Efficacy of Botox Injection of the Masticatory Muscles in Head &Neck Cancer Patients with Trismus After Radiotherapy

This study is testing whether injecting Botox (botulinum toxin) into the jaw muscles can help head and neck cancer patients who developed trismus — difficulty opening their mouth — as a side effect of radiation therapy. **You may be eligible if...** - You are over 18 years old - You are a head and neck cancer patient who finished radiation therapy at least 3 months ago - You can open your mouth less than 3.5 cm wide and experience tightness or pain in your jaw muscles - Your cancer is not currently active (stable medical condition) **You may NOT be eligible if...** - You have had surgery on your jaw muscles - Your jaw muscles are severely wasted or completely scarred - Your cancer has come back - Your vital signs are unstable Talk to your doctor to see if this trial is right for you.