Abstract
PURPOSE: This study evaluates the hypothesis that a volumetric skin-sparing planning technique (SSPT) will reduce acute dermatitis in patients treated to the breast or chest wall (CW) with proton pencil-beam scanning (PBS). METHODS AND MATERIALS: In January 2022, our center incorporated volumetric-based skin-sparing objectives in addition to skin hot spot evaluation as an SSPT. The SSPT incorporated an objective to limit the volume of a skin evaluation structure (skin-eval) receiving 95% of the prescription dose or more (V95%Rx) to ideally < 50%. We compared target coverage, robustness, skin-eval dosimetry, and acute on-treatment skin toxicity in patients treated with and without incorporation of this SSPT. Patients with skin/dermal lymphatic invasion or inflammatory breast cancer were excluded. RESULTS: A total of 84 patients who received breast/CW PBS were included (43 planned without and 41 with the SSPT). There was no difference in percentages of patients treated with intact breast/CW/immediate CW reconstruction between groups. Mean skin-evalV95%Rx was 72% vs 30%, P < .0001, for those treated without versus with an SSPT. Maximum %Rx to the skin-eval volume of 0.03, 0.3, and 1 cc was higher in patients treated without versus with an SSPT (103.1% vs 101.5%; 101.3% vs 100.4%; and 101.8% vs 99.7% [all P ≤ .0001]), respectively. There was a small difference in the mean clinical target volume V97.5%Rx in patients treated without versus with the SSPT (97.8% vs 96.5%, P = .0003). Patients planned using the SSPT demonstrated reduced rates of grade 1 breast pain at week 2 (12% vs 33%, P = .0424) and grades 2 and 3 dermatitis at weeks 4 and 5 (week 4 dermatitis ≥ grade 2, 18% vs 43%, P = .0224; week 5 dermatitis ≥ grade 2, 45% vs 69%, P = .0006). There were numerically more patients requiring a treatment break or not completing the full intended prescription (4 vs 1) in the pre-SSPT cohort. CONCLUSIONS: The use of an SSPT may reduce acute skin toxicity in patients with breast cancer treated with PBS.