Transtympanic STS Against Cisplatin-induced SNHL: the SOUND Trial

The goal of this clinical trial is to learn if transtympanic sodium thiosulfate (STS) injections can prevent hearing loss caused by cisplatin chemotherapy in adults with head and neck cancer. The main question it aims to answer is: Researchers will compare the ear treated with STS gel to the untreated ear within the same patient to see if STS prevents hearing loss. Participants will: 1. Receive STS gel injections into the middle ear of one ear (randomized) within 3 hours before each cisplatin infusion (3-7 injections per patient). 2. Undergo hearing tests at baseline and 2-4 months after the last cisplatin treatment. 3. Complete questionnaires about hearing and tinnitus at baseline and 2-4 months after treatment.