Distribution Of Brain Metastases In Relation To The Hippocampus And Its Implication To Whole Brain Radiotherapy

Purpose:With the advent of intensity-modulated radiotherapy(IMRT) and tomo therapy system(TOMO), the ability to limit the radiation dose to normal tissue offers an avenue to limit side effects. This study attempted to delineate the distribution of brain metastasis with relation to the hippocampus and identify variables that correlate with the presence of metastases within the hippocampal sparing region for the propose of exploring the viability of the Tomotherapy-guided hippocampal sparing therapy potentially to reduce neurocognitive deficits from radiation..Methods:Through the retrospective analysis of 271 cases of cancer patients with brain metastases who received whole brain radiotherapy, stereotactic radiosurgery, or a radiosurgical boost following whole brain radiotherapy between November 2012 to November 2014 at Cancer Hospital of Shandong Provence, got the pre-radiotherapy T1-weighted, postcontrast axial, sagittal, coronal MR image of patients who meet our standard from the PCAS system. Delineate every metastases, hippocampus, and hippocampi with 5mm,10mm and 15mm expansion envelopes. Using SPSS 19.0, analyze the relation between the distribution and Primary tumor type, aggregate number and volume of metastasis, RPA, volume of hippocampus, age, gender Analyze the data using a binary logistical regression analysis, with two-side p<0.05 for statistical significance.Results:Of the 271 patients with 933 metastases,4 patients have metastases located in hippocampus, and 12.2%(n=33) patients have metastases located within 5mm of the hippocampus.And 44.3%(n=120) patients have metastasis located greater than 15mm from the hippocampus. NSCLC showed a relatively high rate of metastases around the hippocampus within 5mm (14.7% of all NSCLC patients). SCLC and breast cancer have a relatively low rate of metastases around the hippocampus within 5mm, with the ratio 9.1%å'Œ3.1% respective. The median volume of brain metastases is 5.5cm3.75.8% patients who have metastasis located within 15mm shows a greater aggregate volume of metastases than the median volume, and 84.5% patients who have metastasis located within 15mm have only one brain metastasis. The aggregate volume of metastases with an odds ratio of 1.059(95% confidence interval 1.004-1.182, p=0.037) and the aggregate number of metastases with an odds ratio of 1.038(95% confidence interval 1.011-1.078, p=0.049) were statistically significant predictors for the risk of perihippocampal metastasis.Conclusion:This study confirmed a low incidence of brain metastasis in the hippocampal sparing region at diagnosis, especially for SCLC. The aggregate volume of metastasis and the aggregate number of metastasis are related to the brain metastases around hippocampus within 5mm, regardless of the hippocampal volume. 5-mm margin around the hippocampus for conformal avoidance whole brain radiotherapy represents an acceptable risk, especially because these patients in the absence of any other intracranial disease could be salvaged using stereotactic radiosurgery.