Prediction of acute skin toxicity in tomotherapy of breast cancer using skin DVH data

Investigation and quantification of the relationship between the skin dose-volume histogram (DVH) and the risk of acute skin toxicity in breast cancer patients undergoing Tomotherapy by regression modeling. This prospective study included 52 breast cancer patients treated with Tomotherapy in the dose range of 42.5-60 Gy to the planned target volume. Grading of acute skin toxicity in patients was assessed by the maximum score recorded in weekly follow-ups during and up to three months' post-radiation therapy using the Common Terminology Criteria for Adverse Events (CTCAE) v4.0 guidelines. A superficial layer with a thickness of 2 mm was designated as the Skin Representative Layer (SRL-2) on the Tomotherapy planning, and DVH was extracted for that. Then, multivariable and univariable logistic analyses were performed to identify the most predictive variables of acute skin toxicity from SRL-2 DVH values and patients' clinical parameters. The regression analysis identified V51Gy, representing the absolute SRL-2 volume receiving 51 Gy or more in physical dose, as the most predictive dosimetric parameter for grade 2-3 acute skin toxicity. The optimal cut-off value was 4.74 cc for the physical dose, with an Area Under the Receiver Operating Characteristic (ROC) Curve (AUC) value of 0.749, even when adjusted for clinical and treatment-related variables. The logistic model based on V51Gy demonstrated superior calibration, with a slope and R² value approaching 1, indicating better agreement between predicted and observed outcomes. The risk of acute skin toxicity during breast cancer Tomotherapy is correlated with the V_51Gy parameter of skin DVH. Limiting V_51Gy < 4.74 cc, or 23.7 cm² of skin area, should keep the risk of grade 2-3 acute skin toxicity below 26%.