The Tokai Study Group for Therapeutic Radiology and Oncology (TOSTRO) started managing T1 glottic cancer using 2.25 Gy/fraction radiotherapy in 2011. The aim was to evaluate the local control (LC) rate and toxicity with 2.25-Gy radiotherapy in clinical practice and identify prognostic factors.The eligibility criteria were T1 glottic squamous cell carcinoma patients with age ≥20 years, treated with 2.25 Gy/fraction without chemotherapy between 2011 and 2017. LC rates were evaluated based on age, performance status, sex, T-category, tumor type (ulcerative or non-ulcerative), presence of anterior commissure invasion, tumor size, X-ray beam energy, and overall treatment time. Acute and late adverse events were evaluated using CTCAE version 4.0. A total of 202 patients were enrolled. The median follow-up period was 34.2 months. The 2- and 4-year LC rates were 93.8% and 93.1%, respectively. There was a significant difference in the LC rate between non-ulcerative type and ulcerative type (95.2% vs. 74.1% at 2 years, 94.4% vs. 74.1% at 4 years; p = 0.01). On univariate analysis, only tumor type was significantly correlated with a poor LC rate (hazard ratio 4.3; 95% confidence interval 1.2-15.4; p = 0.03). Acute grade 3 adverse events occurred in 17 patients. However, no late adverse events of grade 3 or higher have occurred to date. T1 glottic cancer treatment outcomes using hypofractionated radiotherapy with 2.25 Gy/fraction in clinical practice were comparable to previously reported results. However, ulcerative type tumor was associated with a poor LC rate.
Keywords: 2.25 Gy; T1 glottic cancer; hypofractionated radiotherapy; ulcerative tumor type.