Proton beam therapy for external auditory canal and middle ear cancers

Few studies have evaluated the efficacy of proton beam therapy (PBT) for external auditory canal cancer (EACC) or middle ear cancer (MEC). Therefore, the present study aimed to evaluate the efficacy and toxicity of PBT for EACC and MEC. Between December 2009 and August 2018, 15 patients (seven males and eight females) underwent PBT for EACC or MEC. The median patient age was 64 years (range: 40-82 years). Ten patients had EACC, and five patients had MEC. PBT was administered using the passive scattering method. The median total dose of the BED10 was 88.8 Gy relative biological effectiveness (RBE) (range = 85.6-99.3 Gy [RBE]), administered in 2 Gy fractions (EQD2) (α/β = 10). Chemotherapy was conducted in 14 patients, systemic chemotherapy in five and intra-arterial infusion chemotherapy in nine. The median follow-up period for all patients was 60 months (range: 7-136 months). The 3-year overall survival, local control and progression free survival rates were 65%, 66.7% and 53.3%, respectively. Four patients had grade 3 hearing impairment owing to late toxicity. However, these patients had hearing impairment before treatment as well. No grade 4 or higher late toxicity was observed during the follow-up period. PBT is an effective treatment for EACC and MEC with tolerable toxicity, including in the setting of combined chemotherapy.