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Justus Adamson - One of the best experts on this subject based on the ideXlab platform.
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sbrt treatment of multiple extracranial oligometastases using a single Isocenter with distinct optimizations
Journal of radiosurgery and SBRT, 2017Co-Authors: Michael Trager, F Yin, Joseph K Salama, Justus AdamsonAbstract:Purpose We address the challenges associated with applying a single Isocenter treatment technique to extracranial oligometastases. Methods We propose a technique that uses a Single Isocenter with Distinct Optimizations (SIDO) in which all Volumetric Modulated Arc Therapy (VMAT) fields share an Isocenter but each field treats only one target. When necessary, setup uncertainties from rotations and deformations are mitigated by applying a couch translation between VMAT arcs, and interplay is minimized using dynamic conformal arcs (DCA) as the starting point for inverse optimization. Using CBCTs from eleven previous SBRT cases we determined the likelihood of needing a translational shift between SIDO arcs to correct rotational uncertainties. We also compared SIDO and SIDO with DCA to single (VMAT) and dual (VMAT and DCA) Isocenter plans for phantom (N=11) and patient (N=4) cases. Results Spatial uncertainties from inter-fractional rotations were greatest for large target separation and small margins, with ~30% of fractions requiring a correction (3mm margin and 10cm separation). SIDO with DCA greatly decreased arc modulation, with approximately 20% more modulation than DCA, and similar conformity to conventional VMAT. SIDO and SIDO with DCA had comparable conformity to single and dual Isocenter plans when separation between PTVs is >3cm, while traditional single Isocenter VMAT had superior conformity for <3cm. SIDO with DCA had superior GI over other planning techniques for almost all cases. Conclusion SIDO for extracranial oligometastases allows flexibility to mitigate spatial uncertainties from rotation and deformation, and has comparable dosimetry to traditional VMAT with low modulation when inverse optimization begins with DCA.
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is a single Isocenter sufficient for volumetric modulated arc therapy radiosurgery when multiple itracranial metastases are spatially dispersed
Medical Dosimetry, 2016Co-Authors: Jay Morrison, Rodney Hood, F Yin, Joseph K Salama, John P Kirkpatrick, Justus AdamsonAbstract:Abstract Previous work demonstrated improved dosimetry of single Isocenter volumetric modulated arc therapy (VMAT) of multiple intracranial targets when they are located ≤ 4 cm from Isocenter because of narrower multileaf collimators (MLCs). In follow-up, we sought to determine if decreasing Isocenter-target distance (diso) by using 2 to 3 Isocenters would improve dosimetry for spatially dispersed targets. We also investigated the effect of a maximum dose constraint during VMAT optimization, and the dosimetric effect of the number of VMAT arcs used for a larger number of targets (i.e., 7 to 9). We identified radiosurgery cases that had multiple intracranial targets with diso of at least 1 target > 5 cm. A single Isocenter VMAT plan was created using a standardized 4-arc technique with 18 Gy per target. Each case was then replanned (1) using 2 to 3 Isocenters, (2) including a maximum dose constraint per target, and in the case of 7 to 9 targets, (3) using 3 to 6 arcs. Dose evaluation included brain V6 Gy and V12 Gy, and conformity index (CI), gradient index (GI), and heterogeneity index (HI) per target. Two Isocenters were sufficient to limit diso to ≤ 4 cm and ≤ 5 cm for 11/15 and 13/15 cases, respectively; after replanning with 2 to 3 Isocenters, diso decreased from 5.8 ± 2.8 cm (2.3 14.9) to 2.5 ± 1.4 cm (0 5.2). All dose statistics improved on average, albeit modestly: V6 Gy = 6.9 ± 7.1%, V12 Gy = 0.9% ± 4.4%, CI = 2.6% ± 4.6%, GI = 0.9% ± 12.7%, and HI = 2.6% ± 5.2%; however, the number of arcs doubled and monitor units increase by nearly 2-fold. A maximum dose constraint had a negative effect on all dose indices, increasing V12 Gy by 9.7 ± 6.9%. For ≥ 7 targets, increasing number of arcs to > 3 improved CI, V12 Gy, and V6 Gy. A single Isocenter is likely sufficient for VMAT radiosurgery of multiple intracranial metastases. Optimal treatment plan quality is achieved when no constraint is placed on the maximum target dose; for cases with many targets at least 4 arcs are needed for optimal plan quality.
