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Church C, MacDonald RL, Parsons D, Syme A. Evaluation of plan quality and treatment efficiency in cranial stereotactic radiosurgery treatment plans with a variable source-to-axis distance. Med Phys 2023; 50:3039-3054. [PMID: 36774531 DOI: 10.1002/mp.16288] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2022] [Revised: 10/03/2022] [Accepted: 01/31/2023] [Indexed: 02/13/2023] Open
Abstract
INTRODUCTION Radiotherapy deliveries with dynamic couch motions that shorten the source-to-axis distance (SAD) on a C-arm linac have the potential to increase treatment efficiency through the increase of the effective dose rate. In this investigation, we convert clinically deliverable volumetric modulated arc therapy (VMAT) and dynamic conformal arc (DCA) plans for cranial radiosurgery into virtual isocenter plans through implementation of couch trajectories that maintain the target at a shortened but variable SAD throughout treatment. MATERIALS AND METHODS A randomly sampled population of patients treated with cranial radiosurgery from within the last three years were separated into groups with one, two, and three lesions. All plans had a single isocenter (regardless of number of targets), and a single prescription dose. Patient treatment plans were converted from their original delivery at a standard isocenter to a dynamic virtual isocenter in MATLAB. The virtual isocenter plan featured a variable isocenter position based upon the closest achievable source-to-target distance (referred to herein as a virtual source-to-axis distance [vSAD]) which avoided collision zones on a TrueBeam STx platform. Apertures were magnified according to the vSAD and monitor units at a given control point were scaled based on the inverse square law. Doses were calculated for the plans with a virtual isocenter in the Eclipse (v13.6.23) treatment planning system (TPS) and were compared with the clinical plans. Plan metrics (MU, Paddick conformity index, gradient index, and the volume receiving 12 Gy or more), normal brain dose-volume differences, as well as maximum doses received by organs at risk (OARs) were assessed. The values were compared between standard and virtual isocenter plans with Wilcoxon Sign Ranked tests to determine significance. A subset of the plans were mapped to the MAX-HD anthropomorphic phantom which contained an insert housing EBT3 GafChromic film and a PTW 31010 microion chamber for dose verification on a linac. RESULTS Delivering plans at a virtual isocenter resulted in an average reduction of 20.9% (p = 3×10-6 ) and 20.6% (p = 3.0×10-6 ) of MUs across all VMAT and all DCA plans, respectively. There was no significant change in OAR max doses received by plans delivered at a virtual isocenter. The low dose wash (1.0-2.0 Gy or 5-11% of the prescription dose) was increased (by approximately 20 cc) for plans with three lesions. This was equivalent to a 2.7%-3.8% volumetric increase in normal tissue receiving the respective dose level when comparing the plan with a virtual isocenter to a plan with a standard isocenter. Gamma pass rates with a 5%/1mm analysis criteria were 96.40% ± 2.90% and 95.07% ± 3.10% for deliveries at standard and virtual isocenter, respectively. Absolute point dose agreements were within -0.36% ± 3.45% and -0.55% ± 3.39% for deliveries at a standard and virtual isocenter, respectively. Potential time savings per arc were found to have linear relationship with the monitor units delivered per arc (savings of 0.009 s/MU with an r2 = 0.866 when fit to plans with a single lesion). CONCLUSIONS Converting clinical plans at standard isocenter to a virtual isocenter design did not show any losses to plan quality while simultaneously improving treatment efficiency through MU reductions.
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Affiliation(s)
- Cody Church
- Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada
| | - R Lee MacDonald
- Department of Radiation Oncology and Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada
| | - David Parsons
- Department of Radiation Oncology, University of Texas Southwestern Medical Centre, Dallas, Texas, USA
| | - Alasdair Syme
- Department of Radiation Oncology and Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada
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Lincoln JD, MacDonald RL, Little B, Syme A, Thomas CG. Comparison of anatomically informed class solution template trajectories with patient-specific trajectories for stereotactic radiosurgery and radiotherapy. J Appl Clin Med Phys 2022; 23:e13765. [PMID: 36052983 DOI: 10.1002/acm2.13765] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Revised: 04/08/2022] [Accepted: 08/08/2022] [Indexed: 11/06/2022] Open
Abstract
Class solution template trajectories are used clinically for efficiency, safety, and reproducibility. The aim was to develop class solutions for single cranial metastases radiotherapy/radiosurgery based on intracranial target positioning and compare to patient-specific trajectories in the context of 4π optimization. Template trajectories were constructed based on the open-source Montreal Neurological Institute (MNI) average brain. The MNI brain was populated with evenly spaced spherical target volumes (2 cm diameter, N = 243) and organs-at-risk (OARs) were identified. Template trajectories were generated for six anatomical regions (frontal, medial, and posterior, each with laterality dependence) based on previously published 4π optimization methods. Volumetric modulated arc therapy (VMAT) treatment plans generated using anatomically informed template 4π trajectories and patientspecific 4π trajectories were compared against VMAT plans from a standard four-arc template. Four-arc optimization techniques were compared to the standard VMAT template by placing three spherical targets in each of six anatomical regions of a test patient. This yielded 54 plans to compare various plan quality metrics. Increasing plan technique complexity, the total number of OAR maximum dose reductions compared to the standard arc template for the 6 anatomical classes was 4+/-2 (OFIXEDc) and 7+/-2 (OFIXEDi). In 65.6% of all cases, optimized fixed-couch positions outperformed the standard-arc template. Of the three comparisons, the most complex (OFIXEDi) showed the greatest statistical significance compared to the least complex (VMATi) across 12 plan quality metrics of maximum dose to each OAR, V12Gy, total plan Monitor Units, conformity index, and gradient index (p < 0.00417). In approximately 70% of all cases, 4π optimization methods outperformed the standard-arc template in terms of maximum dose reduction to OAR, by exclusively changing the arc geometry. We conclude that a tradeoff exists between complexity of a class solution methodology compared to patient-specific methods for arc selection, in the context of plan quality improvement.
