Abstract
Desmoplastic small round cell tumor (DSRCT) is a rare and highly aggressive soft tissue tumor that predominantly affects the abdominal and pelvic regions of adolescent males. This case report presents our clinical experience of treating a 33-year-old male with multifocal peritoneal DSRCT using fan beam computed tomography-guided adaptive radiotherapy (FBCT-gART). The patient presented with abdominal pain and was diagnosed with DSRCT following imaging and biopsy. Despite initial treatment with surgery, chemotherapy, and targeted therapy, the patient experienced multifocal peritoneal recurrence. Due to the considerable mobility of the abdominal tumors and the associated risks to adjacent critical organs, the patient underwent daily online FBCT-gART. The prescribed dose regimen was 54 Gy delivered in 27 fractions at 2 Gy per fraction; however, the patient ultimately received only 25 treatments for personal reasons. This case report evaluates the technical workflow of using FBCT-gART for DSRCT and discusses its dosimetric advantages over non-adaptive radiotherapy.