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su f t 591 sbrt treatment of multiple extracranial oligometastases using a single Isocenter with distinct optimizations sido
Medical Physics, 2016Co-Authors: Michael Trager, Justus Adamson, Joseph K SalamaAbstract:Purpose: A new development in linac-based intracranial radiosurgery is treatment of multiple targets using single Isocenter VMAT, which dramatically reduces treatment time while maintaining high conformality and dose gradient. Our purpose is to translate this technique to extracranial SBRT of oligometastases and address additional challenges such as interplay from motion and setup uncertainties. Methods: We propose SIDO (Single Isocenter with Distinct Optimizations) planning in which all VMAT arcs share an Isocenter but each arc treats only one target. Setup uncertainties from rotations and deformations are mitigated by applying a couch translation between VMAT arcs, while interplay is minimized by using dynamic conformal arcs (DCAs) as the starting point for VMAT optimization. We compared SIDO to single (VMAT) and dual (VMAT & DCA) Isocenter plans for phantom and patient (N=2) cases. Dose statistics included conformity index (CI), gradient index (GI), and modulation factor (MLC opening & total MU). Finally, we determined likelihood of needing a translational shift between SIDO arcs to correct rotational uncertainties using CBCTs from eleven previous SBRT cases. Results: For phantoms with target separations of 5–15cm, CI was 0.87±0.02, 0.89±0.05, and 0.91±0.02, for SIDO, single, and dual-Isocenter VMAT respectively. GI was 6.83±1.0, 7.45±1.0 and 5.94±0.7 respectively. SIDO conformity did not trend with increasing distance between PTVs, while gradient decreased for all planning techniques. Using DCAs as the starting point of VMAT optimization decreased modulation, with a 39.4% reduction in monitor units. SIDO had 4.9% and 39% less MU than single and dual-Isocenter VMAT respectively. A translational shift between SIDO arcs would be required in 10–28% of cases due to rotational uncertainties to stay within a 5mm margin, for targets separated by ≥10cm. Conclusion: SIDO for extracranial oligometastases has comparable dosimetry to traditional VMAT with low modulation similar to DCAs. Future work will quantify decrease in dosimetric interplay.
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physics considerations for single Isocenter volumetric modulated arc radiosurgery for treatment of multiple intracranial targets
Practical radiation oncology, 2016Co-Authors: Carl Stanhope, F Yin, Joseph K Salama, John P Kirkpatrick, Z Wang, Z Chang, Grace Kim, Justus AdamsonAbstract:Abstract Objective Our purpose was to address challenges associated with single-Isocenter radiosurgery for multiple intracranial targets (SIRMIT) including increased sensitivity to rotational uncertainties (resulting from distance of the targets from Isocenter) as well as potential for decreased plan quality from larger multileaf collimator width >4 cm from Isocenter. Methods and materials We evaluated the effect that a 6 degrees-of-freedom couch correction had on localization uncertainty for SIRMIT using thermoplastic mask immobilization. Required setup margin was determined from rotation of the skull and mask (setup kV cone beam computed tomography relative to planning computed tomography). Intraoperational margin was determined from skull rotation within the mask (difference between pre- and posttreatment cone beam computed tomography). We also investigated 4 Isocenter placement strategies: volume centroid, centroid of equally weighted points (1 per target), centroid of points weighted by inverse of volume, and Eclipse's built-in method. Results When no 6 degrees-of-freedom couch correction is performed after initial setup, a 0.35-mm margin is required per centimeter of target-Isocenter separation to account for 95% of rotational uncertainties at initial setup. This margin is reduced to 0.10 mm/cm of target-Isocenter separation to account for intraoperative rotational uncertainties when the initial setup uncertainty is eliminated via image guided 6 degrees-of-freedom couch correction. Analysis of 11 multitarget plans (37 targets) showed that conformity index and gradient index improved with decreasing distance from Isocenter, this trend being more pronounced for targets Conclusions Rotational corrections via image guidance are necessary for SIRMIT with a thermoplastic mask for immobilization. There is a clear tradeoff between dosimetric quality of small and large targets that should be considered carefully when placing the Isocenter.
