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Population-Based Metaheuristic Approximation For Dosimetric Optimization in CyberKnife Radiation Therapy Treatment Planning
Proceedings of the 53rd Annual ASTRO Meeting with IMRT using rectal catheter technique, five to nine additional series of CT were performed just before treatment to verify the isocenter and investigate the rectal volume reproducibility during the course of IMRT. All CT was scanned with a slice-thickness of 3.0mm. The rectal volumes and rectal gas-volumes were measured using CT images of isocenter plane ± 6 slices on 3D radiation treatment planning computer. The rectal volumes and gas-volumes were compared between the patients with and without rectal catheter. And also, the inter-fractional variability of rectal volume and gas-volume was evaluated in the 15 patients treated with rectal catheter technique. Results: The rectal gas-volumes of the patients with rectal catheter technique (1.9+ 2.1cc) were significantly reduced in comparison to those of the patients without rectal catheter (9.5 ± 11.4cc). However, there was no significant difference in the rectal volumes between the two groups. The mean and standard deviation (SD) of rectal gas-volume in each patient with catheter technique ranged from 0.06 to 9.49cc (median: 1.42cc) and from 0.08 to 13.09cc (median: 1.70cc), respectively. The mean and SD of rectal volume ranged from 22.74 to 74.42cc (median: 38.68cc) and from 1.87 to 15.38cc (median:5.17 cc), respectively. Conclusions: Rectal catheter technique is feasible with good reproducibility of rectal volume and gas-volume in IMRT for prostate cancer. Author Disclosure: S. Ohga: None. Y. Shioyama: None. T. Nonoshita: None. T. Yoshitake: None. K. Asai: None. K. Matsumoto: None. H. Honda: None.
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Population-Based Metaheuristic Approximation For Dosimetric Optimization in CyberKnife Radiation Therapy Treatment Planning
M. R. Witten, O. C. Clancey Witten Clancey Partners, LLC, Great Neck, NY Purpose/Objective(s): To evaluate the performance of a mimetic algorithm for dosimetric optimization in CyberKnife treatment planning, and to compare it with that of a commercially-available sequential simplex algorithm. Materials/Methods: Dosimetric optimization in radiation therapy treatment planning has historically been accomplished via trajectory algorithms; such algorithms involve the refinement of a single candidate solution iteratively, selecting a direction and step size to search the solution space in a well-defined manner. By contrast, population-based metaheuristic approximation involves the simultaneous refinement of a large set of candidate solutions, without any specific path through the space. In this study, a mimetic algorithm which optimized a quadratic fitness function was used to generate treatment plans for CyberKnife (Accuray, Inc., Sunnyvale, CA) robotic IMRT, administered in 38 fractions of 2 Gy each. Dose-volume histogram (DVH) objectives were as follows: PTV V76Gy . 95%, rectum V65Gy \ 17%, rectum V40Gy \ 35%, bladder V65Gy \ 25%, bladder V40Gy \ 50%. The memetic optimization ran in the MATLAB (The Mathworks, Natick, MA) environment version 7.8, while sequential simplex treatment plans were generated with MultiPlan (Accuray, Inc., Sunnyvale, CA) version 4.0. Five distinct anonymized CT data sets for patients with prostate cancer were used to generate ten treatment plans, one optimized with the memetic algorithm, and one with the sequential simplex algorithm. Results: The memetic algorithm produced treatment plans satisfying the DVH objectives with a uniform success rate of 100%. The success rate of the satisfaction of the DVH objectives for the plans generated with the sequential simplex optimization ranged from 0% (for rectum V40Gy \ 35%) to 100% (for bladder V65 Gy \ 25%). For the memetic plans, the mean total monitor units (MU) was 65,846 (range: 44753 - 75002) and the mean number of beams was 90.8 (range: 55 - 113), while for the sequential simplex plans those means were 78,937 (range: 76872 - 80848) and 115.4 (range: 95 - 135), respectively. The total MU was significantly (p = 0.0039) lower for the memetic algorithm. Conclusions: The memetic algorithm is a population-based metaheuristic approximation method which provides an alternative to traditional trajectory optimization algorithms, particularly in problems of high dimensionality, such as treatment planning for the complex delivery methods of contemporary radiotherapy. It has demonstrated superior performance to that of sequential simplex optimization in the context of CyberKnife treatment planning, when the plan metrics are satisfaction of DVH objectives, MU, and total number of beams. Further study is indicated. Author Disclosure: M.R. Witten: None. O.C. Clancey: None.
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Stereotactic Body Radiation Therapy (SBRT) Using Respiratory-Gated Volumetric Modulated Arc Therapy (VMAT) With Flattening Filter Free (FFF) Beams
J. Qian, G. Luxton, E. Mok, L. Wang, P. Maxim, K. Kielar, T. Atwood, L. Xing Stanford University School of Medicine, Stanford, CA Purpose/Objective(s): Respiratory-gated VMAT with high dose-rate (2400 MU/min) FFF beams is now available in Varian TrueBeam linac, providing an unprecedented means for efficient SBRT of moving tumors in thorax or upper abdomen. This work addresses two important and timely questions in the clinical implementation of this modality: (1) Can SBRT plans with such extremely high dose rate be faithfully realized by delivery system in the complex modulated rotational arc mode and with frequent interruptions of a broad range of gating signals? (2) Can non-flat FFF beams produce dose distributions comparable to VMAT plans using beams with flattening-filter (WFF)? Materials/Methods: A TrueBeam system was used for this study. Fifteen lung patients previously treated with SBRT using ungated 6MV WFF VMAT were selected. For each case, two gated SBRT VMAT plans with high dose-rate FFF beams (1400 MU/ min for 6 MVand 2400 MU/min for 10 MV) were created using the same constraints and isocenter as the original treatment plan in Varian Eclipse TPS. Each FFF plan was then delivered four times under different clinic-relevant respiratory conditions: without gating, and with gating (25%-70% phase cycle) for three different respiratory periods (3, 4.5 and 6 seconds). A previously-developed dose reconstruction technique was adapted to evaluate the fidelity of gated dose delivery of VMAT FFF plans by TrueBeam, supplemented by two other independent methods using a ScandiDos Delta4 device and PTW Seven29 ion chamber array (27x27). A variety of dosimetric metrics including homogeneity (HI), conformity (CI) and gamma indices, dose endpoints and DVH were used to assess treatment plans and deliveries.
