radiation therapy (IMRT). The hypothalamus, pituitary and hippocampus were contoured based on T1-weighted MRI, and avoidance regions were created using a 5-mm volumetric expansion around the organs. The prescribed dose was 25 Gy in 10 fractions to the whole brain, and two treatment plans were generated: WBRT with hippocampus avoiding (HA-WBRT), and HPA-HA-WBRT. The mean and max dose to the hippocampus, hypothalamus, pituitary and target were calculated, and the target coverage and homogeneity index of HA-WBRT and HPA-HA-WBRT were compared with Paired t test. Results: On average, the hippocampal avoidance volume was 41.9 cm 3 , occupying 3.1% of the whole-brain planned target volume. In addition, hypothalamic-pituitary avoidance volume was 10.3 cm 3 , occupying 0.7% of the whole-brain planned target volume. Both of the HA-WBRT and HPA-HA-WBRT could successfully spare the hippocampus. The mean dose to the hippocampus was 8.30 Gy and 8.29 Gy respectively (PZ0.956), the max dose of which were 10.58 Gy and 10.71 Gy, respectively (PZ0.371). HPA-HA-WBRT could decrease the dose to the hypothalamus and pituitary. The mean dose to the hypothalamus were 25.21 Gy and 13.81 Gy, respectively (PZ0.0003), the max dose of which were 28.67 Gy and 17.22 Gy, respectively (P< 0.0001). The mean dose to the pituitary were 26.19 Gy and 14.41 Gy, respectively (PZ0.0003), the max dose of which were 30.04 Gy and 17.10 Gy, respectively (P<0.0001). The mean dose to the target of HA-WBRT and HPA-HA-WBRT were 26.59 Gy and 26.39 Gy, respectively (PZ0.118), the max dose of which were 34.93 Gy and 34.5 Gy, respectively (PZ0.549). Target coverage were 92.67% and 91.94%, respectively (PZ0.655), and homogeneity index were 0.11 and 0.12, respectively (PZ0.619). Conclusion: Both of HPA-HA-WBRT and HA-WBRT were able to achieve adequate whole brain coverage and hippocampus avoiding. However, HPA-HA-WBRT could preserve hypothalamic-pituitary axis better. Author Disclosure: X. Fan: None.