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su e t 613 physics considerations for single Isocenter volumetric modulated arc radiosurgery for treatment of multiple intracranial targets
Medical Physics, 2015Co-Authors: Carl Stanhope, F Yin, Joseph K Salama, John P Kirkpatrick, Z Wang, Z Chang, Grace Kim, Justus AdamsonAbstract:Purpose: To address physics challenges associated with single Isocenter radiosurgery for multiple intracranial metastases (SIRMIT). Because the Varian High Definition MLC has thicker leaves >4cm from the Isocenter, we predict inferior dose falloff and plan quality for small targets located >4cm from Isocenter. To address this concern, we evaluate various Isocenter placement strategies including one that places the Isocenter closer to smaller targets. We also evaluate the significance of arc geometry avoidance angles to limit lens dose. Methods: 11 SIRMIT plans with Isocenter at centroid were retrospectively analyzed to determine the relationship between relevant dosimetric indices and distance from Isocenter (e.g. relative tumor volume). We investigated three Isocenter placements for four SIRMIT patients whose lesions had larger variations in target volume; placements included: centroid, Eclipse’s built-in method, and an “inverse center of mass” (ICM) method that weights the Isocenter towards smaller lesions. Three VMAT SIRMIT plans were prepared according to institutional and Clark et al.’s guidelines to investigate the effect of arc geometry on lens dose. Results: Dose conformity and gradient fall-off tended to be better for larger tumors (>1cc) close to Isocenter. For the four largest tumors (per plan), centroid CI, GI, and HI values were 9±9%, 12±4%, and 3.8±4.9% better than the next best Isocenter placement strategy. None of the methods yielded significantly higher conformity for small tumors, however ICM GI and HI values were better for three of the small tumors by 6±12% and 1.8±2.2% respectively. Lens dose range decreased from [3.3%, 11.4%] to [0.1%, 0.5%] by avoiding arc geometries that enter/exit through the eyes. Conclusion: CI and GI values were poorer for small distal targets, especially >6cm. Large tumors benefited from centroid placement more than small tumors did from ICM. It is necessary to consider arc geometry avoidance angles to adequately reduce lens dose.
Grant M Clark - One of the best experts on this subject based on the ideXlab platform.
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plan quality and treatment planning technique for single Isocenter cranial radiosurgery with volumetric modulated arc therapy
Practical radiation oncology, 2012Co-Authors: Grant M Clark, Richard Popple, Brendan M Prendergast, Evan M Thomas, John G Stewart, Barton L Guthrie, James M Markert, S A Spencer, John B FiveashAbstract:Abstract Purpose To demonstrate plan quality and provide a practical, systematic approach to the treatment planning technique for single Isocenter cranial radiosurgery with volumetric modulated arc therapy (VMAT; RapidArc, Varian Medical systems, Palo Alto, CA). Methods and materials Fifteen patients with 1 or more brain metastases underwent single Isocenter VMAT radiosurgery. All plans were normalized to deliver 100% of the prescription dose to 99%-100% of the target volume. All targets per plan were treated to the same dose. Plans were created with dose control tuning structures surrounding targets to maximize conformity and dose gradient. Plan quality was evaluated by calculation of conformity index (CI = 100% isodose volume/target volume) and homogeneity index (HI = maximum dose/prescription dose) scores for each target and a Paddick gradient index (GI = 50% isodose volume/100% isodose volume) score for each plan. Results The median number of targets per patient was 2 (range, 1-5). The median number of non-coplanar arcs utilized per plan was 2 (range, 1- 4). Single target plans were created with 1 or 2 non-coplanar arcs while multitarget plans utilized 2 to 4 non-coplanar arcs. Prescription doses ranged from 5-16 Gy in 1-5 fractions. The mean conformity index was 1.12 (± SD, 0.13) and the mean HI was 1.44 (± SD, 0.11) for all targets. The mean GI per plan was 3.34 (± SD, 0.42). Conclusions We have outlined a practical approach to cranial radiosurgery treatment planning using the single Isocenter VMAT platform. One or 2 arc single Isocenter plans are often adequate for treatment of single targets, while 2-4 arcs may be more advantageous for multiple targets. Given the high plan quality and extreme clinical efficiency, this single Isocenter VMAT approach will continue to become more prevalent for linac-based radiosurgical treatment of 1 or more intracranial targets and will likely replace multiple Isocenter techniques.
