Accelerated partial-breast irradiation using proton beams: initial clinical experience.

PURPOSE: We present our initial clinical experience with proton, three-dimensional, conformal, external beam, partial-breast irradiation (3D-CPBI). METHODS AND MATERIALS: Twenty patients with Stage I breast cancer were treated with proton 3D-CPBI in a Phase I/II clinical trial. Patients were followed at 3 to 4 weeks, 6 to 8 weeks, 6 months, and every 6 months thereafter for recurrent disease, cosmetic outcome, toxicity, and patient satisfaction.
RESULTS: With a median follow-up of 12 months (range, 8-22 months), no recurrent disease has been detected. Global breast cosmesis was judged by physicians to be good or excellent in 89% and 100% of cases at 6 months and 12 months, respectively. Patients rated global breast cosmesis as good or excellent in 100% of cases at both 6 and 12 months. Proton 3D-CPBI produced significant acute skin toxicity with moderate to severe skin color changes in 79% of patients at 3 to 4 weeks and moderate to severe moist desquamation in 22% of patients at 6 to 8 weeks. Telangiectasia was noted in 3 patients. Three patients reported rib tenderness in the treated area, and one rib fracture was documented. At last follow-up, 95% of patients reported total satisfaction with proton 3D-CPBI.
CONCLUSIONS: Based on our study results, proton 3D-CPBI offers good-to-excellent cosmetic outcomes in 89% to 100% of patients at 6-month and 12-month follow-up and nearly universal patient satisfaction. However, proton 3D-CPBI, as used in this study, does result in significant acute skin toxicity and may potentially be associated with late skin (telangiectasia) and rib toxicity. Because of the dosimetric advantages of proton 3D-CPBI, technique modifications are being explored to improve acute skin tolerance.