Single Pontine Relapse Shortly After Hippocampal Avoidance Whole Brain Radiotherapy: A Case Report

Brain metastasis represents the most prevalent form of brain tumors in adults, with a rising incidence resulting from significant advancements in cancer detection and therapeutic interventions. Current treatment protocols advocate for whole brain radiotherapy (WBRT) for patients who are not candidates for either surgical resection or stereotactic irradiation. However, cognitive decline remains a major side effect of this treatment modality. Hippocampal-sparing WBRT (HA-WBRT) has been shown to decrease brain toxicity, with the main concern being the probability of developing new brain metastasis in the hippocampal avoidance region.

We report a case of a 73-year-old male presenting with multiple brain metastases and treated with HA-WBRT, who then developed a new single pontine lesion shortly after that was found to be located in an under-dosed peri-hippocampal area. We dosimetrically compared the patient's original IMRT plan to three new plans: a standard VMAT plan, an optimized IMRT plan, and an optimized VMAT plan, where optimization incorporated brainstem coverage as a planning objective, resulting in a notable improvement in brainstem dose distribution.

HA-WBRT poses a risk of peri-hippocampal metastasis due to underdosing of the upper brainstem that is inherent in HA-WBRT plans. Planning techniques should focus on optimizing coverage of the brainstem in an attempt to decrease this uncommon occurrence.