Topical Diclofenac for Prevention of Radiation-induced Dermatitis

This study is testing whether applying a topical diclofenac gel (an anti-inflammatory medicine) to the skin during radiation therapy can prevent or reduce radiation dermatitis — the painful, red, burned skin reaction that many cancer patients experience during radiation treatment. **You may be eligible if...** - You are 18 or older - You have head and neck cancer (oropharynx, nasopharynx, larynx, hypopharynx, or salivary glands) or breast cancer - You are planned to receive at least 50 Gy of radiation - Your skin in the treatment area is healthy with no current irritation - Your blood counts and organ function are within acceptable ranges **You may NOT be eligible if...** - You have had prior radiation therapy that causes significant scarring or skin changes in the treatment area - You have a known allergy to diclofenac or NSAIDs - Your blood counts or organ function do not meet minimum requirements Talk to your doctor to see if this trial is right for you.