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Affiliation(s)
- John David Lincoln
- Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Robert Lee MacDonald
- Department of Medical Physics, Nova Scotia Health Authority, Halifax, Nova Scotia, Canada
| | - Brian Little
- Department of Medical Physics, Nova Scotia Health Authority, Halifax, Nova Scotia, Canada
| | - Alasdair Syme
- Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada.,Department of Medical Physics, Nova Scotia Health Authority, Halifax, Nova Scotia, Canada.,Department of Radiation Oncology, Dalhousie University, Halifax, Nova Scotia, Canada.,Beatrice Hunter Cancer Research Institute, Halifax, Nova Scotia, Canada
| | - Christopher Grant Thomas
- Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada.,Department of Medical Physics, Nova Scotia Health Authority, Halifax, Nova Scotia, Canada.,Department of Radiation Oncology, Dalhousie University, Halifax, Nova Scotia, Canada.,Beatrice Hunter Cancer Research Institute, Halifax, Nova Scotia, Canada.,Department of Radiology, Dalhousie University, Halifax, Nova Scotia, Canada
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MacDonald L, Lincoln J, Church CM, Thomas C, Syme A. Mean Arc Distance (MAD): a quantity to compare trajectory 4 πsampling in single target cranial stereotactic radiotherapy. Biomed Phys Eng Express 2022; 8. [PMID: 35764061 DOI: 10.1088/2057-1976/ac7c92] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2022] [Accepted: 06/28/2022] [Indexed: 11/12/2022]
Abstract
Purpose:C-arm linac-based radiotherapy has seen a recent interest in 4 methods of delivery using simultaneous rotations of couch and gantry to reduce doses to organs-at-risk (OARs) and increase dose compactness. While many methods use heuristics to generate trajectories that avoid OARs, combined with arbitrary trajectory restrictions to prevent oversampling, a quantity has not yet been developed to succinctly compare sampling of the 4 space for candidate trajectories as a surrogate for dosimetric compactness.Methods:Evenly spaced sampling points were distributed across a 4 sphere centred on isocentre. A metric, mean arc distance (MAD), was defined that quantifies the average arc distance between all fields in a radiotherapy trajectory and their nearest sampling point. The relationship between isodose volume and MAD was examined in 2,047 plans: 900 unique trajectories of fixed port DCA plans, 900 unique trajectories of contiguous field DCA plans, 192 VMAT plans (eight volumes in four locations, each with six trajectories) in matRad with 5 VMAT plans repeated for validation in a clinical planning system, and 10 clinical VMAT cases replanned with five trajectories in a clinical treatment planning system.Results:All isodose volumes greater than 10 % of the prescription dose decreased with decreasing MAD in all comparisons. In the range of 10 % to 100 % of the prescription dose, the rate of isodose volume decrease was exponential as a function of MAD in all comparisons. Reduction of absolute isodose volume is seen with increased 4 sampling, with larger target volumes exhibiting larger absolute reductions. Very low isodoses (0 % to 10 % of prescription) increased with decreasing MAD.Conclusions:MAD is a 4 sampling quantity useful in quantifying the decrease of isodose volume, relevant for sparing normal tissues. By quantifying this feature, candidate dynamic trajectories can be efficiently compared for 4 sampling. This quantity is explored here for single target cranial radiotherapy but may have applications to other radiotherapy treatment site.
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Affiliation(s)
- Lee MacDonald
- Medical Physics, Nova Scotia Health Authority, 5788 University Avenue, Halifax, Halifax, Nova Scotia, B3L 2C2, CANADA
| | - John Lincoln
- Medical Physics, Dalhousie University, Department of Medical Physics, QEII Health Sciences Centre, 5820 University Ave, Dickson Building, Halifax, Nova Scotia, B3H 4R2, CANADA
| | - Cody Mathew Church
- Physics and Atmospheric Science, Dalhousie University, 6310 Coburg Road, Halifax, Nova Scotia, B3H 4R2, CANADA
| | - Christopher Thomas
- Medical Physics, Nova Scotia Health Authority, 5788 University Avenue, Halifax, Halifax, Nova Scotia, B3L 2C2, CANADA
| | - Alasdair Syme
- Radiation Oncology, Dalhousie University, Department of Medical Physics, QEII Health Sciences Centre, 5820 University Ave, Dickson Building, Halifax, Nova Scotia, B3H 4R2, CANADA
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Mullins J, Renaud MA, Serban M, Seuntjens J. Simultaneous trajectory generation and volumetric modulated arc therapy optimization. Med Phys 2020; 47:3078-3090. [PMID: 32215936 DOI: 10.1002/mp.14155] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2019] [Revised: 03/04/2020] [Accepted: 03/04/2020] [Indexed: 12/25/2022] Open
Abstract
PURPOSE Trajectory-based treatment planning involves the combination of a gantry-couch trajectory with volumetric modulated arc therapy (VMAT) treatment plan optimization. This work presents the implementation of an optimization methodology that generates a trajectory simultaneous with treatment plan optimization (simTr-VMAT). METHODS The optimization algorithm is based on the column generation approach, in which a treatment plan is iteratively constructed through the solution of a subproblem called the "pricing problem." The property of the pricing problem to rank candidate apertures based on their associated price is leveraged to select an optimal aperture while simultaneously determining the trajectory path. A progressively increasing gantry-couch grid resolution is used to provide an initial coarse sampling of the angular solution space while maintaining fine control point spacing with the final treatment plan. The trajectory optimization was applied and compared to coplanar VMAT treatment plans for a lung patient, a glioblastoma patient, and a prostate patient. Algorithm validation was performed through the generation of 5000 random trajectories and optimization using column generation VMAT for each patient case, representing the solution space for the trajectory optimization problem. The simTr-VMAT trajectories were compared against these random trajectories based on a quality metric that prefers trajectories with few control points and low objective function value over long, inefficient trajectories. RESULTS For the lung patient, the simTr-VMAT plan resulted in a decrease of the mean dose of 1.5 and 1.0 Gy to the heart and ipsilateral lung, respectively. For the glioblastoma patient, the simTr-VMAT plan resulted in improved planning target volume coverage with a decrease in mean dose to the eyes, lens, nose, and contralateral temporal lobe between 2 and 7 Gy. The prostate patient showed no clinically relevant dosimetric improvement. The simTr-VMAT treatment plans ranked at the 99.6, 96.3, and 99.4 percentiles compared to the distribution of randomly generated trajectories for the lung, glioblastoma, and prostate patients, respectively. CONCLUSION The simTr-VMAT optimization methodology resulted in treatment plans with equivalent or improved dosimetric outcomes compared to coplanar VMAT treatment plans, with the trajectories resulting from the optimization ranking among the optimal trajectories for each patient case.
