Verification of Low Risk for Perihippocampal Recurrence in Patients with Brain Metastases Who Received Whole-Brain Radiotherapy with Hippocampal Avoidance.

Purpose: The purpose of this study was to analyze the patterns of failure and survival outcome in patients with brain metastases who received whole-brain radiotherapy (WBRT) with hippocampal avoidance (HA) using simultaneous integrated boost (SIB) on metastatic brain tumors.

Materials And Methods: We retrospectively reviewed 42 patients treated with HA-WBRT for brain metastases. A total of 25 Gy for whole brain and 35-55 Gy for gross tumors were delivered with 10 fractionations. Local tumor and intracranial progression were defined as a recurrence or tumor progression in SIB field and any recurrence or tumor progression within whole brain, respectively. Progression in HA zone was defined as the recurrence within the area expanded 5 mm from HA zone.

Results: Median follow-up duration was 10.0 months (range, 4.1 to 56.4 months). Intracranial progression was observed in 13 patients (31.0%) and the median duration from the start of HA-WBRT to progression was 10.6 months (range, 0.9 to 33.0 months). Local tumor progression and new metastasis outside SIB field occurred in 10 patients (23.8%) and nine patients (21.4%), respectively. There was no isolated hippocampal metastasis, except only one patient (2.4%) with multiple metastases inside and outside HA zone simultaneously. Median survival time and intracranial progression-free survival rate at 1 year were 19.4 months (95% confidence interval [CI], 9.6 to 29.2) and 71.5%, respectively, and those for overall survival were 26.5 months (95% CI, 15.4 to 37.5) and 67.9%, respectively.

Conclusion: HA-WBRT was associated with low risk of new metastasis in HA region in the patients with brain metastases. These findings would serve as useful guidance on applying HA-WBRT in clinical practice.