ms. The LFOF measured with the DMG agreed within error with the CT detector measured LFOF. Conclusions: The DMG with its 0.2 mm spatial resolution coupled to TERA ASIC allowed real-time high temporal resolution measurements of the tomotherapy leaf movement. In conclusion, DMG was shown to be a suitable tool for machine-independent QA of a tomotherapy unit.

  8. Helical Tomotherapy Versus Single-Arc Intensity-Modulated Arc Therapy: A Collaborative Dosimetric Comparison Between Two Institutions

    SciTech Connect

    Rong Yi; Tang, Grace; Welsh, James S.; Mohiuddin, Majid M.; Paliwal, Bhudatt; Yu, Cedric X.

    2011-09-01

    Purpose: Both helical tomotherapy (HT) and single-arc intensity-modulated arc therapy (IMAT) deliver radiation using rotational beams with multileaf collimators. We report a dual-institution study comparing dosimetric aspects of these two modalities. Methods and Materials: Eight patients each were selected from the University of Maryland (UMM) and the University of Wisconsin Cancer Center Riverview (UWR), for a total of 16 cases. Four cancer sites including brain, head and neck (HN), lung, and prostate were selected. Single-arc IMAT plans were generated at UMM using Varian RapidArc (RA), and HT plans were generated at UWR using Hi-Art II TomoTherapy. All 16 cases were planned based on the identical anatomic contours, prescriptions, and planning objectives. All plans were swapped for analysis at the same time after final approval. Dose indices for targets and critical organs were compared based on dose-volume histograms, the beam-on time, monitor units, and estimated leakage dose. After the disclosure of comparison results, replanning was done for both techniques to minimize diversity in optimization focus from different operators. Results: For the 16 cases compared, the average beam-on time was 1.4 minutes for RA and 4.8 minutes for HT plans. HT provided better target dose homogeneity (7.6% for RA and 4.2% for HT) with a lower maximum dose (110% for RA and 105% for HT). Dose conformation numbers were comparable, with RA being superior to HT (0.67 vs. 0.60). The doses to normal tissues using these two techniques were comparable, with HT showing lower doses for more critical structures. After planning comparison results were exchanged, both techniques demonstrated improvements in dose distributions or treatment delivery times. Conclusions: Both techniques created highly conformal plans that met or exceeded the planning goals. The delivery time and total monitor units were lower in RA than in HT plans, whereas HT provided higher target dose uniformity.

  9. Parotid Gland Sparing With Helical Tomotherapy in Head-and-Neck Cancer

    SciTech Connect

    Voordeckers, Mia; Farrag, Ashraf; Everaert, Hendrik; Tournel, Koen; Storme, Guy; Verellen, Dirk; De Ridder, Mark

    2012-10-01

    Purpose: This study evaluated the ability of helical tomotherapy to spare the function of the parotid glands in patients with head-and-neck cancer by analyzing dose-volume histograms, salivary gland scintigraphy, and quality of life assessment. Methods and Materials: Data from 76 consecutive patients treated with helical tomotherapy (Hi-Art Tomotherapy) at University Hospital Brussel were analyzed. During planning, priority was given to planning target volume (PTV) coverage: {>=}95% of the dose must be delivered to {>=}95% of the PTV. Elective nodal regions received 54 Gy (1.8 Gy/fraction). A dose of 70.5 Gy (2.35 Gy/fraction) was prescribed to the primary tumor and pathologic lymph nodes (simultaneous integrated boost scheme). Objective scoring of salivary excretion was performed by salivary gland scintigraphy. Subjective scoring of salivary gland function was evaluated by the European Organization for Research and Treatment of Cancer quality of life questionnaires Quality of Life Questionnaire-C30 (QLQ-C30) and Quality of Life Questionnaire-Head and Neck 35 (H and N35). Results: Analysis of dose-volume histograms (DVHs) showed excellent coverage of the PTV. The volume of PTV receiving 95% of the prescribed dose (V95%) was 99.4 (range, 96.3-99.9). DVH analysis of parotid gland showed a median value of the mean parotid dose of 32.1 Gy (range, 17.5-70.3 Gy). The median parotid volume receiving a dose <26 Gy was 51.2%. Quality of life evaluation demonstrated an initial deterioration of almost all scales and items in QLQ-C30 and QLQ-H and N35. Most items improved in time, and some reached baseline values 18 months after treatment. Conclusion: DVH analysis, scintigraphic evaluation of parotid function, and quality of life assessment of our patient group showed that helical tomotherapy makes it possible to preserve parotid gland function without compromising disease control. We recommend mean parotid doses of <34 Gy and doses <26 Gy to a maximum 47% of the parotid

  10. Phase II Study of Preoperative Helical Tomotherapy With a Simultaneous Integrated Boost for Rectal Cancer

    SciTech Connect

    Engels, Benedikt; Tournel, Koen; Everaert, Hendrik; Hoorens, Anne; Sermeus, Alexandra; Christian, Nicolas; Storme, Guy; Verellen, Dirk; De Ridder, Mark

    2012-05-01

    Purpose: The addition of concomitant chemotherapy to preoperative radiotherapy is considered the standard of care for patients with cT3-4 rectal cancer. The combined treatment modality increases the complete response rate and local control (LC), but has no impact on survival or the incidence of distant metastases. In addition, it is associated with considerable toxicity. As an alternative strategy, we explored prospectively, preoperative helical tomotherapy with a simultaneous integrated boost (SIB). Methods and Materials: A total of 108 patients were treated with intensity-modulated and image-guided radiotherapy using the Tomotherapy Hi-Art II system. A dose of 46 Gy, in daily fractions of 2 Gy, was delivered to the mesorectum and draining lymph nodes, without concomitant chemotherapy. Patients with an anticipated circumferential resection margin (CRM) of less than 2 mm, based on magnetic resonance imaging, received a SIB to the tumor up to a total dose of 55.2 Gy. Acute and late side effects were scored using the National Cancer Institute Common Terminology Criteria for Adverse Events version 3.0. Results: A total of 102 patients presented with cT3-4 tumors; 57 patients entered the boost group and 51 the no-boost group. One patient in the no-boost group developed a radio-hypersensitivity reaction, resulting in a complete tumor remission, a Grade 3 acute and Grade 5 late enteritis. No other Grade {>=}3 acute toxicities occurred. With a median follow-up of 32 months, Grade {>=}3 late gastrointestinal and urinary toxicity were observed in 6% and 4% of the patients, respectively. The actuarial 2-year LC, progression-free survival and overall survival were 98%, 79%, and 93%. Conclusions: Preoperative helical tomotherapy displays a favorable acute toxicity profile in patients with cT3-4 rectal cancer. A SIB can be safely administered in patients with a narrow CRM and resulted in a promising LC.

  11. Comparing step-and-shoot IMRT with dynamic helical tomotherapy IMRT plans for head-and-neck cancer

    SciTech Connect

    Vulpen, Marco van . E-mail: M.vanVulpen@azu.nl; Field, Colin; Raaijmakers, Cornelis P.J.; Parliament, Matthew B.; Terhaard, Chris H.J.; MacKenzie, Marc A.; Scrimger, Rufus; Lagendijk, Jan J.W.; Fallone, B. Gino

    2005-08-01

    Purpose: The goal of this planning study was to compare step-and-shoot intensity-modulated radiotherapy (IMRT) plans with helical dynamic IMRT plans for oropharynx patients on the basis of dose distribution. Methods and Materials: Five patients with oropharynx cancer had been previously treated by step-and-shoot IMRT at University Medical Centre Utrecht, The Netherlands, applying five fields and approximately 60-90 segments. Inverse planning was carried out using Plato, version 2.6.2. For each patient, an inverse IMRT plan was also made using Tomotherapy Hi-Art System, version 2.0, and using the same targets and optimization goals. Statistical analysis was performed by a paired t test. Results: All tomotherapy plans compared favorably with the step-and-shoot plans regarding sparing of the organs at risk and keeping an equivalent target dose homogeneity. Tomotherapy plans in particular realized sharper dose gradients compared with the step-and-shoot plans. The mean dose to all parotid glands (n = 10) decreased on average 6.5 Gy (range, -4 to 14; p = 0.002). The theoretical reduction in normal tissue complication probabilities in favor of the tomotherapy plans depended on the parotid normal tissue complication probability model used (range, -3% to 32%). Conclusion: Helical tomotherapy IMRT plans realized sharper dose gradients compared with the clinically applied step-and shoot plans. They are expected to be able to reduce the parotid normal tissue complication probability further, keeping a similar target dose homogeneity.

  12. Helical tomotherapy optimized planning parameters for nasopharyngeal cancer

    NASA Astrophysics Data System (ADS)

    Yawichai, K.; Chitapanarux, I.; Wanwilairat, S.

    2016-03-01

    Helical TomoTherapy(HT) planning depends on optimize parameters including field width (FW), pitch factor (PF) and modulation factor (MF). These optimize parameters are effect to quality of plans and treatment time. The aim of this study was to find the optimized parameters which compromise between plan quality and treatment times. Six nasopharyngeal cancer patients were used. For each patient data set, 18 treatment plans consisted of different optimize parameters combination (FW=5.0, 2.5, 1.0 cm; PF=0.43, 0.287, 0.215; MF2.0, 3.0) were created. The identical optimization procedure followed ICRU83 recommendations. The average D50 of both parotid glands and treatment times per fraction were compared for all plans. The study show treatment plan with FW1.0 cm showed the lowest average D50 of both parotid glands. The treatment time increased inversely to FW. The FW1.0 cm the average treatment time was 4 times longer than FW5.0 cm. PF was very little influence on the average D50 of both parotid glands. Finally, MF increased from 2.0 to 3.0 the average D50 of both parotid glands was slightly decreased. However, the average treatment time was increased 22.28%. For routine nasopharyngeal cancer patients with HT, we suggest the planning optimization parameters consist of FW=5.0 cm, PF=0.43 and MF=2.0.

  13. Dosimetric comparison of helical tomotherapy and dynamic conformal arc therapy in stereotactic radiosurgery for vestibular schwannomas.

    PubMed

    Lee, Tsair-Fwu; Chao, Pei-Ju; Wang, Chang-Yu; Lan, Jen-Hong; Huang, Yu-Je; Hsu, Hsuan-Chih; Sung, Chieh-Cheng; Su, Te-Jen; Lian, Shi-Long; Fang, Fu-Min

    2011-01-01

    The dosimetric results of stereotactic radiosurgery (SRS) for vestibular schwannoma (VS) performed using dynamic conformal arc therapy (DCAT) with the Novalis system and helical TomoTherapy (HT) were compared using plan quality indices. The HT plans were created for 10 consecutive patients with VS previously treated with SRS using the Novalis system. The dosimetric indices used to compare the techniques included the conformity index (CI) and homogeneity index (HI) for the planned target volume (PTV), the comprehensive quality index (CQI) for nine organs at risk (OARs), gradient score index (GSI) for the dose drop-off outside the PTV, and plan quality index (PQI), which was verified using the plan quality discerning power (PQDP) to incorporate 3 plan indices, to evaluate the rival plans. The PTV ranged from 0.27-19.99 cm(3) (median 3.39 cm(3)), with minimum required PTV prescribed doses of 10-16 Gy (median 12 Gy). Both systems satisfied the minimum required PTV prescription doses. HT conformed better to the PTV (CI: 1.51 ± 0.23 vs. 1.94 ± 0.34; p < 0.01), but had a worse drop-off outside the PTV (GSI: 40.3 ± 10.9 vs. 64.9 ± 13.6; p < 0.01) compared with DCAT. No significant difference in PTV homogeneity was observed (HI: 1.08 ± 0.03 vs. 1.09 ± 0.02; p = 0.20). HT had a significantly lower maximum dose in 4 OARs and significant lower mean dose in 1 OAR; by contrast, DCAT had a significantly lower maximum dose in 1 OAR and significant lower mean dose in 2 OARs, with the CQI of the 9 OARs = 0.92 ± 0.45. Plan analysis using PQI (HT 0.37 ± 0.12 vs. DCAT 0.65 ± 0.08; p < 0.01), and verified using the PQDP, confirmed the dosimetric advantage of HT. However, the HT system had a longer beam-on time (33.2 ± 7.4 vs. 4.6 ± 0.9 min; p < 0.01) and consumed more monitor units (16772 ± 3803 vs. 1776 ± 356.3; p < 0.01). HT had a better dose conformity and similar dose homogeneity but worse dose gradient than DCAT. Plan analysis confirmed the dosimetric advantage of HT

  14. Dosimetric Comparison of Helical Tomotherapy and Dynamic Conformal Arc Therapy in Stereotactic Radiosurgery for Vestibular Schwannomas

    SciTech Connect

    Lee, Tsair-Fwu; Chao, Pei-Ju; Wang, Chang-Yu; Lan, Jen-Hong; Huang, Yu-Je; Hsu, Hsuan-Chih; Sung, Chieh-Cheng; Su, Te-Jen; Lian, Shi-Long; Fang, Fu-Min

    2011-04-01

    The dosimetric results of stereotactic radiosurgery (SRS) for vestibular schwannoma (VS) performed using dynamic conformal arc therapy (DCAT) with the Novalis system and helical TomoTherapy (HT) were compared using plan quality indices. The HT plans were created for 10 consecutive patients with VS previously treated with SRS using the Novalis system. The dosimetric indices used to compare the techniques included the conformity index (CI) and homogeneity index (HI) for the planned target volume (PTV), the comprehensive quality index (CQI) for nine organs at risk (OARs), gradient score index (GSI) for the dose drop-off outside the PTV, and plan quality index (PQI), which was verified using the plan quality discerning power (PQDP) to incorporate 3 plan indices, to evaluate the rival plans. The PTV ranged from 0.27-19.99 cm{sup 3} (median 3.39 cm{sup 3}), with minimum required PTV prescribed doses of 10-16 Gy (median 12 Gy). Both systems satisfied the minimum required PTV prescription doses. HT conformed better to the PTV (CI: 1.51 {+-} 0.23 vs. 1.94 {+-} 0.34; p < 0.01), but had a worse drop-off outside the PTV (GSI: 40.3 {+-} 10.9 vs. 64.9 {+-} 13.6; p < 0.01) compared with DCAT. No significant difference in PTV homogeneity was observed (HI: 1.08 {+-} 0.03 vs. 1.09 {+-} 0.02; p = 0.20). HT had a significantly lower maximum dose in 4 OARs and significant lower mean dose in 1 OAR; by contrast, DCAT had a significantly lower maximum dose in 1 OAR and significant lower mean dose in 2 OARs, with the CQI of the 9 OARs = 0.92 {+-} 0.45. Plan analysis using PQI (HT 0.37 {+-} 0.12 vs. DCAT 0.65 {+-} 0.08; p < 0.01), and verified using the PQDP, confirmed the dosimetric advantage of HT. However, the HT system had a longer beam-on time (33.2 {+-} 7.4 vs. 4.6 {+-} 0.9 min; p < 0.01) and consumed more monitor units (16772 {+-} 3803 vs. 1776 {+-} 356.3; p < 0.01). HT had a better dose conformity and similar dose homogeneity but worse dose gradient than DCAT. Plan analysis

  15. A quality assurance tool for helical tomotherapy using a step-wedge phantom and the on-board MVCT detector.

    PubMed

    Althof, Vincent; van Haaren, Paul; Westendorp, Rik; Nuver, Tonnis; Kramer, Dinant; Ikink, Marijke; Bel, Arjen; Minken, Andre

    2012-01-05

    The purpose of this study was to develop and evaluate filmless quality assurance (QA) tools for helical tomotherapy by using the signals from the on-board megavoltage computed tomography (MVCT) detector and applying a dedicated step-wedge phantom. The step-wedge phantom is a 15 cm long step-like aluminum block positioned on the couch. The phantom was moved through the slit beam and MVCT detector signals were analyzed. Two QA procedures were developed, with gantry fixed at 0°: 1) step-wedge procedure: to check beam energy consistency, field width, laser alignment with respect to the virtual isocenter, couch movement, and couch velocity; and 2) completion procedure: to check the accuracy of a field abutment made by the tomotherapy system after a treatment interruption. The procedures were designed as constancy tool and were validated by measurement of deliberately induced variations and comparison with a reference method. Two Hi-Art II machines were monitored over a period of three years using the step-wedge procedures. The data acquisition takes 5 minutes. The analysis is fully automated and results are available directly after acquisition. Couch speed deviations up to 2% were induced. The mean absolute difference between expected and measured couch speed was 0.2% ± 0.2% (1 standard deviation SD). Field width was varied around the 10 mm nominal size, between 9.7 and 11.1 mm, in steps of 0.2 mm. Mean difference between the step-wedge analysis and the reference method was < 0.01 mm ± 0.03 mm (1 SD). Laser (mis)alignment relative to a reference situation was detected with 0.3 mm precision (1SD). The step-wedge profile was fitted to a PDD in water. The PDD ratio D20/D10, measured at depths of 20 cm and 10 cm, was used to check beam energy consistency. Beam energy variations were induced. Mean difference between step-wedge and water PDD ratios was 0.2% ± 0.3% (1SD). The completion procedure was able to reveal abutment mismatches with a mean error of -0.6 mm ± 0.2 mm

  16. SU-E-T-657: Quantitative Assessment of Plan Robustness for Helical Tomotherapy for Head and Neck Cancer Radiotherapy

    SciTech Connect

    Matney, J; Lian, J; Chera, B; Marks, L; Das, S; Chao, E

    2015-06-15

    Introduction: Geometric uncertainties in daily patient setup can lead to variations in the planned dose, especially when using highly conformal techniques such as helical Tomotherapy. To account for the potential effect of geometric uncertainty, our clinical practice is to expand critical structures by 3mm expansion into planning risk volumes (PRV). The PRV concept assumes the spatial dose cloud is insensitive to patient positioning. However, no tools currently exist to determine if a Tomotherapy plan is robust to the effects of daily setup variation. We objectively quantified the impact of geometric uncertainties on the 3D doses to critical normal tissues during helical Tomotherapy. Methods: Using a Matlab-based program created and validated by Accuray (Madison, WI), the planned Tomotherapy delivery sinogram recalculated dose on shifted CT datasets. Ten head and neck patients were selected for analysis. To simulate setup uncertainty, the patient anatomy was shifted ±3mm in the longitudinal, lateral and vertical axes. For each potential shift, the recalculated doses to various critical normal tissues were compared to the doses delivered to the PRV in the original plan Results: 18 shifted scenarios created from Tomotherapy plans for three patients with head and neck cancers were analyzed. For all simulated setup errors, the maximum doses to the brainstem, spinal cord, parotids and cochlea were no greater than 0.6Gy of the respective original PRV maximum. Despite 3mm setup shifts, the minimum dose delivered to 95% of the CTVs and PTVs were always within 0.4Gy of the original plan. Conclusions: For head and neck sites treated with Tomotherapy, the use of a 3mm PRV expansion provide a reasonable estimate of the dosimetric effects of 3mm setup uncertainties. Similarly, target coverage appears minimally effected by a 3mm setup uncertainty. Data from a larger number of patients will be presented. Future work will include other anatomical sites.

  17. High-dose Helical Tomotherapy With Concurrent Full-dose Chemotherapy for Locally Advanced Pancreatic Cancer

    SciTech Connect

    Chang, Jee Suk; Wang, Michael L.C.; Koom, Woong Sub; Yoon, Hong In; Chung, Yoonsun; Song, Si Young; Seong, Jinsil

    2012-08-01

    Purpose: To improve poor therapeutic outcome of current practice of chemoradiotherapy (CRT), high-dose helical tomotherapy (HT) with concurrent full-dose chemotherapy has been performed on patients with locally advanced pancreatic cancer (LAPC), and the results were analyzed. Methods and Materials: We retrospectively reviewed 39 patients with LAPC treated with radiotherapy using HT (median, 58.4 Gy; range, 50.8-59.9 Gy) and concomitant chemotherapy between 2006 and 2009. Radiotherapy was directed to the primary tumor with a 0.5-cm margin without prophylactic nodal coverage. Twenty-nine patients (79%) received full-dose (1000 mg/m{sup 2}) gemcitabine-based chemotherapy during HT. After completion of CRT, maintenance chemotherapy was administered to 37 patients (95%). Results: The median follow-up was 15.5 months (range, 3.4-43.9) for the entire cohort, and 22.5 months (range, 12.0-43.9) for the surviving patients. The 1- and 2-year local progression-free survival rates were 82.1% and 77.3%, respectively. Eight patients (21%) were converted to resectable status, including 1 with a pathological complete response. The median overall survival and progression-free survival were 21.2 and 14.0 months, respectively. Acute toxicities were acceptable with no gastrointestinal (GI) toxicity higher than Grade 3. Severe late GI toxicity ({>=}Grade 3) occurred in 10 patients (26%); 1 treatment-related death from GI bleeding was observed. Conclusion: High-dose helical tomotherapy with concurrent full-dose chemotherapy resulted in improved local control and long-term survival in patients with LAPC. Future studies are needed to widen the therapeutic window by minimizing late GI toxicity.

  18. A motion phantom study on helical tomotherapy: the dosimetric impacts of delivery technique and motion

    NASA Astrophysics Data System (ADS)

    Kanagaki, Brian; Read, Paul W.; Molloy, Janelle A.; Larner, James M.; Sheng, Ke

    2007-01-01

    Helical tomotherapy (HT) can potentially be used for lung cancer treatment including stereotactic radiosurgery because of its advanced image guidance and its ability to deliver highly conformal dose distributions. However, previous theoretical and simulation studies reported that the effect of respiratory motion on statically planned tomotherapy treatments may cause substantial differences between the calculated and actual delivered radiation isodose distribution, particularly when the treatment is hypofractionated. In order to determine the dosimetric effects of motion upon actual HT treatment delivery, phantom film dosimetry measurements were performed under static and moving conditions using a clinical HT treatment unit. The motion phantom system was constructed using a programmable motor, a base, a moving platform and a life size lung heterogeneity phantom with wood inserts representing lung tissue with a 3.0 cm diameter spherical tumour density equivalent insert. In order to determine the effects of different motion and tomotherapy delivery parameters, treatment plans were created using jaw sizes of 1.04 cm and 2.47 cm, with incremental gantry rotation periods between the minimum allowed (10 s) and the maximum allowed (60 s). The couch speed varied from 0.009 cm s-1 to 0.049 cm s-1, and delivered to a phantom under static and dynamic conditions with peak-to-peak motion amplitudes of 1.2 cm and 2 cm and periods of 3 and 5 s to simulate human respiratory motion of lung tumours. A cylindrical clinical target volume (CTV) was contoured to tightly enclose the tumour insert. 2.0 Gy was prescribed to 95% of the CTV. Two-dimensional dose was measured by a Kodak EDR2 film. Dynamic phantom doses were then quantitatively compared to static phantom doses in terms of axial dose profiles, cumulative dose volume histograms (DVH), percentage of CTV receiving the prescription dose and the minimum dose received by 95% of the CTV. The larger motion amplitude resulted in more

  19. SU-E-J-203: Reconstruction of the Treatment Area by Use of Sinogram in Helical Tomotherapy

    SciTech Connect

    Haga, A; Nakagawa, K; Ida, S; Sakata, D; Magome, T; Nakano, M; Masutani, Y; Maurer, C; Ruchala, K; Chao, E; Casey, D

    2014-06-01

    Purpose: TomoTherapy (Accuray Co.) has an image-guided radiotherapy system with megavoltage (MV) X-ray source and the on-board imaging device. With the MV computed tomography (MVCT), it became feasible to perform the efficient daily-3D registration of the patient position before each treatment delivery. This system also allows one to acquire the delivery sinogram during the actual treatment, which partly includes the information of the irradiated object. In this study, we try to develop the image reconstruction during treatment in helical Tomotherapy. Methods: Sinogram data were acquired during helical Tomotherapy delivery using an arc-shaped detector array that consists of 738 xenon-gas filled detector cells. In preprocessing, these were normalized by full air-scan data. A software program was developed that reconstructs 3D images during treatment with corrections as; (1) the regions outside the field were masked not to be added in the backprojection (a masking correction), and (2) each voxel of the reconstructed image was divided by the number of the X-ray passing through its voxel (a ray-passing correction). Results: Without masking and ray-passing corrections, the image reconstruction was failed. The masking correction made the image clear, however, the streak artifact was accompanied. The ray-passing correction reduced this artifact. Although the SNR (the ratio of mean to standard deviation in homogeneous region) and the contrast of the reconstructed image were slightly improved with the ray-passing correction, the masking correction only is enough for the visualization purpose. Conclusion: The visualization of the treatment area was feasible by use of the sinogram in helical Tomotherapy. This proposed method can be utilized in the treatment verification. This work was partly supported by JSPS KAKENHI 24234567. No COI, but the data in this paper were prepared by collaborators in Accuray.

  20. Megavoltage Computed Tomography Image Guidance With Helical Tomotherapy in Patients With Vertebral Tumors: Analysis of Factors Influencing Interobserver Variability

    SciTech Connect

    Levegruen, Sabine; Poettgen, Christoph; Abu Jawad, Jehad; Berkovic, Katharina; Hepp, Rodrigo; Stuschke, Martin

    2013-02-01

    Purpose: To evaluate megavoltage computed tomography (MVCT)-based image guidance with helical tomotherapy in patients with vertebral tumors by analyzing factors influencing interobserver variability, considered as quality criterion of image guidance. Methods and Materials: Five radiation oncologists retrospectively registered 103 MVCTs in 10 patients to planning kilovoltage CTs by rigid transformations in 4 df. Interobserver variabilities were quantified using the standard deviations (SDs) of the distributions of the correction vector components about the observers' fraction mean. To assess intraobserver variabilities, registrations were repeated after {>=}4 weeks. Residual deviations after setup correction due to uncorrectable rotational errors and elastic deformations were determined at 3 craniocaudal target positions. To differentiate observer-related variations in minimizing these residual deviations across the 3-dimensional MVCT from image resolution effects, 2-dimensional registrations were performed in 30 single transverse and sagittal MVCT slices. Axial and longitudinal MVCT image resolutions were quantified. For comparison, image resolution of kilovoltage cone-beam CTs (CBCTs) and interobserver variability in registrations of 43 CBCTs were determined. Results: Axial MVCT image resolution is 3.9 lp/cm. Longitudinal MVCT resolution amounts to 6.3 mm, assessed as full-width at half-maximum of thin objects in MVCTs with finest pitch. Longitudinal CBCT resolution is better (full-width at half-maximum, 2.5 mm for CBCTs with 1-mm slices). In MVCT registrations, interobserver variability in the craniocaudal direction (SD 1.23 mm) is significantly larger than in the lateral and ventrodorsal directions (SD 0.84 and 0.91 mm, respectively) and significantly larger compared with CBCT alignments (SD 1.04 mm). Intraobserver variabilities are significantly smaller than corresponding interobserver variabilities (variance ratio [VR] 1.8-3.1). Compared with 3-dimensional

  1. Reference dosimetry for helical tomotherapy: Practical implementation and a multicenter validation

    SciTech Connect

    De Ost, B.; Schaeken, B.; Vynckier, S.; Sterpin, E.; Van den Weyngaert, D.

    2011-11-15

    Purpose: The aim of this study was to implement a protocol for reference dosimetry in tomotherapy and to validate the beam output measurements with an independent dosimetry system. Methods: Beam output was measured at the reference depth of 10 cm in water for the following three cases: (1) a 5 x 10 cm{sup 2} static machine specific reference field (MSR), (2) a rotational 5 x 10 cm{sup 2} field without modulation and no tabletop in the beam, (3) a plan class specific reference (PCSR) field defined as a rotational homogeneous dose delivery to a cylindrical shaped target volume: plan with modulation and table-top movement. The formalism for reference dosimetry of small and nonstandard fields [Med.Phys.35: 5179-5186, 2008] and QA recommendations [Med.Phys.37: 4817-4853, 2010] were adopted in the dose measurement protocol. All ionization chamber measurements were verified independently using alanine/EPR dosimetry. As a pilot study, the beam output was measured on tomotherapy Hi-art systems at three other centers and directly compared to the centers specifications and to alanine dosimetry. Results: For the four centers, the mean static output at a depth of 10 cm in water and SAD = 85 cm, measured with an A1SL chamber following the TG-148 report was 6.238 Gy/min {+-} 0.058 (1 SD); the rotational output was 6.255 Gy/min {+-} 0.069 (1 SD). The dose stated by the center was found in good agreement with the measurements of the visiting team: D{sub center}/D{sub visit} = 1.000 {+-} 0.003 (1 SD). The A1SL chamber measurements were all in good agreement with Alanine/EPR dosimetry. Going from the static reference field to the rotational/non modulated field the dose rate remains constant within 0.2% except for one center where a deviation of 1.3% was detected. Conclusions: Following the TG-148 report, beam output measurements in water at the reference depth using a local protocol, as developed at different centers, was verified. The measurements were found in good agreement with

  2. An automatic dose verification system for adaptive radiotherapy for helical tomotherapy

    NASA Astrophysics Data System (ADS)

    Mo, Xiaohu; Chen, Mingli; Parnell, Donald; Olivera, Gustavo; Galmarini, Daniel; Lu, Weiguo

    2014-03-01

    Purpose: During a typical 5-7 week treatment of external beam radiotherapy, there are potential differences between planned patient's anatomy and positioning, such as patient weight loss, or treatment setup. The discrepancies between planned and delivered doses resulting from these differences could be significant, especially in IMRT where dose distributions tightly conforms to target volumes while avoiding organs-at-risk. We developed an automatic system to monitor delivered dose using daily imaging. Methods: For each treatment, a merged image is generated by registering the daily pre-treatment setup image and planning CT using treatment position information extracted from the Tomotherapy archive. The treatment dose is then computed on this merged image using our in-house convolution-superposition based dose calculator implemented on GPU. The deformation field between merged and planning CT is computed using the Morphon algorithm. The planning structures and treatment doses are subsequently warped for analysis and dose accumulation. All results are saved in DICOM format with private tags and organized in a database. Due to the overwhelming amount of information generated, a customizable tolerance system is used to flag potential treatment errors or significant anatomical changes. A web-based system and a DICOM-RT viewer were developed for reporting and reviewing the results. Results: More than 30 patients were analysed retrospectively. Our in-house dose calculator passed 97% gamma test evaluated with 2% dose difference and 2mm distance-to-agreement compared with Tomotherapy calculated dose, which is considered sufficient for adaptive radiotherapy purposes. Evaluation of the deformable registration through visual inspection showed acceptable and consistent results, except for cases with large or unrealistic deformation. Our automatic flagging system was able to catch significant patient setup errors or anatomical changes. Conclusions: We developed an automatic dose

  3. Implant breast reconstruction followed by radiotherapy: Can helical tomotherapy become a standard irradiation treatment?

    SciTech Connect

    Massabeau, Carole; Fournier-Bidoz, Nathalie; Wakil, Georges; Castro Pena, Pablo; Viard, Romain; Zefkili, Sofia; Reyal, Fabien; Campana, Francois; Fourquet, Alain; Kirova, Youlia M.

    2012-01-01

    To evaluate the benefits and limitations of helical tomotherapy (HT) for loco-regional irradiation of patients after a mastectomy and immediate implant-based reconstruction. Ten breast cancer patients with retropectoral implants were randomly selected for this comparative study. Planning target volumes (PTVs) 1 (the volume between the skin and the implant, plus margin) and 2 (supraclavicular, infraclavicular, and internal mammary nodes, plus margin) were 50 Gy in 25 fractions using a standard technique and HT. The extracted dosimetric data were compared using a 2-tailed Wilcoxon matched-pair signed-rank test. Doses for PTV1 and PTV2 were significantly higher with HT (V95 of 98.91 and 97.91%, respectively) compared with the standard technique (77.46 and 72.91%, respectively). Similarly, the indexes of homogeneity were significantly greater with HT (p = 0.002). HT reduced ipsilateral lung volume that received {>=}20 Gy (16.7 vs. 35%), and bilateral lungs (p = 0.01) and neighboring organs received doses that remained well below tolerance levels. The heart volume, which received 25 Gy, was negligible with both techniques. HT can achieve full target coverage while decreasing high doses to the heart and ipsilateral lung. However, the low doses to normal tissue volumes need to be reduced in future studies.

  4. Dosimetric comparison of stereotactic body radiotherapy for spinal metastasis in cyberknife and helical tomotherapy

    NASA Astrophysics Data System (ADS)

    Kang, Young-nam; Kay, Chul Seung; Son, Seok Hyun; Choi, Byung Ock; Jung, Ji-Young; Shin, Hun-Joo; Kay, Chul Seung; Son, Seok Hyun; Kim, Myong Ho; Seo, Jae-Hyuk; Lee, Gi Woong

    2012-12-01

    This study seeks to evaluate the stereotactic body radiation therapy (SBRT) dosimetric benefit of cyberknife (CK) and helical tomotherapy (HT) for spinal tumor patients in regards to successful plan acceptance and lower dosage to critical structures. This study used dose volume histogram (DVH) compared the two systems quantitatively, by using several indices for the dosimetric comparisons, including the conformity index (CI) and homogeneity index (HI) for the planned target volume (PTV). We planned L3 (n = 2), L5 (n = 1), T12 (n = 1), C3 (n = 1), and T5 (n = 1) spinal tumors case with planning target volumes ranging from 3.55-17.95 cc. Prescription doses were 1600 ˜ 2000 cGy per single fraction. CK prescribed 80 ˜ 85% in PTV and HT 90 ˜ 95%, respectively. The dosimetric data were compared between the two treatment systems by calculating the CI, HI, and maximum doses to the OARs based on the treatment plans, generated for each site. Regarding the homogeneity of PTV, both plans gave satisfactory results, and no significant differences were observed. The partial volume tolerance dose (received dose of 10 Gy at a spinal cord volume 10%) to the spinal cord in 16 ˜ 18 Gy single fraction was satisfactory. We found that both planning systems satisfied the required PTV prescription, but better dose conformity and better dose homogeneity with a poorer dose gradient were achieved with HT then with CK.

  5. Tumor cell survival dependence on helical tomotherapy, continuous arc and segmented dose delivery

    NASA Astrophysics Data System (ADS)

    Yang, Wensha; Wang, Li; Larner, James; Read, Paul; Benedict, Stan; Sheng, Ke

    2009-11-01

    The temporal pattern of radiation delivery has been shown to influence the tumor cell survival fractions for the same radiation dose. To study the effect more specifically for state of the art rotational radiation delivery modalities, 2 Gy of radiation dose was delivered to H460 lung carcinoma, PC3 prostate cancer cells and MCF-7 breast tumor cells by helical tomotherapy (HT), seven-field LINAC (7F), and continuous dose delivery (CDD) over 2 min that simulates volumetric rotational arc therapy. Cell survival was measured by the clonogenic assay. The number of viable H460 cell colonies was 23.2 ± 14.4% and 27.7 ± 15.6% lower when irradiated by CDD compared with HT and 7F, respectively, and the corresponding values were 36.8 ± 18.9% and 35.3 ± 18.9% lower for MCF7 cells (p < 0.01). The survival of PC3 was also lower when irradiated by CDD than by HT or 7F but the difference was not as significant (p = 0.06 and 0.04, respectively). The higher survival fraction from HT delivery was unexpected because 90% of the 2 Gy was delivered in less than 1 min at a significantly higher dose rate than the other two delivery techniques. The results suggest that continuous dose delivery at a constant dose rate results in superior in vitro tumor cell killing compared with prolonged, segmented or variable dose rate delivery.

  6. Helical Tomotherapy Planning for Lung Cancer Based on Ventilation Magnetic Resonance Imaging

    SciTech Connect

    Cai Jing; McLawhorn, Robert; Altes, Tallisa A.; Lange, Eduard de; Read, Paul W.; Larner, James M.; Benedict, Stanley H.; Sheng Ke

    2011-01-01

    To investigate the feasibility of lung ventilation-based treatment planning, computed tomography and hyperpolarized (HP) helium-3 (He-3) magnetic resonance imaging (MRI) ventilation images of 6 subjects were coregistered for intensity-modulated radiation therapy planning in Tomotherapy. Highly-functional lungs (HFL) and less-functional lungs (LFL) were contoured based on their ventilation image intensities, and a cylindrical planning-target-volume was simulated at locations adjacent to both HFL and LFL. Annals of an anatomy-based plan (Plan 1) and a ventilation-based plan (Plan 2) were generated. The following dosimetric parameters were determined and compared between the 2 plans: percentage of total/HFL volume receiving {>=}20 Gy, 15 Gy, 10 Gy, and 5 Gy (TLV{sub 20}, HFLV{sub 20}, TLV{sub 15}, HFLV{sub 15}, TLV{sub 10}, HFLV{sub 10}, TLV{sub 5}, HFLV{sub 5}), mean total/HFL dose (MTLD/HFLD), maximum doses to all organs at risk (OARs), and target dose conformality. Compared with Plan 1, Plan 2 reduced mean HFLD (mean reduction, 0.8 Gy), MTLD (mean reduction, 0.6 Gy), HFLV{sub 20} (mean reduction, 1.9%), TLV{sub 20} (mean reduction, 1.5%), TLV{sub 15} (mean reduction, 1.7%), and TLV{sub 10} (mean reduction, 2.1%). P-values of the above comparisons are less than 0.05 using the Wilcoxon signed rank test. For HFLV{sub 15}, HFLV{sub 10}, TLV{sub 5}, and HTLV{sub 5}, Plan 2 resulted in lower values than plan 1 but the differences are not significant (P-value range, 0.063-0.219). Plan 2 did not significantly change maximum doses to OARs (P-value range, 0.063-0.563) and target conformality (P = 1.000). HP He-3 MRI of patients with lung disease shows a highly heterogeneous ventilation capacity that can be utilized for functional treatment planning. Moderate but statistically significant improvements in sparing functional lungs were achieved using helical tomotherapy plans.

  7. Dosimetric evaluation of a three-phase adaptive radiotherapy for nasopharyngeal carcinoma using helical tomotherapy

    SciTech Connect

    Fung, Winky Wing Ki; Wu, Vincent Wing Cheung; Teo, Peter Man Lung

    2012-04-01

    helical tomotherapy of NPC.

  8. Dosimetric Study and Verification of Total Body Irradiation Using Helical Tomotherapy and its Comparison to Extended SSD Technique

    SciTech Connect

    Zhuang, Audrey H.; Liu An; Schultheiss, Timothy E.; Wong, Jeffrey Y.C.

    2010-01-01

    The American College of Radiology practice guideline for total body irradiation (TBI) requires a back-up treatment delivery system. This study investigates the development of helical tomotherapy (HT) for delivering TBI and compares it with conventional extended source-to-surface distance (X-SSD) technique. Four patients' head-to-thigh computed tomographic images were used in this study, with the target defined as the body volume without the left and right lungs. HT treatment plans with the standard TBI prescription (1.2 Gy/fx, 10 fractions) were generated and verified on phantoms. To compare HT plans with X-SSD treatment, the dose distribution of X-SSD technique was simulated using the Eclipse software. The average dose received by 90% of the target volume was 12.3 Gy (range, 12.2-12.4 Gy) for HT plans and 10.3 Gy (range, 10.08-10.58 Gy) for X-SSD plans (p < 0.001). The left and right lung median doses were 5.44 Gy and 5.40 Gy, respectively, for HT plans and 8.34 Gy and 8.95 Gy, respectively, for X-SSD treatment. The treatment planning time was comparable between the two methods. The beam delivery time of HT treatment was longer than X-SSD treatment. In conclusion, HT-based TBI plans have better dose coverage to the target and better dose sparing to the lungs compared with X-SSD technique, which applies dose compensators, lung blocks, and electron boosts. This study demonstrates that HT is possible for delivering TBI. Clinical validation of the feasibility of this approach would be of interest in the future.

  9. Dosimetric Comparison of Helical Tomotherapy and Linac-IMRT Treatment Plans for Head and Neck Cancer Patients

    SciTech Connect

    Zhang Xin; Penagaricano, Jose; Moros, Eduardo G.; Corry, Peter M.; Yan Yulong; Ratanatharathorn, Vaneerat

    2010-01-01

    The rapid development and clinical implementation of external beam radiation treatment technologies continues. The existence of various commercially available technologies for intensity-modulated radiation therapy (IMRT) has stimulated interest in exploring the differential potential advantage one may have compared with another. Two such technologies, Hi-Art Helical Tomotherapy (HT) and conventional medical linear accelerator-based IMRT (LIMRT) have been shown to be particularly suitable for the treatment of head and neck cancers. In this study, 23 patients who were diagnosed with stages 3 or 4 head and neck cancers, without evidence of distance metastatic disease, were treated in our clinic. Treatment plans were developed for all patients simultaneously on the HT planning station and on the Pinnacle treatment planning system for step-and-shoot IMRT. Patients were treated only on the HT unit, with the LIMRT plan serving as a backup in case the HT system might not be available. All plans were approved for clinical use by a physician. The prescription was that patients receive at least 95% of the planning target volume (PTV), which is 66 Gy at 2.2 Gy per fraction. Several dosimetric parameters were computed: PTV dose coverage; PTV volume conformity index; the normalized total dose (NTD), where doses were converted to 2 Gy per fraction to organs at risk (OAR); and PTV dose homogeneity. Both planning systems satisfied our clinic's PTV prescription requirements. The results suggest that HT plans had, in general, slightly better dosimetric characteristics, especially regarding PTV dose homogeneity and normal tissue sparing. However, for both techniques, doses to OAR were well below the currently accepted normal tissue tolerances. Consequently, factors other than the dosimetric parameters studied here may have to be considered when making a choice between IMRT techniques.

  10. Prospective Phase I-II Trial of Helical Tomotherapy With or Without Chemotherapy for Postoperative Cervical Cancer Patients

    SciTech Connect

    Schwarz, Julie K.; Wahab, Sasa; Grigsby, Perry W.

    2011-12-01

    Purpose: To investigate, in a prospective trial, the acute and chronic toxicity of patients with cervical cancer treated with surgery and postoperative intensity-modulated radiotherapy (RT) delivered using helical tomotherapy, with or without the administration of concurrent chemotherapy. Patients and Methods: A total of 24 evaluable patients entered the study between March 2006 and August 2009. The indications for postoperative RT were tumor size, lymphovascular space invasion, and the depth of cervical stromal invasion in 15 patients; 9 patients underwent postoperative RT because of surgically positive lymph nodes. All patients underwent pelvic RT delivered with helical tomotherapy and intracavitary high-dose-rate brachytherapy. Treatment consisted of concurrent weekly platinum in 17, sequential carboplatin/Taxol in 1, and RT alone in 6. The patients were monitored for acute and chronic toxicity using the Common Toxicity Criteria, version 3.0. Results: The median follow-up was 24 months (range, 4-49). At the last follow-up visit, 23 patients were alive and disease free. Of the 24 patients, 12 (50%) experienced acute Grade 3 gastrointestinal toxicity (anorexia in 5, diarrhea in 4, and nausea in 3). One patient developed acute Grade 4 genitourinary toxicity (vesicovaginal fistula). For patients treated with concurrent chemotherapy, the incidence of acute Grade 3 and 4 hematologic toxicity was 71% and 24%, respectively. For patients treated without concurrent chemotherapy, the incidence of acute Grade 3 and 4 hematologic toxicity was 29% and 14%, respectively. Two long-term toxicities occurred (vesicovaginal fistula at 25 months and small bowel obstruction at 30 months). The overall and progression-free survival rate at 3 years for all patients was 100% and 89%, respectively. Conclusion: The results of our study have shown that postoperative external RT for cervical cancer delivered with helical tomotherapy and high-dose-rate brachytherapy and with or without

  11. Treatment of nasopharyngeal carcinoma using simultaneous modulated accelerated radiation therapy via helical tomotherapy: a phase II study

    PubMed Central

    Du, Lei; Zhang, Xin Xin; Feng, Lin Chun; Chen, Jing; Yang, Jun; Liu, Hai Xia; Xu, Shou Ping; Xie, Chuan Bin

    2016-01-01

    Abstract Background The aim of the study was to evaluate short-term safety and efficacy of simultaneous modulated accelerated radiation therapy (SMART) delivered via helical tomotherapy in patients with nasopharyngeal carcinoma (NPC). Methods Between August 2011 and September 2013, 132 newly diagnosed NPC patients were enrolled for a prospective phase II study. The prescription doses delivered to the gross tumor volume (pGTVnx) and positive lymph nodes (pGTVnd), the high risk planning target volume (PTV1), and the low risk planning target volume (PTV2), were 67.5 Gy (2.25 Gy/F), 60 Gy (2.0 Gy/F), and 54 Gy (1.8 Gy/F), in 30 fractions, respectively. Acute toxicities were evaluated according to the established RTOG/EORTC criteria. This group of patients was compared with the 190 patients in the retrospective P70 study, who were treated between September 2004 and August 2009 with helical tomotherapy, with a dose of 70-74 Gy/33F/6.5W delivered to pGTVnx and pGTVnd. Results The median follow-up was 23.7 (12–38) months. Acute radiation related side-effects were mainly problems graded as 1 or 2. Only a small number of patients suffered from grade 4 leucopenia (4.5%) or thrombocytopenia (2.3%). The local relapse-free survival (LRFS), nodal relapse-free survival (NRFS), local-nodal relapse-free survival (LNRFS), distant metastasis-free survival (DMFS) and overall survival (OS) were 96.7%, 95.5%, 92.2%, 92.7% and 93.2%, at 2 years, respectively, with no significant difference compared with the P70 study. Conclusions Smart delivered via the helical tomotherapy technique appears to be associated with an acceptable acute toxicity profile and favorable short-term outcomes for patients with NPC. Long-term toxicities and patient outcomes are under investigation. PMID:27247555

  12. Voxel-Based Dose Reconstruction for Total Body Irradiation With Helical TomoTherapy

    SciTech Connect

    Chao Ming; Penagaricano, Jose; Yan Yulong; Moros, Eduardo G.; Corry, Peter; Ratanatharathorn, Vaneerat

    2012-04-01

    Purpose: We have developed a megavoltage CT (MVCT)-based dose reconstruction strategy for total body irradiation (TBI) with helical TomoTherapy (HT) using a deformable registration model to account for the patient's interfraction changes. The proposed technique serves as an efficient tool for delivered dose verification and, potentially, plan adaptation. Methods and Materials: Four patients with acute myelogenous leukemia treated with TBI using HT were selected for this study. The prescription was 12 Gy, 2 Gy/fraction, twice per day, given at least 6 h apart. The original plan achieved coverage of 80% of the clinical target volume (CTV) by the 12 Gy isodose surface. MVCTs were acquired prior to each treatment. Regions of interest were contoured on each MVCT. The dose for each fraction was calculated based on the MVCT using the HT planned adaptive station. B-spline deformable registration was conducted to establish voxel-to-voxel correspondence between the MVCT and the planning CT. The resultant deformation vector was employed to map the reconstructed dose from each fraction to the same point as the plan dose, and a voxel-to-voxel summed dose from all six fractions was obtained. The reconstructed dose distribution and its dosimetric parameters were compared with those of the original treatment plan. Results: While changes in CTV contours occurred in all patients, the reconstructed dose distribution showed that the dose-volume histogram for CTV coverage was close (<1.5%) to that of the original plan. For sensitive structures, the differences between the reconstructed and the planned doses were less than 3.0%. Conclusion: Voxel-based dose reconstruction strategy that takes into account interfraction anatomical changes using MVCTs is a powerful tool for treatment verification of the delivered doses. This proposed technique can also be applied to adaptive TBI therapy using HT.

  13. Feasibility of Helical Tomotherapy for Debulking Irradiation Before Stem Cell Transplantation in Malignant Lymphoma

    SciTech Connect

    Chargari, Cyrus; Vernant, Jean-Paul; Tamburini, Jerome; Zefkili, Sofia; Fayolle, Maryse; Campana, Francois; Fourquet, Alain; Kirova, Youlia M.

    2011-11-15

    Purpose: Preliminary clinical experience has suggested that radiation therapy (RT) may be effectively incorporated into conditioning therapy before transplant for patients with refractory/relapsed malignant lymphoma. We investigated the feasibility of debulking selective lymph node irradiation before autologous and/or allogeneic stem cell transplantation (SCT) using helical tomotherapy (HT). Methods and Materials: Six consecutive patients with refractory malignant lymphoma were referred to our institution for salvage HT before SCT. All patients had been previously heavily treated but had bulky residual tumor despite chemotherapy (CT) intensification. Two patients had received previous radiation therapy. HT delivered 30-40 Gy in the involved fields (IF), using 6 MV photons, 2 Gy per daily fraction. Total duration of treatment was 28 to 35 days. Results: Using HT, doses to critical organs (heart, lungs, esophagu, and parotids) were significantly decreased and highly conformational irradiation could be delivered to all clinical target volumes. HT delivery was technically possible, even in patients with lesions extremely difficult to irradiate in other conditions or in patients with previous radiation therapy. No Grade 2 or higher toxicity occurred. Four months after the end of HT, 5 patients experienced complete clinical, radiologic, and metabolic response and were subsequently referred for SCT. Conclusions: By more effectively sparing critical organs, HT may contribute to improving the tolerance of debulking irradiation before allograft. Quality of life may be preserved, and doses to the heart may be decreased. This is particularly relevant in heavily treated patients who are at risk for subsequent heart disease. These preliminary results require further prospective assessment.

  14. Treatment and Dosimetric Advantages Between VMAT, IMRT, and Helical TomoTherapy in Prostate Cancer

    SciTech Connect

    Tsai, Chiao-Ling; Wu, Jian-Kuen; Chao, Hsiao-Ling; Tsai, Yi-Chun; Cheng, Jason Chia-Hsien

    2011-10-01

    We investigated the possible treatment and dosimetric advantage of volumetric modulated arc therapy (VMAT) over step-and-shoot intensity-modulated radiation therapy (step-and-hhoot IMRT) and helical tomotherapy (HT). Twelve prostate cancer patients undergoing VMAT to the prostate were included. Three treatment plans (VMAT, step-and-shoot IMRT, HT) were generated for each patient. The doses to clinical target volume and 95% of planning target volume were both {>=}78 Gy. Target coverage, conformity index, dose to rectum/bladder, monitor units (MU), treatment time, equivalent uniform dose (EUD), normal tissue complication probability (NTCP) of targets, and rectum/bladder were compared between techniques. HT provided superior conformity and significantly less rectal volume exposed to 65 Gy and 40 Gy, as well as EUD/NTCP of rectum than step-and-shoot IMRT, whereas VMAT had a slight dosimetric advantage over step-and-shoot IMRT. Notably, significantly lower MUs were needed for VMAT (309.7 {+-} 35.4) and step-and-shoot IMRT (336.1 {+-} 16.8) than for HT (3368 {+-} 638.7) (p < 0.001). The treatment time (minutes) was significantly shorter for VMAT (2.6 {+-} 0.5) than step-and-shoot IMRT (3.8 {+-} 0.3) and HT (3.8 {+-} 0.6) (p < 0.001). Dose verification of VMAT using point dose and film dosimetry met the accepted criteria. VMAT and step-and-shoot IMRT have comparable dosimetry, but treatment efficiency is significantly higher for VMAT than for step-and-shoot IMRT and HT.

  15. Accelerated large volume irradiation with dynamic Jaw/Dynamic Couch Helical Tomotherapy

    PubMed Central

    2012-01-01

    Background Helical Tomotherapy (HT) has unique capacities for the radiotherapy of large and complicated target volumes. Next generation Dynamic Jaw/Dynamic Couch HT delivery promises faster treatments and reduced exposure of organs at risk due to a reduced dose penumbra. Methods Three challenging clinical situations were chosen for comparison between Regular HT delivery with a field width of 2.5 cm (Reg 2.5) and 5.0 cm (Reg 5.0) and DJDC delivery with a maximum field width of 5.0 cm (DJDC 5.0): Hemithoracic Irradiation, Whole Abdominal Irradiation (WAI) and Total Marrow Irradiation (TMI). For each setting, five CT data sets were chosen, and target coverage, conformity, integral dose, dose exposure of organs at risk (OAR) and treatment time were calculated. Results Both Reg 5.0 and DJDC 5.0 achieved a substantial reduction in treatment time while maintaining similar dose coverage. Treatment time could be reduced from 10:57 min to 3:42 min / 5:10 min (Reg 5.0 / DJDC 5.0) for Hemithoracic Irradiation, from 18:03 min to 8:02 min / 8:03 min for WAI and to 18:25 min / 18:03 min for TMI. In Hemithoracic Irradiation, OAR exposure was identical in all modalities. For WAI, Reg 2.5 resulted in lower exposure of liver and bone. DJDC plans showed a small but significant increase of ∼ 1 Gy to the kidneys, the parotid glans and the thyroid gland. While Reg 5.0 and DJDC were identical in terms of OAR exposure, integral dose was substantially lower with DJDC, caused by a smaller dose penumbra. Conclusions Although not clinically available yet, next generation DJDC HT technique is efficient in improving the treatment time while maintaining comparable plan quality. PMID:23146914

  16. Split-Field Helical Tomotherapy With or Without Chemotherapy for Definitive Treatment of Cervical Cancer

    SciTech Connect

    Chang, Albert J.; Richardson, Susan; Grigsby, Perry W.; Schwarz, Julie K.

    2012-01-01

    Objective: The objective of this study was to investigate the chronic toxicity, response to therapy, and survival outcomes of patients with cervical cancer treated with definitive pelvic irradiation delivered by helical tomotherapy (HT), with or without concurrent chemotherapy. Methods and Materials: There were 15 patients with a new diagnosis of cervical cancer evaluated in this study from April 2006 to February 2007. The clinical stages of their disease were Stage Ib1 in 3 patients, Ib2 in 3, IIa in 2, IIb in 4, IIIb in 2, and IVa in 1 patient. Fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) simulation was performed in all patients. All patients received pelvic irradiation delivered by HT and high-dose-rate (HDR) brachytherapy. Four patients also received para-aortic irradiation delivered by HT. Thirteen patients received concurrent chemotherapy. Patients were monitored for chronic toxicity using the Common Terminology Criteria for Adverse Events version 3.0 criteria. Results: The median age of the cohort was 51 years (range, 29-87 years), and the median follow-up for all patients alive at time of last follow-up was 35 months. The median overall radiation treatment time was 54 days. One patient developed a chronic Grade 3 GI complication. No other Grade 3 or 4 complications were observed. At last follow-up, 3 patients had developed a recurrence, with 1 patient dying of disease progression. The 3-year progression-free and cause-specific survival estimates for all patients were 80% and 93%, respectively. Conclusion: Intensity-modulated radiation therapy delivered with HT and HDR brachytherapy with or without chemotherapy for definitive treatment of cervical cancer is feasible, with acceptable levels of chronic toxicity.

  17. SU-E-T-371: Validation of Organ Doses Delivered During Craniospinal Irradiation with Helical Tomotherapy

    SciTech Connect

    Perez-Andujar, A; Chen, J; Garcia, A; Haas-Kogan, D

    2014-06-01

    Purpose: New techniques have been developed to deliver more conformal treatments to the craniospinal axis. One concern, however, is the widespread low dose delivered and implications for possible late effects. The purpose of this work is for the first time to validate the organ doses calculated by the treatment planning system (TPS), including out-of-field doses for a pediatric craniospinal treatment (CSI). Methods: A CSI plan prescribed to 23.4 Gy and a posterior fossa boost plan to 30.6 Gy (total dose 54.0 Gy) was developed for a pediatric anthropomorphic phantom representing a 13 yearold- child. For the CSI plan, the planning target volumes (PTV) consisted of the brain and spinal cord with 2 mm and 5 mm expansions, respectively. Organs at risk (OAR) were contoured and included in the plan optimization. The plans were delivered on a helical tomotherapy unit. Thermoluminescent dosimeters (TLDs) were used to measure the dose at 54 positions within the PTV and OARs. Results: For the CSI treatment, the mean percent difference between TPS dose calculations and measurements was 5% for the PTV and 10% for the OARs. For the boost, the average was 3% for the PTV. The percent difference for the OARs, which lie outside the field and received a small fraction of the prescription dose, varied from 15% to 200%. However in terms of absolute dose, the average difference between measurement and TPS per treatment Gy was 2 cGy/Gy and 3 mGy/Gy for the CSI and boost plans, respectively. Conclusion: There was good agreement between doses calculated by the TPS and measurements for the CSI treatment. Higher percent differences were observed for out-of-field doses in the boost plan, but absolute dose differences were very small compared to the prescription dose. These findings can help in the estimation of late effects after radiotherapy for pediatric patients.

  18. Investigation of Pitch and Jaw Width to Decrease Delivery Time of Helical Tomotherapy Treatments for Head and Neck Cancer

    SciTech Connect

    Moldovan, Monica; Fontenot, Jonas D.; Gibbons, John P.; Lee, Tae Kyu; Rosen, Isaac I.; Fields, Robert S.; Hogstrom, Kenneth R.

    2011-01-01

    Helical tomotherapy plans using a combination of pitch and jaw width settings were developed for 3 patients previously treated for head and neck cancer. Three jaw widths (5, 2.5, and 1 cm) and 4 pitches (0.86, 0.43, 0.287, and 0.215) were used with a (maximum) modulation factor setting of 4. Twelve plans were generated for each patient using an identical optimization procedure (e.g., number of iterations, objective weights, and penalties, etc.), based on recommendations from TomoTherapy (Madison, WI). The plans were compared using isodose plots, dose volume histograms, dose homogeneity indexes, conformity indexes, radiobiological models, and treatment times. Smaller pitches and jaw widths showed better target dose homogeneity and sparing of normal tissue, as expected. However, the treatment time increased inversely proportional to the jaw width, resulting in delivery times of 24 {+-} 1.9 min for the 1-cm jaw width. Although treatment plans produced with the 2.5-cm jaw were dosimetrically superior to plans produced with the 5-cm jaw, subsequent calculations of tumor control probabilities and normal tissue complication probabilities suggest that these differences may not be radiobiologically meaningful. Because treatment plans produced with the 5-cm jaw can be delivered in approximately half the time of plans produced with the 2.5-cm jaw (5.1 {+-} 0.6 min vs. 9.5 {+-} 1.1 min), use of the 5-cm jaw in routine treatment planning may be a viable approach to decreasing treatment delivery times from helical tomotherapy units.

  19. Effect of CT contrast on volumetric arc therapy planning (RapidArc and helical tomotherapy) for head and neck cancer

    SciTech Connect

    Liu, Alan J.; Vora, Nayana; Suh, Steve; Liu, An; Schultheiss, Timothy E.; Wong, Jeffrey Y.C.

    2015-04-01

    The objectives of the study were to evaluate the effect of intravenous contrast in the dosimetry of helical tomotherapy and RapidArc treatment for head and neck cancer and determine if it is acceptable during the computed tomography (CT) simulation to acquire only CT with contrast for treatment planning of head and neck cancer. Overall, 5 patients with head and neck cancer (4 men and 1 woman) treated on helical tomotherapy were analyzed retrospectively. For each patient, 2 consecutive CT scans were performed. The first CT set was scanned before the contrast injection and secondary study set was scanned 45 seconds after contrast. The 2 CTs were autoregistered using the same Digital Imaging and Communications in Medicine coordinates. Tomotherapy and RapidArc plans were generated on 1 CT data set and subsequently copied to the second CT set. Dose calculation was performed, and dose difference was analyzed to evaluate the influence of intravenous contrast media. The dose matrix used for comparison included mean, minimum and maximum doses of planning target volume (PTV), PTV dose coverage, and V{sub 45} {sub Gy}, V{sub 30} {sub Gy}, and V{sub 20} {sub Gy} organ doses. Treatment planning on contrasted images generally showed a lower dose to both organs and target than plans on noncontrasted images. The doses for the points of interest placed in the organs and target rarely changed more than 2% in any patient. In conclusion, treatment planning using a contrasted image had insignificant effect on the dose to the organs and targets. In our opinion, only CT with contrast needs to be acquired during the CT simulation for head and neck cancer. Dose calculations performed on contrasted images can potentially underestimate the delivery dose slightly. However, the errors of planning on a contrasted image should not affect the result in clinically significant way.

  20. Helical Tomotherapy Delivery of an IMRT Boost in Lieu of Interstitial Brachytherapy in the Setting of Gynecologic Malignancy: Feasibility and Dosimetric Comparison

    SciTech Connect

    Gielda, Benjamin T.; Shah, Anand P.; Marsh, James C.; Smart, Joseph P.; Bernard, Damian; Rotmensch, Jacob; Griem, Katherine L.

    2011-07-01

    Interstitial brachytherapy is an important means by which to improve local control in gynecologic malignancy when intracavitary brachytherapy is untenable. Patients unable to receive brachytherapy have traditionally received conventional external beam radiation alone with modest results. We investigated the ability of Tomotherapy (Tomotherapy Inc., Madison, WI) to replace interstitial brachytherapy. Six patients were selected. The planning CT of each patient was contoured with the planning target volume (PTV), bladder, rectum, femoral heads, and bowel. Identical contour sets were exported to Tomotherapy and Nucletron PLATO (Nucletron B.V., Veenendaal, The Netherlands). With Tomotherapy, the PTV was prescribed 31 Gy in 5 fractions to 90% of the volume. With PLATO, 600 cGy x 5 fractions was prescribed to the surface of the PTV. Dose delivered was normalized to 2 Gy fractions (EQD2) and added to a hypothetical homogenous 45-Gy pelvic dose. Tomotherapy achieved a D90 of 87 Gy EQD2 versus 86 Gy with brachytherapy. PTV dose was more homogeneous with tomotherapy. The dose to the most at-risk 2 mL of bladder and rectum with Tomotherapy was of 78 and 71 Gy EQD2 versus 81 and 75 Gy with brachytherapy. Tomotherapy delivered more dose to the femoral heads (mean 1.23 Gy per fraction) and bowel. Tomotherapy was capable of replicating the peripheral dose achieved with brachytherapy, without the PTV hotspots inherent to interstitial brachytherapy. Similar maximum doses to bowel and bladder were achieved with both methods. Excessive small bowel and femoral head toxicity may result if previous pelvic irradiation is not planned accordingly. Significant challenges related to interfraction and intrafraction motion must be overcome if treatment of this nature is to be contemplated.

  1. Peripheral Dose Heterogeneity Due to the Thread Effect in Total Marrow Irradiation With Helical Tomotherapy

    SciTech Connect

    Takahashi, Yutaka; Verneris, Michael R.; Dusenbery, Kathryn E.; Wilke, Christopher T.; Storme, Guy; Weisdorf, Daniel J.; Hui, Susanta K.

    2013-11-15

    Purpose: To report potential dose heterogeneity leading to underdosing at different skeletal sites in total marrow irradiation (TMI) with helical tomotherapy due to the thread effect and provide possible solutions to reduce this effect. Methods and Materials: Nine cases were divided into 2 groups based on patient size, defined as maximum left-to-right arm distance (mLRD): small mLRD (≤47 cm) and large mLRD (>47 cm). TMI treatment planning was conducted by varying the pitch and modulation factor while a jaw size (5 cm) was kept fixed. Ripple amplitude, defined as the peak-to-trough dose relative to the average dose due to the thread effect, and the dose–volume histogram (DVH) parameters for 9 cases with various mLRD was analyzed in different skeletal regions at off-axis (eg, bones of the arm or femur), at the central axis (eg, vertebrae), and planning target volume (PTV), defined as the entire skeleton plus 1-cm margin. Results: Average ripple amplitude for a pitch of 0.430, known as one of the magic pitches that reduce thread effect, was 9.2% at 20 cm off-axis. No significant differences in DVH parameters of PTV, vertebrae, or femur were observed between small and large mLRD groups for a pitch of ≤0.287. Conversely, in the bones of the arm, average differences in the volume receiving 95% and 107% dose (V95 and V107, respectively) between large and small mLRD groups were 4.2% (P=.016) and 16% (P=.016), respectively. Strong correlations were found between mLRD and ripple amplitude (rs=.965), mLRD and V95 (rs=−.742), and mLRD and V107 (rs=.870) of bones of the arm. Conclusions: Thread effect significantly influences DVH parameters in the bones of the arm for large mLRD patients. By implementing a favorable pitch value and adjusting arm position, peripheral dose heterogeneity could be reduced.

  2. Helical tomotherapy and volumetric modulated arc therapy: New therapeutic arms in the breast cancer radiotherapy

    PubMed Central

    Lauche, Olivier; Kirova, Youlia M; Fenoglietto, Pascal; Costa, Emilie; Lemanski, Claire; Bourgier, Celine; Riou, Olivier; Tiberi, David; Campana, Francois; Fourquet, Alain; Azria, David

    2016-01-01

    AIM To analyse clinical and dosimetric results of helical tomotherapy (HT) and volumetric modulated arc therapy (VMAT) in complex adjuvant breast and nodes irradiation. METHODS Seventy-three patients were included (31 HT and 42 VMAT). Dose were 63.8 Gy (HT) and 63.2 Gy (VMAT) in the tumour bed, 52.2 Gy in the breast, 50.4 Gy in supraclavicular nodes (SCN) and internal mammary chain (IMC) with HT and 52.2 Gy and 49.3 Gy in IMC and SCN with VMAT in 29 fractions. Margins to particle tracking velocimetry were greater in the VMAT cohort (7 mm vs 5 mm). RESULTS For the HT cohort, the coverage of clinical target volumes was as follows: Tumour bed: 99.4% ± 2.4%; breast: 98.4% ± 4.3%; SCN: 99.5% ± 1.2%; IMC: 96.5% ± 13.9%. For the VMAT cohort, the coverage was as follows: Tumour bed: 99.7% ± 0.5%, breast: 99.3% ± 0.7%; SCN: 99.6% ± 1.4%; IMC: 99.3% ± 3%. For ipsilateral lung, Dmean and V20 were 13.6 ± 1.2 Gy, 21.1% ± 5% (HT) and 13.6 ± 1.4 Gy, 20.1% ± 3.2% (VMAT). Dmean and V30 of the heart were 7.4 ± 1.4 Gy, 1% ± 1% (HT) and 10.3 ± 4.2 Gy, 2.5% ± 3.9% (VMAT). For controlateral breast Dmean was 3.6 ± 0.2 Gy (HT) and 4.6 ± 0.9 Gy (VMAT). Acute skin toxicity grade 3 was 5% in the two cohorts. CONCLUSION HT and VMAT in complex adjuvant breast irradiation allow a good coverage of target volumes with an acceptable acute tolerance. A longer follow-up is needed to assess the impact of low doses to healthy tissues. PMID:27648167

  3. SU-E-T-337: Dosimetric Study of TMI Using Helical Tomotherapy

    SciTech Connect

    Phurailatpam, R; Swamidas, J; Sastri, J; Josi, K; Mathankar, M; Paul, S; Sawant, M; Moundekar, P

    2015-06-15

    Purpose: The purpose of this study is to evaluate the dosimtry of TMI using Helical Tomotherapy (HT). Methods: Whole body CT data sets of 4 patients (median age : range:12–37 years) with 5mm slice thickness were used for planning in HT (TPS version 4.2.3). The contouring of the target and organ at risks (OAR) were delineated ( Oncentra Master Plan v 4.1). Two plans were generated using 5cm and 2.5 cm field widths.The modulation factor and pitch was 3 and 0.3 respectively. Dose to PTV, OARs and the dose homogeneity were evaluated. The doses obtained were compared with the existimg literature. Dose delivery verification was carried out by point dose and 2D array measurements with ion chamber and Arc check dosimetry (Sun NuclearTM) system repectively. The prescribed dose was 14.4 Gy in 8 fractions. Results: The mean PTV volume was 7341.28cc (sd=2353) The dose homogeneity index of PTV was 12.03(sd=2.98) for 2.5cm-FW and 14.61 (sd=1.33) for 5cm-FW.The conformation number for 2.5 and 5 cm plans are 0.6328(sd=0.09) and 0.5915 (sd=0.0376) respectively. The mean dose(Gy) to the OARs were as follows for 2.5cm-FW : eyes, lens, lungs, kidneys, heart, liver,thyroid and testes for are 4.12,1.9,6.61,4.04,4.85,6.06,7.17 and 1.27. The mean dose(Gy) to the OARs were as follows for 5cm-FW :eyes, lens, lungs, kidneys, heart, liver,thyroid and testes for are 4.45,3.14,6.79,4.02,5.01,6.01,10.8 and 1.33. The mean variation of the point dose as compared to the expected dose was within 2% and the gamma analysis was at 91%. Conclusion: It was concluded that 5cm field width plans produces optimal dose volume parameters with deliverable treatment time. From this initial dissymmetric study, it was concluded that the treatment planning and the dose delivery verification was feasible considering the complexity of the TMI.

  4. The sensitivity of ArcCHECK-based gamma analysis to manufactured errors in helical tomotherapy radiation delivery.

    PubMed

    Templeton, Alistair K; Chu, James C H; Turian, Julius V

    2015-01-08

    Three-dimensional measurement arrays are an efficient means of acquiring a distribution of data for patient plan delivery QA. However, the tie between plan integrity and traditional gamma-based analysis of these data are not clear. This study explores the sensitivity of such analysis by creating errors in Helical Tomotherapy delivery and measuring the passing rates with an ArcCHECK cylindrical diode array. Errors were introduced in each of the couch speed, leaf open time, and gantry starting position in increasing magnitude while the resulting gamma passing rates were tabulated. The error size required to degrade the gamma passing rate to 90% or below was on average a 3% change in couch speed, 5° in gantry synchronization, or a 5 ms in leaf closing speed for a 3%/3 mm Van Dyk gamma analysis. This varied with plan type, with prostate plans exhibiting less sensitivity than head and neck plans and with gamma analysis criteria, but in all cases the error magnitudes were large compared to actual machine tolerances. These findings suggest that the sensitivity of ArcCHECK-based gamma analysis to single-mode errors in tomotherapy plans is dependent upon plan and analysis type and at traditional passing thresholds unable to detect small defects in the plan.

