A comparison of the biological effect of iodine 125 and tantalum 182 gamma rays using<i>vicia faba</i>roots

Abstract

Seeds containing iodine 125 as supplied by Lawrence Soft Ray Corporation have now been used at this hospital to treat a variety of patients with tumours which would have been treated with applicators or moulds loaded with 182Ta or 226Ra if the seeds had not been available. Iodine seeds have also been extensively used at other hospitals, e.g. Kim and Hilaris (1975), Hilaris (1976), and Charyulu et al. (1976). The advantages of 125I over 182Ta have already been outlined earlier (Sealy et al., 1976; Hering et al., 1977). However, whereas the radiobiological effectiveness (RBE) of the 182Ta radiation relative to 250 kV X rays is well known, there is at present no such information available for 125I. By considering the LET spectrum of the X rays of 125I, Kim and Hilaris (1975) have predicted an RBE of the seeds for human tumours higher than one and less than 1.5. Some radiobiological studies are needed to test this prediction and this has led to some preliminary investigations on vicia faba as outlined below.