There are many causes for Ototoxicity, mostly medication induced, and by chemo, mostly platinum based, like Cisplatin, and this is called, Cochlearotoxicity, which can either be reversable, temporary or permament, and is dose dependant, meaning it depends on the dosage of Cisplatin you received, and it's found this occurs in high doses, above 60 mg, instead of lower doses weekly. The Cisplatin is absorbed in the cochlear's sound detecting hearing cells, and damages them, being chemo destroys fast acting cells like hair, nails, nerves, etc. Toxicities also depend on the speed of infusion, and duration of exposure. Also factoring in is any prior hearing problems, underlying medical conditions, like diabetes, that can cause tinnitus, and increase the risk. Tell your doctor, and they can regulate the dosage, stop it or change to another, so not to make this adverse effect permament. You should have a hearing test, prefably before treatment, during, and after to monitor any changes.

While on the subject, chemo can also cause Ocular Toxicity, which can lead to damage to the eyes, especially the optic nerve, leading to blurred vision, perpiheal loss, and even blindess, especially with Cisplatin, other platinum based drugs, taxanes, 5-FU, and others, so if you have any vision changes to tell your doctor, and should have an eye exam too. I'm blind in one eye from chemo.

I hope this helps