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Endorectal Balloon in Stereotactic Body Radiation Therapy (SBRT) for Early-Stage Prostate Cancer: A Planning and Dosimetry Analysis
S832
International Journal of Radiation Oncology Biology Physics
dose, 0.30 0.003% for dose to 1 cc of spinal cord volume, 0.29 0.001% for dose to 0.5 cc of spinal cord, and 0.73 0.006% for dose to 0.1 cc of spinal cord. Conclusions: SBRT using helical tomotherapy can be a safe treatment modality for spine metastasis in the aspect of accurate targeting. Author Disclosure: Y. Chung: None. M. Kim: None. J. Kim: None. W. Koom: None.
Purpose/Objective(s): Recently, powerful on-board imaging technologies have propelled SRS into the frameless era. Yet, all the mainstream onboard imaging systems resort to ionizing X-rays as imaging sources. Moreover, most SRS procedures are planned with IMRT, a modality that suffers from an elevated MU, a reduced MU-to-cGy coefficient, and a prolonged treatment time. To tackle these issues, we commissioned a novel frameless stereotactic system for intracranial SRS immobilization, a 3D optical surface imaging system for target localization and real-time patient monitoring, and a homegrown VMAT system for SRS planning. Here, we present our initial results of a feasibility study. Materials/Methods: The frameless stereotactic system includes carbon fiber base boards, a cranial stereotactic localizer frame, a support bridge, patient-specific mouthpiece assemblies, and a portable vacuum pump. The portable vacuum pump applies a negative pressure to the patient mouthpiece. The resulting vacuum suction seals the mouthpiece precisely into the palate of the mouth. VMAT-SRS plans were computed with a single 360 arc containing 180 equally-spaced beams, optimized incrementally using a differentiated optimization scheme. The target localization was accomplished with a video-based 3D optical surface imaging system, consisting of three 3D camera units and fast 3D image registration software. After the patient had been initially setup, the 3D optical surface imaging system acquired a verification skin surface of the patient. This verification image was registered to a reference skin surface created from the planning 3DCT in a user-defined region of interest. The registration software calculated three translational shifts (DVRT, DLNG, and DLAT), and three rotational shifts (DPITCH, DROLL, and DYAW) for patient repositioning. Results: The frameless system was found to be able to secure a sustained immobilization accuracy of w 1.0 mm and 1.0 for intracranial SRS as measured by CBCT and 3D real-time optical surface imaging. With this system, the patient could be simulated, planned, and treated on different days. VMAT-SRS plan optimization converged in 10 minutes for a PTV of w 35 cm3 and 6 other critical structures. VMAT-SRS plans exhibited superior dose distribution to IMRT-SRS plans as measured by conformality and homogeneity indices. The target dose inhomogeneity was less than 17% compared to about 30% for conventional SRS plans. The doses to the critical structures for VMAT-SRS plans were less than or comparable to those for conventional SRS plans. With this new approach, the treatment time was reduced by more than one hour. Conclusion: Our initial data revealed that the synergistic combination of the frameless system, VMAT-SRS, and the 3D real-time optical surface imaging could be an optimal intracranial SRS sub-modality. Author Disclosure: Y. Song: None. C. Obcemea: None. C. Burman: None. Q. Zhang: None.
