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Title: SU-E-T-626: Practical Method to Implement Arc Therapy Using Scanned Particle Beams

Abstract

Purpose: The purpose of this study was to propose a method to implement arc therapy that is compatible with existing particle therapy systems having gantries and pencil-beam scanning capacities. Furthermore, we sought to demonstrate expected benefits of this method for selected clival chordoma patients. Methods: We propose that a desired particle arc treatment plan can be discretized into a finite number of fixed beams and that only one (or a subset) of these beams be delivered in any single treatment fraction; the target should receive uniform dose during each fraction. For 3 clival-chordoma patients, robust-optimized, scanned proton beams were simulated to deliver 78 Gy (RBE) to clinical target volumes (CTVs), using either a single-field plan with a posterior-anterior (PA) beam or a discrete-arc plan with 16 beams that were equally spaced throughout a 360-degree axial arc. Dose-volume metrics were compared with emphasis on the brainstem, since risk of radiation necrosis there can often restrict application of tumoricidal doses for chordomas. Results: The mean volume of brainstem receiving a dose of 60 Gy (RBE) or higher (V60Gy) was 10.3±0.9 cm{sup 3} for the single-field plan and 4.7±1.8 cm{sup 3} for the discrete-arc plan, a reduction of 55% in favor of arcs.more » The mean dose to the brainstem was also reduced using arcs, by 18%, while the maximum dose was nearly identical for both methods. For the whole brain, V60Gy was reduced by 23%, in favor of arcs. Mean dose to the CTVs were nearly identical for both strategies, within 0.3%. Conclusion: Discrete arc treatments can be implemented using existing scanned particle-beam facilities. Aside from the physical advantages, the biological uncertainties of particle therapy, particularly high in the distal edge, can be reduced by arc therapy via rotational smearing, which may be of benefit for tumors near the brainstem.« less

Authors:
; ; ; ;  [1]
  1. University of Maryland School of Medicine, Baltimore, MD (United States)
Publication Date:
OSTI Identifier:
22538135
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 42; Journal Issue: 6; Other Information: (c) 2015 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; GY RANGE 10-100; NEOPLASMS; OPTIMIZATION; PARTICLES; PROTON BEAMS; RADIATION DOSES; RADIOTHERAPY; VERTEBRAE