  5. SU-E-P-30: Clinical Applications of Spatially Fractionated Radiation Therapy (GRID) Using Helical Tomotherapy

    SciTech Connect

    Zhang, X; Liang, X; Penagaricano, J; Morrill, S; Corry, P; Paudel, N; Vaneerat, V Ratanatharathorn; Yan, Y; Griffin, R

    2015-06-15

    Purpose: To present the first clinical applications of Helical Tomotherapy-based spatially fractionated radiotherapy (HT-GRID) for deep seated tumors and associated dosimetric study. Methods: Ten previously treated GRID patients were selected (5 HT-GRID and 5 LINAC-GRID using a commercially available GRID block). Each case was re-planned either in HT-GRID or LINAC-GRID for a total of 10 plans for both techniques using same prescribed dose of 20 Gy to maximum point dose of GRID GTV. For TOMO-GRID, a programmable virtual TOMOGRID template mimicking a GRID pattern was generated. Dosimetric parameters compared included: GRID GTV mean dose (Dmean) and equivalent uniform dose (EUD), GRID GTV dose inhomogeneity (Ratio(valley/peak)), normal tissue Dmean and EUD, and other organs-at-risk(OARs) doses. Results: The median tumor volume was 634 cc, ranging from 182 to 4646 cc. Median distance from skin to the deepest part of tumor was 22cm, ranging from 8.9 to 38cm. The median GRID GTV Dmean and EUD was 10.65Gy (9.8–12.5Gy) and 7.62Gy (4.31–11.06Gy) for HT-GRID and was 6.73Gy (4.44–8.44Gy) and 3.95Gy (0.14–4.2Gy) for LINAC-GRID. The median Ratio(valley/peak) was 0.144(0.05–0.29) for HT-GRID and was 0.055(0.0001–0.14) for LINAC-GRID. For normal tissue in HT-GRID, the median Dmean and EUD was 1.24Gy (0.34–2.54Gy) and 5.45 Gy(3.45–6.89Gy) and was 0.61 Gy(0.11–1.52Gy) and 6Gy(4.45–6.82Gy) for LINAC-GRID. The OAR doses were comparable between the HT-GRID and LINAC-GRID. However, in some cases it was not possible to avoid a critical structure in LINAC-GRID; while HT-GRID can spare more tissue doses for certain critical structures. Conclusion: HT-GRID delivers higher GRID GTV Dmean, EUD and Ratio(valley/peak) compared to LINAC-GRID. HT-GRID delivers higher Dmean and lower EUD for normal tissue compared to LINAC-GRID. TOMOGRID template can be highly patient-specific and allows adjustment of the GRID pattern to different tumor sizes and shapes when they are deeply

  6. Preliminary Results of Helical Tomotherapy in Patients with Complex-Shaped Meningiomas Close to the Optic Pathway

    SciTech Connect

    Schiappacasse, Luis Cendales, Ricardo; Sallabanda, Kita; Schnitman, Franco; Samblas, Jose

    2011-01-01

    Meningiomas are the most common benign intracranial tumor. Meningiomas close to the optic pathway represent a treatment challenge both for surgery and radiotherapy. The aim of this article is to describe early results of helical tomotherapy treatment in complex-shaped meningiomas close to the optic pathway. Twenty-eight patients were consecutively treated. All patients were immobilized with a thermoplastic head mask and planned with the aid of a magnetic resonance imaging-computed tomography fusion. All treatments included daily image guidance. Pretreatment symptoms and acute toxicity were recorded. Median age was 57.5 years, and 92.8% patients had Eastern Cooperative Oncology Group performance status scale {<=}1. The most common localizations were the sella turcica, followed by the cavernous sinus and the sphenoid. The most common symptoms were derived from cranial nerve deficits. Tomotherapy was administered as primary treatment in 35.7% of patients, as an adjuvant treatment in 32.4%, and as a rescue treatment after postsurgical progression in 32.1% patients. Most patients were either inoperable or Simpson IV. Total dose varied between 5000 and 5400 cGy; fractionation varied between 180 and 200 cGy. Median dose to the planning target volume was 51.7 Gy (range, 50.2-55.9 Gy). Median coverage index was 0.89 (range, 0.18-0.97). Median homogeneity index was 1.05 (range, 1-1.12). Acute transient toxicity was grade 1 and included headache in 35.7% patients, ocular pain/dryness in 28.5%, and radiation dermatitis in 25%. Thus far, with a maximal follow-up of 3 years, no late effects have been seen and all patients have a radiological stabilization of the disease. Helical tomotherapy offered a safe and effective therapeutic alternative for patients with inoperable or subtotally resected complex-shaped meningiomas close to the optic pathway. Acceptable coverage and homogeneity indexes were achieved with appropriate values for maximal doses delivered to the eyes, lenses

  7. Hippocampal-Sparing Whole-Brain Radiotherapy: A 'How-To' Technique Using Helical Tomotherapy and Linear Accelerator-Based Intensity-Modulated Radiotherapy

    SciTech Connect

    Gondi, Vinai; Tolakanahalli, Ranjini; Mehta, Minesh P.; Tewatia, Dinesh; Rowley, Howard; Kuo, John S.; Khuntia, Deepak; Tome, Wolfgang A.

    2010-11-15

    Purpose: Sparing the hippocampus during cranial irradiation poses important technical challenges with respect to contouring and treatment planning. Herein we report our preliminary experience with whole-brain radiotherapy using hippocampal sparing for patients with brain metastases. Methods and Materials: Five anonymous patients previously treated with whole-brain radiotherapy with hippocampal sparing were reviewed. The hippocampus was contoured, and hippocampal avoidance regions were created using a 5-mm volumetric expansion around the hippocampus. Helical tomotherapy and linear accelerator (LINAC)-based intensity-modulated radiotherapy (IMRT) treatment plans were generated for a prescription dose of 30 Gy in 10 fractions. Results: On average, the hippocampal avoidance volume was 3.3 cm{sup 3}, occupying 2.1% of the whole-brain planned target volume. Helical tomotherapy spared the hippocampus, with a median dose of 5.5 Gy and maximum dose of 12.8 Gy. LINAC-based IMRT spared the hippocampus, with a median dose of 7.8 Gy and maximum dose of 15.3 Gy. On a per-fraction basis, mean dose to the hippocampus (normalized to 2-Gy fractions) was reduced by 87% to 0.49 Gy{sub 2} using helical tomotherapy and by 81% to 0.73 Gy{sub 2} using LINAC-based IMRT. Target coverage and homogeneity was acceptable with both IMRT modalities, with differences largely attributed to more rapid dose fall-off with helical tomotherapy. Conclusion: Modern IMRT techniques allow for sparing of the hippocampus with acceptable target coverage and homogeneity. Based on compelling preclinical evidence, a Phase II cooperative group trial has been developed to test the postulated neurocognitive benefit.

  8. Helical tomotherapy and larynx sparing in advanced oropharyngeal carcinoma: a dosimetric study.

    PubMed

    Gielda, Benjamin T; Millunchick, Cheryl H; Smart, Joseph P; Marsh, James C; Turian, Julius V; Coleman, Joy L

    2010-01-01

    Intensity-modulated radiation therapy (IMRT) is gaining acceptance as a standard treatment technique for advanced squamous cell carcinoma (SCC) of the oropharynx. Dose to the uninvolved larynx and surrounding structures can pose a problem in patients with significant neck disease, potentially compromising laryngeal function and quality of life. Tomotherapy may allow greater laryngeal sparing. Seven patients with stage IV SCC of the oropharynx were replanned using Tomotherapy version 3.1. All contours/planning target volumes (PTVs) from the original plans were preserved, with the exception of the larynx, which was drawn to include all soft tissue encompassed by the thyroid/cricoid cartilage. A simultaneous integrated boost technique was used with PTV 1, 2, and 3 receiving 69.96, 59.40, and 54.00 Gy, respectively in 33 fractions. Dosimetry was evaluated via the Pinnacle treatment planning system (TPS). Equivalent uniform dose (EUD) was calculated from the dose volume histogram (DVH) using the general method with "a" = 5.0. Mean larynx dose for all patients was 24.4 Gy. Mean EUD to the larynx was 34.2 Gy. Homogeneity was adequate; average maximum dose was 109.7% of the highest prescription. All other organs at risk (OAR) were adequately spared. Tomotherapy can spare the uninvolved larynx in the setting of advanced SCC of the oropharynx to levels that are similar to or better than those reported with other techniques. Sparing is achieved without compromising target coverage or other OAR sparing. The clinical benefit of this sparing remains to be determined in a prospective study.

  9. Helical Tomotherapy and Larynx Sparing in Advanced Oropharyngeal Carcinoma: A Dosimetric Study

    SciTech Connect

    Gielda, Benjamin T.; Millunchick, Cheryl H.; Smart, Joseph P.; Marsh, James C.; Turian, Julius V.; Coleman, Joy L.

    2010-10-01

    Intensity-modulated radiation therapy (IMRT) is gaining acceptance as a standard treatment technique for advanced squamous cell carcinoma (SCC) of the oropharynx. Dose to the uninvolved larynx and surrounding structures can pose a problem in patients with significant neck disease, potentially compromising laryngeal function and quality of life. Tomotherapy may allow greater laryngeal sparing. Seven patients with stage IV SCC of the oropharynx were replanned using Tomotherapy version 3.1. All contours/planning target volumes (PTVs) from the original plans were preserved, with the exception of the larynx, which was drawn to include all soft tissue encompassed by the thyroid/cricoid cartilage. A simultaneous integrated boost technique was used with PTV 1, 2, and 3 receiving 69.96, 59.40, and 54.00 Gy, respectively in 33 fractions. Dosimetry was evaluated via the Pinnacle treatment planning system (TPS). Equivalent uniform dose (EUD) was calculated from the dose volume histogram (DVH) using the general method with 'a' = 5.0. Mean larynx dose for all patients was 24.4 Gy. Mean EUD to the larynx was 34.2 Gy. Homogeneity was adequate; average maximum dose was 109.7% of the highest prescription. All other organs at risk (OAR) were adequately spared. Tomotherapy can spare the uninvolved larynx in the setting of advanced SCC of the oropharynx to levels that are similar to or better than those reported with other techniques. Sparing is achieved without compromising target coverage or other OAR sparing. The clinical benefit of this sparing remains to be determined in a prospective study.

  10. Efficacy of the Dynamic Jaw Mode in Helical Tomotherapy With Static Ports for Breast Cancer.

    PubMed

    Sugie, Chikao; Manabe, Yoshihiko; Hayashi, Akihiro; Murai, Taro; Takaoka, Taiki; Hattori, Yukiko; Iwata, Hiromitsu; Takenaka, Ran; Shibamoto, Yuta

    2015-08-01

    The recently developed dynamic jaw technology of tomotherapy can reduce craniocaudal dose spread without much prolonging the treatment time. This study aimed to investigate the efficacy of the dynamic jaw mode for tomotherapy of breast cancer. Static tomotherapy plans of the whole breast and supraclavicular regional lymph nodes, and plans for the whole breast only were generated in 25 patients with left-sided breast cancer. Plans with a field width of 2.5 or 5 cm with the dynamic or fixed jaw modes were made for each patient. The prescribed dose was 50 Gy in 25 fractions. In whole breast and supraclavicular nodal radiotherapy, dose distributions and homogeneity of the planning target volume (PTV) with the dynamic jaw mode were slightly inferior to those with the fixed jaw mode with a 5-cm field width (P < .05). However, lung low-dose volumes and mean doses of the larynx, thyroid, skin, and all the healthy tissues combined were smaller with the dynamic jaw mode than with the fixed jaw mode with a 5-cm field width (P < .001). In whole breast radiotherapy, mean doses of the skin and healthy tissues were lower with the dynamic jaw mode than with the fixed jaw mode with a 5-cm field width (P < .001) without significant differences in PTV dose distributions, homogeneity, and conformity. The dynamic jaw mode provided better sparing of organs at risks with minimal disturbance of dose-volume indices of PTV. Considering the treatment time, the 5-cm-field dynamic jaw mode is more efficient than the 2.5-cm fixed jaw mode.

  11. Clinical Evaluation of an Immbolization System for Stereotactic Body Radiotherapy Using Helical Tomotherapy

    SciTech Connect

    Gutierrez, Alonso N.; Stathakis, Sotirios; Crownover, Richard; Esquivel, Carlos; Shi Chengyu; Papanikolaou, Niko

    2011-07-01

    In this study, a clinical evaluation of the Body Pro-Lok{sup TM} System combined with the TomoTherapy megavoltage computed tomography (MVCT) was performed for lung and liver stereotactic body radiotherapy (SBRT) to reduce interfractional setup uncertainty. Twenty patients treated with 3-5 fractions of SBRT were analyzed retrospectively. The Body Pro-Lok{sup TM} system was used in both CT simulation and during patient treatment setup. Patients were immobilized with a vacuum cushion placed posteriorly over the thoracic region, an abdominal compression plate, and a knee and foot sponge. Pretreatment MVCT scans of the TomoTherapy HI-ART II unit were fused with the planning kVCT before delivery of each fraction to determine the interfractional setup error. A total of 84 shifts were analyzed to assess the interfractional setup accuracy. Results showed that the mean interfractional setup errors and standard deviations were -0.9 {+-} 3.1 mm, 1.2 {+-} 5.5 mm, and 6.5 {+-} 2.6 mm for lateral (IEC-X), longitudinal (IEC-Y), and vertical (IEC-Z) variations, respectively. The maximum motion was 17.1 mm in the longitudinal direction. When all 3 translational coordinates were analyzed, a mean composite displacement vector of 8.2 {+-} 2.0 mm (range 4.1-11.7 mm) was obtained for all patients. Based on the findings, image-guided SBRT using the Body Pro-Lok{sup TM} system in conjunction with the MVCT of TomoTherapy is capable of minimizing interfractional setup error and improving treatment accuracy.

  12. Helical and Static-port Tomotherapy Using the Newly-developed Dynamic Jaws Technology for Lung Cancer.

    PubMed

    Manabe, Yoshihiko; Shibamoto, Yuta; Sugie, Chikao; Hayashi, Akihiro; Murai, Taro; Yanagi, Takeshi

    2015-10-01

    With the newly developed dynamic jaws technology, radiation dose for the cranio-caudal edges of a target can be lowered in the treatment with tomotherapy. We compared dynamic-jaw- and fixed-jaw-mode plans for lung cancer. In 35 patients, four plans using the 2.5-cm dynamic-, 2.5-cm fixed-, 5.0-cm dynamic-, and 5.0-cm fixed-jaw modes were generated. For 10 patients with upper lobe stage I lung cancer, the helical tomotherapy mode was used. Fifty-six Gy in 8 fractions was prescribed as a minimum coverage dose for 95% of the target (D95%). For 25 patients with locally advanced lung cancer, plans using four static ports (TomoDirect® mode) were made. Sixty Gy in 30 daily fractions for the primary tumor and swollen lymph nodes and 51 Gy in 30 fractions for prophylactic lymph node areas were prescribed as median doses. The mean conformity index of the planning target volume were similar among the four plans. The mean V5 Gy of the lung for 2.5-cm dynamic-, 2.5-cm fixed-, 5.0-cm dynamic-, and 5.0-cm fixed-jaw mode plans were 18.5%, 21.8%, 20.1%, and 29.4%, respectively (p < 0.0001), for patients with stage I lung cancer, and 37.3%, 38.7%, 40.4%, and 44.0%, respectively (p < 0.0001), for patients with locally advanced lung cancer. The mean V5 Gy of the whole body was 1,826, 2,143, 1,983, and 2,939 ml, respectively (p < 0.0001), for patients with stage I lung cancer and 4,849, 5,197, 5,220, and 6,154 ml, respectively (p < 0.0001), for patients with locally advanced lung cancer. Treatment time was reduced by 21-39% in 5.0-cm dynamic-jaw plans compared to 2.5-cm plans. Regarding dose distribution, 2.5-cm dynamic-jaw plans were the best, and 5.0-cm dynamic-jaw plans were comparable to 2.5-cm fixed-jaw plans with shorter treatment times. The dynamic-jaw mode should be used instead of the conventional fixed-jaw mode in tomotherapy for lung cancer.

  13. SU-F-BRB-13: Correlation of Improved Target and Organ-At-Risk Dosimetric Quantities and Clinical Outcomes for Helical Tomotherapy Treated Mesothelioma

    SciTech Connect

    Qi, S; Kishan, A; Alexander, S; Lee, P; Selch, M; Kupelian, P; Steiberg, M; Low, D

    2015-06-15

    Purpose: We have observed improved local control probability (LCP) for adjuvant mesothelioma radiotherapy following pleurectomy/decortication using Tomotherapy compared to the conventional 3D technique (p<0.05). This work assesses the correlation between the improved clinical outcomes against dosimetry quantities. Methods: Thirty-eight mesothelioma cases consecutively treated at our clinic were retrospectively analyzed. Sixteen patients were treated using 3D technique planned on the Eclipse for c-arm accelerators prior to 7/2012; the other 22 cases were treated on Tomotherapy using helical IMRT after 7/2012. Typical 3D plans consisting of 15 MV AP/PA photon fields prescribed to 10 cm depth followed by matching electron fields with energy ranging from 8–16 MeV. Tomotherapy plans were designed using 2.5cm jaw, 0.287 pitch with directional blocking of the contralateral lung. The same prescription of 45 Gy (1.8GyX25) was used for both techniques. The dosimetry metrics for the critical structures: ipsilateral-/contralateral-lung, heart, cord, esophagus, etc were compared between two techniques. Results: Superior LCP is closely associated with improved target coverage. Tomotherapy plans yielded dramatically better target coverage and less dose heterogeneity despite of more advanced/larger disease. The averaged PTV volumes were 2287.3±569.9 (Tomotherapy) vs. 1904.8±312.3cc (3D); V100s were: 91.1±4.0 (%) vs. 47.8±12.7 (%) with heterogeneity indices of 1.20±0.1 vs.1.37±0.38 and for the Tomotherapy and 3D plans, respectively. Compared to the 3D technique, we observed significant lower maximum cord doses (p<0.001), lower mean esophagus doses (p<0.002), and lower heart mean doses when tumor was left-sided (p=0.002). For ipsilateral-/contralateral-lungs, however, the mean doses and V20, V5 of Tomotherapy plans were significantly higher than the 3D plans (p<0.01) regardless which sides of lung were treated. However, rates of radiation pneumonitis were no different

  14. Helical Tomotherapy With Simultaneous Integrated Boost After Laparoscopic Staging in Patients With Cervical Cancer: Analysis of Feasibility and Early Toxicity

    SciTech Connect

    Marnitz, Simone; Koehler, Christhardt; Burova, Elena; Wlodarczyk, Waldemar; Jahn, Ulrich; Gruen, Arne; Budach, Volker; Stromberger, Carmen

    2012-02-01

    Purpose: To demonstrate the feasibility and safety of the simultaneous integrated boost technique for dose escalation in combination with helical tomotherapy in patients with cervical cancer. Methods and Materials: Forty patients (International Federation of Gynecology and Obstetrics Stage IB1 pN1-IVA) underwent primary chemoradiation with helical tomotherapy. Before therapy, 29/40 patients underwent laparoscopic pelvic and para-aortic lymphadenectomy. In 21%, 31%, and 3% of the patients, pelvic, pelvic and para-aortic, and skip metastases in the para-aortic region could be confirmed. All patients underwent radiation with 1.8-50.4 Gy to the tumor region and the pelvic (para-aortic) lymph node region (planning target volume-A), and a simultaneous boost with 2.12-59.36 Gy to the boost region (planning target volume-B). The boost region was defined using titan clips during laparoscopic staging. In all other patients, standardized borders for the planning target volume-B were defined. High-dose-rate brachytherapy was performed in 39/40 patients. The mean biologic effective dose to the macroscopic tumor ranged from 87.5 to 97.5 Gy. Chemotherapy consisted of weekly cisplatin 40 mg/m{sup 2}. Dose-volume histograms and acute gastrointestinal, genitourinary, and hematologic toxicity were evaluated. Results: The mean treatment time was 45 days. The mean doses to the small bowel, rectum, and bladder were 28.5 {+-} 6.1 Gy, 47.9 {+-} 3.8 Gy, and 48 {+-} 3 Gy, respectively. Hematologic toxicity Grade 3 occurred in 20% of patients, diarrhea Grade 2 in 5%, and diarrhea Grade 3 in 2.5%. There was no Grade 3 genitourinary toxicity. All patients underwent curettage 3 months after chemoradiation, which confirmed complete pathologic response in 38/40 patients. Conclusions: The concept of simultaneous integrated boost for dose escalation in patients with cervical cancer is feasible, with a low rate of acute gastrointestinal and genitourinary toxicity. Whether dose escalation can be

  15. Sparing of the Neural Stem Cell Compartment During Whole-Brain Radiation Therapy: A Dosimetric Study Using Helical Tomotherapy

    SciTech Connect

    Marsh, James C.; Godbole, Rohit H.; Herskovic, Arnold M.; Gielda, Benjamin T.; Turian, Julius V.

    2010-11-01

    Purpose: To assess the feasibility of dosimetrically sparing the hippocampus and neural stem cell (NSC) compartment during whole-brain radiotherapy (WBRT) and prophylactic cranial irradiation (PCI). Methods and Materials: We contoured the brain/brainstem on fused magnetic resonance /computed tomography images as the planning target volume (PTV) in 10 patients, excluding the hippocampus and NSC compartment as organs at risk. PCI and WBRT helical tomotherapy plans were prepared for each patient, with 1.0-cm field width, a pitch of 0.285, and a modulation factor of 2.5. We attempted to maximally spare the hippocampus and NSC compartment while treating the rest of the brain to 30 Gy in 15 fractions (PCI) or 35 Gy in 14 fractions (WBRT) with a V{sub 100} of {>=}95%. Plan quality was assessed by calculating mean dose, equivalent uniform dose (EUD), and biologically equivalent dose (BED) for organs at risk and the percent volume of the PTV receiving the prescribed dose of V{sub 100}. Results: In the PCI plans, mean doses/EUD/BED for the hippocampus and NSC compartment were 11.5 Gy/13.1 Gy/15.7 Gy{sub 2} (BED assuming alpha/beta ratio of 2Gy) and 11.5 Gy/13.1 Gy/12.3 Gy{sub 10} (BED assuming alpha/beta ratio of 10Gy), respectively. In the WBRT plans, mean doses/EUD/BED for the hippocampus and NSC compartment were 11.8 Gy/14.8 Gy/16.8 Gy{sub 2} and 11.8 Gy/14.8 Gy/12.8 Gy{sub 10}, respectively. The mean V{sub 95} for the rest of the brain (PTV) was 96.9% for both the PCI and WBRT plans. Mean PCI and WBRT treatment times were 15.93 min (range, 14.28 min-17.50 min) and 20.18 min (range, 18.43 min-22.32 min), respectively. Conclusions: It is dosimetrically feasible to spare the hippocampus and NSC compartment using helical tomotherapy during the administration of whole-brain irradiation.

  16. Dose calculation software for helical tomotherapy, utilizing patient CT data to calculate an independent three-dimensional dose cube

    SciTech Connect

    Thomas, Simon J.; Eyre, Katie R.; Tudor, G. Samuel J.; Fairfoul, Jamie

    2012-01-15

    Purpose: Treatment plans for the TomoTherapy unit are produced with a planning system that is integral to the unit. The authors have produced an independent dose calculation system, to enable plans to be recalculated in three dimensions, using the patient's CT data. Methods: Software has been written using MATLAB. The DICOM-RT plan object is used to determine the treatment parameters used, including the treatment sinogram. Each projection of the sinogram is segmented and used to calculate dose at multiple calculation points in a three-dimensional grid using tables of measured beam data. A fast ray-trace algorithm is used to determine effective depth for each projection angle at each calculation point. Calculations were performed on a standard desktop personal computer, with a 2.6 GHz Pentium, running Windows XP. Results: The time to perform a calculation, for 3375 points averaged 1 min 23 s for prostate plans and 3 min 40 s for head and neck plans. The mean dose within the 50% isodose was calculated and compared with the predictions of the TomoTherapy planning system. When the modified CT (which includes the TomoTherapy couch) was used, the mean difference for ten prostate patients, was -0.4% (range -0.9% to +0.3%). With the original CT (which included the CT couch), the mean difference was -1.0% (range -1.7% to 0.0%). The number of points agreeing with a gamma 3%/3 mm averaged 99.2% with the modified CT, 96.3% with the original CT. For ten head and neck patients, for the modified and original CT, respectively, the mean difference was +1.1% (range -0.4% to +3.1%) and 1.1% (range -0.4% to +3.0%) with 94.4% and 95.4% passing a gamma 4%/4 mm. The ability of the program to detect a variety of simulated errors has been tested. Conclusions: By using the patient's CT data, the independent dose calculation performs checks that are not performed by a measurement in a cylindrical phantom. This enables it to be used either as an additional check or to replace phantom

  17. Prostate treatment with helical TomoTherapy in patients with bilateral hip prostheses—Two case studies

    SciTech Connect

    Kling, Justin; Patel, Kamal M.

    2013-04-01

    Prostate cancer patients with bilateral hip prostheses require additional planning and treatment considerations. Visualization of the organs at risk (OAR) and the planning target volume (PTV) is hindered by the large amount of artifact streaking between the metallic implants. The density of this area must be accounted for when using heterogeneity correction. Fusion of a megavolt computed tomography (MVCT) to the planning CT aids in viewing the prostate, bladder, and rectum, and implantation of 6 fiducial markers along the posterior border of the prostate helps with the delineation between it and the rectum. When planning, the amount of beam entry angles is limited because of the position of the prostheses and prevents the use of any lateral beams. Therefore, TomoTherapy presents an effective option for these patients because of the ability to use a directional block, which prevents any primary beams from entering through the bilateral hip prostheses (but the beams may exit through the structures), use of MVCT for daily localization, and delivery of radiation with intensity modulation allows for effective sparing of the OAR.

  18. Dosimetric comparison of three different treatment modalities for total scalp irradiation: the conventional lateral photon-electron technique, helical tomotherapy, and volumetric-modulated arc therapy.

    PubMed

    Song, Jin Ho; Jung, Ji-Young; Park, Hyung-Wook; Lee, Gi Woong; Chae, Soo-Min; Kay, Chul Seung; Son, Seok Hyun

    2015-07-01

    The aim of this study was to compare lateral photon-electron (LPE), helical tomotherapy (HT), and volumetric-modulated arc therapy (VMAT) plans for total scalp irradiation. We selected a single adult model case and compared the dosimetric results for the three plans. All plans mainly used 6-MV photon beams, and the prescription dose was 60 Gy in 30 fractions. First, we compared the LPE, HT and VMAT plans, with all plans including a 1-cm bolus. We also compared HT plans with and without the bolus. The conformity indices for LPE, HT and VMAT were 1.73, 1.35 and 1.49, respectively. The HT plan showed the best conformity and the LPE plan showed the worst. However, the plans had similar homogeneity indexes. The dose to the hippocampus was the highest in the VMAT plan, with a mean of 6.7 Gy, compared with 3.5 Gy in the LPE plan and 4.8 Gy in the HT plan. The doses to the optical structures were all within the clinically acceptable range. The beam-on time and monitor units were highest in the HT plan. The HT plans with and without a bolus showed similar target coverage and organ-at-risk (OAR) sparing. The HT plan showed the best target coverage and conformity, with low doses to the brain and hippocampus. This plan also had the advantage of not necessarily requiring a bolus. Although the VMAT plan showed better conformity than the LPE plan and acceptable OAR sparing, the dose to the hippocampus should be considered when high doses are prescribed.

  19. A Dosimetric Comparison of Accelerated Partial Breast Irradiation Techniques: Multicatheter Interstitial Brachytherapy, Three-Dimensional Conformal Radiotherapy, and Supine Versus Prone Helical Tomotherapy

    SciTech Connect

    Patel, Rakesh R. . E-mail: patel@humonc.wisc.edu; Becker, Stewart J.; Das, Rupak K.; Mackie, Thomas R.

    2007-07-01

    Purpose: To compare dosimetrically four different techniques of accelerated partial breast irradiation (APBI) in the same patient. Methods and Materials: Thirteen post-lumpectomy interstitial brachytherapy (IB) patients underwent imaging with preimplant computed tomography (CT) in the prone and supine position. These CT scans were then used to generate three-dimensional conformal radiotherapy (3D-CRT) and prone and supine helical tomotherapy (PT and ST, respectively) APBI plans and compared with the treated IB plans. Dose-volume histogram analysis and the mean dose (NTD{sub mean}) values were compared. Results: Planning target volume coverage was excellent for all methods. Statistical significance was considered to be a p value <0.05. The mean V100 was significantly lower for IB (12% vs. 15% for PT, 18% for ST, and 26% for 3D-CRT). A greater significant differential was seen when comparing V50 with mean values of 24%, 43%, 47%, and 52% for IB, PT, ST, and 3D-CRT, respectively. The IB and PT were similar and delivered an average lung NTD{sub mean} dose of 1.3 Gy{sub 3} and 1.2 Gy{sub 3}, respectively. Both of these methods were statistically significantly lower than the supine external beam techniques. Overall, all four methods yielded similar low doses to the heart. Conclusions: The use of IB and PT resulted in greater normal tissue sparing (especially ipsilateral breast and lung) than the use of supine external beam techniques of 3D-CRT or ST. However, the choice of APBI technique must be tailored to the patient's anatomy, lumpectomy cavity location, and overall treatment goals.

  20. Muon Beam Helical Cooling Channel Design

    SciTech Connect

    Johnson, Rolland; Ankenbrandt, Charles; Flanagan, G; Kazakevich, G M; Marhauser, Frank; Neubauer, Michael; Roberts, T; Yoshikawa, C; Derbenev, Yaroslav; Morozov, Vasiliy; Kashikhin, V S; Lopes, Mattlock; Tollestrup, A; Yonehara, Katsuya; Zloblin, A

    2013-06-01

    The Helical Cooling Channel (HCC) achieves effective ionization cooling of the six-dimensional (6d) phase space of a muon beam by means of a series of 21st century inventions. In the HCC, hydrogen-pressurized RF cavities enable high RF gradients in strong external magnetic fields. The theory of the HCC, which requires a magnetic field with solenoid, helical dipole, and helical quadrupole components, demonstrates that dispersion in the gaseous hydrogen energy absorber provides effective emittance exchange to enable longitudinal ionization cooling. The 10-year development of a practical implementation of a muon-beam cooling device has involved a series of technical innovations and experiments that imply that an HCC of less than 300 m length can cool the 6d emittance of a muon beam by six orders of magnitude. We describe the design and construction plans for a prototype HCC module based on oxygen-doped hydrogen-pressurized RF cavities that are loaded with dielectric, fed by magnetrons, and operate in a superconducting helical solenoid magnet.

  1. Bolus-dependent dosimetric effect of positioning errors for tangential scalp radiotherapy with helical tomotherapy.

    PubMed

    Lobb, Eric

    2014-01-01

    The dosimetric effect of errors in patient position is studied on-phantom as a function of simulated bolus thickness to assess the need for bolus utilization in scalp radiotherapy with tomotherapy. A treatment plan is generated on a cylindrical phantom, mimicking a radiotherapy technique for the scalp utilizing primarily tangential beamlets. A planning target volume with embedded scalplike clinical target volumes (CTVs) is planned to a uniform dose of 200cGy. Translational errors in phantom position are introduced in 1-mm increments and dose is recomputed from the original sinogram. For each error the maximum dose, minimum dose, clinical target dose homogeneity index (HI), and dose-volume histogram (DVH) are presented for simulated bolus thicknesses from 0 to 10mm. Baseline HI values for all bolus thicknesses were in the 5.5 to 7.0 range, increasing to a maximum of 18.0 to 30.5 for the largest positioning errors when 0 to 2mm of bolus is used. Utilizing 5mm of bolus resulted in a maximum HI value of 9.5 for the largest positioning errors. Using 0 to 2mm of bolus resulted in minimum and maximum dose values of 85% to 94% and 118% to 125% of the prescription dose, respectively. When using 5mm of bolus these values were 98.5% and 109.5%. DVHs showed minimal changes in CTV dose coverage when using 5mm of bolus, even for the largest positioning errors. CTV dose homogeneity becomes increasingly sensitive to errors in patient position as bolus thickness decreases when treating the scalp with primarily tangential beamlets. Performing a radial expansion of the scalp CTV into 5mm of bolus material minimizes dosimetric sensitivity to errors in patient position as large as 5mm and is therefore recommended.

  2. Bolus-dependent dosimetric effect of positioning errors for tangential scalp radiotherapy with helical tomotherapy

    SciTech Connect

    Lobb, Eric

    2014-04-01

    The dosimetric effect of errors in patient position is studied on-phantom as a function of simulated bolus thickness to assess the need for bolus utilization in scalp radiotherapy with tomotherapy. A treatment plan is generated on a cylindrical phantom, mimicking a radiotherapy technique for the scalp utilizing primarily tangential beamlets. A planning target volume with embedded scalplike clinical target volumes (CTVs) is planned to a uniform dose of 200 cGy. Translational errors in phantom position are introduced in 1-mm increments and dose is recomputed from the original sinogram. For each error the maximum dose, minimum dose, clinical target dose homogeneity index (HI), and dose-volume histogram (DVH) are presented for simulated bolus thicknesses from 0 to 10 mm. Baseline HI values for all bolus thicknesses were in the 5.5 to 7.0 range, increasing to a maximum of 18.0 to 30.5 for the largest positioning errors when 0 to 2 mm of bolus is used. Utilizing 5 mm of bolus resulted in a maximum HI value of 9.5 for the largest positioning errors. Using 0 to 2 mm of bolus resulted in minimum and maximum dose values of 85% to 94% and 118% to 125% of the prescription dose, respectively. When using 5 mm of bolus these values were 98.5% and 109.5%. DVHs showed minimal changes in CTV dose coverage when using 5 mm of bolus, even for the largest positioning errors. CTV dose homogeneity becomes increasingly sensitive to errors in patient position as bolus thickness decreases when treating the scalp with primarily tangential beamlets. Performing a radial expansion of the scalp CTV into 5 mm of bolus material minimizes dosimetric sensitivity to errors in patient position as large as 5 mm and is therefore recommended.

  3. Dosimetric effects of swelling or shrinking tissue during helical tomotherapy breast irradiation: A phantom study.

    PubMed

    Klepper, Rudolf; Höfel, Sebastian; Botha, Ulrike; Köhler, Peter; Zwicker, Felix

    2014-07-08

    During radiation therapy of the female breast, the actual target volume compared to the planning target volume may change due to swelling or shrinking of the tissue. Under- or overdosage is to be expected, especially when performing IMRT or tomotherapy techniques. The objective of this study is to develop a model-based quantification of these dose effects, with a particular focus on the changes in the surface dose. A cylindrical phantom was used as an artificial surrogate of the human torso. By adding and removing Superflab layers of various thicknesses, both radial breast swelling and shrinking could be simulated. The effects on dose distribution were evaluated using film dosimetry. The results were compared to dose calculations. To estimate the true surface doses, we subtracted the influence of the film material on air measurements. During a swelling of 5, 10, and 15 mm, the planning target volume was consistently underdosed by 2%, 5%, and 7% of the prescribed dose, respectively. Swelling led to reduced dose values of up to 72%, 55%, and 50% at the outer edge of the actual target volume. The measured surface dose decreased successively from 31% to 23%. During shrinking, the dose in the planning target volume increased successively from 100% to 106%. The measured surface doses increased from 29% to 36%. The calculated dose values agreed with the measured values within error limits. During radiotherapy of the female breast, new planning appears to be essential for radial tissue swelling of 5 mm or more because of severe underdosing. Shrinking leads to moderate overdosing and an increased surface dose. In addition, caution is advised when removing bolus material with respect to the planned situation.

  4. Dosimetric effects of swelling or shrinking tissue during helical tomotherapy breast irradiation. A phantom study.

    PubMed

    Klepper, Rudolf; Höfel, Sebastian; Botha, Ulrike; Köhler, Peter; Zwicker, Felix

    2014-07-01

    During radiation therapy of the female breast, the actual target volume compared to the planning target volume may change due to swelling or shrinking of the tissue. Under- or overdosage is to be expected, especially when performing IMRT or tomotherapy techniques. The objective of this study is to develop a model-based quantification of these dose effects, with a particular focus on the changes in the surface dose. A cylindrical phantom was used as an artificial surrogate of the human torso. By adding and removing Superflab layers of various thicknesses, both radial breast swelling and shrinking could be simulated. The effects on dose distribution were evaluated using film dosimetry. The results were compared to dose calculations. To estimate the true surface doses, we subtracted the influence of the film material on air measurements. During a swelling of 5, 10, and 15 mm, the planning target volume was consistently underdosed by 2%, 5%, and 7% of the prescribed dose, respectively. Swelling led to reduced dose values of up to 72%, 55%, and 50% at the outer edge of the actual target volume. The measured surface dose decreased successively from 31% to 23%. During shrinking, the dose in the planning target volume increased successively from 100% to 106%. The measured surface doses increased from 29% to 36%. The calculated dose values agreed with the measured values within error limits. During radiotherapy of the female breast, new planning appears to be essential for radial tissue swelling of 5 mm or more because of severe underdosing. Shrinking leads to moderate overdosing and an increased surface dose. In addition, caution is advised when removing bolus material with respect to the planned situation. PACS numbers: 87.53.Bn, 87.55.dk, 87.55.D.

  5. Dosimetric Comparison of 6 MV and 15 MV Single Arc Rapidarc to Helical TomoTherapy for the Treatment of Pancreatic Cancer

    SciTech Connect

    Cai Jing; Yue Jinbo; McLawhorn, Robert; Yang Wensha; Wijesooriya, Krishni; Dunlap, Neal E.; Sheng Ke; Yin Fangfang; Benedict, Stanley H.

    2011-10-01

    We conducted a planning study to compare Varian's RapidArc (RA) and helical TomoTherapy (HT) for the treatment of pancreatic cancer. Three intensity-modulated radiotherapy (IMRT) plans were generated for 8 patients with pancreatic cancer: one using HT with 6-MV beam (Plan{sub HT6}), one using single-arc RA with 6-MV beam (Plan{sub RA6}), and one using single-arc RA with 15-MV beam (Plan{sub RA15}). Dosimetric indices including high/low conformality index (CI{sub 100%}/CI{sub 50%}), heterogeneity index (HI), monitor units (MUs), and doses to organs at risk (OARs) were compared. The mean CI{sub 100%} was statistically equivalent with respect to the 2 treatment techniques, as well as beam energy (0.99, 1.01, and 1.02 for Plan{sub HT6}, Plan{sub RA6}, and Plan{sub RA156,} respectively). The CI{sub 50%} and HI were improved in both RA plans over the HT plan. The RA plans significantly reduced MU (MU{sub RA6} = 697, MU{sub RA15} = 548) compared with HT (MU{sub HT6} = 6177, p = 0.008 in both cases). The mean maximum cord dose was decreased from 29.6 Gy in Plan{sub HT6} to 21.6 Gy (p = 0.05) in Plan{sub RA6} and 21.7 Gy (p = 0.04) in Plan{sub RA15}. The mean bowel dose decreased from 17.2 Gy in Plan{sub HT6} to 15.2 Gy (p = 0.03) in Plan{sub RA6} and 15.0 Gy (p = 0.03) Plan{sub RA15}. The mean liver dose decreased from 8.4 Gy in Plan{sub HT6} to 6.3 Gy (p = 0.04) in Plan{sub RA6} and 6.2 Gy in Plan{sub RA15}. Variations of the mean dose to the duodenum, kidneys, and stomach were statistically insignificant. RA and HT can both deliver conformal dose distributions to target volumes while limiting the dose to surrounding OARs in the treatment of pancreatic cancer. Dosimetric advantages might be gained by using RA over HT by reducing the dose to OARs and total MUs used for treatment.

  6. Conditioner for a helically transported electron beam

    SciTech Connect

    Wang, C.

    1992-05-01

    The kinetic theory is developed to investigate a conditioner for a helically imported electron beam. Linear expressions for axial velocity spread are derived. Numerical simulation is used to check the theoretical results and examine nonlinear aspects of the conditioning process. The results show that in the linear regime the action of the beam conditioner on a pulsed beam mainly depends on the phase at which the beam enters the conditioner and depends only slightly on the operating wavelength. In the nonlinear regime, however, the action of the conditioner strongly depends on the operating wavelength and only slightly upon the entrance phase. For a properly chosen operating wavelength, a little less than the electron's relativistic cyclotron wavelength, the conditioner can decrease the axial velocity spread of a pulsed beam down to less than one-third of its initial value.

  7. Conditioner for a helically transported electron beam

    SciTech Connect

    Wang, C.

    1992-05-01

    The kinetic theory is developed to investigate a conditioner for a helically imported electron beam. Linear expressions for axial velocity spread are derived. Numerical simulation is used to check the theoretical results and examine nonlinear aspects of the conditioning process. The results show that in the linear regime the action of the beam conditioner on a pulsed beam mainly depends on the phase at which the beam enters the conditioner and depends only slightly on the operating wavelength. In the nonlinear regime, however, the action of the conditioner strongly depends on the operating wavelength and only slightly upon the entrance phase. For a properly chosen operating wavelength, a little less than the electron`s relativistic cyclotron wavelength, the conditioner can decrease the axial velocity spread of a pulsed beam down to less than one-third of its initial value.

  8. Phase I Trial of Simultaneous In-Field Boost With Helical Tomotherapy for Patients With One to Three Brain Metastases

    SciTech Connect

    Rodrigues, George; Yartsev, Slav; Yaremko, Brian; Perera, Francisco; Dar, A. Rashid; Hammond, Alex; Lock, Michael; Yu, Edward; Ash, Robert; Caudrelier, Jean-Michelle; Khuntia, Deepak; Bailey, Laura; Bauman, Glenn

    2011-07-15

    Purpose: Stereotactic radiosurgery is an alternative to surgical resection for selected intracranial lesions. Integrated image-guided intensity-modulated-capable radiotherapy platforms such as helical tomotherapy (HT) could potentially replace traditional radiosurgery apparatus. The present study's objective was to determine the maximally tolerated dose of a simultaneous in-field boost integrated with whole brain radiotherapy for palliative treatment of patients with one to three brain metastases using HT. Methods and Materials: The inclusion/exclusion criteria and endpoints were consistent with the Radiation Therapy Oncology Group 9508 radiosurgery trial. The cohorts were constructed with a 3 + 3 design; however, additional patients were enrolled in the lower dose tolerable cohorts during the toxicity assessment periods. Whole brain radiotherapy (30 Gy in 10 fractions) was delivered with a 5-30-Gy (total lesion dose of 35-60 Gy in 10 fractions) simultaneous in-field boost delivered to the brain metastases. The maximally tolerated dose was determined by the frequency of neurologic Grade 3-5 National Cancer Institute Common Toxicity Criteria, version 3.0, dose-limiting toxicity events within each Phase I cohort. Results: A total of 48 patients received treatment in the 35-Gy (n = 3), 40-Gy (n = 16), 50-Gy (n = 15), 55-Gy (n = 8), and 60-Gy (n = 6) cohorts. No patients experienced dose-limiting toxicity events in any of the trial cohorts. The 3-month RECIST assessments available for 32 of the 48 patients demonstrated a complete response in 2, a partial response in 16, stable disease in 6, and progressive disease in 8 patients. Conclusion: The delivery of 60 Gy in 10 fractions to one to three brain metastases synchronously with 30 Gy whole brain radiotherapy was achieved without dose-limiting central nervous system toxicity as assessed 3 months after treatment. This approach is being tested in a Phase II efficacy trial.

  9. Comparison of the effectiveness of different immobilization systems in different body regions using daily megavoltage CT in helical tomotherapy

    PubMed Central

    Cheng, K-F

    2014-01-01

    Objective: Effective immobilization is crucial for the accurate delivery of radiotherapy. This study aimed to compare the effectiveness of the commonly used immobilization systems for different body regions using megavoltage CT (MVCT). Methods: Daily treatment set-up data from 212 patients treated by helical tomotherapy (Accuray, Sunnyvale, CA) in 6 body regions (52 head and neck, 41 chest, 38 abdomen, 36 pelvis, 18 breast and 27 cranium) were obtained. Based on a verification tool using the pre-treatment MVCT, set-up corrections for each patient were recorded. Mean systematic and random errors of lateral, longitudinal, vertical and roll directions and three-dimensional vectors were compared between immobilization systems of each region. Results: Smaller set-up deviations were observed in the Orfit system (Orfit Industries NV, Wijnegem, Belgium) of the head and neck region, while the performance of immobilization systems for the chest, abdomen and pelvis regions was similar. Larger differences were noted in the breast group, where the prone BodyFIX® system (Medical Intelligence, Medizintechnik GmbH, Schwabmünchen, Germany) was less stable than the supine VacLok® system (CIVCO Medical Solutions, Orange City, IA). Conclusion: Differences were found between the immobilization systems in the head and neck region, in which the Orfit system was relatively more effective, whereas the VacLok and BodyFIX systems performed similarly in the chest, abdomen and pelvis regions. For the breast case, the supine position with VacLok was much more stable than the prone breast technique. The results provided references for the estimation of clinical target volume–planning target volume margins. Advances in knowledge: This is the first article on comprehensive comparisons performed in immobilization systems for main body regions that provides some practical recommendations. PMID:24398111

  10. Helical Tomotherapy Versus Conventional Intensity-Modulated Radiation Therapy for Primary Chemoradiation in Cervical Cancer Patients: An Intraindividual Comparison

    SciTech Connect

    Marnitz, Simone; Lukarski, Dusko; Koehler, Christhardt; Wlodarczyk, Waldemar; Ebert, Andreas; Budach, Volker; Schneider, Achim; Stromberger, Carmen

    2011-10-01

    Purpose: To compare intensity-modulated radiotherapy (IMRT) delivered by helical tomotherapy (HT) with conventional IMRT for primary chemoradiation in cervical cancer patients. Methods and Materials: Twenty cervical cancer patients undergoing primary chemoradiation received radiation with HT; 10 patients underwent pelvic irradiation (PEL) and 10 extended-field irradiation (EXT). For treatment planning, the simultaneously integrated boost (SIB) concept was applied. Tumor, pelvic, with or without para-aortic lymph nodes were defined as planning target volume A (PTV-A) with a prescribed dose of 1.8/50.4 Gy (28 fractions). The SIB dose for the parametrium (PTV-B), was 2.12/59.36 Gy. The lower target constraints were 95% of the prescribed dose in 95% of the target volume, and the upper dose constraint was 107%. The irradiated small-bowel volumes were kept as low as possible. For every HT plan, a conventional IMRT plan was calculated and compared with regard to dose-volume histogram, conformity index and conformity number, and homogeneity index. Results: Both techniques allowed excellent target volume coverage and sufficient SB sparing. Conformity index and conformity number results for both PTV-A and PTV-B, homogeneity index for PTV-B, and SB sparing for V45, V50, Dmax, and D1% were significantly better with HT. SB sparing was significantly better for conventional IMRT at low doses (V10). Conclusions: Both HT and conventional IMRT provide optimal treatment of cervical cancer patients. The HT technique was significantly favored with regard to target conformity, homogeneity, and SB sparing. Randomized trials are needed to assess the oncological outcome, toxicity, and clinical relevance of these differences.

  11. Respiratory gating and 4-D tomotherapy

    SciTech Connect

    Zhang Tiezhi

    2004-12-01

    Helical tomotherapy is a new intensity-modulated radiotherapy (IMRT) delivery process developed at the University of Wisconsin and TomoTherapy Inc. Tomotherapy may be of advantage in lung cancer treatment due to its rotational delivery mode. As with conventional IMRT delivery, however, intrafraction respiratory motion during a tomotherapy treatment causes unnecessary radiation to the healthy tissue. Possible solutions to these problems associated with intrafraction motion have been studied in this thesis. A spirometer is useful for monitoring breathing because of its direct correlation with lung volume changes. However, its inherent drift prevents its application in long-term breathing monitoring. With calibration and stabilization algorithms, a spirometer is able to provide accurate, long-term lung volume change measurements. Such a spirometer system is most suited for deep inspiration breath-hold (DIBH) treatments. An improved laser-spirometer combined system has also been developed for target tracking in 4-D treatment. Spirometer signals are used to calibrate the displacement measurements into lung volume changes, thereby eliminating scaling errors from daily setup variations. The laser displacement signals may also be used to correct spirometer drifts during operation. A new 4-D treatment technique has been developed to account for intrafraction motion in treatment planning. The patient's breathing and the beam delivery are synchronized, and the target motion/deformation is incorporated into treatment plan optimization. Results show that this new 4D treatment technique significantly reduces motion effects and provides improved patient tolerance.

  12. Helical Muon Beam Cooling Channel Engineering Design

    SciTech Connect

    Kashikhin, V.S.; Lopes, M.L.; Romanov, G.V.; Tartaglia, M.A.; Yonehara, K.; Yu, M.; Zlobin, A.V.; Flanagan, G.; Johnson, R.P.; Kazakevich, G.M.; Marhauser, F.; /MUONS Inc., Batavia

    2012-05-01

    The Helical Cooling Channel (HCC), a novel technique for six-dimensional (6D) ionization cooling of muon beams, has shown considerable promise based on analytic and simulation studies. However, the implementation of this revolutionary method of muon cooling requires new techniques for the integration of hydrogen-pressurized, high-power RF cavities into the low-temperature superconducting magnets of the HCC. We present the progress toward a conceptual design for the integration of 805 MHz RF cavities into a 10 T Nb{sub 3}Sn based HCC test section. We include discussions on the pressure and thermal barriers needed within the cryostat to maintain operation of the magnet at 4.2 K while operating the RF and energy absorber at a higher temperature. Additionally, we include progress on the Nb{sub 3}Sn helical solenoid design.

  13. Helical muon beam cooling channel engineering design

    SciTech Connect

    Johnson, Rolland

    2015-08-07

    The Helical Cooling Channel (HCC) achieves effective ionization cooling of the six-dimensional (6d) phase space of a muon beam by means of a series of 21st century inventions. In the HCC, hydrogen-pressurized RF cavities enable high RF gradients in strong external magnetic fields. The theory of the HCC, which requires a magnetic field with solenoid, helical dipole, and helical quadrupole components, demonstrates that dispersion in the gaseous hydrogen energy absorber provides effective emittance exchange to enable longitudinal ionization cooling. The 10-year development of a practical implementation of a muon-beam cooling device has involved a series of technical innovations and experiments that imply that an HCC of less than 300 m length can cool the 6d emittance of a muon beam by six orders of magnitude. We describe the design and construction plans for a prototype HCC module based on oxygen-doped hydrogen-pressurized RF cavities that are loaded with dielectric, fed by magnetrons, and operate in a superconducting helical solenoid magnet. The first phase of this project saw the development of a conceptual design for the integration of 805 MHz RF cavities into a 10 T Nb3Sn-based HS test section. Two very novel ideas are required to realize the design. The first idea is the use of dielectric inserts in the RF cavities to make them smaller for a given frequency so that the cavities and associated plumbing easily fit inside the magnet cryostat. Calculations indicate that heat loads will be tolerable, while RF breakdown of the dielectric inserts will be suppressed by the pressurized hydrogen gas. The second new idea is the use of a multi-layer Nb3Sn helical solenoid. The technology demonstrations for the two aforementioned key components of a 10T, 805 MHz HCC were begun in this project. The work load in the Fermilab Technical Division made it difficult to test a multi-layer Nb3Sn solenoid as originally planned. Instead, a complementary

  14. Skin-sparing Helical Tomotherapy vs 3D-conformal Radiotherapy for Adjuvant Breast Radiotherapy: In Vivo Skin Dosimetry Study

    SciTech Connect

    Capelle, Lisa; Warkentin, Heather; MacKenzie, Marc; Joseph, Kurian; Gabos, Zsolt; Pervez, Nadeem; Tankel, Keith; Chafe, Susan; Amanie, John; Ghosh, Sunita; Parliament, Matthew; Abdulkarim, Bassam

    2012-08-01

    Purpose: We investigated whether treatment-planning system (TPS)-calculated dose accurately reflects skin dose received for patients receiving adjuvant breast radiotherapy (RT) with standard three-dimensional conformal RT (3D-CRT) or skin-sparing helical tomotherapy (HT). Methods and Materials: Fifty patients enrolled in a randomized controlled trial investigating acute skin toxicity from adjuvant breast RT with 3D-CRT compared to skin-sparing HT, where a 5-mm strip of ipsilateral breast skin was spared. Thermoluminescent dosimetry or optically stimulated luminescence measurements were made in multiple locations and were compared to TPS-calculated doses. Skin dosimetric parameters and acute skin toxicity were recorded in these patients. Results: With HT there was a significant correlation between calculated and measured dose in the medial and lateral ipsilateral breast (r = 0.67, P<.001; r = 0.44, P=.03, respectively) and the medial and central contralateral breast (r = 0.73, P<.001; r = 0.88, P<.001, respectively). With 3D-CRT there was a significant correlation in the medial and lateral ipsilateral breast (r = 0.45, P=.03; r = 0.68, P<.001, respectively); the medial and central contralateral breast (r = 0.62, P=.001; r = 0.86, P<.001, respectively); and the mid neck (r = 0.42, P=.04, respectively). On average, HT-calculated dose overestimated the measured dose by 14%; 3D-CRT underestimated the dose by 0.4%. There was a borderline association between highest measured skin dose and moist desquamation (P=.05). Skin-sparing HT had greater skin homogeneity (homogeneity index of 1.39 vs 1.65, respectively; P=.005) than 3D-CRT plans. HT plans had a lower skin{sub V50} (1.4% vs 5.9%, respectively; P=.001) but higher skin{sub V40} and skin{sub V30} (71.7% vs 64.0%, P=.02; and 99.0% vs 93.8%, P=.001, respectively) than 3D-CRT plans. Conclusion: The 3D-CRT TPS more accurately reflected skin dose than the HT TPS, which tended to overestimate dose received by 14% in patients

  15. Superposition of helical beams by using a Michelson interferometer.

    PubMed

    Gao, Chunqing; Qi, Xiaoqing; Liu, Yidong; Weber, Horst

    2010-01-04

    Orbital angular momentum (OAM) of a helical beam is of great interests in the high density optical communication due to its infinite number of eigen-states. In this paper, an experimental setup is realized to the information encoding and decoding on the OAM eigen-states. A hologram designed by the iterative method is used to generate the helical beams, and a Michelson interferometer with two Porro prisms is used for the superposition of two helical beams. The experimental results of the collinear superposition of helical beams and their OAM eigen-states detection are presented.

  16. NOTE: The effect of tomotherapy imaging beam output instabilities on dose calculation

    NASA Astrophysics Data System (ADS)

    Duchateau, Michael; Tournel, Koen; Verellen, Dirk; Van de Vondel, Iwein; Reynders, Truus; Linthout, Nadine; Gevaert, Thierry; de Coninck, Peter; Depuydt, Tom; Storme, Guy

    2010-06-01

    A radiotherapy treatment plan is based on an anatomical 'snapshot' of the patient acquired during the preparation stage using a kVCT (kilovolt computed tomography) scanner. Anatomical changes will occur during the treatment course, in some cases requiring a new treatment plan to deliver the prescribed dose. With the introduction of 3D volumetric on-board imaging devices, it became feasible to use the produced images for dose recalculation. However, the use of these on-board imaging devices in clinical routine for the calculation of dose depends on the stability of the images. In this study the validation of tomotherapy MVCT (megavolt computed tomography) produced images, for the purpose of dose recalculation by the Planned Adaptive software, has been performed. To investigate the validity of MVCT images for dose calculation, a treatment plan was created based on kVCT-acquired images of a solid water phantom. During a period of 4 months, MVCT images of the phantom have been acquired and were used by the planned adaptive software to recalculate the initial kVCT-based dose on the MVCT images. The influence of the adapted IVDTs (image value-to-density tables) has been investigated as well as the effect of image acquisition with or without preceding airscan. Output fluctuations and/or instabilities of the imaging beam result in MV images of different quality yielding different results when used for dose calculation. It was shown that the output of the imaging beam is not stable, leading to differences of nearly 3% between the original kV-based dose and the recalculated MV-based dose, for solid water only. MVCT images can be used for dose calculation purposes bearing in mind that the output beam is liable to fluctuations. The acquisition of an IVDT together with the MVCT image set, that is going to be used for dose calculation, is highly recommended.

  17. Image-Guided Total-Marrow Irradiation Using Helical Tomotherapy in Patients With Multiple Myeloma and Acute Leukemia Undergoing Hematopoietic Cell Transplantation

    SciTech Connect

    Wong, Jeffrey Y.C. Rosenthal, Joseph; Liu An; Schultheiss, Timothy; Forman, Stephen; Somlo, George

    2009-01-01

    Purpose: Total-body irradiation (TBI) has an important role in patients undergoing hematopoietic cell transplantation (HCT), but is associated with significant toxicities. Targeted TBI using helical tomotherapy results in reduced doses to normal organs, which predicts for reduced toxicities compared with standard TBI. Methods and Materials: Thirteen patients with multiple myeloma were treated in an autologous tandem transplantation Phase I trial with high-dose melphalan, followed 6 weeks later by total-marrow irradiation (TMI) to skeletal bone. Dose levels were 10, 12, 14, and 16 Gy at 2 Gy daily/twice daily. In a separate allogeneic HCT trial, 8 patients (5 with acute myelogenous leukemia, 1 with acute lymphoblastic leukemia, 1 with non-Hodgkin's lymphoma, and 1 with multiple myeloma) were treated with TMI plus total lymphoid irradiation plus splenic radiotherapy to 12 Gy (1.5 Gy twice daily) combined with fludarabine/melphalan. Results: For the 13 patients in the tandem autologous HCT trial, median age was 54 years (range, 42-66 years). Median organ doses were 15-65% that of the gross target volume dose. Primarily Grades 1-2 acute toxicities were observed. Six patients reported no vomiting; 9 patients, no mucositis; 6 patients, no fatigue; and 8 patients, no diarrhea. For the 8 patients in the allogeneic HCT trial, median age was 52 years (range, 24-61 years). Grades 2-3 nausea, vomiting, mucositis, and diarrhea were observed. In both trials, no Grade 4 nonhematologic toxicity was observed, and all patients underwent successful engraftment. Conclusions: This study shows that TMI using helical tomotherapy is clinically feasible. The reduced acute toxicities observed compare favorably with those seen with standard TBI. Initial results are encouraging and warrant further evaluation as a method to dose escalate with acceptable toxicity or to offer TBI-containing regimens to patients unable to tolerate standard approaches.

  18. Radiobiologic comparison of helical tomotherapy, intensity modulated radiotherapy, and conformal radiotherapy in treating lung cancer accounting for secondary malignancy risks

    SciTech Connect

    Komisopoulos, Georgios; Mavroidis, Panayiotis; Rodriguez, Salvador; Stathakis, Sotirios; Papanikolaou, Nikos; Nikiforidis, Georgios C.; Sakellaropoulos, Georgios C.

    2014-01-01

    The aim of the present study is to examine the importance of using measures to predict the risk of inducing secondary malignancies in association with the clinical effectiveness of treatment plans in terms of tumor control and normal tissue complication probabilities. This is achieved by using radiobiologic parameters and measures, which may provide a closer association between clinical outcome and treatment delivery. Overall, 4 patients having been treated for lung cancer were examined. For each of them, 3 treatment plans were developed based on the helical tomotherapy (HT), multileaf collimator-based intensity modulated radiation therapy (IMRT), and 3-dimensional conformal radiation therapy (CRT) modalities. The different plans were evaluated using the complication-free tumor control probability (p{sub +}), the overall probability of injury (p{sub I}), the overall probability of control/benefit (p{sub B}), and the biologically effective uniform dose (D{sup ¯¯}). These radiobiologic measures were used to develop dose-response curves (p-D{sup ¯¯} diagram), which can help to evaluate different treatment plans when used in conjunction with standard dosimetric criteria. The risks for secondary malignancies in the heart and the contralateral lung were calculated for the 3 radiation modalities based on the corresponding dose-volume histograms (DVHs) of each patient. Regarding the overall evaluation of the different radiation modalities based on the p{sub +} index, the average values of the HT, IMRT, and CRT are 67.3%, 61.2%, and 68.2%, respectively. The corresponding average values of p{sub B} are 75.6%, 70.5%, and 71.0%, respectively, whereas the average values of p{sub I} are 8.3%, 9.3%, and 2.8%, respectively. Among the organs at risk (OARs), lungs show the highest probabilities for complications, which are 7.1%, 8.0%, and 1.3% for the HT, IMRT, and CRT modalities, respectively. Similarly, the biologically effective prescription doses (D{sub B}{sup ¯¯}) for the

  19. Comparing the quality of passively-scattered proton and photon tomotherapy plans for brain and head and neck disease sites.

    PubMed

    Kainz, Kristofer; Firat, Selim; Wilson, J Frank; Schultz, Christopher; Siker, Malika; Wang, Andrew; Olson, Dan; Li, X Allen

    2015-03-21

    We compare the quality of photon IMRT (helical tomotherapy) with classic proton plans for brain, head and neck tumors, in terms of target dose uniformity and conformity along with organ-at-risk (OAR) sparing. Plans were created for twelve target volumes among eight cases. All patients were originally planned and treated using helical tomotherapy. Proton plans were generated using a passively-scattered beam model with a maximum range of 32 g cm(-2) (225 MeV), range modulation in 0.5 g cm(-2) increments and range compensators with 4.8 mm milling tool diameters. All proton plans were limited to two to four beams. Plan quality was compared using uniformity index (UI), conformation number (CN) and a EUD-based plan quality index (fEUD). For 11 of the 12 targets, UI was improved for the proton plan; on average, UI was 1.05 for protons versus 1.08 for tomotherapy. For 7 of the 12 targets, the tomotherapy plan exhibited more favorable CN. For proximal OARs, the improved dose conformity to the target volume from tomotherapy led to a lower maximum dose. For distal OARs, the maximum dose was much lower for proton plans. For 6 of the 8 cases, near-total avoidance for distal OARs provided by protons leads to improved fEUD. However, if distal OARs are excluded in the fEUD calculation, the proton plans exhibit better fEUD in only 3 of the 8 cases. The distal OAR sparing and target dose uniformity are generally better with passive-scatter proton planning than with photon tomotherapy; proton therapy may be preferred if the clinician deems those attributes critical. However, tomotherapy may serve equally as well as protons for cases where superior target dose conformity from tomotherapy leads to plan quality nearly identical to or better than protons and for cases where distal OAR sparing is not concerning.

  20. A Comprehensive Assessment by Tumor Site of Patient Setup using Daily MVCT Imaging from Over Three Thousand Eight Hundred Helical Tomotherapy Treatments

    PubMed Central

    Schubert, Leah K.; Westerly, David C.; Tomé, Wolfgang A.; Mehta, Minesh P.; Soisson, Emilie T.; Mackie, Thomas R.; Ritter, Mark A.; Khuntia, Deepak; Harari, Paul M.; Paliwal, Bhudatt R.

    2009-01-01

    Purpose To assess patient setup corrections based on daily megavoltage CT (MVCT) imaging for four different anatomical treatment sites treated on tomotherapy. Method and Materials Translational and rotational per-fraction setup corrections, based on registration of daily helical MVCT to planning CT images, were analyzed for 1179 brain and head and neck (H&N), 1414 lung, and 1274 prostate tomotherapy treatment fractions. Frequencies of 3D vector lengths, overall distributions of setup corrections, and patient-specific distributions of random and systematic setup errors were analyzed. Results Brain and H&N had lower magnitude positioning corrections and smaller variations in setup errors in the translational directions, but were comparable in roll rotations. 3D vector translational shifts of larger magnitudes occurred more frequently for lung and prostate than for brain and H&N treatments, yet this was not observed for roll rotations. The global systematic error for prostate was 4.7 mm in the vertical direction, most likely due to couch sag caused by large couch extension distances. Patient-to-patient variations in systematic errors and magnitudes of random translational errors ranged from 1.6-2.6 mm for brain and H&N and 3.2-7.2 mm for lung and prostate while roll rotational errors ranged from 0.8-1.2° for brain and H&N and 0.5-1.0° for lung and prostate. Conclusions Differences in setup were observed between brain, H&N, lung, and prostate treatments. Patient setup can be improved if daily imaging is performed. This analysis can assess the utilization of daily image guidance and allows for further investigation into improved anatomical site-specific and patient-specific treatments. PMID:19251098

  1. Helical Channel Design and Technology for Cooling of Muon Beams

    NASA Astrophysics Data System (ADS)

    Yonehara, K.; Derbenev, Y. S.; Johnson, R. P.

    2010-11-01

    Novel magnetic helical channel designs for capture and cooling of bright muon beams are being developed using numerical simulations based on new inventions such as helical solenoid (HS) magnets and hydrogen-pressurized RF (HPRF) cavities. We are close to the factor of a million six-dimensional phase space (6D) reduction needed for muon colliders. Recent experimental and simulation results are presented.

  2. Comprehensive dosimetric planning comparison for early-stage, non-small cell lung cancer with SABR: fixed-beam IMRT versus VMAT versus TomoTherapy.

    PubMed

    Xhaferllari, Ilma; El-Sherif, Omar; Gaede, Stewart

    2016-09-01

    Volumetric-modulated arc therapy (VMAT) is emerging as a leading technology in treating early-stage, non-small cell lung cancer (NSCLC) with stereotactic ablative radiotherapy (SABR). However, two other modalities capable of delivering intensity-modulated radiation therapy (IMRT) include fixed-beam and helical TomoTherapy (HT). This study aims to provide an extensive dosimetric comparison among these various IMRT techniques for treating early-stage NSCLC with SABR. Ten early-stage NSCLC patients were retrospectively optimized using three fixed-beam techniques via nine to eleven beams (high and low modulation step-and-shoot (SS), and sliding window (SW)), two VMAT techniques via two partial arcs (SmartArc (SA) and RapidArc (RA)), and three HT techniques via three different fan beam widths (1 cm, 2.5 cm, and 5 cm) for 80 plans total. Fixed-beam and VMAT plans were generated using flattening filter-free beams. SS and SA, HT treatment plans, and SW and RA were optimized using Pinnacle v9.1, Tomoplan v.3.1.1, and Eclipse (Acuros XB v11.3 algorithm), respectively. Dose-volume histogram statistics, dose conformality, and treatment delivery efficiency were analyzed. VMAT treatment plans achieved significantly lower values for contralateral lung V5Gy(p≤0.05) compared to the HT plans, and significantly lower mean lung dose (p<0.006) compared to HT 5 cm treatment plans. In the comparison between the VMAT techniques, a significant reduction in the total monitor units (p=0.05) was found in the SA plans, while a significant decrease was observed in the dose falloff parameter, D2cm, (p=0.05), for the RA treatments. The maximum cord dose was significantly reduced (p=0.017) in grouped RA&SA plans compared to SS. Estimated treatment time was significantly higher for HT and fixed-beam plans compared to RA&SA (p<0.001). Although, a significant difference was not observed in the RA vs. SA (p=0.393). RA&SA outperformed HT in all parameters measured. Despite an increase in dose to the

  3. Comprehensive dosimetric planning comparison for early-stage, non-small cell lung cancer with SABR: fixed-beam IMRT versus VMAT versus TomoTherapy.

    PubMed

    Xhaferllari, Ilma; El-Sherif, Omar; Gaede, Stewart

    2016-09-08

    Volumetric-modulated arc therapy (VMAT) is emerging as a leading technology in treating early-stage, non-small cell lung cancer (NSCLC) with stereotactic ablative radiotherapy (SABR). However, two other modalities capable of deliver-ing intensity-modulated radiation therapy (IMRT) include fixed-beam and helical TomoTherapy (HT). This study aims to provide an extensive dosimetric compari-son among these various IMRT techniques for treating early-stage NSCLC with SABR. Ten early-stage NSCLC patients were retrospectively optimized using three fixed-beam techniques via nine to eleven beams (high and low modulation step-and-shoot (SS), and sliding window (SW)), two VMAT techniques via two partial arcs (SmartArc (SA) and RapidArc (RA)), and three HT techniques via three different fan beam widths (1 cm, 2.5 cm, and 5 cm) for 80 plans total. Fixed-beam and VMAT plans were generated using flattening filter-free beams. SS and SA, HT treatment plans, and SW and RA were optimized using Pinnacle v9.1, Tomoplan v.3.1.1, and Eclipse (Acuros XB v11.3 algorithm), respectively. Dose-volume histogram statistics, dose conformality, and treatment delivery efficiency were analyzed. VMAT treatment plans achieved significantly lower values for contralat-eral lung V5Gy (p ≤ 0.05) compared to the HT plans, and significantly lower mean lung dose (p < 0.006) compared to HT 5 cm treatment plans. In the comparison between the VMAT techniques, a significant reduction in the total monitor units (p = 0.05) was found in the SA plans, while a significant decrease was observed in the dose falloff parameter, D2cm, (p = 0.05), for the RA treatments. The maximum cord dose was significantly reduced (p = 0.017) in grouped RA&SA plans com-pared to SS. Estimated treatment time was significantly higher for HT and fixed-beam plans compared to RA&SA (p < 0.001). Although, a significant difference was not observed in the RA vs. SA (p = 0.393). RA&SA outperformed HT in all parameters measured. Despite an

  4. A Phase II Study of Stereotactic Body Radiation Therapy for Low-Intermediate-High-Risk Prostate Cancer Using Helical Tomotherapy: Dose-Volumetric Parameters Predicting Early Toxicity

    PubMed Central

    Macias, Victor A.; Blanco, Manuel L.; Barrera, Inmaculada; Garcia, Rafael

    2014-01-01

    Endpoint: To assess early urinary (GU) and rectal (GI) toxicities after helical tomotherapy Stereotactic body radiation therapy (SBRT), and to determine their predictive factors. Methods: Since May 2012, 45 prostate cancer patients were treated with eight fractions of 5.48 (low risk, 29%) or 5.65 Gy (intermediate-high risk, 71%) on alternative days over 2.5 weeks. The exclusion criteria were Gleason score 9–10, PSA >40 ng/mL, cT3b-4, IPSS ≥20, and history of acute urinary retention. During the follow-up, a set of potential prognostic factors was correlated with urinary or rectal toxicity. Results: The median follow-up was 13.8 months (2–25 months). There were no grade ≥3 toxicities. Acute grade 2 GU complications were found in a 22.7% of men, but in 2.3% of patients at 1 month, 0% at 6 months, and 0% at 12 months. The correspondent figures for grade 2 GI toxicities were 20.4% (acute), 2.3% (1 month), 3.6% (6 months), and 5% (12 months). Acute GI toxicity was significantly correlated with the rectal volume (>15 cm3) receiving 28 Gy, only when expressed as absolute volume. The age (>72 years old) was a predictor of GI toxicity after 1 month of treatment. No correlation was found, however, between urinary toxicity and the other analyzed variables. IPSS increased significantly at the time of the last fraction and within the first month, returning to the baseline at sixth month. Urinary-related quality of life (IPSS question 8 score), it was not significantly worsen during radiotherapy returning to the baseline levels 1 month after the treatment. At 12 months follow-up patient’s perception of their urinary function improved significantly in comparison with the baseline. Conclusion: Our scheme of eight fractions on alternative days delivered using helical tomotherapy is well tolerated. We recommend using actual volume instead of percentual volume in the treatment planning, and not to exceed 15 cm3 of rectal volume receiving

  5. A case study comparing the relative benefit of optimizing beam weights, wedge angles, beam orientations and tomotherapy in stereotactic radiotherapy of the brain

    NASA Astrophysics Data System (ADS)

    Oldham, M.; Khoo, V. S.; Rowbottom, C. G.; Bedford, J. L.; Webb, S.

