Modified simultaneous integrated boost radiotherapy for large retroperitoneal malignant tumor: A case report.

The current study reports the case of a large retroperitoneal tumor treated with modified simultaneous integrated boost (SIB) radiotherapy. A 45-year-old female presented to the emergency department complaining of left abdominal pain and fever. A computed tomography scan detected a retroperitoneal tumor of 12×16×16 cm, and a biopsy revealed a poorly-differentiated adenocarcinoma. The patient was diagnosed with a large adenocarcinoma originating from the left ureter, with no distant metastasis. Due to the patient's poor physical condition, surgery was not recommended, and the patient was referred to the Department of Radiation Oncology (Yamagata University Hospital, Yamagata, Japan). Modified SIB radiotherapy was administered following the acquisition of written consent from the patient. The total irradiation dose to the center of the tumor and to the surrounding healthy tissue was ∼96 Gy/33 fractions and <60 Gy/33 fractions, respectively. At the end of the radiotherapeutic course, the tumor volume was reduced by ≥80%, and the residual tumor was surgically resected. As a result of the resection, a complete pathological response was confirmed; the patient has been recurrence-free for >3 years with no complications. Modified SIB radiotherapy may be safely administered, with favorable outcomes. Complete recovery can be achieved with this technique, even in a patient with a large radioresistant tumor.