The Use of Adaptive Radiation in a Retroperitoneal Seminoma Patient with Poor Candidacy for Chemotherapy: A Teaching Case

Abstract Testicular cancers are a common etiology for painless testicular masses occurring in young adult males between the ages of 20 and 34, with 50% diagnosed as seminomas. Seminomas are a malignant germ-cell tumor most commonly confined to the testicles with less frequent de novo involvement of structures outside of the seminiferous tubules. Radiation therapy (RT) has historically been indicated for patients with stage 1-2 seminoma, but its use is declining due to increased uptake of surveillance and modern chemotherapy. However, seminoma is a radiosensitive tumor, and RT may play a role in select cases. This case report describes a nontypical presentation of a large IIC retroperitoneal seminoma measuring 15 cm in an older patient who was a suboptimal candidate for chemotherapy. He was treated with an online adaptive external-beam radiation platform, leading to a significant reduction in body and bowel dose compared with standard-of-care radiation treatment. Clinical regression of tumor was achieved while sparing exposure to significant volumes of bowel and healthy pelvic tissue. The patient had an uneventful recovery and showed no signs of radiation dermatitis or gastrointestinal toxicity.