    1998-08-01

    A treatment-planning case study has been performed on a patient with a medium-sized, convex brain tumour. The study involved the application of advanced treatment-plan optimization techniques to improve on the dose distribution of the `standard plan' used to treat the patient. The standard plan was created according to conventional protocol at the Royal Marsden NHS Trust, and consisted of a three-field (one open and two wedged) non-coplanar arrangement, with field shaping to the beam's-eye view of the planning target volume (PTV). Three optimized treatment plans were created corresponding to (i) the optimization of the beam weights and wedge angles of the standard plan, (ii) the optimization of the beam orientations, beam weights and wedge angles of the standard plan, and (iii) a full fluence tomotherapy optimization of 1 cm wide (at isocentre), arcs. (i) and (ii) were created on the VOXELPLAN research 3D treatment-planning system, using in-house developed optimization algorithms, and (iii) was created on the PEACOCK tomotherapy planning system. The downhill-simplex optimization algorithm is used, in conjuction with `threshold-dose' cost-function terms enabling the algorithm to optimize specific regions of the dose-volume histogram (DVH) curve. The `beam-cost plot' tool is presented as a visual aid to the selection of beneficial beam directions. The methods and pitfalls in the transfer of plans and patient data between the two planning systems are discussed. Each optimization approach was evaluated, relative to the standard plan, on the basis of DVH and dose statistics in the PTV and organs at risk (OARs). All three optimization approaches were able to improve on the dose distribution of the standard plan. The magnitude of the improvement was greater for the optimized beam-orientation and tomotherapy plans (up to 15% and 30% for the maximum and mean OAR doses). A smaller improvement

  6. Experimental observation of helical microbunching of a relativistic electron beam

    SciTech Connect

    Hemsing, E.; Knyazik, A.; O'Shea, F.; Marinelli, A.; Musumeci, P.; Williams, O.; Rosenzweig, J. B.; Tochitsky, S.

    2012-02-27

    Experimental observation of the microbunching of a relativistic electron beam at the second harmonic interaction frequency of a helical undulator is presented. The microbunching signal is observed from the coherent transition radiation of the electron beam and indicates experimental evidence of a dominantly helical electron beam density distribution. This result is in agreement with theoretical and numerical predictions and provides a proof-of-principle demonstration of proposed schemes designed to generate light with orbital angular momentum in high-gain free-electron lasers.

  7. Metastatic brain cancer: prediction of response to whole-brain helical tomotherapy with simultaneous intralesional boost for metastatic disease using quantitative MR imaging features

    NASA Astrophysics Data System (ADS)

    Sharma, Harish; Bauman, Glenn; Rodrigues, George; Bartha, Robert; Ward, Aaron

    2014-03-01

    The sequential application of whole brain radiotherapy (WBRT) and more targeted stereotactic radiosurgery (SRS) is frequently used to treat metastatic brain tumors. However, SRS has side effects related to necrosis and edema, and requires separate and relatively invasive localization procedures. Helical tomotherapy (HT) allows for a SRS-type simultaneous infield boost (SIB) of multiple brain metastases, synchronously with WBRT and without separate stereotactic procedures. However, some patients' tumors may not respond to HT+SIB, and would be more appropriately treated with radiosurgery or conventional surgery despite the additional risks and side effects. As a first step toward a broader objective of developing a means for response prediction to HT+SIB, the goal of this study was to investigate whether quantitative measurements of tumor size and appearance (including first- and second-order texture features) on a magnetic resonance imaging (MRI) scan acquired prior to treatment could be used to differentiate responder and nonresponder patient groups after HT+SIB treatment of metastatic disease of the brain. Our results demonstrated that smaller lesions may respond better to this form of therapy; measures of appearance provided limited added value over measures of size for response prediction. With further validation on a larger data set, this approach may lead to a means for prediction of individual patient response based on pre-treatment MRI, supporting appropriate therapy selection for patients with metastatic brain cancer.

  8. Hypofractionated breast cancer radiotherapy. Helical tomotherapy in supine position or classic 3D-conformal radiotherapy in prone position: which is better?

    PubMed

    Cammarota, Fabrizio; Giugliano, Francesca Maria; Iadanza, Luciano; Cutillo, Luisa; Muto, Matteo; Toledo, Diego; Ravo, Vincenzo; Falivene, Sara; Muto, Paolo

    2014-03-01

    We propose a comparative dosimetric study of whole-breast hypofractionated radiation therapy using helical tomotherapy (HT) in supine position and 3-D conformal radiotherapy (3D-CRT) in prone position. Twelve patients undergoing breast-conserving therapy were retrospectively selected from October to December 2012. Specific dose-volume parameters were selected for the study. The target coverage was adequate in all patients for both techniques. Significant differences in lung dose distribution were observed: maximum dose (mean value over the 12 plans) was 23.41 Gy in HT plans and 6.65 Gy in 3D-CRT; V20 (i.e. the lung volume receiving 20 Gy) was 0.31% in HT plans and 0.0% in 3D-CRT plans. The mean dose to the heart was 5.57 Gy and 0.93 Gy, respectively. The differences between the two techniques were significant (p<0.05) only for some parameters. We noted better results in the prone position, but with HT, dose constraints were mentioned for the whole set of considered organs.

  9. Assessing the Role of Volumetric Modulated Arc Therapy (VMAT) Relative to IMRT and Helical Tomotherapy in the Management of Localized, Locally Advanced, and Post-Operative Prostate Cancer

    SciTech Connect

    Davidson, Melanie T.M.; Blake, Samuel J.; Batchelar, Deidre L.; Cheung, Patrick; Mah, Katherine

    2011-08-01

    Purpose: To quantify differences in treatment delivery efficiency and dosimetry between step-and-shoot intensity-modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT), and helical tomotherapy (HT) for prostate treatment. Methods and Materials: Twenty-five prostate cancer patients were selected retrospectively for this planning study. Treatment plans were generated for: prostate alone (n = 5), prostate + seminal vesicles (n = 5), prostate + seminal vesicles + pelvic lymph nodes (n = 5), prostate bed (n = 5), and prostate bed + pelvic lymph nodes (n = 5). Target coverage, dose homogeneity, integral dose, monitor units (MU), and sparing of organs at risk (OAR) were compared across techniques. Time required to deliver each plan was measured. Results: The dosimetric quality of IMRT, VMAT, and HT plans were comparable for target coverage (planning target volume V95%, clinical target volume V100% all >98.7%) and sparing of organs at risk (OAR) for all treatment groups. Although HT resulted in a slightly higher integral dose and mean doses to the OAR, it yielded a lower maximum dose to all OAR examined. VMAT resulted in reductions in treatment times over IMRT (mean = 75%) and HT (mean = 70%). VMAT required 15-38% fewer monitor units than IMRT over all treatment volumes, with the reduction per fraction ranging from 100-423 MU from the smallest to largest volumes. Conclusions: VMAT improves efficiency of delivery for equivalent dosimetric quality as IMRT and HT across various prostate cancer treatment volumes in the intact and postoperative settings.

  10. Automatic registration of megavoltage to kilovoltage CT images in helical tomotherapy: An evaluation of the setup verification process for the special case of a rigid head phantom

    SciTech Connect

    Boswell, Sarah; Tome, Wolfgang; Jeraj, Robert; Jaradat, Hazim; Mackie, T. Rock

    2006-11-15

    Precise daily target localization is necessary to achieve highly conformal radiation delivery. In helical tomotherapy, setup verification may be accomplished just prior to delivering each fraction by acquiring a megavoltage CT scan of the patient in the treatment position. This daily image set may be manually or automatically registered to the image set on which the treatment plan was calculated, in order to determine any needed adjustments. The system was tested by acquiring 104 MVCT scans of an anthropomorphic head phantom to which translational displacements had been introduced with respect to the planning image set. Registration results were compared against an independent, optically guided positioning system. The total experimental uncertainty was within approximately 1 mm. Although the registration of phantom images is not fully analogous to the registration of patient images, this study confirms that the system is capable of phantom localization with sub-voxel accuracy. In seven registration problems considered, expert human observers were able to perform manual registrations with comparable or inferior accuracy to automatic registration by mutual information. The time to compute an automatic registration is considerably shorter than the time required for manual registration. However, human evaluation of automatic results is necessary in order to identify occasional outliers, and to ensure that the registration is clinically acceptable, especially in the case of deformable patient anatomy.

  11. Helical Tomotherapy-Based STAT Stereotactic Body Radiation Therapy: Dosimetric Evaluation for a Real-Time SBRT Treatment Planning and Delivery Program

    SciTech Connect

    Dunlap, Neal; McIntosh, Alyson; Sheng Ke; Yang Wensha; Turner, Benton; Shoushtari, Asal; Sheehan, Jason; Jones, David R.; Lu Weigo; Ruchala, Keneth; Olivera, Gustavo; Parnell, Donald; Larner, James L.; Benedict, Stanley H.; Read, Paul W.

    2010-01-01

    Stereotactic body radiation therapy (SBRT) treatments have high-dose gradients and even slight patient misalignment from the simulation to treatment could lead to target underdosing or organ at risk (OAR) overdosing. Daily real-time SBRT treatment planning could minimize the risk of geographic miss. As an initial step toward determining the clinical feasibility of developing real-time SBRT treatment planning, we determined the calculation time of helical TomoTherapy-based STAT radiation therapy (RT) treatment plans for simple liver, lung, and spine SBRT treatments to assess whether the planning process was fast enough for practical clinical implementation. Representative SBRT planning target volumes for hypothetical liver, peripheral lung, and thoracic spine lesions and adjacent OARs were contoured onto a planning computed tomography scan (CT) of an anthropomorphic phantom. Treatment plans were generated using both STAT RT 'full scatter' and conventional helical TomoTherapy 'beamlet' algorithms. Optimized plans were compared with respect to conformality index (CI), heterogeneity index (HI), and maximum dose to regional OARs to determine clinical equivalence and the number of required STAT RT optimization iterations and calculation times were determined. The liver and lung dosimetry for the STAT RT and standard planning algorithms were clinically and statistically equivalent. For the liver lesions, 'full scatter' and 'beamlet' algorithms showed a CI of 1.04 and 1.04 and HI of 1.03 and 1.03, respectively. For the lung lesions, 'full scatter' and 'beamlet' algorithms showed a CI of 1.05 and 1.03 and HI of 1.05and 1.05, respectively. For spine lesions, 'full scatter' and 'beamlet' algorithms showed a CI of 1.15 and 1.14 and HI of 1.22 and 1.14, respectively. There was no difference between treatment algorithms with respect to maximum doses to the OARs. The STAT RT iteration time with current treatment planning systems is 45 sec, and the treatment planning required 3

  12. Dose-volume histogram comparison between static 5-field IMRT with 18-MV X-rays and helical tomotherapy with 6-MV X-rays.

    PubMed

    Hayashi, Akihiro; Shibamoto, Yuta; Hattori, Yukiko; Tamura, Takeshi; Iwabuchi, Michio; Otsuka, Shinya; Sugie, Chikao; Yanagi, Takeshi

    2015-03-01

    We treated prostate cancer patients with static 5-field intensity-modulated radiation therapy (IMRT) using linac 18-MV X-rays or tomotherapy with 6-MV X-rays. As X-ray energies differ, we hypothesized that 18-MV photon IMRT may be better for large patients and tomotherapy may be more suitable for small patients. Thus, we compared dose-volume parameters for the planning target volume (PTV) and organs at risk (OARs) in 59 patients with T1-3 N0M0 prostate cancer who had been treated using 5-field IMRT. For these same patients, tomotherapy plans were also prepared for comparison. In addition, plans of 18 patients who were actually treated with tomotherapy were analyzed. The evaluated parameters were homogeneity indicies and a conformity index for the PTVs, and D2 (dose received by 2% of the PTV in Gy), D98, Dmean and V10-70 Gy (%) for OARs. To evaluate differences by body size, patients with a known body mass index were grouped by that index ( <21; 21-25; and >25 kg/m(2)). For the PTV, all parameters were higher in the tomotherapy plans compared with the 5-field IMRT plans. For the rectum, V10 Gy and V60 Gy were higher, whereas V20 Gy and V30 Gy were lower in the tomotherapy plans. For the bladder, all parameters were higher in the tomotherapy plans. However, both plans were considered clinically acceptable. Similar trends were observed in 18 patients treated with tomotherapy. Obvious trends were not observed for body size. Tomotherapy provides equivalent dose distributions for PTVs and OARs compared with 18-MV 5-field IMRT. Tomotherapy could be used as a substitute for high-energy photon IMRT for prostate cancer regardless of body size.

  13. Multi-institutional Feasibility Study of a Fast Patient Localization Method in Total Marrow Irradiation With Helical Tomotherapy: A Global Health Initiative by the International Consortium of Total Marrow Irradiation

    PubMed Central

    Takahashi, Yutaka; Vagge, Stefano; Agostinelli, Stefano; Han, Eunyoung; Matulewicz, Lukasz; Schubert, Kai; Chityala, Ravishankar; Ratanatharathorn, Vaneerat; Tournel, Koen; Penagaricano, Jose A.; Florian, Sterzing; Mahe, Marc-Andre; Verneris, Michael R.; Weisdorf, Daniel J.; Corvo, Renzo; Dusenbery, Kathryn E.; Storme, Guy; Hui, Susanta K.

    2014-01-01

    Purpose To develop, characterize, and implement a fast patient localization method for total marrow irradiation. Methods and Materials Topographic images were acquired using megavoltage computed tomography (MVCT) detector data by delivering static orthogonal beams while the couch traversed through the gantry. Geometric and detector response corrections were performed to generate a megavoltage topogram (MVtopo). We also generated kilovoltage topograms (kVtopo) from the projection data of 3-dimensional CT images to reproduce the same geometry as helical tomotherapy. The MVtopo imaging dose and the optimal image acquisition parameters were investigated. A multi-institutional phantom study was performed to verify the image registration uncertainty. Forty-five MVtopo images were acquired and analyzed with in-house image registration software. Results The smallest jaw size (front and backup jaws of 0) provided the best image contrast and longitudinal resolution. Couch velocity did not affect the image quality or geometric accuracy. The MVtopo dose was less than the MVCT dose. The image registration uncertainty from the multi-institutional study was within 2.8 mm. In patient localization, the differences in calculated couch shift between the registration with MVtopo-kVtopo and MVCT-kVCT images in lateral, cranial–caudal, and vertical directions were 2.2 ± 1.7 mm, 2.6 ± 1.4 mm, and 2.7 ± 1.1 mm, respectively. The imaging time in MVtopo acquisition at the couch speed of 3 cm/s was <1 minute, compared with ≥15 minutes in MVCT for all patients. Conclusion Whole-body MVtopo imaging could be an effective alternative to time-consuming MVCT for total marrow irradiation patient localization. PMID:25442340

  14. Multi-institutional Feasibility Study of a Fast Patient Localization Method in Total Marrow Irradiation With Helical Tomotherapy: A Global Health Initiative by the International Consortium of Total Marrow Irradiation

    SciTech Connect

    Takahashi, Yutaka; Vagge, Stefano; Agostinelli, Stefano; Han, Eunyoung; Matulewicz, Lukasz; Schubert, Kai; Chityala, Ravishankar; Ratanatharathorn, Vaneerat; Tournel, Koen; Penagaricano, Jose A.; Florian, Sterzing; Mahe, Marc-Andre; Verneris, Michael R.; Weisdorf, Daniel J.; and others

    2015-01-01

    Purpose: To develop, characterize, and implement a fast patient localization method for total marrow irradiation. Methods and Materials: Topographic images were acquired using megavoltage computed tomography (MVCT) detector data by delivering static orthogonal beams while the couch traversed through the gantry. Geometric and detector response corrections were performed to generate a megavoltage topogram (MVtopo). We also generated kilovoltage topograms (kVtopo) from the projection data of 3-dimensional CT images to reproduce the same geometry as helical tomotherapy. The MVtopo imaging dose and the optimal image acquisition parameters were investigated. A multi-institutional phantom study was performed to verify the image registration uncertainty. Forty-five MVtopo images were acquired and analyzed with in-house image registration software. Results: The smallest jaw size (front and backup jaws of 0) provided the best image contrast and longitudinal resolution. Couch velocity did not affect the image quality or geometric accuracy. The MVtopo dose was less than the MVCT dose. The image registration uncertainty from the multi-institutional study was within 2.8 mm. In patient localization, the differences in calculated couch shift between the registration with MVtopo-kVtopo and MVCT-kVCT images in lateral, cranial–caudal, and vertical directions were 2.2 ± 1.7 mm, 2.6 ± 1.4 mm, and 2.7 ± 1.1 mm, respectively. The imaging time in MVtopo acquisition at the couch speed of 3 cm/s was <1 minute, compared with ≥15 minutes in MVCT for all patients. Conclusion: Whole-body MVtopo imaging could be an effective alternative to time-consuming MVCT for total marrow irradiation patient localization.

  15. Feasibility of Helical Tomotherapy in Stereotactic Body Radiation Therapy for Centrally Located Early Stage Non-Small-Cell Lung Cancer or Lung Metastases

    SciTech Connect

    Chi, Alexander; Jang, Si Young; Welsh, James S.; Nguyen, Nam P.; Ong, Evan; Gobar, Lisa; Komaki, Ritsuko

    2011-11-01

    Purpose: To investigate the ability of helical tomotherapy (HT) to spare critical organs immediately adjacent to the tumor target in stereotactic body radiation therapy (SBRT) for centrally located lung lesions. Methods and Materials: HT SBRT plans for 10 patients with centrally located lesions or lesions immediately adjacent to a critical structure were generated. A total of 70 Gy in 10 fractions was prescribed to the planning target volume (PTV) to satisfy a target volume coverage of {>=}95% PTV receiving 70 Gy and an established set of dose constraints for the organs at risk (OARs). Quality assurance (QA) of the HT plans was performed with both ion chamber and film measurements. Results: The PTV coverage criteria was met with 95% of the PTV receiving 70.68 {+-} 0.33 Gy for all cases even though the OARs immediately adjacent to the PTV ranged from 0.38 to 0.85 cm away. The mean lung dose (MLD), and V{sub 20} were 7.15 {+-} 1.44 Gy, and 11.93 {+-} 3.24 % for the total lung, respectively. The dose parameters of MLD, V{sub 5}, V{sub 10}, and V{sub 20} for the contralateral lung were significantly lower than those for the ipsilateral lung (p < 0.05). An average dose fall off from the PTV periphery to the edge of the immediately adjacent OAR was 47.6% over an average distance of 4.87 mm. Comparison of calculated and measured doses with the ion chamber showed an average of 1.85% point dose error, whereas an average mean gamma and the area with a gamma larger than 1 of 0.20 and 0.94% were observed, respectively. Conclusion: HT allows the sparing of critical structures immediately adjacent to the tumor target, thus making SBRT for these centrally located lesions feasible.

  16. Superiority of helical tomotherapy on liver sparing and dose escalation in hepatocellular carcinoma: a comparison study of three-dimensional conformal radiotherapy and intensity-modulated radiotherapy

    PubMed Central

    Zhao, Qianqian; Wang, Renben; Zhu, Jian; Jin, Linzhi; Zhu, Kunli; Xu, Xiaoqing; Feng, Rui; Jiang, Shumei; Qi, Zhonghua; Yin, Yong

    2016-01-01

    Background and purpose To compare the difference of liver sparing and dose escalation between three-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT), and helical tomotherapy (HT) for hepatocellular carcinoma. Patients and methods Sixteen unresectable HCC patients were enrolled in this study. First, some evaluation factors of 3DCRT, IMRT, and HT plans were calculated with prescription dose at 50 Gy/25 fractions. Then, the doses were increased using HT or IMRT independently until either the plans reached 70 Gy or any normal tissue reached the dose limit according to quantitative analysis of normal tissue effects in the clinic criteria. Results The conformal index of 3DCRT was lower than that of IMRT (P<0.001) or HT (P<0.001), and the homogeneity index of 3DCRT was higher than that of IMRT (P<0.001) or HT (P<0.001). HT took the longest treatment time (P<0.001). For V50% (fraction of normal liver treated to at least 50% of the isocenter dose) of the normal liver, there was a significant difference: 3DCRT > IMRT > HT (P<0.001). HT had a lower Dmean (mean dose) and V20 (Vn, the percentage of organ volume receiving ≥n Gy) of liver compared with 3DCRT (P=0.005 and P=0.005, respectively) or IMRT (P=0.508 and P=0.007, respectively). Dmean of nontarget normal liver and V30 of liver were higher for 3DCRT than IMRT (P=0.005 and P=0.005, respectively) or HT (P=0.005 and P=0.005, respectively). Seven patients in IMRT (43.75%) and nine patients in HT (56.25%) reached the isodose 70 Gy, meeting the dose limit of the organs at risk. Conclusion HT may provide significantly better liver sparing and allow more patients to achieve higher prescription dose in HCC radiotherapy. PMID:27445485

  17. 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.

  18. Bowel sparing in pediatric cranio-spinal radiotherapy: a comparison of combined electron and photon and helical TomoTherapy techniques to a standard photon method

    SciTech Connect

    Harron, Elizabeth; Lewis, Joanne

    2012-07-01

    The aim of this study was to compare the dose to organs at risk (OARs) from different craniospinal radiotherapy treatment approaches available at the Northern Centre for Cancer Care (NCCC), with a particular emphasis on sparing the bowel. Method: Treatment plans were produced for a pediatric medulloblastoma patient with inflammatory bowel disease using 3D conformal 6-MV photons (3DCP), combined 3D 6-MV photons and 18-MeV electrons (3DPE), and helical photon TomoTherapy (HT). The 3DPE plan was a modification of the standard 3DCP technique, using electrons to treat the spine inferior to the level of the diaphragm. The plans were compared in terms of the dose-volume data to OARs and the nontumor integral dose. Results: The 3DPE plan was found to give the lowest dose to the bowel and the lowest nontumor integral dose of the 3 techniques. However, the coverage of the spine planning target volume (PTV) was least homogeneous using this technique, with only 74.6% of the PTV covered by 95% of the prescribed dose. HT was able to achieve the best coverage of the PTVs (99.0% of the whole-brain PTV and 93.1% of the spine PTV received 95% of the prescribed dose), but delivered a significantly higher integral dose. HT was able to spare the heart, thyroid, and eyes better than the linac-based techniques, but other OARs received a higher dose. Conclusions: Use of electrons was the best method for reducing the dose to the bowel and the integral dose, at the expense of compromised spine PTV coverage. For some patients, HT may be a viable method of improving dose homogeneity and reducing selected OAR doses.

  19. Treatment-Related Pneumonitis and Acute Esophagitis in Non-Small-Cell Lung Cancer Patients Treated With Chemotherapy and Helical Tomotherapy

    SciTech Connect

    Song, Chang Hoon; Pyo, Hongryull; Moon, Sung Ho; Kim, Tae Hyun; Kim, Dae Woong; Cho, Kwan Ho

    2010-11-01

    Purpose: To assess clinical outcomes and complications in patients with non-small-cell lung cancer (NSCLC) treated with helical tomotherapy (HT) with or without chemotherapy. Methods and Materials: Data from 37 NSCLC patients treated between January 2007 and August 2008 were analyzed retrospectively. Twenty-eight patients had Stage III disease. Concurrent and neoadjuvant chemotherapy was given to 24 and 14 patients, respectively. Radiotherapy was delivered to a total dose of 60-70.4 Gy at 2.0-2.4 Gy per fraction to the gross tumor volume and 50-64 Gy at 1.8-2.0 Gy per fraction to the planning target volume. Results: With a median follow-up of 18 months (range, 6-27 months), 2-year local control and overall survival rates were 63% and 56% for all 37 patients, respectively, and were 78% and 75% for the patients with Stage III disease who received concurrent chemoradiotherapy alone. Acute esophagitis and treatment-related pneumonitis (TRP) {>=}Grade 3 occurred in 5 and 7 patients, respectively. Four patients died of treatment-related death (TRD) after HT. In univariate analysis, poor performance status, total lung V{sub 5}, contralateral lung (CL) V{sub 5}, and V{sub 10} were associated with TRD. Only CL V{sub 5} remained significant in the multivariate analysis (p = 0.029). Conclusions: HT with chemotherapy has shown promising clinical outcomes, esophagitis, and TRPs. However, HT has produced a somewhat high rate of fatal pulmonary complications. Our data suggest that CL V{sub 5} should be considered and kept as low as possible (<60%) in addition to the conventional dosimetric factors.

  20. Helical tractor beam: analytical solution of Rayleigh particle dynamics.

    PubMed

    Carretero, Luis; Acebal, Pablo; Garcia, Celia; Blaya, Salvador

    2015-08-10

    We analyze particle dynamics in an optical force field generated by helical tractor beams obtained by the interference of a cylindrical beam with a topological charge and a co-propagating temporally de-phased plane wave. We show that, for standard experimental conditions, it is possible to obtain analytical solutions for the trajectories of particles in such force field by using of some approximations. These solutions show that, in contrast to other tractor beams described before, the intensity becomes a key parameter for the control of particle trajectories. Therefore, by tuning the intensity value the particle can describe helical trajectories upstream and downstream, a circular trajectory in a fixed plane, or a linear displacement in the propagation direction. The approximated analytical solutions show good agreement to the corresponding numerical solutions of the exact dynamical differential equations.

  1. Electron cyclotron beam measurement system in the Large Helical Device

    SciTech Connect

    Kamio, S. Takahashi, H.; Kubo, S.; Shimozuma, T.; Yoshimura, Y.; Igami, H.; Ito, S.; Kobayashi, S.; Mizuno, Y.; Okada, K.; Osakabe, M.; Mutoh, T.

    2014-11-15

    In order to evaluate the electron cyclotron (EC) heating power inside the Large Helical Device vacuum vessel and to investigate the physics of the interaction between the EC beam and the plasma, a direct measurement system for the EC beam transmitted through the plasma column was developed. The system consists of an EC beam target plate, which is made of isotropic graphite and faces against the EC beam through the plasma, and an IR camera for measuring the target plate temperature increase by the transmitted EC beam. This system is applicable to the high magnetic field (up to 2.75 T) and plasma density (up to 0.8 × 10{sup 19} m{sup −3}). This system successfully evaluated the transmitted EC beam profile and the refraction.

  2. Dose as a Function of Lung Volume and Planned Treatment Volume in Helical Tomotherapy Intensity-Modulated Radiation Therapy-Based Stereotactic Body Radiation Therapy for Small Lung Tumors

    SciTech Connect

    Baisden, Joseph M.; Romney, Davis A.; Reish, Andrew G.; Cai Jing; Sheng Ke; Jones, David R.; Benedict, Stanley H.; Read, Paul W.; Larner, James M. . E-mail: JML2P@virginia.edu

    2007-07-15

    Purpose: To evaluate the limitations of Hi-Art Helical Tomotherapy (Middleton, WI) stereotactic body radiotherapy (SBRT) for lung lesions, and to provide an initial report on patients treated with this method. Stereotactic body radiotherapy was shown to be an effective, well-tolerated treatment for early-stage, non-small-cell lung carcinoma (NSCLC). The Radiation Therapy Oncology Group (RTOG) 0236 protocol is currently evaluating three-dimensional conformal SBRT that delivers 60 Gy in three fractions. Methods and Materials: Inverse treatment planning for hypothetical lung gross tumor volumes (GTV) and planned treatment volume (PTV) expansions were performed. We tested the hypothesis that the maximum acceptable dose (MAD) to be delivered to the lesion by SBRT could be predicted by PTV and lung volume. Dose constraints on normal tissue were as designated by the RTOG protocol. Inverse planning was performed to find the maximum tolerated SBRT dose up to 60 Gy. Results: Regression analysis of the data obtained indicated a linear relationship between MAD, PTV, and lung volume. This generated two equations which may be useful predictive tools. Seven patients with Stage I and II NSCLC treated at University of Virginia with this method tolerated the treatment extremely well, and suffered no greater than grade I toxicity, with no evidence of disease recurrence in follow-up from 2-20 months. Conclusions: Helical tomotherapy SBRT for lung lesions is well-tolerated. In addition, the likely MAD for patients considered for this type of treatment can be predicted by PTV and lung volume.

  3. Out-of-field doses from pediatric craniospinal irradiations using 3D-CRT, IMRT, helical tomotherapy and electron-based therapy.

    PubMed

    De Saint-Hubert, Marijke; Verellen, Dirk; Poels, Kenneth; Crijns, Wouter; Magliona, Federica; Depuydt, Tom; Vanhavere, Filip; Struelens, Lara

    2017-04-11

    Medulloblastoma treatment involves irradiation of the entire central nervous system, i.e craniospinal irradiation (CSI). This is associated with significant exposure of large volumes of healthy tissue with a growing concern regarding treatment associated side effects. The current study compares out-of-field organ doses in children receiving CSI with three-dimensional-conformal radiotherapy (3D-CRT), intensity modulated radiotherapy (IMRT), helical tomotherapy (HT) and an electron-based technique, including as well radiation doses resulting from imaging performed during treatment. An extensive phantom study is performed, using an anthropomorphic phantom corresponding to a 5-year old child, in which organ absorbed doses are measured using thermoluminescent detectors (TLDs). Additionally the study evaluates and explores tools for calculating out-of-field patient doses using the treatment planning system (TPS) and analytical models. In our study, 3D-CRT resulted in very high doses to a limited number of organs while it was able to spare organs such as the lungs and breast when compared to IMRT and HT. Both IMRT and HT spread the dose over more organs and were able to spare heart, thyroid, bladder, uterus and testes when compared to 3D-CRT. The electron-based technique considerably decreased the out-of-field doses in deep seated organs but cannot avoid nearby out-of-field organs such as lungs, ribs, adrenals, kidneys and uterus. Daily imaging dose is small compared to the treatment dose burden. TPS error for out-of-field doses was most pronounced for organs further away from the target nevertheless no systematic underestimation was observed for any of the studied TPS systems. Finally analytical modeling was most optimal for 3D-CRT although the number of organs that can be modeled was limited. To conclude none of the techniques studied was able to spare doses in all organs. Nevertheless the electron-based technique showed most promising for out-of-field organ dose

  4. Do We Need Daily Image-Guided Radiotherapy by Megavoltage Computed Tomography in Head and Neck Helical Tomotherapy? The Actual Delivered Dose to the Spinal Cord

    SciTech Connect

    Duma, Marciana Nona; Kampfer, Severin; Schuster, Tibor; Aswathanarayana, Nandana; Fromm, Laura-Sophie; Molls, Michael; Andratschke, Nicolaus; Geinitz, Hans

    2012-09-01

    Purpose: To quantify the actual delivered dose to the cervical spinal cord with different image-guided radiotherapy (IGRT) approaches during head and neck (HN) cancer helical tomotherapy. Methods and Materials: Twenty HN patients (HNpts) treated with bilateral nodal irradiation were analyzed. Daily megavoltage computed tomography MVCT) scans were performed for setup purposes. The maximum dose on the planning CT scan (plan-Dmax) and the magnitude and localization of the actual delivered Dmax (a-Dmax) were analyzed for four scenarios: daily image-guided radiotherapy (dIGRT), twice weekly IGRT (2 Multiplication-Sign WkIGRT), once weekly IGRT (1 Multiplication-Sign WkIGRT), and no IGRT at all (non-IGRT). The spinal cord was recontoured on 236 MVCTs for each scenario (total, 944 fractions), and the delivered dose was recalculated for each fraction (fx) separately. Results: Fifty-one percent of the analyzed fx for dIGRT, 56% of the analyzed fx for the 2 Multiplication-Sign WkIGRT, 62% of the analyzed fx for the 1 Multiplication-Sign WkIGRT, and 63% of the analyzed fx for the non-IGRT scenarios received a higher a-Dmax than the plan-Dmax. The median increase of dose in these fx was 3.3% more for dIGRT, 5.8% more for 2 Multiplication-Sign WkIGRT, 10.0% more for 1 Multiplication-Sign WkIGRT, and 9.5% more for non-IGRT than the plan-Dmax. The median spinal cord volumes receiving a higher dose than the plan-Dmax were 0.02 cm{sup 3} for dIGRT, 0.11 cm{sup 3} for 2 Multiplication-Sign WkIGRT, 0.31 cm{sup 3} for 1 Multiplication-Sign WkIGRT, and 0.22 cm{sup 3} for non-IGRT. Differences between the dIGRT and all other scenarios were statistically significant (p < 0.05). Conclusions: Compared to the Dmax of the initial plan, daily IGRT had the smallest increase in dose. Furthermore, daily IGRT had the lowest proportion of fractions and the smallest volumes affected by a dose that was higher than the planned dose. For patients treated with doses close to the tolerance dose of the

  5. Experimental Validation of Monte Carlo Simulations Based on a Virtual Source Model for TomoTherapy in a RANDO Phantom.

    PubMed

    Yuan, Jiankui; Zheng, Yiran; Wessels, Barry; Lo, Simon S; Ellis, Rodney; Machtay, Mitchell; Yao, Min

    2016-12-01

    A virtual source model for Monte Carlo simulations of helical TomoTherapy has been developed previously by the authors. The purpose of this work is to perform experiments in an anthropomorphic (RANDO) phantom with the same order of complexity as in clinical treatments to validate the virtual source model to be used for quality assurance secondary check on TomoTherapy patient planning dose. Helical TomoTherapy involves complex delivery pattern with irregular beam apertures and couch movement during irradiation. Monte Carlo simulation, as the most accurate dose algorithm, is desirable in radiation dosimetry. Current Monte Carlo simulations for helical TomoTherapy adopt the full Monte Carlo model, which includes detailed modeling of individual machine component, and thus, large phase space files are required at different scoring planes. As an alternative approach, we developed a virtual source model without using the large phase space files for the patient dose calculations previously. In this work, we apply the simulation system to recompute the patient doses, which were generated by the treatment planning system in an anthropomorphic phantom to mimic the real patient treatments. We performed thermoluminescence dosimeter point dose and film measurements to compare with Monte Carlo results. Thermoluminescence dosimeter measurements show that the relative difference in both Monte Carlo and treatment planning system is within 3%, with the largest difference less than 5% for both the test plans. The film measurements demonstrated 85.7% and 98.4% passing rate using the 3 mm/3% acceptance criterion for the head and neck and lung cases, respectively. Over 95% passing rate is achieved if 4 mm/4% criterion is applied. For the dose-volume histograms, very good agreement is obtained between the Monte Carlo and treatment planning system method for both cases. The experimental results demonstrate that the virtual source model Monte Carlo system can be a viable option for the

  6. Investigation of electron beam transport in a helical undulator

    SciTech Connect

    Jeong, Y.U.; Lee, B.C.; Kim, S.K.

    1995-12-31

    Lossless transport of electrons through the undulator is essential for CW operation of the FELs driven by recirculating electrostatic accelerators. We calculate the transport ratio of an electron beam in a helical undulator by using a 3-D simulation code and compare the results with the experimental results. The energy and the current of the electron beam are 400 keV and 2 A, respectively. The 3-D distribution of the magnetic field of a practical permanent-magnet helical undulator is measured and is used in the calculations. The major parameters of the undutlator are : period = 32 mm, number of periods = 20, number of periods in adiabatic region = 3.5, magnetic field strength = 1.3 kG. The transport ratio is very sensitive to the injection condition of the electron beam such as the emittance, the diameter, the divergence, etc.. The injection motion is varied in the experiments by changing the e-gun voltage or the field strength of the focusing magnet located at the entrance of the undulator. It is confirmed experimentally and with simulations that most of the beam loss occurs at the adiabatic region of the undulator regardless of the length of the adiabatic region The effect of axial guiding magnetic field on the beam finish is investigated. According to the simulations, the increase of the strength of axial magnetic field from 0 to 1 kG results in the increase of the transport ratio from 15 % to 95%.

  7. Measurements of Beam Ion Loss from the Compact Helical System

    SciTech Connect

    D. S. Darrow, M. Isobe, Takashi Kondo, M. Sasao, and the CHS Group National Institute for Fusion Science, Toki, Gifu, Japan

    2010-02-03

    Beam ion loss from the Compact Helical System (CHS) has been measured with a scintillator-type probe. The total loss to the probe, and the pitch angle and gyroradius distributions of that loss, have been measured as various plasma parameters were scanned. Three classes of beam ion loss were observed at the probe position: passing ions with pitch angles within 10o of those of transition orbits, ions on transition orbits, and ions on trapped orbits, typically 15o or more from transition orbits. Some orbit calculations in this geometry have been performed in order to understand the characteristics of the loss. Simulation of the detector signal based upon the following of orbits from realistic beam deposition profiles is not able to reproduce the pitch angle distribution of the losses measured. Consequently it is inferred that internal plasma processes, whether magnetohydrodynamic modes, radial electric fields, or plasma turbulence, move previously confined beam ions to transition orbits, resulting in their loss.

  8. Generating polarization vortices by using helical beams and a Twyman Green interferometer.

    PubMed

    Fu, Shiyao; Gao, Chunqing; Shi, Yang; Dai, Kunjian; Zhong, Lei; Zhang, Shikun

    2015-04-15

    A stable interferometric arrangement consisting of a polarizing beam splitter, a reflector, and a right-angle prism is designed to transform helical beams into polarization vortices. The computer-generated holograms are loaded on the liquid crystal spatial light modulator (LC-SLM) in order to generate different helical beams. Then the helical beams are transformed into polarization vortices with different kinds of intensity distribution successfully.

  9. Note: A helical velocity selector for continuous molecular beams.

    PubMed

    Szewc, Carola; Collier, James D; Ulbricht, Hendrik

    2010-10-01

    We report on a modern realization of the classic helical velocity selector for gas phase particle beams. The device operates stably under high vacuum conditions at rotational frequencies limited only by commercial dc motor capabilities. Tuning the rotational frequency allows selective scanning over a broad velocity band. The width of the selected velocity distributions at full-width-half-maximum is as narrow as a few percent of the selected mean velocity and independent of the rotational speed of the selector. The selector generates low vibrational noise amplitudes comparable to mechanically damped state-of-the-art turbo-molecular pumps and is therefore compatible with vibration sensitive experiments like molecule interferometry.

  10. Note: A helical velocity selector for continuous molecular beams

    NASA Astrophysics Data System (ADS)

    Szewc, Carola; Collier, James D.; Ulbricht, Hendrik

    2010-10-01

    We report on a modern realization of the classic helical velocity selector for gas phase particle beams. The device operates stably under high vacuum conditions at rotational frequencies limited only by commercial dc motor capabilities. Tuning the rotational frequency allows selective scanning over a broad velocity band. The width of the selected velocity distributions at full-width-half-maximum is as narrow as a few percent of the selected mean velocity and independent of the rotational speed of the selector. The selector generates low vibrational noise amplitudes comparable to mechanically damped state-of-the-art turbo-molecular pumps and is therefore compatible with vibration sensitive experiments like molecule interferometry.

  11. Helical Tomotherapy for Whole-Brain Irradiation With Integrated Boost to Multiple Brain Metastases: Evaluation of Dose Distribution Characteristics and Comparison With Alternative Techniques

    SciTech Connect

    Levegrün, Sabine; Pöttgen, Christoph; Wittig, Andrea; Lübcke, Wolfgang; Abu Jawad, Jehad; Stuschke, Martin

    2013-07-15

    Purpose: To quantitatively evaluate dose distribution characteristics achieved with helical tomotherapy (HT) for whole-brain irradiation (WBRT) with integrated boost (IB) to multiple brain metastases in comparison with alternative techniques. Methods and Materials: Dose distributions for 23 patients with 81 metastases treated with WBRT (30 Gy/10 fractions) and IB (50 Gy) were analyzed. The median number of metastases per patient (N{sub mets}) was 3 (range, 2-8). Mean values of the composite planning target volume of all metastases per patient (PTV{sub mets}) and of the individual metastasis planning target volume (PTV{sub ind} {sub met}) were 8.7 ± 8.9 cm{sup 3} (range, 1.3-35.5 cm{sup 3}) and 2.5 ± 4.5 cm{sup 3} (range, 0.19-24.7 cm{sup 3}), respectively. Dose distributions in PTV{sub mets} and PTV{sub ind} {sub met} were evaluated with respect to dose conformity (conformation number [CN], RTOG conformity index [PITV]), target coverage (TC), and homogeneity (homogeneity index [HI], ratio of maximum dose to prescription dose [MDPD]). The dependence of dose conformity on target size and N{sub mets} was investigated. The dose distribution characteristics were benchmarked against alternative irradiation techniques identified in a systematic literature review. Results: Mean ± standard deviation of dose distribution characteristics derived for PTV{sub mets} amounted to CN = 0.790 ± 0.101, PITV = 1.161 ± 0.154, TC = 0.95 ± 0.01, HI = 0.142 ± 0.022, and MDPD = 1.147 ± 0.029, respectively, demonstrating high dose conformity with acceptable homogeneity. Corresponding numbers for PTV{sub ind} {sub met} were CN = 0.708 ± 0.128, PITV = 1.174 ± 0.237, TC = 0.90 ± 0.10, HI = 0.140 ± 0.027, and MDPD = 1.129 ± 0.030, respectively. The target size had a statistically significant influence on dose conformity to PTV{sub mets} (CN = 0.737 for PTV{sub mets} ≤4.32 cm{sup 3} vs CN = 0.848 for PTV{sub mets} >4.32 cm{sup 3}, P=.006), in contrast to N{sub mets}. The achieved

  12. The frequency split method for helical cone-beam reconstruction.

    PubMed

    Shechter, G; Köhler, Th; Altman, A; Proksa, R

    2004-08-01

    A new approximate method for the utilization of redundant data in helical cone-beam CT is presented. It is based on the observation that the original WEDGE method provides excellent image quality if only little more than 180 degrees data are used for back-projection, and that significant low-frequency artifacts appear if a larger amount of redundant data are used. This degradation is compensated by the frequency split method: The low-frequency part of the image is reconstructed using little more than 180 degrees of data, while the high frequency part is reconstructed using all data. The resulting algorithm shows no cone-beam artifacts in a simulation of a 64-row scanner. It is further shown that the frequency split method hardly degrades the signal-to-noise ratio of the reconstructed images and that it behaves robustly in the presence of motion.

  13. Studies of a gas-filled helical muon beam cooling channel

    SciTech Connect

    Yonehara, K.; Derbenev, Y.; Johnson, R.P.; Roberts, T.J.; /MUONS Inc., Batavia

    2006-06-01

    A helical cooling channel (HCC) can quickly reduce the six dimensional phase space of muon beams for muon colliders, neutrino factories, and intense muon sources. The HCC is composed of solenoidal, helical dipole, and helical quadrupole magnetic fields to provide the focusing and dispersion needed for emittance exchange as the beam follows an equilibrium helical orbit through a continuous homogeneous absorber. The beam dynamics of a gas-filled helical muon beam cooling channel is studied by using Monte Carlo simulations. The results verify the cooling theory [1] of the helical magnet. The cooling performance has been improved by correcting chromatic aberration and the non-linear effects caused by the ionization energy loss process. With these improvements, a simulated cooling channel of 160 meters length has achieved a reduction of 6-dimensional (6D) phase space by a factor of 50,000.

  14. Resonant excitation of whistler waves by a helical electron beam

    NASA Astrophysics Data System (ADS)

    An, X.; Van Compernolle, B.; Bortnik, J.; Thorne, R. M.; Chen, L.; Li, W.

    2016-03-01

    Chorus-like whistler mode waves that are known to play a fundamental role in driving radiation belt dynamics are excited on the Large Plasma Device by the injection of a helical electron beam into a cold plasma. The mode structure of the excited whistler wave is identified using a phase correlation technique showing that the waves are excited through a combination of Landau resonance, cyclotron resonance, and anomalous cyclotron resonance. The dominant wave mode excited through cyclotron resonance is quasi-parallel propagating, whereas wave modes excited through Landau resonance and anomalous cyclotron resonance propagate at oblique angles that are close to the resonance cone. An analysis of the linear wave growth rates captures the major observations in the experiment. The results have important implications for the generation process of whistler waves in the Earth's inner magnetosphere.

  15. Application of Monte Carlo methods in tomotherapy and radiation biophysics

    NASA Astrophysics Data System (ADS)

    Hsiao, Ya-Yun

    Helical tomotherapy is an attractive treatment for cancer therapy because highly conformal dose distributions can be achieved while the on-board megavoltage CT provides simultaneous images for accurate patient positioning. The convolution/superposition (C/S) dose calculation methods typically used for Tomotherapy treatment planning may overestimate skin (superficial) doses by 3-13%. Although more accurate than C/S methods, Monte Carlo (MC) simulations are too slow for routine clinical treatment planning. However, the computational requirements of MC can be reduced by developing a source model for the parts of the accelerator that do not change from patient to patient. This source model then becomes the starting point for additional simulations of the penetration of radiation through patient. In the first section of this dissertation, a source model for a helical tomotherapy is constructed by condensing information from MC simulations into series of analytical formulas. The MC calculated percentage depth dose and beam profiles computed using the source model agree within 2% of measurements for a wide range of field sizes, which suggests that the proposed source model provides an adequate representation of the tomotherapy head for dose calculations. Monte Carlo methods are a versatile technique for simulating many physical, chemical and biological processes. In the second major of this thesis, a new methodology is developed to simulate of the induction of DNA damage by low-energy photons. First, the PENELOPE Monte Carlo radiation transport code is used to estimate the spectrum of initial electrons produced by photons. The initial spectrum of electrons are then combined with DNA damage yields for monoenergetic electrons from the fast Monte Carlo damage simulation (MCDS) developed earlier by Semenenko and Stewart (Purdue University). Single- and double-strand break yields predicted by the proposed methodology are in good agreement (1%) with the results of published

  16. Gaussian laser beam transformation into an optical vortex beam by helical lens

    NASA Astrophysics Data System (ADS)

    Janicijevic, Ljiljana; Topuzoski, Suzana

    2016-01-01

    In this article, we investigate the Fresnel diffraction characteristics of the hybrid optical element which is a combination of a spiral phase plate (SPP) with topological charge p and a thin lens with focal length f, named the helical lens (HL). As incident a Gaussian laser beam is treated, having its waist a distance ζ from the HL plane and its axis passing through the centre of the HL. It is shown that the SPP introduces a phase singularity of pth order to the incident beam, while the lens transforms the beam characteristic parameters. The output light beam is analyzed in detail: its characteristic parameters and focusing properties, amplitude and intensity distributions and the vortex rings profiles, and radii, at any z distance behind the HL plane, as well as in the near and far field.

  17. SU-E-T-197: Helical Cranial-Spinal Treatments with a Linear Accelerator

    SciTech Connect

    Anderson, J; Bernard, D; Liao, Y; Templeton, A; Turian, J; Chu, J

    2014-06-01

    Purpose: Craniospinal irradiation (CSI) of systemic disease requires a high level of beam intensity modulation to reduce dose to bone marrow and other critical structures. Current helical delivery machines can take 30 minutes or more of beam-on time to complete these treatments. This pilot study aims to test the feasibility of performing helical treatments with a conventional linear accelerator using longitudinal couch travel during multiple gantry revolutions. Methods: The VMAT optimization package of the Eclipse 10.0 treatment planning system was used to optimize pseudo-helical CSI plans of 5 clinical patient scans. Each gantry revolution was divided into three 120° arcs with each isocenter shifted longitudinally. Treatments requiring more than the maximum 10 arcs used multiple plans with each plan after the first being optimized including the dose of the others (Figure 1). The beam pitch was varied between 0.2 and 0.9 (couch speed 5- 20cm/revolution and field width of 22cm) and dose-volume histograms of critical organs were compared to tomotherapy plans. Results: Viable pseudo-helical plans were achieved using Eclipse. Decreasing the pitch from 0.9 to 0.2 lowered the maximum lens dose by 40%, the mean bone marrow dose by 2.1% and the maximum esophagus dose by 17.5%. (Figure 2). Linac-based helical plans showed dose results comparable to tomotherapy delivery for both target coverage and critical organ sparing, with the D50 of bone marrow and esophagus respectively 12% and 31% lower in the helical linear accelerator plan (Figure 3). Total mean beam-on time for the linear accelerator plan was 8.3 minutes, 54% faster than the tomotherapy average for the same plans. Conclusions: This pilot study has demonstrated the feasibility of planning pseudo-helical treatments for CSI targets using a conventional linac and dynamic couch movement, and supports the ongoing development of true helical optimization and delivery.

  18. Orbital angular momentum of helical necklace beams in colloid-based nonlinear optical metamaterials (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Walasik, Wiktor T.; Silahli, Salih Z.; Litchinitser, Natalia M.

    2016-09-01

    Colloidal metamaterials are a robust and flexible platform for engineering of optical nonlinearities and studies of light filamentation. To date, nonlinear propagation and modulation instability of Gaussian beams and optical vortices carrying orbital angular momentum were studied in such media. Here, we investigate the propagation of necklace beams and the conservation of the orbital angular momentum in colloidal media with saturable nonlinearity. We study various scenarios leading to generation of helical necklace beams or twisted beams, depending on the radius, power, and charge of the input vortex beam. Helical beams are build of two separate solitary beams with circular cross-sections that spiral around their center of mass as a result of the equilibrium between the attraction force of in-phase solitons and the centrifugal force associated with the rotational movement. A twisted beam is a single beam with an elliptical cross-section that rotates around it's own axis. We show that the orbital angular momentum is converted into the rotational motion at different rates for helical and twisted beams. While earlier studies reported that solitary beams are expelled form the initial vortex ring along straight trajectories tangent to the vortex ring, we show that depending on the charge and the power of the initial beam, these trajectories can diverge from the tangential direction and may be curvilinear. These results provide a detailed description of necklace beam dynamics in saturable nonlinear media and may be useful in studies of light filamentation in liquids and light propagation in highly scattering colloids and biological samples.

  19. A Comprehensive Assessment by Tumor Site of Patient Setup Using Daily MVCT Imaging From More Than 3,800 Helical Tomotherapy Treatments

    SciTech Connect

    Schubert, Leah K. Westerly, David C.; Tome, Wolfgang A.; Mehta, Minesh P.; Soisson, Emilie T.; Mackie, Thomas R.; Ritter, Mark A.; Khuntia, Deepak; Harari, Paul M.; Paliwal, Bhudatt R.

    2009-03-15

    Purpose: To assess patient setup corrections based on daily megavoltage CT (MVCT) imaging for four anatomic treatment sites treated on tomotherapy. Method and Materials: Translational and rotational setup corrections, based on registration of daily MVCT to planning CT images, were analyzed for 1,179 brain and head and neck (H and N), 1,414 lung, and 1,274 prostate treatment fractions. Frequencies of three-dimensional vector lengths, overall distributions of setup corrections, and patient-specific distributions of random and systematic setup errors were analyzed. Results: Brain and H and N had lower magnitude positioning corrections and smaller variations in translational setup errors but were comparable in roll rotations. Three-dimensional vector translational shifts of larger magnitudes occurred more frequently for lung and prostate than for brain and H and N treatments, yet this was not observed for roll rotations. The global systematic error for prostate was 4.7 mm in the vertical direction, most likely due to couch sag caused by large couch extension distances. Variations in systematic errors and magnitudes of random translational errors ranged from 1.6 to 2.6 mm for brain and H and N and 3.2 to 7.2 mm for lung and prostate, whereas roll rotational errors ranged from 0.8{sup o} to 1.2{sup o} for brain and H and N and 0.5{sup o} to 1.0{sup o} for lung and prostate. Conclusions: Differences in setup were observed between brain, H and N, lung, and prostate treatments. Patient setup can be improved if daily imaging is performed. This analysis can assess the utilization of daily image guidance and allows for further investigation into improved anatomic site-specific and patient-specific treatments.

  20. Superposition and detection of two helical beams for optical orbital angular momentum communication

    NASA Astrophysics Data System (ADS)

    Liu, Yi-Dong; Gao, Chunqing; Gao, Mingwei; Qi, Xiaoqing; Weber, Horst

    2008-07-01

    A loop-like system with a Dove prism is used to generate a collinear superposition of two helical beams with different azimuthal quantum numbers in this manuscript. After the generation of the helical beams distributed on the circle centered at the optical axis by using a binary amplitude grating, the diffractive field is separated into two polarized ones with the same distribution. Rotated by the Dove prism in the loop-like system in counter directions and combined together, the two fields will generate the collinear superposition of two helical beams in certain direction. The experiment shows consistency with the theoretical analysis. This method has potential applications in optical communication by using orbital angular momentum of laser beams (optical vortices).

  1. Encouraging Early Clinical Outcomes With Helical Tomotherapy-Based Image-Guided Intensity-Modulated Radiation Therapy for Residual, Recurrent, and/or Progressive Benign/Low-Grade Intracranial Tumors: A Comprehensive Evaluation

    SciTech Connect

    Gupta, Tejpal

    2012-02-01

    Purpose: To report early clinical outcomes of helical tomotherapy (HT)-based image-guided intensity-modulated radiation therapy (IMRT) in brain tumors of varying shape, size, and location. Materials and Methods: Patients with residual, recurrent, and/or progressive low-grade intracranial and skull-base tumors were treated on a prospective protocol of HT-based IMRT and followed clinicoradiologically. Standardized metrics were used for plan evaluation and outcome analysis. Results: Twenty-seven patients with 30 lesions were treated to a median radiotherapy dose of 54 Gy in 30 fractions. All HT plans resulted in excellent target volume coverage with steep dose-gradients. The mean (standard deviation) dose homogeneity index and conformity index was 0.07 (0.05) and 0.71 (0.08) respectively. At first response assessment, 20 of 30 lesions were stable, whereas 9 showed partial regression. One patient with a recurrent clival chordoma though neurologically stable showed imaging-defined progression, whereas another patient with stable disease on serial imaging had sustained neurologic worsening. With a median follow-up of 19 months (interquartile range, 11-26 months), the 2-year clinicoradiological progression-free survival and overall survival was 93.3% and 100% respectively. Conclusions: Careful selection of radiotherapy technique is warranted for benign/low-grade brain tumors to achieve durable local control with minimum long-term morbidity. Large or complex-shaped tumors benefit most from IMRT. Our early clinical experience of HT-based IMRT for brain tumors has been encouraging.

  2. Helical Tomotherapy vs. Intensity-Modulated Proton Therapy for Whole Pelvis Irradiation in High-Risk Prostate Cancer Patients: Dosimetric, Normal Tissue Complication Probability, and Generalized Equivalent Uniform Dose Analysis

    SciTech Connect

    Widesott, Lamberto; Pierelli, Alessio; Fiorino, Claudio; Lomax, Antony J.; Amichetti, Maurizio; Cozzarini, Cesare; Soukup, Martin; Schneider, Ralf; Hug, Eugen; Di Muzio, Nadia; Calandrino, Riccardo; Schwarz, Marco

    2011-08-01

    Purpose: To compare intensity-modulated proton therapy (IMPT) and helical tomotherapy (HT) treatment plans for high-risk prostate cancer (HRPCa) patients. Methods and Materials: The plans of 8 patients with HRPCa treated with HT were compared with IMPT plans with two quasilateral fields set up (-100{sup o}; 100{sup o}) and optimized with the Hyperion treatment planning system. Both techniques were optimized to simultaneously deliver 74.2 Gy/Gy relative biologic effectiveness (RBE) in 28 fractions on planning target volumes (PTVs)3-4 (P + proximal seminal vesicles), 65.5 Gy/Gy(RBE) on PTV2 (distal seminal vesicles and rectum/prostate overlapping), and 51.8 Gy/Gy(RBE) to PTV1 (pelvic lymph nodes). Normal tissue calculation probability (NTCP) calculations were performed for the rectum, and generalized equivalent uniform dose (gEUD) was estimated for the bowel cavity, penile bulb and bladder. Results: A slightly better PTV coverage and homogeneity of target dose distribution with IMPT was found: the percentage of PTV volume receiving {>=}95% of the prescribed dose (V{sub 95%}) was on average >97% in HT and >99% in IMPT. The conformity indexes were significantly lower for protons than for photons, and there was a statistically significant reduction of the IMPT dosimetric parameters, up to 50 Gy/Gy(RBE) for the rectum and bowel and 60 Gy/Gy(RBE) for the bladder. The NTCP values for the rectum were higher in HT for all the sets of parameters, but the gain was small and in only a few cases statistically significant. Conclusions: Comparable PTV coverage was observed. Based on NTCP calculation, IMPT is expected to allow a small reduction in rectal toxicity, and a significant dosimetric gain with IMPT, both in medium-dose and in low-dose range in all OARs, was observed.

  3. Single-slice reconstruction method for helical cone-beam differential phase-contrast CT.

    PubMed

    Fu, Jian; Chen, Liyuan

    2014-01-01

    X-ray phase-contrast computed tomography (PC-CT) can provide the internal structure information of biomedical specimens with high-quality cross-section images and has become an invaluable analysis tool. Here a simple and fast reconstruction algorithm is reported for helical cone-beam differential PC-CT (DPC-CT), which is called the DPC-CB-SSRB algorithm. It combines the existing CB-SSRB method of helical cone-beam absorption-contrast CT with the differential nature of DPC imaging. The reconstruction can be performed using 2D fan-beam filtered back projection algorithm with the Hilbert imaginary filter. The quality of the results for large helical pitches is surprisingly good. In particular, with this algorithm comparable quality is obtained using helical cone-beam DPC-CT data with a normalized pitch of 10 to that obtained using the traditional inter-row interpolation reconstruction with a normalized pitch of 2. This method will push the future medical helical cone-beam DPC-CT imaging applications.

  4. Fraunhofer diffraction of Laguerre-Gaussian laser beam by helical axicon

    NASA Astrophysics Data System (ADS)

    Topuzoski, S.

    2014-11-01

    In this article we present a theoretical study for Fraunhofer diffraction of a Laguerre-Gaussian laser beam with “0” radial mode number and “l” azimuthal mode number (LG0l) by helical axicon. Analytical expressions describing the diffracted wave field amplitude and intensity distributions in the back focal plane of a convergent lens are derived in a form of product of a Gauss-doughnut function and a sum of hypergeometric Kummer functions. Also, the diffracted LG beam by axicon only, as well as by spiral phase plate only, and the diffracted Gaussian beam by helical axicon, are described mathematically in the back focal plane of a convergent lens. Different possibilities for obtaining output vortex beam with reduced or increased topological charge compared to that of the incident beam, or for obtaining chargeless beam are analyzed.

  5. Tomotherapy and stereotactic radiosurgery

    NASA Astrophysics Data System (ADS)

    Soisson, Emilie T.

    Currently, at the University of Wisconsin-Madison, a linear accelerator equipped with circular collimators and a floor stand is used for stereotactic radiosurgery (SRS) delivery. In the interest of providing a more efficient delivery option for patients with multiple brain metastases, a Tomotherapy-based radiosurgery program was developed to serve as an intensity modulated compliment to our existing delivery method. The unique advantage of Tomotherapy over other radiotherapy delivery units is the on board megavoltage CT that can be used for both stereotactic localization and treatment planning. As such, a workflow was designed in which the planning image is acquired on the treatment unit itself and, instead using a patient-frame based coordinate system for stereotactic localization, volumetric imaging is used to precisely locate the target at the time of treatment. Localization and delivery accuracy was found to be comparable to conventional approaches and well within stated tolerances. A Tomotherapy-specific treatment planning technique was also developed using the Tomotherapy treatment planning system that reliably produces plans that achieve both conformal target coverage and sufficiently steep dose falloff into surrounding normal brain. Tomotherapy plans have been compared to conventional circular collimator based plans for both the treatment of brain metastases and arteriovenous malformations in terms of both target conformity and dose to normal brain. To determine the effect of plan differences on patient outcome, clinical data was used to predict the resulting risk of treatment induced symptomatic brain necrosis for both conventional and Tomotherapy based plans. Overall, it was determined that plans generated using the described planning technique are acceptable for radiosurgery. In addition, delivery time for complex cases is comparable to or improved over conventional isocentric approaches. Finally, this work explores the impact of future product

  6. Formation and nonlinear dynamics of the squeezed state of a helical electron beam with additional deceleration

    SciTech Connect

    Egorov, E. N. Koronovskii, A. A.; Kurkin, S. A.; Hramov, A. E.

    2013-11-15

    Results of numerical simulations and analysis of the formation and nonlinear dynamics of the squeezed state of a helical electron beam in a vircator with a magnetron injection gun as an electron source and with additional electron deceleration are presented. The ranges of control parameters where the squeezed state can form in such a system are revealed, and specific features of the system dynamics are analyzed. It is shown that the formation of a squeezed state of a nonrelativistic helical electron beam in a system with electron deceleration is accompanied by low-frequency longitudinal dynamics of the space charge.

  7. Iterative image reconstruction for limited-angle inverse helical cone-beam computed tomography.

    PubMed

    Yu, Wei; Zeng, Li

    2016-01-01

    Helical trajectory satisfying the condition of exact reconstruction, has been widely utilized in the commercial computed tomography (CT). While limited by the scanning environment in some practical applications, the conventional helical cone-beam CT imaging is hard to complete, thus, developing an imaging system suited for long-object may be valuable. Three-dimensional C-arm CT is an innovative imaging technique which has been greatly concerned. Since there is a high degree of freedom of C-arm, more flexible image acquisition trajectories for 3D imaging can be achieved. In this work, a fast iterative reconstruction algorithm based on total variation minimization is developed for a trajectory of limited-angle inverse helical cone-beam CT, which can be applied to detect long-object without slip-ring technology. The experimental results show that the developed algorithm can yield reconstructed images of low noise level and high image quality.

  8. Investigation of Fully Three-Dimensional Helical RF Field Effects on TWT Beam/Circuit Interaction

    NASA Technical Reports Server (NTRS)

    Kory, Carol L.

    2000-01-01

    A fully three-dimensional (3D), time-dependent, helical traveling wave-tube (TWT) interaction model has been developed using the electromagnetic particle-in-cell (PIC) code MAFIA. The model includes a short section of helical slow-wave circuit with excitation fed by RF input/output couplers, and electron beam contained by periodic permanent magnet (PPM) focusing. All components of the model are simulated in three dimensions allowing the effects of the fully 3D helical fields on RF circuit/beam interaction to be investigated for the first time. The development of the interaction model is presented, and predicted TWT performance using 2.5D and 3D models is compared to investigate the effect of conventional approximations used in TWT analyses.

  9. Comparison of Effects Between Central and Peripheral Stage I Lung Cancer Using Image-Guided Stereotactic Body Radiotherapy via Helical Tomotherapy.

    PubMed

    He, Jian; Huang, Yan; Shi, Shiming; Hu, Yong; Zeng, Zhaochong

    2015-12-01

    Lung cancer is a common malignant tumor with high morbidity and mortality. Here we compared the effects and outcome between central and peripheral stage I lung cancer using image-guided stereotactic body radiotherapy. From June 2011 to July 2013, a total of 33 patients with stage I lung cancer were enrolled. A total of 50 Gy in 10 fractions or 60 Gy in 10 fractions was delivered in the central arm (n = 18), while 50 Gy in 5 fractions in the peripheral arm (n = 15). Statistical analyses were performed using logistic regression analysis and Kaplan-Meier method. The mean follow-up time was 38.1 months. Three-month, 1-, 2-, and 3-year overall response rates were 66.7%, 83.3%, 61.1%, and 72.2% and 66.7%, 80%, 80%, and 80% in the central and peripheral arms, respectively. Three-year local control rates (94.4% vs 93.3%, P = .854), regional control rates (94.4% vs 86.7%, P = .412), and distant control rates (64.2% vs 61.7%, P = .509) had no differences between the central and the peripheral arms. Grade 2 radiation pneumonitis was observed in 6 of 18 patients in the central arm and in 1 of 15 patients in the peripheral arm (P = .92). Grade 2 radiation esophagitis was 5.7% in the central arm, while none occurred in the peripheral arm (P = .008). Five (15.1%) of all patients felt slight fatigue during radiotherapy. Other major complications were not observed. In conclusion, helical image-guided stereotactic body radiotherapy for central stage I lung cancer is safe and effective compared to peripheral stage I lung cancer.

  10. PI-line-based image reconstruction in helical cone-beam computed tomography with a variable pitch

    SciTech Connect

    Zou Yu; Pan Xiaochuan; Xia Dan; Wang Ge

    2005-08-15

    Current applications of helical cone-beam computed tomography (CT) involve primarily a constant pitch where the translating speed of the table and the rotation speed of the source-detector remain constant. However, situations do exist where it may be more desirable to use a helical scan with a variable translating speed of the table, leading a variable pitch. One of such applications could arise in helical cone-beam CT fluoroscopy for the determination of vascular structures through real-time imaging of contrast bolus arrival. Most of the existing reconstruction algorithms have been developed only for helical cone-beam CT with constant pitch, including the backprojection-filtration (BPF) and filtered-backprojection (FBP) algorithms that we proposed previously. It is possible to generalize some of these algorithms to reconstruct images exactly for helical cone-beam CT with a variable pitch. In this work, we generalize our BPF and FBP algorithms to reconstruct images directly from data acquired in helical cone-beam CT with a variable pitch. We have also performed a preliminary numerical study to demonstrate and verify the generalization of the two algorithms. The results of the study confirm that our generalized BPF and FBP algorithms can yield exact reconstruction in helical cone-beam CT with a variable pitch. It should be pointed out that our generalized BPF algorithm is the only algorithm that is capable of reconstructing exactly region-of-interest image from data containing transverse truncations.

  11. WE-G-18A-06: Sinogram Restoration in Helical Cone-Beam CT

    SciTech Connect

    Little, K; Riviere, P La

    2014-06-15

    Purpose: To extend CT sinogram restoration, which has been shown in 2D to reduce noise and to correct for geometric effects and other degradations at a low computational cost, from 2D to a 3D helical cone-beam geometry. Methods: A method for calculating sinogram degradation coefficients for a helical cone-beam geometry was proposed. These values were used to perform penalized-likelihood sinogram restoration on simulated data that were generated from the FORBILD thorax phantom. Sinogram restorations were performed using both a quadratic penalty and the edge-preserving Huber penalty. After sinogram restoration, Fourier-based analytical methods were used to obtain reconstructions. Resolution-variance trade-offs were investigated for several locations within the reconstructions for the purpose of comparing sinogram restoration to no restoration. In order to compare potential differences, reconstructions were performed using different groups of neighbors in the penalty, two analytical reconstruction methods (Katsevich and single-slice rebinning), and differing helical pitches. Results: The resolution-variance properties of reconstructions restored using sinogram restoration with a Huber penalty outperformed those of reconstructions with no restoration. However, the use of a quadratic sinogram restoration penalty did not lead to an improvement over performing no restoration at the outer regions of the phantom. Application of the Huber penalty to neighbors both within a view and across views did not perform as well as only applying the penalty to neighbors within a view. General improvements in resolution-variance properties using sinogram restoration with the Huber penalty were not dependent on the reconstruction method used or the magnitude of the helical pitch. Conclusion: Sinogram restoration for noise and degradation effects for helical cone-beam CT is feasible and should be able to be applied to clinical data. When applied with the edge-preserving Huber penalty

  12. Studies of a Gas-filled Helical Muon Beam Cooling Channel

    SciTech Connect

    R.P. Johnson; K. Paul; T.J. Roberts; Y.S. Derbenev; K. Yonehara

    2006-06-26

    A helical cooling channel (HCC) can quickly reduce the six dimensional phase space of muon beams for muon colliders, neutrino factories, and intense muon sources. The HCC is composed of solenoidal, helical dipole, and helical quadrupole magnetic fields to provide the focusing and dispersion needed for emittance exchange as the beam follows an equilibrium helical orbit through a continuous homogeneous absorber. We consider liquid helium and liquid hydrogen absorbers in HCC segments that alternate with RF accelerating sections and we also consider gaseous hydrogen absorber in pressurized RF cavities imbedded in HCC segments. In the case of liquid absorber, the possibility of using superconducting RF in low magnetic field regions between the HCC segments may provide a cost effective solution to the high repetition rate needed for an intense neutrino factory or high average luminosity muon collider. In the gaseous hydrogen absorber case, the pressurized RF cavities can be operated at low temperature to improve their efficiency for higher repetition rates. Numerical simulations are used to optimize and compare the liquid and gaseous HCC techniques.

  13. On the Helical Fields Guiding Near-Relativistic Electron Beams in the Heliosphere

    NASA Astrophysics Data System (ADS)

    Rust, David M.; Haggerty, D. K.; Georgoulis, M. K.; Stenborg, G.

    2009-05-01

    Wavelet processing of the LASCO images of the solar corona brings out many subtle details that are easily missed in the intensity images. Specifically, wavelet processing can enhance the edges on large and small scales making it easier to detect and define helical features. We used the processed LASCO images obtained during the period 1997 -2001 to study the structure and motions of nearly radial streamers extending from coronal holes adjacent to flaring active regions. Some of the streamers show outward-propagating twist. These helical fields extend into the heliosphere where they would reach 1 AU with a path length generally greater than the 1.2 AU of idealized fields following the Parker spiral. We focused on the regions from our earlier work (Rust et al., ApJ 687, 635, 2008) on flares associated with beams of near-relativistic electrons detected at 1 AU with the ACE spacecraft. Our study shows that the electron beam's typical delay of about 10 min in arriving at 1 AU may be due to their following a helical path from Sun to Earth. According to the reconnection jet model, the helical component may be introduced to open fields by earlier events involving reconnections with emerging, twisted flux ropes. Our study implies that the escaping electrons may be accelerated at the same time as the trapped electrons that produce X-ray flare emissions. NASA supported this work with grant NNG 05GM69G.

