Cochlea sparing optimized radiotherapy for nasopharyngeal carcinoma

Abstract

Background Definitive chemoradiotherapy (CRT) is standard of care for nasopharyngeal carcinoma. Due to the tumor localization and concomitant platinum-based chemotherapy, hearing impairment is a frequent complication, without defined dose-threshold. In this study, we aimed to achieve the maximum possible cochleae sparing. Materials and methods Treatment plans of 20 patients, treated with CRT (6 IMRT and 14 VMAT) based on the QUANTEC organs-at-risk constraints were investigated. The cochleae were re-delineated independently by two radiation oncologists, whereas target volumes and other organs at risk (OARs) were not changed. The initial plans, aiming to a mean cochlea dose < 45 Gy, were re-optimized with VMAT, using 2–2.5 arcs without compromising the dose coverage of the target volume. Mean cochlea dose, PTV coverage, Homogeneity Index, Conformity Index and dose to other OAR were compared to the reference plans. Wilcoxon signed-rank test was used to evaluate differences, a p value < 0.05 was considered significant. Results The re-optimized plans achieved a statistically significant lower dose for both cochleae (median dose for left and right 14.97 Gy and 18.47 Gy vs. 24.09 Gy and 26.05 Gy respectively, p < 0.001) compared to the reference plans, without compromising other plan quality parameters. The median NTCP for tinnitus of the most exposed sites was 11.3% (range 3.52–91.1%) for the original plans, compared to 4.60% (range 1.46–90.1%) for the re-optimized plans (p < 0.001). For hearing loss, the median NTCP of the most exposed sites could be improved from 0.03% (range 0–99.0%) to 0.00% (range 0–98.5%, p < 0.001). Conclusions A significantly improved cochlea sparing beyond current QUANTEC constraints is feasible without compromising the PTV dose coverage in nasopharyngeal carcinoma patients treated with VMAT. As there appears to be no threshold for hearing toxicity after CRT, this should be considered for future treatment planning.

Definition of an Normal Tissue Complication Probability Model for the Inner Ear in Definitive Radiochemotherapy of Nasopharynx Carcinoma

“…In the plan-study by Lamaj et al, irradiation plans were optimized retrospectively to reduce the dose for both cochlea without affecting PTV and other values. A mean dose of (left) and (right) could be achieved with VMAT which was significantly lower as in the previous plans with (left) and (right) [ 31 ].…”

Head and Neck Cancer: United Kingdom National Multidisciplinary Guidelines, Sixth Edition

“…679,680 Even with these modern advancements in RT techniques, in the context of NPC, it is hard to limit the radiation dose to the cochlea to less than 15 Gy. 681 As a consequence, some authors have advocated pre-treatment risk stratification to try and identify patients who are at high risk of developing ototoxicity, so patients can be appropriately counselled and RT planning tailored. 682,683 Increasing age, cochlear dose, the addition of cisplatin and poor pre-existing hearing have all been identified as risk factors for developing clinically significant ototoxicity following RT.…”

Current Radiotherapy Considerations for Nasopharyngeal Carcinoma

“…However, this threshold should not be viewed as risk-free, as the hearing impairment rate is still up to 30% for plans in which this criterion is fulfilled [ 51 ]. To achieve better cochlea-sparing, special optimization procedures with volumetric arc therapy may be considered [ 52 , 53 , 54 ]. By combining jaw closure, jaw tracking, a modification of the beam angle and a reordering of structure priority, mean cochlea doses could be significantly reduced as opposed to conventional planning without compromising PTV coverage, even in situations of advanced tumors with gross invasion to the petrous bone.…”