Out-of-field dosimetry in VMAT for medulloblastoma using OSLDs

Volumetric modulated arc therapy for pediatric medulloblastoma improves target precision but increases low-dose exposure to healthy tissues, elevating secondary cancer risks. This study evaluates treatment planning system (TPS) accuracy for out-of-field dose (OOFD) predictions by performing measurements with optically stimulated luminescence dosemeters (OSLDs) in an anthropomorphic phantom. TPS predictions were accurate near the field (<3% at 5.5 cm) but significantly underestimated doses at larger distances, with discrepancies ranging from 16% (thyroid) to 64% (heart). These findings highlight TPS limitations in modeling peripheral leakage and scatter and underscore the critical role of OSLD-based monitoring for pediatric patients. Accurate OOFD verification is essential for risk assessment and long-term safety. Future work should focus on refining TPS algorithms and integrating direct dosimetry into clinical practice for this vulnerable population.