  14. Collective instabilities of the electron beam in magnetic fields of a helical undulator and solenoid

    NASA Astrophysics Data System (ADS)

    Artamonov, A. S.; Inozemtsev, N. I.

    1989-03-01

    The collective instabilities of a continuous electron beam propagating in the magnetic fields of a helical undulator and solenoid are analyzed theoretically in the framework of a one-dimensional model. Modulation of charge density is investigated along with modulation of the transverse velocity of the electrons by an electromagnetic wave. A dispersion equation describing the collective-excitation spectrum is obtained, and analyzed in the hydrodynamic approximation for two-, three-, and four-wave interaction.

  15. Assessment of three-dimensional set-up errors using megavoltage computed tomography (MVCT) during image-guided intensity-modulated radiation therapy (IMRT) for craniospinal irradiation (CSI) on helical tomotherapy (HT).

    PubMed

    Gupta, Tejpal; Upasani, Maheshkumar; Master, Zubin; Patil, Anita; Phurailatpam, Reena; Nojin, Siji; Kannan, Sadhana; Godasastri, Jayant; Jalali, Rakesh

    2015-02-01

    The purpose of this study was to assess three-dimensional (3D) set-up errors using megavoltage computed tomography (MVCT) during image-guided intensity-modulated radiation therapy (IMRT) for supine craniospinal irradiation (CSI) on helical tomotherapy (HT). Patients were immobilized in a customized 4-clamp thermoplastic head mask with or without whole-body vacuum cradle. Set-up was based primarily on a set of cranial fiducial markers. MVCT scans were acquired and co-registered with planning scan separately at three different levels (brain, upper, and lower spine) at every fraction. Only translational displacements were analysed, wherein positive sign denotes deviation in anterior, left, and superior direction; while negative sign denotes deviation in posterior, right, and inferior direction. Mean displacements, systematic, and random errors of the study population were calculated at all three levels separately. Local residual uncertainty of the upper and lower spine was also derived assuming perfect co-registration of the skull. Set-up margins for clinical target volume (CTV) to planning target volume (PTV) were derived at these three levels separately using published margin recipes. Data from 1868 co-registrations in 674 fractions on 33 patients was included. The mean displacements in the lateral, longitudinal, and vertical directions were -1.21, -1.36, and 1.38 mm; -1.25, -0.34, and 0.65 mm; and -1.47, -2.78, and 0.22 mm for the brain; upper spine; and lumbar spine respectively. The corresponding 3D vector of displacement was 2.28; 1.45; and 3.15 mm respectively. There was a distinct systematic trend towards increasing inaccuracy from the brain towards the lower spine. Using Stroom's formula, the minimum recommended CTV to PTV margins in absence of daily image-guidance were 6.5; 7.0; and 9.5 mm for the brain; upper spine; and lower spine respectively. This increased to 7.5; 8.5; and 11.5 mm using van Herk's formula. Subset and sensitivity analyses

  16. Determining helicity and topological structure of coherent vortex beam from laser speckle

    NASA Astrophysics Data System (ADS)

    R. V, Vinu; Singh, Rakesh Kumar

    2016-09-01

    We propose and experimentally demonstrate a technique to quantitatively determine the topological structure of the vortex beam coaxially launched into the random scattering media with another non-vortex beam of the orthogonal polarization component. The proposed technique applies the coherent superposition of the random electromagnetic fields and a priori knowledge of correlation of one of the random fields to determine the polarization correlation of the other. The polarization correlation of the random field is used to determine the topological charge and phase structure of the vortex beam from the laser speckle. The application of the proposed technique is demonstrated by determining the helicity and topological charge of the vortex beam for three different cases.

  17. A theoretically exact reconstruction algorithm for helical cone-beam differential phase-contrast computed tomography.

    PubMed

    Li, Jing; Sun, Yi; Zhu, Peiping

    2013-08-21

    Differential phase-contrast computed tomography (DPC-CT) reconstruction problems are usually solved by using parallel-, fan- or cone-beam algorithms. For rod-shaped objects, the x-ray beams cannot recover all the slices of the sample at the same time. Thus, if a rod-shaped sample is required to be reconstructed by the above algorithms, one should alternately perform translation and rotation on this sample, which leads to lower efficiency. The helical cone-beam CT may significantly improve scanning efficiency for rod-shaped objects over other algorithms. In this paper, we propose a theoretically exact filter-backprojection algorithm for helical cone-beam DPC-CT, which can be applied to reconstruct the refractive index decrement distribution of the samples directly from two-dimensional differential phase-contrast images. Numerical simulations are conducted to verify the proposed algorithm. Our work provides a potential solution for inspecting the rod-shaped samples using DPC-CT, which may be applicable with the evolution of DPC-CT equipments.

  18. Single-fraction spine SBRT end-to-end testing on TomoTherapy, Vero, TrueBeam, and CyberKnife treatment platforms using a novel anthropomorphic phantom.

    PubMed

    Gallo, John J; Kaufman, Isaac; Powell, Rachel; Pandya, Shalini; Somnay, Archana; Bossenberger, Todd; Ramirez, Ezequiel; Reynolds, Robert; Solberg, Timothy; Burmeister, Jay

    2015-01-08

    Spine SBRT involves the delivery of very high doses of radiation to targets adjacent to the spinal cord and is most commonly delivered in a single fraction. Highly conformal planning and accurate delivery of such plans is imperative for successful treatment without catastrophic adverse effects. End-to-end testing is an important practice for evaluating the entire treatment process from simulation through treatment delivery. We performed end-to-end testing for a set of representative spine targets planned and delivered using four different treatment planning systems (TPSs) and delivery systems to evaluate the various capabilities of each. An anthropomorphic E2E SBRT phantom was simulated and treated on each system to evaluate agreement between measured and calculated doses. The phantom accepts ion chambers in the thoracic region and radiochromic film in the lumbar region. Four representative targets were developed within each region (thoracic and lumbar) to represent different presentations of spinal metastases and planned according to RTOG 0631 constraints. Plans were created using the TomoTherapy TPS for delivery using the Hi·Art system, the iPlan TPS for delivery using the Vero system, the Eclipse TPS for delivery using the TrueBeam system in both flattened and flattening filter free (FFF), and the MultiPlan TPS for delivery using the CyberKnife system. Delivered doses were measured using a 0.007 cm3 ion chamber in the thoracic region and EBT3 GAFCHROMIC film in the lumbar region. Films were scanned and analyzed using an Epson Expression 10000XL flatbed scanner in conjunction with FilmQAPro2013. All treatment platforms met all dose constraints required by RTOG 0631. Ion chamber measurements in the thoracic targets delivered an overall average difference of 1.5%. Specifically, measurements agreed with the TPS to within 2.2%, 3.2%, 1.4%, 3.1%, and 3.0% for all three measureable cases on TomoTherapy, Vero, TrueBeam (FFF), TrueBeam (flattened), and Cyber

  19. Status of the heavy ion beam probe system in the Large Helical Device

    SciTech Connect

    Nishiura, M.; Ido, T.; Shimizu, A.; Nakano, H.; Kato, T.; Kato, S.; Hamada, Y.; Shevelko, V. P.; Janev, R. K.; Wada, M.

    2008-02-15

    A heavy ion beam probe (HIBP) system has been installed into the Large Helical Device (LHD) to measure the spatial profile of the plasma potential and density fluctuations. The optimization of the HIBP system, especially the beam injector, is described. The negative ion beam is required for the MeV beam production in a tandem accelerator. A sputter-type heavy negative ion source has been developed as an intense Au{sup -} beam source to produce Au{sup +} beams with energy in the MeV range. The extraction electrodes and the Einzel lens system of the ion source have been designed taking into account the beam optics, and installed into the real machine. Throughout the plasma diagnostics on LHD experiments, the consumptions of vaporized caesium and gold target are being characterized for practical operations. In addition, the experimental charge fractions are compared with the theoretical fractions for understanding the charge-changing behavior of Au{sup -} ions and optimizing the fraction of Au{sup +} ions at the exit of the tandem accelerator of the HIBP system.

  20. Dosimetric comparison of helical tomothearpy and linac-based IMRT in whole abdomen radiotherapy

    NASA Astrophysics Data System (ADS)

    Kang, Young-nam; Kim, Dae-Hyun; Jang, Hong Seok; Song, Jin Ho; Choi, Byung Ock; Cho, Seok Goo; Jung, Ji-Young; Kay, Chul Seung

    2012-10-01

    Recent advances in radiotherapy techniques have allowed a significant improvement in the therapeutic ratio of whole abdominal irradiation (WAI) through linear-accelerator (Linac) based intensity-modulated radiotherapy (IMRT) and helical tomotherapy (HT). IMRT has been shown to reduce the dose to organs at risk (OAR) while adequately treating the tumor volume. HT operates by adjusting 51 beam directions, couch speed, pitch and shapes of a binary multileaf collimator (MLC), with the purpose of clinically increasing the befit to the patient. We incorporated helical tomotherapy as a new modality for WAI for the treatment of non-Hodgkin's lymphoma patients whose disease involved the intestine and the mesenteric lymph nodes. Excellent tumor coverage with effective sparing of normal organ sparings, and homogeneous dose distribution could be achieved. This study dosimetrically compared HT and linac-based IMRT by using several indices, including the conformity index (CI) and the homogeneity index (HI) for the planning target volume (PTV), as well as the, max dose and the mean dose and the quality index (QI) for five organs at risk (OARs). The HI and the CI were used to compare the quality of target coverage while the QI was used compare the dosimetric performans for OAR systems. The target coverages between the two systems were similar, but the most QIs were lower than 1, what means that HT is batter at sparing OARs than IMRT. Tomotherapy enabled excellent target coverage, effective sparing of normal tissues, and homogeneous dose distribution without severe acute toxicity.

  1. Ion Compensation for Space Charge in the Helical Electron Beams of Gyrotrons

    NASA Astrophysics Data System (ADS)

    Manuilov, V. N.; Semenov, V. E.

    2016-06-01

    We solve analytically the problem about ion compensation for the space charge of a helical electron beam in a gyrotron operated in the long-pulse regime. Elementary processes, which take place during ionization of residual gas in the tube under typical pressures of 10-6-10-7 mm Hg, are considered. It is shown that distribution of the space charge is affected mainly by the electrons of the initial beam and slow-moving ions produced by ionization of the residual gas. Steady-state density of ions in the operating space of the gyrotron after the end of the transitional processes is found, as well as the electron density profile in the channel of electron beam transportation. The results obtained allow us to evaluate the pitch-factor variations caused by partial compensations for the potential "sagging" in the gyrotron cavity, thus being useful for analysis of starting currents, efficiency, and mode competition in high-power gyrotrons.

  2. Modeling activities on the negative-ion-based Neutral Beam Injectors of the Large Helical Device

    SciTech Connect

    Agostinetti, P.; Antoni, V.; Chitarin, G.; Pilan, N.; Serianni, G.; Veltri, P.; Cavenago, M.; Nakano, H.; Takeiri, Y.; Tsumori, K.

    2011-09-26

    At the National Institute for Fusion Science (NIFS) large-scaled negative ion sources have been widely used for the Neutral Beam Injectors (NBIs) mounted on the Large Helical Device (LHD), which is the world-largest superconducting helical system. These injectors have achieved outstanding performances in terms of beam energy, negative-ion current and optics, and represent a reference for the development of heating and current drive NBIs for ITER.In the framework of the support activities for the ITER NBIs, the PRIMA test facility, which includes a RF-drive ion source with 100 keV accelerator (SPIDER) and a complete 1 MeV Neutral Beam system (MITICA) is under construction at Consorzio RFX in Padova.An experimental validation of the codes has been undertaken in order to prove the accuracy of the simulations and the soundness of the SPIDER and MITICA design. To this purpose, the whole set of codes have been applied to the LHD NBIs in a joint activity between Consorzio RFX and NIFS, with the goal of comparing and benchmarking the codes with the experimental data. A description of these modeling activities and a discussion of the main results obtained are reported in this paper.

  3. SU-E-T-393: Investigation of Hot Spots in Tomotherapy 3D Conformal Breast Plan

    SciTech Connect

    Chen, Q; Siebers, J; Khandelwal, S

    2014-06-01

    Purpose: The purpose of this study is to determine the root-cause of hotspots inherent to Tomotherapy static beam 3D conformal radiotherapy (3DCRT) for breast treatment. ASTRO (ref here) recommends that IMRT be avoided for breast treatments. Despite Tomotherapy's inherent IMRT-like optimization and delivery, our experience at a Tomotherapy-only site has been that Tomotherapy 3DCRT fail to produce a clinically acceptable plan for 79% of our breast patients. Hot-spots have been one of the major obstacles. Methods: Eight lumpectomy patients were planned according to RTOG-1005 specification. Two or four tangential beams were used for 3DCRT breast planning. To spare the contralateral breast and ipsilateral lung, part of the PTV was not covered by the primary beam, yielding adjacent hot-spots. We hypothesize that the planning system creates hotspots adjacent to the cold spots to yield scatter radiation dose compensation in the blocked region. Various phantom and patient setup were used to test the hypothesis. Results: Hot spots outside of PTV in the range of 135% - 174% were observed for patient plan. It is confirmed that the PTV partial block causes the adjacent hot spot. The root cause is the optimizer quadratic objective function over- weighs improving the cold spot. The IMRT flexibility offered by Tomotherapy is counter-productive in static-beam 3DCRT breast treatment. For phantom case, as the Modulation-Factor increases from 1.1 to 5, the hot spot increases from 110% to 300%. Limiting the 3DCRT intensity modulation is shown to produce clinically acceptable plan. Conclusion: Most of the hot spots in Tomotherapy 3DCRT breast plan originate from the planning-system optimizer attempting to cover PTV cold spots rather than from the beam energy. Altering the objective function could improve clinical acceptability of static beam Tomotherapy 3DCRT.

  4. Comparing efficiency and accuracy of the kinoform and the helical axicon as Bessel-Gauss beam generators.

    PubMed

    Arrizón, Victor; Ruiz, Ulises; Aguirre-Olivas, Dilia; Sánchez-de-la-Llave, David; Ostrovsky, Andrey S

    2014-03-01

    We compare two phase optical elements that are employed to generate approximate Bessel-Gauss beams of arbitrary order. These elements are the helical axicon (HA) and the kinoform of the desired Bessel-Gauss beam. The HA generates a Bessel beam (BB) by free propagation, and the kinoform is employed in a Fourier spatial filtering optical setup. As the main result, it is obtained that the error in the BBs generated with the kinoform is smaller than the error in the beams obtained with the HA. On the other hand, it is obtained that the efficiencies of the methods are approximately 1.0 (HA) and 0.7 (kinoform).

  5. High-quality electron beams from a helical inverse free-electron laser accelerator

    NASA Astrophysics Data System (ADS)

    Duris, J.; Musumeci, P.; Babzien, M.; Fedurin, M.; Kusche, K.; Li, R. K.; Moody, J.; Pogorelsky, I.; Polyanskiy, M.; Rosenzweig, J. B.; Sakai, Y.; Swinson, C.; Threlkeld, E.; Williams, O.; Yakimenko, V.

    2014-09-01

    Compact, table-top sized accelerators are key to improving access to high-quality beams for use in industry, medicine and academic research. Among laser-based accelerating schemes, the inverse free-electron laser (IFEL) enjoys unique advantages. By using an undulator magnetic field in combination with a laser, GeV m-1 gradients may be sustained over metre-scale distances using laser intensities several orders of magnitude less than those used in laser wake-field accelerators. Here we show for the first time the capture and high-gradient acceleration of monoenergetic electron beams from a helical IFEL. Using a modest intensity (~1013 W cm-2) laser pulse and strongly tapered 0.5 m long undulator, we demonstrate >100 MV m-1 accelerating gradient, >50 MeV energy gain and excellent output beam quality. Our results pave the way towards compact, tunable GeV IFEL accelerators for applications such as driving soft X-ray free-electron lasers and producing γ-rays by inverse Compton scattering.

  6. High-quality electron beams from a helical inverse free-electron laser accelerator.

    PubMed

    Duris, J; Musumeci, P; Babzien, M; Fedurin, M; Kusche, K; Li, R K; Moody, J; Pogorelsky, I; Polyanskiy, M; Rosenzweig, J B; Sakai, Y; Swinson, C; Threlkeld, E; Williams, O; Yakimenko, V

    2014-09-15

    Compact, table-top sized accelerators are key to improving access to high-quality beams for use in industry, medicine and academic research. Among laser-based accelerating schemes, the inverse free-electron laser (IFEL) enjoys unique advantages. By using an undulator magnetic field in combination with a laser, GeV m(-1) gradients may be sustained over metre-scale distances using laser intensities several orders of magnitude less than those used in laser wake-field accelerators. Here we show for the first time the capture and high-gradient acceleration of monoenergetic electron beams from a helical IFEL. Using a modest intensity (~10(13) W cm(-2)) laser pulse and strongly tapered 0.5 m long undulator, we demonstrate >100 MV m(-1) accelerating gradient, >50 MeV energy gain and excellent output beam quality. Our results pave the way towards compact, tunable GeV IFEL accelerators for applications such as driving soft X-ray free-electron lasers and producing γ-rays by inverse Compton scattering.

  7. Recent Progress in the Negative-Ion-Based Neutral Beam Injectors in Large Helical Device

    SciTech Connect

    Takeiri, Y.; Tsumori, K.; Ikeda, K.; Osakabe, M.; Nagaoka, K.; Oka, Y.; Asano, E.; Kondo, T.; Sato, M.; Shibuya, M.; Komada, S.; Kaneko, O.

    2009-03-12

    Negative-ion-based neutral beam injection (negative-NBI) system has been operated for 10 years in Large Helical Device (LHD). The injection power has been increased year by year, according to the improvement of the negative ion sources. Up to now, every injector achieves the designed injection energy and power of 180 keV-5 MW with hydrogen beams, and the total injection power exceeds 16 MW with three injectors. In the multi-round aperture grounded grid (GG), the diameter of a round aperture has been enlarged for higher GG transparency. Then, the GG heat load is reduced, as well as in the multi-slotted GG, and the voltage holding ability in the beam acceleration was improved. As a result, the beam energy is raised and the injection power is increased. To improve the anisotropic property of the beamlet convergence condition between the perpendicular and the parallel directions to the slots in the multi-slotted GG, a round-shape aperture of the steering grid (SG) has been changed to a racetrack shape. As a result, the difference of the beamlet conversion condition is much mitigated, and the injection efficiency (port-transmission efficiency) is improved, leading to 188 keV-6.4 MW injection. The Cs consumption is observed to be proportional to the tungsten evaporation from filaments. The Cs behavior is investigated with optical emission spectroscopy. During the beam extraction, the Cs recycling is dominated by Cs on the backplate, which is evaporated into the plasma by the backstreaming positive ions, and the wall surfaces should be loss regions for the supplied Cs.

  8. Recent Progress in the Negative-Ion-Based Neutral Beam Injectors in Large Helical Device

    NASA Astrophysics Data System (ADS)

    Takeiri, Y.; Tsumori, K.; Ikeda, K.; Osakabe, M.; Nagaoka, K.; Oka, Y.; Asano, E.; Kondo, T.; Sato, M.; Shibuya, M.; Komada, S.; Kaneko, O.

    2009-03-01

    Negative-ion-based neutral beam injection (negative-NBI) system has been operated for 10 years in Large Helical Device (LHD). The injection power has been increased year by year, according to the improvement of the negative ion sources. Up to now, every injector achieves the designed injection energy and power of 180 keV-5 MW with hydrogen beams, and the total injection power exceeds 16 MW with three injectors. In the multi-round aperture grounded grid (GG), the diameter of a round aperture has been enlarged for higher GG transparency. Then, the GG heat load is reduced, as well as in the multi-slotted GG, and the voltage holding ability in the beam acceleration was improved. As a result, the beam energy is raised and the injection power is increased. To improve the anisotropic property of the beamlet convergence condition between the perpendicular and the parallel directions to the slots in the multi-slotted GG, a round-shape aperture of the steering grid (SG) has been changed to a racetrack shape. As a result, the difference of the beamlet conversion condition is much mitigated, and the injection efficiency (port-transmission efficiency) is improved, leading to 188 keV-6.4 MW injection. The Cs consumption is observed to be proportional to the tungsten evaporation from filaments. The Cs behavior is investigated with optical emission spectroscopy. During the beam extraction, the Cs recycling is dominated by Cs on the backplate, which is evaporated into the plasma by the backstreaming positive ions, and the wall surfaces should be loss regions for the supplied Cs.

  9. Limited-angle reverse helical cone-beam CT for pipeline with low rank decomposition

    NASA Astrophysics Data System (ADS)

    Wu, Dong; Zeng, Li

    2014-10-01

    In this paper, tomographic imaging of pipeline in service by cone-beam computed tomography (CBCT) is studied. With the developed scanning strategy and image model, the quality of reconstructed image is improved. First, a limited-angle reverse helical scanning strategy based on C-arm computed tomography (C-arm CT) is developed for the projection data acquisition of pipeline in service. Then, an image model which considering the resemblance among slices of pipeline is developed. Finally, split Bregman method based algorithm is implemented in solving the model aforementioned. Preliminary results of simulation experiments show that the projection data acquisition strategy and reconstruction method are efficient and feasible, and our method is superior to Feldkamp-Davis-Kress (FDK) algorithm and simultaneous algebraic reconstruction technique (SART).

  10. 2D potential measurements by applying automatic beam adjustment system to heavy ion beam probe diagnostic on the Large Helical Device

    SciTech Connect

    Shimizu, A. Ido, T.; Kato, S.; Hamada, Y.; Kurachi, M.; Makino, R.; Nishiura, M.; Nishizawa, A.

    2014-11-15

    Two-dimensional potential profiles in the Large Helical Device (LHD) were measured with heavy ion beam probe (HIBP). To measure the two-dimensional profile, the probe beam energy has to be changed. However, this task is not easy, because the beam transport line of LHD-HIBP system is very long (∼20 m), and the required beam adjustment consumes much time. To reduce the probe beam energy adjustment time, an automatic beam adjustment system has been developed. Using this system, required time to change the probe beam energy is dramatically reduced, such that two-dimensional potential profiles were able to be successfully measured with HIBP by changing the probe beam energy shot to shot.

  11. 2D spatial profile measurements of potential fluctuation with heavy ion beam probe on the Large Helical Device

    NASA Astrophysics Data System (ADS)

    Shimizu, A.; Ido, T.; Nishiura, M.; Kato, S.; Ogawa, K.; Takahashi, H.; Igami, H.; Yoshimura, Y.; Kubo, S.; Shimozuma, T.

    2016-11-01

    Two-dimensional spatial profiles of potential fluctuation were measured with the heavy ion beam probe (HIBP) in the Large Helical Device (LHD). For 2D spatial profile measurements, the probe beam energy has to be changed, which requires the adjustment of many deflectors in the beam transport line to optimize the beam trajectory, since the transport line of LHD-HIBP system is long. The automatic beam adjustment system was developed, which allows us to adjust the beam trajectory easily. By analyzing coherence between potential fluctuation and magnetic probe signal, the noise level of the mode power spectrum of the potential fluctuation can be reduced. By using this method, the 2D spatial profile of potential fluctuation profile was successfully obtained.

  12. Handling data redundancy in helical cone beam reconstruction with a cone-angle-based window function and its asymptotic approximation

    SciTech Connect

    Tang Xiangyang; Hsieh Jiang

    2007-06-15

    A cone-angle-based window function is defined in this manuscript for image reconstruction using helical cone beam filtered backprojection (CB-FBP) algorithms. Rather than defining the window boundaries in a two-dimensional detector acquiring projection data for computed tomographic imaging, the cone-angle-based window function deals with data redundancy by selecting rays with the smallest cone angle relative to the reconstruction plane. To be computationally efficient, an asymptotic approximation of the cone-angle-based window function is also given and analyzed in this paper. The benefit of using such an asymptotic approximation also includes the avoidance of functional discontinuities that cause artifacts in reconstructed tomographic images. The cone-angle-based window function and its asymptotic approximation provide a way, equivalent to the Tam-Danielsson-window, for helical CB-FBP reconstruction algorithms to deal with data redundancy, regardless of where the helical pitch is constant or dynamically variable during a scan. By taking the cone-parallel geometry as an example, a computer simulation study is conducted to evaluate the proposed window function and its asymptotic approximation for helical CB-FBP reconstruction algorithm to handle data redundancy. The computer simulated Forbild head and thorax phantoms are utilized in the performance evaluation, showing that the proposed cone-angle-based window function and its asymptotic approximation can deal with data redundancy very well in cone beam image reconstruction from projection data acquired along helical source trajectories. Moreover, a numerical study carried out in this paper reveals that the proposed cone-angle-based window function is actually equivalent to the Tam-Danielsson-window, and rigorous mathematical proofs are being investigated.

  13. SU-E-T-303: Dosimetric Comparison of a LINAC Fallback Plan Generated From Tomotherapy System

    SciTech Connect

    Yang, C; Chen, Y

    2015-06-15

    Purpose: Quantitatively evaluate the Multi Criteria Optimization (MCO) based MLC step and shoot (sMLC) fallback plan derived from Tomotherapy of multiple lesions lung SBRT Methods: Inter-comparison of various IMRT planning systems tends to be difficult due to the vendor-specific functionalities. The methodology of defining dose constraints and beam geometries is challenging. Raysearch™ planning system offers an alternative replanning to deliver same intensity map from Tomotherapy without modifying original fluence. This intuitive comparison comes from the final fluence map converted without any embedded system dependent dose optimization. This planner independent approach could be utilized to study the merits of individual machines. The term “fallback” was utilized to (A) transfer plans in among treatment delivery systems; (B) maintain acceptable plan qualities; and (C) minimize the biological dose impact due to machine breakdown. The Tomotherapy specific DICOM RT dose and plan are retrieved into Raystation’s pre-defined sMLC protocol. Based on specific machine characteristics, same fluence maps were converted to generate equivalent deliverable segments. Therefore, the treatment plans were evaluated among two planning tools, Tomotherapy and MCO based sMLC delivery plans. Results: By converting the fluence map with the pre-defined machine characteristics, the 9-fields fallback plan has similar ITV coverage compared to the original Tomotherapy plan. ITV average doses, the D95 consisted of 0.9% variation. The total lung doses of fallback plan drifted from 17.4% to 30.5% which represents the limitations of the static beam delivery. D2 of fallback spinal cord increased from 22.4% to 36.4% but still within tolerances. Ipsilateral lung changed from 11.0% to 22.6%. Low dose region between ITVs presented increased dose to the normal lung tissues. Conclusion: Acceptable fallback plan for Tomotherapy SBRT has similar ITVs coverage, but lack of the normal tissues

  14. Cobalt-60 tomotherapy: Clinical treatment planning and phantom dose delivery studies

    SciTech Connect

    Dhanesar, Sandeep; Darko, Johnson; Joshi, Chandra P.; Kerr, Andrew; John Schreiner, L.

    2013-08-15

    Purpose: Investigations have shown that a Cobalt-60 (Co-60) radioactive source has the potential to play a role in intensity modulated radiation therapy (IMRT). In this paper, Co-60 tomotherapy's conformal dose delivery potential is evaluated by delivering conformal dose plans on a cylindrical homogeneous phantom containing clinical structures similar to those found in a typical head and neck (H and N) cancer. Also, the clinical potential of Co-60 tomotherapy is investigated by generating 2D clinical treatment plans for H and N and prostate anatomical regions. These plans are compared with the 6 MV based treatment plans for modalities such as linear accelerator-based tomotherapy and broad beam IMRT, and 15 MV based 3D conformal radiation therapy (3DCRT).Methods: For experimental validation studies, clinical and nonclinical conformal dose patterns were delivered on circular, homogeneous phantoms containing GafChromic film. For clinical planning study, dose calculations were performed with the EGSnrc Monte Carlo program, where a Theratronics 780C Co-60 unit and a 6 MV linear accelerator were modeled with a MIMiC binary multileaf collimator. An inhouse inverse treatment planning system was used to optimize tomotherapy plans using the same optimization parameters for both Co-60 and 6 MV beams. The IMRT and 3DCRT plans for the clinical cases were generated entirely in the Eclipse treatment planning system based on inhouse IMRT and 3DCRT site specific protocols.Results: The doses delivered to the homogeneous phantoms agreed with the calculations, indicating that it is possible to deliver highly conformal doses with the Co-60 unit. The dose distributions for Co-60 tomotherapy clinical plans for both clinical cases were similar to those obtained with 6 MV based tomotherapy and IMRT, and much more conformal compared to 3DCRT plans. The dose area histograms showed that the Co-60 plans achieve the dose objectives for the targets and organs at risk.Conclusions: These results

  15. Beam-helicity asymmetry in photon and pion electroproduction in the Δ(1232)-resonance region at Q2 = 0.35(GeV/c)2

    NASA Astrophysics Data System (ADS)

    Bensafa, I. K.; Achenbach, P.; Ases Antelo, M.; Ayerbe, C.; Baumann, D.; Böhm, R.; Bosnar, D.; Burtin, E.; Defaÿ, X.; D'Hose, N.; Ding, M.; Distler, M. O.; Doria, L.; Fonvieille, H.; Friedrich, J. M.; Friedrich, J.; García Llongo, J.; Janssens, P.; Jover Mañas, G.; Kohl, M.; Laveissière, G.; Lloyd, M.; Makek, M.; Marroncle, J.; Merkel, H.; Merle, P.; Müller, U.; Nungesser, L.; Pasquini, B.; Pérez Benito, R.; Pochodzalla, J.; Potokar, M.; Rosner, G.; Sánchez Majos, S.; Seimetz, M.; Širca, S.; Spitzenberg, T.; Tamas, G.; van de Vyver, R.; van Hoorebeke, L.; Walcher, Th.; Weis, M.

    2007-04-01

    The beam-helicity asymmetry has been measured simultaneously for the reactions stackrel{{rightarrow}}{{e}} p→ epγ and stackrel{{rightarrow}}{{e}} p→ epπ 0 in the Δ(1232)-resonance region at Q 2 = 0.35( GeV/ c)2. The experiment was performed at MAMI with a longitudinally polarized beam and an out-of-plane detection of the proton. The results are compared with calculations based on dispersion relations for virtual Compton scattering and with the MAID model for pion electroproduction. There is an overall good agreement between experiment and theoretical calculations. The remaining discrepancies may be ascribed to an imperfect parametrization of some γ (*) N→ πN multipoles, mainly contributing to the non-resonant background. The beam-helicity asymmetry in both channels ( γ and π 0) shows a good sensitivity to these multipoles and should allow future improvement in their parametrization.

  16. A motion-compensated scheme for helical cone-beam reconstruction in cardiac CT angiography

    SciTech Connect

    Stevendaal, U. van; Berg, J. von; Lorenz, C.; Grass, M.

    2008-07-15

    Since coronary heart disease is one of the main causes of death all over the world, cardiac computed tomography (CT) imaging is an application of very high interest in order to verify indications timely. Due to the cardiac motion, electrocardiogram (ECG) gating has to be implemented into the reconstruction of the measured projection data. However, the temporal and spatial resolution is limited due to the mechanical movement of the gantry and due to the fact that a finite angular span of projections has to be acquired for the reconstruction of each voxel. In this article, a motion-compensated reconstruction method for cardiac CT is described, which can be used to increase the signal-to-noise ratio or to suppress motion blurring. Alternatively, it can be translated into an improvement of the temporal and spatial resolution. It can be applied to the entire heart in common and to high contrast objects moving with the heart in particular, such as calcified plaques or devices like stents. The method is based on three subsequent steps: As a first step, the projection data acquired in low pitch helical acquisition mode together with the ECG are reconstructed at multiple phase points. As a second step, the motion-vector field is calculated from the reconstructed images in relation to the image in a reference phase. Finally, a motion-compensated reconstruction is carried out for the reference phase using those projections, which cover the cardiac phases for which the motion-vector field has been determined.

  17. A new experiment to investigate the origin of optical activity using a low energy positron beam of controlled helicity. [molecular biology

    NASA Technical Reports Server (NTRS)

    Gidley, D. W.; Rich, A.; Van House, J. C.; Zitzewitz, P. W.

    1981-01-01

    Previous experiments undertaken in search of a correlation between the origin of optical activity in biological molecules and the helicity of beta particles emitted in nuclear beta decay have not provided any useful results. A description is presented of an experiment in which a low energy polarized positron beam of controlled helicity interacts with an optically active material to form positronium in vacuum. Advantages of the current study compared to the previous experiments are mainly related to a much greater sensitivity. Initially, it will be possible to detect a helicity-dependent asymmetry in triplet positronium formation of 1 part in 10,000. Improvements to better than 1 part in 100,000 should be attainable.

  18. A diagnostic tool for basic daily quality assurance of a Tomotherapy Hi*Art machine.

    PubMed

    Van de Vondel, Iwein; Tournel, Koen; Verellen, Dirk; Duchateau, Michael; Lelie, Steven; Storme, Guy

    2009-10-15

    To investigate and evaluate the use of an in-house developed diagnostic software tool using the imaging detector data for a quick daily quality assurance check of the output (dose) and lateral profile (cone) of a tomotherapy Hi*Art system. The Hi*Art treatment system is a radiation therapy machine for delivering intensity modulated radiation therapy (IMRT) in a helical fashion with an integrated CT scanner used for improved patient positioning before treatment. Since the system was developed specifically for IMRT, flat fields can be obtained by modulating the beam and therefore the flattening filter could be omitted. Because of this, the field has a cone-like profile in both lateral and transversal directions. Patients are treated in a helical fashion with a tight pitch and a constant gantry rotation speed, while modulation is performed by a binary MLC. Consequently dose output per time-unit (dose rate) as well as the shape of the cone-profile are very important for correct patient treatment and should be closely monitored. However, using the company-provided initial tools and conventional dosimetry, this can be a time consuming daily procedure. The aim of this work is to develop a fast, automated method of quality assurance based on the detector signal. A software tool called "tomocheck" running on the operation station has been developed to evaluate the output (dose rate) and the lateral cone profile (energy) of the Hi*Art system, comparing actual output and cone profile with a reference (previously approved against ionization chamber measurements). This is done by using the data of the 640 on-board detector array that are directly retrieved and processed after a specific QA procedure. The detector file consists of the CT detector data and the three monitoring dose chamber readings over a time period of 200 sec. To evaluate the method, the system was benchmarked against ionization chamber measurements and classical IMRT QA methods. Action levels (final status

  19. Plasmonic gold helices for the visible range fabricated by oxygen plasma purification of electron beam induced deposits

    NASA Astrophysics Data System (ADS)

    Haverkamp, Caspar; Höflich, Katja; Jäckle, Sara; Manzoni, Anna; Christiansen, Silke

    2017-02-01

    Electron beam induced deposition (EBID) currently provides the only direct writing technique for truly three-dimensional nanostructures with geometrical features below 50 nm. Unfortunately, the depositions from metal-organic precursors suffer from a substantial carbon content. This hinders many applications, especially in plasmonics where the metallic nature of the geometric surfaces is mandatory. To overcome this problem a post-deposition treatment with oxygen plasma at room temperature was investigated for the purification of gold containing EBID structures. Upon plasma treatment, the structures experience a shrinkage in diameter of about 18 nm but entirely keep their initial shape. The proposed purification step results in a core-shell structure with the core consisting of mainly unaffected EBID material and a gold shell of about 20 nm in thickness. These purified structures are plasmonically active in the visible wavelength range as shown by dark field optical microscopy on helical nanostructures. Most notably, electromagnetic modeling of the corresponding scattering spectra verified that the thickness and quality of the resulting gold shell ensures an optical response equal to that of pure gold nanostructures.

  20. Plasmonic gold helices for the visible range fabricated by oxygen plasma purification of electron beam induced deposits.

    PubMed

    Haverkamp, Caspar; Höflich, Katja; Jäckle, Sara; Manzoni, Anna; Christiansen, Silke

    2017-02-03

    Electron beam induced deposition (EBID) currently provides the only direct writing technique for truly three-dimensional nanostructures with geometrical features below 50 nm. Unfortunately, the depositions from metal-organic precursors suffer from a substantial carbon content. This hinders many applications, especially in plasmonics where the metallic nature of the geometric surfaces is mandatory. To overcome this problem a post-deposition treatment with oxygen plasma at room temperature was investigated for the purification of gold containing EBID structures. Upon plasma treatment, the structures experience a shrinkage in diameter of about 18 nm but entirely keep their initial shape. The proposed purification step results in a core-shell structure with the core consisting of mainly unaffected EBID material and a gold shell of about 20 nm in thickness. These purified structures are plasmonically active in the visible wavelength range as shown by dark field optical microscopy on helical nanostructures. Most notably, electromagnetic modeling of the corresponding scattering spectra verified that the thickness and quality of the resulting gold shell ensures an optical response equal to that of pure gold nanostructures.

  1. Preliminary Retrospective Analysis of Daily Tomotherapy Output Constancy Checks Using Statistical Process Control

    PubMed Central

    Menghi, Enrico; Marcocci, Francesco; Bianchini, David

    2016-01-01

    The purpose of this study was to retrospectively evaluate the results from a Helical TomoTherapy Hi-Art treatment system relating to quality controls based on daily static and dynamic output checks using statistical process control methods. Individual value X-charts, exponentially weighted moving average charts, and process capability and acceptability indices were used to monitor the treatment system performance. Daily output values measured from January 2014 to January 2015 were considered. The results obtained showed that, although the process was in control, there was an out-of-control situation in the principal maintenance intervention for the treatment system. In particular, process capability indices showed a decreasing percentage of points in control which was, however, acceptable according to AAPM TG148 guidelines. Our findings underline the importance of restricting the acceptable range of daily output checks and suggest a future line of investigation for a detailed process control of daily output checks for the Helical TomoTherapy Hi-Art treatment system. PMID:26848962

  2. Monte Carlo-based simulation of dynamic jaws tomotherapy

    SciTech Connect

    Sterpin, E.; Chen, Y.; Chen, Q.; Lu, W.; Mackie, T. R.; Vynckier, S.

    2011-09-15

    Purpose: Original TomoTherapy systems may involve a trade-off between conformity and treatment speed, the user being limited to three slice widths (1.0, 2.5, and 5.0 cm). This could be overcome by allowing the jaws to define arbitrary fields, including very small slice widths (<1 cm), which are challenging for a beam model. The aim of this work was to incorporate the dynamic jaws feature into a Monte Carlo (MC) model called TomoPen, based on the MC code PENELOPE, previously validated for the original TomoTherapy system. Methods: To keep the general structure of TomoPen and its efficiency, the simulation strategy introduces several techniques: (1) weight modifiers to account for any jaw settings using only the 5 cm phase-space file; (2) a simplified MC based model called FastStatic to compute the modifiers faster than pure MC; (3) actual simulation of dynamic jaws. Weight modifiers computed with both FastStatic and pure MC were compared. Dynamic jaws simulations were compared with the convolution/superposition (C/S) of TomoTherapy in the ''cheese'' phantom for a plan with two targets longitudinally separated by a gap of 3 cm. Optimization was performed in two modes: asymmetric jaws-constant couch speed (''running start stop,'' RSS) and symmetric jaws-variable couch speed (''symmetric running start stop,'' SRSS). Measurements with EDR2 films were also performed for RSS for the formal validation of TomoPen with dynamic jaws. Results: Weight modifiers computed with FastStatic were equivalent to pure MC within statistical uncertainties (0.5% for three standard deviations). Excellent agreement was achieved between TomoPen and C/S for both asymmetric jaw opening/constant couch speed and symmetric jaw opening/variable couch speed, with deviations well within 2%/2 mm. For RSS procedure, agreement between C/S and measurements was within 2%/2 mm for 95% of the points and 3%/3 mm for 98% of the points, where dose is greater than 30% of the prescription dose (gamma analysis

  3. SU-E-T-372: Dosimetric Comparison of Craniospinal Irradiation Using Different Tomotherapy Techniques

    SciTech Connect

    Zhang, X; Penagaricano, J; Han, E; Liang, X; Morrill, S; Hardee, M; Gupta, S; Vaneerat, R

    2014-06-01

    Purpose: TomoHDA can treat with fixed jaws, dynamic jaws, and fixed gantry using either 3DCRT or IMRT. This study compares PTV coverage, OAR sparing, and beam-on-time (BOT) among these techniques for craniospinal irradiation (CSI). Methods: This study includes ten CSI patients treated to 23.4 Gy/13 fractions with Hi-Art 3.0 unit (HT-IMRT fixed 5 cm jaw). New plans were regenerated with 5 cm jaw for TomoHDA Hi-Art 5.0 using dynamic jaw (HD-IMRT), TomoDirect-IMRT (TD-IMRT), and Helical Tomotherapy 3DCRT (HT-3DCRT using 5 cm and 2.5 cm jaws with various pitches). Studied parameters include PTV mean dose, D95 (dose covering 95% of PTV), Paddick's conformity index (CI) and homogeneity index (HI – standard deviation of PTV dose/average PTV dose), BOT, and average OAR doses. Results: PTV coverage from these techniques were comparable (p>0.05). The main differences were in OAR sparing; HDIMRT reduced more OAR doses for lenses, bladder and rectum compared to HT-IMRT. For the sparing of visceral organs: liver, lung, heart, and kidneys, the three IMRT techniques gave comparable results. HD-IMRT gave best heart sparing; HT-IMRT best kidney sparing. Liver and lung doses were best reduced by TD-IMRT. All three IMRT techniques gave comparable BOT. OARs sparing was achieved for jaw size of 2.5 cm. HI was also improved but with doubling of BOT. Increasing the pitch number from 0.2 to 0.43 produced no significant improvement in OAR sparing but CI and HI did improve. Conclusion: HT-3DCRT, HT-IMRT, HD-IMRT or TD-IMRT techniques give comparable PTV coverage but the three IMRT plans better spared OARs compared with 3DCRT plans. Dynamic jaw plan is superior to fixed jaw plan to spare more OAR doses at field edge. TD-IMRT cannot reduce BOT for CSI patient but for sparing certain OAR, TD-IMRT may be used to avoid the beam going through the structures of interest.

  4. MO-D-213-04: The Proximity to the Skin of PTV Affects PTV Coverage and Skin Dose for TomoTherapy

    SciTech Connect

    Reynolds, T; Higgins, P; Watanabe, Y

    2015-06-15

    Purpose: The proximity to the skin surface of the PTV for the patients with skin disease could be a concern in terms of the PTV coverage and actual surface dose (SD). IMRT optimization algorithms increase the beam intensity close to the skin in order to compensate for lack of scattering material, leading to enhanced SD but potential hot spots. This study aims to investigate the effect of PTV proximity to the skin on planning and measured SD Methods: All measurements were done for 6 MV X-ray beam of Helical TomoTherapy. An anthropomorphic phantom was scanned in a CT simulator in a routine manner with thermoplastic mask immobilization. PTVs were created with varying distances to the skin of 0 mm -(PTV1), 1 mm- (PTV2), 2 mm-(PTV3) and 3 mm-(PTV4). Also, a 5 mm bolus was used with PTV1 (PTV5). All planning constraints were kept the same in all studies (hard constraint: 95% of the prescription dose covered 95% of the PTV). Gafchromic film (EBT3) was placed under the mask on the phantom surface, and the resulting dose was estimated using RIT software. Results: Optimizing the dose using different PTVs lead to average planned target doses of 10.8, 10.3, 10.2, 10.3 and 10.0 Gy, with maximum doses 12.2, 11.2, 11.1, 11.1 and 10.0 Gy for PTV1, PTV2, PTV3, PTV4 and PTV5, respectively. EBT3 measurements indicated a significant decrease of SD with skin distance by 12.7% (PTV1), 21.9% (PTV2), 24.8% (PTV3) and 28.4% (PTV4) comparing to prescription dose. Placement of a 5 mm bolus on the phantom surface resulted in a SD close to prescribed (+0.5%). Conclusion: This work provides a clear demonstration of the relationship between the skin dose and the PTV to the skin distance. The results indicate the necessity of a bolus even for TomoTherapy when high skin dose is required.

  5. The concept and challenges of TomoTherapy accelerators

    NASA Astrophysics Data System (ADS)

    Bailat, Claude J.; Baechler, Sébastien; Moeckli, Raphael; Pachoud, Marc; Pisaturo, Olivier; Bochud, François O.

    2011-08-01

    A currently used intensity-modulated radiotherapy system is the TomoTherapy® Hi-Art® accelerator (Tomotherapy Inc., Madison, WI, USA), which started clinical treatments at the beginning of the new millennium. The innovative idea behind tomotherapy units is to marry an x-ray computed tomography unit with a linear particle accelerator. This concept has answered some of the needs of the medical physicist community, but epidemiological evaluations are still needed in order to compare the technique with other modalities. This paper summarizes the basic concepts of tomotherapy units as well as current challenges and implications for users.

  6. The Evolution of External Beam Radiation Therapy (EBRT) from a Technological Perspective.

    NASA Astrophysics Data System (ADS)

    Detorie, Nicholas

    2008-03-01

    Since the discovery of x-rays by Roentgen in 1895 ionizing radiations have been used as a treatment for cancer. Such treatments have been based on either implantation of radioactive materials at the site of disease or by aiming external radiation beams at the diseased site. This later method is referred to as teletherapy because the beams originate from a location outside of the body distant from the disease site itself. A brief review of the basic radiation biology will be given to illustrate the rationale for therapeutic use of ionizing radiations and the effects of beam energy and beam type- particulate or photon. The remainder of the presentation will focus on the technological teletherapy developments supported by the required physical properties of the beams and their associated characteristics that make them suitable for patient treatments. Chronological highlights will include the following sources or devices: superficial x-rays, orthovaltage x-rays, megavoltage x-rays and Cobalt 60 photons, electron beams, neutron beams, negative pi mesons, protons, and heavy ions. The presentation will illustrate how the physical beam properties have been incorporated into modern radiation treatment devices, many of which are equipped with radiation imaging capability. Such devices include: linacs equipped with multileaf collimators for beam shaping and intensity modulation, the Gamma Knife for precise and accurate irradiation of brain tumors or arterial-venous malformations (AVM), the robotic arm based Cyber Knife, and the Helical Tomotherapy unit.

  7. Development of A Novel Image Guidance Alternative for Patient Localization using Topographic Images for TomoTherapy

    NASA Astrophysics Data System (ADS)

    Qi, X. Sharon; White, Benjamin; Low, Daniel A.

    2014-03-01

    To develop a faster and lower dose topogram based image registration for TomoTherapy as an alternative image guidance tool to volumetric megavoltage computed tomography (MVCT). Topogram procedures were performed for an anthropomorphic thorax phantom on a TomoTherapy HD unit (Accuray Inc., Sunnyvale, CA) using couch speeds from 1-4 cm/s and gantry angles of 0 and 90 degrees, other scanning parameters are: 1 mm imaging jaw, compression factor of 1, 30 seconds scanning duration with all multileaf collimators (MLCs) open. The raw exit detector data was exported after each scan. The topogram was reconstructed from a fan beam source for TomoTherapy beam and detector geometry at a SSD of 85 cm. A reference image, so called Digitally Reconstructed Topogram (DRT) was created by integrating the trajectories through the kVCT simulation with the topogram geometry. Image registration was performed by visually aligning the bony structure in topogram to the DRT. Image resolution was determined by the radius of curvature for the detector array, source to axis distance, source to detector distance, detector spacing, and number of detectors. The localization errors were 1.5, 2.5 mm in medio-lateral and anterior-posterior direction, larger errors in cranial-caudal direction was observed for faster couch speeds (i.e., >=3cm/s). The topographic imaging time was 30 sec (versus 3-5 minutes for MVCT thorax scan) with imaging dose less than 1% of MVCT scan. Topograms with appropriate couch speed provide reliable patient localization images while significantly reducing pre-treatment imaging time. Topogram can be used as an alternative and/or additional patient alignment tool to MVCT on TomoTherapy.

  8. SU-E-T-370: Evaluating Plan Quality and Dose Delivery Accuracy of Tomotherapy SBRT Treatments for Lung Cancer

    SciTech Connect

    Blake, S; Thwaites, D; Hansen, C; Deshpande, S; Phan, P; Franji, I; Holloway, L

    2015-06-15

    Purpose: This study evaluated the plan quality and dose delivery accuracy of stereotactic body radiotherapy (SBRT) helical Tomotherapy (HT) treatments for lung cancer. Results were compared with those previously reported by our group for flattening filter (FF) and flattening filter free (FFF) VMAT treatments. This work forms part of an ongoing multicentre and multisystem planning and dosimetry audit on FFF beams for lung SBRT. Methods: CT datasets and DICOM RT structures delineating the target volume and organs at risk for 6 lung cancer patients were selected. Treatment plans were generated using the HT treatment planning system. Tumour locations were classified as near rib, near bronchial tree or in free lung with prescribed doses of 48Gy/4fr, 50Gy/5fr and 54Gy/3fr respectively. Dose constraints were specified by a modified RTOG0915 protocol used for an Australian SBRT phase II trial. Plan quality was evaluated using mean PTV dose, PTV volume receiving 100% of the prescribed dose (V100%), target conformity (CI=VD100%/VPTV) and low dose spillage (LDS=VD50%/VPTV). Planned dose distributions were compared to those measured using an ArcCheck phantom. Delivery accuracy was evaluated using a gamma-index pass rate of 95% with 3% (of max dose) and 3mm criteria. Results: Treatment plans for all patients were clinically acceptable in terms of quality and accuracy of dose delivery. The following DVH metrics are reported as averages (SD) of all plans investigated: mean PTV dose was 115.3(2.4)% of prescription, V100% was 98.8(0.9)%, CI was 1.14(0.03) and LDS was 5.02(0.37). The plans had an average gamma-index passing rate of 99.3(1.3)%. Conclusion: The results reported in this study for HT agree within 1 SD to those previously published by our group for VMAT FF and FFF lung SBRT treatments. This suggests that HT delivers lung SBRT treatments of comparable quality and delivery accuracy as VMAT using both FF and FFF beams.

  9. Reference dosimetry on TomoTherapy: an addendum to the 1990 UK MV dosimetry code of practice

    NASA Astrophysics Data System (ADS)

    Thomas, S. J.; Aspradakis, M. M.; Byrne, J. P.; Chalmers, G.; Duane, S.; Rogers, J.; Thomas, R. A. S.; Tudor, G. S. J.; Twyman, N.

    2014-03-01

    The current UK code of practice for high-energy photon therapy dosimetry (Lillicrap et al 1990 Phys. Med. Biol. 35 1355-60) gives instructions for measuring absorbed dose to water under reference conditions for megavoltage photons. The reference conditions and the index used to specify beam quality require that a machine be able to set a 10 cm × 10 cm field at the point of measurement. TomoTherapy machines have a maximum collimator setting of 5 cm × 40 cm at a source to axis distance of 85 cm, making it impossible for users of these machines to follow the code. This addendum addresses the specification of reference irradiation geometries, the choice of ionization chambers and the determination of dosimetry corrections, the derivation of absorbed dose to water calibration factors and choice of appropriate chamber correction factors, for carrying out reference dosimetry measurements on TomoTherapy machines. The preferred secondary standard chamber remains the NE2611 chamber, which with its associated secondary standard electrometer, is calibrated at the NPL through the standard calibration service for MV photon beams produced on linear accelerators with conventional flattening filters. Procedures are given for the derivation of a beam quality index specific to the TomoTherapy beam that can be used in the determination of a calibration coefficient for the secondary standard chamber from its calibration certificate provided by the NPL. The recommended method of transfer from secondary standard to field instrument is in a static beam, at a depth of 5 cm, by sequential substitution or by simultaneous side by side irradiation in either a water phantom or a water-equivalent solid phantom. Guidance is given on the use of a field instrument in reference fields.

  10. Self-consistent analysis of radiation and relativistic electron beam dynamics in a helical wiggler using Lienard-Wiechert fields

    SciTech Connect

    Tecimer, M.; Elias, L.R.

    1995-12-31

    Lienard-Wiechert (LW) fields, which are exact solutions of the Wave Equation for a point charge in free space, are employed to formulate a self-consistent treatment of the electron beam dynamics and the evolution of the generated radiation in long undulators. In a relativistic electron beam the internal forces leading to the interaction of the electrons with each other can be computed by means of retarded LW fields. The resulting electron beam dynamics enables us to obtain three dimensional radiation fields starting from an initial incoherent spontaneous emission, without introducing a seed wave at start-up. Based on the formalism employed here, both the evolution of the multi-bucket electron phase space dynamics in the beam body as well as edges and the relative slippage of the radiation with respect to the electrons in the considered short bunch are naturally embedded into the simulation model. In this paper, we present electromagnetic radiation studies, including multi-bucket electron phase dynamics and angular distribution of radiation in the time and frequency domain produced by a relativistic short electron beam bunch interacting with a circularly polarized magnetic undulator.

  11. Two new DOSXYZnrc sources for 4D Monte Carlo simulations of continuously variable beam configurations, with applications to RapidArc, VMAT, TomoTherapy and CyberKnife

    NASA Astrophysics Data System (ADS)

    Lobo, Julio; Antoniu Popescu, I.

    2010-08-01

    We present two new Monte Carlo sources for the DOSXYZnrc code, which can be used to compute dose distributions due to continuously variable beam configurations. These sources support a continuously rotating gantry and collimator, dynamic multileaf collimator (MLC) motion, variable monitor unit (MU) rate, couch rotation and translation in any direction, arbitrary isocentre motion with respect to the patient and variable source-to-axis distance (SAD). These features make them applicable to Monte Carlo simulations for RapidArc™, Elekta VMAT, TomoTherapy™ and CyberKnife™. Unique to these sources is the synchronization between the motion in the DOSXYZnrc geometry and the motion within the linac head, represented by a shared library (either a BEAMnrc accelerator with dynamic component modules, or an external library). The simulations are achieved in single runs, with no intermediate phase space files.

  12. Application of failure mode and effects analysis (FMEA) to pretreatment phases in tomotherapy.

    PubMed

    Broggi, Sara; Cantone, Marie Claire; Chiara, Anna; Di Muzio, Nadia; Longobardi, Barbara; Mangili, Paola; Veronese, Ivan

    2013-09-06

    The aim of this paper was the application of the failure mode and effects analysis (FMEA) approach to assess the risks for patients undergoing radiotherapy treatments performed by means of a helical tomotherapy unit. FMEA was applied to the preplanning imaging, volume determination, and treatment planning stages of the tomotherapy process and consisted of three steps: 1) identification of the involved subprocesses; 2) identification and ranking of the potential failure modes, together with their causes and effects, using the risk probability number (RPN) scoring system; and 3) identification of additional safety measures to be proposed for process quality and safety improvement. RPN upper threshold for little concern of risk was set at 125. A total of 74 failure modes were identified: 38 in the stage of preplanning imaging and volume determination, and 36 in the stage of planning. The threshold of 125 for RPN was exceeded in four cases: one case only in the phase of preplanning imaging and volume determination, and three cases in the stage of planning. The most critical failures appeared related to (i) the wrong or missing definition and contouring of the overlapping regions, (ii) the wrong assignment of the overlap priority to each anatomical structure, (iii) the wrong choice of the computed tomography calibration curve for dose calculation, and (iv) the wrong (or not performed) choice of the number of fractions in the planning station. On the basis of these findings, in addition to the safety strategies already adopted in the clinical practice, novel solutions have been proposed for mitigating the risk of these failures and to increase patient safety.

  13. Effects of changing modulation and pitch parameters on tomotherapy delivery quality assurance plans.

    PubMed

    Binny, Diana; Lancaster, Craig M; Harris, Selina; Sylvander, Steven R

    2015-09-01

    This study was aimed at investigating delivery quality assurance (DQA) discrepancies observed for helical tomotherapy plans. A selection of tomotherapy plans that initially failed the DQA process was chosen for this investigation. These plans failed the fluence analysis as assessed using gamma criteria (3%, 3 mm) with radiographic film. Each of these plans was modified (keeping the planning constraints the same), beamlets rebatched and reoptimized. By increasing and decreasing the modulation factor, the fluence in a circumferential plane as measured with a diode array was assessed. A subset of these plans was investigated using varied pitch values. Metrics for each plan that were examined were point doses, fluences, leaf opening times, planned leaf sinograms, and uniformity indices. In order to ensure that the treatment constraints remained the same, the dose-volume histograms (DVHs) of all the modulated plans were compared to the original plan. It was observed that a large increase in the modulation factor did not significantly improve DVH uniformity, but reduced the gamma analysis pass rate. This also increased the treatment delivery time by slowing down the gantry rotation speed which then increases the maximum to mean non-zero leaf open time ratio. Increasing and decreasing the pitch value did not substantially change treatment time, but the delivery accuracy was adversely affected. This may be due to many other factors, such as the complexity of the treatment plan and site. Patient sites included in this study were head and neck, right breast, prostate, abdomen, adrenal, and brain. The impact of leaf timing inaccuracies on plans was greater with higher modulation factors. Point-dose measurements were seen to be less susceptible to changes in pitch and modulation factors. The initial modulation factor used by the optimizer, such that the TPS generated 'actual' modulation factor within the range of 1.4 to 2.5, resulted in an improved deliverable plan. PACS

  14. Effects of changing modulation and pitch parameters on tomotherapy delivery quality assurance plans.

    PubMed

    Binny, Diana; Lancaster, Craig M; Harris, Selina; Sylvander, Steven R

    2015-09-08

    This study was aimed at investigating delivery quality assurance (DQA) discrepancies observed for helical tomotherapy plans. A selection of tomotherapy plans that initially failed the DQA process was chosen for this investigation. These plans failed the fluence analysis as assessed using gamma criteria (3%, 3 mm) with radiographic film. Each of these plans was modified (keeping the planning constraints the same), beamlets rebatched and reoptimized. By increasing and decreasing the modulation factor, the fluence in a circumferential plane as measured with a diode array was assessed. A subset of these plans was investigated using varied pitch values. Metrics for each plan that were examined were point doses, fluences, leaf opening times, planned leaf sinograms, and uniformity indices. In order to ensure that the treatment constraints remained the same, the dose-volume histograms (DVHs) of all the modulated plans were compared to the original plan. It was observed that a large increase in the modulation factor did not significantly improve DVH uniformity, but reduced the gamma analysis pass rate. This also increased the treatment delivery time by slowing down the gantry rotation speed which then increases the maximum to mean non-zero leaf open time ratio. Increasing and decreasing the pitch value did not substantially change treatment time, but the delivery accuracy was adversely affected. This may be due to many other factors, such as the complexity of the treatment plan and site. Patient sites included in this study were head and neck, right breast, prostate, abdomen, adrenal, and brain. The impact of leaf timing inaccuracies on plans was greater with higher modulation factors. Point-dose measurements were seen to be less susceptible to changes in pitch and modulation factors. The initial modulation factor used by the optimizer, such that the TPS generated 'actual' modulation factor within the range of 1.4 to 2.5, resulted in an improved deliverable plan.

  15. Diffraction of a finite-radius plane wave and a Gaussian beam by a helical axicon and a spiral phase plate.

    PubMed

    Kotlyar, Victor V; Kovalev, Alexey A; Skidanov, Roman V; Moiseev, Oleg Yu; Soifer, Victor A

    2007-07-01

    We derive what we believe to be new analytical relations to describe the Fraunhofer diffraction of the finite-radius plane wave by a helical axicon (HA) and a spiral phase plate (SPP). The solutions are deduced in the form of a series of the Bessel functions for the HA and a finite sum of the Bessel functions for the SPP. The solution for the HA changes to that for the SPP if the axicon parameter is set equal to zero. We also derive what we believe to be new analytical relations to describe the Fresnel and Fraunhofer diffraction of the Gaussian beam by a HA are derived. The solutions are deduced in the form of a series of the hypergeometric functions. We have fabricated by photolithography a binary diffractive optical element (a HA with number n=10) able to produce in the focal plane of a spherical lens an optical vortex, which was then used to perform rotation of several polystyrene beads of diameter 5 microm.

  16. Synthesis of Current-Voltage Characteristics of 670 GHz Gyrotron Magnetron Injection Gun and Calculation of the Helical Electron Beam Parameters at the Leading Edge of a High-Voltage Pulse

    NASA Astrophysics Data System (ADS)

    Manuilov, V. N.; Glyavin, M. Yu.

    2013-02-01

    A method of synthesis of current-voltage characteristics (CVC) and calculation of the parameters of a helical electron beam (HEB) at the leading edge of the accelerating voltage pulse for gyrotron electron guns is proposed. These data can be used for a study of the gyrotron startup scenario with the mode competition taken into account. As an example, the results of calculations for a pulsed gyrotron with a frequency of 670 GHz are presented.

  17. 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

  18. 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

  19. SU-E-I-15: Quantitative Evaluation of Dose Distributions From Axial, Helical and Cone-Beam CT Imaging by Measurement Using a Two-Dimensional Diode-Array Detector

    SciTech Connect

    Chacko, M; Aldoohan, S; Sonnad, J; Ahmad, S; Ali, I

    2015-06-15

    Purpose: To evaluate quantitatively dose distributions from helical, axial and cone-beam CT clinical imaging techniques by measurement using a two-dimensional (2D) diode-array detector. Methods: 2D-dose distributions from selected clinical protocols used for axial, helical and cone-beam CT imaging were measured using a diode-array detector (MapCheck2). The MapCheck2 is composed from solid state diode detectors that are arranged in horizontal and vertical lines with a spacing of 10 mm. A GE-Light-Speed CT-simulator was used to acquire axial and helical CT images and a kV on-board-imager integrated with a Varian TrueBeam-STx machine was used to acquire cone-beam CT (CBCT) images. Results: The dose distributions from axial, helical and cone-beam CT were non-uniform over the region-of-interest with strong spatial and angular dependence. In axial CT, a large dose gradient was measured that decreased from lateral sides to the middle of the phantom due to large superficial dose at the side of the phantom in comparison with larger beam attenuation at the center. The dose decreased at the superior and inferior regions in comparison to the center of the phantom in axial CT. An asymmetry was found between the right-left or superior-inferior sides of the phantom which possibly to angular dependence in the dose distributions. The dose level and distribution varied from one imaging technique into another. For the pelvis technique, axial CT deposited a mean dose of 3.67 cGy, helical CT deposited a mean dose of 1.59 cGy, and CBCT deposited a mean dose of 1.62 cGy. Conclusions: MapCheck2 provides a robust tool to measure directly 2D-dose distributions for CT imaging with high spatial resolution detectors in comparison with ionization chamber that provides a single point measurement or an average dose to the phantom. The dose distributions measured with MapCheck2 consider medium heterogeneity and can represent specific patient dose.

  20. Adaptive planning using megavoltage fan-beam CT for radiation therapy with testicular shielding

    SciTech Connect

    Yadav, Poonam; Kozak, Kevin; Tolakanahalli, Ranjini; Ramasubramanian, V.; Paliwal, Bhudatt R.; Welsh, James S.; Rong, Yi

    2012-07-01

    This study highlights the use of adaptive planning to accommodate testicular shielding in helical tomotherapy for malignancies of the proximal thigh. Two cases of young men with large soft tissue sarcomas of the proximal thigh are presented. After multidisciplinary evaluation, preoperative radiation therapy was recommended. Both patients were referred for sperm banking and lead shields were used to minimize testicular dose during radiation therapy. To minimize imaging artifacts, kilovoltage CT (kVCT) treatment planning was conducted without shielding. Generous hypothetical contours were generated on each 'planning scan' to estimate the location of the lead shield and generate a directionally blocked helical tomotherapy plan. To ensure the accuracy of each plan, megavoltage fan-beam CT (MVCT) scans were obtained at the first treatment and adaptive planning was performed to account for lead shield placement. Two important regions of interest in these cases were femurs and femoral heads. During adaptive planning for the first patient, it was observed that the virtual lead shield contour on kVCT planning images was significantly larger than the actual lead shield used for treatment. However, for the second patient, it was noted that the size of the virtual lead shield contoured on the kVCT image was significantly smaller than the actual shield size. Thus, new adaptive plans based on MVCT images were generated and used for treatment. The planning target volume was underdosed up to 2% and had higher maximum doses without adaptive planning. In conclusion, the treatment of the upper thigh, particularly in young men, presents several clinical challenges, including preservation of gonadal function. In such circumstances, adaptive planning using MVCT can ensure accurate dose delivery even in the presence of high-density testicular shields.

  1. Adaptive planning using megavoltage fan-beam CT for radiation therapy with testicular shielding.

    PubMed

    Yadav, Poonam; Kozak, Kevin; Tolakanahalli, Ranjini; Ramasubramanian, V; Paliwal, Bhudatt R; Welsh, James S; Rong, Yi

    2012-01-01

    This study highlights the use of adaptive planning to accommodate testicular shielding in helical tomotherapy for malignancies of the proximal thigh. Two cases of young men with large soft tissue sarcomas of the proximal thigh are presented. After multidisciplinary evaluation, preoperative radiation therapy was recommended. Both patients were referred for sperm banking and lead shields were used to minimize testicular dose during radiation therapy. To minimize imaging artifacts, kilovoltage CT (kVCT) treatment planning was conducted without shielding. Generous hypothetical contours were generated on each "planning scan" to estimate the location of the lead shield and generate a directionally blocked helical tomotherapy plan. To ensure the accuracy of each plan, megavoltage fan-beam CT (MVCT) scans were obtained at the first treatment and adaptive planning was performed to account for lead shield placement. Two important regions of interest in these cases were femurs and femoral heads. During adaptive planning for the first patient, it was observed that the virtual lead shield contour on kVCT planning images was significantly larger than the actual lead shield used for treatment. However, for the second patient, it was noted that the size of the virtual lead shield contoured on the kVCT image was significantly smaller than the actual shield size. Thus, new adaptive plans based on MVCT images were generated and used for treatment. The planning target volume was underdosed up to 2% and had higher maximum doses without adaptive planning. In conclusion, the treatment of the upper thigh, particularly in young men, presents several clinical challenges, including preservation of gonadal function. In such circumstances, adaptive planning using MVCT can ensure accurate dose delivery even in the presence of high-density testicular shields.

  2. Technical Note: FreeCT_wFBP: A robust, efficient, open-source implementation of weighted filtered backprojection for helical, fan-beam CT

    PubMed Central

    Hoffman, John; Young, Stefano; Noo, Frédéric

    2016-01-01

    Purpose: With growing interest in quantitative imaging, radiomics, and CAD using CT imaging, the need to explore the impacts of acquisition and reconstruction parameters has grown. This usually requires extensive access to the scanner on which the data were acquired and its workflow is not designed for large-scale reconstruction projects. Therefore, the authors have developed a freely available, open-source software package implementing a common reconstruction method, weighted filtered backprojection (wFBP), for helical fan-beam CT applications. Methods: FreeCT_wFBP is a low-dependency, GPU-based reconstruction program utilizing c for the host code and Nvidia CUDA C for GPU code. The software is capable of reconstructing helical scans acquired with arbitrary pitch-values, and sampling techniques such as flying focal spots and a quarter-detector offset. In this work, the software has been described and evaluated for reconstruction speed, image quality, and accuracy. Speed was evaluated based on acquisitions of the ACR CT accreditation phantom under four different flying focal spot configurations. Image quality was assessed using the same phantom by evaluating CT number accuracy, uniformity, and contrast to noise ratio (CNR). Finally, reconstructed mass-attenuation coefficient accuracy was evaluated using a simulated scan of a FORBILD thorax phantom and comparing reconstructed values to the known phantom values. Results: The average reconstruction time evaluated under all flying focal spot configurations was found to be 17.4 ± 1.0 s for a 512 row × 512 column × 32 slice volume. Reconstructions of the ACR phantom were found to meet all CT Accreditation Program criteria including CT number, CNR, and uniformity tests. Finally, reconstructed mass-attenuation coefficient values of water within the FORBILD thorax phantom agreed with original phantom values to within 0.0001 mm2/g (0.01%). Conclusions: FreeCT_wFBP is a fast, highly configurable reconstruction package for

  3. Minimum detection windows, PI-line existence and uniqueness for helical cone-beam scanning of variable pitch.

    PubMed

    Ye, Yangbo; Zhu, Jiehua; Wang, Ge

    2004-03-01

    The goal of this paper is to study Cone-beam CT scanning along a helix of variable pitch. First the rationale and applications in medical imaging of variable pitch CT reconstruction are explained. Then formulas for the minimum detection window are derived. The main part of the paper proves a necessary and sufficient condition for the existence and uniqueness of PI-lines inside this variable pitch helix. These results are necessary steps toward an exact reconstruction algorithm for helix scanning of variable pitch, generalizing Katsevich's formula on constant pitch exact reconstruction. It is shown through an example that, when the derivative of the pitch function is not convex, or when the pitch function passes a inflection point and begins to slow down, PI-lines may be not unique near the rim of the helix cylinder. The conclusion is that the restriction on the pitch function is weaker, if the object is placed well within the helix cylinder and far from its rim, in order to preserve the uniqueness of PI-lines. If the object is near the rim, the restriction condition on the allowable pitch functions becomes stronger.

