EADIATION-INDUCED BONE TUMOURS— 

 FRACTIONATION STUDIES 



J. P. M. BENSTED, N. M. BLACKETT, V. D. COURTENAY, and 



L. F. LAMERTON* 



Physics Department, Institute of Cancer Research, Royal Cancer Hospital, London, 



England 



INTRODUCTION 



The finding that the incidence of radiation-induced thymic lymphoma in 

 mice was dependent on the fractionation of the exposure, for the same total 

 dose, opened up a fruitful field for the study of the mechanisms of lymphoma 

 induction. If a similar dependence on fractionation or protraction of exposure 

 could be shown for other types of radiation-induced tumour, a much more 

 direct attack on mechanisms would be possible than has hitherto been provided 

 from studies of dose-incidence relationships. It is probably true to say that, 

 apart from a few special cases (e.g. when linearity is demonstrated), a dose- 

 incidence curve without additional data can give little information about the 

 mechanisms involved. 



Only a few fractionation studies have been reported for radiation- 

 induced bone tumours and most of these have been made with bone-seeking 

 isotopes of relatively long half- life and with short intervals between successive 

 injections. Under these circumstances the radiation exposure conditions in 

 the bone may not be very diiferent from those with single injections. This 

 could explain why little effect of fractionation was found by Finkel (1959) 

 using repeated ^°Sr injections in mice, or by Kuzma and Zander (1957), using 

 daily injections of *^Ca. If bone-seeking isotopes are to be used for fractiona- 

 tion studies, the interval between injections should be of the same order as, or 

 greater than, the half- life of the isotope in order to produce sufficient change 

 in the pattern of radiation dose and dose-rate to the bone. For this purpose a 

 suitable bone-seeking isotope would be ^^P although, as in all studies with 

 bone-seeking isotopes, it must be recognized that growth and remodelling of 

 the bone will complicate the radiation dose pattern within the bone 

 from successive injections. 



In this paper a brief resume will be given of the effect of fractionation on 

 bone-tumour production in young rats using {a) ^^P, a high energy ^-emitter, 

 with a relatively short half-life (14 days), (6) ^^^Pu, an a-emitter with a long 

 half-life ( > 20,000 years), and (c) localized external radiation with X-rays. 



* Read by L. F. Lamerton. 

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