Enhancing heart and lung dose reconstruction in breast cancer radiotherapy using publicly available out-of-field dose profiles

PURPOSE Accurate dose estimation to the heart and lungs is essential for assessing cardiopulmonary toxicity in women treated with radiotherapy (RT). However, DICOM-RT datasets often lack reliable dose information for organs located partly or entirely outside the beam path, limiting large-scale dose-response studies. We introduce an approach that supplements native DICOM-RT dose data with publicly available out-of-field (OOF) dose profiles to improve dose estimation in these regions, and apply it to breast cancer RT. METHODS Dose-volume histogram (DVH) metrics for the heart and lungs were evaluated in 149 patients. Voxels inside the beam path were assigned TPS doses from RT-Dose. Outside, a percent-depth-dose (PDD) and off-axis-ratio formalism was used to re-estimate voxel dose. Extended off-axis-ratio values were derived from empirical OOF-dose datasets. Geometric beam parameters for patient-specific 3D dose reconstruction were obtained from DICOM-RT files. Paired DVH metrics from TPS and re-evaluated doses were compared using the Wilcoxon signed-rank test. RESULTS For volumetric-modulated arc therapy (VMAT), no significant differences were observed between DVH metrics derived from the TPS and those obtained from re-evaluated dose distributions. In contrast, significant differences were found in the low-dose region (<10 Gy) for non-VMAT techniques, with the largest discrepancies for three-dimensional conformal RT (3DCRT). CONCLUSIONS For studies of normal-tissue responses below 10 Gy, limitations of TPS dose calculations beyond the field edge must be considered.