  4. A Dosimetric Comparison of Tomotherapy and Volumetric Modulated Arc Therapy in the Treatment of High-Risk Prostate Cancer With Pelvic Nodal Radiation Therapy

    SciTech Connect

    Pasquier, David; Cavillon, Fabrice; Lacornerie, Thomas; Touzeau, Claire; Tresch, Emmanuelle; Lartigau, Eric

    2013-02-01

    Purpose: To compare the dosimetric results of volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT) in the treatment of high-risk prostate cancer with pelvic nodal radiation therapy. Methods and Materials: Plans were generated for 10 consecutive patients treated for high-risk prostate cancer with prophylactic whole pelvic radiation therapy (WPRT) using VMAT and HT. After WPRT, a sequential boost was delivered to the prostate. Plan quality was assessed according to the criteria of the International Commission on Radiation Units and Measurements 83 report: the near-minimal (D98%), near-maximal (D2%), and median (D50%) doses; the homogeneity index (HI); and the Dice similarity coefficient (DSC). Beam-on time, integral dose, and several organs at risk (OAR) dosimetric indexes were also compared. Results: For WPRT, HT was able to provide a higher D98% than VMAT (44.3 {+-} 0.3 Gy and 43.9 {+-} 0.5 Gy, respectively; P=.032) and a lower D2% than VMAT (47.3 {+-} 0.3 Gy and 49.1 {+-} 0.7 Gy, respectively; P=.005), leading to a better HI. The DSC was better for WPRT with HT (0.89 {+-} 0.009) than with VMAT (0.80 {+-} 0.02; P=.002). The dosimetric indexes for the prostate boost did not differ significantly. VMAT provided better rectum wall sparing at higher doses (V70, V75, D2%). Conversely, HT provided better bladder wall sparing (V50, V60, V70), except at lower doses (V20). The beam-on times for WPRT and prostate boost were shorter with VMAT than with HT (3.1 {+-} 0.1 vs 7.4 {+-} 0.6 min, respectively; P=.002, and 1.5 {+-} 0.05 vs 3.7 {+-} 0.3 min, respectively; P=.002). The integral dose was slightly lower for VMAT. Conclusion: VMAT and HT provided very similar and highly conformal plans that complied well with OAR dose-volume constraints. Although some dosimetric differences were statistically significant, they remained small. HT provided a more homogeneous dose distribution, whereas VMAT enabled a shorter delivery time.

  5. 4D-Imaging of the Lung: Reproducibility of Lesion Size and Displacement on Helical CT, MRI, and Cone Beam CT in a Ventilated Ex Vivo System

    SciTech Connect

    Biederer, Juergen Dinkel, Julien; Remmert, Gregor; Jetter, Siri; Nill, Simeon; Moser, Torsten; Bendl, Rolf; Thierfelder, Carsten; Fabel, Michael; Oelfke, Uwe; Bock, Michael; Plathow, Christian; Bolte, Hendrik; Welzel, Thomas; Hoffmann, Beata; Hartmann, Guenter; Schlegel, Wolfgang; Debus, Juergen; Heller, Martin

    2009-03-01

    Purpose: Four-dimensional (4D) imaging is a key to motion-adapted radiotherapy of lung tumors. We evaluated in a ventilated ex vivo system how size and displacement of artificial pulmonary nodules are reproduced with helical 4D-CT, 4D-MRI, and linac-integrated cone beam CT (CBCT). Methods and Materials: Four porcine lungs with 18 agarose nodules (mean diameters 1.3-1.9 cm), were ventilated inside a chest phantom at 8/min and subject to 4D-CT (collimation 24 x 1.2 mm, pitch 0.1, slice/increment 24x10{sup 2}/1.5/0.8 mm, pitch 0.1, temporal resolution 0.5 s), 4D-MRI (echo-shared dynamic three-dimensional-flash; repetition/echo time 2.13/0.72 ms, voxel size 2.7 x 2.7 x 4.0 mm, temporal resolution 1.4 s) and linac-integrated 4D-CBCT (720 projections, 3-min rotation, temporal resolution {approx}1 s). Static CT without respiration served as control. Three observers recorded lesion size (RECIST-diameters x/y/z) and axial displacement. Interobserver- and interphase-variation coefficients (IO/IP VC) of measurements indicated reproducibility. Results: Mean x/y/z lesion diameters in cm were equal on static and dynamic CT (1.88/1.87; 1.30/1.39; 1.71/1.73; p > 0.05), but appeared larger on MRI and CBCT (2.06/1.95 [p < 0.05 vs. CT]; 1.47/1.28 [MRI vs. CT/CBCT p < 0.05]; 1.86/1.83 [CT vs. CBCT p < 0.05]). Interobserver-VC for lesion sizes were 2.54-4.47% (CT), 2.29-4.48% (4D-CT); 5.44-6.22% (MRI) and 4.86-6.97% (CBCT). Interphase-VC for lesion sizes ranged from 2.28% (4D-CT) to 10.0% (CBCT). Mean displacement in cm decreased from static CT (1.65) to 4D-CT (1.40), CBCT (1.23) and MRI (1.16). Conclusions: Lesion sizes are exactly reproduced with 4D-CT but overestimated on 4D-MRI and CBCT with a larger variability due to limited temporal and spatial resolution. All 4D-modalities underestimate lesion displacement.

  6. The AGS synchrotron with four helical magnets

    SciTech Connect

    Tsoupas N.; Huang, H.; Roser, T.; MacKay, W.W.; Trbojevic, D.

    2012-05-20

    The idea of using two partial helical magnets was applied successfully to the AGS synchrotron to preserve the proton beam polarization. In this paper we explore in details the idea of using four helical magnets placed symmetrically in the AGS ring. The placement of four helical magnets in the AGS ring provides many advantages over the present setup of the AGS which uses two partial helical magnets. First, the symmetric placement of the four helical magnets allows for a better control of the AGS optics with reduced values of the beta functions especially near beam injection, second, the vertical spin direction during beam injection and extraction is closer to vertical, and third, it provides for a larger 'spin tune gap', which allows the vertical and horizontal tunes to be placed, and prevent the horizontal and vertical intrinsic spin resonances of the AGS to occur during the acceleration cycle. Although the same spin gap can be obtained with a single or two partial helices, the required high field strength of a single helix makes its use impractical, and that of the double helix rather difficult. In this paper we will provide results on the spin tune and on the optics of the AGS with four partial helical magnets, and compare these results with the present setup of the AGS that uses two partial helical magnets.

  7. Preliminary results of tomotherapy for treatment of inoperable recurrent non-small cell lung cancer at bronchial stump site after right pneumonectomy

    PubMed Central

    Moon, Seong Kwon

    2015-01-01

    Aim of the study This study aimed to prospectively investigate the clinical outcomes of curative radical helical tomotherapy (HT) applied to recurrent non-small cell lung cancer (NSCLC) at the bronchial stump site after right pneumonectomy. After right pneumonectomy, the heart shifted right laterally. The chambers of the heart closed with a recurrent mass at the bronchial stump were the right atrium and left atrium due to right shifting of the heart. The unfavorable bronchial stump recurrent cancer-heart geometry due to a right shift of the heart might serve as a reliable predictor of cardiac morbidity for aggressive radiotherapy. Material and methods The 23 patients received HT for the recurrent NSCLC at the bronchial stump site after right pneumonectomy between 2008 and 2011. The median age of the patients was 65 years (range 56–74). Results We prescribed 95% volume of the primary planning target volume (PTV) to a total dose of 69 Gy in 30 fractions, and 95% of the secondary PTV to a total dose of 54 Gy in 30 fractions with reduction of the 50% volume of the heart < 20 Gy. The median conformal index in the 23 plans was 1.21. The mean fraction of primary PTV receiving more than 95% of the prescribed dose was 97.8%. The mean V45, V50, V60 of the heart were 10.5%, 6.5%, 0.2%, respectively. The median follow-up after tomotherapy was 19.86 months. Median survival was 20 months. The 2-year OS was 39.1%. Conclusions The relatively high dose tomotherapy alone for patients with a recurrent bronchial stump mass which was proximal to the heart demonstrated favorable clinical results without severe heart or pulmonary complications. PMID:26199573

  8. Decay of magnetic helicity producing polarized Alfven waves

    SciTech Connect

    Yoshida, Z.; Mahajan, S.M.

    1994-02-01

    When a super-Alfvenic electron beam propagates along an ambient magnetic field, the left-hand circularly polarized Alfven wave is Cherenkov-emitted (two stream instability). This instability results in a spontaneous conversion of the background plasma helicity to the wave helicity. The background helicity induces a frequency (energy) shift in the eigenmodes, which changes the critical velocity for Cherenkov emission, and it becomes possible for a sub-Alfvenic electron beam to excite a nonsingular Alfven mode.

  9. Helical tomotherapy setup variations in canine nasal tumor patients immobilized with a bite block.

    PubMed

    Kubicek, Lyndsay N; Seo, Songwon; Chappell, Richard J; Jeraj, Robert; Forrest, Lisa J

    2012-01-01

    The purpose of our study was to compare setup variation in four degrees of freedom (vertical, longitudinal, lateral, and roll) between canine nasal tumor patients immobilized with a mattress and bite block, versus a mattress alone. Our secondary aim was to define a clinical target volume (CTV) to planning target volume (PTV) expansion margin based on our mean systematic error values associated with nasal tumor patients immobilized by a mattress and bite block. We evaluated six parameters for setup corrections: systematic error, random error, patient-patient variation in systematic errors, the magnitude of patient-specific random errors (root mean square [RMS]), distance error, and the variation of setup corrections from zero shift. The variations in all parameters were statistically smaller in the group immobilized by a mattress and bite block. The mean setup corrections in the mattress and bite block group ranged from 0.91 mm to 1.59 mm for the translational errors and 0.5°. Although most veterinary radiation facilities do not have access to Image-guided radiotherapy (IGRT), we identified a need for more rigid fixation, established the value of adding IGRT to veterinary radiation therapy, and define the CTV-PTV setup error margin for canine nasal tumor patients immobilized in a mattress and bite block.

  10. Efficacy of stereotactic radiotherapy for brain metastases using dynamic jaws technology in the helical tomotherapy system

    PubMed Central

    Hayashi, Akihiro; Manabe, Yoshihiko; Sugie, Chikao; Takaoka, Taiki; Yanagi, Takeshi; Oguri, Tetsuya; Matsuo, Masayuki; Mori, Yoshimasa; Shibamoto, Yuta

    2016-01-01

    Objective: Dynamic jaws (DJ) are expected to be useful in stereotactic radiotherapy (SRT) for brain metastases (BM). The efficacy and optimal dose fractionation were investigated. Methods: In a planning study, 63 treatment plans were generated for the following 3 conditions: 1.0-cm fixed jaws (FJ), 2.5-cm FJ and 2.5-cm DJ. In a clinical study, 30 Gy/3 fr, 35 Gy/5 fr or 37.5 Gy/5 fr were prescribed depending on tumour size. Clinical results of groups treated with 2.5-cm DJ plans and 1.0-cm FJ were compared. Results: In the planning study, the treatment times in 2.5-cm DJ and FJ plans were less than that in 1.0-cm FJ plans (p < 0.001). The brain doses in 1.0-cm FJ plans and 2.5-cm DJ plans were smaller than those in 2.5-cm FJ plans (p < 0.05). In the clinical study, 34 patients with 68 BM were treated with SRT. Of those, 15 patients with 34 BM were treated with 2.5-cm DJ plans and 19 patients with 34 BM were treated with 1.0-cm FJ plans. The overall survival and local tumour control (LC) rates were 52 and 93% at 12 months, respectively. The DJ system achieved favourable LC and 29% shorter treatment time compared with the FJ system (p < 0.001). Grade 2 or 3 necrosis occurred more frequently in patients with 15 cc or larger tumour volumes (p = 0.05). Conclusion: DJ technology enables treatment time to be reduced without worsening the dose distribution and clinical efficacy. The prescribed doses in this study may be acceptable for patients with small tumour volumes. Advances in knowledge: DJ technology enables treatment time to be reduced without worsening the dose. PMID:27556639

  11. SU-E-J-174: Adaptive PET-Based Dose Painting with Tomotherapy

    SciTech Connect

    Darwish, N; Mackie, T; Thomadsen, B

    2014-06-01

    Purpose: PET imaging can be converted into dose prescription directly. Due to the variability of the intensity of PET the image, PET prescription maybe superior over uniform dose prescription. Furthermore, unlike the case in image reconstruction of not knowing the image solution in advance, the prescribed dose is known from a PET image a priori. Therefore, optimum beam orientations are derivable. Methods: We can assume the PET image to be the prescribed dose and invert it to determine the energy fluence. The same method used to reconstruct tissue images from projections could be used to solve the inverse problem of determining beam orientations and modulation patterns from a dose prescription [10]. Unlike standard tomographic reconstruction of images from measured projection profiles, the inversion of the prescribed dose results in photon fluence which may be negative and therefore unphysical. Two-dimensional modulated beams can be modelled in terms of the attenuated or exponential radon transform of the prescribed dose function (assumed to be the PET image in this case), an application of a Ram-Lak filter, and inversion by backprojection. Unlike the case in PET processing, however, the filtered beam obtained from the inversion represents a physical photon fluence. Therefore, a positivity constraint for the fluence (setting negative fluence to zero) must be applied (Brahme et al 1982, Bortfeld et al 1990) Results: Truncating the negative profiles from the PET data results in an approximation of the derivable energy fluence. Backprojection of the deliverable fluence is an approximation of the dose delivered. The deliverable dose is comparable to the original PET image and is similar to the PET image. Conclusion: It is possible to use the PET data or image as a direct indicator of deliverable fluence for cylindrical radiotherapy systems such as TomoTherapy.

  12. Elliptical Muon Helical Cooling Channel Coils

    SciTech Connect

    Kahn, S. A.; Flanagan, G.; Lopes, M. L.; Yonehara, K.

    2013-09-01

    A helical cooling channel (HCC) consisting of a pressurized gas absorber imbedded in a magnetic channel that provides solenoid, helical dipole and helical quadrupole fields has shown considerable promise in providing six-dimensional phase space reduction for muon beams. The most effective approach to implementing the desired magnetic field is a helical solenoid (HS) channel composed of short solenoid coils arranged in a helical pattern. The HS channel along with an external solenoid allows the B$_z$ and B$_{\\phi}$ components along the reference orbit to be set to any desired values. To set dB$_{\\phi}$/dr to the desired value for optimum focusing requires an additional variable to tune. We shall show that using elliptical shaped coils in the HS channel allows the flexibility to achieve the desired dB$_{\\phi}$/dr on the reference orbit without significant change to B$_z$ and B$_{\\phi}$.

  13. Dosimetric effect on pediatric conformal treatment plans using dynamic jaw with Tomotherapy HDA

    SciTech Connect

    Han, Eun Young; Kim, Dong-Wook; Zhang, Xin; Penagaricano, Jose; Liang, Xiaoying; Hardee, Matthew; Morrill, Steve; Ratanatharathorn, Vaneerat

    2015-10-01

    It is important to minimize the radiation dose delivered to healthy tissues in pediatric cancer treatment because of the risk of secondary malignancies. Tomotherapy HDA provides a dynamic jaw (DJ) delivery mode that creates a sharper penumbra at the craniocaudal ends of a target in addition to a fixed jaw (FJ) delivery mode. The purpose of this study was to evaluate its dosimetric effect on the pediatric cancer cases. We included 6 pediatric cases in this study. The dose profiles and plan statistics—target dose conformity, uniformity, organ-at-risk (OAR) mean dose, beam-on time, and integral dose—were compared for each case. Consequently, the target dose coverage and uniformity were similar for different jaw settings. The OAR dose sparing depended on its relative location to the target and disease sites. For example, in the head and neck cancer cases, the brain stem dose using DJ 2.5 was reduced by more than two-fold (2.4 Gy vs. 6.3 Gy) than that obtained with FJ 2.5. The integral dose with DJ 2.5 decreased by more than 9% compared with that with FJ 2.5. Thus, using dynamic jaw in pediatric cases could be critical to reduce a probability of a secondary malignancy.

  14. Optimization of the Helical Orbits in the Tevatron

    SciTech Connect

    Alexahin, Y.; /Fermilab

    2007-06-01

    To avoid multiple head-on collisions the proton and antiproton beams in the Tevatron move along separate helical orbits created by 7 horizontal and 8 vertical electrostatic separators. Still the residual long-range beam-beam interactions can adversely affect particle motion at all stages from injection to collision. With increased intensity of the beams it became necessary to modify the orbits in order to mitigate the beam-beam effect on both antiprotons and protons. This report summarizes the work done on optimization of the Tevatron helical orbits, outlines the applied criteria and presents the achieved results.

  15. Helicity content and tokamak applications of helicity

    SciTech Connect

    Boozer, A.H.

    1986-05-01

    Magnetic helicity is approximately conserved by the turbulence associated with resistive instabilities of plasmas. To generalize the application of the concept of helicity, the helicity content of an arbitrary bounded region of space will be defined. The definition has the virtues that both the helicity content and its time derivative have simple expressions in terms of the poloidal and toroidal magnetic fluxes, the average toroidal loop voltage and the electric potential on the bounding surface, and the volume integral of E-B. The application of the helicity concept to tokamak plasmas is illustrated by a discussion of so-called MHD current drive, an example of a stable tokamak q profile with q less than one in the center, and a discussion of the possibility of a natural steady-state tokamak due to the bootstrap current coupling to tearing instabilities.

  16. Breathing-Synchronized Delivery: A Potential Four-Dimensional Tomotherapy Treatment Technique

    SciTech Connect

    Zhang Tiezhi . E-mail: tiezhi.zhang@beaumont.edu; Lu Weiguo; Olivera, Gustavo H.; Keller, Harry; Jeraj, Robert; Manon, Rafael; Mehta, Minesh; Mackie, Thomas R.; Paliwal, Bhudatt

    2007-08-01

    Purpose: To introduce a four-dimensional (4D) tomotherapy treatment technique with improved motion control and patient tolerance. Methods and Materials: Computed tomographic images at 10 breathing phases were acquired for treatment planning. The full exhalation phase was chosen as the planning phase, and the CT images at this phase were used as treatment-planning images. Region of interest delineation was the same as in traditional treatment planning, except that no breathing motion margin was used in clinical target volume-planning target volume expansion. The correlation between delivery and breathing phases was set assuming a constant gantry speed and a fixed breathing period. Deformable image registration yielded the deformation fields at each phase relative to the planning phase. With the delivery/breathing phase correlation and voxel displacements at each breathing phase, a 4D tomotherapy plan was obtained by incorporating the motion into inverse treatment plan optimization. A combined laser/spirometer breathing tracking system has been developed to monitor patient breathing. This system is able to produce stable and reproducible breathing signals representing tidal volume. Results: We compared the 4D tomotherapy treatment planning method with conventional tomotherapy on a static target. The results showed that 4D tomotherapy can achieve dose distributions on a moving target similar to those obtained with conventional delivery on a stationary target. Regular breathing motion is fully compensated by motion-incorporated breathing-synchronized delivery planning. Four-dimensional tomotherapy also has close to 100% duty cycle and does not prolong treatment time. Conclusion: Breathing-synchronized delivery is a feasible 4D tomotherapy treatment technique with improved motion control and patient tolerance.

  17. The AGS with four helical magnets

    SciTech Connect

    Tsoupas, N.; Huang, H.; MacKay, W.W.; Roser, T.; Trbojevic, D.

    2010-02-25

    The idea of using multiple partial helical magnets was applied successfully to the AGS synchrotron, to preserve the proton beam polarization. In this paper we explore in details the idea of using four helical magnets placed symmetrically in the AGS ring. This modification provides many advantages over the present setup of the AGS that uses two partial helical magnets. First, it provides a larger 'spin tune gap' for the placement of the vertical betatron tune of the AGS during acceleration, second, the vertical spin direction during the beam injection and extraction is closer to vertical, third, the symmetric placement of the snakes allows for a better control of the AGS optics, and for reduced values of the beta and eta functions, especially near injection, fourth, the optical properties of the helical magnets also favor the placement of the horizontal betatron tune in the 'spin tune gap', thus eliminating the horizontal spin resonances. In this paper we provide results on the spin tune and on the optics of the AGS with four partial helical magnets, and we compare these results with the present setup of the AGS that uses two partial helical magnets.

  18. Helical dipole magnets for polarized protons in RHIC

    SciTech Connect

    Syphers, M.; Courant, E.; Fischer, W.

    1997-07-01

    Superconducting helical dipole magnets will be used in the Brookhaven Relativistic Heavy Ion Collider (RHIC) to maintain polarization of proton beams and to perform localized spin rotations at the two major experimental detector regions. Requirements for the helical dipole system are discussed, and magnet prototype work is reported.

  19. Superconducting helical solenoid systems for muon cooling experiment at Fermilab

    SciTech Connect

    Kashikhin, Vladimir S.; Andreev, Nikolai; Johnson, Rolland P.; Kashikhin, Vadim V.; Lamm, Michael J.; Romanov, Gennady; Yonehara, Katsuya; Zlobin, Alexander V.; /Fermilab

    2007-08-01

    Novel configurations of superconducting magnet system for Muon Beam Cooling Experiment is under design at Fermilab. The magnet system has to generate longitudinal and transverse dipole and quadrupole helical magnetic fields providing a muon beam motion along helical orbit. It was found that such complicated field configuration can be formed by a set of circular coils shifted in transverse directions in such a way that their centers lay on the center of the helical beam orbit. Closed beam orbit configurations were also proposed and investigated. This paper describes the magnetic and mechanical designs and parameters of such magnetic system based on a NbTi Rutherford type cable. The helical solenoid fabrication, assembly and quench protection issues are presented.

  20. A Helical Cooling Channel System for Muon Colliders

    SciTech Connect

    Katsuya Yonehara, Rolland Johnson, Michael Neubauer, Yaroslav Derbenev

    2010-03-01

    Fast muon beam six dimensional (6D) phase space cooling is essential for muon colliders. The Helical Cooling Channel (HCC) uses hydrogen-pressurized RF cavities imbedded in a magnet system with solenoid, helical dipole, and helical quadrupole components that provide the continuous dispersion needed for emittance exchange and effective 6D beam cooling. A series of HCC segments, each with sequentially smaller aperture, higher magnetic field, and higher RF frequency to match the beam size as it is cooled, has been optimized by numerical simulation to achieve a factor of 105 emittance reduction in a 300 m long channel with only a 40% loss of beam. Conceptual designs of the hardware required for this HCC system and the status of the RF studies and HTS helical solenoid magnet prototypes are described.

  1. Design of Helical Cooling Channel for Muon Collider

    SciTech Connect

    Yonehara, Katsuya; /Fermilab

    2010-07-30

    Fast muon beam six dimensional (6D) phase space cooling is essential for muon colliders. The Helical Cooling Channel (HCC) uses hydrogen-pressurized RF cavities imbedded in a magnet system with solenoid, helical dipole, and helical quadrupole components that provide the continuous dispersion needed for emittance exchange and effective 6D beam cooling. A series of HCC segments, each with sequentially smaller aperture, higher magnetic field, and higher RF frequency to match the beam size as it is cooled, has been optimized by numerical simulation to achieve a factor of 10{sup 5} emittance reduction in a 300 m long channel with only a 40% loss of beam. Conceptual designs of the hardware required for this HCC system and the status of the RF studies and HTS helical solenoid magnet prototypes are described.

  2. Analysis of Daily Setup Variation With Tomotherapy Megavoltage Computed Tomography

    SciTech Connect

    Zhou Jining Uhl, Barry; Dewit, Kelly; Young, Mark; Taylor, Brian; Fei Dingyu; Lo, Y-C

    2010-04-01

    The purpose of this study was to evaluate different setup uncertainties for various anatomic sites with TomoTherapy (registered) pretreatment megavoltage computed tomography (MVCT) and to provide optimal margin guidelines for these anatomic sites. Ninety-two patients with tumors in head and neck (HN), brain, lung, abdominal, or prostate regions were included in the study. MVCT was used to verify patient position and tumor target localization before each treatment. With the anatomy registration tool, MVCT provided real-time tumor shift coordinates relative to the positions where the simulation CT was performed. Thermoplastic facemasks were used for HN and brain treatments. Vac-Lok{sup TM} cushions were used to immobilize the lower extremities up to the thighs for prostate patients. No respiration suppression was administered for lung and abdomen patients. The interfractional setup variations were recorded and corrected before treatment. The mean interfractional setup error was the smallest for HN among the 5 sites analyzed. The average 3D displacement in lateral, longitudinal, and vertical directions for the 5 sites ranged from 2.2-7.7 mm for HN and lung, respectively. The largest movement in the lung was 2.0 cm in the longitudinal direction, with a mean error of 6.0 mm and standard deviation of 4.8 mm. The mean interfractional rotation variation was small and ranged from 0.2-0.5 deg., with the standard deviation ranging from 0.7-0.9 deg. Internal organ displacement was also investigated with a posttreatment MVCT scan for HN, lung, abdomen, and prostate patients. The maximum 3D intrafractional displacement across all sites was less than 4.5 mm. The interfractional systematic errors and random errors were analyzed and the suggested margins for HN, brain, prostate, abdomen, and lung in the lateral, longitudinal, and vertical directions were between 4.2 and 8.2 mm, 5.0 mm and 12.0 mm, and 1.5 mm and 6.8 mm, respectively. We suggest that TomoTherapy (registered

  3. Evaluation of radiosurgery techniques–Cone-based linac radiosurgery vs tomotherapy-based radiosurgery

    SciTech Connect

    Yip, Ho Yin; Mui, Wing Lun A.; Lee, Joseph W.Y.; Fung, Winky Wing Ki; Chan, Jocelyn M.T.; Chiu, G.; Law, Maria Y.Y.

    2013-07-01

    Performances of radiosurgery of intracranial lesions between cone-based Linac system and Tomotherapy-based system were compared in terms of dosimetry and time. Twelve patients with single intracranial lesion treated with cone-based Linac radiosurgery system from 2005 to 2009 were replanned for Tomotherapy-based radiosurgery treatment. The conformity index, homogeneity index (HI), and gradient score index (GSI) of each case was calculated. The Wilcoxon matched-pair test was used to compare the 3 indices between both systems. The cases with regular target (n = 6) and those with irregular target (n = 6) were further analyzed separately. The estimated treatment time between both systems was also compared. Significant differences were found in HI (p = 0.05) and in GSI (p = 0.03) for the whole group. Cone-based radiosurgery was better in GSI whereas Tomotherapy-based radiosurgery was better in HI. Cone-based radiosurgery was better in conformity index (p = 0.03) and GSI (p = 0.03) for regular targets, whereas Tomotherapy-based radiosurgery system performed significantly better in HI (p = 0.03) for irregular targets. The estimated total treatment time for Tomotherapy-based radiosurgery ranged from 24 minutes to 35 minutes, including 15 minutes of pretreatment megavoltage computed tomography (MVCT) and image registration, whereas that for cone-based radiosurgery ranged from 15 minutes for 1 isocenter to 75 minutes for 5 isocenters. As a rule of thumb, Tomotherapy-based radiosurgery system should be the first-line treatment for irregular lesions because of better dose homogeneity and shorter treatment time. Cone-based Linac radiosurgery system should be the treatment of choice for regular targets because of the better dose conformity, rapid dose fall-off, and reasonable treatment time.

  4. Monte Carlo simulations of patient dose perturbations in rotational-type radiotherapy due to a transverse magnetic field: A tomotherapy investigation

    SciTech Connect

    Yang, Y. M.; Geurts, M.; Smilowitz, J. B.; Bednarz, B. P.; Sterpin, E.

    2015-02-15

    Purpose: Several groups are exploring the integration of magnetic resonance (MR) image guidance with radiotherapy to reduce tumor position uncertainty during photon radiotherapy. The therapeutic gain from reducing tumor position uncertainty using intrafraction MR imaging during radiotherapy could be partially offset if the negative effects of magnetic field-induced dose perturbations are not appreciated or accounted for. The authors hypothesize that a more rotationally symmetric modality such as helical tomotherapy will permit a systematic mediation of these dose perturbations. This investigation offers a unique look at the dose perturbations due to homogeneous transverse magnetic field during the delivery of Tomotherapy{sup ®} Treatment System plans under varying degrees of rotational beamlet symmetry. Methods: The authors accurately reproduced treatment plan beamlet and patient configurations using the Monte Carlo code GEANT4. This code has a thoroughly benchmarked electromagnetic particle transport physics package well-suited for the radiotherapy energy regime. The three approved clinical treatment plans for this study were for a prostate, head and neck, and lung treatment. The dose heterogeneity index metric was used to quantify the effect of the dose perturbations to the target volumes. Results: The authors demonstrate the ability to reproduce the clinical dose–volume histograms (DVH) to within 4% dose agreement at each DVH point for the target volumes and most planning structures, and therefore, are able to confidently examine the effects of transverse magnetic fields on the plans. The authors investigated field strengths of 0.35, 0.7, 1, 1.5, and 3 T. Changes to the dose heterogeneity index of 0.1% were seen in the prostate and head and neck case, reflecting negligible dose perturbations to the target volumes, a change from 5.5% to 20.1% was observed with the lung case. Conclusions: This study demonstrated that the effect of external magnetic fields can

  5. SU-E-T-485: Investigation of a Synthetic Diamond Detector for Tomotherapy Dosimetry

    SciTech Connect

    Knill, C; Nalichowski, A; Halford, R; Zakjevskii, V; Zhuang, L; Snyder, M; Burmeister, J

    2014-06-01

    Purpose: Tomotherapy treatments are characterized by rotational deliveries of flattening-filter free fields resulting in high-gradient dose distributions. Small volume, rotationally independent detectors are needed for accurate dosimetry. PTWs microDiamond detector, with its small sensitive volume (0.004mm{sup 3}), could potentially be an ideal detector for Tomotherapy. The microDiamond detector was tested against a small volume Exradin A1SL ion chamber for Tomotherapy open-field and IMRT commissioning measurements. Methods: Custom detector holders were fabricated to allow A1SL and microDiamond measurements in the Tomotherapy Cheese phantom and a square solid water phantom. The microDiamond rotational dependence within the Tomotherapy phantom was tested by incrementally rotating the detector in between static-gantry angle Tomotherapy irradiations. Longitudinal Tomotherapy profiles, for all field sizes, were measured with the microDiamond and A1SL detectors at 1.5cm depth in the square phantom, and compared to film. Detector axes were aligned parallel to table motion. Per TG-119 recommendations, both detectors were calibrated to known doses in phantoms and used to measure high-dose points in TG-119 H and N and Prostate plans. The measurements were compared to the treatment planning system and subsequently compared to published TG-119 confidence limits. Results: The microDiamond angular dependence was less than 0.5%. The average difference between the detectors and film-measured longitudinal profile 80–20% penumbras were 0.03+/-0.04mm and 1.36+/-0.22mm for the microDiamond and A1SL, respectively. The average difference between the detector and filmmeasured field sizes were 0.07+/-0.01mm and 0.09+/-0.02mm for the microDiamond and A1SL, respectively. The measured confidence limits were 0.023 and 0.015 for microDiamond and A1SL, respectively. TG-119 reported a confidence limit of 0.034. Conclusion: The microDiamond measured open-field longitudinal Tomotherapy profiles

  6. SU-E-T-331: To Evaluate Planning Quality of SBRT with Multiple Lung Metastases Generated with Pinnacle and Tomotherapy

    SciTech Connect

    Chen, Y; Zhang, Y; Zhang, Y; Doxsee, K; Yang, C

    2014-06-01

    Purpose: To evaluate planning quality of SBRT with multiple lung metastases generated with Pinnacle and Tomotherapy Methods: Nine randomly selected patients diagnosed with non small-cell lung cancer with multiple lesions were planned with Pinnacle (version 9.2) and Tomotherapy (version 4.2). Coplanar and non-coplanar plans were generated on Pinnacle. A total dose of 60 Gy was prescribed to 95% of PTV in 3 fractions. Single isocenter was used. Nine static beams were used for Pinnacle plans. Planning outcomes such as minimum and mean dose, V{sub 9} {sub 5}, D{sub 9} {sub 5} (95% of target volume receives prescription dose), D{sub 5}, and D{sub 1} to PTV, maximum dose to heart, esophagus, cord, trachea, brachial plexus, rib, chest wall, and liver, mean dose to liver, total lung, right and left lung, volume of chest wall receives 30 Gy, volume of lungs receives 5 Gy and 20Gy, conformity index (CI = PIV / PTV) and heterogeneity index (HI = D{sub 5} / D{sub 9} {sub 5}) were reported for evaluation. Results: The mean volume of PTV was 37.77 ± 23.4 cm3. D{sub 9} {sub 5} of PTV with Tomo, coplanar, non-coplanar was 60.2 ± 0.3 Gy, 58.6 ± 1.2 Gy, and 59.1 ± 0.7 Gy, respectively. Mean dose to PTV was lower for Tomo (p < 0.0001), so were D{sub 5} (p < 0.0001) and D{sub 1} (p = 0.001). CI was better with Tomo (p < 0.0001), so was HI (p < 0.0001). Maximum dose to other critical organs were also lower exclusively with Tomo plans. Treatment time was recorded only for Tomo plans (73.0 ± 20.6 min). Conclusion: With 51 beam angles, Tomo plans could generally achieve better tumor coverage while sparing more critical structures for multiple lung lesions study. Non-coplanar also has better tumor coverage with lower dose to critical organs such as lungs, liver, chest wall and cord compare to coplanar plans.

  7. Emerging double helical nanostructures.

    PubMed

    Zhao, Meng-Qiang; Zhang, Qiang; Tian, Gui-Li; Wei, Fei

    2014-08-21

    As one of the most important and land-mark structures found in nature, a double helix consists of two congruent single helices with the same axis or a translation along the axis. This double helical structure renders the deoxyribonucleic acid (DNA) the crucial biomolecule in evolution and metabolism. DNA-like double helical nanostructures are probably the most fantastic yet ubiquitous geometry at the nanoscale level, which are expected to exhibit exceptional and even rather different properties due to the unique organization of the two single helices and their synergistic effect. The organization of nanomaterials into double helical structures is an emerging hot topic for nanomaterials science due to their promising exceptional unique properties and applications. This review focuses on the state-of-the-art research progress for the fabrication of double-helical nanostructures based on 'bottom-up' and 'top-down' strategies. The relevant nanoscale, mesoscale, and macroscopic scale fabrication methods, as well as the properties of the double helical nanostructures are included. Critical perspectives are devoted to the synthesis principles and potential applications in this emerging research area. A multidisciplinary approach from the scope of nanoscience, physics, chemistry, materials, engineering, and other application areas is still required to the well-controlled and large-scale synthesis, mechanism, property, and application exploration of double helical nanostructures.

  8. A Helical Stairway Project

    ERIC Educational Resources Information Center

    Farmer, Tom

    2008-01-01

    We answer a geometric question that was raised by the carpenter in charge of erecting helical stairs in a 10-story hospital. The explanation involves the equations of lines, planes, and helices in three-dimensional space. A brief version of the question is this: If A and B are points on a cylinder and the line segment AB is projected radially onto…

  9. Design of Helical Solenoid Combined with RF Cavity

    SciTech Connect

    Kashikhin, Vladimir; Andreev, Nicolai; Kashikhin, Vadim; Lamm, Michael; Makarov, Alexander; Romanov, Gennady; Yonehara, Katsuya; Yu, Miao; Zlobin, Alexander; /Fermilab

    2010-05-01

    Helical Solenoids (HS) were proposed for a muon beam ionization cooling. There are substantial energy losses, up to 30 MeV/m, during the passing of the muon beam through the absorber. The main issue of such a system is the muon beam energy recovery. A conventional RF cavity is too large to be placed inside HS. In the paper the results of a dielectric-filled RF cavity design is presented. The proposed RF cavity has a helical configuration. Helical Cooling Channel (HCC) module design which includes high pressure vessel, RF cavity, and superconducting HS is presented. The parameters of these module sub-systems are discussed, and the results of muon beam tracking in combined magnetic and electric 3D fields are shown.

  10. Squeezed helical elastica.

    PubMed

    Bouzar, Lila; Müller, Martin Michael; Gosselin, Pierre; Kulić, Igor M; Mohrbach, Hervé

    2016-11-01

    We theoretically study the conformations of a helical semi-flexible filament confined to a flat surface. This squeezed helix exhibits a variety of unexpected shapes resembling circles, waves or spirals depending on the material parameters. We explore the conformation space in detail and show that the shapes can be understood as the mutual elastic interaction of conformational quasi-particles. Our theoretical results are potentially useful to determine the material parameters of such helical filaments in an experimental setting.

  11. 3D Dose Verification Using Tomotherapy CT Detector Array

    SciTech Connect

    Sheng Ke; Jones, Ryan; Yang Wensha; Saraiya, Siddharth; Schneider, Bernard; Chen Quan; Sobering, Geoff; Olivera, Gustavo; Read, Paul

    2012-02-01

    Purpose: To evaluate a three-dimensional dose verification method based on the exit dose using the onboard detector of tomotherapy. Methods and Materials: The study included 347 treatment fractions from 24 patients, including 10 prostate, 5 head and neck (HN), and 9 spinal stereotactic body radiation therapy (SBRT) cases. Detector sonograms were retrieved and back-projected to calculate entrance fluence, which was then forward-projected on the CT images to calculate the verification dose, which was compared with ion chamber and film measurement in the QA plans and with the planning dose in patient plans. Results: Root mean square (RMS) errors of 2.0%, 2.2%, and 2.0% were observed comparing the dose verification (DV) and the ion chamber measured point dose in the phantom plans for HN, prostate, and spinal SBRT patients, respectively. When cumulative dose in the entire treatment is considered, for HN patients, the error of the mean dose to the planning target volume (PTV) varied from 1.47% to 5.62% with a RMS error of 3.55%. For prostate patients, the error of the mean dose to the prostate target volume varied from -5.11% to 3.29%, with a RMS error of 2.49%. The RMS error of maximum doses to the bladder and the rectum were 2.34% (-4.17% to 2.61%) and 2.64% (-4.54% to 3.94%), respectively. For the nine spinal SBRT patients, the RMS error of the minimum dose to the PTV was 2.43% (-5.39% to 2.48%). The RMS error of maximum dose to the spinal cord was 1.05% (-2.86% to 0.89%). Conclusions: An excellent agreement was observed between the measurement and the verification dose. In the patient treatments, the agreement in doses to the majority of PTVs and organs at risk is within 5% for the cumulative treatment course doses. The dosimetric error strongly depends on the error in multileaf collimator leaf opening time with a sensitivity correlating to the gantry rotation period.

  12. Adjuvant Radiotherapy for Gastric Cancer: A Dosimetric Comparison of 3-Dimensional Conformal Radiotherapy, Tomotherapy (registered) and Conventional Intensity Modulated Radiotherapy Treatment Plans

    SciTech Connect

    Dahele, Max; Skinner, Matthew; Schultz, Brenda; Cardoso, Marlene; Bell, Chris; Ung, Yee C.

    2010-07-01

    Some patients with gastric cancer benefit from post-operative chemo-radiotherapy, but adequately irradiating the planning target volume (PTV) whilst avoiding organs at risk (OAR) can be difficult. We evaluate 3-dimensional conformal radiotherapy (CRT), conventional intensity-modulated radiotherapy (IMRT) and helical tomotherapy (TT). TT, 2 and 5-field (F) CRT and IMRT treatment plans with the same PTV coverage were generated for 5 patients and compared. Median values are reported. The volume of left/right kidney receiving at least 20Gy (V20) was 57/51% and 51/60% for 2 and 5F-CRT, and 28/14% for TT and 27/19% for IMRT. The volume of liver receiving at least 30Gy (V30) was 45% and 62% for 2 and 5F-CRT, and 37% for TT and 35% for IMRT. With TT, 98% of the PTV received 95-105% of the prescribed dose, compared with 45%, 34% and 28% for 2F-CRT, 5F-CRT and IMRT respectively. Using conventional metrics, conventional IMRT can achieve comparable PTV coverage and OAR sparing to TT, but at the expense of PTV dose heterogeneity. Both irradiate large volumes of normal tissue to low doses. Additional studies are needed to demonstrate the clinical impact of these technologies.

  13. Tomotherapy treatment plan quality assurance: The impact of applied criteria on passing rate in gamma index method

    SciTech Connect

    Bresciani, Sara; Di Dia, Amalia; Maggio, Angelo; Cutaia, Claudia; Miranti, Anna; Infusino, Erminia; Stasi, Michele

    2013-12-15

    Purpose: Pretreatment patient plan verification with gamma index (GI) metric analysis is standard procedure for intensity modulated radiation therapy (IMRT) treatment. The aim of this paper is to evaluate the variability of the local and global gamma index obtained during standard pretreatment quality assurance (QA) measurements for plans performed with Tomotherapy unit. The QA measurements were performed with a 3D diode array, using variable passing criteria: 3%/3 mm, 2%/2 mm, 1%/1 mm, each with both local and global normalization.Methods: The authors analyzed the pretreatment QA results for 73 verifications; 37 were prostate cancer plans, 16 were head and neck plans, and 20 were other clinical sites. All plans were treated using the Tomotherapy Hi-Art System. Pretreatment QA plans were performed with the commercially available 3D diode array ArcCHECK™. This device has 1386 diodes arranged in a helical geometry spaced 1 cm apart. The dose measurements were acquired on the ArcCHECK™ and then compared with the calculated dose using the standard gamma analysis method. The gamma passing rate (%GP), defined as the percentage of points satisfying the condition GI < 1, was calculated for different criteria (3%/3 mm, 2%/2 mm, 1%/1 mm) and for both global and local normalization. In the case of local normalization method, the authors set three dose difference threshold (DDT) values of 2, 3, and 5 cGy. Dose difference threshold is defined as the minimum absolute dose error considered in the analysis when using local normalization. Low-dose thresholds (TH) of 5% and 10% were also applied and analyzed.Results: Performing a paired-t-test, the authors determined that the gamma passing rate is independent of the threshold values for all of the adopted criteria (5%TH vs 10%TH, p > 0.1). Our findings showed that mean %GPs for local (or global) normalization for the entire study group were 93% (98%), 84% (92%), and 66% (61%) for 3%/3 mm, 2%/2 mm, and 1%/1 mm criteria

  14. Helical plasma thruster

    SciTech Connect

    Beklemishev, A. D.

    2015-10-15

    A new scheme of plasma thruster is proposed. It is based on axial acceleration of rotating magnetized plasmas in magnetic field with helical corrugation. The idea is that the propellant ionization zone can be placed into the local magnetic well, so that initially the ions are trapped. The E × B rotation is provided by an applied radial electric field that makes the setup similar to a magnetron discharge. Then, from the rotating plasma viewpoint, the magnetic wells of the helically corrugated field look like axially moving mirror traps. Specific shaping of the corrugation can allow continuous acceleration of trapped plasma ions along the magnetic field by diamagnetic forces. The accelerated propellant is expelled through the expanding field of magnetic nozzle. By features of the acceleration principle, the helical plasma thruster may operate at high energy densities but requires a rather high axial magnetic field, which places it in the same class as the VASIMR{sup ®} rocket engine.

  15. Helical plasma thruster

    NASA Astrophysics Data System (ADS)

    Beklemishev, A. D.

    2015-10-01

    A new scheme of plasma thruster is proposed. It is based on axial acceleration of rotating magnetized plasmas in magnetic field with helical corrugation. The idea is that the propellant ionization zone can be placed into the local magnetic well, so that initially the ions are trapped. The E × B rotation is provided by an applied radial electric field that makes the setup similar to a magnetron discharge. Then, from the rotating plasma viewpoint, the magnetic wells of the helically corrugated field look like axially moving mirror traps. Specific shaping of the corrugation can allow continuous acceleration of trapped plasma ions along the magnetic field by diamagnetic forces. The accelerated propellant is expelled through the expanding field of magnetic nozzle. By features of the acceleration principle, the helical plasma thruster may operate at high energy densities but requires a rather high axial magnetic field, which places it in the same class as the VASIMR® rocket engine.

  16. Helical screw viscometer

    DOEpatents

    Aubert, J.H.; Chapman, R.N.; Kraynik, A.M.

    1983-06-30

    A helical screw viscometer for the measurement of the viscosity of Newtonian and non-Newtonian fluids comprising an elongated cylindrical container closed by end caps defining a circular cylindrical cavity within the container, a cylindrical rotor member having a helical screw or ribbon flight carried by the outer periphery thereof rotatably carried within the cavity whereby the fluid to be measured is confined in the cavity filling the space between the rotor and the container wall. The rotor member is supported by axle members journaled in the end caps, one axle extending through one end cap and connectable to a drive source. A pair of longitudinally spaced ports are provided through the wall of the container in communication with the cavity and a differential pressure meter is connected between the ports for measuring the pressure drop caused by the rotation of the helical screw rotor acting on the confined fluid for computing viscosity.

  17. A robust procedure for verifying TomoTherapy Hi-Art™ source models for small fields

    NASA Astrophysics Data System (ADS)

    Hundertmark, B.; Sterpin, E.; Mackie, T.

    2011-06-01

    The dosimetric measurement and modeling of small radiation treatment fields (<2 × 2 cm2) are difficult to perform and prone to error. Measurements of small fields are often adversely influenced by the properties of the detectors used to make them. The dosimetric properties of small fields have been difficult to accurately model due to the effects of source occlusion caused by the collimating jaws. In this study, small longitudinal slice widths (SWs) of the TomoTherapy® Hi-Art® machine are characterized by performing dosimetric measurements topographically. By using a static gantry, opening the central 16 MLC leaves during the irradiations, and symmetrically scanning detectors 10 cm through each longitudinal SW, integral doses to a 'TomoTherapy equivalent' 10 × 10 cm2 area are topographically measured. To quantify the effects of source occlusion for TomoTherapy, a quantity referred to as the integral scanned dose to slice width ratio (D/SW) is introduced. (D/SW) ratios are measured for SWs ranging from 0.375 to 5 cm in size using ion chambers and a radiographic film. The measurements of the (D/SW) ratio are shown to be insensitive to the detectors used in this study. The (D/SW) ratios for TomoTherapy have values of unity in the range of SW sizes from 5 cm to approximately 2 cm. For SWs smaller than 2 cm in size, the source-occlusion effect substantially reduces the measured machine output and the value of the (D/SW) ratios. The topographic measurement method presented provides a way to directly evaluate the accuracy of the small-field source model parameters used in dose calculation algorithms. As an example, the electron source spot size of a Penelope Monte Carlo (MC) model of TomoTherapy was varied to match computed and measured (D/SW) ratios. It was shown that the MC results for small SW sizes were sensitive to that particular parameter.

  18. Helical spring holder assembly

    NASA Technical Reports Server (NTRS)

    Newman, Wyatt S. (Inventor)

    1987-01-01

    A helically-threaded spring holder on which a helically wound spring is mounted has a groove formed in one side of the thread at the end where the spring engages the spring holder. The groove relieves the portion of the side in which it is formed from restricting the spring against axial movement during deflection of the spring. The circumferential length of this groove is chosen to establish the number of spring coils which can be deflected without contacting the side of the thread. The end of the thread is also made rigid to prevent flexing thereof during maximal elongation of the spring.

  19. Helical-D pinch

    SciTech Connect

    Schaffer, M.J.

    1997-08-01

    A stabilized pinch configuration is described, consisting of a D-shaped plasma cross section wrapped tightly around a guiding axis. The {open_quotes}helical-D{close_quotes} geometry produces a very large axial (toroidal) transform of magnetic line direction that reverses the pitch of the magnetic lines without the need of azimuthal (poloidal) plasma current. Thus, there is no need of a {open_quotes}dynamo{close_quotes} process and its associated fluctuations. The resulting configuration has the high magnetic shear and pitch reversal of the reversed field pinch (RFP). (Pitch = P = qR, where R = major radius). A helical-D pinch might demonstrate good confinement at q << 1.

  20. Generation of hybrid sinograms for the recovery of kV-CT images with metal artifacts for helical tomotherapy

    SciTech Connect

    Jeon, Hosang; Park, Dahl; Kim, Wontaek; Ki, Yongkan; Kim, Yong Ho; Lee, Ju Hye; Kim, Dongwon; Youn, Hanbean; Nam, Jiho; Lee, Jayoung; Kim, Ho Kyung

    2015-08-15

    Purpose: The overall goal of this study is to restore kilovoltage computed tomography (kV-CT) images which are disfigured by patients’ metal prostheses. By generating a hybrid sinogram that is a combination of kV and megavoltage (MV) projection data, the authors suggest a novel metal artifact-reduction (MAR) method that retains the image quality to match that of kV-CT and simultaneously restores the information of metal prostheses lost due to photon starvation. Methods: CT projection data contain information about attenuation coefficients and the total length of the attenuation. By normalizing raw kV projections with their own total lengths of attenuation, mean attenuation projections were obtained. In the same manner, mean density projections of MV-CT were obtained by the normalization of MV projections resulting from the forward projection of density-calibrated MV-CT images with the geometric parameters of the kV-CT device. To generate the hybrid sinogram, metal-affected signals of the kV sinogram were identified and replaced by the corresponding signals of the MV sinogram following a density calibration step with kV data. Filtered backprojection was implemented to reconstruct the hybrid CT image. To validate the authors’ approach, they simulated four different scenarios for three heads and one pelvis using metallic rod inserts within a cylindrical phantom. Five inserts describing human body elements were also included in the phantom. The authors compared the image qualities among the kV, MV, and hybrid CT images by measuring the contrast-to-noise ratio (CNR), the signal-to-noise ratio (SNR), the densities of all inserts, and the spatial resolution. In addition, the MAR performance was compared among three existing MAR methods and the authors’ hybrid method. Finally, for clinical trials, the authors produced hybrid images of three patients having dental metal prostheses to compare their MAR performances with those of the kV, MV, and three existing MAR methods. Results: The authors compared the image quality and MAR performance of the hybrid method with those of other imaging modalities and the three MAR methods, respectively. The total measured mean of the CNR (SNR) values for the nonmetal inserts was determined to be 14.3 (35.3), 15.3 (37.8), and 25.5 (64.3) for the kV, MV, and hybrid images, respectively, and the spatial resolutions of the hybrid images were similar to those of the kV images. The measured densities of the metal and nonmetal inserts in the hybrid images were in good agreement with their true densities, except in cases of extremely low densities, such as air and lung. Using the hybrid method, major streak artifacts were suitably removed and no secondary artifacts were introduced in the resultant image. In clinical trials, the authors verified that kV and MV projections were successfully combined and turned into the resultant hybrid image with high image contrast, accurate metal information, and few metal artifacts. The hybrid method also outperformed the three existing MAR methods with regard to metal information restoration and secondary artifact prevention. Conclusions: The authors have shown that the hybrid method can restore the overall image quality of kV-CT disfigured by severe metal artifacts and restore the information of metal prostheses lost due to photon starvation. The hybrid images may allow for the improved delineation of structures of interest and accurate dose calculations for radiation treatment planning for patients with metal prostheses.

  1. RF Modeling of a Helical Kicker for Fast Chopping

    SciTech Connect

    Awida, Mohamed; Chen, Alex; Khabiboulline, Timergali; Saewert, Gregory; Yakovlev, Vyacheslav

    2015-06-01

    High intensity proton particle accelerators that supports several simultaneous physics experiments requires sharing the beam. A bunch by bunch beam chopper system located after the Radio Frequency Quadrupole (RFQ) is required in this case to structure the beam in the proper bunch format required by the several experiments. The unused beam will need to be kicked out of the beam path and is disposed in a beam dumb. In this paper, we report on the RF modeling results of a proposed helical kicker. Two beam kickers constitutes the proposed chopper. The beam sequence is formed by kicking in or out the beam bunches from the streamline. The chopper was developed for Project X Injection Experiment (PXIE).

  2. Epicyclic Helical Channels for Parametric Resonance Ionization Cooling

    SciTech Connect

    Andrei Afanaciev, Alex Bogacz, Yaroslav Derbenev, Kevin Beard, Valentin Ivanov, Rolland Johnson, Guimei Wang, Katsuya Yonehara

    2009-05-01

    In order to achieve cooling of muons in addition to 6D helical cooling channel (HCC) [1], we develop a technique based on a parametric resonance. The use of parametric resonances requires alternating dispersion, minimized at locations of thin absorbers, but maximized in between in order to compensate for chromatic aberrations [2]. These solutions can be combined in an Epicyclic Helical Cooling Channel (EHCC) that meets requirements of alternating dispersion of beam periodic orbit with best conditions for maintenance of stable beam transport in a continuous solenoid-type field [3]. We discuss here basic features and new simulation results for EHCC.

  3. The Helicity of Vortex Filaments.

    NASA Astrophysics Data System (ADS)

    Petrich, Dean; Tao, Louis

    1996-03-01

    The helicity, defined by H = int dV v \\cdot nabla × v, is a conserved quantity of the three-dimensional Euler equations. Traditionally the helicity has been viewed as a measure of the topology of vortex lines, but it is shown that the helicity measures their geometry as well as their topology (J.D. Bekenstein, Physics Letters B), 282 (1992) 44-49.. The existence of helicity-preserving reconnection events is discussed.

  4. Helicity and celestial magnetism

    NASA Astrophysics Data System (ADS)

    Moffatt, H. K.

    2016-06-01

    This informal article discusses the central role of magnetic and kinetic helicity in relation to the evolution of magnetic fields in geophysical and astrophysical contexts. It is argued that the very existence of magnetic fields of the intensity and scale observed is attributable in large part to the chirality of the background turbulence or random-wave field of flow, the simplest measure of this chirality being non-vanishing helicity. Such flows are responsible for the generation of large-scale magnetic fields which themselves exhibit magnetic helicity. In the geophysical context, the turbulence has a `magnetostrophic' character in which the force balance is primarily that between buoyancy forces, Coriolis forces and Lorentz forces associated with the dynamo-generated magnetic field; the dominant nonlinearity here arises from the convective transport of buoyant elements erupting from the `mushy zone' at the inner core boundary. At the opposite extreme, in a highly conducting low-density plasma, the near-invariance of magnetic field topology (and of associated helicity) presents the challenging problem of `magnetic relaxation under topological constraints', of central importance both in astrophysical contexts and in controlled-fusion plasma dynamics. These problems are reviewed and open issues, particularly concerning saturation mechanisms, are reconsidered.

  5. Helical dipole partial Siberian snake for the AGS

    NASA Astrophysics Data System (ADS)

    Takano, J.; Ahrens, L. A.; Alforque, R.; Bai, M.; Brown, K.; Courant, E. D.; Ganetis, G.; Gardner, C. J.; Glenn, J. W.; Hattori, T.; Huang, H.; Jain, A.; Luccio, A. U.; MacKay, W. W.; Okamura, M.; Roser, T.; Tsoupas, N.; Tepikian, S.; Tuozzolo, J.; Wood, J.; Zelenski, A.; Zeno, K.

    2006-11-01

    Overcoming depolarization resonances in medium class synchrotrons (3 to 50 GeV) is one of the key issues in accelerating a highly polarized proton beam up to very high energies. Since such synchrotrons, including the Alternating Gradient Synchrotron (AGS) and the J-PARC Main Ring, generally do not have sufficiently long straight sections to accommodate full Siberian snakes with reasonable beam excursions, the practical solution is to use partial Siberian snakes that rotate the particle spin about a horizontal axis by a fraction of 180 degrees. For the AGS, we designed and installed a new partial Siberian snake consisting of a helical dipole magnet with a double pitch structure. The helical structure reduced the amount of transverse coupling as compared to that achieved by the previous solenoidal partial snake. This coupling led to partial depolarization at certain energies from horizontal betatron oscillations. The helical magnetic field in the snake magnet was calculated using a 3D magnetic field code TOSCA, and was optimized by segmenting the helical pitch and varying the lengths of the segments. Fabrication errors were checked and verified to be within required tolerances. Finally, the transverse field was measured by rotating harmonic coils. After installation, we achieved a 37.5% improvement in polarization - from 40% with the old solenoid to 55% with the new helical snake, thereby demonstrating that the helical partial snake is an effective device to suppress depolarization resonances in medium-sized synchrotrons.

  6. SU-E-T-374: Sensitivity of ArcCHECK to Tomotherapy Delivery Errors: Dependence On Analysis Technique

    SciTech Connect

    Templeton, A; Chu, J; Turian, J

    2014-06-01

    Purpose: ArcCHECK (Sun Nuclear) is a cylindrical diode array detector allowing three-dimensional sampling of dose, particularly useful in treatment delivery QA of helical tomotherapy. Gamma passing rate is a common method of analyzing results from diode arrays, but is less intuitive in 3D with complex measured dose distributions. This study explores the sensitivity of gamma passing rate to choice of analysis technique in the context of its ability to detect errors introduced into the treatment delivery. Methods: Nine treatment plans were altered to introduce errors in: couch speed, gantry/sonogram synchronization, and leaf open time. Each plan was then delivered to ArcCHECK in each of the following arrangements: “offset,” when the high dose area of the plan is delivered to the side of the phantom so that some diode measurements will be on the order of the prescription dose, and “centered,” when the high dose is in the center of the phantom where an ion chamber measurement may be acquired, but the diode measurements are in the mid to low-dose region at the periphery of the plan. Gamma analysis was performed at 3%/3mm tolerance and both global and local gamma criteria. The threshold of detectability for each error type was calculated as the magnitude at which the gamma passing rate drops below 90%. Results: Global gamma criteria reduced the sensitivity in the offset arrangement (from 2.3% to 4.5%, 8° to 21°, and 3ms to 8ms for couch-speed decrease, gantry-error, and leaf-opening increase, respectively). The centered arrangement detected changes at 3.3%, 5°, and 4ms with smaller variation. Conclusion: Each arrangement has advantages; offsetting allows more sampling of the higher dose region, while centering allows an ion chamber measurement and potentially better use of tools such as 3DVH, at the cost of positioning more of the diodes in the sometimes noisy mid-dose region.

  7. Poster — Thur Eve — 57: Evaluation of laryngeal mucosal dose with conventional linac and TomoTherapy

    SciTech Connect

    Nusrat, H; Lekx, K; Eapen, L

    2014-08-15

    The purpose of this study was to examine whether or not underdosing occurs in the mucosal layer during treatment of glottis cancer. A larynx phantom was produced and regions at risk of recurrence due to suspected underdosing were identified and wells drilled into the phantom for flush placement of TLDs. Seven interest points were chosen. CT simulation was completed prior to the wells being drilled, and again afterwards with the TLD locations indicated using BBs. Treatment plans created for this investigation included: 3DCRT using Elekta-XiO (n=9) and VMAT created using Elekta-Monaco (n=9), both delivered on an Elekta linac; standard TomoTherapy plan (n=11) and a directionally blocked TomoTherapy plan to approximate a 3D-conformal approach (n=5). Imaging dose during TomoTherapy deliveries was accounted for. The average TLD result at each interest point was compared to the planned value using a paired t-test. There was no significant difference between the planned and measured 3DCRT dose (268.9 vs. 267.0 cGy, respectively; p>0.05). Similarly, the planned and measured TomoTherapy treatment did not show any significant differences (271.7 vs 269.7 cGy; p>0.05). In the blocked TomoTherapy plan, significant overdosing was seen (274.5 vs 294.9 cGy; p<0.05) and underdosing was not seen in the VMAT treatment (303.5 vs 321.8 cGy; p>0.05). Further investigation is ongoing to ensure appropriate normalization of results and to investigate the overdosing noted with the blocked TomoTherapy plan. Results from this study suggest that significant underdosing does not occur in the conventional treatment of early glottic cancer using 6MV photons.

  8. Helically Coiled Graphene Nanoribbons.

    PubMed

    Daigle, Maxime; Miao, Dandan; Lucotti, Andrea; Tommasini, Matteo; Morin, Jean-François

    2017-03-07

    Graphene is a zero-gap, semiconducting 2D material that exhibits outstanding charge-transport properties. One way to open a band gap and make graphene useful as a semiconducting material is to confine the electron delocalization in one dimension through the preparation of graphene nanoribbons (GNR). Although several methods have been reported so far, solution-phase, bottom-up synthesis is the most promising in terms of structural precision and large-scale production. Herein, we report the synthesis of a well-defined, helically coiled GNR from a polychlorinated poly(m-phenylene) through a regioselective photochemical cyclodehydrochlorination (CDHC) reaction. The structure of the helical GNR was confirmed by (1) H NMR, FT-IR, XPS, TEM, and Raman spectroscopy. This Riemann surface-like GNR has a band gap of 2.15 eV and is highly emissive in the visible region, both in solution and the solid state.

  9. Analysis of Helical Waveguide.

    DTIC Science & Technology

    1985-12-23

    tube Efficiency Helix structure Backward wave oscillation Gain 19. ABSTRACT (Continue on reverse if necessary and identofy by block number) The...4,vailabilitY CCdes -vai aidIorDist spec a ." iii "- -. .5- S.. . ANALYSIS OF HELICAL WAVEGUIDE I. INTRODUCTION High power (- 10 kW) and broadband ...sys- tems. The frequency range of interest is 60-100 GHz. In this frequency range, the conventional slow wave circuits such as klystrons and TWTs have

  10. Helically linked mirror arrangement

    SciTech Connect

    Ranjan, P.

    1986-08-01

    A scheme is described for helical linking of mirror sections, which endeavors to combine the better features of toroidal and mirror devices by eliminating the longitudinal loss of mirror machines, having moderately high average ..beta.. and steady state operation. This scheme is aimed at a device, with closed magnetic surfaces having rotational transform for equilibrium, one or more axisymmetric straight sections for reduced radial loss, a simple geometrical axis for the links and an overall positive magnetic well depth for stability. We start by describing several other attempts at linking of mirror sections, made both in the past and the present. Then a description of our helically linked mirror scheme is given. This example has three identical straight sections connected by three sections having helical geometric axes. A theoretical analysis of the magnetic field and single-particle orbits in them leads to the conclusion that most of the passing particles would be confined in the device and they would have orbits independent of pitch angle under certain conditions. Numerical results are presented, which agree well with the theoretical results as far as passing particle orbits are concerned.

  11. Magnetic helicity in astrophysical dynamos

    NASA Astrophysics Data System (ADS)

    Candelaresi, Simon

    2012-09-01

    The broad variety of ways in which magnetic helicity affects astrophysical systems, in particular dynamos, is discussed. The so-called alpha effect is responsible for the growth of large-scale magnetic fields. The conservation of magnetic helicity, however, quenches the alpha effect, in particular for high magnetic Reynolds numbers. Predictions from mean-field theories state particular power law behavior of the saturation strength of the mean fields, which we confirm in direct numerical simulations. The loss of magnetic helicity in the form of fluxes can alleviate the quenching effect, which means that large-scale dynamo action is regained. Physically speaking, galactic winds or coronal mass ejections can have fundamental effects on the amplification of galactic and solar magnetic fields. The gauge dependence of magnetic helicity is shown to play no effect in the steady state where the fluxes are represented in form of gauge-independent quantities. This we demonstrate in the Weyl-, resistive- and pseudo Lorentz-gauge. Magnetic helicity transport, however, is strongly affected by the gauge choice. For instance the advecto-resistive gauge is more efficient in transporting magnetic helicity into small scales, which results in a distinct spectrum compared to the resistive gauge. The topological interpretation of helicity as linking of field lines is tested with respect to the realizability condition, which imposes a lower bound for the spectral magnetic energy in presence of magnetic helicity. It turns out that the actual linking does not affect the relaxation process, unlike the magnetic helicity content. Since magnetic helicity is not the only topological variable, I conduct a search for possible others, in particular for non-helical structures. From this search I conclude that helicity is most of the time the dominant restriction in field line relaxation. Nevertheless, not all numerical relaxation experiments can be described by the conservation of magnetic helicity

  12. Fluence field modulated CT on a clinical TomoTherapy radiation therapy machine

    NASA Astrophysics Data System (ADS)

    Szczykutowicz, Timothy P.; Hermus, James

    2015-03-01

    Purpose: The multi-leaf collimator (MLC) assembly present on TomoTherapy (Accuray, Madison WI) radiation therapy (RT) and mega voltage CT machines is well suited to perform fluence field modulated CT (FFMCT). In addition, there is a demand in the RT environment for FFMCT imaging techniques, specifically volume of interest (VOI) imaging. Methods: A clinical TomoTherapy machine was programmed to deliver 30% imaging dose outside predefined VOIs. Four different size ROIs were placed at varying distances from isocenter. Projections intersecting the VOI received "full dose" while those not intersecting the VOI received 30% of the dose (i.e. the incident fluence for non VOI projections was 30% of the incident fluence for projections intersecting the VOI). Additional scans without fluence field modulation were acquired at "full" and 30% dose. The noise (pixel standard deviation) was measured inside the VOI region and compared between the three scans. Results: The VOI-FFMCT technique produced an image noise 1.09, 1.05, 1.05, and 1.21 times higher than the "full dose" scan for ROI sizes of 10 cm, 13 cm, 10 cm, and 6 cm respectively within the VOI region. Conclusions: Noise levels can be almost unchanged within clinically relevant VOIs sizes for RT applications while the integral imaging dose to the patient can be decreased, and/or the image quality in RT can be dramatically increased with no change in dose relative to non-FFMCT RT imaging. The ability to shift dose away from regions unimportant for clinical evaluation in order to improve image quality or reduce imaging dose has been demonstrated. This paper demonstrates that FFMCT can be performed using the MLC on a clinical TomoTherapy machine for the first time.

  13. Far-field measurements of vortex beams interacting with nanoholes

    PubMed Central

    Zambrana-Puyalto, Xavier; Vidal, Xavier; Fernandez-Corbaton, Ivan; Molina-Terriza, Gabriel

    2016-01-01

    We measure the far-field intensity of vortex beams going through nanoholes. The process is analyzed in terms of helicity and total angular momentum. It is seen that the total angular momentum is preserved in the process, and helicity is not. We compute the ratio between the two transmitted helicity components, γm,p. We observe that this ratio is highly dependent on the helicity (p) and the angular momentum (m) of the incident vortex beam in consideration. Due to the mirror symmetry of the nanoholes, we are able to relate the transmission properties of vortex beams with a certain helicity and angular momentum, with the ones with opposite helicity and angular momentum. Interestingly, vortex beams enhance the γm,p ratio as compared to those obtained by Gaussian beams. PMID:26911547

  14. Field of a helical Siberian Snake

    SciTech Connect

    Luccio, A.

    1995-02-01

    To preserve the spin polarization of a beam of high energy protons in a circular accelerator, magnets with periodic magnetic field, called Siberian Snakes are being used. Recently, it was proposed to build Siberian Snakes with superconducting helical dipoles. In a helical, or twisted dipole, the magnetic field is perpendicular to the axis of the helix and rotates around it as one proceeds along the magnet. In an engineering study of a 4 Tesla helical snake, the coil geometry is derived, by twisting, from the geometry of a cosine superconducting dipole. While waiting for magnetic measurement data on such a prototype, an analytical expression for the field of the helice is important, to calculate the particle trajectories and the spin precession in the helix. This model will also allow to determine the optical characteristics of the snake, as an insertion in the lattice of the accelerator. In particular, one can calculate the integrated multipoles through the magnet and the equivalent transfer matrix. An expression for the field in the helix body, i.e., excluding the fringe field was given in a classical paper. An alternate expression can be found by elaborating on the treatment of the field of a transverse wiggler obtained under the rather general conditions that the variables are separable. This expression exactly satisfies Maxwell`s div and curl equations for a stationary field, {del} {center_dot} B = 0, {del} x B = 0. This approach is useful in that it will allow one to use much of the work already done on the problem of inserting wigglers and undulators in the lattice of a circular accelerator.

  15. Prediction of buried helices in multispan alpha helical membrane proteins.

    PubMed

    Adamian, Larisa; Liang, Jie

    2006-04-01

    Analysis of a database of structures of membrane proteins shows that membrane proteins composed of 10 or more transmembrane (TM) helices often contain buried helices that are inaccessible to phospholipids. We introduce a method for identifying TM helices that are least phospholipid accessible and for prediction of fully buried TM helices in membrane proteins from sequence information alone. Our method is based on the calculation of residue lipophilicity and evolutionary conservation. Given that the number of buried helices in a membrane protein is known, our method achieves an accuracy of 78% and a Matthew's correlation coefficient of 0.68. A server for this tool (RANTS) is available online at http://gila.bioengr.uic.edu/lab/.

  16. Helical phases in superconductors

    NASA Astrophysics Data System (ADS)

    Sandhu, Raminder P. Kaur

    In conventional superconductors, the Cooper pairs are formed from quasiparticles with opposite momentum and spins because of the degeneracy of the quasiparticles under time reversal and inversion. The absence of any of these symmetries will have pronounced effects on superconducting states. Time reversal symmetry can be broken in the presence of magnetic impurities or by the application of a magnetic field. Similarly, the dislocation of crystal ions from their higher symmetric positions can cause broken inversion symmetry. We studied the effects of broken time reversal and inversion symmetries on unconventional superconductors, such as high temperature cuprates, Sr2RuO 4, and CePt3Si. In the cuprates, the superconducting state exists near the antiferromagnetic order. Sr2RuO4 and CePt3Si do not have spatial inversion, and the superconducting states coexist with magnetic order. In cuprates, the broken time reversal symmetry has been reported in the pseudogap phase which will effect the d-wave superconducting state of underdoped regime. On the basis of symmetry analysis we found that a mixture of spin-singlet and -triplet state, d+ip, which is shown to give rise to a helical superconducting phase. Consequences of this d+ip state on Josephson experiments are also discussed. Sr2RuO 4 is known to be another broken time reversal superconductor with spin triplet superconductivity. The widely believed superconducting state, the chiral p wave state, has been extensively studied through Ginzburg Landau theory, but the predictions for this state contradict some experimental observations like anisotropy in the upper critical field, and the existence of a second vortex state. We have formalize quasiclassical theory to find the origin of these contradictions, and also extended the theory to study other possible super-conducting states. Surprisingly, we find that a superconducting state corresponding to freely rotating in-plane d-vector explains the existing experimental results

  17. The validation of tomotherapy dose calculations in low-density lung media.

    PubMed

    Chaudhari, Summer R; Pechenaya, Olga L; Goddu, S Murty; Mutic, Sasa; Rangaraj, Dharanipathy; Bradley, Jeffrey D; Low, Daniel

    2009-04-21

    The dose-calculation accuracy of the tomotherapy Hi-Art II(R) (Tomotherapy, Inc., Madison, WI) treatment planning system (TPS) in the presence of low-density lung media was investigated. In this evaluation, a custom-designed heterogeneous phantom mimicking the mediastinum geometry was used. Gammex LN300 and balsa wood were selected as two lung-equivalent materials with different densities. Film analysis and ionization chamber measurements were performed. Treatment plans for esophageal cancers were used in the evaluation. The agreement between the dose calculated by the TPS and the dose measured via ionization chambers was, in most cases, within 0.8%. Gamma analysis using 3% and 3 mm criteria for radiochromic film dosimetry showed that 98% and 95% of the measured dose distribution had passing gamma values < or =1 for LN300 and balsa wood, respectively. For a homogeneous water-equivalent phantom, 95% of the points passed the gamma test. It was found that for the interface between the low-density medium and water-equivalent medium, the TPS calculated the dose distribution within acceptable limits. The phantom developed for this work enabled detailed quality-assurance testing under realistic conditions with heterogeneous media.

