Case report of ablative magnetic resonance-guided stereotactic body radiation therapy for oligometastatic mesenteric lymph nodes from bladder cancer

Abstract

: Several randomized trials have demonstrated that stereotactic body radiation therapy (SBRT) can significantly improve long-term clinical outcomes for patients with oligometastatic (OM) cancer, commonly defined as 1–5 metastatic lesions. Some lesions, especially those in the abdomen and pelvis, may not be appropriate candidates for receiving ablative dose if daily on-board computed tomography (CT) is used because of limited target lesion and normal anatomy visualization. Magnetic resonance imaging (MRI) inherently provides superior soft tissue delineation as compared to CT and only recently have MR-guided linear accelerators (LINACs) become commercially available. MR-LINACs can also perform daily online adaptive replanning based on the current day’s anatomy, further positioning this novel technology as a preferred means to safely deliver ablative dose, even to targets in anatomically challenging locations. Here we present the case of a 49-year-old man with bladder cancer who underwent cystectomy and developed metachronous disease in 2 mesenteric lymph nodes for which he received MR-guided SBRT with daily online adaptive replanning to a prescription dose of 50 Gy in 5 fractions. He achieved a significant radiographic response and did not experience significant treatment-related toxicity. We discuss unique advantages of MR guidance and novel applications, especially in the context of OM disease.