Evaluation of Dose Calculation Accuracy of Intermediate-To-Low Dose Spillage in Single-Isocenter Multitarget Radiosurgery Using 3D Dosimetry
Y Wang1*, P Fan2, A Xu3, J Choi4, T Wang5, J Adamovics6, C Wuu7, (1) New York Presbyterian/Columbia University Irving Medical Center, New York, NY, (2) New York Presbyterian/Columbia University Irving Medical Center, Bronxville, NY, (3) New York Presbyterian/Columbia University Irving Medical Center, New York, NY, (4) New York Presbyterian/Columbia University Irving Medical Center, ,,(5) New York Presbyterian/Columbia University Irving Medical Center, New York, NY, (6) HEURIS, INC., Skillman, NJ, (7) New York Presbyterian/Columbia University Irving Medical Center, New York, NY
Presentations
TH-E-TRACK 6-3 (Thursday, 7/29/2021) 3:30 PM - 4:30 PM [Eastern Time (GMT-4)]
Purpose: Single-isocenter multitarget (SIMT) stereotactic radiosurgery using volumetric modulated arc therapy provides rapid delivery of high dose radiation to multiple brain metastases. However, the intermediate-to-low dose spillage to normal brain is unclear. Dosimetric accuracy of the dose spillage calculation in treatment planning system involves modeling of out-of-field doses, and multileaf collimator characteristics, which is challenging to be evaluated using 1D/2D dosimeters. This study presents a comprehensive 3D dose comparison between calculated and measured dose distribution with various treatment geometries.
Methods: Ten SIMT plans for treating multiple brain lesions with different sizes and target separations were created using HyperArc treatment planning system (Varian Medical System). Hybrid plan verification of each plan was generated on computed tomography images of the 3D dosimeters, PRESAGE (Heuris Inc.). Hybrid plans were then delivered to the dosimeters using a TrueBeam (Varian Medical System) linear accelerator. Using fiducial registration, target and normal tissue structures were registered to the measured dose image. A comprehensive comparison of the 3D dose distribution between measurement and calculation was performed.
Results: Most of the gamma failing points are at the intermediate dose regions (50-70%). Measured 3D dose distribution presents higher dose spillage to normal tissue up to 5-10% in regions connecting the two close targets. In addition, dose discrepancies were observed in off-axis low dose regions where out-of-field dose is underestimated by the treatment planning system. Using convectional portal dosimetry, observed errors in 3D measurement were washed out due to dose summation.
Conclusion: A comprehensive view of the dose discrepancies between calculated and measured inter-target dose spillage in different SIMT treatment geometries was presented. The results provide insights into the planning strategy of SIMT treatments and lay the path for future comparison of Gamma Knife to linear accelerator radiosurgery using 3D dosimetry.
Funding Support, Disclosures, and Conflict of Interest: The dosimeters were provided by Heuris Inc. free of charge.
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