Provided are a radiation treatment planning system and a radiation treatment system that are capable of achieving time shortening and labor saving of treatment planning making when a radiation treatment is planned. A predicted DVH calculation portion 4034 of an arithmetic processing device 403 in a radiation treatment planning system 400 anisotropically enlarges a target region 501 in an irradiated body image which is input to the radiation treatment planning system 400, and calculates an overlap volume OV with an organ-at-risk region 502 per the number of times of enlargement. A DVH (Dose Volume Histogram) is predicted from a volume of the calculated OV, and a dose histogram in the OV per the number of times of enlargement which is calculated from a past treatment planning data group, and is displayed on a display device 401.