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Total Marrow Irradiation: A Clinical Evaluation of a Volumetric Modulated Arc Therapy Technique
Proceedings of the 52nd Annual ASTRO Meeting residual error magnitude in the CTV centroid position after a GTV-based localization was 2.9 mm +/- 3.0 mm, and varied from 0.8 mm to 14.3 mm over all patients. Residual error of the CTV centroid was associated with GTV regression during treatment (p = 0.02, Spearman rank correlation). 46% of patients had mean residual error in the centroid over 2 mm. 77% of patients and 50% of fractions had residual error in CTV border position greater than 2 mm. of these fractions, residual error of the CTV borders was 3.5 +/- 1.6 mm (LR), 3.1 +/- 0.9 mm (AP), and 6.4 +/- 7.5 mm (SI). Conclusions: Online guidance based on the visible GTV produces substantial error in CTV localization, particularly for highlyregressing tumors. The results of this study will be useful in designing margins for CTV localization or for developing new online localization strategies for the CTV. Supported by NIH R01CA116249. Author Disclosure: G.D. Hugo, None; E. Weiss, None; A. Badawi, None; M. Orton, None.
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Atlas-based Dose Optimization via Linear Programming for IMRT using a High-throughput Computing Environment
H. H. Zhang1, R. R. Meyer2, S. A. Naqvi1, L. Shi2, W. D. D’Souza1 1
University of Maryland School of Medicine, Baltimore, MD, 2University of Wisconsin, Madison, WI
Purpose/Objective(s): To develop and evaluate an atlas-based dose optimization (DO) scheme using linear programming (LP) for disease site specific IMRT treatment planning using a high-throughput computing environment (HTC). Materials/Methods: Ten locally advanced head and neck cases were retrospectively selected for this study. The treatment targets involved primary tumor, high risk and low risk nodal volumes. Organs-at-risk (OARs) included both parotids and the spinal cord. Seven-beam IMRT plans were generated using the Pinnacle3 planning system. More than 2000 apertures from these 10 cases were extracted (on average 30 apertures per beam per case). These apertures served as the basis for the atlas from which prospective casespecific apertures were derived. Aperture-based 3D dose distributions were calculated in parallel using Monte Carlo-based Kernel Superposition (MCKS) and facilitated using Condor in the HTC environment consisting of 48 2.26GHz CPUs. Condor provided the job queuing mechanism, priority scheme, resource monitoring, and resource management. Aperture weights of each case were optimized via an in-house developed sequential linear program (SLP) DO approach. The SLP approach involved solving the DO problem by dividing the problem into sub-problems (due to the size of the DO problem), each of which was solved using LP while maintaining a global view of the full problem. Our approach was compared with three approaches: conventional IMRT, two-arc intensity-modulated arc therapy (IMAT) (generated using Pinnacle SmartArc 9.0) and SLP corresponding to apertures derived from the conventional IMRT plans for the specific case. Results: Approximately 200 apertures per case were returned with non-zero weight assignments via the atlas-based SLP scheme and 40% of the selected atlas apertures were from other cases. Superior plan quality was achieved with atlas-based plans. On average, at dose constraint levels parotid gland sparing improved 30% (±7%), 31% (±9%) and 18% (±5%), respectively using the atlas-based DO scheme compared with conventional IMRT, two-arc IMAT and the SLP scheme using apertures derived from the conventional IMRT plans. The improvement in the maximum dose to the spinal cord was 10% (±4%), 20% (±6%) and 6% (±2%), respectively when compared with the other three approaches. t-test results showed that these improvements were significant (p \ 0.001). Dose homogeneity for all PTVs (tumor and nodes) was higher for the atlas-based plans compared with the other approaches. The atlas-based approach also resulted in lower integral dose to non-PTV and non-OAR tissues. Conclusions: Our results suggest that atlas-based DO using the SLP approach results in superior plan quality compared with conventional IMRT and IMAT. Author Disclosure: H.H. Zhang, None; R.R. Meyer, NIH CA130814, B. Research Grant; S.A. Naqvi, None; L. Shi, NIH CA130814, B. Research Grant; W.D. D’Souza, NIH CA130814, B. Research Grant.