3631 Endorectal Balloon in Stereotactic Body Radiation Therapy (SBRT) for Early-Stage Prostate Cancer: A Planning and Dosimetry Analysis H.F. Xiang,1,2 H. Lu,1 A.E. Hirsch,1,2 J.A. Efstathiou,1 A.L. Zietman,1 K. Harris,3 N. Bloch,2 S. Keohan,2 J. Willins,1,2 and L.A. Kachnic1,2; 1 Massachusetts General Hospital and Harvard Medical School, Boston, MA, 2Boston Medical Center and Boston University School of Medicine, Boston, MA, 3Massachusetts Institute of Technology, Cambridge, MA Purpose/Objective(s): The use of an endorectal balloon (ERB) has been reported to significantly reduce intra-fractional prostate motion during standard fractionated intensity-modulated radiation therapy (IMRT) for prostate cancer. Recently, hypofractionated IMRT and SBRT strategies are under investigation; however, to date, there have been no dosimetric analyses on the use of ERB with these approaches. This study investigates the dose-volume characteristics for the rectum when using ERB as part of SBRT planning for early-stage prostate cancer. Materials/Methods: Twelve patients with prostate cancer who had received conventional IMRT at our institutions were included in this study. Six patients (Group-ERB) had been planned and treated with ERB containing 60-100 cc of water, and the other six (Group-noERB) without ERB. For each case, an optimized SBRT plan was generated by using sequential optimization in TPS according to the 5 fraction (5 x 7.25 Gy) dosespecification and dose-volume constraints of the RTOG 0938 randomized phase II study of hypofractionated RT for early-stage prostate cancer. Dosimetric characteristics for the rectum were compared between the two groups, including maximum dose, mean dose for the entire rectum and the anterior half of the rectum, and the percentages of rectal volume and anterior-half rectal volume receiving 50%, 80%, 90% and 100% of the prescription dose (36.25 Gy). Results: While the maximum dose to the rectum was comparable between the two groups (range 37.8-39.9 Gy), the mean dose to the entire rectum was lower for Group-ERB (10.3 Gy, range 8.2-13.5 Gy) than GroupnoERB (12.9 Gy, range 11.4-15.1 Gy). The mean dose to the anterior half of the rectum was also lower for Group-ERB (15.0 Gy, range 13.0-19.5 Gy) than Group-noERB (16.2 Gy, range 12.2-19.1 Gy). A consistent dosimetric advantage was also noted in the rectal volume receiving 50%, 80%, 90% and 100% of the prescription dose for Group-ERB compared to Group-noERB. The mean V50%, V80%, V90% and V100% of the entire rectum for Group-ERB was 16.7%, 6.3%, 3.5% and 0.9%, in comparison to 26.3%, 10.9%, 6.3% and 1.4% for Group-noERB. Similarly, the mean V50%, V80%, V90% and V100% of the anterior half of the rectum for GroupERB was 31.6%, 11.8%, 6.6% and 1.6%, in comparison to 39.7%, 18.4%, 10.6% and 2.6% for Group-noERB. Conclusions: Consistent rectal dose-volume improvements were observed with the use of endorectal balloons in five fraction SBRT treatment planning for early-stage prostate cancer. Confirmation of these dosimetric results with additional cases is warranted before investigating the impact of ERB on minimizing acute and long-term rectal toxicity. Author Disclosure: H.F. Xiang: None. H. Lu: None. A.E. Hirsch: None. J.A. Efstathiou: None. A.L. Zietman: None. K. Harris: None. N. Bloch: None. S. Keohan: None. J. Willins: None. L.A. Kachnic: None.
3632 Investigation of 3-dimensional Optical Image Guided Frameless Stereotactic Radiosurgery Using Homegrown Volumetric Modulated Arc Therapy Y. Song, C. Obcemea, C. Burman, and Q. Zhang; Memorial SloanKettering Cancer Center, New York, NY
3633 Patient Clearance Simulation for Stereotactic Body Radiation Therapy A. Saito,1,2 R. Kashani,1 S. Ozawa,2 K. Karasawa,2,3 and E.E. Klein1; 1 Washington University in St. Louis, St. Louis, MO, 2Juntendo University, Tokyo, Japan, 3National Institute of Radiological Sciences, Chiba, Japan Purpose/Objective(s): This study provides a tool to evaluate geometric clearance for stereotactic body radiation therapy (SBRT) using a linear accelerator. This linac has a built-in collision model which generates an interlock based on the relative position of the gantry and the couch. As a result the allowed gantry and couch rotations are limited compared to other linacs which can affect non-coplanar SBRT treatments. Another concern is patient clearance for both CBCT and treatment fields which may not be accounted for by the machine collision model. In this study, a simulation tool is developed to model both machine and patient clearance. Specifically, an algorithm to estimate the position of the patient’s arm extending outside the planning CT image, was generated to provide a robust estimation of patient clearance. Materials/Methods: Geometric information of the gantry head and couch were obtained by measurement. The patient and immobilization devices were contoured on the planning CT and exported along with the treatment
International Journal of Radiation Oncology Biology Physics
dose, 0.30 0.003% for dose to 1 cc of spinal cord volume, 0.29 0.001% for dose to 0.5 cc of spinal cord, and 0.73 0.006% for dose to 0.1 cc of spinal cord. Conclusions: SBRT using helical tomotherapy can be a safe treatment modality for spine metastasis in the aspect of accurate targeting. Author Disclosure: Y. Chung: None. M. Kim: None. J. Kim: None. W. Koom: None.
