Room: AAPM ePoster Library
Purpose: To determine the most suitable Aperture Shape Controller (ASC) in Eclipse V15.6 Photon Optimizer (PO) for Lung SBRT by analyzing the impact of different ASC modes to plan quality.
Methods: Six Lung SBRT patients with different PTV volume – small (9.38 cc and 24.3 cc), medium (43.17 cc and 45.58 cc), and large (115.59 cc and 114.86 cc) were selected. Six plans were generated for each patient with same algorithm and optimization parameters, but different ASC modes including off, very low, low, moderate, high, very high. All plans met RTOG0653 criteria, and in-house dose constraints to OARs. Modulation factor (MF), PTVmax, PTVmin, R50%, and D2cm were analyzed and compared.
Results: Based on the statistical analysis, ASC mode does not make significant difference to all 5 parameters (p-value > 0.05). However, the p-value for MF is 0.084, which provides at least 90% confidence that ASC mode has the influence on MF. Further analysis shows that MF is significant lower (p-value < 0.05) with ASC low or moderate mode than ASC off mode in small PTV volume patients.
Conclusion: This work indicates the usage of proper ASC mode during Lung SBRT planning. For patients with small PTV volume (< 30 cc), Monitor Unit can be significantly less without losing plan quality when utilizing ASC low or moderate mode. There is no significant difference among 5 individual “on” modes for PTVmax, PTVmin, R50%, and D2cm. For patients with medium and large PTV volume (> 30 cc), ASC plays less important role in Lung SBRT planning. More patient data will be added for statistical analysis to make this study more robust in the future.