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Population-Based Metaheuristic Approximation For Dosimetric Optimization in CyberKnife Radiation Therapy Treatment Planning
M. R. Witten, O. C. Clancey Witten Clancey Partners, LLC, Great Neck, NY Purpose/Objective(s): To evaluate the performance of a mimetic algorithm for dosimetric optimization in CyberKnife treatment planning, and to compare it with that of a commercially-available sequential simplex algorithm. Materials/Methods: Dosimetric optimization in radiation therapy treatment planning has historically been accomplished via trajectory algorithms; such algorithms involve the refinement of a single candidate solution iteratively, selecting a direction and step size to search the solution space in a well-defined manner. By contrast, population-based metaheuristic approximation involves the simultaneous refinement of a large set of candidate solutions, without any specific path through the space. In this study, a mimetic algorithm which optimized a quadratic fitness function was used to generate treatment plans for CyberKnife (Accuray, Inc., Sunnyvale, CA) robotic IMRT, administered in 38 fractions of 2 Gy each. Dose-volume histogram (DVH) objectives were as follows: PTV V76Gy . 95%, rectum V65Gy \ 17%, rectum V40Gy \ 35%, bladder V65Gy \ 25%, bladder V40Gy \ 50%. The memetic optimization ran in the MATLAB (The Mathworks, Natick, MA) environment version 7.8, while sequential simplex treatment plans were generated with MultiPlan (Accuray, Inc., Sunnyvale, CA) version 4.0. Five distinct anonymized CT data sets for patients with prostate cancer were used to generate ten treatment plans, one optimized with the memetic algorithm, and one with the sequential simplex algorithm. Results: The memetic algorithm produced treatment plans satisfying the DVH objectives with a uniform success rate of 100%. The success rate of the satisfaction of the DVH objectives for the plans generated with the sequential simplex optimization ranged from 0% (for rectum V40Gy \ 35%) to 100% (for bladder V65 Gy \ 25%). For the memetic plans, the mean total monitor units (MU) was 65,846 (range: 44753 - 75002) and the mean number of beams was 90.8 (range: 55 - 113), while for the sequential simplex plans those means were 78,937 (range: 76872 - 80848) and 115.4 (range: 95 - 135), respectively. The total MU was significantly (p = 0.0039) lower for the memetic algorithm. Conclusions: The memetic algorithm is a population-based metaheuristic approximation method which provides an alternative to traditional trajectory optimization algorithms, particularly in problems of high dimensionality, such as treatment planning for the complex delivery methods of contemporary radiotherapy. It has demonstrated superior performance to that of sequential simplex optimization in the context of CyberKnife treatment planning, when the plan metrics are satisfaction of DVH objectives, MU, and total number of beams. Further study is indicated. Author Disclosure: M.R. Witten: None. O.C. Clancey: None.
3343
Stereotactic Body Radiation Therapy (SBRT) Using Respiratory-Gated Volumetric Modulated Arc Therapy (VMAT) With Flattening Filter Free (FFF) Beams
J. Qian, G. Luxton, E. Mok, L. Wang, P. Maxim, K. Kielar, T. Atwood, L. Xing Stanford University School of Medicine, Stanford, CA Purpose/Objective(s): Respiratory-gated VMAT with high dose-rate (2400 MU/min) FFF beams is now available in Varian TrueBeam linac, providing an unprecedented means for efficient SBRT of moving tumors in thorax or upper abdomen. This work addresses two important and timely questions in the clinical implementation of this modality: (1) Can SBRT plans with such extremely high dose rate be faithfully realized by delivery system in the complex modulated rotational arc mode and with frequent interruptions of a broad range of gating signals? (2) Can non-flat FFF beams produce dose distributions comparable to VMAT plans using beams with flattening-filter (WFF)? Materials/Methods: A TrueBeam system was used for this study. Fifteen lung patients previously treated with SBRT using ungated 6MV WFF VMAT were selected. For each case, two gated SBRT VMAT plans with high dose-rate FFF beams (1400 MU/ min for 6 MVand 2400 MU/min for 10 MV) were created using the same constraints and isocenter as the original treatment plan in Varian Eclipse TPS. Each FFF plan was then delivered four times under different clinic-relevant respiratory conditions: without gating, and with gating (25%-70% phase cycle) for three different respiratory periods (3, 4.5 and 6 seconds). A previously-developed dose reconstruction technique was adapted to evaluate the fidelity of gated dose delivery of VMAT FFF plans by TrueBeam, supplemented by two other independent methods using a ScandiDos Delta4 device and PTW Seven29 ion chamber array (27x27). A variety of dosimetric metrics including homogeneity (HI), conformity (CI) and gamma indices, dose endpoints and DVH were used to assess treatment plans and deliveries.
S851