To investigate the rate of hippocampus injury during whole brain radiotherapy for intracranial metastasis and explore the effect of whole brain radiotherapy in reducing the radiotherapy induced neurocognitive dysfunction of hippocampu and provide reference for the treatment of intracranial metastatic tumors.

The intracranial metastases in 123 patients from January 2015 to December 2016 were enrolled in this study. The MRI image data before and after radiotherapy were analyzed retrospectively.The anatomical position of tumor and the hippocampus in patients with intracranial metastasis was outlined. According to outlined position, the relationship between location of intracranial metastatic tumor and the hippocampus was analyzed, and the probability of the hippocampal damage by tumor radiotherapy was calculated in the treatment of intracranial metastatic brain. Neurocognitive dysfunction improvement by protective irradiation of hippocampus was compared between different radiotherapy methods.

Four hundred and seventeen intracranial metastatic tumors were observed in 123 patients, among which the sites of 15 tumors(3.60%) were within the 5mm of hippocampus, the sites of 146 tumors (35.01%) were 5-10 mm from the hippocampus, and the sites of 256 tumors(61.39%) were beyond 10 mm of hippocampus. The distribution of 417 metastatic tumors in the brain was as followings: 137 tumors (32.85%) were in frontal lobe, 98 tumors(23.50%) were in temporal lobe, 59 tumors (14.15%) were in parietal lobe, 46 tumors(11.03%) were in occipital lobe, 41 tumors (9.83%) were in cerebellum and 36 tumors (8.63%) were in basal ganglia. Using helical tomotherapy, intracranial metastasis radiotherapy and volumetric modulated arc radiotherapy, the rate of patients with cognitive dysfunction induced by hippocampal injury was 1.96% (1/51), 10.26% (4/39) and 18.18% (6/33), and there was significant difference (χ² = 6.595, P = 0.000).

The hippocampus injury possibility is very small, when whole brain radiotherapy is used in the treatment of intracranial metastatic tumors. Avoiding the hippocampus in radiation therapy of intracranial metastasis has high feasibility, among which the helical tomotherapy can effectively reduce hippocampus injury and improve patients′cognitive function.

Neoplasm metastasis; Brain neoplasms; Hippocampus; Whole brain radiotherapy; Neurocognitive function