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feasibility of single Isocenter volumetric modulated arc radiosurgery for treatment of multiple brain metastases
International Journal of Radiation Oncology Biology Physics, 2010Co-Authors: Grant M Clark, Richard Popple, Edward P Young, John B FiveashAbstract:Purpose To evaluate the relative plan quality of single-Isocenter vs. multi-Isocenter volumetric modulated arc therapy (VMAT) for radiosurgical treatment of multiple central nervous system metastases. Methods and Materials VMAT plans were created using RapidArc technology for treatment of simulated patients with three brain metastases. The plans consisted of single-arc/single-Isocenter, triple-arc (noncoplanar)/single-Isocenter, and triple-arc (coplanar)/triple-Isocenter configurations. All VMAT plans were normalized to deliver 100% of the 20-Gy prescription dose to all lesions. The plans were evaluated by calculation of Paddick and Radiation Therapy Oncology Group conformity index scores, Paddick gradient index scores, and 12-Gy isodose volumes. Results All plans were judged clinically acceptable, but differences were observed in the dosimetric parameters, with the use of multiple noncoplanar arcs showing small improvements in the conformity indexes compared with the single-arc/single-Isocenter and triple-arc (coplanar)/triple-Isocenter plans. Multiple arc plans (triple-arc [noncoplanar]/single-Isocenter and triple-arc [coplanar]/triple-Isocenter) showed smaller 12-Gy isodose volumes in scenarios involving three metastases spaced closely together, with only small differences noted among all plans involving lesions spaced further apart. Conclusion Our initial results suggest that single-Isocenter VMAT plans can be used to deliver conformity equivalent to that of multiple Isocenter VMAT techniques. For targets that are closely spaced, multiple noncoplanar single-Isocenter arcs might be required. VMAT radiosurgery for multiple targets using a single Isocenter can be efficiently delivered, requiring less than one-half the beam time required for multiple Isocenter set ups. VMAT radiosurgery will likely replace multi-Isocenter techniques for linear accelerator-based treatment of multiple targets.
John B Fiveash - One of the best experts on this subject based on the ideXlab platform.
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plan quality and treatment planning technique for single Isocenter cranial radiosurgery with volumetric modulated arc therapy
Practical radiation oncology, 2012Co-Authors: Grant M Clark, Richard Popple, Brendan M Prendergast, Evan M Thomas, John G Stewart, Barton L Guthrie, James M Markert, S A Spencer, John B FiveashAbstract:Abstract Purpose To demonstrate plan quality and provide a practical, systematic approach to the treatment planning technique for single Isocenter cranial radiosurgery with volumetric modulated arc therapy (VMAT; RapidArc, Varian Medical systems, Palo Alto, CA). Methods and materials Fifteen patients with 1 or more brain metastases underwent single Isocenter VMAT radiosurgery. All plans were normalized to deliver 100% of the prescription dose to 99%-100% of the target volume. All targets per plan were treated to the same dose. Plans were created with dose control tuning structures surrounding targets to maximize conformity and dose gradient. Plan quality was evaluated by calculation of conformity index (CI = 100% isodose volume/target volume) and homogeneity index (HI = maximum dose/prescription dose) scores for each target and a Paddick gradient index (GI = 50% isodose volume/100% isodose volume) score for each plan. Results The median number of targets per patient was 2 (range, 1-5). The median number of non-coplanar arcs utilized per plan was 2 (range, 1- 4). Single target plans were created with 1 or 2 non-coplanar arcs while multitarget plans utilized 2 to 4 non-coplanar arcs. Prescription doses ranged from 5-16 Gy in 1-5 fractions. The mean conformity index was 1.12 (± SD, 0.13) and the mean HI was 1.44 (± SD, 0.11) for all targets. The mean GI per plan was 3.34 (± SD, 0.42). Conclusions We have outlined a practical approach to cranial radiosurgery treatment planning using the single Isocenter VMAT platform. One or 2 arc single Isocenter plans are often adequate for treatment of single targets, while 2-4 arcs may be more advantageous for multiple targets. Given the high plan quality and extreme clinical efficiency, this single Isocenter VMAT approach will continue to become more prevalent for linac-based radiosurgical treatment of 1 or more intracranial targets and will likely replace multiple Isocenter techniques.
