Room: Exhibit Hall | Forum 4
Purpose: For brain stereotactic radiotherapy(SRT) of multiple metastatic lesions, it is difficult to determine the optimal treatment isocenters because orientation and volumes of PTVs and proximity to critical structures are unique. Currently in our clinic, each lesion is commonly treated with its own isocenter. This could reduce the setup error of each lesion but may not be optimal for plan quality and treatment time. The purpose of this study is to assess the automatic plan optimization including scenario based isocenter selection for multi-metastatic brain SRT using RayStation scripting.
Methods: Plans were automatically generated using a Python-based script in RayStation TPS for ten randomly selected cases. For each case, four plans with four isocenters were generated: two separate isocenters at their PTV centroids, a single isocenter at the mid-point of two centroids, a single isocenter at PTV1, and a single isocenter at PTV2. The plans were compared by plan quality parameters , including D_95%, V_95%, V_12Gy of normal brain excluding PTVs, max dose of brainstem, and homogeneity index, conformity index , and gradient index of PTVs. E2E testing with radiochromic film was performed for the best scenario plan applied to an anthropomorphic head phantom.
Results: Python script is executed within 5-6 min to generate four scenario-based automatic plans with DVHs and dose metrics. The best plan per patient was selected by a radiation oncologist. For distance of PTVs < 5cm, the best plan depends rather on the patient specific. When the distance of two PTVs are 5cm, measured doses at each PTV centroid agreed within 3-4% and dose distribution agrees well compared to the plan with a single isocenter at the mid-point.
Conclusion: Automatic plan optimization using the scripting of scenario based-isocenter selection was evaluated. Newly established workflow is cost and time effective as well as improves the plan quality.