Effect of Thermoplastic Mask Cut-out on Radiation Dermatitis in Radiation Therapy for Early-Stage Glottic Cancer: Basic Assessment and Clinical Outcomes.

Abstract

Radiation dermatitis is among the most common adverse events associated with radiation therapy for early-stage glottic cancer. This study evaluated the effect of cutting out a portion of the thermoplastic mask overlapping with the irradiation field on surface dose and investigated its benefit in reducing radiation dermatitis in patients with early-stage glottic cancer. The surface dose on the anthropomorphic phantom with and without a thermoplastic mask was measured using Gafchromic EBT4 films (Ashland). The treatment plan was created with 2 opposed lateral fields, with a field size of 5.5 cm × 6.5 cm, and photon energies of 4 and 6 MV, produced by TrueBeam (Varian). For clinical investigation, we retrospectively reviewed patients with early-stage glottic cancer who received definitive radiation therapy between January 2008 and April 2024 at our institution. The inclusion criteria were clinical stages I and II, total irradiation dose of 60 Gy or more, and a 2-opposed lateral field technique employed for radiation therapy delivery. The incidence of radiation dermatitis in grades ≥2 and ≤1 was compared by age, clinical stage, radiation therapy fractionation, total dose, and cut-out thermoplastic mask using Fisher's exact test. P values less than .05 were considered statistically significant. The percentage increase in the surface dose by a thermoplastic mask was 47.1% for 4 MV and 59.4% for 6 MV. Fifty-nine patients were included in the clinical investigation. For the incidence of ≥grade 2 dermatitis, the only significant factor was the cut-out thermoplastic mask (41.7% with cut-out thermoplastic mask vs 74.5% without, P = .042). Cutting out the thermoplastic mask over the irradiation field reduced the surface dose by eliminating the bolus effect, thereby mitigating radiation dermatitis in patients with early-stage glottic cancer.