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feasibility of single Isocenter volumetric modulated arc radiosurgery for treatment of multiple brain metastases
International Journal of Radiation Oncology Biology Physics, 2010Co-Authors: Grant M Clark, Richard Popple, Edward P Young, John B FiveashAbstract:Purpose To evaluate the relative plan quality of single-Isocenter vs. multi-Isocenter volumetric modulated arc therapy (VMAT) for radiosurgical treatment of multiple central nervous system metastases. Methods and Materials VMAT plans were created using RapidArc technology for treatment of simulated patients with three brain metastases. The plans consisted of single-arc/single-Isocenter, triple-arc (noncoplanar)/single-Isocenter, and triple-arc (coplanar)/triple-Isocenter configurations. All VMAT plans were normalized to deliver 100% of the 20-Gy prescription dose to all lesions. The plans were evaluated by calculation of Paddick and Radiation Therapy Oncology Group conformity index scores, Paddick gradient index scores, and 12-Gy isodose volumes. Results All plans were judged clinically acceptable, but differences were observed in the dosimetric parameters, with the use of multiple noncoplanar arcs showing small improvements in the conformity indexes compared with the single-arc/single-Isocenter and triple-arc (coplanar)/triple-Isocenter plans. Multiple arc plans (triple-arc [noncoplanar]/single-Isocenter and triple-arc [coplanar]/triple-Isocenter) showed smaller 12-Gy isodose volumes in scenarios involving three metastases spaced closely together, with only small differences noted among all plans involving lesions spaced further apart. Conclusion Our initial results suggest that single-Isocenter VMAT plans can be used to deliver conformity equivalent to that of multiple Isocenter VMAT techniques. For targets that are closely spaced, multiple noncoplanar single-Isocenter arcs might be required. VMAT radiosurgery for multiple targets using a single Isocenter can be efficiently delivered, requiring less than one-half the beam time required for multiple Isocenter set ups. VMAT radiosurgery will likely replace multi-Isocenter techniques for linear accelerator-based treatment of multiple targets.
Joseph K Salama - One of the best experts on this subject based on the ideXlab platform.
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sbrt treatment of multiple extracranial oligometastases using a single Isocenter with distinct optimizations
Journal of radiosurgery and SBRT, 2017Co-Authors: Michael Trager, F Yin, Joseph K Salama, Justus AdamsonAbstract:Purpose We address the challenges associated with applying a single Isocenter treatment technique to extracranial oligometastases. Methods We propose a technique that uses a Single Isocenter with Distinct Optimizations (SIDO) in which all Volumetric Modulated Arc Therapy (VMAT) fields share an Isocenter but each field treats only one target. When necessary, setup uncertainties from rotations and deformations are mitigated by applying a couch translation between VMAT arcs, and interplay is minimized using dynamic conformal arcs (DCA) as the starting point for inverse optimization. Using CBCTs from eleven previous SBRT cases we determined the likelihood of needing a translational shift between SIDO arcs to correct rotational uncertainties. We also compared SIDO and SIDO with DCA to single (VMAT) and dual (VMAT and DCA) Isocenter plans for phantom (N=11) and patient (N=4) cases. Results Spatial uncertainties from inter-fractional rotations were greatest for large target separation and small margins, with ~30% of fractions requiring a correction (3mm margin and 10cm separation). SIDO with DCA greatly decreased arc modulation, with approximately 20% more modulation than DCA, and similar conformity to conventional VMAT. SIDO and SIDO with DCA had comparable conformity to single and dual Isocenter plans when separation between PTVs is >3cm, while traditional single Isocenter VMAT had superior conformity for <3cm. SIDO with DCA had superior GI over other planning techniques for almost all cases. Conclusion SIDO for extracranial oligometastases allows flexibility to mitigate spatial uncertainties from rotation and deformation, and has comparable dosimetry to traditional VMAT with low modulation when inverse optimization begins with DCA.
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is a single Isocenter sufficient for volumetric modulated arc therapy radiosurgery when multiple itracranial metastases are spatially dispersed
Medical Dosimetry, 2016Co-Authors: Jay Morrison, Rodney Hood, F Yin, Joseph K Salama, John P Kirkpatrick, Justus AdamsonAbstract:Abstract Previous work demonstrated improved dosimetry of single Isocenter volumetric modulated arc therapy (VMAT) of multiple intracranial targets when they are located ≤ 4 cm from Isocenter because of narrower multileaf collimators (MLCs). In follow-up, we sought to determine if decreasing Isocenter-target distance (diso) by using 2 to 3 Isocenters would improve dosimetry for spatially dispersed targets. We also investigated the effect of a maximum dose constraint during VMAT optimization, and the dosimetric effect of the number of VMAT arcs used for a larger number of targets (i.e., 7 to 9). We identified radiosurgery cases that had multiple intracranial targets with diso of at least 1 target > 5 cm. A single Isocenter VMAT plan was created using a standardized 4-arc technique with 18 Gy per target. Each case was then replanned (1) using 2 to 3 Isocenters, (2) including a maximum dose constraint per target, and in the case of 7 to 9 targets, (3) using 3 to 6 arcs. Dose evaluation included brain V6 Gy and V12 Gy, and conformity index (CI), gradient index (GI), and heterogeneity index (HI) per target. Two Isocenters were sufficient to limit diso to ≤ 4 cm and ≤ 5 cm for 11/15 and 13/15 cases, respectively; after replanning with 2 to 3 Isocenters, diso decreased from 5.8 ± 2.8 cm (2.3 14.9) to 2.5 ± 1.4 cm (0 5.2). All dose statistics improved on average, albeit modestly: V6 Gy = 6.9 ± 7.1%, V12 Gy = 0.9% ± 4.4%, CI = 2.6% ± 4.6%, GI = 0.9% ± 12.7%, and HI = 2.6% ± 5.2%; however, the number of arcs doubled and monitor units increase by nearly 2-fold. A maximum dose constraint had a negative effect on all dose indices, increasing V12 Gy by 9.7 ± 6.9%. For ≥ 7 targets, increasing number of arcs to > 3 improved CI, V12 Gy, and V6 Gy. A single Isocenter is likely sufficient for VMAT radiosurgery of multiple intracranial metastases. Optimal treatment plan quality is achieved when no constraint is placed on the maximum target dose; for cases with many targets at least 4 arcs are needed for optimal plan quality.
