The relative biologic effects of x-rays and beta rays.

Abstract

Investigations of the biologic effects of different types of ionizing radiations suggest that quantitative differences in response occur even though identical amounts of energy are absorbed per unit volume of tissue. Since the development of technics for the treatment of cancer and other diseases with radioactive isotopes, information regarding the relative biologic efficiency of the emitted beta particles and x-rays is required to utilize properly the knowledge that has been acquired by experience with x-rays. We, as well as others (9), have been impressed with the striking tolerance of normal tissue for beta irradiation. The dosage that may be given without producing necrosis or other serious reactions seems to be many times greater for beta rays than for 200-kv x-rays. Most of the data in the literature regarding relative biologic efficiency deal with alpha rays, neutrons, gamma rays, and supervoltage x-rays. Among the reports comparing beta rays and x-rays there is a lack of uniformity in results obtained. Stapleton and Zirkle (15) compared the efficiency of beta rays from P32 with the gamma emission from Ta181 in inhibiting the hatching of Drosophila ova and found no significant difference. Using the same material, Zirkle (17) compared 200-kv x-rays and P32 beta rays and found the latter to be less efficient by a factor of 0.64. Snyder and Kisieleski (13), studying the twenty-day LD 50 dose in mice for the beta emission of Na24 and 200-kv x-rays, reported a ratio of 0.7. Evans and Quimby (4), using Na24 beta rays and 200-kv x-rays to produce lymphopenia in mice, reported the former to be less efficient, the ratio of beta to x-rays having the value 0.66. Taking the graying of hair in mice as a biological end point, Austin et al. (1) compared 17 Mev electrons with 100-kv x-rays and found a ratio of 0.6. Gartner (6) compared the effects of fast electrons from a 6-Mev betatron and 90-kv x-rays on cultures of chicken heart fibroblasts and demonstrated a relative electron efficiency of 0.51. Friedell et al. (5) reported comparable skin reactions following physically equivalent doses from Sr90, RaD and E, and Ru106, and stated that these reactions approximated the skin effects produced by a 44-kv Philips contact unit. Wirth and Raper (16) found the threshold erythema dose on human skin for P32 to be 813 rep, while Low-Beer (11) estimated that a dose of 143 rep from P32 produced a similar reaction. Crabtree and Gray (3) found no quantitative differences between beta, gamma, and roentgen rays in efficiency for inhibition of anaerobic glycolysis in the rat retina. We are presenting a preliminary report of our study of the relative biologic effects of medium voltage (120 and 200 kv) x-rays and beta rays emitted by P32.