Dosimetric impact of CT-RED calibration curve variations from different kVp settings on breast cancer treatment planning.

The choice of a CT-RED calibration curve directly influences the accuracy of dose calculation in treatment planning systems (TPS), depending on treatment technique, anatomical site and calculation algorithm. This study aimed to evaluate the impact of variations in CT-RED calibration curves due to different tube voltages (kVp) on breast cancer treatment plans as a function of calculation algorithm. CT-RED calibration curves were generated using a CIRS M062 phantom scanned with a 16-slice HITACHI Supria CT scanner at 80, 100, 120, and 140 kVp. These curves were applied to treatment plans for left breast cancer using the Collapsed Cone (CC) and X-ray Voxel-based Monte Carlo (XVMC++) algorithms in MONACO TPS (v6.6.2). Dose-volume histograms and dose statistics were analyzed to assess dose metrics for planned target volumes (PTV) and organs at risk (OAR). Monte Carlo-based dose calculations showed significant sensitivity to kVp settings, while CC results exhibited clinically negligible effects, underscoring that the impact of kVp on dose calculation depends on the algorithm used. Thus, to ensure accurate dose calculations, it is important to adjust calibration curves for each kVp setting when using Monte Carlo algorithms. Furthermore, it is recommended to include this adjustment into the CC algorithm, despite the minimal differences observed, in order to ensure consistency with the ALARA (As Low As Reasonably Achievable) principle.