Single-Isocenter, Multiple-Target Abdominal Cone-Beam Computed Tomography (CBCT)-Guided Online Adaptive Stereotactic Body Radiotherapy (SBRT).

Stereotactic body radiotherapy (SBRT) is increasingly being prescribed for treating patients with multiple metastases, especially in the setting of oligometastatic disease. Treating multiple targets presents unique challenges in radiotherapy planning and delivery, including practical considerations relating to treatment time, resource allocation, and treatment planning complexity. Treating targets in a common isocenter reduces the time required for treatment and simplifies planning, but historically, it has often not been feasible due to inter- and intra-fractional variation in relative target positions. With online adaptation, individual targets can be re-contoured on each treatment fraction to obviate inter-fractional variation, and with appropriate margin selection intra-fractional motion can be managed. In this case report, we describe single-isocenter, multiple-target treatment via online adaptation of a 93-year-old man with a history of metastatic hepatocellular carcinoma. He initially presented with a 9.1 cm liver mass, suspicious lung lesions, and an enlarged porta hepatis lymph node, which were biopsy proven to be hepatocellular carcinoma. Following 18 months of systemic immunotherapy, he demonstrated a favorable response, including a reduction in primary liver mass to 5.1 cm and resolution of pulmonary lesions; however, recent serial imaging demonstrated oligoprogression of two peripancreatic lymph node conglomerates that were biopsy proven to be poorly differentiated carcinoma. The patient was offered adaptive SBRT to a dose of 35-40 Gy in five fractions as a consolidative approach for treating both the primary liver mass and oligoprogressive lymph nodes. He tolerated treatment without any grade 2 or higher acute toxicity and had stable disease on three-month post-treatment imaging. By leveraging online adaptation, especially for the daily re-definition of target volumes, we were able to treat three targets in the abdomen accurately in a common isocenter. Treating in this manner vastly shortened and simplified the patient's radiation course. Quantitative evaluation of re-contoured targets and post-treatment imaging highlighted the value of online adaption with careful margin specification and alignment instructions.