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Affiliation(s)
- Joel Mullins
- Department of Physics & Medical Physics Unit, McGill University, Montréal, QC, H4A 3J1, Canada
| | - Marc-André Renaud
- Department of Mathematics and Industrial Engineering, Polytechnique Montréal, Montréal, QC, H3T 1J4, Canada
| | - Monica Serban
- Medical Physics Unit, McGill University Health Centre, Montréal, QC, H4A 3J1, Canada
| | - Jan Seuntjens
- Medical Physics Unit, McGill University & Research Institute of the McGill University Health Centre, Montréal, QC, H4A 3J1, Canada
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Mullins J, Renaud MA, Heng V, Ruo R, DeBlois F, Seuntjens J. Trajectory-based VMAT for cranial targets with delivery at shortened SAD. Med Phys 2020; 47:3103-3112. [PMID: 32198933 DOI: 10.1002/mp.14151] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Revised: 03/04/2020] [Accepted: 03/07/2020] [Indexed: 01/17/2023] Open
Abstract
INTRODUCTION Trajectory-based volumetric modulated arc therapy (tr-VMAT) treatment plans enable the option for noncoplanar delivery yielding steeper dose gradients and increased sparing of critical structures compared to conventional treatment plans. The addition of translational couch motion to shorten the effective source-to-axis distance (SAD) may result in improved delivery precision and an increased effective dose rate. In this work, tr-VMAT treatment plans using a noncoplanar "baseball stitch" trajectory were implemented, applied to patients presented with cranial targets, and compared to the clinical treatment plans. METHODS A treatment planning workflow was implemented: (a) beamlet doses were calculated for control points defined along a baseball stitch trajectory using a collapsed-cone convolution-superposition algorithm; (b) VMAT treatment plans were optimized using the column generation approach; (c) a final dose distribution was calculated in Varian Eclipse using the analytical anisotropic algorithm by importing the optimized treatment plan parameters. Tr-VMAT plans were optimized for ten patients presented with cranial targets at both standard and shortened SAD, and compared to the clinical treatment plans through isodose distributions, dose-volume histograms, and dosimetric indices. The control point specifications of the optimized tr-VMAT plans were used to estimate the delivery time. RESULTS The optimized tr-VMAT plans with both shortened and standard SAD delivery yielded a comparable plan quality to the clinical treatment plans. A statistically significant benefit was observed for dose gradient index and monitor unit efficiency for shortened SAD tr-VMAT plans, while improved target volume conformity was observed for the clinical treatment plan (P ≤ 0.05). A clear dosimetric benefit was not demonstrated between tr-VMAT delivery at shortened SAD compared to standard SAD, but shortened SAD delivery yielded a fraction size-dependent reduction in the estimated delivery time. CONCLUSION The implementation of "baseball stitch" tr-VMAT treatment plans to patients presented with cranial targets demonstrated comparable plan quality to clinical treatment plans. The delivery at shortened SAD produced a fraction size-dependent decrease in estimated delivery time.
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Affiliation(s)
- Joel Mullins
- Department of Physics & Medical Physics Unit, McGill University, Montréal, QC, H4A 3J1, Canada
| | - Marc-André Renaud
- Department of Mathematics and Industrial Engineering, Polytechnique Montréal, Montréal, QC, H3T 1J4, Canada
| | - Veng Heng
- Department of Physics & Medical Physics Unit, McGill University, Montréal, QC, H4A 3J1, Canada
| | - Russell Ruo
- Medical Physics Unit, McGill University Health Centre, Montréal, QC, H4A 3J1, Canada
| | - François DeBlois
- Centre Hospitalier de l'Université de Montréal & Département de Physique, Université de Montréal, Montréal, QC, H2X 3E4, Canada.,McGill University, Montréal, QC, H4A 3J1, Canada
| | - Jan Seuntjens
- Medical Physics Unit, McGill University & Research Institute of the McGill University Health Centre, Montréal, QC, H4A 3J1, Canada
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Lyu Q, Neph R, Yu VY, Ruan D, Boucher S, Sheng K. Many-isocenter optimization for robotic radiotherapy. Phys Med Biol 2020; 65:045003. [PMID: 31851958 PMCID: PMC7100370 DOI: 10.1088/1361-6560/ab63b8] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Despite significant dosimetric gains, clinical implementation of the 4π non-coplanar radiotherapy on the widely available C-arm gantry system is hindered by limited clearance, and the need to perform complex coordinated gantry and couch motion. A robotic radiotherapy platform would be conducive to such treatment but a new conflict between field size and MLC modulation resolution needs to be managed for versatile applications. This study investigates the dosimetry and delivery efficiency of purposefully creating many isocenters to achieve simultaneously high MLC modulation resolution and large tumor coverage. An integrated optimization framework was proposed for simultaneous beam orientation optimization (BOO), isocenter selection, and fluence map optimization (FMO). The framework includes a least-square dose fidelity objective, a total variation term for regularizing the fluence smoothness, and a group sparsity term for beam selection. A minimal number of isocenters were identified for efficient target coverage. Colliding beams excluded, high-resolution small-field 4π intensity-modulated radiotherapy (IMRT) treatment plans with 50 cm source-to-isocenter distance (SID-50) on 10 Head and Neck (H&N) cancer patients were compared with low-resolution large-field plans with 100 cm SID (SID-100). With the same or better target coverage, the average reduction of [Dmean, Dmax] of 20-beam SID-50 plans from 20-beam SID-100 plans were [2.09 Gy, 1.19 Gy] for organs at risk (OARs) overall, [3.05 Gy, 0.04 Gy] for parotid gland, [3.62 Gy, 5.19 Gy] for larynx, and [3.27 Gy, 1.10 Gy] for mandible. R50 and integral dose were reduced by 5.3% and 9.6%, respectively. Wilcoxon signed-rank test showed significant difference (p < 0.05) in planning target volume (PTV) homogeneity, PTV Dmax, R50, Integral dose, and OAR Dmean and Dmax. The estimated delivery time of 20-beam [SID-50, SID-100] plans were [19, 18] min and [14, 9] min, assuming 5 fractions and 30 fractions, respectively. With clinically acceptable delivery efficiency, many-isocenter optimization is dosimetrically desirable for treating large targets with high modulation resolution on the robotic platform.