Purpose/Objective(s): Recently, powerful on-board imaging technologies have propelled SRS into the frameless era. Yet, all the mainstream onboard imaging systems resort to ionizing X-rays as imaging sources. Moreover, most SRS procedures are planned with IMRT, a modality that suffers from an elevated MU, a reduced MU-to-cGy coefficient, and a prolonged treatment time. To tackle these issues, we commissioned a novel frameless stereotactic system for intracranial SRS immobilization, a 3D optical surface imaging system for target localization and real-time patient monitoring, and a homegrown VMAT system for SRS planning. Here, we present our initial results of a feasibility study. Materials/Methods: The frameless stereotactic system includes carbon fiber base boards, a cranial stereotactic localizer frame, a support bridge, patient-specific mouthpiece assemblies, and a portable vacuum pump. The portable vacuum pump applies a negative pressure to the patient mouthpiece. The resulting vacuum suction seals the mouthpiece precisely into the palate of the mouth. VMAT-SRS plans were computed with a single 360 arc containing 180 equally-spaced beams, optimized incrementally using a differentiated optimization scheme. The target localization was accomplished with a video-based 3D optical surface imaging system, consisting of three 3D camera units and fast 3D image registration software. After the patient had been initially setup, the 3D optical surface imaging system acquired a verification skin surface of the patient. This verification image was registered to a reference skin surface created from the planning 3DCT in a user-defined region of interest. The registration software calculated three translational shifts (DVRT, DLNG, and DLAT), and three rotational shifts (DPITCH, DROLL, and DYAW) for patient repositioning. Results: The frameless system was found to be able to secure a sustained immobilization accuracy of w 1.0 mm and 1.0 for intracranial SRS as measured by CBCT and 3D real-time optical surface imaging. With this system, the patient could be simulated, planned, and treated on different days. VMAT-SRS plan optimization converged in 10 minutes for a PTV of w 35 cm3 and 6 other critical structures. VMAT-SRS plans exhibited superior dose distribution to IMRT-SRS plans as measured by conformality and homogeneity indices. The target dose inhomogeneity was less than 17% compared to about 30% for conventional SRS plans. The doses to the critical structures for VMAT-SRS plans were less than or comparable to those for conventional SRS plans. With this new approach, the treatment time was reduced by more than one hour. Conclusion: Our initial data revealed that the synergistic combination of the frameless system, VMAT-SRS, and the 3D real-time optical surface imaging could be an optimal intracranial SRS sub-modality. Author Disclosure: Y. Song: None. C. Obcemea: None. C. Burman: None. Q. Zhang: None.
