Phase II Study of Proton Beam Radiation Therapy for Patients With Breast Cancer Requiring Regional Nodal Irradiation

Abstract

Purpose: To evaluate the safety and efficacy of proton beam radiation therapy (RT) for patients with breast cancer who require regional nodal irradiation.

Methods: Patients with nonmetastatic breast cancer who required postoperative RT to the breast/chest wall and regional lymphatics and who were considered suboptimal candidates for conventional RT were eligible. The primary end point was the incidence of grade 3 or higher radiation pneumonitis (RP) or any grade 4 toxicity within 3 months of RT. Secondary end points were 5-year locoregional failure, overall survival, and acute and late toxicities per Common Terminology Criteria for Adverse Events (version 4.0). Strain echocardiography and cardiac biomarkers were obtained before and after RT to assess early cardiac changes.

Results: Seventy patients completed RT between 2011 and 2016. Median follow-up was 55 months (range, 17 to 82 months). Of 69 evaluable patients, median age was 45 years (range, 24 to 70 years). Sixty-three patients (91%) had left-sided breast cancer, two had bilateral breast cancer, and five had right-sided breast cancer. Sixty-five (94%) had stage II to III breast cancer. Sixty-eight (99%) received systemic chemotherapy. Fifty (72%) underwent immediate reconstruction. Median dose to the chest wall/breast was 49.7 Gy (relative biological effectiveness) and to the internal mammary nodes, 48.8 Gy (relative biological effectiveness), which indicates comprehensive coverage. Among 62 surviving patients, the 5-year rates for locoregional failure and overall survival were 1.5% and 91%, respectively. One patient developed grade 2 RP, and none developed grade 3 RP. No grade 4 toxicities occurred. The unplanned surgical re-intervention rate at 5 years was 33%. No significant changes in echocardiography or cardiac biomarkers after RT were found.

Conclusion: Proton beam RT for breast cancer has low toxicity rates and similar rates of disease control compared with historical data of conventional RT. No early cardiac changes were observed, which paves the way for randomized studies to compare proton beam RT with standard RT.

Trial registration: ClinicalTrials.gov NCT01340495.

FIG 1.

(A) Locoregional failure (LRF) and (B) overall survival (OS) after proton beam radiation therapy.

FIG A1.

Cosmetic outcome approximately 5.5 years after three-dimensional passively scattered protons to the chest wall after implant reconstruction. Telangiectasia are noted in the inferior chest wall below the implant.

FIG A2.

Positron emission tomography scan fused to radiation treatment planning computed tomography scans with doses shown demonstrate an in-field regional nodal failure for the patient in the study with a locoregional failure.

FIG A3.

Cosmetic outcome 5 years after pencil beam scanning proton radiation. Photographs of the breast at baseline before radiation therapy and at 5 years are shown.