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su f t 591 sbrt treatment of multiple extracranial oligometastases using a single Isocenter with distinct optimizations sido
Medical Physics, 2016Co-Authors: Michael Trager, Justus Adamson, Joseph K SalamaAbstract:Purpose: A new development in linac-based intracranial radiosurgery is treatment of multiple targets using single Isocenter VMAT, which dramatically reduces treatment time while maintaining high conformality and dose gradient. Our purpose is to translate this technique to extracranial SBRT of oligometastases and address additional challenges such as interplay from motion and setup uncertainties. Methods: We propose SIDO (Single Isocenter with Distinct Optimizations) planning in which all VMAT arcs share an Isocenter but each arc treats only one target. Setup uncertainties from rotations and deformations are mitigated by applying a couch translation between VMAT arcs, while interplay is minimized by using dynamic conformal arcs (DCAs) as the starting point for VMAT optimization. We compared SIDO to single (VMAT) and dual (VMAT & DCA) Isocenter plans for phantom and patient (N=2) cases. Dose statistics included conformity index (CI), gradient index (GI), and modulation factor (MLC opening & total MU). Finally, we determined likelihood of needing a translational shift between SIDO arcs to correct rotational uncertainties using CBCTs from eleven previous SBRT cases. Results: For phantoms with target separations of 5–15cm, CI was 0.87±0.02, 0.89±0.05, and 0.91±0.02, for SIDO, single, and dual-Isocenter VMAT respectively. GI was 6.83±1.0, 7.45±1.0 and 5.94±0.7 respectively. SIDO conformity did not trend with increasing distance between PTVs, while gradient decreased for all planning techniques. Using DCAs as the starting point of VMAT optimization decreased modulation, with a 39.4% reduction in monitor units. SIDO had 4.9% and 39% less MU than single and dual-Isocenter VMAT respectively. A translational shift between SIDO arcs would be required in 10–28% of cases due to rotational uncertainties to stay within a 5mm margin, for targets separated by ≥10cm. Conclusion: SIDO for extracranial oligometastases has comparable dosimetry to traditional VMAT with low modulation similar to DCAs. Future work will quantify decrease in dosimetric interplay.
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physics considerations for single Isocenter volumetric modulated arc radiosurgery for treatment of multiple intracranial targets
Practical radiation oncology, 2016Co-Authors: Carl Stanhope, F Yin, Joseph K Salama, John P Kirkpatrick, Z Wang, Z Chang, Grace Kim, Justus AdamsonAbstract:Abstract Objective Our purpose was to address challenges associated with single-Isocenter radiosurgery for multiple intracranial targets (SIRMIT) including increased sensitivity to rotational uncertainties (resulting from distance of the targets from Isocenter) as well as potential for decreased plan quality from larger multileaf collimator width >4 cm from Isocenter. Methods and materials We evaluated the effect that a 6 degrees-of-freedom couch correction had on localization uncertainty for SIRMIT using thermoplastic mask immobilization. Required setup margin was determined from rotation of the skull and mask (setup kV cone beam computed tomography relative to planning computed tomography). Intraoperational margin was determined from skull rotation within the mask (difference between pre- and posttreatment cone beam computed tomography). We also investigated 4 Isocenter placement strategies: volume centroid, centroid of equally weighted points (1 per target), centroid of points weighted by inverse of volume, and Eclipse's built-in method. Results When no 6 degrees-of-freedom couch correction is performed after initial setup, a 0.35-mm margin is required per centimeter of target-Isocenter separation to account for 95% of rotational uncertainties at initial setup. This margin is reduced to 0.10 mm/cm of target-Isocenter separation to account for intraoperative rotational uncertainties when the initial setup uncertainty is eliminated via image guided 6 degrees-of-freedom couch correction. Analysis of 11 multitarget plans (37 targets) showed that conformity index and gradient index improved with decreasing distance from Isocenter, this trend being more pronounced for targets Conclusions Rotational corrections via image guidance are necessary for SIRMIT with a thermoplastic mask for immobilization. There is a clear tradeoff between dosimetric quality of small and large targets that should be considered carefully when placing the Isocenter.
