Recently, CT images are being used over a wide range in radiation therapy. CT data is used to calculate the dose in high dose rate intracavitary irradiation therapy. In conventional method it is difficult to place the sources upon the CT image correctly. Therefore, the metalic dummy source are inserted into the applicators and two directional scout views are taken. Location of the sources are calculated using twice enlarged scout views. CT images with 5mm spacing are taken after exchanging the dummy sources which do not cause artifact. Dose calculation points are obtained from CT image by pixel position. The calculation points are displayed on CT image by brightening the points and the doses are printed out to CRT and printer. The rectum sigmoid colon, bladder, intestine and arbitrary point dose are calculated using these data for each slice. About 20 patients have been computed with this method from Oct. 1982 to Jul. 1983 and from which the damage was tried to be guessed.