ISSN: 1859 - 2872
Evaluation of changes in treatment planning quality indices when applying a specific beam model dedicated for MLC-based radiosurgery
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Abstract
Objective: To evaluate the changes in plan quality indices when applying a radiosurgery-specific MLC-based beam model called sAXB (specific Acuros-XB) to compare with the standard AXB beam model. Subject and method: The 6MV-WFF and 6MV-FFF sAXB beam models were previously validated by the MD Anderson Laboratory (Texas, Houston, USA) and the Seiberdorf Dosimetry Laboratory (Vienna, Austria) under the IAEA-E24022 Coordination Research Project. Treatment plans were created based on CT data (computed tomography) of a radiosurgery head phantom and 13 patients with 6MV-WFF and 6MV-FFF beams. After dose calculations were done with the standard AXB beam model, these plans were recalculated using the sAXB beam model. For dosimetric comparison, the plan quality metrics CI, HI, CQ, CN, COIN, and Dmean were utilized. Result: For the 6MV-WFF beam, differences in values of HI, CQ, CN, and Dmean between AXB and sAXB were within 2.5% ÷ 14%, 3.6% ÷ 14.9%, -9.5% ÷ -59.5% and 3.0% ÷ 14% by reducing the target volume diameter of the phantom from 4 cm down to 0.5 cm. For the 6MV-WFF beam, they were within 3.4% ÷ 18.4%, 3.8% ÷ 19.2%, -9.3% ÷ -63.7%, and 3.2% ÷ 19.2%. In patient data, the mean differences in values of HI, CQ, CN, COIN, and Dmean between AXB and sAXB were 2.7%, -1%, -5.0%, -5.0%, -2.0% for 6MV-FFF beams, and 1.9%, 5.7%, 3.2%, 3.2%, and 2.5% for 6MV-WFF, respectively. Conclusion: There were significant changes in values of calculated plan quality metrics between the radiosurgery-specific beam model and the standard beam model, which were MLC-based, especially for target sizes smaller than 4cm in diameter.
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References
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