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Total Marrow Irradiation: A Clinical Evaluation of a Volumetric Modulated Arc Therapy Technique 1
L. Cozzi , P. Mancosu2, P. Navarria2, G. Nicolini1, E. Vanetti1, A. Clivio1, A. Fogliata1, A. Ibatici2, A. Santoro2, M. Scorsetti2 1
Oncology Institute Southern Switzerland, Bellinzona, Switzerland, 2Istituto Clinico Humanitas, Milan, Italy
Purpose/Objective(s): To test, at a pre-clinical level, the feasibility of performing total marrow irradiation employing volumetric modulated arc therapy (VMAT) with the RapidArc (RA) technology. Materials/Methods: An analysis of plans for five patients realized with a pre-clinical version of the RapidArc engine (PROIII) was carried out. 10 arcs were simultaneously optimized, eight of these were set up with 90 collimator angle; in order to cover the bones in the patient’s body, the eight isocenters were placed along the cranio-caudal axis of the patients; the arms were covered with two more arcs whose isocenters were not placed on the patient’s axis. 12 Gy in 2 Gy/fraction were prescribed on the PTV and the plan was normalized so as to have V100%.85%. All body bones from the cranium to mid of the femurs were considered as Planning Target Volume (PTV), the maximum length achieved in this study was 130 cm. For all organs at risk (including brain, optical structures, oral and neck structures, lungs, heart, liver, kidneys, spleen, bowels, bladder, rectum, genitals) planning strategy aimed to maximize sparing according to ALARA principles. Results: Median doses were calculated for the various anatomical regions obtaining values that ranged from 4 to 7 Gy for abdominal and pelvic structures, from 6 to 7 Gy for lungs and from 2 to 5 Gy for brain, optical, oral and neck structures. The plans were tested on a Clinac 2100, an automatic isocentre shift was set and a dosimetric control was carried out obtaining a gamma pass rate .98% for all arcs (with 3% and 3mm thresholds). Comparing with literature data from similar treatments (e.g., Wong et al. IJROBP 2009;73:273-279), VMAT with RA seems to be appropriate to provide linac based total marrow irradiation. Conclusions: A total marrow irradiation performed with RapidArc technique shows a good reliability and accuracy, though in a pre-clinical phase. A clinical protocol is being studied in order to treat 15 patients in the next year, clinical results will be reported. Author Disclosure: L. Cozzi, Varian Medical Systems, F. Consultant/Advisory Board; P. Mancosu, None; P. Navarria, None; G. Nicolini, None; E. Vanetti, None; A. Clivio, None; A. Fogliata, None; A. Ibatici, None; A. Santoro, None; M. Scorsetti, None.
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199
Atlas-based Dose Optimization via Linear Programming for IMRT using a High-throughput Computing Environment
H. H. Zhang1, R. R. Meyer2, S. A. Naqvi1, L. Shi2, W. D. D’Souza1 1
University of Maryland School of Medicine, Baltimore, MD, 2University of Wisconsin, Madison, WI
Purpose/Objective(s): To develop and evaluate an atlas-based dose optimization (DO) scheme using linear programming (LP) for disease site specific IMRT treatment planning using a high-throughput computing environment (HTC). Materials/Methods: Ten locally advanced head and neck cases were retrospectively selected for this study. The treatment targets involved primary tumor, high risk and low risk nodal volumes. Organs-at-risk (OARs) included both parotids and the spinal cord. Seven-beam IMRT plans were generated using the Pinnacle3 planning system. More than 2000 apertures from these 10 cases were extracted (on average 30 apertures per beam per case). These apertures served as the basis for the atlas from which prospective casespecific apertures were derived. Aperture-based 3D dose distributions were calculated in parallel using Monte Carlo-based Kernel Superposition (MCKS) and facilitated using Condor in the HTC environment consisting of 48 2.26GHz CPUs. Condor provided the job queuing mechanism, priority scheme, resource monitoring, and resource management. Aperture weights of each case were optimized via an in-house developed sequential linear program (SLP) DO approach. The SLP approach involved solving the DO problem by dividing the problem into sub-problems (due to the size of the DO problem), each