Citation Formats

Eley, J, Mehta, M, Molitoris, J, Langner, U, and Langen, K. SU-E-T-626: Practical Method to Implement Arc Therapy Using Scanned Particle Beams. United States: N. p., 2015. Web. doi:10.1118/1.4924989.
Eley, J, Mehta, M, Molitoris, J, Langner, U, & Langen, K. SU-E-T-626: Practical Method to Implement Arc Therapy Using Scanned Particle Beams. United States. doi:10.1118/1.4924989.
Eley, J, Mehta, M, Molitoris, J, Langner, U, and Langen, K. Mon . "SU-E-T-626: Practical Method to Implement Arc Therapy Using Scanned Particle Beams". United States. doi:10.1118/1.4924989.
@article{osti_22538135,
title = {SU-E-T-626: Practical Method to Implement Arc Therapy Using Scanned Particle Beams},
author = {Eley, J and Mehta, M and Molitoris, J and Langner, U and Langen, K},
abstractNote = {Purpose: The purpose of this study was to propose a method to implement arc therapy that is compatible with existing particle therapy systems having gantries and pencil-beam scanning capacities. Furthermore, we sought to demonstrate expected benefits of this method for selected clival chordoma patients. Methods: We propose that a desired particle arc treatment plan can be discretized into a finite number of fixed beams and that only one (or a subset) of these beams be delivered in any single treatment fraction; the target should receive uniform dose during each fraction. For 3 clival-chordoma patients, robust-optimized, scanned proton beams were simulated to deliver 78 Gy (RBE) to clinical target volumes (CTVs), using either a single-field plan with a posterior-anterior (PA) beam or a discrete-arc plan with 16 beams that were equally spaced throughout a 360-degree axial arc. Dose-volume metrics were compared with emphasis on the brainstem, since risk of radiation necrosis there can often restrict application of tumoricidal doses for chordomas. Results: The mean volume of brainstem receiving a dose of 60 Gy (RBE) or higher (V60Gy) was 10.3±0.9 cm{sup 3} for the single-field plan and 4.7±1.8 cm{sup 3} for the discrete-arc plan, a reduction of 55% in favor of arcs. The mean dose to the brainstem was also reduced using arcs, by 18%, while the maximum dose was nearly identical for both methods. For the whole brain, V60Gy was reduced by 23%, in favor of arcs. Mean dose to the CTVs were nearly identical for both strategies, within 0.3%. Conclusion: Discrete arc treatments can be implemented using existing scanned particle-beam facilities. Aside from the physical advantages, the biological uncertainties of particle therapy, particularly high in the distal edge, can be reduced by arc therapy via rotational smearing, which may be of benefit for tumors near the brainstem.},
doi = {10.1118/1.4924989},
journal = {Medical Physics},
number = 6,
volume = 42,
place = {United States},
year = {Mon Jun 15 00:00:00 EDT 2015},
month = {Mon Jun 15 00:00:00 EDT 2015}
}
  • Purpose: Rotational proton radiotherapy would be an interesting treatment modality if it proves to produce dose distributions that conform to the target as well or better than currently available treatment modalities, while reducing the dose to the surrounding organs at risk. A treatment planning study is presented, showing how this objective can be achieved using a single or small number of scanned mono-energetic pencil beams delivered while the proton gantry rotates at the same time that they may deliver faster and more biologically effective treatments than current proton modalities.Methods Proton treatment using single- (SFO) and multi-field optimized (MFO) PBS plansmore » are compared with PMAT plans in phantoms of different shape and uniformity as well as on a brain case. The method followed in ECLIPSE to produce PMAT plans is presented and the feasibility is discussed. Results Table 1 shows that the conformity and uniformity of the PMAT plans is of similar order than those of the SFO and MFO plans. However, in the brain case, the DVHs shown in Figure 1 indicate a significant reduction of the dose to the OARs when PMAT is used. Similarly, the use of PMAT increases the LET in the treatment area, which could translate into a more biologically effective treatment.Conclusions PMAT could provide dose distributions as conformal as current PBS plans but could also offer faster beam delivery and more biologically effective proton plans.« less
  • Purpose: Flattening Filter Free (FFF) beams offer the potential for higher dose rates, short treatment time, and lower out of field dose. Therefore, the aim of this study was to investigate the dosimetric effects and out of field dose of Volumetric Modulated Arc Therapy (VMAT) plans using FFF vs Flattening Filtering (FF) beams for partial brain irradiation. Methods: Ten brain patients treated with a 6FF beam from a Truebeam STX were analyzed retrospectively for this study. These plans (46Gy at 2 Gy per fraction) were re-optimized for 6FFF beams using the same dose constraints as the original plans. PTV coverage,more » PTV Dmax, total MUs, and mean dose to organs-at-risk (OAR) were evaluated. In addition, the out-of-field dose for 6FF and 6FFF plans for one patient was measured on an anthropomorphic phantom. TLDs were placed inside (central axis) and outside (surface) the phantom at distances ranging from 0.5 cm to 17 cm from the field edge. Paired T-test was used for statistical analysis. Results: PTV coverage and PTV Dmax were comparable for the FF and FFF plans with 95.9% versus 95.6% and 111.2% versus 111.9%, respectively. Mean dose to the OARs were 3.7% less for FFF than FF plans (p<0.0001). Total MUs were, on average, 12.5% greater for FFF than FF plans with 481±55 MU (FFF) versus 429±50 MU (FF), p=0.0003. On average, the measured out of field dose was 24% less for FFF compared to FF, p<0.0001. A similar beam-on time was observed for the FFF and FF treatment. Conclusion: It is beneficial to use 6FFF beams for regular fractionated brain VMAT treatments. VMAT treatment plans using FFF beams can achieve comparable PTV coverage but with more OAR sparing. The out of field dose is significant less with mean reduction of 24%.« less