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Affiliation(s)
- Qihui Lyu
- Department of Radiation Oncology, University of California Los Angeles, Los Angeles, CA 90095, United States of America
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Sarkar B, Ganesh T, Munshi A, Manikandan A, Mohanti BK. 4π Radiotherapy Using a Linear Accelerator: A Misnomer in Violation of the Solid Geometric Boundary Conditions in Three-Dimensional Euclidean Space. J Med Phys 2019; 44:283-286. [PMID: 31908388 PMCID: PMC6936196 DOI: 10.4103/jmp.jmp_2_19] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2019] [Revised: 08/31/2019] [Accepted: 08/31/2019] [Indexed: 11/12/2022] Open
Abstract
Purpose: The concept of 4πc radiotherapy is a radiotherapy planning technique receiving much attention in recent times. The aim of this article is to disprove the feasibility of the 4π radiotherapy using a cantilever-type linear accelerator or any other external-beam delivery machines. Materials and Methods: A surface integral-based mathematical derivation for the maximum achievable solid angle for a linear accelerator was carried out respecting the rotational boundary conditions for gantry and couch in three-dimensional Euclidean space. The allowed movements include a gantry rotation of 0–2πc and a table rotation of . Results: Total achievable solid angle by cantilever-type linear accelerator (or any teletherapy machine employing a cantilever design) is , which is applicable only for the foot and brain radiotherapy where the allowed table rotation is 90°–0°–270°. For other sites such as pelvis, thorax, or abdomen, achievable solid angle as the couch rotation comes down significantly. Practically, only suitable couch angle is 0° by avoiding gantry–couch–patient collision. Conclusions: Present cantilever design of linear accelerator prevents achieving a 4π radian solid angle at any point in the patient. Even the most modern therapy machines like CyberKnife which has a robotic arm also cannot achieve 4π geometry. Maximum achievable solid angle under the highest allowable boundary condition(s) cannot exceed 2πc, which is restricted for only extremities such as foot and brain radiotherapy. For other parts of the body such as pelvis, thorax, and abdomen, the solid angle is reduced to 1/5th (maximum value) of the 4πc. To obtain a 4πc solid angle in a three-dimensional Euclidean space, the patient has to be a zero-dimensional point and X-ray head of the linear accelerator has a freedom to rotate in every point of a hypothetical sphere of radius 1 m. This article establishes geometrically why it is not possible to achieve a 4πc solid angle.
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Affiliation(s)
- Biplab Sarkar
- Department of Radiation Oncology, Manipal Hospitals, Dwarka, New Delhi, India
| | - Tharmarnadar Ganesh
- Department of Radiation Oncology, Manipal Hospitals, Dwarka, New Delhi, India
| | - Anusheel Munshi
- Department of Radiation Oncology, Manipal Hospitals, Dwarka, New Delhi, India
| | - Arjunan Manikandan
- Department of Medical Physics, Apollo Proton Cancer Center, Chennai, Tamil Nadu, India
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MacDonald RL, Syme A, Little B, Ward L, Thomas CG. Toward the combined optimization of dynamic axes (CODA) for stereotactic radiotherapy and radiosurgery using fixed couch trajectories. Med Phys 2019; 47:307-316. [PMID: 31659750 DOI: 10.1002/mp.13887] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2019] [Revised: 10/17/2019] [Accepted: 10/18/2019] [Indexed: 11/11/2022] Open
Abstract
PURPOSE To develop a novel system for patient-specific combined optimization of couch, collimator, and gantry angles for use in volumetric modulated arc therapy (VMAT) treatment planning. The system was designed to produce highly compact dose distributions by extensively sampling the 4π space. Automated fixed couch trajectory planning was used to reduce normal tissue doses by avoiding beams-eye-view (BEV) overlap with organs-at-risk (OARs) and improve monitor unit (MU) efficiency through collimator angle optimization. METHODS By merging distinct BEV objective functions used to optimize the couch rotation angle and collimator angle, a three-dimensional (3D) cost space (the CODA cube) was constructed with axes of gantry, couch, and collimator rotation angles. At each voxel in this CODA cube, the cost of implementing this combination of axes positions in fixed couch trajectories was quantified. The CODA cube was sampled and explored using a modified constrained Bellman-Ford algorithm to suggest low-cost fixed candidate arcs on each plane of the space, from which 10-arcs are chosen throughout the 3D space using a k-means clustering algorithm. These fixed couch trajectories were then imported into the Eclipse treatment planning system (v.11) and inverse-optimized according to clinical standards. Eight artificial cranial targets were contoured in a test-patient anatomy, and seven treatment plans were generated from combinations of three and four targets. The CODA cube optimized plans were compared to standard 4-arc VMAT plans for cranial stereotactic radiotherapy/surgery that were optimized for the same sets of targets; maximum dose to each OAR, V12Gy to normal brain, conformity, and total MUs were compared. Both planning methods were inverse-optimized with identical dosimetric objectives. RESULTS CODA plans resulted in a reduction in maximum dose to OARs of 20.6% (P < 0.01), with maximum brainstem dose decreased by 2.63 Gy (P = 0.031) on average when compared to the standard arc arrangement. The mean reduction in total MU was 8.6% (P = 0.156), the mean increase in the inverse of the van't Riet conformation number was 0.1%, (P = 0.67) and the mean decrease in normal brain tissue receiving 12 Gy or higher was 3.9% (P = 0.16), when compared to the standard VMAT arc configuration (n = 7). CONCLUSIONS The optimization of couch, collimator, and gantry angles simultaneously using a 3D optimization space achieved improvement on multiple clinical metrics when compared to the standard VMAT arc configuration. A statistically significant sparing to OAR maximum doses was seen. Combining these optimizations may yield superior results to independent optimization.
