(Saturday, 3/30/2019)
Room: Exhibit Hall
Purpose: To quantify and compare the effect of calculating dose using a Collapsed Cone Convolution Superposition (CCCS) algorithm and a Monte Carlo algorithm for spine patients being treated with SBRT.
Methods: Four spine patients (two thoracic, two lumbar) were included in this study. All patients were prescribed 1600 cGy over one fraction. Plans were optimized in the Pinnacle3 TPS and dose was calculated using a CCCS algorithm. Plans were then exported to the Monaco TPS and the dose was recalculated using a Monte Carlo algorithm. Comparison metrics included Conformity Index (CI), Conformal Index (CoIn), Gradient Index (GI), maximum spinal cord dose, and PTV D98 (near minimum) and D2 (near maximum) values.
Results: For all cases, the Monte Carlo algorithm in Monaco showed a lower overall PTV coverage than what the CCCS algorithm in Pinnacle3 initially calculated. Lower dose regions were not affected. The average CI for all patients was 0.947 and 0.808 for Pinnacle and Monaco, respectively. The average CoIn for all patients was 0.837 and 0.736 for Pinnacle and Monaco, respectively. For all evaluation metrics and for all patients, the Monte Carlo algorithm in Monaco calculated a lower dose than the CCCS in Pinnacle3.
Conclusion: Monte Carlo remains in the most accurate of dose calculation algorithms. SBRT planning and delivery requires a higher level of precision and accuracy than conventional radiation therapy. These results indicate the possible need for Monte Carlo calculations as a second check for spine SBRT patients to ensure adequate target coverage.
Funding Support, Disclosures, and Conflict of Interest: This research is supported by the CPRIT Research Training Award (RP 170345).
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