Stereotactic radiosurgery optimization with hippocampal-sparing in patients treated for brain metastases

Cranial irradiation is associated with significant neurocognitive sequelae, secondary to radiation-induced damage to hippocampal cells. It has been shown that hippocampal-sparing (HS) leads to modest benefit in neurocognitive function in patients with brain metastases, but further improvement is possible. We hypothesized that improved benefits could be seen using HS in patients treated with stereotactic radiation (HS-SRS). Our study evaluated whether the hippocampal dose could be significantly reduced in the treatment of brain metastases using SRS, while maintaining target coverage.

Sixty SRS plans were re-planned to minimize dose to the hippocampus while maintaining target coverage. Patients with metastases within 5 mm of the hippocampus were excluded. Minimum, mean, maximum and dose to 40% (mean equivalent dose in 2 Gy per fraction, EQD₂ to the hippocampus) were compared between SRS and HS-SRS plans. Median number of brain metastases was two.

Compared to baseline SRS plans, hippocampal-sparing plans demonstrated D_min was reduced by 35%, from 0.4 Gy to 0.3 Gy (p-value 0.02). Similarly, D_max was reduced by 55%, from 8.2 Gy to 3.6 Gy, D_mean by 52%, from 1.6 Gy to 0.5 Gy, and D₄₀ by 50%, from 1.8 Gy to 0.9 Gy (p-values <0.001).

Our study demonstrated that further reduction of hippocampal doses of more than 50% is possible in the treatment of brain metastases with SRS using dose optimization. This could result in significantly improved neurocognitive outcomes for patients treated for brain metastases.