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Affiliation(s)
- R Lee MacDonald
- Department of Radiation Oncology, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, M4N 3M5, Canada
| | - Alasdair Syme
- Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, B3H 4J5, Canada.,Department of Medical Physics, Nova Scotia Health Authority, Queen Elizabeth II Health Sciences Centre, Halifax, NS, B3H 1V7, Canada.,Department of Radiation Oncology, Dalhousie University, Halifax, NS, B3H 4R2, Canada
| | - Brian Little
- Department of Medical Physics, Nova Scotia Health Authority, Queen Elizabeth II Health Sciences Centre, Halifax, NS, B3H 1V7, Canada
| | - Lucy Ward
- Department of Medical Physics, Nova Scotia Health Authority, Queen Elizabeth II Health Sciences Centre, Halifax, NS, B3H 1V7, Canada
| | - Christopher G Thomas
- Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, B3H 4J5, Canada.,Department of Medical Physics, Nova Scotia Health Authority, Queen Elizabeth II Health Sciences Centre, Halifax, NS, B3H 1V7, Canada.,Department of Radiation Oncology, Dalhousie University, Halifax, NS, B3H 4R2, Canada.,Department of Radiology, Dalhousie University, Halifax, NS, B3H 4R2, Canada
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Uto M, Ogura K, Mukumoto N, Miyabe Y, Nakamura M, Hirashima H, Katagiri T, Takehana K, Hiraoka M, Mizowaki T. Single-isocenter volumetric-modulated Dynamic WaveArc therapy for two brain metastases. Jpn J Radiol 2019; 37:619-625. [PMID: 31230185 DOI: 10.1007/s11604-019-00849-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2019] [Accepted: 06/16/2019] [Indexed: 10/26/2022]
Abstract
PURPOSE A new irradiation technique, volumetric-modulated Dynamic WaveArc therapy (VMDWAT), based on sequential non-coplanar trajectories, can be performed using the Vero4DRT. This planning study compared the dose distribution and treatment time between single-isocenter volumetric-modulated arc therapy (VMAT) with multiple straight non-coplanar arcs and single-isocenter VMDWAT in patients with two brain metastases. MATERIALS AND METHODS Twenty patients with two planning target volumes exceeding 2.0 cm3 were included. Both VMAT and VMDWAT plans were created with single isocenter and a prescribed dose of 28 Gy delivered in five fractions. Target conformity was evaluated using indices modified from the RTOG-CI (mRTOG-CI) and IP-CI (mIP-CI). RESULTS VMDWAT significantly improved both mRTOG-CI and mIP-CI and reduced the volume of normal brain tissue receiving 25 and 28 Gy compared to VMAT. The two modalities did not significantly differ in terms of the volume of normal brain tissue receiving 5, 10, 12, 15, and 20 Gy. The mean treatment time was significantly shorter in the VMDWAT group. CONCLUSION VMDWAT significantly improved dose distribution in a shorter treatment time compared to VMAT in patients treated for two brain metastases. Single-isocenter VMDWAT may thus be a promising treatment for two brain metastases.
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Affiliation(s)
- Megumi Uto
- Department of Radiation Oncology and Image-Applied Therapy, Kyoto University Graduate School of Medicine, 54, Shogoin Kawahara-cho, Sakyo-ku, Kyoto, 606-8507, Japan
| | - Kengo Ogura
- Department of Radiation Oncology and Image-Applied Therapy, Kyoto University Graduate School of Medicine, 54, Shogoin Kawahara-cho, Sakyo-ku, Kyoto, 606-8507, Japan.,Department of Therapeutic Radiology, Kobe City Medical Center General Hospital, 2-2-1, Minatojimaminamimachi, Chuo-ku, Kobe, Hyogo, Japan
| | - Nobutaka Mukumoto
- Department of Radiation Oncology and Image-Applied Therapy, Kyoto University Graduate School of Medicine, 54, Shogoin Kawahara-cho, Sakyo-ku, Kyoto, 606-8507, Japan
| | - Yuki Miyabe
- Department of Radiation Oncology and Image-Applied Therapy, Kyoto University Graduate School of Medicine, 54, Shogoin Kawahara-cho, Sakyo-ku, Kyoto, 606-8507, Japan
| | - Mitsuhiro Nakamura
- Department of Radiation Oncology and Image-Applied Therapy, Kyoto University Graduate School of Medicine, 54, Shogoin Kawahara-cho, Sakyo-ku, Kyoto, 606-8507, Japan.,Division of Medical Physics, Department of Information Technology and Medical Engineering, Human Health Sciences, Graduate School of Medicine, Kyoto University Graduate School of Medicine, 53, Shogoin Kawahara-cho, Sakyo-ku, Kyoto, Japan
| | - Hideaki Hirashima
- Department of Radiation Oncology and Image-Applied Therapy, Kyoto University Graduate School of Medicine, 54, Shogoin Kawahara-cho, Sakyo-ku, Kyoto, 606-8507, Japan
| | - Tomohiro Katagiri
- Department of Radiation Oncology and Image-Applied Therapy, Kyoto University Graduate School of Medicine, 54, Shogoin Kawahara-cho, Sakyo-ku, Kyoto, 606-8507, Japan.,Department of Radiation Oncology, Shizuoka City Shizuoka Hospital, 10-93, Otemachi, Aoi-ku, Shizuoka, Shizuoka, Japan
| | - Keiichi Takehana
- Department of Radiation Oncology and Image-Applied Therapy, Kyoto University Graduate School of Medicine, 54, Shogoin Kawahara-cho, Sakyo-ku, Kyoto, 606-8507, Japan
| | - Masahiro Hiraoka
- Department of Radiation Oncology and Image-Applied Therapy, Kyoto University Graduate School of Medicine, 54, Shogoin Kawahara-cho, Sakyo-ku, Kyoto, 606-8507, Japan.,Japanese Red Cross Wakayama Medical Center, 4-20, Komatsubara-dori, Wakayama, Wakayama, Japan
| | - Takashi Mizowaki
- Department of Radiation Oncology and Image-Applied Therapy, Kyoto University Graduate School of Medicine, 54, Shogoin Kawahara-cho, Sakyo-ku, Kyoto, 606-8507, Japan.
