Gonad dose to children in voiding urethrocystography performed with 70-mm image-intensifier fluorography.

Abstract

In roentgen examination of the lower urinary tract the ovaries lie in the primary roentgen beam, and the testes cannot always be effectively shielded without interfering with the examination. In such studies, therefore, low-dose radiographic methods are important. In conjunction with the clinical use of 70-mm fluorography in voiding urethrocystography (7), gonad doses in 41 children were measured and compared with doses from full-scale serial radiography. The subjects included 17 boys from the ages of three months to ten years and 24 girls from the ages of two to thirteen years. Technical Details A single-phase 500 mA generator was used with an under-couch tube having a 1-mm focal spot. Beam filtration was 2 mm A1. Focal spot-table-top distance was 46 cm and the distance from the focal spot to the input screen of the 6-in. image intensifier was usually 65 to 70 cm. Films were made with a Philips 70-mm camera. The exposure, regulated by a phototimer, was about 3 to 8 mAs/frame at 65 to 90 kV. Eight to thirty-four 70-mm films were obtained per examination. Kodak Linagraph Shellburst (Estar Base Emulsion #2474) 70-mm film was used and processed in a Kodak RP-Xomat. Fluoroscopy was performed with image-intensifier and transistorized Plumbikon television, usually with 1 mA at 65–90 kV. The exact duration for fluoroscopy could not be measured because the apparatus lacked such a recorder. Total time for fluoroscopy was usually less than one minute but was longer in cases with pathological findings. For full-scale serial radiography the overhead tube had a 2-mm focal spot and the beam filtration was 2 mm A1. An Elema-Schönander 14 × 14-inch cut film-changer with Lyshom grid and high-intensity screens was used, along with a focal-spot-table top distance of 90 cm. Kodak RP/S-54 films were employed and processed in a Kodak RP-Xomat. Exposures were made with 25–75 mAs at 75–90 kV. Dose measurements were carried out with two types of ionization chambers: the Victoreen pocket dosimeter and the LiF-thermoluminescent dosimeter. The pocket dosimeter was too big to be inserted into the rectum of small children, and furthermore it could not be used in measurements of exposure exceeding 200 mR. Therefore, we built a thermoluminescent dosimeter in which LiF powder was used as radiation-sensitive material. The LiF-ionization chamber was smaller (0.6 cm in diameter and 2.5 cm in length), and with it exposures over 200 mR could be measured. This system was calibrated against a conventional Victoreen dosimeter and found to agree with it within about 10 per cent. The exposure values were determined with a Controls for Radiation Model 5100 TLD Readout Instrument. Method of Measurements In girls, the ionization chamber was inserted into the rectum. In boys, it was placed between the right thigh and scrotum. The patients were supine during the filling of the bladder and in deep right posterior oblique position during voiding.