(P022) Proton Therapy on an Incline Beam Line: Acute Toxicity Outcomes in Locally Advanced Breast Cancer Patients

Lisa A. McGee, MD, Molly McGue, Megan Dunn, PhD, Stacey Schmidt, Darren Kaplan, Mark Pankuch, William Hartsell, MD; CDH Proton Center; Proton Collaborative Group

BACKGROUND: Adjuvant radiotherapy for locally advanced breast cancer (LABC) is known to reduce local recurrence. Proton therapy can be used to improve the therapeutic ratio by sparing the dose to adjacent nontargeted tissues, including the heart and lung, in breast cancer patients requiring treatment of comprehensive regional lymphatics, including the internal mammary lymph nodes (IMNs). This retrospective series evaluates the acute toxicity outcomes for LABC patients treated with uniform scanning (US) proton therapy (PT) on an incline beam line (IBL).

METHODS: From September 2011 to May 2014, a total of 35 patients with LABC received adjuvant US PT targeting either the chest wall (n = 25) or intact breast (n = 10) plus comprehensive regional lymphatics, including the IMNs. Patients were treated on the IBL with one of the following techniques: superior and inferior anterior superior oblique (ASO) fields alternated every other day with a superior and inferior en face anterior oblique (AO) field (n = 12), all 4 fields daily (n = 22), or a superior and inferior en face AO field only (n = 1). Patients were simulated in a supine position, immobilized in an alpha cradle with the thorax rotated 30 degrees to approximate an en face angle achieved with the AO fields. Toxicity was prospectively assessed using Common Terminology Criteria for Adverse Events version 4.0 (CTCAE v4.0) weekly during treatment and at 4 weeks following treatment completion.

Outcomes: Median follow-up was 3 months. A total of 34 women and 1 man were treated with adjuvant US PT for stage I (n = 1), II (n = 7), III (n = 27) LABC; 20 were left-sided, 12 were right-sided, and 3 were bilateral. Of the 25 postmastectomy patients, 14 were reconstructed. Initial fields were planned to 50.4 cobalt gray equivalent (CGE) (n = 33) or 45 CGE (n = 2), with 13 patients having a planned boost of 10 CGE (n = 9), 14 CGE (n = 1), 16 CGE (n = 1), and 20 CGE (n = 1). Median total dose received was 50.51 CGE (range: 45.11–70.36 CGE)

All patients experienced acute radiation dermatitis: grade 1 (n = 8), grade 2 (n = 26), and grade 3 (n = 3). Five patients required a break in treatment, and two patients did not complete their full course of prescribed PT due to skin toxicity. Also, 16 patients experienced grade 1 esophagitis, and 13 patients experienced grade 1 chest wall pain. Two patients experienced skin infection following treatment, requiring antibiotic treatment, which occurred the second week following treatment completion.

CONCLUSIONS: These early results demonstrate the feasibility of adjuvant breast cancer treatment with US PT on an IBL. Acute toxicity results appear acceptable. Longer follow-up is needed.

Proceedings of the 97th Annual Meeting of the American Radium Society - americanradiumsociety.org