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10
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Smyth G, Evans PM, Bamber JC, Bedford JL. Recent developments in non-coplanar radiotherapy. Br J Radiol 2019; 92:20180908. [PMID: 30694086 PMCID: PMC6580906 DOI: 10.1259/bjr.20180908] [Citation(s) in RCA: 51] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2018] [Revised: 01/15/2019] [Accepted: 01/17/2019] [Indexed: 11/05/2022] Open
Abstract
This paper gives an overview of recent developments in non-coplanar intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT). Modern linear accelerators are capable of automating motion around multiple axes, allowing efficient delivery of highly non-coplanar radiotherapy techniques. Novel techniques developed for C-arm and non-standard linac geometries, methods of optimization, and clinical applications are reviewed. The additional degrees of freedom are shown to increase the therapeutic ratio, either through dose escalation to the target or dose reduction to functionally important organs at risk, by multiple research groups. Although significant work is still needed to translate these new non-coplanar radiotherapy techniques into the clinic, clinical implementation should be prioritized. Recent developments in non-coplanar radiotherapy demonstrate that it continues to have a place in modern cancer treatment.
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Affiliation(s)
- Gregory Smyth
- Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, UK
| | | | - Jeffrey C Bamber
- Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, UK
| | - James L Bedford
- Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, UK
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11
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Hirashima H, Nakamura M, Miyabe Y, Mukumoto N, Ono T, Iramina H, Mizowaki T. Quality assurance of non-coplanar, volumetric-modulated arc therapy employing a C-arm linear accelerator, featuring continuous patient couch rotation. Radiat Oncol 2019; 14:62. [PMID: 30971273 PMCID: PMC6458733 DOI: 10.1186/s13014-019-1264-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2018] [Accepted: 03/27/2019] [Indexed: 12/21/2022] Open
Abstract
Purpose To perform quality assurance of non-coplanar, volumetric-modulated arc therapy featuring continuous couch rotation (CCR-VMAT) using a C-arm linear accelerator. Methods We planned and delivered CCR-VMAT using the TrueBeam Developer Mode. Treatment plans were created for both a C-shaped phantom and five prostate cancer patients using seven CCR trajectories that lacked collisions; we used RayStation software (ver. 4.7) to this end. Subsequently, verification plans were generated. The mean absolute error (MAE) between the center of an MV-imaged steel ball and the radiation field was calculated using the Winston–Lutz test. The MAEs between planned and actual irradiation values were also calculated from trajectory logs. In addition, correlation coefficients (r values) among the MAEs of gantry angle, couch angle, and multi-leaf collimator (MLC) position, and mechanical parameters including gantry speed, couch speed, MLC speed, and beam output, were estimated. The dosimetric accuracies of planned and measured values were also assessed using ArcCHECK. Results The MAEs ±2 standard deviations as revealed by the Winston–Lutz test for all trajectories were 0.3 ± 0.3 mm in two dimensions. The MAEs of the gantry, couch, and MLC positions calculated from all trajectory logs were within 0.04°, 0.08°, and 0.02 mm, respectively. Deviations in the couch angle (r = 0.98, p < 0.05) and MLC position (r = 0.86, p < 0.05) increased significantly with speed. The MAE of the beam output error was less than 0.01 MU. The mean gamma passing rate ± 2 SD (range) of the 3%/3 mm, 3%/1 mm, and 5%/1 mm was 98.1 ± 1.9% (95.7–99.6%), 87.2 ± 2.8% (80.2–96.7%), and 96.3 ± 2.8% (93.9–99.6%), respectively. Conclusions CCR-VMAT delivered via the TrueBeam Developer Mode was associated with high-level geometric and mechanical accuracy, thus affording to high dosimetric accuracy. The CCR-VMAT performance was stable regardless of the trajectory chosen. Electronic supplementary material The online version of this article (10.1186/s13014-019-1264-6) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Hideaki Hirashima
- Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto, 606-8507, Japan
| | - Mitsuhiro Nakamura
- Division of Medical Physics, Department of Information Technology and Medical Engineering, Human Health Sciences, Graduate School of Medicine, Kyoto University, 53 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto, 606-8507, Japan.
