Proton beam radiation therapy results in significantly reduced toxicity compared with intensity-modulated radiation therapy for head and neck tumors that require ipsilateral radiation.

BACKGROUND: As proton beam radiation therapy (PBRT) may allow greater normal tissue sparing when compared with intensity-modulated radiation therapy (IMRT), we compared the dosimetry and treatment-related toxicities between patients treated to the ipsilateral head and neck with either PBRT or IMRT.
METHODS: Between 01/2011 and 03/2014, 41 consecutive patients underwent ipsilateral irradiation for major salivary gland cancer or cutaneous squamous cell carcinoma. The availability of PBRT, during this period, resulted in an immediate shift in practice from IMRT to PBRT, without any change in target delineation. Acute toxicities were assessed using the National Cancer Institute Common Terminology Criteria for Adverse Events version 4.0.
RESULTS: Twenty-three (56.1%) patients were treated with IMRT and 18 (43.9%) with PBRT. The groups were balanced in terms of baseline, treatment, and target volume characteristics. IMRT plans had a greater median maximum brainstem (29.7 Gy vs. 0.62 Gy (RBE), ​P < 0.001), maximum spinal cord (36.3 Gy vs. 1.88 Gy (RBE), ​P < 0.001), mean oral cavity (20.6 Gy vs. 0.94 Gy (RBE), ​P < 0.001), mean contralateral parotid (1.4 Gy vs. 0.0 Gy (RBE), P<0.001), and mean contralateral submandibular (4.1 Gy vs. 0.0 Gy (RBE), ​P < 0.001) dose when compared to PBRT plans. PBRT had significantly lower rates of grade 2 or greater acute dysgeusia (5.6% vs. 65.2%, P<0.001), mucositis (16.7% vs. 52.2%, P=0.019), and nausea (11.1% vs. 56.5%, P=0.003).
CONCLUSIONS: The unique properties of PBRT allow greater normal tissue sparing without sacrificing target coverage when irradiating the ipsilateral head and neck. This dosimetric advantage seemingly translates into lower rates of acute treatment-related toxicity.