(P086) Proton vs Photon/Electron-Based Therapy in the Treatment of Pediatric Salivary Gland Tumors: A Comparison of Dosimetric Data and Acute Toxicities

April 30, 2015

This report of adjuvant RT for pediatric salivary gland tumors is one of the largest to date and the only one to document outcomes following proton therapy. Compared with conventional photon/electron-based therapy, proton therapy significantly reduced doses to multiple normal tissues. Moreover, clinically, no grade 3 toxicities were observed in the proton group vs 45% in the photon/electron cohort. Continued follow-up is required to determine long-term outcomes.

Stephen R. Grant, BS, David R. Grosshans, MD, PhD, Anita Mahajan, MD; Baylor College of Medicine; Department of Radiation Oncology, UT MD Anderson Cancer

PURPOSE: Adjuvant radiotherapy (RT) is frequently indicated for high-risk salivary gland tumors. For pediatric patients, minimizing radiation to surrounding normal tissues is of particular importance. We retrospectively compared clinical outcomes and toxicity profiles for pediatric patients with parotid and submandibular tumors treated with either adjuvant proton- or photon/electron-based RT.

MATERIALS AND METHODS: We retrospectively identified all patients aged ≤ 18 years treated with radiation for salivary gland tumors between 1996 and 2014 at our institution. Demographic, disease-control, and survival data were recorded, and dosimetric data were compiled. Toxicities were scored according to National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events version 4.0 (CTCAE 4.0) criteria. Statistical analyses were performed using GraphPad Prism, with two-sided t-tests determined to be significant when P < .05.

RESULTS: A total of 24 pediatric patients treated with adjuvant RT were identified (20 parotid, 4 submandibular). Histologies included mucoepidermoid carcinoma (12), adenoid cystic carcinoma (5), adenocarcinoma (2), acinic cell carcinoma (2), myoepithelioma (1), undifferentiated carcinoma (1), and pleomorphic adenoma (1). A total of 13 patients received proton therapy, and 11 received photon/electron-based therapy. The mean prescribed dose was 60 Gy in each cohort (range: 54–66 Gy). No acute grade 3 dermatitis or mucositis was seen in the proton cohort vs 27% and 18% in the photon/electron cohort, respectively. Significantly greater weight loss was reported in those receiving photon/electron radiotherapy (median 5.2% vs 0%), with one patient requiring placement of a feeding tube (compared with none in the proton cohort). With a mean follow-up of 49 months (range: 2 mo–18 yr), no disease recurrence or deaths were observed in either cohort. Compared with photon/electron-based therapy, proton therapy was associated with significantly lower mean doses to the spinal cord (0.2 Gy vs 19 Gy), pituitary gland (0.0 Gy vs 5.7 Gy), optic nerves (0.0 Gy vs 3 Gy), oral cavity (4.6 Gy vs 19 Gy), thyroid gland (1.5 Gy vs 24 Gy), larynx (11 Gy vs 39 Gy), and contralateral structures, including the eye (0.0 Gy vs 1.4 Gy), mandible (0.0 Gy vs 7.7 Gy), and parotid (0.0 Gy vs 5.2 Gy) and submandibular glands (0.0 Gy vs 8.1 Gy) (all P < .05).

CONCLUSION: This report of adjuvant RT for pediatric salivary gland tumors is one of the largest to date and the only one to document outcomes following proton therapy. Compared with conventional photon/electron-based therapy, proton therapy significantly reduced doses to multiple normal tissues. Moreover, clinically, no grade 3 toxicities were observed in the proton group vs 45% in the photon/electron cohort. Continued follow-up is required to determine long-term outcomes. 

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