Room: AAPM ePoster Library
Purpose: The purpose of this study is to streamline the planning process for prostate cancer patients treated on a 0.345T 6MV MR-LINAC by retrospectively varying TPS parameters to determine the optimal plan. We propose this is feasible due to similarities in anatomical geometry between patients and beneficial due to strict OAR/PTV dose criteria.
Methods: IMRT plans were calculated with the MR-LINAC’s dedicated TPS. IMRT Efficiency (IE), an optimization parameter, and number of beams were varied with 20 unique runs (1,3,5,7,9 IE and 11,13,15,17 beams) to determine the best plan, assessing DVH values and treatment time. Physician-defined structure objectives were held constant for each calculation, as was a 70Gy/28fx prescription. A scoring system was used to rank plans based on a weighted average of plan quality metrics (PQM). Possible scores range from 20 (maximizing all metrics) to 1.
Results: Five patients (one prostate, four prostate+SV) were analyzed with calculations performed twice per run. Eight PQMs were used to score runs for a total of 1600 data points. Scores for each run were averaged across the patient population and ranked. 15 beams/ IE of 1 scored best (12.84), while 11 beams/ IE of 9 ranked last (7.55). 17 beams ranked first (11.35) on average, and 11 beams ranked last (9.33). An IE of 1 scored best on average (12.67), while 9 ranked last (8.73).
Conclusion: 15 beams and IE of 1 is recommended to achieve the best overall plan based on our physicians’ goals. Although this score did not achieve the best PTV min./max. doses, it ranked first in minimizing OAR doses. Increasing beam number improved plan score but did not show a statistically significant benefit beyond 15. Decreasing IE improved plan score on average. A clear trend favoring 15 beams and IE of 1 demonstrates feasibility in standardizing the planning process.
Not Applicable / None Entered.