Dose de-escalation to the normal larynx using conformal radiotherapy reduces toxicity while maintaining oncologic outcome for T1/T2 glottic cancer

Abstract

We evaluated the efficacy of dose de-escalation to the normal larynx using conformal radiotherapy (CRT) for T1/T2 glottic cancer. For conventional RT (2DRT, n = 38), the laryngeal box received a median equivalent dose in 2 Gy fractions (EQD2) of 66 Gy. For CRT (n = 42; 3D-CRT, 20; intensity-modulated RT, 22), clinical target volume (CTV)1 (gross tumor with a 3-mm margin) and CTV2 (laryngeal box) received median EQD2s of 66.6 Gy and 52.2 Gy, respectively. With a 71-month median follow-up, five-year local control and overall survival rates for 2DRT vs. CRT were 88.1% vs. 95.1% (p = 0.405) and 94.7% vs. 90.7% (p = 0.102), respectively. Grade 2 and 3 pharyngitis rates were 52.6% and 5.3% for 2DRT vs. 35.7% and 2.4% for CRT (p = 0.121). Grade 2 and 3 dermatitis rates were 42.1% and 2.6% for 2DRT vs. 35.7% and 0% for CRT (p = 0.013). The maximum phonation time increased from 12.1 ± 7.1 to 14.0 ± 6.6 seconds after 2DRT (p = 0.375) and from 12.0 ± 5.5 to 13.8 ± 10.1 seconds after CRT (p = 0.313). Fundamental frequency decreased from 150.6 ± 40.3 to 121.9 ± 30.2 Hz after 2DRT (p = 0.039) and from 138.5 ± 31.9 to 126.1 ± 23.7 Hz after CRT (p = 0.058). CRT can effectively de-escalate the normal larynx dose while maintaining oncologic outcome and voice quality.