Hippocampal-Sparing Prophylactic Cranial Irradiation In Small Cell Lung Cancer:a Exploratory Clinical Trail

Purpose:The study was a exploratory trail to compare the dosimetric distribution of three different radiation technique and evaluate the neurocognitive toxicities in Hippocampal-Sparing Prophylactic Cranial Irradiation.Methods:Between April 2014 and March 2015,9 patients with LS-SCLC who had achieved complete remission were assigned to this trail. The hippocampus was contoured, and hippocampal avoidance regions were created using a 3-mm volumetric expansion around the hippocampus. Tomotherapy, Intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) treatment plans were generated for a prescription dose of 25Gy in 10 fractions. The dosimetric distribution of different plan will be compared to find an optimal one. The toxicities, cranial metastasis, neurocognitive function of patients will be evaluated.Results:Tomotherapy spared the hippocampus, with a mean dose of 5.76Gy and maximum dose of 6.68Gy. IMRT spared the hippocampus, with a mean dose of 16.99Gy and maximum dose of 18.26Gy. VMAT spared the hippocampus, with a mean dose of 17.81Gy and maximum dose of 19.05Gy. Mean dose to the hippocampus was reduced by 77% using Tomotherapy, by 32% using IMRT and by 27% using VMAT. Target coverage and homogeneity was acceptable with Tomotherapy. The acute toxicities were acceptable,≥grade 2 toxicity were not occurred in 9 patients. One patient was dead and two cranial metastasis were occurred in the observation period but no hippocampal metastasis were occurred. The MMSE average score was 29.3 at 6 month after cranial irradiation. The memory score was 5.86. There was no significant decline in MMSE scores.Conclusions:Tomotherapy techniques allow for sparing of the hippocampus with acceptable target coverage and homogeneity. It can achieve a lower dose of hippocampus than IMRT and VMAT. The acute toxicities were acceptable. There was no significant decline in neurocognitive function.