Application of stereo x-ray photogrammetry (SRM) in the determination of absorbed dose values during intracavitary radiation therapy

The method of stereo x-ray photogrammetry is described, using a stereo x-ray comparator, as well as some clinical applications. The x-ray equipment consists of two x-ray tubes and a pneumatically driven cassette changer, developed to reduce effects of patient or organ motion between stero radiographs. The accuracy of the set-up is demonstated with measurements on a geometrical model and on a gelatine phantom containing radium needles. The clinical use is reported in determining dose rates to points of the intestinal wall during intracavitary radiotherapy of gynecological cancer. In a number of cases the stereo measurements have resulted in a change in the application time or in the charge or position of the applicator, possibly preventing later complications, as a result of a high dose. Future applications for implant dosimetry (192Ir, 125I) are suggested