[The role of whole brain radiotherapy with hippocampal-sparing]

Hippocampi plays a fundamental role in immediate or long-term memory and the spatial learning. This structure is rarely involved by metastasis and their irradiation is at the origin of some impairment of the neurocognitive function. Sparing hippocampi during whole brain radiation therapy becomes possible with volumetric modulated arc therapy (VMAT) or with helical tomotherapy. The delineation of the structures should be performed after coregistration of gadolinium-enhanced T1-weighted MR-images with the planning. The D40 to both hippocampi should not be greater than 7.3 Gy. Patients who are more likely to benefit from a hippocampal-sparing strategy must have a 6 months or longer life expectancy and a Karnosky index above 70. Hence, patients who are more likely to be deemed fit for this strategy are frequently patients with NSCLC, breast cancer, gastointestinal cancers or patients. Patients with small cell lung carcinoma who are selected for prophylactic cerebral irradiation should be also considered, as they are unfit for ablative treatments such as stereotactic radiotherapy or brain surgery. Moreover, brain metastasis located in the area surrounding the hippocampi are unlikely. To date, no randomized study is available to confirm these assumptions. Two on-going prospective trials (RTOG 0933 and a French phase II trial) are currently investigating whether breast cancer patients with a single resected metastasis could benefit from the hippocampal-sparing strategy during whole brain radiotherapy.