RADT-49. A SYSTEMATIC REVIEW AND META-ANALYSIS OF HIPPOCAMPAL AVOIDANCE IN WHOLE BRAIN RADIOTHERAPY AND PROPHYLACTIC CRANIAL IRRADIATION

Abstract PURPOSE: Hippocampal-avoidance radiotherapy has been under investigation as a technique to improve neurocognitive function in patients undergoing whole brain radiotherapy (WBRT) for intracerebral tumor treatment and control. To understand the effectiveness of hippocampal-avoidance radiotherapy compared to conventional radiotherapy, we systematically reviewed hippocampal-avoidance WBRT (HAWBRT) and hippocampal-avoidance prophylactic cranial irradiation (HAPCI). METHODS: We searched the PubMed database for studies involving hippocampal-avoidance radiation therapy, adhering to PRISMA guidelines. Included studies were analyzed for median overall survival, progression-free survival, hippocampal relapse rates, and neurocognitive function testing. RESULTS: Our initial search identified 3709 results, of which 22 studies were ultimately included and a total of 1749 patients analyzed. Seven of the included studies were randomized controlled trials, five were prospective cohort studies, and ten were retrospective cohort studies. Brain metastases were the most commonly treated tumor. There were 19 studies (86.4%) that evaluated HAWBRT and/or HAPCI in patients with brain metastases. Rates of hippocampal relapse were low (overall effect size = 0.04; 95% confidence interval [0.03, 0.05]) and there was no significant difference in risk of relapse between HAWBRT and conventional WBRT (n=5 studies; risk difference = 0.01; 95% confidence interval [-0.02, 0.03]; p = 0.63). Among the thirteen studies that assessed changes in neurocognitive function, significant differences were identified in overall cognitive function and memory/verbal learning 3-24 months post-RT. Significant differences in processing speed and executive function were reported by some studies at 4 and 6 months. No studies reported differences in verbal fluency, visual learning, concentration, and psychomotor speed at any timepoint. CONCLUSION: Analyzed studies in HA-WBRT/HA-PCI showed low hippocampal relapse or metastasis rates. Significant differences in neurocognitive testing were most prominent in overall cognitive function, memory, and verbal learning. Studies were often hampered by loss to follow-up. Further studies into the effectiveness of HA-WBRT are warranted.