  • Purpose: To evaluate the lateral beam penumbra in pencil beam scanning proton therapy delivered using a dynamic collimator device capable of trimming a portion of the primary beam in close proximity to the patient. Methods: Monte Carlo simulations of pencil beams were performed using MCNPX. Each simulation transported a 125 MeV proton pencil beam through a range shifter, past acollimator, and into a water phantom. Two parameters were varied among the simulations, the source beam size (sigma in air from 3 to 9 mm), and the position of the edge of the collimator (placed from 0 to 30 mm frommore » the central axis of the beam). Proton flux was tallied at the phantom surface to determine the effective beam sizefor all combinations of source beam size and collimator edge position. Results: Quantifying beam size at the phantom surface provides a useful measure tocompare performance among varying source beam sizes and collimation conditions. For arelatively large source beam size (9 mm) entering the range shifter, sigma at thesurface was found to be 10 mm without collimation versus 4 mm with collimation. Additionally, sigma at the surface achievable with collimation was found to be smallerthan for any uncollimated beam, even for very small source beam sizes. Finally, thelateral penumbra achievable with collimation was determined to be largely independentof the source beam size. Conclusion: Collimation can significantly reduce proton pencil beam lateral penumbra.Given the known dosimetric disadvantages resulting from large beam spot sizes,employing a dynamic collimation system can significantly improve lateral tissuesparing in spot-scanned dose distributions.« less
  • Purpose: We implemented the Gafchromic film-based patient specific QA of volumetric modulated arc therapy (VMAT) with flattening-filter free (FFF) beams for spine metastases and validated the accuracy of fast arc delivery. Methods: EBT3 films and a homemade cylindrical QA phantom were employed for dosimetric verification of VMATs. For 14 FFF VMAT plans (10 with 10-MV FFF beams and 4 with 6-MV FFF beams), the doses were recalculated on the phantom and delivered by a TrueBeam STx accelerator equipped with a high-definition 120 leaf MLC. The EBT3 films were scanned using an Epson 10000XL scanner through the FilmQA Pro software. Allmore » the irradiated film images were converted to dose map using a calibration response curve. The resulting dose map of film measurement was compared with treatment plan and evaluated using gamma analysis with dose tolerance of 2% within 2 mm. In addition, the point-dose measurement in the phantom using an ion chamber was evaluated as a reference in a ratio of measured and planned doses. Results: The gamma pass rates averaged over all FFF plans for composite-field measurements were 96.0 ± 3.6% (88.9%–99.5%). When adopting a tolerance level of 3% - 3 mm, the gamma pass rates were improved with the ranges from 98% to 100%. In addition, dose profiles and dose distributions showed that spinal cord was protected by the rapid dose fall-off and by delivering the treatment with high precision. In point-dose measurements, the average differences between the measured and planned doses were 0.5% ± 1.0% of the prescription dose. Conclusion: We demonstrated that Gafchromic EBT3 film would be an effective patient-specific QA tool, especially for VMAT of spine SBRT with treatment of small fields and highly gradient dose distributions. The results of film QA verified that the dosimetric accuracy of spine SBRT utilizing RapidArc with FFF beams in our institution is reliable.« less
  • Purpose: In prostate proton radiotherapy, three fiducial markers are used for patient daily alignment. However fiducial alignment can change beamline heterogeneity in proton therapy. The purpose of this study is to determine the difference in fiducial and boney anatomy alignment for patient treatment. Methods and materials: Prostate cancer patients who received proton treatment were included in this study. 3 fiducial markers were implanted before the initial CT. All the patients were re-CT’d every 2 weeks to check the fiducial marker position reproducibility as well as dosimetric consistence of target coverage. In geometry study, re-CT were fused to the initial CTmore » base on the boney anatomy and the average fiducial marker displacement was measured the centers of the fiducials. Dosimetrically, the initial plan was recalculated directly to re-CT image set based on the boney alignment and fiducial alignment to determine the difference from daily treatment. Prostate coverage and hotspots were evaluated using the dose to 98% of the CTV (D98) and dose to 2% (D2), respectively. Results: The shift from the initial 6 patient CT image sets resulted in an average change in the fiducial location of 5.70 +/− 3 mm. Dosimetric comparison from a single patient revealed that differences from the planned dose resulted from both boney and fiducial alignment. Planned clinical treatment volume coverage resulted in a D98 of 70.44Gy and D2 of 70.84Gy compared to a D98 of 70.13Gy and D2 70.94Gy for boney alignment and a D98 of 70.08Gy and D2 71.18Gy for fiducial alignment respectively. Conclusion: This study demonstrates that with boney anatomy alignment there is little change to CTV coverage and only slightly worse CTV coverage and hotspot production with fiducial alignment. An increase patient cohort and further investigation is necessary to determine the whether boney alignment can help better control dose heterogeneity.« less