OA073] A prospective study of dose–response relationship and NTCP of conductive hearing loss in patients undergoing head and neck radiotherapy

Abstract

Purpose Head-and-neck (H&N) radiotherapy may cause hearing loss. Despite its negative effects on patients’ quality of life, little has been published on the dose–response relationship and normal tissue complication probability (NTCP) of the conductive subtype of hearing loss. The goals of this study were: (i) to observe the incidence of hearing loss in patients undergoing non-intensity-modulated H&N radiotherapy, (ii) to obtain the relationship between dose and conductive hearing loss, (iii) to test the current parameters of the Lyman-Kutcher-Burman (LKB) radiobiological model for estimating its NTCP, and (iv) to assess the need for considering the dose to middle and external ear as organ-at-risk when optimizing treatment plans. Methods In this prospective study, the dose–response relationship in the auditory system of 35 patients (70 ears) undergoing 3D conformal H&N radiotherapy was studied using the physical parameter of mean dose as well as the LKB NTCP model (with parameters TD50 = 40 Gy, M = 0.15, n = 0.10) calculated by BioSuite software. In order to include a wider dose range, the study was conducted at a clinic where, at the time, more advanced treatment delivery techniques were unavailable. The patients underwent routine external-beam megavoltage X-ray treatments following 3D treatment planning involving dose calculation using collapsed-cone convolution superposition. Prescribed doses were in the range 30–72 Gy, delivered 1.8–2.0 Gy per fraction. Hearing status was evaluated by pure tone audiometry one day before the start and one and three months after the end of the radiotherapy course. Results Nineteen ears (27%) suffered hearing loss. Sixteen ears (23%) had conductive hearing loss and 3 ears (4%) the sensorineural subtype (p 0.05). An approximately 40 Gy mean dose to the middle-ear planning organ-at-risk volume was predicted by the LKB NTCP model to cause a 50% risk of conductive hearing loss, which was also observed in the studied patients. Conclusions Incidence of conductive hearing loss in typical 3D conformal H&N radiotherapy can be significant. This suggests that the auditory system should also be considered in treatment plan optimization. The LKB model parameters provided a reasonably accurate NTCP. However, a study is underway to optimize its parameters.