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su e t 613 physics considerations for single Isocenter volumetric modulated arc radiosurgery for treatment of multiple intracranial targets
Medical Physics, 2015Co-Authors: Carl Stanhope, F Yin, Joseph K Salama, John P Kirkpatrick, Z Wang, Z Chang, Grace Kim, Justus AdamsonAbstract:Purpose: To address physics challenges associated with single Isocenter radiosurgery for multiple intracranial metastases (SIRMIT). Because the Varian High Definition MLC has thicker leaves >4cm from the Isocenter, we predict inferior dose falloff and plan quality for small targets located >4cm from Isocenter. To address this concern, we evaluate various Isocenter placement strategies including one that places the Isocenter closer to smaller targets. We also evaluate the significance of arc geometry avoidance angles to limit lens dose. Methods: 11 SIRMIT plans with Isocenter at centroid were retrospectively analyzed to determine the relationship between relevant dosimetric indices and distance from Isocenter (e.g. relative tumor volume). We investigated three Isocenter placements for four SIRMIT patients whose lesions had larger variations in target volume; placements included: centroid, Eclipse’s built-in method, and an “inverse center of mass” (ICM) method that weights the Isocenter towards smaller lesions. Three VMAT SIRMIT plans were prepared according to institutional and Clark et al.’s guidelines to investigate the effect of arc geometry on lens dose. Results: Dose conformity and gradient fall-off tended to be better for larger tumors (>1cc) close to Isocenter. For the four largest tumors (per plan), centroid CI, GI, and HI values were 9±9%, 12±4%, and 3.8±4.9% better than the next best Isocenter placement strategy. None of the methods yielded significantly higher conformity for small tumors, however ICM GI and HI values were better for three of the small tumors by 6±12% and 1.8±2.2% respectively. Lens dose range decreased from [3.3%, 11.4%] to [0.1%, 0.5%] by avoiding arc geometries that enter/exit through the eyes. Conclusion: CI and GI values were poorer for small distal targets, especially >6cm. Large tumors benefited from centroid placement more than small tumors did from ICM. It is necessary to consider arc geometry avoidance angles to adequately reduce lens dose.
Z Wang - One of the best experts on this subject based on the ideXlab platform.
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physics considerations for single Isocenter volumetric modulated arc radiosurgery for treatment of multiple intracranial targets
Practical radiation oncology, 2016Co-Authors: Carl Stanhope, F Yin, Joseph K Salama, John P Kirkpatrick, Z Wang, Z Chang, Grace Kim, Justus AdamsonAbstract:Abstract Objective Our purpose was to address challenges associated with single-Isocenter radiosurgery for multiple intracranial targets (SIRMIT) including increased sensitivity to rotational uncertainties (resulting from distance of the targets from Isocenter) as well as potential for decreased plan quality from larger multileaf collimator width >4 cm from Isocenter. Methods and materials We evaluated the effect that a 6 degrees-of-freedom couch correction had on localization uncertainty for SIRMIT using thermoplastic mask immobilization. Required setup margin was determined from rotation of the skull and mask (setup kV cone beam computed tomography relative to planning computed tomography). Intraoperational margin was determined from skull rotation within the mask (difference between pre- and posttreatment cone beam computed tomography). We also investigated 4 Isocenter placement strategies: volume centroid, centroid of equally weighted points (1 per target), centroid of points weighted by inverse of volume, and Eclipse's built-in method. Results When no 6 degrees-of-freedom couch correction is performed after initial setup, a 0.35-mm margin is required per centimeter of target-Isocenter separation to account for 95% of rotational uncertainties at initial setup. This margin is reduced to 0.10 mm/cm of target-Isocenter separation to account for intraoperative rotational uncertainties when the initial setup uncertainty is eliminated via image guided 6 degrees-of-freedom couch correction. Analysis of 11 multitarget plans (37 targets) showed that conformity index and gradient index improved with decreasing distance from Isocenter, this trend being more pronounced for targets Conclusions Rotational corrections via image guidance are necessary for SIRMIT with a thermoplastic mask for immobilization. There is a clear tradeoff between dosimetric quality of small and large targets that should be considered carefully when placing the Isocenter.