| | - Yuki Miyabe
- Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto, 606-8507, Japan
| | - Nobutaka Mukumoto
- Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto, 606-8507, Japan
| | - Tomohiro Ono
- Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto, 606-8507, Japan
| | - Hiraku Iramina
- Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto, 606-8507, Japan
| | - Takashi Mizowaki
- Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto, 606-8507, Japan
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12
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Smyth G, Evans PM, Bamber JC, Mandeville HC, Rollo Moore A, Welsh LC, Saran FH, Bedford JL. Dosimetric accuracy of dynamic couch rotation during volumetric modulated arc therapy (DCR-VMAT) for primary brain tumours. Phys Med Biol 2019; 64:08NT01. [PMID: 30808011 PMCID: PMC6877349 DOI: 10.1088/1361-6560/ab0a8e] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Radiotherapy treatment plans using dynamic couch rotation during volumetric modulated arc therapy (DCR-VMAT) reduce the dose to organs at risk (OARs) compared to coplanar VMAT, while maintaining the dose to the planning target volume (PTV). This paper seeks to validate this finding with measurements. DCR-VMAT treatment plans were produced for five patients with primary brain tumours and delivered using a commercial linear accelerator (linac). Dosimetric accuracy was assessed using point dose and radiochromic film measurements. Linac-recorded mechanical errors were assessed by extracting deviations from log files for multi-leaf collimator (MLC), couch, and gantry positions every 20 ms. Dose distributions, reconstructed from every fifth log file sample, were calculated and used to determine deviations from the treatment plans. Median (range) treatment delivery times were 125 s (123-133 s) for DCR-VMAT, compared to 78 s (64-130 s) for coplanar VMAT. Absolute point doses were 0.8% (0.6%-1.7%) higher than prediction. For coronal and sagittal films, respectively, 99.2% (96.7%-100%) and 98.1% (92.9%-99.0%) of pixels above a 20% low dose threshold reported gamma <1 for 3% and 3 mm criteria. Log file analysis showed similar gantry rotation root-mean-square error (RMSE) for VMAT and DCR-VMAT. Couch rotation RMSE for DCR-VMAT was 0.091° (0.086-0.102°). For delivered dose reconstructions, 100% of pixels above a 5% low dose threshold reported gamma <1 for 2% and 2 mm criteria in all cases. DCR-VMAT, for the primary brain tumour cases studied, can be delivered accurately using a commercial linac.
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Affiliation(s)
- Gregory Smyth
- Joint Department of Physics at The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, United Kingdom. Author to whom any correspondence should be addressed
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13
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Grams MP, de Los Santos LEF. Design and clinical use of a rotational phantom for dosimetric verification of IMRT/VMAT treatments. Phys Med 2018; 50:59-65. [PMID: 29891095 DOI: 10.1016/j.ejmp.2018.05.019] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/08/2018] [Revised: 05/11/2018] [Accepted: 05/17/2018] [Indexed: 11/29/2022] Open
Abstract
PURPOSE To describe the design and clinical use of a rotational phantom for dosimetric verification of IMRT/VMAT treatment plans using radiochromic film. METHODS A solid water cylindrical phantom was designed with separable upper and lower halves and rests on plastic bearings allowing for 360° rotation about its central axis. The phantom accommodates a half sheet of radiochromic film, and by rotating the cylinder, the film can be placed in any plane between coronal and sagittal. Calculated dose planes coinciding with rotated film measurements are exported by rotating the CT image and dose distribution within the treatment planning system. The process is illustrated with 2 rotated film measurements of an SRS treatment plan involving 4 separate targets. Additionally, 276 patient specific QA measurements were obtained with the phantom and analyzed with a 2%/2 mm gamma criterion. RESULTS The average 2%/2 mm gamma passing rate for all 276 plans was 99.3%. Seventy-two of the 276 plans were measured with the plane of the film rotated between the coronal and sagittal planes and had an average passing rate of 99.4%. CONCLUSIONS The rotational phantom allows for accurate film measurements in any plane. With this technique, regions of a dose distribution which might otherwise require multiple sagittal or coronal measurements can be verified with as few as a single measurement. This increases efficiency and, in combination with the high spatial resolution inherent to film dosimetry, makes the rotational technique an attractive option for patient-specific QA.
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Affiliation(s)
- Michael P Grams
- Department of Radiation Oncology, Mayo Clinic, 200 First St SW, Rochester, MN 55905, USA.
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14
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Manser P, Frauchiger D, Frei D, Volken W, Terribilini D, Fix MK. Dose calculation of dynamic trajectory radiotherapy using Monte Carlo. Z Med Phys 2018; 29:31-38. [PMID: 29631759 DOI: 10.1016/j.zemedi.2018.03.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2017] [Revised: 03/19/2018] [Accepted: 03/19/2018] [Indexed: 11/19/2022]
Abstract
PURPOSE Using volumetric modulated arc therapy (VMAT) delivery technique gantry position, multi-leaf collimator (MLC) as well as dose rate change dynamically during the application. However, additional components can be dynamically altered throughout the dose delivery such as the collimator or the couch. Thus, the degrees of freedom increase allowing almost arbitrary dynamic trajectories for the beam. While the dose delivery of such dynamic trajectories for linear accelerators is technically possible, there is currently no dose calculation and validation tool available. Thus, the aim of this work is to develop a dose calculation and verification tool for dynamic trajectories using Monte Carlo (MC) methods. METHODS The dose calculation for dynamic trajectories is implemented in the previously developed Swiss Monte Carlo Plan (SMCP). SMCP interfaces the treatment planning system Eclipse with a MC dose calculation algorithm and is already able to handle dynamic MLC and gantry rotations. Hence, the additional dynamic components, namely the collimator and the couch, are described similarly to the dynamic MLC by defining data pairs of positions of the dynamic component and the corresponding MU-fractions. For validation purposes, measurements are performed with the Delta4 phantom and film measurements using the developer mode on a TrueBeam linear accelerator. These measured dose distributions are then compared with the corresponding calculations using SMCP. First, simple academic cases applying one-dimensional movements are investigated and second, more complex dynamic trajectories with several simultaneously moving components are compared considering academic cases as well as a clinically motivated prostate case. RESULTS The dose calculation for dynamic trajectories is successfully implemented into SMCP. The comparisons between the measured and calculated dose distributions for the simple as well as for the more complex situations show an agreement which is generally within 3% of the maximum dose or 3mm. The required computation time for the dose calculation remains the same when the additional dynamic moving components are included. CONCLUSION The results obtained for the dose comparisons for simple and complex situations suggest that the extended SMCP is an accurate dose calculation and efficient verification tool for dynamic trajectory radiotherapy. This work was supported by Varian Medical Systems.