  18. Tomotherapy dose distribution verification using MAGIC-f polymer gel dosimetry

    SciTech Connect

    Pavoni, J. F.; Pike, T. L.; Snow, J.; DeWerd, L.; Baffa, O.

    2012-05-15

    Purpose: This paper presents the application of MAGIC-f gel in a three-dimensional dose distribution measurement and its ability to accurately measure the dose distribution from a tomotherapy unit. Methods: A prostate intensity-modulated radiation therapy (IMRT) irradiation was simulated in the gel phantom and the treatment was delivered by a TomoTherapy equipment. Dose distribution was evaluated by the R2 distribution measured in magnetic resonance imaging. Results: A high similarity was found by overlapping of isodoses of the dose distribution measured with the gel and expected by the treatment planning system (TPS). Another analysis was done by comparing the relative absorbed dose profiles in the measured and in the expected dose distributions extracted along indicated lines of the volume and the results were also in agreement. The gamma index analysis was also applied to the data and a high pass rate was achieved (88.4% for analysis using 3%/3 mm and of 96.5% using 4%/4 mm). The real three-dimensional analysis compared the dose-volume histograms measured for the planning volumes and expected by the treatment planning, being the results also in good agreement by the overlapping of the curves. Conclusions: These results show that MAGIC-f gel is a promise for tridimensional dose distribution measurements.

  19. Radiation Necrosis Secondary to Trigeminal Nerve TomoTherapy: A Cautionary Case Study

    PubMed Central

    Montoure, Andrew; Zaidi, Hasan; Sheehy, John P; Shetter, Andrew G

    2015-01-01

    New radiation delivery modalities have recently challenged Gamma Knife surgery as the historic gold standard in the treatment of trigeminal neuralgia (TN). TomoTherapy, a relative newcomer, has been approved by the U.S. FDA for various intracranial pathologies but is currently off label for the treatment of TN. A 73-year-old female presented with gait instability, intermittent headaches, and confusion. She was treated with TomoTherapy for refractory TN at an outside facility, which failed to reduce her symptoms. Magnetic resonance imaging demonstrated a lesion in the right mesial temporal lobe. A standard right anterior temporal lobectomy was performed and the final pathological report was notable for necrosis, gliosis, and edema consistent with a remote radiation injury. The patient improved postoperatively, but at her two-year follow up, she continued to have persistent bilateral TN and new onset seizures. Imaging revealed no new mass in the resection field. Stereotactic radiosurgery (SRS) is an evolving field with broadening indications, which makes it ever more important for physicians to be aware of differences between various SRS modalities. This case report highlights a cautionary example, and emphasizes the need for a more systematic evaluation of novel SRS methods before clinical application. PMID:26180667

  20. Helical Nanofilament Phases

    SciTech Connect

    L Hough; H Jung; D Kruerke; M Heberling; M Nakata; C Jones; D Chen; D Link; N Clark; et al.

    2011-12-31

    In the formation of chiral crystals, the tendency for twist in the orientation of neighboring molecules is incompatible with ordering into a lattice: Twist is expelled from planar layers at the expense of local strain. We report the ordered state of a neat material in which a local chiral structure is expressed as twisted layers, a state made possible by spatial limitation of layering to a periodic array of nanoscale filaments. Although made of achiral molecules, the layers in these filaments are twisted and rigorously homochiral - a broken symmetry. The precise structural definition achieved in filament self-assembly enables collective organization into arrays in which an additional broken symmetry - the appearance of macroscopic coherence of the filament twist-produces a liquid crystal phase of helically precessing layers.

  1. Mixing in Helical Pipes

    NASA Astrophysics Data System (ADS)

    Gratton, Michael B.; Bernoff, Andrew J.

    2001-11-01

    We consider advection and diffusion of a passive scalar in a helical pipe. By assuming that the curvature and torsion are small (equivalent to small Dean number) and the Reynolds number is moderate, we can use a closed form approximation, due to Dean (1927) and Germano (1982), for the induced recirculation. We investigate the problem numerically using a split-step particle method for a variety of localized initial conditions. The problem is governed by two parameters: a nondimensional diffusion constant D (typically small), and the scaled ratio of torsion to curvature λ. At small times, the longitudinal width of the particle distribution, σ, is governed by diffusive effects (σ ∝ √Dt). At large times, Taylor diffusion dominates (σ ∝ √t/D). However, at intermediate times, a ballistic region exists where the width spreads linearly, as postulated by Mezic & Wiggins (1994). We also discuss how these various behaviors scale with the parameters D and λ.

  2. Helical Emg Effective Resistance

    NASA Astrophysics Data System (ADS)

    Chernyshev, V. K.; Zharinov, E. I.; Busin, V. N.; Grinevich, B. E.; Sokolova, O. V.; Smirnova, G. N.; Klimushkin, K. N.

    2004-11-01

    The efficiency of explosive-magnetic system operation depends on the magnetic flux losses produced under circuit deformation. Losses primarily arise from circuit ohmic resistance and flux pocketing due to the disturbed continuity of helix wires deformation. This is because of technological faults in fabrication and potential electric breakdowns resulting from the voltage overload in the generator circuit. Since it is rather difficult to identify each type of loss mentioned, all soles are expressed as the effective resistance of the circuit, Reff. The EMG-160 multi-sectional helical generator with a 760 mm long helix having an inner diameter of 160 mm is considered as an example. EMG-160 initial conductance was 34 μH and the final inductance was 25 nH. The effective resistance of the circuit was calculated for this experiment. The method of determining the effective resistance allows estimation of EMG efficiency at all stages of generator operation.

  3. Helical Siberian snakes

    SciTech Connect

    Courant, E.D.

    1988-01-01

    To eliminate spin resonances in circular accelerators ''Siberian Snakes'' may be inserted at one or more azimuths in such a way that the overall spin precession tune ..nu../sub s/ equals 1/2. A snake is a sequence of horizontal and vertical deflection magnets whose overall effect is to rotate the spin by ..pi.. about an axis in the plane of the orbit, either longitudinal or transverse or any angle /var phi/ in between. At the same time the magnets of the snake should be arranged so as to produce zero net deflection and displacement of the particle orbit. We investigate here how the orbit deflections can be made small by using helical deflecting magnets rather than discrete horizontal and vertical deflectors.

  4. The Advanced Helical Generator

    SciTech Connect

    Reisman, D B; Javedani, J B; Ellsworth, G F; Kuklo, R M; Goerz, D A; White, A D; Tallerico, L J; Gidding, D A; Murphy, M J; Chase, J B

    2009-10-26

    A high explosive pulsed power (HEPP) generator called the Advanced Helical Generator (AHG) has been designed, built, and successfully tested. The AHG incorporates design principles of voltage and current management to obtain a high current and energy gain. Its design was facilitated by the use of modern modeling tools as well as high precision manufacture. The result was a first-shot success. The AHG delivered 16 Mega-Amperes of current and 11 Mega-Joules of energy to a quasi-static 80 nH inductive load. A current gain of 154 times was obtained with a peak exponential rise time of 20 {micro}s. We will describe in detail the design and testing of the AHG.

  5. Simulation of a Helical Channel using GEANT4

    SciTech Connect

    Elvira, V. D.; Lebrun, P.; Spentzouris, P.

    2001-02-01

    We present a simulation of a 72 m long cooling channel proposed by V. Balbekov based on the helical cooling concept developed by Ya. Derbenev. LiH wedge absorbers provide the energy loss mechanism and 201 MHz cavities are used for re-acceleration. They are placed inside a main solenoidal field to focus the beam. A helical field with an amplitude of 0.3 T and a period of 1.8 m provides momentum dispersion for emittance exchange.The simulation is performed using GEANT4. The total fractional transmission is 0.85, and the transverse, longitudinal, and 3-D cooling factors are 3.75, 2.27, and 14.61, respectively. Some version of this helical channel could eventually be used to replace the first section of the double flip channel to keep the longitudinal emittance under control and increase transmission. Although this is an interesting option, the technical challenges are still significant.

  6. Beam Profile Monitor With Accurate Horizontal And Vertical Beam Profiles

    DOEpatents

    Havener, Charles C [Knoxville, TN; Al-Rejoub, Riad [Oak Ridge, TN

    2005-12-26

    A widely used scanner device that rotates a single helically shaped wire probe in and out of a particle beam at different beamline positions to give a pair of mutually perpendicular beam profiles is modified by the addition of a second wire probe. As a result, a pair of mutually perpendicular beam profiles is obtained at a first beamline position, and a second pair of mutually perpendicular beam profiles is obtained at a second beamline position. The simple modification not only provides more accurate beam profiles, but also provides a measurement of the beam divergence and quality in a single compact device.

  7. Plasma driven by helical electrodes

    NASA Astrophysics Data System (ADS)

    Akcay, Cihan; Finn, John; Nebel, Richard; Barnes, Daniel

    2016-10-01

    A novel plasma state, obtained by applying a helical voltage at the wall with a uniform axial magnetic field, is studied by means of zero-pressure resistive MHD simulations in a periodic cylinder. The radial magnetic field at the wall is taken to be zero. For a small helical electrode voltage, the helical perturbation in the plasma is small and localized to the edge. Beyond a critical electrode voltage, there is a bifurcation to the newly discovered state, which is a single-helicity Ohmic equilibrium with the same helicity as the electrodes, i.e., the fields depend only on radius and mθ - nφ , where θ and φ = z / R are the poloidal and toroidal angles. For electrostatic driving with m = 1 , the mean magnetic field (m = n = 0) has field line safety factor q(r) equal to the pitch of the electrodes m / n = 1 / n except near the edge, where it monotonically increases an amount of order unity. The plasma is force-free in the interior. Near the edge, however, the current crosses the field lines to enter and exit through the helical electrodes. A large helical plasma flow related Pfirsch-Schlüter-like currents exist in this edge vicinity. Applications to current drive in tokamaks, as well as to straight plasmas with endcap electrodes are discussed.

  8. Twist Helicity in Classical Vortices

    NASA Astrophysics Data System (ADS)

    Scheeler, Martin W.; Kedia, Hridesh; Kleckner, Dustin; Irvine, William T. M.

    2015-11-01

    Recent experimental work has demonstrated that a partial measure of fluid Helicity (the sum of linking and writhing of vortex tubes) is conserved even as those vortices undergo topology changing reconnections. Measuring the total Helicity, however, requires additional information about how the vortex lines are locally twisted inside the vortex core. To bridge this gap, we have developed a novel technique for experimentally measuring twist Helicity. Using this method, we are able to measure the production and eventual decay of twist for a variety of vortex evolutions. Remarkably, we observe twist dynamics capable of conserving total Helicity even in the presence of rapidly changing writhe. This work was supported by the NSF MRSEC shared facilities at the University of Chicago (DMR-0820054) and an NSF CAREER award (DMR-1351506). W.T.M.I. further acknowledges support from the A.P. Sloan Foundation and the Packard Foundation.

  9. Magnetic Helicity and Planetary Dynamos

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.

    2012-01-01

    A model planetary dynamo based on the Boussinesq approximation along with homogeneous boundary conditions is considered. A statistical theory describing a large-scale MHD dynamo is found, in which magnetic helicity is the critical parameter

  10. Helicity multiplexed broadband metasurface holograms

    PubMed Central

    Wen, Dandan; Yue, Fuyong; Li, Guixin; Zheng, Guoxing; Chan, Kinlong; Chen, Shumei; Chen, Ming; Li, King Fai; Wong, Polis Wing Han; Cheah, Kok Wai; Yue Bun Pun, Edwin; Zhang, Shuang; Chen, Xianzhong

    2015-01-01

    Metasurfaces are engineered interfaces that contain a thin layer of plasmonic or dielectric nanostructures capable of manipulating light in a desirable manner. Advances in metasurfaces have led to various practical applications ranging from lensing to holography. Metasurface holograms that can be switched by the polarization state of incident light have been demonstrated for achieving polarization multiplexed functionalities. However, practical application of these devices has been limited by their capability for achieving high efficiency and high image quality. Here we experimentally demonstrate a helicity multiplexed metasurface hologram with high efficiency and good image fidelity over a broad range of frequencies. The metasurface hologram features the combination of two sets of hologram patterns operating with opposite incident helicities. Two symmetrically distributed off-axis images are interchangeable by controlling the helicity of the input light. The demonstrated helicity multiplexed metasurface hologram with its high performance opens avenues for future applications with functionality switchable optical devices. PMID:26354497

  11. Tunable Helical Origami

    NASA Astrophysics Data System (ADS)

    Chen, Zi; Dai, Eric; Zheng, Huang

    2014-03-01

    Origami, the Japanese art of paper folding, is traditionally viewed as an amusing pastime and medium of artistic expression. However, in recent years, origami has begun to inspire innovations in science and engineering. For example, K. Miura led the study of a paper folding pattern in regards to deployment of solar panels to outer space, resulting in more efficient packing and unpacking of the solar panels into tightly constrained spaces. In this work, we study the geometric and mechanical properties of a twisting origami pattern. The pattern created by the fold exhibits several interesting properties, including rigid foldibility, and finely tunable helical coiling, with control over pitch, radius, and handedness of the helix. In addition, the pattern closely mimics the twist buckling patterns shown by thin materials, for example, a mobius strip. In our work, we relate the six parameters of the twisting origami pattern to generate a fully tunable graphical model of the fold. In addition, we demonstrate that the morphogenesis of such folding pattern can be modeled through finite element analysis. We hope our research into the diagonal fold brings insight into the potential scientific and engineering applications of origami and spark further research into how the traditional paper art can be applied as a simple, inexpensive model for complex problems.

  12. An efficient procedure for tomotherapy treatment plan verification using the on-board detector.

    PubMed

    Pisaturo, O; Miéville, F; Tercier, P-A; Allal, A S

    2015-02-21

    In this work, a fast and simple procedure for tomotherapy treatment plan verification using the on-board detector (OBD) has been developed. This procedure allows verification of plans with static and dynamic jaws (TomoEDGE). A convolution-based calculation model has been derived in order to link the leaf control sinogram from the treatment planning system to the data acquired by the OBD during a static couch procedure. The convolution kernel has been optimized using simple plans calculated in the Tomotherapy Cheese phantom. The optimal kernel has been found to be a lorentzian function, whose parameter Γ is 0.186 for the 1 cm jaw opening, 0.232 for the 2.5 cm jaw opening and 0.373 for the 5 cm jaw opening. The evaluation has been performed with a γ-index analysis. The dose criterion was 3% of the 95th percentile of the dose distribution and the distance-to-agreement criterion is 2 mm. In order to validate the procedure, it has been applied to around 50 clinical treatment plans, which had already been validated by the Delta4 phantom (Scandidos, Sweden). 96% of the tested plans have passed the criteria. Concerning the other 4%, significant discrepancies between the leaf pattern in the leaf control sinogram and the OBD data have been shown, which might be due to differences in the leaf open time. This corresponds also to a higher sensitivity of this method over the Delta4, adding the possibility of better monitoring the treatment delivery.

  13. An efficient procedure for tomotherapy treatment plan verification using the on-board detector

    NASA Astrophysics Data System (ADS)

    Pisaturo, O.; Miéville, F.; Tercier, P.-A.; Allal, A. S.

    2015-02-01

    In this work, a fast and simple procedure for tomotherapy treatment plan verification using the on-board detector (OBD) has been developed. This procedure allows verification of plans with static and dynamic jaws (TomoEDGE). A convolution-based calculation model has been derived in order to link the leaf control sinogram from the treatment planning system to the data acquired by the OBD during a static couch procedure. The convolution kernel has been optimized using simple plans calculated in the Tomotherapy Cheese phantom. The optimal kernel has been found to be a lorentzian function, whose parameter Γ is 0.186 for the 1 cm jaw opening, 0.232 for the 2.5 cm jaw opening and 0.373 for the 5 cm jaw opening. The evaluation has been performed with a γ-index analysis. The dose criterion was 3% of the 95th percentile of the dose distribution and the distance-to-agreement criterion is 2 mm. In order to validate the procedure, it has been applied to around 50 clinical treatment plans, which had already been validated by the Delta4 phantom (Scandidos, Sweden). 96% of the tested plans have passed the criteria. Concerning the other 4%, significant discrepancies between the leaf pattern in the leaf control sinogram and the OBD data have been shown, which might be due to differences in the leaf open time. This corresponds also to a higher sensitivity of this method over the Delta4, adding the possibility of better monitoring the treatment delivery.

  14. Recalculation of dose for each fraction of treatment on TomoTherapy

    PubMed Central

    Romanchikova, Marina; Harrison, Karl; Parker, Michael A; Bates, Amy M; Scaife, Jessica E; Sutcliffe, Michael PF; Burnet, Neil G

    2016-01-01

    Objective: The VoxTox study, linking delivered dose to toxicity requires recalculation of typically 20–37 fractions per patient, for nearly 2000 patients. This requires a non-interactive interface permitting batch calculation with multiple computers. Methods: Data are extracted from the TomoTherapy® archive and processed using the computational task-management system GANGA. Doses are calculated for each fraction of radiotherapy using the daily megavoltage (MV) CT images. The calculated dose cube is saved as a digital imaging and communications in medicine RTDOSE object, which can then be read by utilities that calculate dose–volume histograms or dose surface maps. The rectum is delineated on daily MV images using an implementation of the Chan–Vese algorithm. Results: On a cluster of up to 117 central processing units, dose cubes for all fractions of 151 patients took 12 days to calculate. Outlining the rectum on all slices and fractions on 151 patients took 7 h. We also present results of the Hounsfield unit (HU) calibration of TomoTherapy MV images, measured over an 8-year period, showing that the HU calibration has become less variable over time, with no large changes observed after 2011. Conclusion: We have developed a system for automatic dose recalculation of TomoTherapy dose distributions. This does not tie up the clinically needed planning system but can be run on a cluster of independent machines, enabling recalculation of delivered dose without user intervention. Advances in knowledge: The use of a task management system for automation of dose calculation and outlining enables work to be scaled up to the level required for large studies. PMID:26728661

  15. omega-Helices in proteins.

    PubMed

    Enkhbayar, Purevjav; Boldgiv, Bazartseren; Matsushima, Norio

    2010-05-01

    A modification of the alpha-helix, termed the omega-helix, has four residues in one turn of a helix. We searched the omega-helix in proteins by the HELFIT program which determines the helical parameters-pitch, residues per turn, radius, and handedness-and p = rmsd/(N - 1)(1/2) estimating helical regularity, where "rmsd" is the root mean square deviation from the best fit helix and "N" is helix length. A total of 1,496 regular alpha-helices 6-9 residues long with p < or = 0.10 A were identified from 866 protein chains. The statistical analysis provides a strong evidence that the frequency distribution of helices versus n indicates the bimodality of typical alpha-helix and omega-helix. Sixty-two right handed omega-helices identified (7.2% of proteins) show non-planarity of the peptide groups. There is amino acid preference of Asp and Cys. These observations and analyses insist that the omega-helices occur really in proteins.

  16. Helical Fiber Amplifier

    DOEpatents

    Koplow, Jeffrey P.; Kliner, Dahy; Goldberg, Lew

    2002-12-17

    A multi-mode gain fiber is provided which affords substantial improvements in the maximum pulse energy, peak power handling capabilities, average output power, and/or pumping efficiency of fiber amplifier and laser sources while maintaining good beam quality (comparable to that of a conventional single-mode fiber source). These benefits are realized by coiling the multimode gain fiber to induce significant bend loss for all but the lowest-order mode(s).

  17. Computational Investigation of Helical Traveling Wave Tube Transverse RF Field Forces

    NASA Technical Reports Server (NTRS)

    Kory, Carol L.; Dayton, James A.

    1998-01-01

    In a previous study using a fully three-dimensional (3D) helical slow-wave circuit cold- test model it was found, contrary to classical helical circuit analyses, that transverse FF electric fields have significant amplitudes compared with the longitudinal component. The RF fields obtained using this helical cold-test model have been scaled to correspond to those of an actual TWT. At the output of the tube, RF field forces reach 61%, 26% and 132% for radial, azimuthal and longitudinal components, respectively, compared to radial space charge forces indicating the importance of considering them in the design of electron beam focusing.

  18. Particle beam injection system

    DOEpatents

    Jassby, Daniel L.; Kulsrud, Russell M.

    1977-01-01

    This invention provides a poloidal divertor for stacking counterstreaming ion beams to provide high intensity colliding beams. To this end, method and apparatus are provided that inject high energy, high velocity, ordered, atomic deuterium and tritium beams into a lower energy, toroidal, thermal equilibrium, neutral, target plasma column that is magnetically confined along an endless magnetic axis in a strong restoring force magnetic field having helical field lines to produce counterstreaming deuteron and triton beams that are received bent, stacked and transported along the endless axis, while a poloidal divertor removes thermal ions and electrons all along the axis to increase the density of the counterstreaming ion beams and the reaction products resulting therefrom. By balancing the stacking and removal, colliding, strong focused particle beams, reaction products and reactions are produced that convert one form of energy into another form of energy.

  19. Flexible helical-axis stellarator

    DOEpatents

    Harris, Jeffrey H.; Hender, Timothy C.; Carreras, Benjamin A.; Cantrell, Jack L.; Morris, Robert N.

    1988-01-01

    An 1=1 helical winding which spirals about a conventional planar, circular central conductor of a helical-axis stellarator adds a significant degree of flexibility by making it possible to control the rotational transform profile and shear of the magnetic fields confining the plasma in a helical-axis stellarator. The toroidal central conductor links a plurality of toroidal field coils which are separately disposed to follow a helical path around the central conductor in phase with the helical path of the 1=1 winding. This coil configuration produces bean-shaped magnetic flux surfaces which rotate around the central circular conductor in the same manner as the toroidal field generating coils. The additional 1=1 winding provides flexible control of the magnetic field generated by the central conductor to prevent the formation of low-order resonances in the rotational transform profile which can produce break-up of the equilibrium magnetic surfaces. Further, this additional winding can deepen the magnetic well which together with the flexible control provides increased stability.

  20. Helical CT in emergency radiology.

    PubMed

    Novelline, R A; Rhea, J T; Rao, P M; Stuk, J L

    1999-11-01

    Today, a wide range of traumatic and nontraumatic emergency conditions are quickly and accurately diagnosed with helical computed tomography (CT). Many traditional emergency imaging procedures have been replaced with newer helical CT techniques that can be performed in less time and with greater accuracy, less patient discomfort, and decreased cost. The speed of helical technology permits CT examination of seriously ill patients in the emergency department, as well as patients who might not have been taken to CT previously because of the length of the examinations of the past. Also, helical technology permits multiple, sequential CT scans to be quickly obtained in the same patient, a great advance for the multiple-trauma patient. Higher quality CT examinations result from decreased respiratory misregistration, enhanced intravenous contrast material opacification of vascular structures and parenchymal organs, greater flexibility in image reconstruction, and improved multiplanar and three-dimensional reformations. This report summarizes the role and recommended protocols for the helical CT diagnosis of thoracic aortic trauma; aortic dissection; pulmonary embolism; acute conditions of the neck soft tissues; abdominal trauma; urinary tract stones; appendicitis; diverticulitis; abdominal aortic aneurysm; fractures of the face, spine, and extremities; and acute stroke.

  1. Generalized helicity and Beltrami fields

    SciTech Connect

    Buniy, Roman V.; Kephart, Thomas W.

    2014-05-15

    We propose covariant and non-abelian generalizations of the magnetic helicity and Beltrami equation. The gauge invariance, variational principle, conserved current, energy–momentum tensor and choice of boundary conditions elucidate the subject. In particular, we prove that any extremal of the Yang–Mills action functional 1/4 ∫{sub Ω}trF{sub μν}F{sup μν}d{sup 4}x subject to the local constraint ε{sup μναβ}trF{sub μν}F{sub αβ}=0 satisfies the covariant non-abelian Beltrami equation. -- Highlights: •We introduce the covariant non-abelian helicity and Beltrami equation. •The Yang–Mills action and instanton term constraint lead to the Beltrami equation. •Solutions of the Beltrami equation conserve helicity.

  2. Helical axis stellarator equilibrium model

    SciTech Connect

    Koniges, A.E.; Johnson, J.L.

    1985-02-01

    An asymptotic model is developed to study MHD equilibria in toroidal systems with a helical magnetic axis. Using a characteristic coordinate system based on the vacuum field lines, the equilibrium problem is reduced to a two-dimensional generalized partial differential equation of the Grad-Shafranov type. A stellarator-expansion free-boundary equilibrium code is modified to solve the helical-axis equations. The expansion model is used to predict the equilibrium properties of Asperators NP-3 and NP-4. Numerically determined flux surfaces, magnetic well, transform, and shear are presented. The equilibria show a toroidal Shafranov shift.

  3. Brownian motion of helical flagella.

    PubMed

    Hoshikawa, H; Saito, N

    1979-07-01

    We develops a theory of the Brownian motion of a rigid helical object such as bacterial flagella. The statistical properties of the random forces acting on the helical object are discussed and the coefficients of the correlations of the random forces are determined. The averages , and are also calculated where z and theta are the position along and angle around the helix axis respectively. Although the theory is limited to short time interval, direct comparison with experiment is possible by using the recently developed cinematography technique.

  4. On steady kinematic helical dynamos

    NASA Astrophysics Data System (ADS)

    Eltayeb, I. A.; Loper, D. E.

    The equations governing steady kinematic helical dynamos are studied, using the formalism of Benton (1979), when the flow has no radial component (in cylindrical coordinates). It is shown that all solutions must decay exponentially to zero at large distances, s, from the axis of the helix. When the flow depends on s only it is shown that a necessary condition for dynamo action is that the flow possesses components along both the primary and secondary helices. It is also found that periodic motion of one mode along the primary helix cannot support dynamo action even if the field is composed of mean and periodic parts.

  5. SU-E-T-527: Prior Knowledge Guided TomoTherapy Treatment Planning

    SciTech Connect

    Lian, J; Yuan, L; Wu, Q; Zhu, X; Chera, B; Chang, S

    2014-06-01

    Purpose: The quality and efficiency of radiotherapy treatment planning are highly planer dependent. Previously we have developed a statistical model to correlate anatomical features with dosimetry features of head and neck Tomotherapy treatment. The model enables us to predict the best achievable dosimetry for individual patient prior to treatment planning. The purpose of this work is to study if the prediction model can facilitate the treatment planning in both the efficiency and dosimetric quality. Methods: The anatomy-dosimetry correlation model was used to calculate the expected DVH for nine patients formerly treated. In Group A (3 patients), the model prediction agreed with the clinic plan; in Group B (3 patients), the model predicted lower larynx mean dose than the clinic plan; in Group C (3 patients), the model suggested the brainstem could be further spared. Guided by the prior knowledge, we re-planned all 9 cases. The number of interactions during the optimization process and dosimetric endpoints between the original clinical plan and model-guided re-plan were compared. Results: For Group A, the difference of target coverage and organs-at-risk sparing is insignificant (p>0.05) between the replan and the clinical plan. For Group B, the clinical plan larynx median dose is 49.4±4.7 Gy, while the prediction suggesting 40.0±6.2 Gy (p<0.05). The re-plan achieved 41.5±6.6 Gy, with similar dose on other structures as clinical plan. For Group C, the clinical plan brainstem maximum dose is 44.7±5.5 Gy. The model predicted lower value 32.2±3.8 Gy (p<0.05). The re-plans reduced brainstem maximum dose to 31.8±4.1 Gy without affecting the dosimetry of other structures. In the replanning of the 9 cases, the times operator interacted with TPS are reduced on average about 50% compared to the clinical plan. Conclusion: We have demonstrated that the prior expert knowledge embedded model improved the efficiency and quality of Tomotherapy treatment planning.

  6. Geometric validation of MV topograms for patient localization on TomoTherapy

    NASA Astrophysics Data System (ADS)

    Blanco Kiely, Janid P.; White, Benjamin M.; Low, Daniel A.; Qi, Sharon X.

    2016-01-01

    Our goal was to geometrically validate the use of mega-voltage orthogonal scout images (MV topograms) as a fast and low-dose alternative to mega-voltage computed tomography (MVCT) for daily patient localization on the TomoTherapy system. To achieve this, anthropomorphic head and pelvis phantoms were imaged on a 16-slice kilo-voltage computed tomography (kVCT) scanner to synthesize kilo-voltage digitally reconstructed topograms (kV-DRT) in the Tomotherapy detector geometry. MV topograms were generated for couch speeds of 1-4 cm s-1 in 1 cm s-1 increments with static gantry angles in the anterior-posterior and left-lateral directions. Phantoms were rigidly translated in the anterior-posterior (AP), superior-inferior (SI), and lateral (LAT) directions to simulate potential setup errors. Image quality improvement was demonstrated by estimating the noise level in the unenhanced and enhanced MV topograms using a principle component analysis-based noise level estimation algorithm. Average noise levels for the head phantom were reduced by 2.53 HU (AP) and 0.18 HU (LAT). The pelvis phantom exhibited average noise level reduction of 1.98 HU (AP) and 0.48 HU (LAT). Mattes Mutual Information rigid registration was used to register enhanced MV topograms with corresponding kV-DRT. Registration results were compared to the known rigid displacements, which assessed the MV topogram localization’s sensitivity to daily positioning errors. Reduced noise levels in the MV topograms enhanced the registration results so that registration errors were  <1 mm. The unenhanced head MV topograms had discrepancies  <2.1 mm and the pelvis topograms had discrepancies  <2.7 mm. Result were found to be consistent regardless of couch speed. In total, 64.7% of the head phantom MV topograms and 60.0% of the pelvis phantom MV topograms exactly measured the phantom offsets. These consistencies demonstrated the potential for daily patient positioning using MV topogram pairs in the

  7. Better understanding of tubular helical buckling

    SciTech Connect

    Wu, J.

    1996-09-01

    Tubular buckling is a significant problem within the oil industry. Although it has been studied for many years, methods to analyze tubular helical buckling continues to appear in the literature. Several criteria have been derived and presented leading to confusion in understanding and correctly predicting tubular helical buckling. The prediction of tubular helical buckling is complicated by the fact that the tubular is confined within the wellbore. The tubular initially buckles sinusoidally, and then changes into the shape of a helix (helical buckling) as the axial load increases. Different approaches in modeling the helical buckling process and the use of energy methods resulted in those different helical buckling criteria. Helical buckling criteria proposed in the literature, as well as their derivations are discussed in this paper, to help better understand and effectively predict tubular helical buckling in engineering operations.

  8. The transport of relative canonical helicity

    SciTech Connect

    You, S.

    2012-09-15

    The evolution of relative canonical helicity is examined in the two-fluid magnetohydrodynamic formalism. Canonical helicity is defined here as the helicity of the plasma species' canonical momentum. The species' canonical helicity are coupled together and can be converted from one into the other while the total gauge-invariant relative canonical helicity remains globally invariant. The conversion is driven by enthalpy differences at a surface common to ion and electron canonical flux tubes. The model provides an explanation for why the threshold for bifurcation in counter-helicity merging depends on the size parameter. The size parameter determines whether magnetic helicity annihilation channels enthalpy into the magnetic flux tube or into the vorticity flow tube components of the canonical flux tube. The transport of relative canonical helicity constrains the interaction between plasma flows and magnetic fields, and provides a more general framework for driving flows and currents from enthalpy or inductive boundary conditions.

  9. Helical Equilibrium Reconstruction using V3FIT on MST

    NASA Astrophysics Data System (ADS)

    Koliner, J. J.; Chapman, B. E.; Sarff, J. S.; Anderson, J. K.; Capecchi, W.; Eilerman, S.; Reusch, J. A.; Hanson, J. D.; Cianciosa, M. R.; Terranova, D.

    2013-10-01

    Plasmas in the MST reversed field pinch bifurcate to a helical equilibrium, forming a Single Helical Axis (SHAx) at high plasma current (Ip ~ 500 kA) and low density (ne ~ 0.5 × 1019 m-3) . Modeling of these plasmas requires an equilibrium solver that does not assume axisymmetry. The V3FIT 3D equilibrium reconstruction code is applied to helical equilibria with diagnostic measurements as constraints. The 11-chord interferometer-polarimeter, 22-point Thomson scattering system, and 4-camera soft X-ray probes have been included in addition to external magnetics. Inputs have been adapted for MST's close-fitting conducting shell. Investigations into the role of shell eddy currents have been made, including comparison to eigenfunctions generated from the Newcomb equation. At the plasma boundary, ~60% of the static n = 5 toroidal field BT seen by magnetic probes is generated by currents in the shell. The generated VMEC equilibrium serves as the input for applications relevant to the 1 MW, 25 keV neutral beam injector. During beam injection, fast ion confinement is reduced in periods with a SHAx compared to axisymmetric plasmas. A single particle orbit code has been applied to calculate particle trajectories in the 3D case, confirming a strong influence of SHAx equilibria on fast ion orbits. EPM magnetic bursts terminate at the transition to SHAx. Alfvén continua have been generated to study this phenomenon with the reduced-MHD code STELLGAP. Work Supported by USDoE and NSF.

  10. Conservation of magnetic helicity during plasma relaxation

    SciTech Connect

    Ji, H.; Prager, S.C.; Sarff, J.S.

    1994-07-01

    Decay of the total magnetic helicity during the sawtooth relaxation in the MST Reversed-Field Pinch is much larger than the MHD prediction. However, the helicity decay (3--4%) is smaller than the magnetic energy decay (7--9%), modestly supportive of the helicity conservation hypothesis in Taylor`s relaxation theory. Enhanced fluctuation-induced helicity transport during the relaxation is observed.

  11. Note: Helical nanobelt force sensors

    NASA Astrophysics Data System (ADS)

    Hwang, G.; Hashimoto, H.

    2012-12-01

    We present the fabrication and characterization of helical nanobelt force sensors. These self-sensing force sensors are based on the giant piezoresistivity of helical nanobelts. The three-dimensional helical nanobelts are self-formed from 27 nm-thick n-type InGaAs/GaAs bilayers using rolled-up techniques, and assembled onto electrodes on a micropipette using nanorobotic manipulations. The helical nanobelt force sensors can be calibrated using a calibrated atomic force microscope cantilever system under scanning electron microscope. Thanks to their giant piezoresistance coefficient (515 × 10-10 Pa-1), low stiffness (0.03125 N/m), large-displacement capability (˜10 μm), and good fatigue resistance, they are well suited to function as stand-alone, compact (˜20 μm without the plug-in support), light (˜5 g including the plug-in support), versatile and large range (˜μN) and high resolution (˜nN) force sensors.

  12. Hybrid helical snakes and rotators for RHIC

    SciTech Connect

    Courant, E.D.

    1995-06-13

    The spin rotators and Siberian snakes presently envisaged for RHIC utilize helical dipole magnets. The snakes and the rotators each consist of four helices, each with a full twist (360{degrees}) of the field. Here we investigate an alternate layout, namely combinations of helical and pure bending magnet, and show that this may have advantages.

  13. Helicity Within and Among Macromolecules

    NASA Astrophysics Data System (ADS)

    Green, Mark M.

    2004-03-01

    There are several classes of helical polymers and supramolecular arrays in which the left and right helical senses are of equal probability and as well in dynamic equilibrium. One example of this class of materials is a polymer first created at Dupont as a commercial fiber candidate almost fifty years ago but which did not rise to the level necessary for commercial use. The polymer, nylon 1, widely known as a polyisocyanate, did become a focal point of research for polymer physics because of its stiff archetypical wormlike nature. An array of research tools was able to elucidate the conformational characteristics of this polymer and therefore reveal in quantitative detail both the source of its stiffness and the limit to this characteristic. Further effort explored the nature of the expected lyotropic liquid crystal properties with similar success. As part of these studies, chiral experiments, which were introduced to determine how to favor one helical sense, played a key role. Statistical physical analysis of these chiral experiments first by Shneior Lifson for uniform chiral fields and later by Jonathan Selinger for quenched random chiral fields gave insight into the cooperative characteristics by which the chiral information influenced the helical senses in these polymers. These kinds of experiments finding parallels to the behavior of sergeants and soldiers and to majority rule were later applied widely in the literature offering insight into the cooperative nature of helical polymers and arrays in general. Moreover, the interplay between the character of the single chains and the liquid crystals that arise in concentrated solutions from the polyisocyanates yielded new kinds of information about the cholesteric state formed by lyotropic liquid crystals in general and even led to new phenomena connecting liquid crystal behavior to temperature.

  14. Three-dimensional dosimetry of TomoTherapy by MRI-based polymer gel technique.

    PubMed

    Watanabe, Yoichi; Gopishankar, N

    2010-09-14

    Verification of the dose calculation model and the software used for treatment planning is an important step for accurate radiation delivery in radiation therapy. Using BANG3 polymer gel dosimeter with a 3 Tesla magnetic resonance imaging (MRI) scanner, we examined the accuracy of TomoTherapy treatment planning and radiation delivery. We evaluated one prostate treatment case and found the calculated three-dimensional (3D) dose distributions agree with the measured 3D dose distributions with an exception in the regions where the dose was much smaller (25% or less) than the maximum dose (2.5 Gy). The analysis using the gamma-index (3% dose difference and 3 mm distance-to-agreement) for a volume of 12 cm × 11 cm × 9 cm containing the planning target volume showed that the gamma values were smaller than unity for 53% of the voxels. Our measurement protocol and analysis tools can be easily applied to the evaluation of other newer complex radiation delivery techniques, such as intensity-modulated arc therapy, with a reasonably low financial investment.

  15. Helical Dipole Magnets for Polarized Protons in RHIC

    NASA Astrophysics Data System (ADS)

    Syphers, M.; Courant, E.; Fischer, W.; Luccio, A.; Mariam, F.; Peggs, S.; Pilat, F.; Roser, T.; Tepikian, S.; Tsoupas, N.; Willen, E.; Katayama, T.; Hatanaka, K.; Kawaguchi, T.; Okamura, M.; Tominaka, T.; Wu, H.; Ptitsin, V.; Shatunov, Y.

    1997-05-01

    The Brookhaven Relativistic Heavy Ion Collider (RHIC) will be able to support experiments using polarized proton beams. Siberian Snakes are used to maintain polarization in this high energy superconducting collider. To make efficient use of available space while taking advantage of high field superconducting magnets, 4 Tesla helical dipole magnets will be used. These magnets generate a central dipole field in which the field direction rotates through 360^circ about the longitudinal axis over the length of the device. An arrangement of four such magnets can produce the desired change in the spin direction while keeping the proton orbit outside of the ``Snake'' unaltered. Similar magnet arrangements will be used to produce longitudinal polarization at the two major interaction points in RHIC. The basic requirements and layout of these magnets are described, as well as tolerances on field quality and integrated field strengths. First results of tests of prototype helical magnets will be discussed.

  16. Predictive supracolloidal helices from patchy particles

    PubMed Central

    Guo, Ruohai; Mao, Jian; Xie, Xu-Ming; Yan, Li-Tang

    2014-01-01

    A priori prediction of supracolloidal architectures from nanoparticle and colloidal assembly is a challenging goal in materials chemistry and physics. Despite intense research in this area, much less has been known about the predictive science of supracolloidal helices from designed building blocks. Therefore, developing conceptually new rules to construct supracolloidal architectures with predictive helicity is becoming an important and urgent task of great scientific interest. Here, inspired by biological helices, we show that the rational design of patchy arrangement and interaction can drive patchy particles to self-assemble into biomolecular mimetic supracolloidal helices. We further derive a facile design rule for encoding the target supracolloidal helices, thus opening the doors to the predictive science of these supracolloidal architectures. It is also found that kinetics and reaction pathway during the formation of supracolloidal helices offer a unique way to study supramolecular polymerization, and that well-controlled supracolloidal helices can exhibit tailorable circular dichroism effects at visible wavelengths. PMID:25387544

  17. Predictive supracolloidal helices from patchy particles

    NASA Astrophysics Data System (ADS)

    Guo, Ruohai; Mao, Jian; Xie, Xu-Ming; Yan, Li-Tang

    2014-11-01

    A priori prediction of supracolloidal architectures from nanoparticle and colloidal assembly is a challenging goal in materials chemistry and physics. Despite intense research in this area, much less has been known about the predictive science of supracolloidal helices from designed building blocks. Therefore, developing conceptually new rules to construct supracolloidal architectures with predictive helicity is becoming an important and urgent task of great scientific interest. Here, inspired by biological helices, we show that the rational design of patchy arrangement and interaction can drive patchy particles to self-assemble into biomolecular mimetic supracolloidal helices. We further derive a facile design rule for encoding the target supracolloidal helices, thus opening the doors to the predictive science of these supracolloidal architectures. It is also found that kinetics and reaction pathway during the formation of supracolloidal helices offer a unique way to study supramolecular polymerization, and that well-controlled supracolloidal helices can exhibit tailorable circular dichroism effects at visible wavelengths.

  18. The Degree of Lipiodol Accumulation Can Be an Indicator of Successful Treatment for Unresectable Hepatocellular Carcinoma (HCC) Patients - in the Case of Transcatheter Arterial Chemoembolization (TACE) and External Beam Radiotherapy (EBRT)

    PubMed Central

    Yang, Ping; Zeng, Zhao-Chong; Wang, Bin-Liang; Zhang, Jian-Ying; Fan, Jia; Zhou, Jian; Hu, Yong

    2016-01-01

    Purpose: Transcatheter arterial chemoembolization (TACE) in combination with external beam radiotherapy (EBRT) results in improved survival due to better local control in patients with unresectable hepatocellular carcinoma (HCC). The purpose of this study was to investigate lipiodol accumulation, as it reflects tumor burden and is a potential prognostic factor, in HCC patients treated with TACE/EBRT. Methods and Materials: We retrospectively studied 147 patients with unresectable HCC treated with TACE and EBRT. Clinical features, adverse reactions, and prognostic factors were analyzed. All patients were treated with TACE 1-6 times in combination with EBRT (44-66 Gy) in dose of 2 Gy/fraction given once a day five times a week. Tumor status and laboratory findings were followed. The degree of lipiodol accumulation was assessed by computed tomography before EBRT, and was categorized as either complete/intense or low/moderate. Results: The response rate of tumor size after EBRT was 68.2%, median survival was 23.1 months, and overall survival rates were 86.6%, 49.2%, and 28.2% at 1, 2, and 3 years, respectively. Univariate analysis showed that lower hemoglobin levels, higher alkaline phosphatase levels, Child-Pugh B, negative alpha-fetoprotein (AFP) response after EBRT, poor treatment response after EBRT, tumor diameter >10 cm, and poor lipiodol accumulation were unfavorable prognostic factors. On multivariate analysis, higher hemoglobin levels, Child-Pugh A, decreased AFP levels after treatment, Helical Tomotherapy (HT) and intense lipiodol accumulation after TACE were significant favorable predictors. Conclusions: The degree of lipiodol accumulation before EBRT is a prognostic factor in patients with unresectable HCC. Increased AFP levels after EBRT are always associated with poor survival. HT is recommended as a potentially better EBRT modality than three-dimensional conformal radiation therapy (3D-CRT). PMID:27471557

  19. Helical screw expander evaluation project

    NASA Astrophysics Data System (ADS)

    McKay, R.

    1982-03-01

    A one MW helical rotary screw expander power system for electric power generation from geothermal brine was evaluated. The technology explored in the testing is simple, potentially very efficient, and ideally suited to wellhead installations in moderate to high enthalpy, liquid dominated field. A functional one MW geothermal electric power plant that featured a helical screw expander was produced and then tested with a demonstrated average performance of approximately 45% machine efficiency over a wide range of test conditions in noncondensing, operation on two-phase geothermal fluids. The Project also produced a computer equipped data system, an instrumentation and control van, and a 1000 kW variable load bank, all integrated into a test array designed for operation at a variety of remote test sites. Data are presented for the Utah testing and for the noncondensing phases of the testing in Mexico. Test time logged was 437 hours during the Utah tests and 1101 hours during the Mexico tests.

  20. Helical screw expander evaluation project

    NASA Technical Reports Server (NTRS)

    Mckay, R.

    1982-01-01

    A one MW helical rotary screw expander power system for electric power generation from geothermal brine was evaluated. The technology explored in the testing is simple, potentially very efficient, and ideally suited to wellhead installations in moderate to high enthalpy, liquid dominated field. A functional one MW geothermal electric power plant that featured a helical screw expander was produced and then tested with a demonstrated average performance of approximately 45% machine efficiency over a wide range of test conditions in noncondensing, operation on two-phase geothermal fluids. The Project also produced a computer equipped data system, an instrumentation and control van, and a 1000 kW variable load bank, all integrated into a test array designed for operation at a variety of remote test sites. Data are presented for the Utah testing and for the noncondensing phases of the testing in Mexico. Test time logged was 437 hours during the Utah tests and 1101 hours during the Mexico tests.

  1. An experimental superconducting helical undulator

    SciTech Connect

    Caspi, S.; Taylor, C.

    1995-12-31

    Improvements in the technology of superconducting magnets for high energy physics and recent advancements in SC materials with the artificial pinning centers (APC){sup 2}, have made a bifilar helical SC device an attractive candidate for a single-pass free electron laser (FEL){sup 3}. Initial studies have suggested that a 6.5 mm inner diameter helical device, with a 27 mm period, can generate a central field of 2-2.5 Tesla. Additional studies have also suggested that with a stored energy of 300 J/m, such a device can be made self-protecting in the event of a quench. However, since the most critical area associated with high current density SC magnets is connected with quenching and training, a short experimental device will have to be built and tested. In this paper we discuss technical issues relevant to the construction of such a device, including a conceptual design, fields, and forces.

  2. Mechanical analysis and test results of 4-coil superconducting helical solenoid model

    SciTech Connect

    Yu, M.; Andreev, N.; Chlachidze, G.; Johnson, R.P.; Kashikhin, V.S.; Kashikhin, V.V.; Lamm, M.J.; Lopes, M.L.; Makarov, A.; Tartaglia, M.; Yonehara, K.; /Fermilab

    2010-01-01

    Novel configurations of helical superconducting magnets for muon beam 6D phase space cooling channels and demonstration experiments are being designed at Fermilab. Operating as needed for the beam cooling in a cryogenic environment, the helical solenoid generates longitudinal and transverse magnetic fields; meanwhile, large Lorentz forces are produced, so rigid coil support structures need to be designed. A short model of a helical solenoid (HS), consisting of four coils and supporting structures, was designed, built and tested at Fermilab. The magnetic and mechanical designs were analyzed using TOSCA and ANSYS. The supporting structures were fabricated and assembled using SSC NbTi cable. Strain gauges were utilized to monitor the deformation of the structures due to both thermal contraction and Lorentz forces. The superconducting coils were trained during the test. The model should prove the design concept, fabrication technology, and the magnet system performance.

  3. Topology of modified helical gears

    NASA Technical Reports Server (NTRS)

    Litvin, F. L.; Zhang, J.; Handschuh, R. F.; Coy, J. J.

    1989-01-01

    The topology of several types of modified surfaces of helical gears is proposed. The modified surfaces allow absorption of a linear or almost linear function of transmission errors. These errors are caused by gear misalignment and an improvement of the contact of gear tooth surfaces. Principles and corresponding programs for computer aided simulation of meshing and contact of gears have been developed. The results of this investigation are illustrated with numerical examples.

  4. Emulsification-Induced Homohelicity in Racemic Helical Polymer for Preparing Optically Active Helical Polymer Nanoparticles.

    PubMed

    Zhao, Biao; Deng, Jinrui; Deng, Jianping

    2016-04-01

    Optically active nano- and microparticles have constituted a significant category of advanced functional materials. However, constructing optically active particles derived from synthetic helical polymers still remains as a big challenge. In the present study, it is attempted to induce a racemic helical polymer (containing right- and left-handed helices in equal amount) to prefer one predominant helicity in aqueous media by using emulsifier in the presence of chiral additive (emulsification process). Excitingly, the emulsification process promotes the racemic helical polymer to unify the helicity and directly provides optically active nanoparticles constructed by chirally helical polymer. A possible mechanism is proposed to explain the emulsification-induced homohelicity effect. The present study establishes a novel strategy for preparing chirally helical polymer-derived optically active nanoparticles based on racemic helical polymers.

  5. Helicity comparison among three magnetographs

    NASA Astrophysics Data System (ADS)

    Xu, Haiqing; Gao, Yu; Zhang, Hongqi; Sakurai, T.; Pevtsov, A. A.; Sokoloff, D.

    We compare vector magnetograms of 228 active regions observed by Solar Magnetic Field Telescope (SMFT) at Huairou (HR) Solar Observing Station and the Solar Flare Telescope (SFT) at Mitaka (MTK) of the National Astronomical Observatory of Japan from 1992 to 2005 and 55 active regions observed by SFT and Haleakala Stokes Polarimeter (HSP) at Mees Solar Observatory, University of Hawaii from 1997 to 2000. Two helicity parameters, current helicity density hc and αff coefficient of linear force free field are calculated. From this comparison we conclude: (1) the mean azimuthal angle differences of transverse fields between HR and MTK data are systematic smaller than that between MTK and Mees data; (2) there are 83.8% of hc and 78.1% of αff for 228 active regions observed at HR and MTK agree in sign, and the Pearson linear correlation coefficient between these two data sets is 0.72 for hc and 0.56 for αff. There are 61.8% of hc and 58.2% of αff for 55 active regions observed at MTK and Mees agree in sign, and the Pearson linear correlation coefficient between these two data sets is 0.34 for hc and 0.31 for αff; (3) there is a basic agreement on time variation of helicity parameters in active regions observed at HR, Mees, and MTK.

  6. Helically twisted photonic crystal fibres.

    PubMed

    Russell, P St J; Beravat, R; Wong, G K L

    2017-02-28

    Recent theoretical and experimental work on helically twisted photonic crystal fibres (PCFs) is reviewed. Helical Bloch theory is introduced, including a new formalism based on the tight-binding approximation. It is used to explore and explain a variety of unusual effects that appear in a range of different twisted PCFs, including fibres with a single core and fibres with N cores arranged in a ring around the fibre axis. We discuss a new kind of birefringence that causes the propagation constants of left- and right-spinning optical vortices to be non-degenerate for the same order of orbital angular momentum (OAM). Topological effects, arising from the twisted periodic 'space', cause light to spiral around the fibre axis, with fascinating consequences, including the appearance of dips in the transmission spectrum and low loss guidance in coreless PCF. Discussing twisted fibres with a single off-axis core, we report that optical activity in a PCF is opposite in sign to that seen in a step-index fibre. Fabrication techniques are briefly described and emerging applications reviewed. The analytical results of helical Bloch theory are verified by an extensive series of 'numerical experiments' based on finite-element solutions of Maxwell's equations in a helicoidal frame.This article is part of the themed issue 'Optical orbital angular momentum'.

  7. Helically twisted photonic crystal fibres

    PubMed Central

    Beravat, R.; Wong, G. K. L.

    2017-01-01

    Recent theoretical and experimental work on helically twisted photonic crystal fibres (PCFs) is reviewed. Helical Bloch theory is introduced, including a new formalism based on the tight-binding approximation. It is used to explore and explain a variety of unusual effects that appear in a range of different twisted PCFs, including fibres with a single core and fibres with N cores arranged in a ring around the fibre axis. We discuss a new kind of birefringence that causes the propagation constants of left- and right-spinning optical vortices to be non-degenerate for the same order of orbital angular momentum (OAM). Topological effects, arising from the twisted periodic ‘space’, cause light to spiral around the fibre axis, with fascinating consequences, including the appearance of dips in the transmission spectrum and low loss guidance in coreless PCF. Discussing twisted fibres with a single off-axis core, we report that optical activity in a PCF is opposite in sign to that seen in a step-index fibre. Fabrication techniques are briefly described and emerging applications reviewed. The analytical results of helical Bloch theory are verified by an extensive series of ‘numerical experiments’ based on finite-element solutions of Maxwell's equations in a helicoidal frame. This article is part of the themed issue ‘Optical orbital angular momentum’. PMID:28069771

  8. Helically twisted photonic crystal fibres

    NASA Astrophysics Data System (ADS)

    Russell, P. St. J.; Beravat, R.; Wong, G. K. L.

    2017-02-01

    Recent theoretical and experimental work on helically twisted photonic crystal fibres (PCFs) is reviewed. Helical Bloch theory is introduced, including a new formalism based on the tight-binding approximation. It is used to explore and explain a variety of unusual effects that appear in a range of different twisted PCFs, including fibres with a single core and fibres with N cores arranged in a ring around the fibre axis. We discuss a new kind of birefringence that causes the propagation constants of left- and right-spinning optical vortices to be non-degenerate for the same order of orbital angular momentum (OAM). Topological effects, arising from the twisted periodic `space', cause light to spiral around the fibre axis, with fascinating consequences, including the appearance of dips in the transmission spectrum and low loss guidance in coreless PCF. Discussing twisted fibres with a single off-axis core, we report that optical activity in a PCF is opposite in sign to that seen in a step-index fibre. Fabrication techniques are briefly described and emerging applications reviewed. The analytical results of helical Bloch theory are verified by an extensive series of `numerical experiments' based on finite-element solutions of Maxwell's equations in a helicoidal frame. This article is part of the themed issue 'Optical orbital angular momentum'.

  9. Helical Antimicrobial Sulfono- {gamma} -AApeptides

    SciTech Connect

    Li, Yaqiong; Wu, Haifan; Teng, Peng; Bai, Ge; Lin, Xiaoyang; Zuo, Xiaobing; Cao, Chuanhai; Cai, Jianfeng

    2015-06-11

    Host-defense peptides (HDPs) such as magainin 2 have emerged as potential therapeutic agents combating antibiotic resistance. Inspired by their structures and mechanism of action, herein we report the fi rst example of antimicrobial helical sulfono- γ - AApeptide foldamers. The lead molecule displays broad-spectrum and potent antimicrobial activity against multi-drug-resistant Gram- positive and Gram-negative bacterial pathogens. Time-kill studies and fl uorescence microscopy suggest that sulfono- γ -AApeptides eradicate bacteria by taking a mode of action analogous to that of HDPs. Clear structure - function relationships exist in the studied sequences. Longer sequences, presumably adopting more-de fi ned helical structures, are more potent than shorter ones. Interestingly, the sequence with less helical propensity in solution could be more selective than the stronger helix-forming sequences. Moreover, this class of antimicrobial agents are resistant to proteolytic degradation. These results may lead to the development of a new class of antimicrobial foldamers combating emerging antibiotic-resistant pathogens.

  10. SU-E-T-417: The Impact of Normal Tissue Constraints On PTV Dose Homogeneity for Intensity Modulated Radiotherapy (IMRT), Volume Modulated Arc Therapy (VMAT) and Tomotherapy

    SciTech Connect

    Peng, J; McDonald, D; Ashenafi, M; Ellis, A; Vanek, K

    2014-06-01

    Purpose: Complex intensity modulated arc therapy tends to spread low dose to normal tissue(NT)regions to obtain improved target conformity and homogeneity and OAR sparing.This work evaluates the trade-offs between PTV homogeneity and reduction of the maximum dose(Dmax)spread to NT while planning of IMRT,VMAT and Tomotherapy. Methods: Ten prostate patients,previously planned with step-and-shoot IMRT,were selected.To fairly evaluate how PTV homogeneity was affected by NT Dmax constraints,original IMRT DVH objectives for PTV and OARs(femoral heads,and rectal and bladder wall)applied to 2 VMAT plans in Pinnacle(V9.0), and Tomotherapy(V4.2).The only constraint difference was the NT which was defined as body contours excluding targets,OARs and dose rings.NT Dmax constraint for 1st VMAT was set to the prescription dose(Dp).For 2nd VMAT(VMAT-NT)and Tomotherapy,it was set to the Dmax achieved in IMRT(~70-80% of Dp).All NT constraints were set to the lowest priority.Three common homogeneity indices(HI),RTOG-HI=Dmax/Dp,moderated-HI=D95%/D5% and complex-HI=(D2%-D98%)/Dp*100 were calculated. Results: All modalities with similar dosimetric endpoints for PTV and OARs.The complex-HI shows the most variability of indices,with average values of 5.9,4.9,9.3 and 6.1 for IMRT,VMAT,VMAT-NT and Tomotherapy,respectively.VMAT provided the best PTV homogeneity without compromising any OAR/NT sparing.Both VMAT-NT and Tomotherapy,planned with more restrictive NT constraints,showed reduced homogeneity,with VMAT-NT showing the worst homogeneity(P<0.0001)for all HI.Tomotherapy gave the lowest NT Dmax,with slightly decreased homogeneity compared to VMAT. Finally, there was no significant difference in NT Dmax or Dmean between VMAT and VMAT-NT. Conclusion: PTV HI is highly dependent on permitted NT constraints. Results demonstrated that VMAT-NT with more restrictive NT constraints does not reduce Dmax NT,but significantly receives higher Dmax and worse target homogeneity.Therefore, it is critical

  11. Dosimetric verification and quality assurance of running-start-stop (RSS) delivery in tomotherapy.

    PubMed

    Lee, Francis Kar-Ho; Chan, Simon Kar-Yiu; Chau, Ricky Ming-Chun

    2015-11-08

    The purpose of this study was to evaluate the dosimetric profiles and delivery accuracy of running-start-stop (RSS) delivery in tomotherapy and to present initial quality assurance (QA) results on the accuracy of the dynamic jaw motion, dosimetric penumbrae of the RSS dynamic jaw and the static jaw were measured by radiographic films. Delivery accuracy of the RSS was evaluated by gamma analysis on film measurements of 12 phantom plans. Consistency in the performance of RSS was evaluated by QA procedures over the first nine months after the installation of the feature. These QA were devised to check: 1) positional accuracy of moving jaws; 2) consistency of relative radiation output collimated by discrete and continuously sweeping jaws; 3) consistency of field widths and profiles. In the longitudinal direction, the dose penumbra in RSS delivery was reduced from 17.3mm to 10.2 mm for 2.5 cm jaw, and from 33.2 mm to 9.6 mm for 5 cm jaw. Gamma analysis on the twelve plans revealed that over 90% of the voxels in the proximity of the penumbra region satisfied the gamma criteria of 2% dose difference and 2 mm distance-to-agreement. The initial QA results during the first nine months after installation of the RSS are presented. Jaw motion was shown to be accurate with maximum encoder error less than 0.42 mm. The consistency of relative output for discrete and continuously sweeping jaws was within 1.2%. Longitudinal radiation profiles agreed to the reference profile with maximum gamma < 1 and field width error < 1.8%. With the same jaw width, RSS showed better dose penumbrae compared to those from static jaw delivery. The initial QA results on the accuracy of moving jaws, reproducibility of dosimetric output and profiles were satisfactory.

  12. Evaluation of Coplanar Partial Left Breast Irradiation Using Tomotherapy-Based Topotherapy

    SciTech Connect

    McIntosh, Alyson; Read, Paul W.; Khandelwal, Shiv R.; Arthur, Douglas W.; Turner, A. Benton C.; Ruchala, Kenneth J.; Olivera, Gustavo H.; Jeswani, Sam; Sheng, Ke

    2008-06-01

    Purpose: To investigate the use of topotherapy for accelerated partial breast irradiation through field-design optimization and dosimetric comparison to linear accelerator-based three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiation therapy (IMRT). Methods and Materials: Hypothetical 3-cm lumpectomy sites were contoured in each quadrant of a left breast by using dosimetric guidelines from the National Surgical Adjuvant Breast and Bowel Project B-39/Radiation Therapy Oncology Group 0413 protocol. Coplanar intensity-modulated topotherapy treatment plans were optimized by using two-, three-, four-, five-, and seven-field arrangements for delivery by the tomotherapy unit with fixed gantry angles. Optimized noncoplanar five-field 3D-CRT and IMRT were compared with corresponding topotherapy plans. Results: On average, 99.5% {+-} 0.5% of the target received 100% of the prescribed dose for all topotherapy plans. Average equivalent uniform doses ranged from 1.20-2.06, 0.79-1.76, and 0.10-0.29 Gy for heart, ipsilateral lung, and contralateral lung, respectively. Average volume of normal breast exceeding 90% of the prescription and average area of skin exceeding 35 Gy were lowest for five-field plans. Average uniformity indexes for five-field plans using 3D-CRT, IMRT, and topotherapy were 1.047, 1.050, and 1.040, respectively. Dose-volume histograms and calculated equivalent uniform doses of all three techniques illustrate clinically equivalent doses to ipsilateral breast, lung, and heart. Conclusions: This dosimetric evaluation for a single patient shows that coplanar partial breast topotherapy provides good target coverage with exceptionally low dose to organs at risk. Use of more than five fields provided no additional dosimetric advantage. A comparison of five-field topotherapy to 3D-CRT and IMRT for accelerated partial breast irradiation illustrates equivalent target conformality and uniformity.

  13. Cumulative dose on fractional delivery of tomotherapy to periodically moving organ: A phantom QA suggestion

    SciTech Connect

    Shin, Eunhyuk; Han, Youngyih; Park, Hee-Chul; Sung Kim, Jin; Hwan Ahn, Sung; Suk Shin, Jung; Gyu Ju, Sang; Ho Choi, Doo; Lee, Jaiki

    2013-01-01

    This study was conducted to evaluate the cumulative dosimetric error that occurs in both target and surrounding normal tissues when treating a moving target in multifractional treatment with tomotherapy. An experiment was devised to measure cumulative error in multifractional treatments delivered to a horseshoe-shaped clinical target volume (CTV) surrounding a cylinder shape of organ at risk (OAR). Treatments differed in jaw size (1.05 vs 2.5 cm), pitch (0.287 vs 0.660), and modulation factor (1.5 vs 2.5), and tumor motion characteristics differing in amplitude (1 to 3 cm), period (3 to 5 second), and regularity (sinusoidal vs irregular) were tested. Treatment plans were delivered to a moving phantom up to 5-times exposure. Dose distribution on central coronal plane from 1 to 5 times exposure was measured with GAFCHROMIC EBT film. Dose differences occurring across 1 to 5 times exposure of treatment and between treatment plans were evaluated by analyzing measurements of gamma index, gamma index histogram, histogram changes, and dose at the center of the OAR. The experiment showed dose distortion due to organ motion increased between multiexposure 1 to 3 times but plateaued and remained constant after 3-times exposure. In addition, although larger motion amplitude and a longer period of motion both increased dosimetric error, the dose at the OAR was more significantly affected by motion amplitude rather than motion period. Irregularity of motion did not contribute significantly to dosimetric error when compared with other motion parameters. Restriction of organ motion to have small amplitude and short motion period together with larger jaw size and small modulation factor (with small pitch) is effective in reducing dosimetric error. Pretreatment measurements for 3-times exposure of treatment to a moving phantom with patient-specific tumor motion would provide a good estimation of the delivered dose distribution.

  14. Artificial helical microswimmers with mastigoneme-inspired appendages

    PubMed Central

    Tottori, Soichiro; Nelson, Bradley J.

    2013-01-01

    A smooth flagellum moves in the opposite direction of the propagation of flagellar waves. Conversely, a flagellum covered with appendages perpendicular to the main flagellum, called mastigonemes, moves in the same direction as the propagation of flagellar waves. Inspired by mastigoneme structures in nature, we report the reversal of the swimming direction of magnetically actuated artificial helical microswimmers. The main flagella and mastigonemes of these microswimmers are fabricated together using three-dimensional lithography and electron beam evaporation of ferromagnetic thin films. The results show that the swimming speed and direction can be controlled by changing the length/spacing ratio of the mastigonemes. PMID:24396533

  15. Quality-of-life outcomes in high-risk prostate cancer patients treated with helical tomotherapy in a hypofractionated radiation schedule with long-term androgen suppression

    PubMed Central

    Pervez, N.; Krauze, A.V.; Yee, D.; Parliament, M.; Mihai, A.; Ghosh, S.; Joseph, K.; Murtha, A.; Amanie, J.; Kamal, M.; Pearcey, R.

    2012-01-01

    Purpose We examined the impact of hypofractionated radiation therapy and androgen suppression therapy (ast) on quality of life (qol) in high-risk prostate cancer patients. Methods Between March 2005 and March 2007, 60 patients with high-risk prostate cancer were enrolled in a prospective phase ii study. All patients received 68 Gy (2.72 Gy per fraction) to the prostate gland and 45 Gy (1.8 Gy per fraction) to the pelvic lymph nodes in 25 fractions over 5 weeks. Of the 60 patients, 58 received ast. The University of California–Los Angeles Prostate Cancer Index questionnaire was used to prospectively measure qol at baseline (month 0) and at 1, 6, 12, 18, 24, 30, and 36 months after radiation treatment. The generalized estimating equation approach was used to compare the qol scores at 1, 6, 12, 18, 24, 30, and 36 months with those at baseline. Results We observed a significant decrease in qol items related to bowel and sexual function. Several qol items related to bowel function were significantly adversely affected at both 1 and 6 months, with improvement toward 6 months. Although decreased qol scores persisted beyond the 6-month mark, they began to re-approach baseline at the 18- to 24-month mark. Most sexual function items were significantly adversely affected at both 1 and 6 months, but the effects were not considered to be a problem by most patients. A complete return to baseline was not observed for either bowel or sexual function. Urinary function items remained largely unaffected, with overall urinary function being the only item adversely affected at 6 months, but not at 1 month. Urinary function returned to baseline and remained unimpaired from 18 months onwards. Conclusions In our study population, who received hypofractionated radiation delivered using dynamic intensity-modulated radiotherapy with inclusion of the pelvic lymph nodes, and 2–3 years of ast prescription, qol with respect to bowel and sexual function was significantly affected; qol with respect to urinary function was largely unaffected. Our results are comparable to those in other published studies. PMID:22670110

  16. First measurement of the helicity-dependent pη differential cross-section

    NASA Astrophysics Data System (ADS)

    GDH and A2 Collaborations; Ahrens, J.; Altieri, S.; Annand, J. R. M.; Anton, G.; Arends, H.-J.; Aulenbacher, K.; Beck, R.; Bradtke, C.; Braghieri, A.; d'Hose, N.; Drechsel, D.; Dutz, H.; Goertz, S.; Grabmayr, P.; Hansen, K.; Harmsen, J.; von Harrach, D.; Hasegawa, S.; Hasegawa, T.; Heid, E.; Helbing, K.; Holvoet, H.; Van Hoorebeke, L.; Horikawa, N.; Iwata, T.; Jahn, O.; Jennewein, P.; Kageya, T.; Kiel, B.; Klein, F.; Kondratiev, R.; Kossert, K.; Krimmer, J.; Lang, M.; Lannoy, B.; Leukel, R.; Lisin, V.; Matsuda, T.; McGeorge, J. C.; Meier, A.; Menze, D.; Meyer, W.; Michel, T.; Naumann, J.; Panzeri, A.; Pedroni, P.; Pinelli, T.; Preobrajenski, I.; Radtke, E.; Reichert, E.; Reicherz, G.; Rohlof, Ch.; Rosner, G.; Ryckbosch, D.; Sauer, M.; Schoch, B.; Schumacher, M.; Seitz, B.; Speckner, T.; Takabayashi, N.; Tamas, G.; Thomas, A.; van de Vyver, R.; Wakai, A.; Weihofen, W.; Wissmann, F.; Zapadtka, F.; Zeitler, G.

    The helicity dependence of the pη reaction has been measured for the first time at a center-of-mass angle θ*η = 70° in the photon energy range from 780 MeV to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4π-detector system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. The helicity 3/2 cross-section is found to be small and the results for helicity 1/2 agree with predictions from the MAID analysis.

  17. Helicity fluctuations in incompressible turbulent flows

    NASA Technical Reports Server (NTRS)

    Rogers, Michael M.; Moin, Parviz

    1987-01-01

    Results from direct numerical simulations of several homogeneous flows and fully developed turbulent channel flow indicate that the probability distribution function (pdf) of relative helicity density exhibits at most a 20 percent deviation from a flat distribution. Isotropic flows exhibit a slight helical nature but the presence of mean strain in homogeneous turbulence suppresses helical behavior. All the homogeneous turbulent flows studied show no correlation between relative helicity density and the dissipation of turbulent kinetic energy. The channel flow simulations indicate that, except for low-dissipation regions near the outer edge of the buffer layer, there is no tendency for the flow to be helical. The strong peaks in the relative helicity density pdf and the association of these peaks with regions of low dissipation found in previous simulations by Pelz et al.(1985) are not observed.

  18. Building blocks for subleading helicity operators

    SciTech Connect

    Kolodrubetz, Daniel W.; Moult, Ian; Stewart, Iain W.

    2016-05-24

    On-shell helicity methods provide powerful tools for determining scattering amplitudes, which have a one-to-one correspondence with leading power helicity operators in the Soft-Collinear Effective Theory (SCET) away from singular regions of phase space. We show that helicity based operators are also useful for enumerating power suppressed SCET operators, which encode subleading amplitude information about singular limits. In particular, we present a complete set of scalar helicity building blocks that are valid for constructing operators at any order in the SCET power expansion. In conclusion, we also describe an interesting angular momentum selection rule that restricts how these building blocks can be assembled.

  19. Magnetic helicity in emerging solar active regions

    SciTech Connect

    Liu, Y.; Hoeksema, J. T.; Bobra, M.; Hayashi, K.; Sun, X.; Schuck, P. W.

    2014-04-10

    Using vector magnetic field data from the Helioseismic and Magnetic Imager instrument aboard the Solar Dynamics Observatory, we study magnetic helicity injection into the corona in emerging active regions (ARs) and examine the hemispheric helicity rule. In every region studied, photospheric shearing motion contributes most of the helicity accumulated in the corona. In a sample of 28 emerging ARs, 17 follow the hemisphere rule (61% ± 18% at a 95% confidence interval). Magnetic helicity and twist in 25 ARs (89% ± 11%) have the same sign. The maximum magnetic twist, which depends on the size of an AR, is inferred in a sample of 23 emerging ARs with a bipolar magnetic field configuration.

