Early toxicity in patients treated with postoperative proton therapy for locally advanced breast cancer

Abstract

Purpose: To report dosimetry and early toxicity data in breast cancer patients treated with postoperative proton radiation therapy.

Methods and materials: From March 2013 to April 2014, 30 patients with nonmetastatic breast cancer and no history of prior radiation were treated with proton therapy at a single proton center. Patient characteristics and dosimetry were obtained through chart review. Patients were seen weekly while on treatment, at 1 month after radiation therapy completion, and at 3- to 6-month intervals thereafter. Toxicity was scored using Common Terminology Criteria for Adverse Events version 4.0. Frequencies of toxicities were tabulated.

Results: Median dose delivered was 50.4 Gy (relative biological equivalent [RBE]) in 5 weeks. Target volumes included the breast/chest wall and regional lymph nodes including the internal mammary lymph nodes (in 93%). No patients required a treatment break. Among patients with >3 months of follow-up (n=28), grade 2 dermatitis occurred in 20 patients (71.4%), with 8 (28.6%) experiencing moist desquamation. Grade 2 esophagitis occurred in 8 patients (28.6%). Grade 3 reconstructive complications occurred in 1 patient. The median planning target volume V95 was 96.43% (range, 79.39%-99.60%). The median mean heart dose was 0.88 Gy (RBE) [range, 0.01-3.20 Gy (RBE)] for all patients, and 1.00 Gy (RBE) among patients with left-sided tumors. The median V20 of the ipsilateral lung was 16.50% (range, 6.1%-30.3%). The median contralateral lung V5 was 0.34% (range, 0%-5.30%). The median maximal point dose to the esophagus was 45.65 Gy (RBE) [range, 0-65.4 Gy (RBE)]. The median contralateral breast mean dose was 0.29 Gy (RBE) [range, 0.03-3.50 Gy (RBE)].

Conclusions: Postoperative proton therapy is well tolerated, with acceptable rates of skin toxicity. Proton therapy favorably spares normal tissue without compromising target coverage. Further follow-up is necessary to assess for clinical outcomes and cardiopulmonary toxicities.

Fig. 1

Lymph node groups were contoured per Radiation Therapy Oncology Group guidelines (A), with the exception of the posterior portion of the supraclavicular fossa (red arrowheads), which were included in the clinical target volume (B; red color wash) and planning target volume (B; yellow color wash).

Fig. 2

(A) The initial Proton Collaborative Group protocol included the clinical target volume contoured to the edge of the esophagus, with expansion causing planning target volume (red color wash) overlap with the esophagus (yellow color wash). (B) The protocol was later modified to minimize planning target volume expansion and overlap around the esophagus.

Fig. 3

(A) A typical beam arrangement used to treat the unreconstructed chest wall and regional lymph nodes. (B) Feathered junction with the match line shift superiorly by 1 cm for the same patient as in (A).

Fig. 4

Representative dose distribution demonstrating full coverage of (A) internal mammary lymph nodes and (B) heart sparing of a patient treated with postmastectomy proton radiation to the left reconstructed chest wall, axilla, supraclavicular fossa, and internal mammary lymph nodes. (C) Dose–volume histogram.

Fig. 5

Skin reactions of patients undergoing proton therapy to the chest wall and regional nodes after mastectomy without reconstruction (top row) and after lumpectomy (bottom row). (A, D) Baseline. (B, E) End of radiation therapy (RT). (C, F) One month follow-up after radiation therapy.