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Affiliation(s)
- Peter Manser
- Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern, Switzerland.
| | - Daniel Frauchiger
- Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern, Switzerland
| | - Daniel Frei
- Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern, Switzerland
| | - Werner Volken
- Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern, Switzerland
| | - Dario Terribilini
- Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern, Switzerland
| | - Michael K Fix
- Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern, Switzerland
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15
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Wilson B, Gete E. Machine-specific quality assurance procedure for stereotactic treatments with dynamic couch rotations. Med Phys 2017; 44:6529-6537. [PMID: 28921564 DOI: 10.1002/mp.12589] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Revised: 07/25/2017] [Accepted: 08/29/2017] [Indexed: 01/16/2023] Open
Abstract
OBJECTIVE We present a method in which the treatment couch's accuracy is measured using the electronic portal imaging device (EPID) and a phantom of our own construction. Using this phantom, we were able to quantify the treatment couch walkout, and the rotation angle accuracy for both static and dynamic couch treatments. These measurements were used to provide an accurate measure of the treatment couch isocenter as well as to verify the couch rotation angle recorded in the trajectory log. METHODS The phantom was constructed using a polystyrene slab in which five ball bearings of 4 mm diameter are placed on the same plane at varying radii (0, 2.8, 4.4, 5.6, and 6.7 cm). The couch was rotated through its full extent (-90, 90 degrees) while MV images were acquired continuously. The couch rotational accuracy was calculated using a least squares minimization which fit the locations of the BBs to their expected locations relative to reference setup conditions. Using this approach, rotation angle and isocenter walkout was calculated in three dimensions. These measurements were used to quantify the accuracy of the couch as well as to validate the Varian TrueBeam trajectory logs. Additionally, a method for an EPID-based couch star-shot measurement was developed and compared with the traditional film-based method. RESULTS The measured couch center of rotation consisted of a cloud of points clustered around the room isocenter within 0.7 mm distance. The trajectory log couch angle values agreed with those recorded in the DICOM header of the EPID images to the third significant digit and the couch rotation angles recorded in the trajectory log and DICOM header agreed with the calculated values to 0.08 degrees. Comparison of couch star-shot measurement developed in this study with film-based star-shot measurements gave an agreement to within 0.2 mm. CONCLUSION We have developed a quality assurance method for the treatment couch which is simple, accurate, and enables the user to access a multitude of consistent data with a single measurement. Using this method, we have shown that the treatment couch is accurate for both static and dynamic stereotactic deliveries.
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Affiliation(s)
- Byron Wilson
- Medical Physics, BC Cancer Agency - Vancouver Centre, Vancouver, British Columbia, Canada.,Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada
| | - Ermias Gete
- Medical Physics, BC Cancer Agency - Vancouver Centre, Vancouver, British Columbia, Canada
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Bratengeier K, Herzog B, Wegener S, Holubyev K. Finer leaf resolution and steeper beam edges using a virtual isocentre in concurrence to PTV-shaped collimators in standard distance - a planning study. Radiat Oncol 2017; 12:88. [PMID: 28545556 PMCID: PMC5445413 DOI: 10.1186/s13014-017-0826-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2017] [Accepted: 05/16/2017] [Indexed: 11/22/2022] Open
Abstract
Purpose Investigation of a reduced source to target distance to improve organ at risk sparing during stereotactic irradiation (STX). Methods The authors present a planning study with perfectly target-volume adapted collimator compared with multi-leaf collimator (MLC) at reduced source to virtual isocentre distance (SVID) in contrast to normal source to isocentre distance (SID) for stereotactic applications. The role of MLC leaf width and 20–80% penumbra was examined concerning the healthy tissue sparing. Several prescription schemes and target diameters are considered. Results Paddick’s gradient index (GI) as well as comparison of the mean doses to spherical shells at several distances to the target is evaluated. Both emphasize the same results: the healthy tissue sparing in the high dose area around the planning target volume (PTV) is improved at reduced SVID ≤ 70 cm. The effect can be attributed more to steeper penumbra than to finer leaf resolution. Comparing circular collimators at different SVID just as MLC-shaped collimators, always the GI was reduced. Even MLC-shaped collimator at SVID 70 cm had better healthy tissue sparing than an optimal shaped circular collimator at SID 100 cm. Regarding penumbra changes due to varying SVID, the results of the planning study are underlined by film dosimetry measurements with Agility™ MLC. Conclusion Penumbra requires more attention in comparing studies, especially studies using different planning systems. Reduced SVID probably allows usage of conventional MLC for STX-like irradiations. Electronic supplementary material The online version of this article (doi:10.1186/s13014-017-0826-8) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Klaus Bratengeier
- Department of Radiation Oncology, University of Würzburg, Josef-Schneider-Str. 11, 97080, Würzburg, Germany.
| | - Barbara Herzog
- Martin-Luther-Universität Halle-Wittenberg, Institute of Physics, Von-Danckelmann-Platz 3, 06120, Halle (Saale), Germany
| | - Sonja Wegener
- Department of Radiation Oncology, University of Würzburg, Josef-Schneider-Str. 11, 97080, Würzburg, Germany
| | - Kostyantyn Holubyev
- University of Freiburg, Klinik für Strahlenheilkunde, Abt. Medizinische Physik, Robert-Koch-Str. 3, 79106, Freiburg, Germany
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