3631 Endorectal Balloon in Stereotactic Body Radiation Therapy (SBRT) for Early-Stage Prostate Cancer: A Planning and Dosimetry Analysis H.F. Xiang,1,2 H. Lu,1 A.E. Hirsch,1,2 J.A. Efstathiou,1 A.L. Zietman,1 K. Harris,3 N. Bloch,2 S. Keohan,2 J. Willins,1,2 and L.A. Kachnic1,2; 1 Massachusetts General Hospital and Harvard Medical School, Boston, MA, 2Boston Medical Center and Boston University School of Medicine, Boston, MA, 3Massachusetts Institute of Technology, Cambridge, MA Purpose/Objective(s): The use of an endorectal balloon (ERB) has been reported to significantly reduce intra-fractional prostate motion during standard fractionated intensity-modulated radiation therapy (IMRT) for prostate cancer. Recently, hypofractionated IMRT and SBRT strategies are under investigation; however, to date, there have been no dosimetric analyses on the use of ERB with these approaches. This study investigates the dose-volume characteristics for the rectum when using ERB as part of SBRT planning for early-stage prostate cancer. Materials/Methods: Twelve patients with prostate cancer who had received conventional IMRT at our institutions were included in this study. Six patients (Group-ERB) had been planned and treated with ERB containing 60-100 cc of water, and the other six (Group-noERB) without ERB. For each case, an optimized SBRT plan was generated by using sequential optimization in TPS according to the 5 fraction (5 x 7.25 Gy) dosespecification and dose-volume constraints of the RTOG 0938 randomized phase II study of hypofractionated RT for early-stage prostate cancer. Dosimetric characteristics for the rectum were compared between the two groups, including maximum dose, mean dose for the entire rectum and the anterior half of the rectum, and the percentages of rectal volume and anterior-half rectal volume receiving 50%, 80%, 90% and 100% of the prescription dose (36.25 Gy). Results: While the maximum dose to the rectum was comparable between the two groups (range 37.8-39.9 Gy), the mean dose to the entire rectum was lower for Group-ERB (10.3 Gy, range 8.2-13.5 Gy) than GroupnoERB (12.9 Gy, range 11.4-15.1 Gy). The mean dose to the anterior half of the rectum was also lower for Group-ERB (15.0 Gy, range 13.0-19.5 Gy) than Group-noERB (16.2 Gy, range 12.2-19.1 Gy). A consistent dosimetric advantage was also noted in the rectal volume receiving 50%, 80%, 90% and 100% of the prescription dose for Group-ERB compared to Group-noERB. The mean V50%, V80%, V90% and V100% of the entire rectum for Group-ERB was 16.7%, 6.3%, 3.5% and 0.9%, in comparison to 26.3%, 10.9%, 6.3% and 1.4% for Group-noERB. Similarly, the mean V50%, V80%, V90% and V100% of the anterior half of the rectum for GroupERB was 31.6%, 11.8%, 6.6% and 1.6%, in comparison to 39.7%, 18.4%, 10.6% and 2.6% for Group-noERB. Conclusions: Consistent rectal dose-volume improvements were observed with the use of endorectal balloons in five fraction SBRT treatment planning for early-stage prostate cancer. Confirmation of these dosimetric results with additional cases is warranted before investigating the impact of ERB on minimizing acute and long-term rectal toxicity. Author Disclosure: H.F. Xiang: None. H. Lu: None. A.E. Hirsch: None. J.A. Efstathiou: None. A.L. Zietman: None. K. Harris: None. N. Bloch: None. S. Keohan: None. J. Willins: None. L.A. Kachnic: None.
3632 Investigation of 3-dimensional Optical Image Guided Frameless Stereotactic Radiosurgery Using Homegrown Volumetric Modulated Arc Therapy Y. Song, C. Obcemea, C. Burman, and Q. Zhang; Memorial SloanKettering Cancer Center, New York, NY
3633 Patient Clearance Simulation for Stereotactic Body Radiation Therapy A. Saito,1,2 R. Kashani,1 S. Ozawa,2 K. Karasawa,2,3 and E.E. Klein1; 1 Washington University in St. Louis, St. Louis, MO, 2Juntendo University, Tokyo, Japan, 3National Institute of Radiological Sciences, Chiba, Japan Purpose/Objective(s): This study provides a tool to evaluate geometric clearance for stereotactic body radiation therapy (SBRT) using a linear accelerator. This linac has a built-in collision model which generates an interlock based on the relative position of the gantry and the couch. As a result the allowed gantry and couch rotations are limited compared to other linacs which can affect non-coplanar SBRT treatments. Another concern is patient clearance for both CBCT and treatment fields which may not be accounted for by the machine collision model. In this study, a simulation tool is developed to model both machine and patient clearance. Specifically, an algorithm to estimate the position of the patient’s arm extending outside the planning CT image, was generated to provide a robust estimation of patient clearance. Materials/Methods: Geometric information of the gantry head and couch were obtained by measurement. The patient and immobilization devices were contoured on the planning CT and exported along with the treatment