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su e t 613 physics considerations for single Isocenter volumetric modulated arc radiosurgery for treatment of multiple intracranial targets
Medical Physics, 2015Co-Authors: Carl Stanhope, F Yin, Joseph K Salama, John P Kirkpatrick, Z Wang, Z Chang, Grace Kim, Justus AdamsonAbstract:Purpose: To address physics challenges associated with single Isocenter radiosurgery for multiple intracranial metastases (SIRMIT). Because the Varian High Definition MLC has thicker leaves >4cm from the Isocenter, we predict inferior dose falloff and plan quality for small targets located >4cm from Isocenter. To address this concern, we evaluate various Isocenter placement strategies including one that places the Isocenter closer to smaller targets. We also evaluate the significance of arc geometry avoidance angles to limit lens dose. Methods: 11 SIRMIT plans with Isocenter at centroid were retrospectively analyzed to determine the relationship between relevant dosimetric indices and distance from Isocenter (e.g. relative tumor volume). We investigated three Isocenter placements for four SIRMIT patients whose lesions had larger variations in target volume; placements included: centroid, Eclipse’s built-in method, and an “inverse center of mass” (ICM) method that weights the Isocenter towards smaller lesions. Three VMAT SIRMIT plans were prepared according to institutional and Clark et al.’s guidelines to investigate the effect of arc geometry on lens dose. Results: Dose conformity and gradient fall-off tended to be better for larger tumors (>1cc) close to Isocenter. For the four largest tumors (per plan), centroid CI, GI, and HI values were 9±9%, 12±4%, and 3.8±4.9% better than the next best Isocenter placement strategy. None of the methods yielded significantly higher conformity for small tumors, however ICM GI and HI values were better for three of the small tumors by 6±12% and 1.8±2.2% respectively. Lens dose range decreased from [3.3%, 11.4%] to [0.1%, 0.5%] by avoiding arc geometries that enter/exit through the eyes. Conclusion: CI and GI values were poorer for small distal targets, especially >6cm. Large tumors benefited from centroid placement more than small tumors did from ICM. It is necessary to consider arc geometry avoidance angles to adequately reduce lens dose.
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su e t 645 treatment of multiple brain metastases using stereotactic radiosurgery with single Isocenter volumetric modulated arc therapy comparison with conventional dynamic conformal arc and static beam stereotactic radiosurgery
Medical Physics, 2012Co-Authors: C Huang, John P Kirkpatrick, L Ren, Z WangAbstract:Purpose: To investigate the treatment of multiple brain metastases using stereotactic radiosurgery with single‐Isocenter volumetric modulated arc therapy (VMAT) compared with conventional multi‐Isocenter dynamic conformal arc therapy (DCAT) and three‐dimensional conformal radiation therapy (3D‐CRT). Methods: Seventeen patients with 2 to 5 brain metastatic lesions were studied. The number of patients with 5, 4, 3, and 2 lesions were 4, 5, 4, and 4, respectively. For patients treated with DCAT/3D‐CRT plans, VMAT plans were retrospectively generated, and vice versa. Single‐Isocenter set up was employed in VMAT plans while the number of Isocenters was proportional to the number of lesions in DCAT/3D‐CRT plans. The DCAT/3D‐CRT and VMAT plans were generated using iPlan® RT Dose Version 4.1.1 (BrainLAB, Germany) and Eclipse™ Version 8.6 (Varian, USA) treatment planning system, respectively. All plans were designed to be delivered on Novalis Tx™ system (Varian, USA and BrainLAB, Germany), in which the accelerator equipped with a high definition multileaf collimator (HDMLC). Results: Conformity index for VMAT plans were equivalent to or better than that for DCAT/3D‐CRT plans. While VMAT and DCAT/3D‐CRT plans were similar in target coverage, quality of coverage for VMAT plans was better. However, the volume receiving 5Gy was 46% larger for VMAT plans. In addition, the distance from individual lesion to the VMAT Isocenter has no impact on VMAT plans. Compared with DCAT/3D‐CRT plans, the mean monitor units (MU) decreased by 42% and the estimated treatment time decreased by 49% for VMAT plans. Conclusions: This work suggests that single‐Isocenter VMAT is promising for stereotactic radiosurgery in the treatment of multiple brain metastases. Single‐Isocenter VMAT is able to achieve comparable conformity, target coverage and quality of coverage with significantly superior delivery efficiency.
