Comparative Analysis of Acute Skin Reactions After Postmastectomy Photon and Intensity Modulated Proton Therapy

We sought to compare target coverage, skin dose, physician-assessed adverse events, and patient-reported skin outcomes in a large cohort of patients receiving postmastectomy intensity modulated proton therapy (IMPT) or photon radiation therapy (XRT).

Women with unilateral, noninflammatory breast cancer treated with postmastectomy radiation therapy using IMPT or XRT to 50 Gy relative biological effectiveness (RBE) were included. Skin planning objectives for both modalities prioritized ≥90% of the skin volume receiving >90% of the prescription dose, which is expected to control microscopic disease, while maintaining dose homogeneity. IMPT planning objectives limited the dose to 1 cc of skin to ≤105% of the prescription dose, with an ideal constraint of ≤96%. Target and skin dosimetry were evaluated. Acute Common Toxicity Criteria for Adverse Events (CTCAE) grade ≥2 dermatitis and skin-specific patient-reported outcomes using the Patient-Reported Outcomes version of the Common Terminology Criteria for Adverse Events (PRO-CTCAE) were compared between modalities.

Among 176 women (93 IMPT, 83 XRT), the median skin D0.01cc, D1cc, and D10cc were higher in XRT plans than in IMPT plans, although the differences were all less than 3%. Acute grade ≥2 dermatitis occurred in 47% (IMPT) and 48% (XRT) and was not associated with treatment modality (P = .91). Grade 3 dermatitis occurred in 3% (IMPT) and 7% (XRT) (P = .22), with no grade 4 events. At 12 months post-RT, XRT patients reported more skin color changes than IMPT patients (26% vs 6%, P = .04), the only significantly different patient-reported skin outcome.

Patient and provider-reported adverse skin events were mild and comparable between IMPT and XRT. These findings highlight the importance of skin constraints for IMPT planning to titrate an optimal skin dose.