Comparison of the efficacy and toxicity of postoperative proton versus carbon ion radiotherapy for head and neck cancers.

Background: To compare the efficacy and toxicity of adjuvant proton beam carbon-ion beam radiotherapy for head and neck cancers after radical resection and to explore the value of particle beam radiotherapy (PBRT) in postoperative radiotherapy for head and neck cancers.

Methods: Data from 38 head and neck cancer patients who received adjuvant PBRT after complete surgical resection at the Shanghai Proton and Heavy Ion Center (SPHIC) between October 2015 and March 2019 were retrospectively analyzed. In total, 18 patients received adjuvant proton beam therapy (54-60 GyE/27-30 fractions) and 20 received adjuvant carbon-ion radiotherapy (CIRT) (54-60 GyE/18-20 fractions). Survival rates were calculated using Kaplan-Meier analysis. Toxicity was evaluated according to the Common Terminology Criteria for Adverse Effects (version 4.03).

Results: With a median follow-up time of 21 (range, 3-45) months, the 2-year overall survival (OS), progression-free survival (PFS), local-regional recurrence-free survival (LRRFS) and distant metastasis-free survival (DMFS) rates were 93.3%, 87.4%, 94.1%, and 90.7%, respectively, for the entire cohort. The rates after proton beam therapy CIRT were 94.1% 91.7% (P=0.96), 88.1% 86.2% (P=0.96), 94.4% 93.3% (P=0.97), and 88.1% 92.9% (P=0.57), respectively. Furthermore, 16 of the 18 (88.9%) patients developed acute grade I/II dermatitis (13 grade I; 3 grade II) after proton beam therapy, and only 7 of the 20 (35%) patients developed acute grade I dermatitis after CIRT (P=0.001). The incidence of acute grade I/II mucositis and xerostomia in proton and carbon ion cases were 45% 55% (P=0.75) and 56% 50% (P=0.87) respectively.

Conclusions: Adjuvant proton beam therapy and CIRT after radical surgical resection for head and neck cancers provided satisfactory therapeutic effectiveness, but no significant difference was observed between the two radiotherapy technologies. However, adjuvant CIRT was associated with a more favorable acute toxicity profile as compared to proton beam therapy with significantly lower frequency and severity of acute dermatitis observed.