  20. Building blocks for subleading helicity operators

    NASA Astrophysics Data System (ADS)

    Kolodrubetz, Daniel W.; Moult, Ian; Stewart, Iain W.

    2016-05-01

    On-shell helicity methods provide powerful tools for determining scattering amplitudes, which have a one-to-one correspondence with leading power helicity operators in the Soft-Collinear Effective Theory (SCET) away from singular regions of phase space. We show that helicity based operators are also useful for enumerating power suppressed SCET operators, which encode subleading amplitude information about singular limits. In particular, we present a complete set of scalar helicity building blocks that are valid for constructing operators at any order in the SCET power expansion. We also describe an interesting angular momentum selection rule that restricts how these building blocks can be assembled.

  1. Helical axis stellarator with noninterlocking planar coils

    DOEpatents

    Reiman, Allan; Boozer, Allen H.

    1987-01-01

    A helical axis stellarator using only noninterlocking planar, non-circular coils, generates magnetic fields having a magnetic well and large rotational transform with resultant large equilibrium beta.

  2. Higher helicity invariants and solar dynamo

    NASA Astrophysics Data System (ADS)

    Sokolov, D. D.; Illarionov, E. A.; Akhmet'ev, P. M.

    2017-01-01

    Modern models of nonlinear dynamo saturation in celestial bodies (specifically, on the Sun) are largely based on the consideration of the balance of magnetic helicity. This physical variable has also a topological meaning: it is associated with the linking coefficient of magnetic tubes. In addition to magnetic helicity, magnetohydrodynamics has a number of topological integrals of motion (the so-called higher helicity moments). We have compared these invariants with magnetic helicity properties and concluded that they can hardly serve as nonlinear constraints on dynamo action.

  3. Neutrino helicity asymmetries in leptogenesis

    SciTech Connect

    Bento, Luis; Santos, Francisco C.

    2005-05-01

    It is pointed out that the heavy singlet neutrinos characteristic of leptogenesis develop asymmetries in the abundances of the two helicity states as a result of the same mechanism that generates asymmetries in the standard lepton sector. Neutrinos and standard leptons interchange asymmetries in collisions with each other. It is shown that an appropriate quantum number, B-L{sup '}, combining baryon, lepton and neutrino asymmetries, is not violated as fast as the standard B-L. This suppresses the washout effects relevant for the derivation of the final baryon asymmetry. One presents detailed calculations for the period of neutrino thermal production in the framework of the singlet seesaw mechanism.

  4. Low-Dose-Area-Constrained Helical TomoTherapy-Based Whole Breast Radiotherapy and Dosimetric Comparison with Tangential Field-in-Field IMRT

    PubMed Central

    Qiu, Jie; Yang, Bo; Hou, Xiaorong; Zhang, Fuquan

    2013-01-01

    Background and Purpose. To present a novel helical TomoTherapy-based method for whole breast radiotherapy that has better dosimetry and also has acceptable low-dose regions for lungs, heart, and contralateral breast compared with tangential field-in-field IMRT (FIF-IMRT). Material and Methods. Ten patients with left-side breast cancer were planned with low-dose-area-constrained helical TomoTherapy (LDC-HT) and FIF-IMRT. Dosimetry was compared for all techniques. Results. Coverage of the whole breast was adequate with both techniques. Homogeneity index (HI) and conformity index (CI) were better with LDC-HT. LDC-HT showed dosimetry advantages over FIF-IMRT for ipsilateral lung and heart in not only high-dose levels but also in low-dose levels such as V10 Gy and V5 Gy. For contralateral lung, both techniques can provide good protection, although the mean dose of LDC-HT is higher than that of FIF-IMRT. Conclusions. With LDC-HT, we obtained adequate target coverage, better HI and CI of target volume, better sparing of organs at risk, and acceptably low-dose areas compared with FIF-IMRT. LDC-HT could be a feasible method in whole breast radiotherapy. Clinical benefits of LDC-HT need further investigation. PMID:24024197

  5. Traveling Wave RF Systems for Helical Cooling Channels

    SciTech Connect

    Yonehara, K.; Lunin, A.; Moretti, A.; Popovic, M.; Romanov, G.; Neubauer, M.; Johnson, R.P.; Thorndahl, L.; /CERN

    2009-05-01

    The great advantage of the helical ionization cooling channel (HCC) is its compact structure that enables the fast cooling of muon beam 6-dimensional phase space. This compact aspect requires a high average RF gradient, with few places that do not have cavities. Also, the muon beam is diffuse and requires an RF system with large transverse and longitudinal acceptance. A traveling wave system can address these requirements. First, the number of RF power coupling ports can be significantly reduced compared with our previous pillbox concept. Secondly, by adding a nose on the cell iris, the presence of thin metal foils traversed by the muons can possibly be avoided. We show simulations of the cooling performance of a traveling wave RF system in a HCC, including cavity geometries with inter-cell RF power couplers needed for power propagation.

  6. Helical coil thermal hydraulic model

    NASA Astrophysics Data System (ADS)

    Caramello, M.; Bertani, C.; De Salve, M.; Panella, B.

    2014-11-01

    A model has been developed in Matlab environment for the thermal hydraulic analysis of helical coil and shell steam generators. The model considers the internal flow inside one helix and its associated control volume of water on the external side, both characterized by their inlet thermodynamic conditions and the characteristic geometry data. The model evaluates the behaviour of the thermal-hydraulic parameters of the two fluids, such as temperature, pressure, heat transfer coefficients, flow quality, void fraction and heat flux. The evaluation of the heat transfer coefficients as well as the pressure drops has been performed by means of the most validated literature correlations. The model has been applied to one of the steam generators of the IRIS modular reactor and a comparison has been performed with the RELAP5/Mod.3.3 code applied to an inclined straight pipe that has the same length and the same elevation change between inlet and outlet of the real helix. The predictions of the developed model and RELAP5/Mod.3.3 code are in fairly good agreement before the dryout region, while the dryout front inside the helical pipes is predicted at a lower distance from inlet by the model.

  7. Segregation of helicity in inertial wave packets

    NASA Astrophysics Data System (ADS)

    Ranjan, A.

    2017-03-01

    Inertial waves are known to exist in the Earth's rapidly rotating outer core and could be important for the dynamo generation. It is well known that a monochromatic inertial plane wave traveling parallel to the rotation axis (along positive z ) has negative helicity while the wave traveling antiparallel (negative z ) has positive helicity. Such a helicity segregation, north and south of the equator, is necessary for the α2-dynamo model based on inertial waves [Davidson, Geophys. J. Int. 198, 1832 (2014), 10.1093/gji/ggu220] to work. The core is likely to contain a myriad of inertial waves of different wave numbers and frequencies. In this study, we investigate whether this characteristic of helicity segregation also holds for an inertial wave packet comprising waves with the same sign of Cg ,z, the z component of group velocity. We first derive the polarization relations for inertial waves and subsequently derive the resultant helicity in wave packets forming as a result of superposition of two or more waves. We find that the helicity segregation does hold for an inertial wave packet unless the wave numbers of the constituent waves are widely separated. In the latter case, regions of opposite color helicity do appear, but the mean helicity retains the expected sign. An illustration of this observation is provided by (a) calculating the resultant helicity for a wave packet formed by superposition of four upward-propagating inertial waves with different wave vectors and (b) conducting the direct numerical simulation of a Gaussian eddy under rapid rotation. Last, the possible effects of other forces such as the viscous dissipation, the Lorentz force, buoyancy stratification, and nonlinearity on helicity are investigated and discussed. The helical structure of the wave packet is likely to remain unaffected by dissipation or the magnetic field, but can be modified by the presence of linearly stable stratification and nonlinearity.

  8. 2-D simulation of a waveguide free electron laser having a helical undulator

    SciTech Connect

    Kim, S.K.; Lee, B.C.; Jeong, Y.U.

    1995-12-31

    We have developed a 2-D simulation code for the calculation of output power from an FEL oscillator having a helical undulator and a cylindrical waveguide. In the simulation, the current and the energy of the electron beam is 2 A and 400 keV, respectively. The parameters of the permanent-magnet helical undulator are : period = 32 mm, number of periods = 20, magnetic field = 1.3 kG. The gain per pass is 10 and the output power is calculated to be higher than 10 kW The results of the 2-D simulation are compared with those of 1-D simulation.

  9. Design and implementation of a water phantom for IMRT, arc therapy, and tomotherapy dose distribution measurements

    SciTech Connect

    Pallotta, Stefania; Marrazzo, Livia; Bucciolini, Marta

    2007-10-15

    The aim of this paper is to present a new phantom for arc therapy, intensity-modulated radiation therapy (IMRT), and tomotherapy dose distribution measurement in pretreatment verification. The presented phantom is innovative for its use of water as the tissue equivalent material, together with a technical solution specifically designed to support radiographic or radiochromic film and ionization chambers in any desired position. The phantom comprise a Plexiglas container, whose present shape and dimensions offer the possibility to simulate a human torso or abdomen; the container can be filled with water by opening the upper cover. On the internal side of the cover, a set of carbon pipes can support film in the desired coronal, axial, or sagittal planes. At one of the two ends of the phantom, an ionization chamber can be positioned parallel to the rotation axis of the accelerator gantry in all possible positions within a 20 cm diameter cylinder, for film calibration purposes. Inhomogeneities can be inserted into the phantom using the same carbon pipes and plastic sheets used to support film. An example of vertebra-shaped inserts made of bone equivalent material is reported. Radiochromic film can be dipped in water, while radiographic film must be protected to prevent damage. To accomplish this, radiographic film is laminated using a cold laminating film. In order to assess the effects of both the lamination itself and the effects of water on laminated Kodak EDR2 film, the optical density (OD) of conventional, laminated, and laminated film immersed in water and exposed to a range of doses from 0 to 300 cGy were compared. The OD of the three samples receiving the same radiation dose did not present any significant difference, thus proving that laminated EDR2 film can also be used in water. A prerequisite for any dosimetric comparison between planned and measured data is a proper film to plan registration. The solution proposed here is an extrinsic in-plane registration

  10. SU-E-T-407: Evaluation of Four Commercial Dosimetry Systems for Routine Patient-Specific Tomotherapy Delivery Quality Assurance

    SciTech Connect

    Xing, A; Arumugam, S; Deshpande, S; George, A; Holloway, L; Vial, P; Goozee, G

    2014-06-01

    Purpose: The purpose of this project was to evaluate the performance of four commercially available dosimetry systems for Tomotherapy delivery quality assurance (DQA). Methods: Eight clinical patient plans were chosen to represent a range of treatment sites and typical clinical plans. Four DQA plans for each patient plan were created using the TomoTherapy DQA Station (Hi-Art version 4.2.1) on CT images of the ScandiDose Delta4, IBA MatriXX Evolution, PTW Octavius 4D and Sun Nuclear ArcCHECK phantoms. Each detector was calibrated following the manufacture-provided procedure. No angular response correction was applied. All DQA plans for each detector were delivered on the Tomotherapy Hi-Art unit in a single measurement session but on different days. The measured results were loaded into the vendor supplied software for each QA system for comparison with the TPS-calculated dose. The Gamma index was calculated using 3%/3mm, 2%/2mm with 10% dose threshold of maximum TPS calculated dose. Results: Four detector systems showed comparable gamma pass rates for 3%/3m, which is recommended by AAPM TG119 and commonly used within the radiotherapy community. The averaged pass rates ± standard deviation for all DQA plans were (98.35±1.97)% for ArcCHECK, (99.9%±0.87)% for Matrix, (98.5%±5.09)% for Octavius 4D, (98.7%±1.27)% for Delata4. The rank of the gamma pass rate for individual plans was consistent between detectors. Using 2%/2mm Gamma criteria for analysis, the Gamma pass rate decreased on average by 9%, 8%, 6.6% and 5% respectively. Profile and Gamma failure map analysis using the software tools from each dosimetry system indicated that decreased passing rate is mainly due to the threading effect of Tomo plan. Conclusion: Despite the variation in detector type and resolution, phantom geometry and software implementation, the four systems demonstrated similar dosimetric performance, with the rank of the gamma pass rate consistent for the plans considered.

  11. Simplified Fabrication of Helical Copper Antennas

    NASA Technical Reports Server (NTRS)

    Petro, Andrew

    2006-01-01

    A simplified technique has been devised for fabricating helical antennas for use in experiments on radio-frequency generation and acceleration of plasmas. These antennas are typically made of copper (for electrical conductivity) and must have a specific helical shape and precise diameter.

  12. Structure and interactions of biological helices

    NASA Astrophysics Data System (ADS)

    Kornyshev, Alexei A.; Lee, Dominic J.; Leikin, Sergey; Wynveen, Aaron

    2007-07-01

    Helices are essential building blocks of living organisms, be they molecular fragments of proteins ( α -helices), macromolecules (DNA and collagen), or multimolecular assemblies (microtubules and viruses). Their interactions are involved in packing of meters of genetic material within cells and phage heads, recognition of homologous genes in recombination and DNA repair, stability of tissues, and many other processes. Helical molecules form a variety of mesophases in vivo and in vitro. Recent structural studies, direct measurements of intermolecular forces, single-molecule manipulations, and other experiments have accumulated a wealth of information and revealed many puzzling physical phenomena. It is becoming increasingly clear that in many cases the physics of biological helices cannot be described by theories that treat them as simple, unstructured polyelectrolytes. The present article focuses on the most important and interesting aspects of the physics of structured macromolecules, highlighting various manifestations of the helical motif in their structure, elasticity, interactions with counterions, aggregation, and poly- and mesomorphic transitions.

  13. Solubilization and fractionation of paired helical filaments.

    PubMed

    González, P J; Correas, I; Avila, J

    1992-09-01

    Paired helical filaments isolated from brains of two different patients with Alzheimer's disease were extensively treated with the ionic detergent, sodium dodecyl sulphate. Filaments were solubilized at different extents, depending on the brain examined, thus suggesting the existence of two types of paired helical filaments: sodium dodecyl sulphate-soluble and insoluble filaments. In the first case, the number of structures resembling paired helical filaments greatly decreased after the detergent treatment, as observed by electron microscopy. Simultaneously, a decrease in the amount of sedimentable protein was also observed upon centrifugation of the sodium dodecyl sulfate-treated paired helical filaments. A sodium dodecyl sulphate-soluble fraction was isolated as a supernatant after low-speed centrifugation of the sodium dodecyl sulphate-treated paired helical filaments. The addition of the non-ionic detergent Nonidet-P40 to this fraction resulted in the formation of paired helical filament-like structures. When the sodium dodecyl sulphate-soluble fraction was further fractionated by high-speed centrifugation, three subfractions were observed: a supernatant, a pellet and a thin layer between these two subfractions. No paired helical filaments were observed in any of these subfractions, even after addition of Nonidet P-40. However, when they were mixed back together, the treatment with Nonidet P-40 resulted in the visualization of paired helical filament-like structures. These results suggest that at least two different components are needed for the reconstitution of paired helical filaments as determined by electron microscopy. The method described here may allow the study of the components involved in the formation of paired helical filaments and the identification of possible factors capable of blocking this process.

  14. Formation of helical ion chains

    NASA Astrophysics Data System (ADS)

    Nigmatullin, R.; del Campo, A.; De Chiara, G.; Morigi, G.; Plenio, M. B.; Retzker, A.

    2016-01-01

    We study the nonequilibrium dynamics of the linear-to-zigzag structural phase transition exhibited by an ion chain confined in a trap with periodic boundary conditions. The transition is driven by reducing the transverse confinement at a finite quench rate, which can be accurately controlled. This results in the formation of zigzag domains oriented along different transverse planes. The twists between different domains can be stabilized by the topology of the trap, and under laser cooling the system has a chance to relax to a helical chain with nonzero winding number. Molecular dynamics simulations are used to obtain a large sample of possible trajectories for different quench rates. The scaling of the average winding number with different quench rates is compared to the prediction of the Kibble-Zurek theory, and a good quantitative agreement is found.

  15. The quantum Hall effect helicity

    SciTech Connect

    Shrivastava, Keshav N.

    2015-04-16

    The quantum Hall effect in semiconductor heterostructures is explained by two signs in the angular momentum j=l±s and g=(2j+1)/(2l+1) along with the Landau factor (n+1/2). These modifications in the existing theories explain all of the fractional charges. The helicity which is the sign of the product of the linear momentum with the spin p.s plays an important role for the understanding of the data at high magnetic fields. In particular it is found that particles with positive sign in the spin move in one direction and those with negative sign move in another direction which explains the up and down stream motion of the particles.

  16. Best packing of identical helices

    NASA Astrophysics Data System (ADS)

    Huh, Youngsik; Hong, Kyungpyo; Kim, Hyoungjun; No, Sungjong; Oh, Seungsang

    2016-10-01

    In this paper we prove the unique existence of a ropelength-minimizing conformation of the θ-spun double helix in a mathematically rigorous way, and find the minimal ropelength {{{Rop}}}* (θ )=-\\tfrac{8π }{t} where t is the unique solution in [-θ ,0] of the equation 2-2\\cos (t+θ )={t}2. Using this result, the pitch angles of the standard, triple and quadruple helices are around 39.3771^\\circ , 42.8354^\\circ and 43.8351^\\circ , respectively, which are almost identical with the approximated pitch angles of the zero-twist structures previously known by Olsen and Bohr. We also find the ropelength of the standard N-helix.

  17. Helicity Evolution at Small x

    NASA Astrophysics Data System (ADS)

    Sievert, Michael; Kovchegov, Yuri; Pitonyak, Daniel

    2017-01-01

    We construct small- x evolution equations which can be used to calculate quark and anti-quark helicity TMDs and PDFs, along with the g1 structure function. These evolution equations resum powers of ln2(1 / x) in the polarization-dependent evolution along with the powers of ln(1 / x) in the unpolarized evolution which includes saturation effects. The equations are written in an operator form in terms of polarization-dependent Wilson line-like operators. While the equations do not close in general, they become closed and self-contained systems of non-linear equations in the large-Nc and large-Nc &Nf limits. After solving the large-Nc equations numerically we obtain the following small- x asymptotics for the flavor-singlet g1 structure function along with quarks hPDFs and helicity TMDs (in absence of saturation effects): g1S(x ,Q2) ΔqS(x ,Q2) g1L S(x ,kT2) (1/x) > αh (1/x) 2.31√{αsNc/2 π. We also give an estimate of how much of the proton's spin may be at small x and what impact this has on the so-called ``spin crisis.'' Work supported by the U.S. DOE, Office of Science, Office of Nuclear Physics under Award Number DE-SC0004286 (YK), the RIKEN BNL Research Center, and TMD Collaboration (DP), and DOE Contract No. DE-SC0012704 (MS).

  18. BEAM-BEAM 2003 SUMMARY.

    SciTech Connect

    FISCHER,W.SEN,T.

    2003-05-19

    This paper summarizes the presentations and discussions of the Beam-Beam'03 workshop, held in Montauk, Long Island, from May 19 to 23, 2003. Presentations and discussions focused on halo generation from beam-beam interactions; beam-beam limits, especially coherent limits and their effects on existing and future hadron colliders; beam-beam compensation techniques, particularly for long-range interactions; and beam-beam study tools in theory, simulation, and experiment.

  19. Helicity within the vortex filament model

    PubMed Central

    Hänninen, R.; Hietala, N.; Salman, H.

    2016-01-01

    Kinetic helicity is one of the invariants of the Euler equations that is associated with the topology of vortex lines within the fluid. In superfluids, the vorticity is concentrated along vortex filaments. In this setting, helicity would be expected to acquire its simplest form. However, the lack of a core structure for vortex filaments appears to result in a helicity that does not retain its key attribute as a quadratic invariant. By defining a spanwise vector to the vortex through the use of a Seifert framing, we are able to introduce twist and henceforth recover the key properties of helicity. We present several examples for calculating internal twist to illustrate why the centreline helicity alone will lead to ambiguous results if a twist contribution is not introduced. Our choice of the spanwise vector can be expressed in terms of the tangential component of velocity along the filament. Since the tangential velocity does not alter the configuration of the vortex at later times, we are able to recover a similar equation for the internal twist angle to that of classical vortex tubes. Our results allow us to explain how a quasi-classical limit of helicity emerges from helicity considerations for individual superfluid vortex filaments. PMID:27883029

  20. Magnetic Helicity in a Cyclic Convective Dynamo

    NASA Astrophysics Data System (ADS)

    Miesch, Mark S.; Zhang, Mei; Augustson, Kyle C.

    2016-05-01

    Magnetic helicity is a fundamental agent for magnetic self-organization in magnetohydrodynamic (MHD) dynamos. As a conserved quantity in ideal MHD, it establishes a strict topological coupling between large and small-scale magnetic fields. The generation of magnetic fields on scales larger than the velocity field is linked to an upscale transfer of magnetic helicity, either locally in spectral space as in the inverse cascade of magnetic helicity in MHD turbulence or non-locally, as in the turbulent alpha-effect of mean-field dynamo theory. Thus, understanding the generation, transport, and dissipation of magnetic helicity is an essential prerequisite to understanding manifestations of magnetic self-organization in the solar dynamo, including sunspots, the prominent dipole and quadrupole moments, and the 22-year magnetic activity cycle. We investigate the role of magnetic helicity in a convective dynamo model that exhibits regular magnetic cycles. The cycle is marked by coherent bands of toroidal field that persist within the convection zone and that are antisymmetric about the equator. When these toriodal bands interact across the equator, it initiates a global restructuring of the magnetic topology that contributes to the reversal of the dipole moment. Thus, the polar field reversals are preceeded by a brief reversal of the subsurface magnetic helicity. There is some evidence that the Sun may exhibit a similar magnetic helicity reversal prior to its polar field reversals.

  1. Helicity within the vortex filament model

    NASA Astrophysics Data System (ADS)

    Hänninen, R.; Hietala, N.; Salman, H.

    2016-11-01

    Kinetic helicity is one of the invariants of the Euler equations that is associated with the topology of vortex lines within the fluid. In superfluids, the vorticity is concentrated along vortex filaments. In this setting, helicity would be expected to acquire its simplest form. However, the lack of a core structure for vortex filaments appears to result in a helicity that does not retain its key attribute as a quadratic invariant. By defining a spanwise vector to the vortex through the use of a Seifert framing, we are able to introduce twist and henceforth recover the key properties of helicity. We present several examples for calculating internal twist to illustrate why the centreline helicity alone will lead to ambiguous results if a twist contribution is not introduced. Our choice of the spanwise vector can be expressed in terms of the tangential component of velocity along the filament. Since the tangential velocity does not alter the configuration of the vortex at later times, we are able to recover a similar equation for the internal twist angle to that of classical vortex tubes. Our results allow us to explain how a quasi-classical limit of helicity emerges from helicity considerations for individual superfluid vortex filaments.

  2. High Efficiency Electron-Laser Interactions in Tapered Helical Undulators

    NASA Astrophysics Data System (ADS)

    Duris, Joseph Patrick

    Efficient coupling of relativistic electron beams with high power radiation lies at the heart of advanced accelerator and light source research and development. The inverse free electron laser is a stable accelerator capable of harnessing very high intensity laser electric fields to efficiently transfer large powers from lasers to electron beams. In this dissertation, we first present the theoretical framework to describe the interaction, and then apply our improved understanding of the IFEL to the design and numerical study of meter-long, GeV IFELs for compact light sources. The central experimental work of the dissertation is the UCLA BNL helical inverse free electron laser experiment at the Accelerator Test Facility in Brookhaven National Laboratory which used a strongly tapered 54cm long, helical, permanent magnet undulator and a several hundred GW CO2 laser to accelerate electrons from 52 to 106MeV, setting new records for inverse free electron laser energy gain (54MeV) and average accelerating gradient (100MeV/m). The undulator design and fabrication as well as experimental diagnostics are presented. In order to improve the stability and quality of the accelerated electron beam, we redesigned the undulator for a slightly reduced output energy by modifying the magnet gap throughout the undulator, and we used this modified undulator to demonstrated capture of >25% of the injected beam without prebunching. In the study of heavily loaded GeV inverse free electron lasers, we show that a majority of the power may be transferred from a laser to the accelerated electron beam. Reversing the process to decelerate high power electron beams, a mechanism we refer to as tapering enhanced stimulated superradiant amplification, offers a clear path to high power light sources. We present studies of radiation production for a wide range of wavelengths (10mum, 13nm, and 0.3nm) using this method and discuss the design for a deceleration experiment using the same undulator used

  3. Recent Innovations in Muon Beam Cooling

    SciTech Connect

    Johnson, Rolland P.; Alsharo'a, Mohammad; Hanlet, Pierrick M.; Hartline, Robert; Kuchnir, Moyses; Paul, Kevin; Roberts, Thomas J.; Ankenbrandt, Charles; Barzi, Emanuela; Del Frate, Licia; Gonin, Ivan; Moretti, Alfred; Neuffer, David; Popovic, Milorad; Romanov, Gennady; Turrioni, Daniele; Yarba, Victor; Beard, Kevin; Bogacz, S. Alex; Derbenev, Yaroslav

    2006-03-20

    Eight new ideas are being developed under SBIR/STTR grants to cool muon beams for colliders, neutrino factories, and muon experiments. Analytical and simulation studies have confirmed that a six-dimensional (6D) cooling channel based on helical magnets surrounding RF cavities filled with dense hydrogen gas can provide effective beam cooling. This helical cooling channel (HCC) has solenoidal, helical dipole, helical quadrupole, and helical sextupole magnetic fields to generate emittance exchange and achieve 6D emittance reduction of over 3 orders of magnitude in a 100 m segment. Four such sequential HCC segments, where the RF frequencies are increased and transverse physical dimensions reduced as the beams become cooler, implies a 6D emittance reduction of almost five orders of magnitude. Two new cooling ideas, Parametric-resonance Ionization Cooling and Reverse Emittance Exchange, then can be employed to reduce transverse emittances to a few mm-mr, which allows high luminosity with fewer muons than previously imagined. We describe these new ideas as well as a new precooling idea based on a HCC with z dependent fields that can be used as MANX, an exceptional 6D cooling demonstration experiment.

  4. Recent Innovations in Muon Beam Cooling

    SciTech Connect

    Rolland P. Johnson; Mohammad Alsharo'a; Charles Ankenbrandt; Emanuela Barzi; Kevin Beard; S. Alex Bogacz; Yaroslav Derbenev; Licia Del Frate; Ivan Gonin; Pierrick M. Hanlet; Robert Hartline; Daniel M. Kaplan; Moyses Kuchnir; Alfred Moretti; David Neuffer; Kevin Paul; Milorad Popovic; Thomas J. Roberts; Gennady Romanov; Daniele Turrioni; Victor Yarba; and Katsuya Yonehara

    2006-03-01

    Eight new ideas are being developed under SBIR/STTR grants to cool muon beams for colliders, neutrino factories, and muon experiments. Analytical and simulation studies have confirmed that a six-dimensional (6D) cooling channel based on helical magnets surrounding RF cavities filled with dense hydrogen gas can provide effective beam cooling. This helical cooling channel (HCC) has solenoidal, helical dipole, helical quadrupole, and helical sextupole magnetic fields to generate emittance exchange and achieve 6D emittance reduction of over 3 orders of magnitude in a 100 m segment. Four such sequential HCC segments, where the RF frequencies are increased and transverse physical dimensions reduced as the beams become cooler, implies a 6D emittance reduction of almost five orders of magnitude. Two new cooling ideas, Parametric-resonance Ionization Cooling and Reverse Emittance Exchange, then can be employed to reduce transverse emittances to a few mm-mr, which allows high luminosity with fewer muons than previously imagined. We describe these new ideas as well as a new precooling idea based on a HCC with z dependent fields that can be used as MANX, an exceptional 6D cooling demonstration experiment.

  5. Hydrodynamic interaction between two helical swimmers

    NASA Astrophysics Data System (ADS)

    Ruiz Esparza, Alejandro; Godinez, Francisco; Lauga, Eric; Zenit, Roberto

    2016-11-01

    Many motile bacteria, such as E. coli, possess several helical flagellar filaments that bundle together to form a coherent helical element for propulsion. In order to understand the process of bundling, we study the interaction between two identical helical magnetic swimmers that self propel in a highly viscous Newtonian fluid due to the rotation of an external magnetic field. Our experiments reveal that hydrodynamic interactions lead to nontrivial collective and relative effects, both in translation and rotation. We will present our experimental results and discuss the physical mechanisms responsible for our observations.

  6. Helicity oscillations of Dirac and Majorana neutrinos

    NASA Astrophysics Data System (ADS)

    Dobrynina, Alexandra; Kartavtsev, Alexander; Raffelt, Georg

    2016-06-01

    The helicity of a Dirac neutrino with mass m evolves under the influence of a B field because it has a magnetic dipole moment proportional to m . Moreover, it was recently shown that a polarized or anisotropic medium engenders the same effect for both Dirac and Majorana neutrinos. Because a B field polarizes a background medium, it instigates helicity oscillations even for Majorana neutrinos unless the medium is symmetric between matter and antimatter. Motivated by these observations, we review the impact of a B field and of an anisotropic or polarized medium on helicity oscillations for Dirac and Majorana neutrinos from the common perspective of in-medium dispersion.

  7. Polymorphic transformation of helical flagella of bacteria

    NASA Astrophysics Data System (ADS)

    Lim, Sookkyung; Howard Berg Collaboration; William Ko Collaboration; Yongsam Kim Collaboration; Wanho Lee Collaboration; Charles Peskin Collaboration

    2016-11-01

    Bacteria such as E. coli swim in an aqueous environment by utilizing the rotation of flagellar motors and alternate two modes of motility, runs and tumbles. Runs are steady forward swimming driven by bundles of flagellar filaments whose motors are turning CCW; tumbles involve a reorientation of the direction of swimming triggered by motor reversals. During tumbling, the helical flagellum undergoes polymorphic transformations, which is a local change in helical pitch, helical radius, and handedness. In this work, we investigate the underlying mechanism of structural conformation and how this polymorphic transition plays a role in bacterial swimming. National Science Foundation.

  8. Thermally activated helicity reversals of skyrmions

    NASA Astrophysics Data System (ADS)

    Yu, X. Z.; Shibata, K.; Koshibae, W.; Tokunaga, Y.; Kaneko, Y.; Nagai, T.; Kimoto, K.; Taguchi, Y.; Nagaosa, N.; Tokura, Y.

    2016-04-01

    Magnetic bubbles with winding number S =1 are topologically equivalent to skyrmions. Here we report the discovery of helicity (in-plane magnetization-swirling direction) reversal of skyrmions, while keeping their hexagonal lattice form, at above room temperature in a thin hexaferrite magnet. We have observed that the frequency of helicity reversals dramatically increases with temperature in a thermally activated manner, revealing that the generation energy of a kink-soliton pair for switching helicity on a skyrmion rapidly decreases towards the magnetic transition temperature.

  9. Experimental studies of helical solenoid model based on YBCO tape-bridge joints

    SciTech Connect

    Yu, M.; Lombardo, V.; Turrioni, D.; Zlobin, A.V.; Flangan, G.; Lopes, M.L.; Johnson, R.P.; /Fermilab

    2011-06-01

    Helical solenoids that provide solenoid, helical dipole and helical gradient field components are designed for a helical cooling channel (HCC) proposed for cooling of muon beams in a muon collider. The high temperature superconductor (HTS), 12 mm wide and 0.1 mm thick YBCO tape, is used as the conductor for the highest-field section of HCC due to certain advantages, such as its electrical and mechanical properties. To study and address the design, and technological and performance issues related to magnets based on YBCO tapes, a short helical solenoid model based on double-pancake coils was designed, fabricated and tested at Fermilab. Splicing joints were made with Sn-Pb solder as the power leads and the connection between coils, which is the most critical element in the magnet that can limit the performance significantly. This paper summarizes the test results of YBCO tape and double-pancake coils in liquid nitrogen and liquid helium, and then focuses on the study of YBCO splices, including the soldering temperatures and pressures, and splice bending test.

  10. Helical and rod-shaped bacteria swim in helical trajectories with little additional propulsion from helical shape.

    PubMed

    Constantino, Maira A; Jabbarzadeh, Mehdi; Fu, Henry C; Bansil, Rama

    2016-11-01

    It has frequently been hypothesized that the helical body shapes of flagellated bacteria may yield some advantage in swimming ability. In particular, the helical-shaped pathogen Helicobacter pylori is often claimed to swim like a corkscrew through its harsh gastric habitat, but there has been no direct confirmation or quantification of such claims. Using fast time-resolution and high-magnification two-dimensional (2D) phase-contrast microscopy to simultaneously image and track individual bacteria in bacterial broth as well as mucin solutions, we show that both helical and rod-shaped H. pylori rotated as they swam, producing a helical trajectory. Cell shape analysis enabled us to determine shape as well as the rotational and translational speed for both forward and reverse motions, thereby inferring flagellar kinematics. Using the method of regularized Stokeslets, we directly compare observed speeds and trajectories to numerical calculations for both helical and rod-shaped bacteria in mucin and broth to validate the numerical model. Although experimental observations are limited to select cases, the model allows quantification of the effects of body helicity, length, and diameter. We find that due to relatively slow body rotation rates, the helical shape makes at most a 15% contribution to propulsive thrust. The effect of body shape on swimming speeds is instead dominated by variations in translational drag required to move the cell body. Because helical cells are one of the strongest candidates for propulsion arising from the cell body, our results imply that quite generally, swimming speeds of flagellated bacteria can only be increased a little by body propulsion.

  11. Helical and rod-shaped bacteria swim in helical trajectories with little additional propulsion from helical shape

    PubMed Central

    Constantino, Maira A.; Jabbarzadeh, Mehdi; Fu, Henry C.; Bansil, Rama

    2016-01-01

    It has frequently been hypothesized that the helical body shapes of flagellated bacteria may yield some advantage in swimming ability. In particular, the helical-shaped pathogen Helicobacter pylori is often claimed to swim like a corkscrew through its harsh gastric habitat, but there has been no direct confirmation or quantification of such claims. Using fast time-resolution and high-magnification two-dimensional (2D) phase-contrast microscopy to simultaneously image and track individual bacteria in bacterial broth as well as mucin solutions, we show that both helical and rod-shaped H. pylori rotated as they swam, producing a helical trajectory. Cell shape analysis enabled us to determine shape as well as the rotational and translational speed for both forward and reverse motions, thereby inferring flagellar kinematics. Using the method of regularized Stokeslets, we directly compare observed speeds and trajectories to numerical calculations for both helical and rod-shaped bacteria in mucin and broth to validate the numerical model. Although experimental observations are limited to select cases, the model allows quantification of the effects of body helicity, length, and diameter. We find that due to relatively slow body rotation rates, the helical shape makes at most a 15% contribution to propulsive thrust. The effect of body shape on swimming speeds is instead dominated by variations in translational drag required to move the cell body. Because helical cells are one of the strongest candidates for propulsion arising from the cell body, our results imply that quite generally, swimming speeds of flagellated bacteria can only be increased a little by body propulsion. PMID:28138539

  12. Three-dimensional printing of freeform helical microstructures: a review

    NASA Astrophysics Data System (ADS)

    Farahani, R. D.; Chizari, K.; Therriault, D.

    2014-08-01

    Three-dimensional (3D) printing is a fabrication method that enables creation of structures from digital models. Among the different structures fabricated by 3D printing methods, helical microstructures attracted the attention of the researchers due to their potential in different fields such as MEMS, lab-on-a-chip systems, microelectronics and telecommunications. Here we review different types of 3D printing methods capable of fabricating 3D freeform helical microstructures. The techniques including two more common microfabrication methods (i.e., focused ion beam chemical vapour deposition and microstereolithography) and also five methods based on computer-controlled robotic direct deposition of ink filament (i.e., fused deposition modeling, meniscus-confined electrodeposition, conformal printing on a rotating mandrel, UV-assisted and solvent-cast 3D printings) and their advantages and disadvantages regarding their utilization for the fabrication of helical microstructures are discussed. Focused ion beam chemical vapour deposition and microstereolithography techniques enable the fabrication of very precise shapes with a resolution down to ~100 nm. However, these techniques may have material constraints (e.g., low viscosity) and/or may need special process conditions (e.g., vacuum chamber) and expensive equipment. The five other techniques based on robotic extrusion of materials through a nozzle are relatively cost-effective, however show lower resolution and less precise features. The popular fused deposition modeling method offers a wide variety of printable materials but the helical microstructures manufactured featured a less precise geometry compared to the other printing methods discussed in this review. The UV-assisted and the solvent-cast 3D printing methods both demonstrated high performance for the printing of 3D freeform structures such as the helix shape. However, the compatible materials used in these methods were limited to UV-curable polymers and

  13. Three-dimensional printing of freeform helical microstructures: a review.

    PubMed

    Farahani, R D; Chizari, K; Therriault, D

    2014-09-21

    Three-dimensional (3D) printing is a fabrication method that enables creation of structures from digital models. Among the different structures fabricated by 3D printing methods, helical microstructures attracted the attention of the researchers due to their potential in different fields such as MEMS, lab-on-a-chip systems, microelectronics and telecommunications. Here we review different types of 3D printing methods capable of fabricating 3D freeform helical microstructures. The techniques including two more common microfabrication methods (i.e., focused ion beam chemical vapour deposition and microstereolithography) and also five methods based on computer-controlled robotic direct deposition of ink filament (i.e., fused deposition modeling, meniscus-confined electrodeposition, conformal printing on a rotating mandrel, UV-assisted and solvent-cast 3D printings) and their advantages and disadvantages regarding their utilization for the fabrication of helical microstructures are discussed. Focused ion beam chemical vapour deposition and microstereolithography techniques enable the fabrication of very precise shapes with a resolution down to ∼100 nm. However, these techniques may have material constraints (e.g., low viscosity) and/or may need special process conditions (e.g., vacuum chamber) and expensive equipment. The five other techniques based on robotic extrusion of materials through a nozzle are relatively cost-effective, however show lower resolution and less precise features. The popular fused deposition modeling method offers a wide variety of printable materials but the helical microstructures manufactured featured a less precise geometry compared to the other printing methods discussed in this review. The UV-assisted and the solvent-cast 3D printing methods both demonstrated high performance for the printing of 3D freeform structures such as the helix shape. However, the compatible materials used in these methods were limited to UV-curable polymers and

  14. Dissecting π-helices: sequence, structure and function.

    PubMed

    Kumar, Prasun; Bansal, Manju

    2015-11-01

    A new procedure for the identification of regular secondary structures using a C(α) trace has identified 659 π-helices in 3582 protein chains, solved at high resolution. Taking advantage of this significantly expanded database of π-helices, we have analysed the functional and structural roles of π-helices and determined the position-wise amino acid propensity within and around them. These helices range from 5 to 18 residues in length with the average twist and rise being 85.2 ± 7.2° and 1.28 ± 0.31 Å, respectively. A total of 546 (~ 83%) out of 659 π-helices occur in conjunction with α-helices, with 101 π-helices being interspersed between two α-helices. The majority of interspersed π-helices were found to be conserved across a large number of structures within a protein family and produce a significant bend in the overall helical segment as well as local distortions in the neighbouring α-helices. The presence of a π-helical fragment leads to appropriate orientation of the constituent residues, so as to facilitate favourable interactions and also help in proper folding of the protein chain. In addition to intra helical 6→1 N-H···O hydrogen bonds, π-helices are also stabilized by several other non-bonded interactions. π-Helices show distinct positional residue preferences, which are different from those of α-helices.

  15. Scaling laws in decaying helical hydromagnetic turbulence

    NASA Astrophysics Data System (ADS)

    Christensson, M.; Hindmarsh, M.; Brandenburg }%, A.

    2005-07-01

    We study the evolution of growth and decay laws for the magnetic field coherence length ξ, energy E_M and magnetic helicity H in freely decaying 3D MHD turbulence. We show that with certain assumptions, self-similarity of the magnetic power spectrum alone implies that ξ σm t1/2. This in turn implies that magnetic helicity decays as Hσm t-2s, where s=(ξ_diff/ξH)2, in terms of ξ_diff, the diffusion length scale, and ξ_H, a length scale defined from the helicity power spectrum. The relative magnetic helicity remains constant, implying that the magnetic energy decays as E_M σm t-1/2-2s. The parameter s is inversely proportional to the magnetic Reynolds number Re_M, which is constant in the self-similar regime.

  16. Helical vortices: viscous dynamics and instability

    NASA Astrophysics Data System (ADS)

    Rossi, Maurice; Selcuk, Can; Delbende, Ivan; Ijlra-Upmc Team; Limsi-Cnrs Team

    2014-11-01

    Understanding the dynamical properties of helical vortices is of great importance for numerous applications such as wind turbines, helicopter rotors, ship propellers. Locally these flows often display a helical symmetry: fields are invariant through combined axial translation of distance Δz and rotation of angle θ = Δz / L around the same z-axis, where 2 πL denotes the helix pitch. A DNS code with built-in helical symmetry has been developed in order to compute viscous quasi-steady basic states with one or multiple vortices. These states will be characterized (core structure, ellipticity, ...) as a function of the pitch, without or with an axial flow component. The instability modes growing in the above base flows and their growth rates are investigated by a linearized version of the DNS code coupled to an Arnoldi procedure. This analysis is complemented by a helical thin-cored vortex filaments model. ANR HELIX.

  17. Helical Microfilaments with Alternating Imprinted Intrinsic Curvatures.

    PubMed

    Silva, Pedro Emanuel Santos; Godinho, Maria Helena

    2017-03-01

    There has been an intense research for developing techniques that can produce filaments with helical shapes, given the widespread of potential applications. In this work, how helices with different curvatures can be precisely imprinted in microfilaments is shown. It is also shown that using this technique, it is possible to produce, in a single fiber, helices with different curvatures. This striking and innovative behavior is observed when one side of the stretched filaments is irradiated with UV light, modifying the mechanical properties at surface. Upon release, the regions with higher curvature start to curl first, while regions with lower intrinsic curvature remain stretched until start to curl later. The results presented here can be important to understand why structures adopt a helical shape in general, which can be of interest in nanotechnology, biomolecular science, or even to understand why plant filaments curl.

  18. Building blocks for subleading helicity operators

    DOE PAGES

    Kolodrubetz, Daniel W.; Moult, Ian; Stewart, Iain W.

    2016-05-24

    On-shell helicity methods provide powerful tools for determining scattering amplitudes, which have a one-to-one correspondence with leading power helicity operators in the Soft-Collinear Effective Theory (SCET) away from singular regions of phase space. We show that helicity based operators are also useful for enumerating power suppressed SCET operators, which encode subleading amplitude information about singular limits. In particular, we present a complete set of scalar helicity building blocks that are valid for constructing operators at any order in the SCET power expansion. In conclusion, we also describe an interesting angular momentum selection rule that restricts how these building blocks canmore » be assembled.« less

  19. Helical modes in boundary layer transition

    NASA Astrophysics Data System (ADS)

    Bose, Rikhi; Durbin, Paul A.

    2016-11-01

    Observations are presented to show that in an adverse pressure gradient boundary layer, beneath free-stream turbulence, the interaction between Klebanoff streaks and naturally arising instability waves leads to helical disturbances which break down to form turbulent spots. This occurs under low to moderate levels, 1%-2%, of free-stream turbulence. At high levels of free-stream turbulence, conventional bypass mechanisms are seen. The helical structures are clearly identifiable in visualizations of isosurfaces of streamwise perturbation velocity. A direct numerical simulation also was performed in zero pressure gradient, with a time-periodic Tollmien-Schlichting wave eigenfunction at the inlet. Again, under a moderate level of free-stream turbulence, helices were observed, and found to trigger transition. Their wave speed is on the order of 1/2 U∞ , so helical breakdown can be viewed as a type of inner mode, secondary instability.

  20. Motion of multiple helical vortices

    NASA Astrophysics Data System (ADS)

    Velasco Fuentes, Oscar

    2015-11-01

    In 1912 Joukowsky deduced that in an unbounded ideal fluid a set of helical vortices--when these are equal, coaxial and symmetrically arranged--would translate and rotate steadily while the vortices preserve their form and relative position. Each vortex is an infinite tube whose cross-section is circular (with radius a) and whose centerline is a helix of pitch L and radius R. The motion is thus determined by three non-dimensional parameters only: the number of vortices N, the vortex radius α = a / R and the vortex pitch τ = L / 2 πR . Here, we express the linear and angular velocities of the vortices as the sum of the mutually induced velocities found by Okulov (2004) and the self-induced velocities found by Velasco Fuentes (2015). We verified that our results are accurate over the whole range of values of the vortices' pitch and radius by numerically computing the vortex motion with two smoothed versions of the Biot-Savart law. It was found that the translation velocity U grows with the number of vortices (N) but decreases as the vortices' radius and pitch (a and τ, respectively) increase; in contrast, the rotation velocity Ω grows with N and a but has a local minimum around τ = 1 for fixed values of N and a.

  1. The motion of helical vortices

    NASA Astrophysics Data System (ADS)

    Velasco Fuentes, Oscar

    2014-11-01

    We study the motion of a helical vortex in an inviscid, incompressible fluid of infinite extent. The vortex is a thin tube, of circular cross section and uniform vorticity, whose centerline is a helix of uniform pitch. Ever since Joukowsky (1912) deduced that this vortex is a steady solution of the Euler equations, numerous attempts have been made to compute its self-induced velocity. Here we use Hardin's (1982) solution for the velocity field in order to compute, for any pitch value, the linear and angular velocities of the vortex. Our formulas were verified by direct numerical integration of both the Biot-Savart and Helmholtz equations, and were also found to compare favourably with previous theoretical results. In terms of the vortex capacity to transport fluid, we identified three regimes: a helix of large pitch moves slowly, carrying a large mass of fluid; a thin helix of small pitch moves fast, carrying a small mass of fluid; and a fat helix of small pitch is a moderate carrier itself but it pushes fluid forward along its axis.

  2. CURRENT HELICITY OF ACTIVE REGIONS AS A TRACER OF LARGE-SCALE SOLAR MAGNETIC HELICITY

    SciTech Connect

    Zhang, H.; Gao, Y.; Xu, H.; Moss, D.; Kleeorin, N.; Rogachevskii, I.; Kuzanyan, K.; Sokoloff, D.

    2012-05-20

    We demonstrate that the current helicity observed in solar active regions traces the magnetic helicity of the large-scale dynamo generated field. We use an advanced two-dimensional mean-field dynamo model with dynamo saturation based on the evolution of the magnetic helicity and algebraic quenching. For comparison, we also studied a more basic two-dimensional mean-field dynamo model with simple algebraic alpha-quenching only. Using these numerical models we obtained butterfly diagrams both for the small-scale current helicity and also for the large-scale magnetic helicity, and compared them with the butterfly diagram for the current helicity in active regions obtained from observations. This comparison shows that the current helicity of active regions, as estimated by -A {center_dot} B evaluated at the depth from which the active region arises, resembles the observational data much better than the small-scale current helicity calculated directly from the helicity evolution equation. Here B and A are, respectively, the dynamo generated mean magnetic field and its vector potential. A theoretical interpretation of these results is given.

  3. Dosimetric difference amongst 3 techniques: TomoTherapy, sliding-window intensity-modulated radiotherapy (IMRT), and RapidArc radiotherapy in the treatment of late-stage nasopharyngeal carcinoma (NPC)

    SciTech Connect

    Lee, Francis Kar-ho Yip, Celia Wai-yi; Cheung, Frankie Chun-hung; Leung, Alex Kwok-cheung; Chau, Ricky Ming-chun; Ngan, Roger Kai-cheong

    2014-04-01

    To investigate the dosimetric difference amongst TomoTherapy, sliding-window intensity-modulated radiotherapy (IMRT), and RapidArc radiotherapy in the treatment of late-stage nasopharyngeal carcinoma (NPC). Ten patients with late-stage (Stage III or IV) NPC treated with TomoTherapy or IMRT were selected for the study. Treatment plans with these 3 techniques were devised according to departmental protocol. Dosimetric parameters for organ at risk and treatment targets were compared between TomoTherapy and IMRT, TomoTherapy and RapidArc, and IMRT and RapidArc. Comparison amongst the techniques was done by statistical tests on the dosimetric parameters, total monitor unit (MU), and expected delivery time. All 3 techniques achieved similar target dose coverage. TomoTherapy achieved significantly lower doses in lens and mandible amongst the techniques. It also achieved significantly better dose conformity to the treatment targets. RapidArc achieved significantly lower dose to the eye and normal tissue, lower total MU, and less delivery time. The dosimetric advantages of the 3 techniques were identified in the treatment of late-stage NPC. This may serve as a guideline for selection of the proper technique for different clinical cases.

  4. Decay of helical and nonhelical magnetic knots

    NASA Astrophysics Data System (ADS)

    Candelaresi, Simon; Brandenburg, Axel

    2011-07-01

    We present calculations of the relaxation of magnetic field structures that have the shape of particular knots and links. A set of helical magnetic flux configurations is considered, which we call n-foil knots of which the trefoil knot is the most primitive member. We also consider two nonhelical knots; namely, the Borromean rings as well as a single interlocked flux rope that also serves as the logo of the Inter-University Centre for Astronomy and Astrophysics in Pune, India. The field decay characteristics of both configurations is investigated and compared with previous calculations of helical and nonhelical triple-ring configurations. Unlike earlier nonhelical configurations, the present ones cannot trivially be reduced via flux annihilation to a single ring. For the n-foil knots the decay is described by power laws that range form t-2/3 to t-1/3, which can be as slow as the t-1/3 behavior for helical triple-ring structures that were seen in earlier work. The two nonhelical configurations decay like t-1, which is somewhat slower than the previously obtained t-3/2 behavior in the decay of interlocked rings with zero magnetic helicity. We attribute the difference to the creation of local structures that contain magnetic helicity which inhibits the field decay due to the existence of a lower bound imposed by the realizability condition. We show that net magnetic helicity can be produced resistively as a result of a slight imbalance between mutually canceling helical pieces as they are being driven apart. We speculate that higher order topological invariants beyond magnetic helicity may also be responsible for slowing down the decay of the two more complicated nonhelical structures mentioned above.

  5. Helical rotary screw expander power system

    NASA Technical Reports Server (NTRS)

    Mckay, R. A.; Sprankle, R. S.

    1974-01-01

    An energy converter for the development of wet steam geothermal fields is described. A project to evaluate and characterize a helical rotary screw expander for geothermal applications is discussed. The helical screw expander is a positive displacement machine which can accept untreated corrosive mineralized water of any quality from a geothermal well. The subjects of corrosion, mineral deposition, the expansion process, and experience with prototype devices are reported.

  6. Dynamic Orthogonal Switching of a Thermoresponsive Self-Organized Helical Superstructure.

    PubMed

    Zhang, Lingli; Wang, Ling; Hiremath, Uma S; Bisoyi, Hari Krishna; Nair, Geetha G; Yelamaggad, Channabasaveshwar V; Urbas, Augustine M; Bunning, Timothy J; Li, Quan

    2017-04-12

    Controllable manipulation of self-organized dynamic superstructures of functional molecular materials by external stimuli is an enabling enterprise. Herein, we have developed a thermally driven, self-organized helical superstructure, i.e., thermoresponsive cholesteric liquid crystal (CLC), by integrating a judiciously chosen thermoresponsive chiral molecular switch into an achiral liquid crystalline medium. The CLC in lying state, in both planar and twisted nematic cells, exhibits reversible in-plane orthogonal switching of its helical axis in response to the combined effect of temperature and electric field. Consequently, the direction of the cholesteric grating has been observed to undergo 90° switching in a single cell, enabling non-mechanical beam steering along two orthogonal directions. The ability to reversibly switch the cholesteric gartings along perpendicular directions by appropriately adjusting temperature and electric field strength could facilitate their applications in 2D beam steering, spectrum scanning, optoelectronics and beyond.

  7. Influence of initial mean helicity on homogeneous turbulent shear flow.

    PubMed

    Jacobitz, Frank G; Schneider, Kai; Bos, Wouter J T; Farge, Marie

    2011-11-01

    Helicity statistics are studied in homogeneous turbulent shear flow. Initial mean helicity is imposed on an isotropic turbulence field using a decomposition of the flow into complex-valued helical waves. The initial decay of the turbulent kinetic energy is weakened in the presence of strong mean helicity, consistent with an analytic analysis of the spectral tensor of velocity correlations. While exponential growth of the mean turbulent kinetic energy is obtained, the mean helicity decays. Probability distribution functions (PDFs) of helicity are skewed and show that the imposed mean helicity prevails throughout the simulations. A wavelet-based scale-dependent analysis shows a trend to two dimensionalization for large scales of motion and a preference for helical motion at small scales. The magnitude of the skewness of the PDFs decreases for smaller scales. Joint PDFs indicate a strong correlation of the signs of both, helicity and superhelicity, for all cases. This correlation supports the conjecture that superhelicity dissipates helicity.

  8. SU-C-210-02: Impact of Intrafractional Motion On TomoTherapy Stereotactic Body Radiotherapy (SBRT) 4D Dosimetry

    SciTech Connect

    Lian, J; Matney, J; Chao, E; Chang, S; Zagar, T; Wang, A; Chera, B; Das, S; Schreiber, E

    2015-06-15

    Purpose: TomoTherapy treatment has unique challenges in handling intrafractional motion compared to conventional LINAC. This study is aimed to gain a realistic and quantitative understanding of motion impact on TomoTherapy SBRT treatment of lung and prostate cancer patients. Methods: A 4D dose engine utilizing GPUs and including motion during treatment was developed for the efficient simulation of TomoTherapy delivered dosimetry. Two clinical CyberKnife lung cases with respiratory motion tracking and two prostate cases with a slower non-periodical organ motion treated by LINAC plus Calypso tracking were used in the study. For each disease site, one selected case has an average motion (6mm); the other has a large motion (10mm for lung and 15mm for prostate). SBRT of lung and prostate cases were re-planned on TomoTherapy with 12 Gyx4 fractions and 7Gyx5 fractions, respectively, all with 95% PTV coverage. Each case was planned with 4 jaw settings: 1) conventional 1cm static, 2) 2.5cm static, 3) 2.5cm dynamic, and 4) 5cm dynamic. The intrafractional rigid motion of the target was applied in the dose calculation of individual fractions of each plan and total dose was accumulated from multiple fractions. Results: For 1cm static jaw plans with motions applied, PTV coverage is related to motion type and amplitude. For SBRT patients with average motion (6mm), the PTV coverage remains > 95% for lung case and 74% for prostate case. For cases with large motion, PTV coverage drops to 61% for lung SBRT and 49% for prostate SBRT. Plans with other jaws improve uniformity of moving target, but still suffer from poor PTV coverage (< 70%). Conclusion: TomoTherapy lung SBRT is less motion-impacted when average amplitude of respiratory-induced intrafractional motion is present (6mm). When motion is large and/or non-periodic (prostate), all studied plans lead to significantly decreased target coverage in actual delivered dosimetry.

  9. A dosimetric comparison of 3D-CRT, IMRT, and static tomotherapy with an SIB for large and small breast volumes

    SciTech Connect

    Michalski, Andrea; Atyeo, John; Cox, Jennifer; Rinks, Marianne; Morgia, Marita; Lamoury, Gillian

    2014-07-01

    Radiation therapy to the breast is a complex task, with many different techniques that can be employed to ensure adequate dose target coverage while minimizing doses to the organs at risk. This study compares the dose planning outcomes of 3 radiation treatment modalities, 3 dimensional conformal radiation therapy (3D-CRT), intensity-modulated radiation therapy (IMRT), and static tomotherapy, for left-sided whole-breast radiation treatment with a simultaneous integrated boost (SIB). Overall, 20 patients with left-sided breast cancer were separated into 2 cohorts, small and large, based on breast volume. Dose plans were produced for each patient using 3D-CRT, IMRT, and static tomotherapy. All patients were prescribed a dose of 45 Gy in 20 fractions to the breast with an SIB of 56 Gy in 20 fractions to the tumor bed and normalized so that D{sub 98%} > 95% of the prescription dose. Dosimetric comparisons were made between the 3 modalities and the interaction of patient size. All 3 modalities offered adequate planning target volume (PTV) coverage with D{sub 98%} > 95% and D{sub 2%} < 107%. Static tomotherapy offered significantly improved (p = 0.006) dose homogeneity to the PTV{sub boost} {sub eval} (0.079 ± 0.011) and breast minus the SIB volume (Breast{sub SIB}) (p < 0.001, 0.15 ± 0.03) compared with the PTV{sub boost} {sub eval} (0.085 ± 0.008, 0.088 ± 0.12) and Breast{sub SIB} (0.22 ± 0.05, 0.23 ± 0.03) for IMRT and 3D-CRT, respectively. Static tomotherapy also offered statistically significant reductions (p < 0.001) in doses to the ipsilateral lung mean dose of 6.79 ± 2.11 Gy compared with 7.75 ± 2.54 Gy and 8.29 ± 2.76 Gy for IMRT and 3D-CRT, respectively, and significantly (p < 0.001) reduced heart doses (mean = 2.83 ± 1.26 Gy) compared to both IMRT and 3D-CRT (mean = 3.70 ± 1.44 Gy and 3.91 ± 1.58 Gy). Static tomotherapy is the dosimetrically superior modality for the whole breast with an SIB compared with IMRT and 3D-CRT. IMRT is superior to 3D

  10. Bioinspired helical microswimmers based on vascular plants.

    PubMed

    Gao, Wei; Feng, Xiaomiao; Pei, Allen; Kane, Christopher R; Tam, Ryan; Hennessy, Camille; Wang, Joseph

    2014-01-08

    Plant-based bioinspired magnetically propelled helical microswimmers are described. The helical microstructures are derived from spiral water-conducting vessels of different plants, harnessing the intrinsic biological structures of nature. Geometric variables of the spiral vessels, such as the helix diameter and pitch, can be controlled by mechanical stretching for the precise fabrication and consistent performance of helical microswimmers. Xylem vessels of a wide variety of different plants have been evaluated for the consistency and reproducibility of their helical parameters. Sequential deposition of thin Ti and Ni layers directly on the spiral vessels, followed by dicing, leads to an extremely simple and cost-efficient mass-production of functional helical microswimmers. The resulting plant-based magnetic microswimmers display efficient propulsion, with a speed of over 250 μm/s, as well as powerful locomotion in biological media such as human serum. The influence of actuation frequencies on the swimming velocity is investigated. Such use of plant vessels results in significant savings in the processing costs and provides an extremely simple, cost-effective fabrication route for the large-scale production of helical magnetic swimmers.

  11. FILAMENT CHANNEL FORMATION VIA MAGNETIC HELICITY CONDENSATION

    SciTech Connect

    Knizhnik, K. J.; Antiochos, S. K.; DeVore, C. R.

    2015-08-20

    A major unexplained feature of the solar atmosphere is the accumulation of magnetic shear in the form of filament channels at photospheric polarity inversion lines (PILs). In addition to free energy, this shear represents magnetic helicity, which is conserved under reconnection. In this paper we address the problem of filament channel formation and show how filaments acquire their shear and magnetic helicity. The results of three-dimensional (3D) simulations using the Adaptively Refined Magnetohydrodynamics Solver are presented. Our findings support the model of filament channel formation by magnetic helicity condensation that was developed by Antiochos. We consider the small-scale photospheric twisting of a quasi-potential flux system that is bounded by a PIL and contains a coronal hole (CH). The magnetic helicity injected by the small-scale photospheric motions is shown to inverse cascade up to the largest allowable scales that define the closed flux system: the PIL and the CH. This process produces field lines that are both sheared and smooth, and are sheared in opposite senses at the PIL and the CH. The accumulated helicity and shear flux are shown to be in excellent quantitative agreement with the helicity condensation model. We present a detailed analysis of the simulations, including comparisons of our analytical and numerical results, and discuss their implications for observations.

  12. Alternative Methods for Field Corrections in Helical Solenoids

    SciTech Connect

    Lopes, M. L.; Krave, S. T.; Tompkins, J. C.; Yonehara, K.; Flanagan, G.; Kahn, S. A.; Melconian, K.

    2015-05-01

    Helical cooling channels have been proposed for highly efficient 6D muon cooling. Helical solenoids produce solenoidal, helical dipole, and helical gradient field components. Previous studies explored the geometric tunability limits on these main field components. In this paper we present two alternative correction schemes, tilting the solenoids and the addition of helical lines, to reduce the required strength of the anti-solenoid and add an additional tuning knob.

  13. Initial State Helicity Correlation in Wide Angle Compton Scattering

    NASA Astrophysics Data System (ADS)

    Zhang, Jixie; Day, Donal; Keller, Dustin; Rondon, Oscar

    2014-09-01

    The applicability of pQCD to exclusive reactions at medium energies is a subject of considerable interest. Real Compton scattering (RCS) has the potential to provide insight to this unsettled issue. In pQCD, three active quarks and two hard gluons are involved when describing RCS. But the cross sections do not agree with the pQCD predictions. In contrast, a handbag dominance model, involving only one single quark coupling to the spectator through generalized parton distributions (GPDs) does a good job of matching the cross section data. A measurement of the longitudinal polarization transfer parameter KLL was found inconsistent with predictions of pQCD yet consistent with calculations within the hand-bag mechanism. Further Miller's handbag approach, which including quark and hadron helicity flip, contradicts pQCD and others which demands that KLL =ALL , the initial state helicity correlation asymmetry, by finding that KLL ≠ALL . The first ever measurement of ALL has been proposed to run in Jefferson Lab's Hall C. This experiment will utilize an untagged bremsstrahlung photon beam and the longitudinally polarized UVA/JLAB proton target. After a brief introduction to the physics, the experiment will be described and the expected results presented.

  14. Initial State Helicity Correlation in Wide Angle Compton Scattering

    NASA Astrophysics Data System (ADS)

    Day, Donal; Keller, Dustin; Zhang, Jixie

    2015-04-01

    Whether pQCD can describe exclusive reactions at medium energies remains an area of active study. Real Compton scattering (RCS) has the potential to provide insight to this unsettled issue. A pQCD description of RCS requires the participation of three quarks and two hard gluons. However its predictions for the RCS cross sections disagree with data while calculations based on the handbag mechanism, involving a single quark coupled to the spectator through generalized parton distributions (GPDs), match the data well. The measured longitudinal polarization transfer parameter KLL is inconsistent with predictions of pQCD yet consistent with calculations of the handbag mechanism. Furthermore, Miller's approach, which includes quark and hadron helicity flip, contradicts pQCD where KLL =ALL , the initial state helicity correlation asymmetry, by finding that KLL ≠ALL . The first ever measurement of ALL (E12-14-006) has been approved to run in Jefferson Lab's Hall C and will be able to discriminate between the various models. E12-14-006 will utilize an untagged bremsstrahlung photon beam and the longitudinally polarized UVA/JLAB proton target. After a brief introduction to the physics, the experiment will be described and the expected results presented.

  15. Quasi-static and dynamic response of viscoelastic helical rods

    NASA Astrophysics Data System (ADS)

    Temel, Beytullah; Fırat Çalim, Faruk; Tütüncü, Naki

    2004-04-01

    In this study, the dynamic behaviour of cylindrical helical rods made of linear viscoelastic materials are investigated in the Laplace domain. The governing equations for naturally twisted and curved spatial rods obtained using the Timoshenko beam theory are rewritten for cylindrical helical rods. The curvature of the rod axis, effect of rotary inertia, and shear and axial deformations are considered in the formulation. The material of the rod is assumed to be homogeneous, isotropic and linear viscoelastic. In the viscoelastic material case, according to the correspondence principle, the material constants are replaced with their complex counterparts in the Laplace domain. Ordinary differential equations in scalar form obtained in the Laplace domain are solved numerically using the complementary functions method to calculate the dynamic stiffness matrix of the problem. In the solutions, the Kelvin model is employed. The solutions obtained are transformed to the real space using the Durbin's numerical inverse Laplace transform method. Numerical results for quasi-static and dynamic response of viscoelastic models are presented in the form of graphics.

  16. Beam-beam simulations for separated beams

    SciTech Connect

    Furman, Miguel A.

    2000-04-10

    We present beam-beam simulation results from a strong-strong gaussian code for separated beams for the LHC and RHIC. The frequency spectrum produced by the beam-beam collisions is readily obtained and offers a good opportunity for experimental comparisons. Although our results for the emittance blowup are preliminary, we conclude that, for nominal parameter values, there is no significant difference between separated beams and center-on-center collisions.

  17. Helicity dependence of the total inclusive cross section on the deuteron

    NASA Astrophysics Data System (ADS)

    Gdh; A2 Collaborations; Ahrens, J.; Altieri, S.; Annand, J. R. M.; Arends, H.-J.; Beck, R.; Blackston, M. A.; Braghieri, A.; D'Hose, N.; Dutz, H.; Heid, E.; Jahn, O.; Klein, F.; Kondratiev, R.; Lang, M.; Lisin, V.; Martinez Fabregate, M.; McGeorge, J. C.; Meyer, W.; Panzeri, A.; Pedroni, P.; Pinelli, T.; Protopopescu, D.; Reichertz, G.; Rohlof, Ch.; Rosner, G.; Rostomyan, T.; Ryckbosch, D.; Schwamb, M.; Tamas, G.; Thomas, A.; Weller, H. R.

    2009-03-01

    A measurement of the helicity dependence of the total inclusive photoabsorption cross section on the deuteron was carried out at MAMI (Mainz) in the energy range 200beam and a frozen spin target which provided longitudinally polarized deuterons. These new results are a significant improvement on the existing data and allow a detailed comparison with state-of-the-art calculations.

  18. Reduction of Helicity-Dependent Instrumental Laser Intensity Asymmetries

    NASA Astrophysics Data System (ADS)

    Burtwistle, Samantha; Dreiling, Joan; Gay, Timothy

    2014-05-01

    We present a new optical system that greatly reduces helicity-dependent instrumental intensity asymmetries. The optical setup is similar to that described in Fabrikant et al., where two beams with orthogonal linear polarizations are sent through a chopper, allowing only one beam to pass through the optical system at a time. The two temporally-separated beams are then spatially recombined. We now use a system, with a second active polarization changing element, that is analogous to that described in Gay and Dunning, which compensates for false asymmetries in Mott polarimetry. In our setup, the orthogonal linear polarizations are now circularly polarized by a Pockels cell switching between a retardance of + λ /4 and - λ/4 at the same frequency as the chopper, but with a 90-degree phase shift. Using this method, we have been able to control the standard deviation of the mean of our asymmetries, as measured by a photodiode with lock-in signal processing, to 3*10-8.

  19. Helicity Amplitudes A1/2 and A3/2 for the D13(1520) Resonance Obtained from the γ-->p-->-->pπ0 Reaction

    NASA Astrophysics Data System (ADS)

    Ahrens, J.; Altieri, S.; Annand, J. R.; Anton, G.; Arends, H.-J.; Aulenbacher, K.; Beck, R.; Bradtke, C.; Braghieri, A.; Degrande, N.; D'Hose, N.; Drechsel, D.; Dutz, H.; Goertz, S.; Grabmayr, P.; Hansen, K.; Harmsen, J.; von Harrach, D.; Hasegawa, S.; Hasegawa, T.; Heid, E.; Helbing, K.; Holvoet, H.; van Hoorebeke, L.; Horikawa, N.; Iwata, T.; Jahn, O.; Jennewein, P.; Kageya, T.; Kamalov, S.; Kiel, B.; Klein, F.; Kondratiev, R.; Kossert, K.; Krimmer, J.; Lang, M.; Lannoy, B.; Leukel, R.; Lisin, V.; Matsuda, T.; McGeorge, J. C.; Meier, A.; Menze, D.; Meyer, W.; Michel, T.; Naumann, J.; Panzeri, A.; Pedroni, P.; Pinelli, T.; Preobrajenski, I.; Radtke, E.; Reichert, E.; Reicherz, G.; Rohlof, Ch.; Rosner, G.; Ryckbosch, D.; Sauer, M.; Schoch, B.; Schumacher, M.; Seitz, B.; Speckner, T.; Takabayashi, N.; Tamas, G.; Thomas, A.; Tiator, L.; van Vyver, R.; Wakai, A.; Weihofen, W.; Wissmann, F.; Zapadtka, F.; Zeitler, G.

    2002-06-01

    The helicity dependence of the γ-->p-->-->pπ0 reaction has been measured for the first time in the photon-energy range from 550 to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4π-detector system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. These data are predominantly sensitive to the D13(1520) resonance and are used to determine its helicity amplitudes.

  20. Measurement of the helicity-dependent total cross-section for the γn rightarrow p π-_{} π0_{} reaction

    NASA Astrophysics Data System (ADS)

    Ahrens, J.; Altieri, S.; Annand, J. R. M.; Arends, H.-J.; Beck, R.; Blackston, M. A.; Bradtke, C.; Braghieri, A.; d'Hose, N.; Dutz, H.; Fix, A.; Heid, E.; Jahn, O.; Klein, F.; Kondratiev, R.; Lang, M.; Lisin, V.; Martinez-Fabregate, M.; McGeorge, J. C.; Meyer, W.; Panzeri, A.; Pedroni, P.; Pinelli, T.; Protopopescu, D.; Reicherz, G.; Rohlof, Ch.; Rosner, G.; Rostomyan, T.; Ryckbosch, D.; Tamas, G.; Thomas, A.; Weller, H. R.

    2011-03-01

    The helicity dependence of the total cross-section for the γ n rightarrow p π-_{} π0_{} reaction has been measured for the first time at incident photon energies from 450 to 800MeV. The measurement was performed with the large-acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. Both the measured unpolarized and the helicity-dependent observables are not well described by the existing theoretical models.

  1. Overcoming Depolarizing Resonances with Dual Helical Partial Siberian Snakes

    NASA Astrophysics Data System (ADS)

    Huang, H.; Ahrens, L. A.; Bai, M.; Brown, K.; Courant, E. D.; Gardner, C.; Glenn, J. W.; Lin, F.; Luccio, A. U.; Mackay, W. W.; Okamura, M.; Ptitsyn, V.; Roser, T.; Takano, J.; Tepikian, S.; Tsoupas, N.; Zelenski, A.; Zeno, K.

