Two-year outcomes of a prospective study of proton therapy for breast cancer regional nodal irradiation.

Abstract

65 Background: Through improved nodal coverage and decreased dose to the heart and lung, proton therapy (PT) may improve the therapeutic ratio for treatment of breast cancer requiring regional nodal irradiation (RNI). The purpose of this study is to report 2-year disease control and toxicity. Methods: From May 2012 to February 2014, 18 women (stage IIA-IIIB) were prospectively enrolled on a pilot study. Median age was 51.8 yrs (range, 42-73), with equal division between breast-conserving therapy (BCT) and mastectomy and right- and left-sided cancers. Median number of positive nodes among the 16 node-positive patients was 2 (range, 1-14). Five patients had ≥ 10 nodes positive on axillary dissection (N3a). Treatment targets (clinical target volumes for breast/chest wall, supraclavicular, axillary, internal mammary nodes) and organs at risk were delineated on CT scans. PT alone was used for 10 patients (9 postmastectomy; 1 postBCT) and combined proton-photon in 8 (all BCT). Toxicity was prospectively recorded using CTCAE v4.0. Results: Median follow-up was 1.9 yrs (range, 0.3 – 1.7). Two-year overall survival was 94% and locoregional control was 100%. Two-year distant metastases-free survival was 76%. No grade 4+ toxicity developed. Two patients developed grade 3 cellulitis. One patient had a reconstructive failure associated with postsurgical cellulitis. A right-sided patient was diagnosed with congestive heart failure 2 months after completing PT after diagnosis of a pulmonary embolus 1 month prior. She had elevated B-type natriuretic peptide before PT after adriamycin-based chemotherapy. Mean heart dose was 0 Gy and cardiac V5 0%. Grade 2 toxicities included pneumonitis in 1 patient who received concurrent chemotherapy, fatigue (n = 1), breast atrophy after removal of a 10x6x3cm lumpectomy cavity (n = 1), and lymphedema in 1 patient with > 20 nodes surgically excised. One patient with a history of rib fractures developed an ipsilateral rib fracture 7 months after PT. Conclusions: For women with locally advanced breast cancer, PT for RNI has proven feasible after either mastectomy or BCT. PT allows for highly conformal radiation delivery without compromise of target coverage or excess exposure of normal tissue. Clinical trial information: NCT01365845.