2778 - Decreased Radiation Dose to Oral Tongue with Tongue-Out Radiotherapy Compared to Non Tongue-Out Radiotherapy for Head and Neck Cancer

Purpose/Objective(s): Altered taste (dysgeusia) is a common radiotherapy (RT)-related toxicity of head and neck cancer (HNC) and reportedly associated with radiation dose to oral tongue (OT). Authors report decreased radiation dose to OT with tongue-out RT (TORT) compared to non-TORT for HNC.

Materials/Methods: For dosimetric comparison, authors contoured virtual T2N0 and T2N2 cancer in nasopharynx, tonsil, base of tongue (BOT), epiglottis, and hypopharynx, respectively, on the two sets of CT-simulation scan with and without tongue-out from two HNC patients (case1: neck node negative; case2: multiple neck nodes positive). High-risk clinical target volume (CTV_High) was defined gross tumor + 5-10 mm. Intermediate-risk CTV (CTV_Int) comprised CTV_High and area at risk for microscopic disease. Low-risk CTV (CTV_Low) included elective nodal stations. Planning target volume (PTV) was CTV + 3 mm. Volumetric modulated arc therapy (VMAT) technique was used for planning with prescription of 70, 63, and 56 Gy in 35 fractions to PTV_High, PTV_Int, and PTV_Low, respectively. Oral tongue was defined from the tip of tongue to circumvallate papillae. Planning objectives required PTV coverage to 95-110%. Radiation dose constraints for OAR followed published recommendations. Student’s t test was used for statistical comparison. A probability level of p < 0.05 was considered significant.

Results: Total of 20 plans (10 TORT and 10 non-TORT) were created. For all virtual primary sites, TORT reduced the mean dose (D_mean) to OT by 24% compared to non-TORT (22.7 vs 29.8 Gy, respectively, p<0.05); OT volume receiving = 30 Gy (V₃₀) by 60% (17.5% vs 44.1%, respectively, p<0.05). For node negative cases, D_mean and V₃₀ to OT was 28 Gy and 23.6% with non-TORT and 21 Gy and 13.1% with TORT (25% and 44% reduction, respectively, all p<0.05). For node positive cases, D_mean and V₃₀ to OT was 32.5 Gy and 64.5% with non-TORT and 24.4 Gy and 21.9% with TORT (25% and 66% reduction, respectively, all p<0.05). In BOT cases, D_mean to OT was lower with TORT (35 Gy) than non-TORT (42 Gy) (p=0.1); V₃₀ to OT was 50% with TORT vs 74.4% with non-TORT, p<0.05. For other primary sites, D_mean was 19 vs 26 Gy; V₃₀ was 7.5% vs 34.1% (TORT vs non-TORT, respectively, all p<0.05).

Conclusion: This study demonstrated significantly lower radiation dose to OT with TORT than non-TORT in all virtual primary HNC regardless of neck nodal status. Those dosimetric advantage with TORT suggests clinical implication for minimizing post-RT dysgeusia in patients with HNC. These findings, along with our retrospective experience, have prompted current efforts to gather prospective patient data with TORT for HNC.