of which was solved using LP while maintaining a global view of the full problem. Our approach was compared with three approaches: conventional IMRT, two-arc intensity-modulated arc therapy (IMAT) (generated using Pinnacle SmartArc 9.0) and SLP corresponding to apertures derived from the conventional IMRT plans for the specific case. Results: Approximately 200 apertures per case were returned with non-zero weight assignments via the atlas-based SLP scheme and 40% of the selected atlas apertures were from other cases. Superior plan quality was achieved with atlas-based plans. On average, at dose constraint levels parotid gland sparing improved 30% (±7%), 31% (±9%) and 18% (±5%), respectively using the atlas-based DO scheme compared with conventional IMRT, two-arc IMAT and the SLP scheme using apertures derived from the conventional IMRT plans. The improvement in the maximum dose to the spinal cord was 10% (±4%), 20% (±6%) and 6% (±2%), respectively when compared with the other three approaches. t-test results showed that these improvements were significant (p \ 0.001). Dose homogeneity for all PTVs (tumor and nodes) was higher for the atlas-based plans compared with the other approaches. The atlas-based approach also resulted in lower integral dose to non-PTV and non-OAR tissues. Conclusions: Our results suggest that atlas-based DO using the SLP approach results in superior plan quality compared with conventional IMRT and IMAT. Author Disclosure: H.H. Zhang, None; R.R. Meyer, NIH CA130814, B. Research Grant; S.A. Naqvi, None; L. Shi, NIH CA130814, B. Research Grant; W.D. D’Souza, NIH CA130814, B. Research Grant.
200
Total Marrow Irradiation: A Clinical Evaluation of a Volumetric Modulated Arc Therapy Technique 1
L. Cozzi , P. Mancosu2, P. Navarria2, G. Nicolini1, E. Vanetti1, A. Clivio1, A. Fogliata1, A. Ibatici2, A. Santoro2, M. Scorsetti2 1
Oncology Institute Southern Switzerland, Bellinzona, Switzerland, 2Istituto Clinico Humanitas, Milan, Italy
Purpose/Objective(s): To test, at a pre-clinical level, the feasibility of performing total marrow irradiation employing volumetric modulated arc therapy (VMAT) with the RapidArc (RA) technology. Materials/Methods: An analysis of plans for five patients realized with a pre-clinical version of the RapidArc engine (PROIII) was carried out. 10 arcs were simultaneously optimized, eight of these were set up with 90 collimator angle; in order to cover the bones in the patient’s body, the eight isocenters were placed along the cranio-caudal axis of the patients; the arms were covered with two more arcs whose isocenters were not placed on the patient’s axis. 12 Gy in 2 Gy/fraction were prescribed on the PTV and the plan was normalized so as to have V100%.85%. All body bones from the cranium to mid of the femurs were considered as Planning Target Volume (PTV), the maximum length achieved in this study was 130 cm. For all organs at risk (including brain, optical structures, oral and neck structures, lungs, heart, liver, kidneys, spleen, bowels, bladder, rectum, genitals) planning strategy aimed to maximize sparing according to ALARA principles. Results: Median doses were calculated for the various anatomical regions obtaining values that ranged from 4 to 7 Gy for abdominal and pelvic structures, from 6 to 7 Gy for lungs and from 2 to 5 Gy for brain, optical, oral and neck structures. The plans were tested on a Clinac 2100, an automatic isocentre shift was set and a dosimetric control was carried out obtaining a gamma pass rate .98% for all arcs (with 3% and 3mm thresholds). Comparing with literature data from similar treatments (e.g., Wong et al. IJROBP 2009;73:273-279), VMAT with RA seems to be appropriate to provide linac based total marrow irradiation. Conclusions: A total marrow irradiation performed with RapidArc technique shows a good reliability and accuracy, though in a pre-clinical phase. A clinical protocol is being studied in order to treat 15 patients in the next year, clinical results will be reported. Author Disclosure: L. Cozzi, Varian Medical Systems, F. Consultant/Advisory Board; P. Mancosu, None; P. Navarria, None; G. Nicolini, None; E. Vanetti, None; A. Clivio, None; A. Fogliata, None; A. Ibatici, None; A. Santoro, None; M. Scorsetti, None.
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