Abstract P1-15-20: Prospective study of proton radiotherapy for treatment of regional lymphatics in breast cancer
Authors: Bradley Julie A , Dagan Roi , Ho Meng Wei , Morris Christopher G , Li Zuofeng , Mendenhall Nancy P 
Published: May 2015

Purpose: To compare dosimetric endpoints between proton therapy (PT) and conventional radiation and to determine the feasibility of PT for regional nodal irradiation (RNI) in women with breast cancer.

Methods: From May 2012 to February 2014, 18 women (stage IIA-IIIB) prospectively enrolled on a pilot study. Median age was 51.8 years (range, 42-73), with equal division between breast-conserving therapy (BCT) and mastectomy and right and left-sided cancers. Treatment targets (CTVs for breast/chest wall, supraclavicular, axillary, internal mammary nodes [IMNs]) and organs at risk were delineated on CT scans, and PT and conventional plans were developed. PT alone was used for 10 patients (9 post-mastectomy, 1 after BCT) and combined proton-photon in 8 (all BCT). Acute toxicity was prospectively recorded using CTCAE v4.0. A Wilcoxon signed-rank sum test compared the dose-volume parameters.

Results: Median followup was 10.6 months (range, 1.1-19.1). For all patients, the PT plan better met the dosimetric goals and was used for treatment. Breast/chest wall coverage was adequate (V47.5=96.6% for both plans). PT improved coverage of level II axilla (median D95, 48.9Gy [range, 44.8-51.4Gy] with PT vs 45.4Gy [range, 39.8-51Gy] with conventional; p=0.0005). Adequate coverage of IMNs was consistently achieved with PT (median D95, 48.9Gy with a range of 44.8-51.4Gy) but not with conventional (median D95, 45.4Gy with range of 39.8-51Gy; p=0.0005); PT reduced heart dose in all patients. Median ipsilateral lung V5 measured 35.3% for PT compared to 60.5% for conventional (p&lt;0.0001). Ipsilateral lung V20 improved with PT (median, 21.6% vs 35.5%; p&lt;0.0001).

Table 1: Cardiac dose in left-sided patients (comparison of medians of the cohort; range in parentheses) Heart V5Mean Heart DoseVentricle V5Mean Ventricle DoseMaximum LAD doseMean LAD doseProton Plan2.7% (0-12%)0.6Gy (0-3.2Gy)0.5% (0-15.6%)0.1Gy (0-4Gy)30.5 (13.4-42.6Gy)1.7Gy (0.5-28.5Gy)Conventional Plan34% (7-60%)5.9Gy (2-9.1Gy)31.4% (8.7-79.8%)5.4Gy (2.4-11Gy)44.6Gy (35.1-54.7Gy)27Gy (16.8-41.9Gy)p-value0.0040.0040.0040.0040.040.02

Table 2. Cardiac dose in right-sided patients (comparison of medians of the cohort; range in parentheses) Heart V5Mean Heart DoseVentricle V5Mean Ventricle DoseProton Plan0.3% (0-2.9%)0.5Gy (0-0.8Gy)3.3% (0-1%)0.2Gy (0-0.5Gy)Conventional Plan13.2% (0.4-24.7%)2.9Gy (1-5.1Gy)3.3% (0-7.1%)1.2Gy (0.8-1.7Gy)p-value0.0040.0040.0080.004

Grade 3 dermatitis developed in 4 patients (22%), which was the only grade 3 toxicity. All patients developed grade 2 dermatitis; other acute grade 2 toxicities included fatigue (n= 6) and esophagitis (n=5). No grade 4+ toxicities developed. Dermatitis resolved by 1 month after PT for all but 1 patient who developed cellulitis (grade 2).

Conclusion: PT for RNI after mastectomy or BCT significantly improves cardiac dose especially for left-sided patients and lung V5 and V20 in all patients without excessive acute toxicity. PT simultaneously improves target coverage for the IMN and level II axilla, which may positively impact long-term survival in breast cancer patients.

Citation Format: Julie A Bradley, Roi Dagan, Meng Wei Ho, Christopher G Morris, Zuofeng Li, Nancy P Mendenhall. Prospective study of proton radiotherapy for treatment of regional lymphatics in breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-15-20.