    2007-10-01

    Acceleration of polarized protons in the energy range of 5 to 25 GeV is challenging. In a medium energy accelerator, the depolarizing spin resonances are strong enough to cause significant polarization loss but full Siberian snakes cause intolerably large orbit excursions and are also not feasible since straight sections usually are too short. Recently, two helical partial Siberian snakes with double pitch design have been installed in the Brookhaven Alternating Gradient Synchrotron (AGS). With a careful setup of optics at injection and along the energy ramp, this combination can eliminate the intrinsic and imperfection depolarizing resonances otherwise encountered during acceleration to maintain a high intensity polarized beam in medium energy synchrotrons. The observation of partial snake resonances of higher than second order will also be described.

  2. Accurate measurement of the helical twisting power of chiral dopants

    NASA Astrophysics Data System (ADS)

    Kosa, Tamas; Bodnar, Volodymyr; Taheri, Bahman; Palffy-Muhoray, Peter

    2002-03-01

    We propose a method for the accurate determination of the helical twisting power (HTP) of chiral dopants. In the usual Cano-wedge method, the wedge angle is determined from the far-field separation of laser beams reflected from the windows of the test cell. Here we propose to use an optical fiber based spectrometer to accurately measure the cell thickness. Knowing the cell thickness at the positions of the disclination lines allows determination of the HTP. We show that this extension of the Cano-wedge method greatly increases the accuracy with which the HTP is determined. We show the usefulness of this method by determining the HTP of ZLI811 in a variety of hosts with negative dielectric anisotropy.

  3. Overcoming Depolarizing Resonances with Dual Helical Partial Siberian Snakes

    SciTech Connect

    Huang, H.; Ahrens, L. A.; Bai, M.; Brown, K.; Courant, E. D.; Gardner, C.; Glenn, J. W.; Luccio, A. U.; MacKay, W. W.; Okamura, M.; Ptitsyn, V.; Roser, T.; Tepikian, S.; Tsoupas, N.; Zelenski, A.; Zeno, K.; Lin, F.; Takano, J.

    2007-10-12

    Acceleration of polarized protons in the energy range of 5 to 25 GeV is challenging. In a medium energy accelerator, the depolarizing spin resonances are strong enough to cause significant polarization loss but full Siberian snakes cause intolerably large orbit excursions and are also not feasible since straight sections usually are too short. Recently, two helical partial Siberian snakes with double pitch design have been installed in the Brookhaven Alternating Gradient Synchrotron (AGS). With a careful setup of optics at injection and along the energy ramp, this combination can eliminate the intrinsic and imperfection depolarizing resonances otherwise encountered during acceleration to maintain a high intensity polarized beam in medium energy synchrotrons. The observation of partial snake resonances of higher than second order will also be described.

  4. Optimization of the AGS superconducting helical partial snake strength.

    SciTech Connect

    Lin,F.; Huang, H.; Luccio, A.U.; Roser, T.

    2008-06-23

    Two helical partial snakes, one super-conducting (a.k.a cold snake) and one normal conducting (a.k.a warm snake), have preserved the polarization of proton beam up to 65% in the Brookhaven Alternating Gradient Synchrotron (AGS) at the extraction energy from 85% at injection. In order to overcome spin resonances, stronger partial snakes would be required. However, the stronger the partial snake, the more the stable spin direction tilted producing a stronger horizontal intrinsic resonance. The balance between increasing the spin tune gap generated by the snakes and reducing the tilted stable spin direction has to be considered to maintain the polarization. Because the magnetic field of the warm snake has to be a constant, only the cold snake with a maximum 3T magnetic field can be varied to find out the optimum snake strength. This paper presents simulation results by spin tracking with different cold snake magnetic fields. Some experimental data are also analyzed.

  5. Overcoming depolarizing resonances with dual helical partial Siberian snakes.

    PubMed

    Huang, H; Ahrens, L A; Bai, M; Brown, K; Courant, E D; Gardner, C; Glenn, J W; Lin, F; Luccio, A U; Mackay, W W; Okamura, M; Ptitsyn, V; Roser, T; Takano, J; Tepikian, S; Tsoupas, N; Zelenski, A; Zeno, K

    2007-10-12

    Acceleration of polarized protons in the energy range of 5 to 25 GeV is challenging. In a medium energy accelerator, the depolarizing spin resonances are strong enough to cause significant polarization loss but full Siberian snakes cause intolerably large orbit excursions and are also not feasible since straight sections usually are too short. Recently, two helical partial Siberian snakes with double pitch design have been installed in the Brookhaven Alternating Gradient Synchrotron (AGS). With a careful setup of optics at injection and along the energy ramp, this combination can eliminate the intrinsic and imperfection depolarizing resonances otherwise encountered during acceleration to maintain a high intensity polarized beam in medium energy synchrotrons. The observation of partial snake resonances of higher than second order will also be described.

  6. Studying the Transfer of Optical Orbital Angular Momentum to a Helical Bacterium

    NASA Astrophysics Data System (ADS)

    Davis, Dana; Horton, Timothy; Reichman, Steven; Link, Justin; Schmitzer, Heidrun; Robbins, Jennifer; Engle, Dorothy

    2014-03-01

    The purpose of this research is to study how the angular momentum of an optical vortex created by a 1064 nm laser is transferred to a helical shaped bacterium. When under the influence of a laser in optical tweezers, the helical shape of the bacteria causes it to spin in the trap. A spatial light modulator reshapes the beam and is twisted either into a left handed or right handed helix. This results in an optical vortex with a diameter which can be adjusted from roughly half a micron to three microns. The rotational speed of a helical bacterium in this type of optical trap should depend on the handedness of the vortex and the handedness of the bacterium being tweezed. When both the tweezing beam and the bacterium have the same handedness, a slight reduction in rotational speed should be observed; when the tweezing beam has the opposite handedness of the bacterium, a slight increase in rotational speed should be expected. We present our first experiments with magnetospirillum magnetotacticum and rhodospirillum rubrum.

  7. The influence of helical background fields on current helicity and electromotive force of magnetoconvection

    NASA Astrophysics Data System (ADS)

    Rüdiger, G.; Küker, M.

    2016-07-01

    Motivated by the empirical finding that the known hemispheric rules for the current helicity at the solar surface are not strict, we demonstrate the excitation of small-scale current helicity by the influence of large-scale helical magnetic background fields on nonrotating magnetoconvection. This is shown within a quasilinear analytic theory of driven turbulence and by nonlinear simulations of magnetoconvection that the resulting small-scale current helicity has the same sign as the large-scale current helicity, while the ratio of both pseudoscalars is of the order of the magnetic Reynolds number of the convection. The same models do not provide finite values of the small-scale kinetic helicity. On the other hand, a turbulence-induced electromotive force is produced including the diamagnetic pumping term, as well as the eddy diffusivity but, however, no α effect. It has thus been argued that the relations for the simultaneous existence of small-scale current helicity and α effect do not hold for the model of nonrotating magnetoconvection under consideration. Calculations for various values of the magnetic Prandtl number demonstrate that, for the considered diffusivities, the current helicity increases for growing magnetic Reynolds number, which is not true for the velocity of the diamagnetic pumping, which is in agreement with the results of the quasilinear analytical approximation.

  8. Helical buckling of pipes in extended reach and horizontal wells -- Part 1: Preventing helical buckling

    SciTech Connect

    Wu, J.; Juvkam-Wold, H.C.; Lu, R. . Petroleum Engineering Dept.)

    1993-09-01

    This paper studies the helical buckling of pipes (drillstring and tubing) in extended reach and horizontal wells, theoretically and experimentally, resulting in new equations to correctly predict and effectively prevent the helical buckling of pipes in such wells. The theoretically study shows that the so-called helical buckling load that appears in the current literature is only the average axial load in the helical buckling development process. The laboratory experiments confirm the theoretical analysis. The new helical buckling load equations are formulated by combining the theoretical analysis and the experimental results, thereby resolving the existing assumption-and-result inconsistency in the current literature. The new equation predicts the true helical buckling load to be about 1.3 times the so-called helical buckling load in the current literature, and about 1.8 times the critical buckling load that predicts the onset of sinusoidal buckling. Consequently, larger bit weights or packer setting loads can be applied to increase the drilling rate or to ensure a proper seal, before the helical buckling of the pipes can occur.

  9. SU-D-BRF-03: Improvement of TomoTherapy Megavoltage Topogram Image Quality for Automatic Registration During Patient Localization

    SciTech Connect

    Scholey, J; White, B; Qi, S; Low, D

    2014-06-01

    Purpose: To improve the quality of mega-voltage orthogonal scout images (MV topograms) for a fast and low-dose alternative technique for patient localization on the TomoTherapy HiART system. Methods: Digitally reconstructed radiographs (DRR) of anthropomorphic head and pelvis phantoms were synthesized from kVCT under TomoTherapy geometry (kV-DRR). Lateral (LAT) and anterior-posterior (AP) aligned topograms were acquired with couch speeds of 1cm/s, 2cm/s, and 3cm/s. The phantoms were rigidly translated in all spatial directions with known offsets in increments of 5mm, 10mm, and 15mm to simulate daily positioning errors. The contrast of the MV topograms was automatically adjusted based on the image intensity characteristics. A low-pass fast Fourier transform filter removed high-frequency noise and a Weiner filter reduced stochastic noise caused by scattered radiation to the detector array. An intensity-based image registration algorithm was used to register the MV topograms to a corresponding kV-DRR by minimizing the mean square error between corresponding pixel intensities. The registration accuracy was assessed by comparing the normalized cross correlation coefficients (NCC) between the registered topograms and the kV-DRR. The applied phantom offsets were determined by registering the MV topograms with the kV-DRR and recovering the spatial translation of the MV topograms. Results: The automatic registration technique provided millimeter accuracy and was robust for the deformed MV topograms for three tested couch speeds. The lowest average NCC for all AP and LAT MV topograms was 0.96 for the head phantom and 0.93 for the pelvis phantom. The offsets were recovered to within 1.6mm and 6.5mm for the processed and the original MV topograms respectively. Conclusion: Automatic registration of the processed MV topograms to a corresponding kV-DRR recovered simulated daily positioning errors that were accurate to the order of a millimeter. These results suggest the clinical

  10. Distance-to-Agreement Investigation of Tomotherapy's Bony Anatomy-Based Autoregistration and Planning Target Volume Contour-Based Optimization

    SciTech Connect

    Suh, Steve; Schultheiss, Timothy E.

    2013-03-01

    Purpose: To compare Tomotherapy's megavoltage computed tomography bony anatomy autoregistration with the best achievable registration, assuming no deformation and perfect knowledge of planning target volume (PTV) location. Methods and Materials: Distance-to-agreement (DTA) of the PTV was determined by applying a rigid-body shift to the PTV region of interest of the prostate from its reference position, assuming no deformations. Planning target volume region of interest of the prostate was extracted from the patient archives. The reference position was set by the 6 degrees of freedom (dof)—x, y, z, roll, pitch, and yaw—optimization results from the previous study at this institution. The DTA and the compensating parameters were calculated by the shift of the PTV from the reference 6-dof to the 4-dof—x, y, z, and roll—optimization. In this study, the effectiveness of Tomotherapy's 4-dof bony anatomy–based autoregistration was compared with the idealized 4-dof PTV contour-based optimization. Results: The maximum DTA (maxDTA) of the bony anatomy-based autoregistration was 3.2 ± 1.9 mm, with the maximum value of 8.0 mm. The maxDTA of the contour-based optimization was 1.8 ± 1.3 mm, with the maximum value of 5.7 mm. Comparison of Pearson correlation of the compensating parameters between the 2 4-dof optimization algorithms shows that there is a small but statistically significant correlation in y and z (0.236 and 0.300, respectively), whereas there is very weak correlation in x and roll (0.062 and 0.025, respectively). Conclusions: We find that there is an average improvement of approximately 1 mm in terms of maxDTA on the PTV going from 4-dof bony anatomy-based autoregistration to the 4-dof contour-based optimization. Pearson correlation analysis of the 2 4-dof optimizations suggests that uncertainties due to deformation and inadequate resolution account for much of the compensating parameters, but pitch variation also makes a statistically significant

  11. Recent Progress of Neutral Beam Injector and Beam Emission Diagnosis in LHD

    NASA Astrophysics Data System (ADS)

    Katsunori, Ikeda; Kenichi, Nagaoka; Yasuhiko, Takeiri; Masaki, Osakabe; Katsuyoshi, Tsumori; Osamu, Kaneko

    2009-08-01

    Large size hydrogen neutral beam injectors (NBI) used a negative ion source (NNBI) as well as a proton source (PNBI) were developed for the large helical device (LHD). The injected power from NNBI and PNBI have reached 16 MW and 6.8 MW, respectively. These injected powers have outstripped the nominal beam powers. A diagnostic system of beam-emitted hydrogen visible spectrum has been installed along the beam injection axis to estimate the energy fraction on PNBI. The full energy beam component is about half which is equivalent to 70% of injected beam power. The attenuation of high energy neutral beam is also observed on NNBI. The peak density distribution is effective to increase beam deposition power.

  12. Hydrogels of Superlong Helices to Synthesize Hybrid Ag-Helical Nanomaterials.

    PubMed

    Li, Guihua; Wang, Yitong; Wang, Ling; Song, Aixin; Hao, Jingcheng

    2016-11-22

    The gelation behavior of mixtures of sodium deoxycholate (NaDC) and glutathione (GSH) in water is investigated. The system exhibits a structural transition of self-assembled hydrogels from nanofibers to nanohelix structures, and then to helical ribbons with increasing GSH concentration. Superlong helical nanofibers with left- and right-handed orientations are produced by tuning the concentration of GSH at a fixed concentration of NaDC. Random coil and β-sheet structures are significant for the formation of the helical structures, and are indicated by circular dichroism (CD) and Fourier transform infrared (FT-IR) spectra. The mechanical strength of the "weak" hydrogels is enhanced by the introduction of appropriate suitable amount of AgNO3. Furthermore, the controlled growth of Ag nanoparticles at spatially arranged locations along the nanohelices (hybrid Ag-helical nanomaterial) is readily achieved by UV reduction of Ag (I) ions on the supramolecular helical templates.

  13. DNS of helicity-induced stratified turbulent flow

    NASA Astrophysics Data System (ADS)

    Chandy, Abhilash J.; Rahimi, Abbas

    2013-11-01

    Helical flows undergoing density stratification have wide applications in meteorological phenomena such as dust devils, tornadoes, and hurricanes due to the complexity and disasters caused by them. Direct numerical simulations (DNS) of transition to turbulence in a stably stratified Boussinesq fluid are presented for different rotation and stratification intensities. In order to understand the effect of velocity on the energy cascade, comparisons are made between helicity initiated and non-helical flows. Results show that stratification decelerates the helicity decay and causes velocity and vorticity to align with each other. With respect to the helical and non-helical flow comparisons, the total energy in the presence of stratification decays faster with helicity. In addition, the behavior of length scales were examined by comparing temporal variations of the vertical shearing of velocities. Results showed a growing asymmetry with time in the case of helical flow, while non-helical flow stayed close to begin symmetric.

  14. Three-dimensional control of the helical axis of a chiral nematic liquid crystal by light

    NASA Astrophysics Data System (ADS)

    Zheng, Zhi-Gang; Li, Yannian; Bisoyi, Hari Krishna; Wang, Ling; Bunning, Timothy J.; Li, Quan

    2016-03-01

    Chiral nematic liquid crystals—otherwise referred to as cholesteric liquid crystals (CLCs)—are self-organized helical superstructures that find practical application in, for example, thermography, reflective displays, tuneable colour filters and mirrorless lasing. Dynamic, remote and three-dimensional control over the helical axis of CLCs is desirable, but challenging. For example, the orientation of the helical axis relative to the substrate can be changed from perpendicular to parallel by applying an alternating-current electric field, by changing the anchoring conditions of the substrate, or by altering the topography of the substrate’s surface; separately, in-plane rotation of the helical axis parallel to the substrate can be driven by a direct-current field. Here we report three-dimensional manipulation of the helical axis of a CLC, together with inversion of its handedness, achieved solely with a light stimulus. We use this technique to carry out light-activated, wide-area, reversible two-dimensional beam steering—previously accomplished using complex integrated systems and optical phased arrays. During the three-dimensional manipulation by light, the helical axis undergoes, in sequence, a reversible transition from perpendicular to parallel, followed by in-plane rotation on the substrate surface. Such reversible manipulation depends on experimental parameters such as cell thickness, surface anchoring condition, and pitch length. Because there is no thermal relaxation, the system can be driven either forwards or backwards from any light-activated intermediate state. We also describe reversible photocontrol between a two-dimensional diffraction state, a one-dimensional diffraction state and a diffraction ‘off’ state in a bilayer cell.

  15. Fabrication and experimentation of FRP helical spring

    NASA Astrophysics Data System (ADS)

    Ekanthappa, J.; Shiva Shankar, G. S.; Amith, B. M.; Gagan, M.

    2016-09-01

    In present scenario, the automobile industry sector is showing increased interest in reducing the unsprung weight of the automobile & hence increasing the fuel Efficiency. One of the feasible sub systems of a vehicle where weight reduction may be attempted is vehicle- suspension system. Usage of composite material is a proven way to lower the component weight without any compromise in strength. The composite materials are having high specific strength, more elastic strain energy storage capacity in comparison with those of steel. Therefore, helical coil spring made of steel is replaceable by composite cylindrical helical coil spring. This research aims at preparing a re-usable mandrel (mould) of Mild steel, developing a setup for fabrication, fabrication of FRP helical spring using continuous glass fibers and Epoxy Resin (Polymer). Experimentation has been conducted on fabricated FRP helical spring to determine its strength parameters & for failure analysis. It is found that spring stiffness (K) of Glass/Epoxy helical-spring is greater than steel-coil spring with reduced weight.

  16. TURBULENT DYNAMOS WITH SHEAR AND FRACTIONAL HELICITY

    SciTech Connect

    Kaepylae, Petri J.; Brandenburg, Axel

    2009-07-10

    Dynamo action owing to helically forced turbulence and large-scale shear is studied using direct numerical simulations. The resulting magnetic field displays propagating wave-like behavior. This behavior can be modeled in terms of an {alpha}{omega} dynamo. In most cases super-equipartition fields are generated. By varying the fraction of helicity of the turbulence the regeneration of poloidal fields via the helicity effect (corresponding to the {alpha}-effect) is regulated. The saturation level of the magnetic field in the numerical models is consistent with a linear dependence on the ratio of the fractional helicities of the small and large-scale fields, as predicted by a simple nonlinear mean-field model. As the magnetic Reynolds number (Re{sub M}) based on the wavenumber of the energy-carrying eddies is increased from 1 to 180, the cycle frequency of the large-scale field is found to decrease by a factor of about 6 in cases where the turbulence is fully helical. This is interpreted in terms of the turbulent magnetic diffusivity, which is found to be only weakly dependent on the Re{sub M}.

  17. Working member of a helical downhole motor for drilling wells

    SciTech Connect

    Kochnev, A.M.; Vshivkov, A.N.; Goldobin, V.B.

    1993-06-22

    A working member of a helical downhole motor is described for drilling wells comprising: separate tubular sections having helical teeth arranged in succession and interconnected by connecting elements, each connecting element having the form of a ring, rigidly secured at the tubular sections and having helical teeth of a pitch and a direction equal to a pitch and a direction, respectively, of the helical teeth of the tubular sections, whereas a profile of the helical teeth of the ring is equidistant to a profile of the helical teeth of the sections.

  18. A helically distorted MHD flux rope model

    NASA Technical Reports Server (NTRS)

    Theobald, Michael L.; Montgomery, David

    1990-01-01

    A flux rope model is proposed which has a variable degree of helical distortion from axisymmetry. The basis for this suggestion is a series of numerical and analytical investigations of magnetohydrodynamic states which result when an axial electric current is directed down on dc magnetic field. The helically distorted states involve a flow velocity and seem to be favored because of their lower rate of energy dissipation. Emphasis is on the magnetometer and particle energy analyzer traces that might be characteristic of such flux ropes. It is shown that even a fractionally small helical distortion may considerably alter the traces in minimum-variance coordinates. In short, what may be fairly common MHD processes can render a flux rope almost unrecognizable under standard diagnostics, even if the departures from axisymmetry are not great.

  19. Helicity and singular structures in fluid dynamics

    PubMed Central

    Moffatt, H. Keith

    2014-01-01

    Helicity is, like energy, a quadratic invariant of the Euler equations of ideal fluid flow, although, unlike energy, it is not sign definite. In physical terms, it represents the degree of linkage of the vortex lines of a flow, conserved when conditions are such that these vortex lines are frozen in the fluid. Some basic properties of helicity are reviewed, with particular reference to (i) its crucial role in the dynamo excitation of magnetic fields in cosmic systems; (ii) its bearing on the existence of Euler flows of arbitrarily complex streamline topology; (iii) the constraining role of the analogous magnetic helicity in the determination of stable knotted minimum-energy magnetostatic structures; and (iv) its role in depleting nonlinearity in the Navier-Stokes equations, with implications for the coherent structures and energy cascade of turbulence. In a final section, some singular phenomena in low Reynolds number flows are briefly described. PMID:24520175

  20. Helical motion of chiral liquid crystal droplets

    NASA Astrophysics Data System (ADS)

    Yamamoto, Takaki; Sano, Masaki

    Artificial swimmers have been intensively studied to understand the mechanism of the locomotion and collective behaviors of cells and microorganisms. Among them, most of the artificial swimmers are designed to move along the straight path. However, in biological systems, chiral dynamics such as circular and helical motion are quite common because of the chirality of their bodies, which are made of chiral biomolecules. To understand the role of the chirality in the physics of microswimmers, we designed chiral artificial swimmers and the theoretical model for the chiral motion. We found that chiral liquid crystal droplets, when dispersed in surfactant solutions, swim in the helical path induced by the Marangoni effect. We will discuss the mechanism of the helical motion with our phenomenological model. This work is supported by Grant-in-Aid for JSPS Fellows (Grant No. 26.9814), and MEXT KAKENHI Grant No. 25103004.

  1. Unusually Stable Helical Coil Allotrope of Phosphorus.

    PubMed

    Liu, Dan; Guan, Jie; Jiang, Jingwei; Tománek, David

    2016-12-14

    We have identified an unusually stable helical coil allotrope of phosphorus. Our ab initio density functional theory calculations indicate that the uncoiled, isolated straight one-dimensional chain is equally stable as a monolayer of black phosphorus dubbed phosphorene. The coiling tendency and the attraction between adjacent coil segments add an extra stabilization energy of ∼12 meV/atom to the coil allotrope, similar in value to the ∼16 meV/atom interlayer attraction in bulk black phosphorus. Thus, the helical coil structure is essentially as stable as black phosphorus, the most stable phosphorus allotrope known to date. With an optimum radius of 2.4 nm, the helical coil of phosphorus may fit well and even form inside wide carbon nanotubes.

  2. Generation of acoustic helical wavefronts using metasurfaces

    NASA Astrophysics Data System (ADS)

    Esfahlani, Hussein; Lissek, Herve; Mosig, Juan R.

    2017-01-01

    It has been shown that acoustic waves with helical wavefronts can carry angular momentum, which can be transmitted towards a propagating medium. Such a wave field can be achieved by using a planar array of electroacoustic transducers, forming a given spatial distribution of phased sound sources which produce the desired helical wavefronts. Here, we introduce a technique to generate acoustic vortices, based on the passive acoustic metasurface concept. The proposed metasurface is composed of space-coiled cylindrical unit cells transmitting sound pressure with a controllable phase shift, which are arranged in a discretized circular configuration, and thus passively transforming an incident plane wavefront into the desired helical wavefront. This method presents the advantage of overcoming the restrictions on using many acoustic sources, and it is implemented with a transmitting metasurface which can be easily three-dimensionally printed. The proposed straightforward design principle can be adopted for easy production of acoustic angular momentum with minimum complexity and using a single source.

  3. Structural Transition from Helices to Hemihelices

    PubMed Central

    Su, Tianxiang; Bertoldi, Katia; Clarke, David R.

    2014-01-01

    Helices are amongst the most common structures in nature and in some cases, such as tethered plant tendrils, a more complex but related shape, the hemihelix forms. In its simplest form it consists of two helices of opposite chirality joined by a perversion. A recent, simple experiment using elastomer strips reveals that hemihelices with multiple reversals of chirality can also occur, a richness not anticipated by existing analyses. Here, we show through analysis and experiments that the transition from a helical to a hemihelical shape, as well as the number of perversions, depends on the height to width ratio of the strip's cross-section. Our findings provides the basis for the deterministic manufacture of a variety of complex three-dimensional shapes from flat strips. PMID:24759785

  4. Large-scale dynamics of magnetic helicity

    NASA Astrophysics Data System (ADS)

    Linkmann, Moritz; Dallas, Vassilios

    2016-11-01

    In this paper we investigate the dynamics of magnetic helicity in magnetohydrodynamic (MHD) turbulent flows focusing at scales larger than the forcing scale. Our results show a nonlocal inverse cascade of magnetic helicity, which occurs directly from the forcing scale into the largest scales of the magnetic field. We also observe that no magnetic helicity and no energy is transferred to an intermediate range of scales sufficiently smaller than the container size and larger than the forcing scale. Thus, the statistical properties of this range of scales, which increases with scale separation, is shown to be described to a large extent by the zero flux solutions of the absolute statistical equilibrium theory exhibited by the truncated ideal MHD equations.

  5. Helicity and nuclear β decay correlations

    NASA Astrophysics Data System (ADS)

    Hong, Ran; Sternberg, Matthew G.; Garcia, Alejandro

    2017-01-01

    We present simple derivations of nuclear β-decay correlations with an emphasis on the special role of helicity. This topic provides a good opportunity to teach students about helicity and chirality in particle physics with exercises that use simple aspects of quantum mechanics. In addition, this paper serves as an introduction to nuclear β-decay correlations from both a theoretical and experimental perspective. This article can be used to introduce students to ongoing experiments searching for hints of new physics in the low-energy precision frontier.

  6. Helical Lattice Vibrational Modes in DNA.

    DTIC Science & Technology

    1988-03-10

    VIBRATIONAL MODES IN DNA(U) PURDUE UNIV l’ LAFAYETTE IND DEPT OF PHYSICS V V PRRGHU ET AL. UNCLR~~lll’ 16I MAR *6 N99914...Initiative Organization 1400014-86-K-0252 Washinton, D.C. 20301-7100 %0 %0 .0 Helical Lattixce Vibrational ’ Modes in DNA V.V. Prabhu, ’.,.K. Sclhrol!, L.L...8217+"+ " ’. % " " % ") . " ". ".",°. " . % % . . ,.-. -.-. -. ,, . . - . -]. o % % % o. -.-. , .%** %-N% Revised version Helical Lattice Vibrational Modes in DNA 1 A recent

  7. EVOLUTION OF RELATIVE MAGNETIC HELICITY AND CURRENT HELICITY IN NOAA ACTIVE REGION 11158

    SciTech Connect

    Jing, Ju; Liu, Chang; Lee, Jeongwoo; Xu, Yan; Deng, Na; Wang, Haimin; Park, Sung-Hong; Wiegelmann, Thomas E-mail: chang.liu@njit.edu E-mail: na.deng@njit.edu E-mail: freemler@kasi.re.kr E-mail: wiegelmann@linmpi.mpg.de

    2012-06-10

    Both magnetic and current helicities are crucial ingredients for describing the complexity of active-region magnetic structure. In this Letter, we present the temporal evolution of these helicities contained in NOAA active region 11158 during five days from 2011 February 12 to 16. The photospheric vector magnetograms of the Helioseismic and Magnetic Imager on board the Solar Dynamic Observatory were used as the boundary conditions for the coronal field extrapolation under the assumption of nonlinear force-free field, from which we calculated both relative magnetic helicity and current helicity. We construct a time-altitude diagram in which altitude distribution of the magnitude of current helicity density is displayed as a function of time. This diagram clearly shows a pattern of upwardly propagating current helicity density over two days prior to the X2.2 flare on February 15 with an average propagation speed of {approx}36 m s{sup -1}. The propagation is synchronous with the emergence of magnetic flux into the photosphere, and indicative of a gradual energy buildup for the X2.2 flare. The time profile of the relative magnetic helicity shows a monotonically increasing trend most of the time, but a pattern of increasing and decreasing magnetic helicity above the monotonic variation appears prior to each of two major flares, M6.6 and X2.2, respectively. The physics underlying this bump pattern is not fully understood. However, the fact that this pattern is apparent in the magnetic helicity evolution but not in the magnetic flux evolution makes it a useful indicator in forecasting major flares.

  8. Treatment plan comparison of linac step and shoot, tomotherapy, rapidarc, and proton therapy for prostate cancer by using the dosimetrical and the biological indices

    NASA Astrophysics Data System (ADS)

    Lee, Suk; Cao, Yuan Jie; Chang, Kyung Hwan; Shim, Jang Bo; Kim, Kwang Hyeon; Lee, Nam Kwon; Park, Young Je; Kim, Chul Yong; Cho, Sam Ju; Lee, Sang Hoon; Min, Chul Kee; Kim, Woo Chul; Cho, Kwang Hwan; Huh, Hyun Do; Lim, Sangwook; Shin, Dongho

    2015-07-01

    The purpose of this study was to use various dosimetrical indices to determine the best intensitymodulated radiation therapy (IMRT) modality - for treating patients with prostate cancer. Ten patients with prostate cancer were included in this study. IMRT plans were designed to include different modalities, including the linac step and shoot, tomotherapy, RapidArc, and proton systems. Various dosimetrical indices, like the prescription isodose to target volume (PITV) ratio, conformity index (CI), homogeneity index (HI), target coverage index (TCI), modified dose homogeneity index (MHI), conformation number (CN), critical organ scoring index (COSI), and quality factor (QF), were determined to compare the different treatment plans. Biological indices, such as the generalized equivalent uniform dose (gEUD) based the tumor control probability (TCP), and the normal tissue complication probability (NTCP), were also calculated and used to compare the treatment plans. The RapidArc plan attained better PTV coverage, as evidenced by its superior PITV, CI, TCI, MHI, and CN values. Regarding organ at risks (OARs), proton therapy exhibited superior dose sparing for the rectum and the bowel in low dose volumes, whereas the tomotherapy and RapidArc plans achieved better dose sparing in high dose volumes. The QF scores showed no significant difference among these plans (p = 0.701). The average TCPs for prostate tumors in the RapidArc, linac and proton plans were higher than the average TCP for Tomotherapy (98.79%, 98.76%, and 98.75% vs. 98.70%, respectively). Regarding the rectum NTCP, RapidArc showed the most favorable result (0.09%) whereas linac resulted in the best bladder NTCP (0.08%).

  9. An electromagnetic helical undulator for polarized x-rays

    SciTech Connect

    Gluskin, E.; Vinokurov, N.; Tcheskidov, V.; Medvedko, A.; Evtushenko, Y. Kolomogorov, V.; Vobly, P.; Antokhin, E.; Ivanov, P.; Vasserman, I. B.; Trakhtenberg, E. M.; Den Hartog, P. K.; Deriy, B.; Erdmann, M.; Makarov, O.; Moog, E. R.

    1999-10-28

    Linearly and circularly polarized x-rays have been very successfully applied to the study of the properties of materials. Many applications can benefit from the availability of energy-turnable, high-brilliance x-ray beams with adjustable polarization properties. A helical undulator that can generate beams of variable (linear to circular) polarization has been designed and built by the Budker Institute of Nuclear Physics and the Advanced Photon Source. The first harmonic of this 12.8-cm-period device will cover the energy range from 0.4 keV to 3.5 keV. An important feature of this fully electromagnetic device is that it will allow one to generate 100% horizontally (K{sub x}=O)or vertically (K{sub y}=O) plane-polarized radiation, which will enable many experiments otherwise not technically feasible. With symmetric deflection parameters (K{sub x}=K{sub y}), the on-axis radiation will be circularly polarized, with a user-selectable handedness. The polarization can be changed at rates up to 10 Hz.

  10. Dynamics of helical states in MST

    NASA Astrophysics Data System (ADS)

    Munaretto, Stefano; Auriemma, F.; Brower, D.; Chapman, B. E.; den Hartog, D. J.; Ding, W. X.; Duff, J.; Franz, P.; Goetz, J. A.; Holly, D.; Lin, L.; McCollam, K. J.; McGarry, M.; Morton, L.; Nornberg, M. D.; Parke, E.; Sarff, J. S.

    2014-10-01

    The thermal and the magnetic dynamics of quasi-single-helicity (QSH) plasmas evolve independently during the formation and sustainment of the core helical structure. At higher plasma current (and Lundquist number) MST plasmas transition from an axisymmetric multi-helicity state to a QSH state characterized by a strong core helical mode and reduced secondary mode amplitudes. Plasmas in the QSH state tend to wall-lock, often in an orientation that is unfavorable for optimized measurements of the 3D structure using MST's advanced diagnostics. Recently a technique to control the locking position through an applied resonant magnetic perturbation has been developed. Using this technique it is possible to adjust the 3D phase more optimally for specific diagnostics, to study the dynamics of the QSH structure and thermal features. The multi-chord FIR interferometer shows the presence of a density structure for the duration of the QSH state. Measurements of the time evolution of the electron temperature profile using the Thomson Scattering diagnostic reveal that the transition to QSH allows the presence of a 3D thermal structure, but this structure is intermittent. Understanding the mechanism(s) driving these dynamics is the goal of this work. Work supported by the US DOE and NSF.

  11. Phase diagram of two interacting helical states

    NASA Astrophysics Data System (ADS)

    Santos, Raul A.; Gutman, D. B.; Carr, Sam T.

    2016-06-01

    We consider two coupled time-reversal-invariant helical edge modes of the same helicity, such as would occur on two stacked quantum spin Hall insulators. In the presence of interaction, the low-energy physics is described by two collective modes, one corresponding to the total current flowing around the edge and the other one describing relative fluctuations between the two edges. We find that quite generically, the relative mode becomes gapped at low temperatures, but only when tunneling between the two helical modes is nonzero. There are two distinct possibilities for the gapped state depending on the relative size of different interactions. If the intraedge interaction is stronger than the interedge interaction, the state is characterized as a spin-nematic phase. However, in the opposite limit, when the interaction between the helical edge modes is strong compared to the interaction within each mode, a spin-density wave forms, with emergent topological properties. First, the gap protects the conducting phase against localization by weak nonmagnetic impurities; second, the protected phase hosts localized zero modes on the ends of the edge that may be created by sufficiently strong nonmagnetic impurities.

  12. Coulomb drag between helical Luttinger liquids

    NASA Astrophysics Data System (ADS)

    Kainaris, N.; Gornyi, I. V.; Levchenko, A.; Polyakov, D. G.

    2017-01-01

    We theoretically study Coulomb drag between two helical edges with broken spin-rotational symmetry, such as would occur in two capacitively coupled quantum spin Hall insulators. For the helical edges, Coulomb drag is particularly interesting because it specifically probes the inelastic interactions that break the conductance quantization for a single edge. Using the kinetic equation formalism, supplemented by bosonization, we find that the drag resistivity ρD exhibits a nonmonotonic dependence on the temperature T . In the limit of low T ,ρD vanishes with decreasing T as a power law if intraedge interactions are not too strong. This is in stark contrast to Coulomb drag in conventional quantum wires, where ρD diverges at T →0 irrespective of the strength of repulsive interactions. Another unusual property of Coulomb drag between the helical edges concerns higher T for which, unlike in the Luttinger liquid model, drag is mediated by plasmons. The special type of plasmon-mediated drag can be viewed as a distinguishing feature of the helical liquid—because it requires peculiar umklapp scattering only available in the presence of a Dirac point in the electron spectrum.

  13. Helical Gears Modified To Decrease Transmission Errors

    NASA Technical Reports Server (NTRS)

    Handschuh, R. F.; Coy, J. J.; Litvin, F. L.; Zhang, J.

    1993-01-01

    Tooth surfaces of helical gears modified, according to proposed design concept, to make gears more tolerant of misalignments and to improve distribution of contact stresses. Results in smaller transmission errors, with concomitant decreases in vibrations and noise and, possibly, increases in service lives.

  14. Helical axis stellarator with noninterlocking planar coils

    DOEpatents

    Reiman, A.; Boozer, A.H.

    1984-03-06

    The present invention generates stellarator fields having favorable properties (magnetic well and large rotational transform) by a simple coil system consisting only of unlinked planar non-circular coils. At large rotational transform toroidal effects on magnetic well and rotational transform are small and can be ignored. We do so herein, specializing in straight helical systems.

  15. Deformation of flexible micro helices under flow

    NASA Astrophysics Data System (ADS)

    Daieff, Marine; Lindner, Anke; Du Roure, Olivia; Morozov, Alexander; Pham, Jonathan; Crosby, Alfred

    The interaction of small helices with fluids is important because of its relevance to both fundamental science and technological applications, such as swimming microrobots or microflow sensors. Helically shaped flagella are also exploited by swimming microorganisms to move through their surrounding fluids. Here we study experimentally the deformation of flexible helical ribbons under flow in a microfluidic channel. The size of the helix is typically microscale for the diameter and nanoscale for the thickness. We focus on two different aspects: the overall shape of the helix and the viscous frictional properties. The frictional coefficients determined by our experiments are consistent with calculated values in the context of resistive force theory. Deformation of helices by viscous flow is well-described by non-linear finite extensibility. Due to the non-uniform distribution of the pitch under distributed loading, we identify both linear and nonlinear behavior along the contour length of a single helix. Utilizing our system, we explore the impact of non-Newtonian fluid properties on the mechanics of helix-fluid interactions.

  16. Synthesis of stabilized alpha-helical peptides.

    PubMed

    Bernal, Federico; Katz, Samuel G

    2014-01-01

    Stabilized alpha-helical (SAH) peptides are valuable laboratory tools to explore important protein-protein interactions. Whereas most peptides lose their secondary structure when isolated from the host protein, stapled peptides incorporate an all-hydrocarbon "staple" that reinforces their natural alpha-helical structure. Thus, stapled peptides retain their functional ability to bind their native protein targets and serve multiple experimental uses. First, they are useful for structural studies such as NMR or crystal structures that map and better define binding sites. Second, they can be used to identify small molecules that specifically target that interaction site. Third, stapled peptides can be used to test the importance of specific amino acid residues or posttranslational modifications to the binding. Fourth, they can serve as structurally competent bait to identify novel binding partners to specific alpha-helical motifs. In addition to markedly improved alpha-helicity, stapled peptides also display resistance to protease cleavage and enhanced cell permeability. Most importantly, they are useful for intracellular experiments that explore the functional consequences of blocking particular protein interactions. Because of their remarkable stability, stapled peptides can be applied to whole-animal, in vivo studies. Here we describe a protocol for the synthesis of a peptide that incorporates an all-hydrocarbon "staple" employing a ring-closing olefin metathesis reaction. With proper optimization, stapled peptides can be a fundamental, accurate laboratory tool in the modern chemical biologist's armory.

  17. Helical mode breakdown in transitional boundary layers

    NASA Astrophysics Data System (ADS)

    Bose, Rikhi; Durbin, Paul

    2016-11-01

    Results of direct numerical simulation of transition to turbulence in adverse pressure gradient boundary layers beneath free-stream turbulence will be presented. Instability waves are excited spontaneously and may be identified when intensity of free-stream turbulence (Tu) is sufficiently low. At very low Tu 0 . 1 % , secondary instability of the TS waves and at high Tu > 2 % , conventional bypass mechanisms trigger turbulent spot formation. At low Tu 1 % transition proceeds through formation of helical modes. Helical structures as in n = 1 instability modes of axisymmetric wakes and jets are clearly identifiable in visualizations of isosurfaces of stream-wise perturbation velocity. Helical modes also trigger transition at same level of Tu in zero pressure gradient boundary layers as well, provided that the inlet disturbances include a low amplitude time-periodic unstable TS wave. This indicates that these secondary instability modes might arise due to interaction of Klebanoff streaks and instability waves. Characteristically, the helical modes are inner instability modes. This work was supported by NSF Grant CBET-1228195. Computer time was provided by the Extreme Science and Engineering Discovery Environment (XSEDE).

  18. On statistical equilibrium in helical fluid flows

    NASA Astrophysics Data System (ADS)

    Kurgansky, M. V.

    2006-06-01

    The statistical mechanics of 3-D helical flows is re-examined for a continuum truncated at a top wavenumber. Based on the principle of equipartition of the flow enstrophy between helical modes, the emerging (i) energy spectrum law "-2" and (ii) formal mathematical analogy between the helicity and the thermodynamic entropy are discussed. It is noted that the "-2" scaling law is consistent with both spectral equilibrium and spectral cascade paradigms. In an attempt to apply the obtained results to a turbulent flow regime within the Earth's outer liquid core, where the net helicity of a turbulent flow component is presumably explained by Earth's rotation, it has been noticed that it is the energy spectral law "-1", but not "-2", which is likely realized there and within the logarithmic accuracy corresponds to the case of the velocity structure function [u(l)]2 independency on the spatial scale l, the latter is consistent with observations. It is argued that the "-1" scaling law can also be interpreted in terms of the spectral equilibrium and it is emphasized that the causes of the likely dominance of the spectral law "-1" over the spectral law "-2" in this geophysical application deserve further investigation and clarification.

  19. Magnetic stripes and skyrmions with helicity reversals

    PubMed Central

    Yu, Xiuzhen; Mostovoy, Maxim; Tokunaga, Yusuke; Zhang, Weizhu; Kimoto, Koji; Matsui, Yoshio; Kaneko, Yoshio; Nagaosa, Naoto; Tokura, Yoshinori

    2012-01-01

    It was recently realized that topological spin textures do not merely have mathematical beauty but can also give rise to unique functionalities of magnetic materials. An example is the skyrmion—a nano-sized bundle of noncoplanar spins—that by virtue of its nontrivial topology acts as a flux of magnetic field on spin-polarized electrons. Lorentz transmission electron microscopy recently emerged as a powerful tool for direct visualization of skyrmions in noncentrosymmetric helimagnets. Topologically, skyrmions are equivalent to magnetic bubbles (cylindrical domains) in ferromagnetic thin films, which were extensively explored in the 1970s for data storage applications. In this study we use Lorentz microscopy to image magnetic domain patterns in the prototypical magnetic oxide–M-type hexaferrite with a hint of scandium. Surprisingly, we find that the magnetic bubbles and stripes in the hexaferrite have a much more complex structure than the skyrmions and spirals in helimagnets, which we associate with the new degree of freedom—helicity (or vector spin chirality) describing the direction of spin rotation across the domain walls. We observe numerous random reversals of helicity in the stripe domain state. Random helicity of cylindrical domain walls coexists with the positional order of magnetic bubbles in a triangular lattice. Most unexpectedly, we observe regular helicity reversals inside skyrmions with an unusual multiple-ring structure. PMID:22615354

  20. Helical Pulse Line Structures for Ion Acceleration

    SciTech Connect

    Briggs, R.J.; Reginato, L.L.; Waldron, W.L.

    2005-05-01

    The basic concept of the ''Pulse Line Ion Accelerator'' is presented, where pulse power sources create a ramped traveling wave voltage pulse on a helical pulse line. Ions can surf on this traveling wave and achieve energy gains much larger than the peak applied voltage. Tapered and untapered lines are compared, and a transformer coupling technique for launching the wave is described.

  1. Magnetic stripes and skyrmions with helicity reversals.

    PubMed

    Yu, Xiuzhen; Mostovoy, Maxim; Tokunaga, Yusuke; Zhang, Weizhu; Kimoto, Koji; Matsui, Yoshio; Kaneko, Yoshio; Nagaosa, Naoto; Tokura, Yoshinori

    2012-06-05

    It was recently realized that topological spin textures do not merely have mathematical beauty but can also give rise to unique functionalities of magnetic materials. An example is the skyrmion--a nano-sized bundle of noncoplanar spins--that by virtue of its nontrivial topology acts as a flux of magnetic field on spin-polarized electrons. Lorentz transmission electron microscopy recently emerged as a powerful tool for direct visualization of skyrmions in noncentrosymmetric helimagnets. Topologically, skyrmions are equivalent to magnetic bubbles (cylindrical domains) in ferromagnetic thin films, which were extensively explored in the 1970s for data storage applications. In this study we use Lorentz microscopy to image magnetic domain patterns in the prototypical magnetic oxide-M-type hexaferrite with a hint of scandium. Surprisingly, we find that the magnetic bubbles and stripes in the hexaferrite have a much more complex structure than the skyrmions and spirals in helimagnets, which we associate with the new degree of freedom--helicity (or vector spin chirality) describing the direction of spin rotation across the domain walls. We observe numerous random reversals of helicity in the stripe domain state. Random helicity of cylindrical domain walls coexists with the positional order of magnetic bubbles in a triangular lattice. Most unexpectedly, we observe regular helicity reversals inside skyrmions with an unusual multiple-ring structure.

  2. Cartesian beams.

    PubMed

    Bandres, Miguel A; Gutiérrez-Vega, Julio C

    2007-12-01

    A new and very general beam solution of the paraxial wave equation in Cartesian coordinates is presented. We call such a field a Cartesian beam. The complex amplitude of the Cartesian beams is described by either the parabolic cylinder functions or the confluent hypergeometric functions, and the beams are characterized by three parameters that are complex in the most general situation. The propagation through complex ABCD optical systems and the conditions for square integration are studied in detail. Applying the general expression of the Cartesian beams, we also derive two new and meaningful beam structures that, to our knowledge, have not yet been reported in the literature. Special cases of the Cartesian beams are the standard, elegant, and generalized Hermite-Gauss beams, the cosine-Gauss beams, the Lorentz beams, and the fractional order beams.

  3. A unified convention for biological assemblies with helical symmetry

    PubMed Central

    Tsai, Chung-Jung; Nussinov, Ruth

    2011-01-01

    Assemblies with helical symmetry can be conveniently formulated in many distinct ways. Here, a new convention is presented which unifies the two most commonly used helical systems for generating helical assemblies from asymmetric units determined by X-ray fibre diffraction and EM imaging. A helical assembly is viewed as being composed of identical repetitive units in a one- or two-dimensional lattice, named 1-­D and 2-D helical systems, respectively. The unification suggests that a new helical description with only four parameters [n 1, n 2, twist, rise], which is called the augmented 1-D helical system, can generate the complete set of helical arrangements, including coverage of helical discontinuities (seams). A unified four-parameter characterization implies similar parameters for similar assemblies, can eliminate errors in reproducing structures of helical assemblies and facilitates the generation of polymorphic ensembles from helical atomic models or EM density maps. Further, guidelines are provided for such a unique description that reflects the structural signature of an assembly, as well as rules for manipulating the helical symmetry presentation. PMID:21795813

  4. A unified convention for biological assemblies with helical symmetry.

    PubMed

    Tsai, Chung Jung; Nussinov, Ruth

    2011-08-01

    Assemblies with helical symmetry can be conveniently formulated in many distinct ways. Here, a new convention is presented which unifies the two most commonly used helical systems for generating helical assemblies from asymmetric units determined by X-ray fibre diffraction and EM imaging. A helical assembly is viewed as being composed of identical repetitive units in a one- or two-dimensional lattice, named 1-D and 2-D helical systems, respectively. The unification suggests that a new helical description with only four parameters [n(1), n(2), twist, rise], which is called the augmented 1-D helical system, can generate the complete set of helical arrangements, including coverage of helical discontinuities (seams). A unified four-parameter characterization implies similar parameters for similar assemblies, can eliminate errors in reproducing structures of helical assemblies and facilitates the generation of polymorphic ensembles from helical atomic models or EM density maps. Further, guidelines are provided for such a unique description that reflects the structural signature of an assembly, as well as rules for manipulating the helical symmetry presentation.

  5. The Effects of Spatial Smoothing on Solar Magnetic Helicity and the Hemispheric Helicity Sign Rule

    NASA Astrophysics Data System (ADS)

    Koch Ocker, Stella; Petrie, Gordon

    2016-05-01

    The hemispheric sign rule for solar magnetic helicity, which states that negative/positive helicity occurs preferentially in the northern/southern hemisphere, provides clues to the causes of twisted, flaring magnetic fields. However, previous studies on the hemisphere rule may have been significantly affected by seeing from atmospheric turbulent motions. Using Hinode/SOT-SP data spanning from 2006 to 2012, we studied the effects of two important data processing steps that imitate the effects of atmospheric seeing: noise reduction by ignoring pixel values that are weaker than the estimated noise threshold, and Gaussian spatial smoothing. We applied these processing techniques to the helicity distribution maps for active regions NOAA 11158 and NOAA 11243, along with the average helicities of 36 active regions, in order to imitate and understand the effects of seeing from atmospheric turbulence. We found that rather than changing trends in the helicity distributions, Gaussian smoothing and noise reduction enhanced existing trends by pushing outliers towards the mean or removing them altogether. We also found that, when separated for weak and strong magnetic fields, the average helicities of the 36 active regions conformed to the hemisphere rule for weak field helicities and breached the rule for strong field helicities. In general, we found that data processing did not affect whether the hemisphere rule held for data taken from space-based instruments, and thus that seeing from atmospheric turbulence did not significantly affect previous studies' ground-based results on the hemisphere rule. This work was carried out through the National Solar Observatory Research Experiences for Undergraduates (REU) Program, which is funded by the National Science Foundation (NSF). The National Solar Observatory is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the NSF.

  6. First measurement of the helicity dependence for the γp → pπreaction

    NASA Astrophysics Data System (ADS)

    Ahrens, J.; Altieri, S.; Annand, J. R. M.; Arends, H.-J.; Beck, R.; Blackston, M. A.; Bradtke, C.; Braghieri, A.; D'Hose, N.; Dutz, H.; Fix, A.; Goertz, S.; Grabmayr, P.; Hasegawa, S.; Heid, E.; Holvoet, H.; Horikawa, N.; Iwata, T.; Jahn, O.; Jennewein, P.; Klein, F.; Kondratiev, R.; Lang, M.; Lannoy, B.; Lisin, V.; Martinez-Fabregate, M.; McGeorge, J. C.; Meyer, W.; Panzeri, A.; Pedroni, P.; Pinelli, T.; Preobrajenski, I.; Reicherz, G.; Rohlof, Ch.; Rosner, G.; Rost, M.; Rostomyan, T.; Ryckbosch, D.; Schumacher, M.; Seitz, B.; Tamas, G.; Thomas, A.; van de Vyver, R.; Weller, H. R.; Zapadtka, F.

    2007-10-01

    The helicity dependence of the total cross-section and the invariant-mass distributions in the ( pπ±) and (π+π-) final states for the γ p → pπ+π- reaction have been measured for the first time at incident photon energies from 400 to 800MeV. The measurement was performed with the large-acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. Although this channel is found to be predominantly excited by the intermediate production of a Δπ state, both the measured unpolarized and the helicity-dependent observables are generally not well described by the existing theoretical models.

  7. Radiative properties of diffractively-coupled optical nano-antennas with helical geometry.

    PubMed

    Wang, Ren; Forestiere, Carlo; Dal Negro, Luca

    2015-10-05

    In this paper, using the rigorous Surface Integral Equation (SIE) method, we study light scattering by Au nano-helices with geometrical dimensions comparable to the wavelength of visible light and we demonstrate that they behave as highly directional nano-antennas with largely controllable radiation and polarization characteristics in the optical regime. In particular, we systematically investigate the radiation properties of helical nano-antennas with realistic Au dispersion parameters in the visible spectral range, and we establish general design rules that enable the engineering of directional scattering with elliptical or circular polarization. Given the realistic material and geometric parameters used in this work, our findings provide novel opportunities for the engineering of chiral sensors, filters, and components for nano-scale antennas with unprecedented beam forming and polarization capabilities.

  8. [Ultra-low-dose spiral (helical) CT of the thorax: a filtering technique].

    PubMed

    Nitta, N; Takahashi, M; Murata, K; Mori, M; Shimoyama, K; Mishina, A; Matsuo, H; Morita, R; Sugii, K; Nomura, A

    1996-01-01

    To reduce the radiation dose from spiral (helical) CT, a custom-made aluminium filter was installed in the X-ray tube and a reduction of effective tube current was attempted. A pronounced reduction of effective tube current, namely, 6 and 3 mA, was achieved with 26 and 37 mm thick aluminium filters, respectively. Visualization of normal lung structure was accomplished with both 6 and 3 mA settings. However, images of 3 mA failed to delineate mediastinal structures because of marked beam hardening resulting from the bone structure of the thoracic inlet. Six mA was considered the lowest dose setting of spiral (helical) CT of the thorax that could be used for lung cancer screening.

  9. Chiral optical fields: a unified formulation of helicity scattered from particles and dichroism enhancement.

    PubMed

    Nieto-Vesperinas, Manuel

    2017-03-28

    We establish a general unified formulation which, using the optical theorem of electromagnetic helicity, shows that dichorism is a phenomenon arising in any scattering-or diffraction-process, elastic or not, of chiral electromagnetic fields by objects either chiral or achiral. It is shown how this approach paves the way to overcoming well-known limitations of standard circular dichroism, like its weak signal or the difficulties of using it with magnetodielectric particles. Based on the angular spectrum, representation of optical fields with only right circular or left circular plane waves, we introduce beams with transverse elliptic polarization and possessing a longitudinal component. Then, our formulation for general optical fields shows how to enhance the extinction rate of incident helicity (and therefore the dichroism signal) versus that of energy of the light scattered or emitted by a particle, or vice versa.This article is part of the themed issue 'New horizons for nanophotonics'.

  10. Helical localized wave solutions of the scalar wave equation.

    PubMed

    Overfelt, P L

    2001-08-01

    A right-handed helical nonorthogonal coordinate system is used to determine helical localized wave solutions of the homogeneous scalar wave equation. Introducing the characteristic variables in the helical system, i.e., u = zeta - ct and v = zeta + ct, where zeta is the coordinate along the helical axis, we can use the bidirectional traveling plane wave representation and obtain sets of elementary bidirectional helical solutions to the wave equation. Not only are these sets bidirectional, i.e., based on a product of plane waves, but they may also be broken up into right-handed and left-handed solutions. The elementary helical solutions may in turn be used to create general superpositions, both Fourier and bidirectional, from which new solutions to the wave equation may be synthesized. These new solutions, based on the helical bidirectional superposition, are members of the class of localized waves. Examples of these new solutions are a helical fundamental Gaussian focus wave mode, a helical Bessel-Gauss pulse, and a helical acoustic directed energy pulse train. Some of these solutions have the interesting feature that their shape and localization properties depend not only on the wave number governing propagation along the longitudinal axis but also on the normalized helical pitch.

  11. Magnetic helicity balance in the Sustained Spheromak Plasma Experiment

    NASA Astrophysics Data System (ADS)

    Stallard, B. W.; Hooper, E. B.; Woodruff, S.; Bulmer, R. H.; Hill, D. N.; McLean, H. S.; Wood, R. D.

    2003-07-01

    The magnetic helicity balance between the helicity input injected by a magnetized coaxial gun, the rate-of-change in plasma helicity content, and helicity dissipation in electrode sheaths and Ohmic losses have been examined in the Sustained Spheromak Plasma Experiment (SSPX) [E. B. Hooper, L. D. Pearlstein, and R. H. Bulmer, Nucl. Fusion 39, 863 (1999)]. Helicity is treated as a flux function in the mean-field approximation, allowing separation of helicity drive and losses between closed and open field volumes. For nearly sustained spheromak plasmas with low fluctuations, helicity balance analysis implies a decreasing transport of helicity from the gun input into the spheromak core at higher spheromak electron temperature. Long pulse discharges with continuously increasing helicity and larger fluctuations show higher helicity coupling from the edge to the spheromak core. The magnitude of the sheath voltage drop, inferred from cathode heating and a current threshold dependence of the gun voltage, shows that sheath losses are important and reduce the helicity injection efficiency in SSPX.

  12. Implementation of dispersion-free slow acoustic wave propagation and phase engineering with helical-structured metamaterials

    PubMed Central

    Zhu, Xuefeng; Li, Kun; Zhang, Peng; Zhu, Jie; Zhang, Jintao; Tian, Chao; Liu, Shengchun

    2016-01-01

    The ability to slow down wave propagation in materials has attracted significant research interest. A successful solution will give rise to manageable enhanced wave–matter interaction, freewheeling phase engineering and spatial compression of wave signals. The existing methods are typically associated with constructing dispersive materials or structures with local resonators, thus resulting in unavoidable distortion of waveforms. Here we show that, with helical-structured acoustic metamaterials, it is now possible to implement dispersion-free sound deceleration. The helical-structured metamaterials present a non-dispersive high effective refractive index that is tunable through adjusting the helicity of structures, while the wavefront revolution plays a dominant role in reducing the group velocity. Finally, we numerically and experimentally demonstrate that the helical-structured metamaterials with designed inhomogeneous unit cells can turn a normally incident plane wave into a self-accelerating beam on the prescribed parabolic trajectory. The helical-structured metamaterials will have profound impact to applications in explorations of slow wave physics. PMID:27198887

  13. Autonomously folded α-helical lockers promote RNAi*

    PubMed Central

    Guyader, Christian P. E.; Lamarre, Baptiste; De Santis, Emiliana; Noble, James E.; Slater, Nigel K.; Ryadnov, Maxim G.

    2016-01-01

    RNAi is an indispensable research tool with a substantial therapeutic potential. However, the complete transition of the approach to an applied capability remains hampered due to poorly understood relationships between siRNA delivery and gene suppression. Here we propose that interfacial tertiary contacts between α-helices can regulate siRNA cytoplasmic delivery and RNAi. We introduce a rationale of helical amphipathic lockers that differentiates autonomously folded helices, which promote gene silencing, from helices folded with siRNA, which do not. Each of the helical designs can deliver siRNA into cells via energy-dependent endocytosis, while only autonomously folded helices with pre-locked hydrophobic interfaces were able to promote statistically appreciable gene silencing. We propose that it is the amphipathic locking of interfacing helices prior to binding to siRNA that enables RNAi. The rationale offers structurally balanced amphipathic scaffolds to advance the exploitation of functional RNAi. PMID:27721465

  14. Autonomously folded α-helical lockers promote RNAi.

    PubMed

    Guyader, Christian P E; Lamarre, Baptiste; De Santis, Emiliana; Noble, James E; Slater, Nigel K; Ryadnov, Maxim G

    2016-10-10

    RNAi is an indispensable research tool with a substantial therapeutic potential. However, the complete transition of the approach to an applied capability remains hampered due to poorly understood relationships between siRNA delivery and gene suppression. Here we propose that interfacial tertiary contacts between α-helices can regulate siRNA cytoplasmic delivery and RNAi. We introduce a rationale of helical amphipathic lockers that differentiates autonomously folded helices, which promote gene silencing, from helices folded with siRNA, which do not. Each of the helical designs can deliver siRNA into cells via energy-dependent endocytosis, while only autonomously folded helices with pre-locked hydrophobic interfaces were able to promote statistically appreciable gene silencing. We propose that it is the amphipathic locking of interfacing helices prior to binding to siRNA that enables RNAi. The rationale offers structurally balanced amphipathic scaffolds to advance the exploitation of functional RNAi.

  15. Autonomously folded α-helical lockers promote RNAi*

    NASA Astrophysics Data System (ADS)

    Guyader, Christian P. E.; Lamarre, Baptiste; de Santis, Emiliana; Noble, James E.; Slater, Nigel K.; Ryadnov, Maxim G.

    2016-10-01

    RNAi is an indispensable research tool with a substantial therapeutic potential. However, the complete transition of the approach to an applied capability remains hampered due to poorly understood relationships between siRNA delivery and gene suppression. Here we propose that interfacial tertiary contacts between α-helices can regulate siRNA cytoplasmic delivery and RNAi. We introduce a rationale of helical amphipathic lockers that differentiates autonomously folded helices, which promote gene silencing, from helices folded with siRNA, which do not. Each of the helical designs can deliver siRNA into cells via energy-dependent endocytosis, while only autonomously folded helices with pre-locked hydrophobic interfaces were able to promote statistically appreciable gene silencing. We propose that it is the amphipathic locking of interfacing helices prior to binding to siRNA that enables RNAi. The rationale offers structurally balanced amphipathic scaffolds to advance the exploitation of functional RNAi.

  16. Multipole Expansion for a Single Helical Current Conductor

    NASA Astrophysics Data System (ADS)

    Tominaka, T.; Hatanaka, K.; Katayama, T.

    1997-05-01

    The purpose of this paper is to give the expression of the multipole expansion for a single helical current conductor. This analytical expression will be useful for the electromagnetic analysis of various helical coils such as helical dipoles, multifilamentary superconductors and superconducting strands. The present treatment of the multipole expansion for a single helical current conductor is derived as the extension of the case for a single straight current conductor. In addition, the comparison between the analytical and numerical calculations is presented for a single helical current conductor. As a result, the agreement between the analytical and numerical calculations is quite good, except the region near the radius of a single helical current conductor. Then, for the sum of the multipole expansion for a single helical current conductor, the Cesaro's method of summation are adopted.

  17. Stabilization of Helical Macromolecular Phases by Confined Bending

    NASA Astrophysics Data System (ADS)

    Williams, Matthew J.; Bachmann, Michael

    2015-07-01

    By means of extensive replica-exchange simulations of generic coarse-grained models for helical polymers, we systematically investigate the structural transitions into all possible helical phases for flexible and semiflexible elastic polymers with self-interaction under the influence of torsion barriers. The competing interactions lead to a variety of conformational phases including disordered helical arrangements, single helices, and ordered, tertiary helix bundles. Most remarkably, we find that a bending restraint entails a clear separation and stabilization of the helical phases. This aids in understanding why semiflexible polymers such as double-stranded DNA tend to form pronounced helical structures and proteins often exhibit an abundance of helical structures, such as helix bundles, within their tertiary structure.

  18. Iterative Assembly of Helical Proteins by Optimal Hydrophobic Packing

    PubMed Central

    Wu, G. Albert; Coutsias, Evangelos A.; Dill, Ken A.

    2008-01-01

    SUMMARY We present a method for the computer-based iterative assembly of native-like tertiary structures of helical proteins from alpha-helical fragments. For any pair of helices, our method, called MATCHSTIX, first generates an ensemble of possible relative orientations of the helices with various ways to form hydrophobic contacts between them. Those conformations having steric clashes, or a large radius of gyration of hydrophobic residues, or with helices too far separated to be connected by the intervening linking region, are discarded. Then, we attempt to connect the two helical fragments by using a robotics-based loop-closure algorithm. When loop closure is feasible, the algorithm generates an ensemble of viable interconnecting loops. After energy minimization and clustering, we use a representative set of conformations for further assembly with the remaining helices, adding one helix at a time. To efficiently sample the conformational space, the order of assembly generally proceeds from the pair of helices connected by the shortest loop, followed by joining one of its adjacent helices, always proceeding with the shorter connecting loop. We tested MATCHSTIX on 28 helical proteins each containing up to 5 helices and found it to heavily sample native-like conformations. The average RMSD of the best conformations for the 17 helix-bundle proteins that have 2 or 3 helices is less than 2 Å; errors increase somewhat for proteins containing more helices. Native-like states are even more densely sampled when disulfide bonds are known and imposed as restraints. We conclude that, at least for helical proteins, if the secondary structures are known, this rapid rigid-body maximization of hydrophobic interactions can lead to small ensembles of highly native-like structures. It may be useful for protein structure prediction. PMID:18682227

  19. Broadband optical isolator based on helical metamaterials.

    PubMed

    Cao, Hu; Yang, ZhenYu; Zhao, Ming; Wu, Lin; Zhang, Peng

    2015-05-01

    Based on helical metamaterials, a new broadband optical isolator with a triple-helix structure is proposed in this paper. The right-handed circularly polarized light can transmit through the isolator with its polarization unchanged. The reverse propagating light, which is caused by the reflection of the latter optical devices, is converted into left-handed circularly polarized light that is suppressed by the proposed isolator because of absorption. Our design has some unprecedented advantages such as broad frequency ranges and a compact structure; moreover, neither polarizers nor adscititious magnetic fields are required. Properties of the isolator are investigated using the finite-difference time-domain method, and this phenomenon is studied by the mechanism of helical antenna theory.

  20. Instabilities of a rotating helical rod

    NASA Astrophysics Data System (ADS)

    Park, Yunyoung; Ko, William; Kim, Yongsam; Lim, Sookkyung

    2016-11-01

    Bacteria such as Escherichia coli and Vibrio alginolyticus have helical flagellar filament. By rotating a motor, which is located at the bottom end of the flagellar filament embedded in the cell body, CCW or CW, they swim forward or backward. We model a left-handed helix by the Kirchhoff rod theory and use regularized Stokes formulation to study an interaction between the surrounding fluid and the flagellar filament. We perform numerical studies focusing on relations between physical parameters and critical angular frequency of the motor, which separates overwhiring from twirling. We are also interested in the buckling instability of the hook, which is very flexible elastic rod. By measuring buckling angle, which is an angle between rotational axis and helical axis, we observe the effects of physical parameters on buckling of the hook.

  1. Spheromak Formation by Steady Inductive Helicity Injection

    SciTech Connect

    Jarboe, T. R.; Hamp, W. T.; Marklin, G. J.; Nelson, B. A.; O'Neill, R. G.; Redd, A. J.; Sieck, P. E.; Smith, R. J.; Wrobel, J. S.

    2006-09-15

    A spheromak is formed for the first time using a new steady state inductive helicity injection method. Using two inductive injectors with odd symmetry and oscillating at 5.8 kHz, a steady state spheromak with even symmetry is formed and sustained through nonlinear relaxation. A spheromak with about 13 kA of toroidal current is formed and sustained using about 3 MW of power. This is a much lower power threshold for spheromak production than required for electrode-based helicity injection. Internal magnetic probe data, including oscillations driven by the injectors, agree with the plasma being in the Taylor state. The agreement is remarkable considering the only fitting parameter is the amplitude of the spheromak component of the state.

  2. Helical propulsion in shear-thinning fluids

    NASA Astrophysics Data System (ADS)

    Gómez, Saúl; Godínez, Francisco A.; Lauga, Eric; Zenit, Roberto

    2017-02-01

    Swimming microorganisms often have to propel in complex, non-Newtonian fluids. We carry out experiments with self-propelling helical swimmers driven by an externally rotating magnetic field in shear-thinning, inelastic fluids. Similarly to swimming in a Newtonian fluid, we obtain for each fluid a locomotion speed which scales linearly with the rotation frequency of the swimmer, but with a prefactor which depends on the power index of the fluid. The fluid is seen to always increase the swimming speed of the helix, up to 50% faster and thus the strongest of such type reported to date. The maximum relative increase for a fluid power index of around 0.6. Using simple scalings, we argue that the speed increase is not due to the local decrease of the flow viscosity around the helical filament but hypothesise instead that it originates from confinement-like effect due to viscosity stratification around the swimmer.

  3. Helicity of a toroidal vortex with swirl

    NASA Astrophysics Data System (ADS)

    Bannikova, E. Yu.; Kontorovich, V. M.; Poslavsky, S. A.

    2016-04-01

    Based on the solutions of the Bragg-Hawthorne equation, we discuss the helicity of a thin toroidal vortex in the presence of swirl, orbital motion along the torus directrix. The relation between the helicity and circulations along the small and large linked circumferences (the torus directrix and generatrix) is shown to depend on the azimuthal velocity distribution in the core of the swirling ring vortex. In the case of nonuniform swirl, this relation differs from the well-known Moffat relation, viz., twice the product of such circulations multiplied by the number of linkages. The results can find applications in investigating the vortices in planetary atmospheres and the motions in the vicinity of active galactic nuclei.

  4. On the energy density of helical proteins.

    PubMed

    Barros, Manuel; Ferrández, Angel

    2014-12-01

    We solve the problem of determining the energy actions whose moduli space of extremals contains the class of Lancret helices with a prescribed slope. We first see that the energy density should be linear both in the total bending and in the total twisting, such that the ratio between the weights of them is the prescribed slope. This will give an affirmative answer to the conjecture stated in Barros and Ferrández (J Math Phys 50:103529, 2009). Then, we normalize to get the best choice for the helical energy. It allows us to show that the energy, for instance of a protein chain, does not depend on the slope and is invariant under homotopic changes of the cross section which determines the cylinder where the helix is lying. In particular, the energy of a helix is not arbitrary, but it is given as natural multiples of some basic quantity of energy.

  5. SUPERCONDUCTING HELICAL SNAKE MAGNETS: CONSTRUCTION AND MEASUREMENTS.

    SciTech Connect

    MACKAY,W.W.

    1999-05-17

    In order to collide polarized protons, the RHIC project will have two snakes in each ring and four rotators around each of two interaction regions. Two snakes on opposite sides of each ring can minimize depolarization during acceleration by keeping the spin tune at a half. Since the spin direction is normally along the vertical direction in a flat ring, spin rotators must be used around an interaction point to have longitudinal polarization in a collider experiment. Each snake or rotator will be composed of four helical dipoles to provide the required rotation of spin with minimal transverse orbit excursions in a compact length of 10m. The basic helical dipole is a superconducting magnet producing a transverse dipole field which is twisted about the magnet axis through 360{degree} in a length of 2.4 m. The design and construction of the magnets is described in this paper.

  6. Patterns of helicity in solar active regions

    NASA Technical Reports Server (NTRS)

    Pevtsov, Alexei A.; Canfield, Richard C.; Metcalf, Thomas R.

    1994-01-01

    Using 46 vector magnetograms from the Stokes Polarimeter of Mees Solar Observatory (MSO), we studied patterns of local helicity in three diverse solar active regions. From these magnetograms we computed maps of the local helicity parameter alpha = J(sub z)/B(sub z). Although such maps are noisy, we found patterns at the level approximately 2 to 3 sigma(sub J(sub z)), which repeat in successive magnetograms for up to several days. Typically, the alpha maps of any given active region contain identifiable patches with both positive and negative values of alpha. Even within a single sunspot complex, several such alpha patches can often be seen. We followed 68 alpha patches that could be identified on at least two successive alpha maps. We found that the persistence fraction of such patches decrease exponentially, with a characteristic time approximately 27 hr.

  7. Viscosity of Sheared Helical filament Suspensions

    NASA Astrophysics Data System (ADS)

    Sartucci, Matthew; Urbach, Jeff; Blair, Dan; Schwenger, Walter

    The viscosity of suspensions can be dramatically affected by high aspect ratio particles. Understanding these systems