Stereotactic Radiation Therapy in 3 Fractions for T1 Glottic Cancer

Abstract

To report the results of a phase I-II study on SBRT for early glottic cancer. This a prospective study at a single Institution enrolling patients with T1 glottic cancer. The true vocal cords (TVC) were divided into thirds and the third(s) containing disease prescribed 36 Gy in 3 fractions. The portions of the TVCs next to the involved one were planned to receive 30 Gy in 3 fxs. SBRT was delivered by a LINAC-based approach using multiple arcs. Toxicity was scored by CTCAE and late events were considered those occurring 3 months after SBRT. Voice quality was investigated by the voice handicap index (VHI) at regular intervals. The planned sample size was 75 patients. Accrual was discontinued after 33 patients due to concerns for late toxicity. T stage was as follows: T1a: 23 pts (69.7%); T1b: 10 pts (30.3%). All patients received the planned treatment and the median follow-up time is 51.5 months (IQR: 47.9-61.0 months). At last follow up, all patients are alive and without evidence of disease but two patients who died for intercurrent causes. The local control rate is 100% at 4 yrs. Six patients (18.2%) developed soft tissue necrosis (N=4) or cartilage necrosis (N=2) after a median time of 14.9 months from SBRT. Five out of 6 necrotic events were observed in patients who kept smoking and/or had a recent COVID infection. All 4 soft tissue events healed with conservative therapy. After an initial deterioration the average VHI score significantly improved at 6 months over baseline. SBRT to 36 Gy in 3 fractions is highly effective in controlling T1 TVC carcinoma, but necrosis, though mostly transient, is a concern. Based on the present results, a reduction in total dose as well as a more accurate patient selection are warranted.