Radiation-induced Parotid Gland Atrophy in Patients with Head and Neck Cancer After Carbon-ion Radiotherapy.

BACKGROUND/AIM This study aimed to clarify the relationship between dosimetric factors and parotid gland (PG) atrophy after carbon ion radiotherapy (C-ion RT). PATIENTS AND METHODS Fifty-four patients with head and neck tumours were enrolled and 93 irradiated PGs were analyzed. Thirty and 24 patients were treated with total doses [relative biological effectiveness (RBE)] of 57.6 Gy and 64.0 Gy, respectively, in 16 fractions. PG volumes were measured using computed tomographic images obtained before C-ion RT and every 3-6 months thereafter. RESULTS The median follow-up period was 46.4 months (range=24.0-123.0 months). Univariate analysis showed that PG volumes receiving more than 5, 10, 15, and 20 Gy RBE (V5, V10, V15 and V20, respectively), mean dose, and maximum dose were significantly associated with PG atrophy. Multivariate analysis indicated that only V5 was significantly associated with atrophy. CONCLUSION Increasing V5 was a significant risk factor for PG atrophy after C-ion RT.