RADT-03. A CASE OF PARTIAL HIPPOCAMPAL-AVOIDANCE WHOLE BRAIN RADIOTHERAPY IN A PATIENT WITH METASTATIC INFILTRATION OF THE LEFT HIPPOCAMPUS

Abstract In addition to surgical resection and systemic therapy, whole brain radiotherapy (WBRT) is a crucial modality in the treatment of cancers that have metastasized to the brain. It has been shown to improve intracranial disease control and overall survival. However, WBRT also increases the risk of radiation-associated damage to sensitive structures like the hippocampus, often resulting in neurocognitive dysfunction and decline. Hippocampal avoidance WBRT (HAWBRT) has been shown to reduce neurocognitive sequalae without worsening survival outcomes or increasing the risk of metastasis to the spared region compared to conventional WBRT. In cases where both hippocampi cannot be completely spared, the effectiveness of partial hippocampal avoidance on neurocognitive function and tumor control have been poorly described. We present the case of a patient diagnosed with triple negative invasive ductal carcinoma of the breast and disease metastatic to the brain, lung, bones, adrenal glands, and liver. Brain imaging revealed multiple brain metastases, two of which were noted near the left hippocampus. The patient underwent partial HAWBRT with complete avoidance of the right hippocampus and partial avoidance of the left. At 1-year follow-up, there was no evidence of metastasis in or near the partially spared left hippocampus. The patient’s neurocognitive functional status remained consistent with the findings of prospective randomized trials in which total bilateral hippocampal sparing was performed. To our knowledge, no such case has been presented in the literature. Further studies assessing the role of partial hippocampal avoidance in WBRT are needed.