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SU‐C‐141‐02: Evaluation of Dosimetric and Geometric Accuracy of Gated Lung SBRT with CIRS Lung Motion Phantom
Author(s) -
Yu S,
Han B,
Wang L,
Mok E
Publication year - 2013
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4813962
Subject(s) - imaging phantom , fiducial marker , gating , nuclear medicine , truebeam , medical imaging , image guided radiation therapy , dosimetry , biomedical engineering , physics , linear particle accelerator , medicine , optics , radiology , beam (structure) , physiology
Purpose: To evaluate the dosimetric and geometric accuracy of the gated SBRT delivery using film measurements and intra‐fractional kV images with predefined software‐markers. Methods: End‐to‐end tests of gated SBRT delivery were performed using a Varian TrueBeam™ linac and a CIRS lung motion phantom with targets of 1 and 2 cm in diameter and implanted fiducials. 4DCT images of the phantom were acquired with 1 mm slice thickness. RapidArc plans were created in Eclipse TPS with software‐markers placed on the fiducials at maximal expiration. SBRT plans were delivered to the phantom in stationary and in gating mode (2 mm and 5 mm‐gating window). Plans were also delivered with 5 mm targets shift with respect to the boney anatomy in stationary mode and 10% phase shift in 2 mm‐gating mode. To investigate the dosimetric accuracy, dose was measured by EBT3 film and compared with the TPS calculation (AcurosXB algorithm) using γ‐index criteria (3mm distance‐to‐agreement and 3% dose‐difference). The geometric accuracy was evaluated using kV intra‐fraction images of the fiducials relative to the predefined software‐markers. Results: Comparing with the stationary mode, the percentage passing γ‐index (%γ) for 1 cm target decreased significantly from 98.0% to 94.8% (2 mm‐gating window) and 84.3% (5 mm‐gating window) while for 2 cm target %y decreased from 99.5% to 99.2% (2 mm‐gating window) and 86.6% (5 mm‐gating window). The %γ for the conditions of target shift and phase shift for the 2 cm target were 89.0% and 89.9%, respectively. Geometric deviation was less than 0.05 mm, except for the phase shift condition (0.45 mm). Conclusion: Higher dosimetric impact from motion was found for the smaller target. With a proper gating window the planned dose can be accurately delivered with the use of kV intra‐fraction image and software‐maker to ensure the geometric accuracy during treatment.