DIAGNOSTIC AND THERAPEUTIC USE OF RADIOACTIVE IODINE

THE NATURE of the radiations from the iodine isotope, I131, makes it valuable as a source of internal radiation for those tissues which will selectively absorb iodine. Although this radioactive isotope emits both beta and gamma rays, the great majority of the biologic activity is due to the beta particles which are entirely absorbed within a distance of about 2 mm. in tissue. In fact, most of the beta rays travel considerably less than 2 mm. Because the beta energy is absorbed so close to its source, intense local radiation effect occurs wherever I131is concentrated and is limited to this range. The gamma radiation penetrates farther through the tissues. and much of it escapes from the body. The effect which the gamma rays do have on the tissues is thus distributed widely. Consequently, the gamma radiation effect in any area is relatively small. Since gamma rays escape