Evaluating Multi-Target Beam Setup Methods for LINAC-Based Stereotactic Treatment of Multiple Brain Metastases with Individual Dose Prescriptions

Background/Objectives: LINAC-based, single-isocenter, non-coplanar, stereotactic radiotherapy (SRT) is an effective treatment for patients with multiple brain metastases (BMs). Within such a treatment plan, individual beams can be assigned to treat a subset of the metastases, this is referred to as multi-target beam setup (MTBS). This work evaluates and compares several strategies for MTBS. Methods: A planning study was performed, comparing plan quality parameters for plans resulting from several MTBS strategies, including two automated approaches. Each BM was individually prescribed a dose depending on its volume, resulting in treatment plans with multiple prescription doses. Paddick conformity index and Paddick gradient index were adapted to work with multiple prescription doses. Results: Given the same number of treatment beams, distributing BMs over treatment beams gave statistically significant improvements over targeting the BMs with all beams by 2% CI, 9% GI, 15% V15Gy, and 10% V5Gy. No statistically significant difference was found between different methods to distribute BMs over treatment beams. Increasing the number of treatment beams gave a further statistically significant improvement in plan quality at the cost of increased treatment time. Conclusions: MTBS is an important tool to increase the quality of non-coplanar LINAC-based stereotactic treatment plans for multiple brain metastases with individual dose prescriptions. MTBS can be automated to save planners a significant amount of time. The MTBS algorithm should be restricted in terms of the number of beams it can generate, to limit treatment times.