Adaptive Stereotactic Body Radiation Therapy in the Management of Oligometastatic Uterine Leiomyosarcoma: A Clinical Case Report.

Safe delivery of stereotactic body radiation therapy (SBRT) to large (>5 cm) oligometastatic abdominopelvic tumors can often be challenging, especially in tumors that require a higher biologically effective dose (BED) for tumor control. Adaptive stereotactic body radiation therapy (A-SBRT) involves inter-fraction and real-time replanning while the patient is on the treatment table, potentially allowing for improved dose coverage and greater sparing of critical structures. Our case report illustrates the benefit of CT-based A-SBRT in the treatment and management of an oligometastatic uterine leiomyosarcoma patient with a rapidly enlarging pelvic recurrence. A 60-year-old female presented to the radiation oncology clinic for treatment of an enlarging, right pelvic oligometastatic leiomyosarcoma. She was prescribed 35 Gy in five fractions. Planning prioritized the sparing of nearby small bowels while maximizing coverage of the planning target volume (PTV). On treatment day, two plans were calculated, the initial plan recalculated on the current CBCT (scheduled plan) and a plan reoptimized using current contours (adapted plan), and the more appropriate one was chosen for delivery. The adapted plan was chosen for all five fractions, with the adapted plan offering better small bowel sparing in five fractions and better target coverage in four fractions, delivering a total of 34 Gy to 95% of the PTV while limiting the small bowel to a maximum point dose of 37 Gy. At approximately six months out from treatment, the patient showed continued radiographic response and resolved acute Grade 1 gastrointestinal toxicity. This case study therefore demonstrates the successful treatment of a large oligometastatic abdominopelvic tumor using CT-based A-SBRT and builds on previous experience treating abdominal cases adaptively.