49 a Retrospective Study of Hearing Outcomes for Pediatric Patients Treated Wproton Beam Therapy (Pbt) in British Columbia (Bc)

INTRODUCTION PBT is an important treatment for pediatric solid and central nervous system (CNS) tumours, minimizing off-target radiation compared to photon therapy. However, critical structures like the cochlea and vestibular organ may still undergo radiation exposure. This study examines auditory function before and after PBT in pediatric cancer patients in BC over 20 years. METHODS Medical records from BC Children’s Hospital were reviewed for patients diagnosed with cancer at age <=20 years between 2001-2021, who were treated with curative-intent PBT and received audiology assessments. Auditory function at three time points (baseline, end of therapy, and most recent follow-up) was analyzed using Fisher’s and Wilcoxon rank sum exact tests. Sensorineural hearing loss (SNHL) probability was estimated using the Kaplan-Meier method. RESULTS Among 49 children (55.1% male), 77.6% had CNS tumours, primarily ependymoma (31.6%) and intracranial germ cell tumours (23.7%). Median ages at diagnosis and PBT initiation were 8.8 and 9.4 years, respectively. 56.5% developed SNHL following treatment, with early PBT (p=0.046) or platinum-based chemotherapy (p=0.019) before age five increasing risk. Frequencies >2000 Hz were most affected, with most cases (45% left ears, 52% right ears) classified as grade 1 hearing loss per SIOP Boston criteria. One-year SNHL probability was 43.5%. CONCLUSIONS Children receiving PBT still suffer from SNHL, especially in those receiving PBT and platinum-therapy before age five. SNHL may impact speech and language development in this age group. Regular audiology management is warranted in all children receiving treatment. Other risk factors for ototoxicity, including genetic susceptibility, will be explored further.