Association between radiation volume and breast density for skin toxicity and breast edema after radiotherapy in breast conserving therapy of breast cancer

Abstract Background Despite the favorable toxicity profiles of whole breast radiotherapy, there are subgroups that tend to experience high toxicity. This study examines anatomical and physiological characteristics that can predict the induction of toxicity for skin and edema. Methods In the present cohort, we examined 387 patients who received only radiation therapy to the breast, did not receive chemotherapy, and whose planning data could be fully constructed for evaluation. Metric parameters of the therapy that correlate directly with physiological/anatomical characteristics, such as the irradiated PTV and the boost volume, were evaluated. We also measured breast gland density in a defined reference structure (surrogate Parameter). We compared the parameters collected between patients who experienced grade II toxicity after therapy and patients who experienced grade I or less toxicity from the therapy. Results There was a significant correlation between volume and grade II toxicity for both skin toxicity and edema formation. There was also a higher risk of grade II for the surrogate marker in patients with a HU of less than − 59. The multivariable model for the parameters confirms the volume of the PTV and the boost as risk factors, but not the HU of less than 59. Conclusion There is evidence of a correlation between breast volume, the density of breast tissue and the resulting toxicity of adjuvant radiotherapy in breast cancer. Multivariate analyses were not statistically significant in the retrospective cohort study, and further research is required. Taking these factors into account could further improve treatment tolerance.