Background: Mycosis fungoides (MF) represents the most common cutaneous T-cell lymphoma and approximately 4% of non-Hodgkin lymphomas. Treatment of skin lesions includes external beam radiation therapy which often provides adequate local control and symptom relief. Case presentation: A 39-year-old male with the diagnosis of MF presents with infiltrative and pruriginous plaques comprising the plantar, interdigital, lateral and posterior surfaces of the foot. A protocol using a water tank was used to provide uniform coverage to an irregular target volume. By creating a tissue-equivalent and homogenous bolus material a total dose of 8Gy in 2 fractions of photon-beam therapy was prescribed. After one month of treatment there was a partial response with minimal toxicity, achieving complete response in most lesions after six months. Conclusion: Photon-beam therapy for irregular surfaces such as extremities is a valid alternative to conventional electron-beam radiation by attaining uniform coverage while minimizing hotspots. Treatment utilizing a water tank is well-tolerated and has good clinical outcomes even in the presence of extensive skin lesions.

Keywords: Case report, radiation therapy, mycosis fungoides, irregular surface, water tank, tissue compensation.