Pilot study of proton therapy for treatment of regional lymphatics in patients with breast cancer.

Abstract

100 Background: To determine the feasibility of proton therapy (PT) for regional nodal irradiation (RNI) in women with breast cancer and to compare target coverage and normal tissue avoidance between PT and conventional radiation. Methods: From May 2012 to May 2013, 14 women were prospectively enrolled in this pilot study; 5 had right-sided and 9 had left-sided. Median age at the time of PT was 53.7 years (range 37-73). The breast or chest wall and supraclavicular, axillary, and internal mammary (IM) lymph nodes were treated in all patients. Proton and conventional plans were developed for each patient; the superior plan, as defined by organ at risk sparing and target coverage, was treated. Targets and normal tissues were delineated on treatment CT scans. Wilcoxon signed rank sum test was used to compare dose-volume parameters. Results: For all 14 patients, the proton plan better met the dosimetric goals, and was used for treatment delivery. Median heart V5 measured 0.8% for the proton plans versus 23% for the conventional plans (p=0.0005). Median mean heart dose measured 0.55 Gy (range 0– 3.2Gy) for the proton plans versus 4.9 Gy (range 2-9.1 Gy) for the conventional plans (p=0.0005). Significant difference in median lung V5 and median V20 were found: 41% and 24% for the proton plans and 67% and 38% for conventional plans, respectively. PTV breast/chest wall coverage was adequate with both plans. Coverage of the level II axilla was higher in the proton plans (D95 48 Gy vs 44 Gy, p=0.01) as was coverage of the IM nodes (D95 50 Gy vs 46 Gy, p=0.01). Acute toxicity data is available for 12 patients. The most common acute toxicity was radiation dermatitis, with 9 patients experiencing grade 2 and 3 patients experiencing grade 3 toxicity. Other grade 2 toxicities included fatigue (n=3), pain (n=2), esophagitis (n=4), and skin infection (n=1). Radiation dermatitis was the only grade 3 toxicity. No grade 4 or 5 toxicities developed. Conclusions: Adjuvant PT is a well-tolerated, technically feasible modality for RNI, with a significant decrease in cardiac V5, V20, and mean heart dose as well as lung V5 and V20. Further investigation of PT for RNI in breast cancer is warranted to improve the therapeutic ratio by decreasing radiation exposure to the heart and lung. Clinical trial information: NCT01365845.