Dosimetric Evaluation of CT-to-RED Calibration Curves on Dosimetric Accuracy in Brain Radiotherapy

Abstract

Accurate radiotherapy dose calculation depends on converting CT Hounsfield Units (HU) to relative electron density (RED) using calibration curves. This study compared three different CT-to-RED calibration curves-two derived from physical phantoms (CIRS 062M and Catphan 604) and one default curve from the Monaco treatment planning system (TPS) by recalculating ten brain tumor VMAT plans. The analysis showed that using the default TPS curve led to dose overestimation (by 3 5 for target volumes and 2 4 for some critical organs) compared to the CIRS phantom-derived curve, which was the most accurate. The Catphan curve had intermediate results. The findings highlight that the choice of calibration curve significantly affects dose accuracy in brain radiotherapy, and site-specific, phantom-based calibration should be prioritized to improve treatment precision and safety.