SELECTIVE IRRADIATION AND ATTEMPTED 



REPLACEMENT OF BONE MARROW IN 



THE RABBIT, USING i««Au 



J. M. Garvan, E. p. George, F. A. Rocke and S. Vince* 



St. Vincents Hospital, Darlinghurst, N.S. W. 



INTRODUCTION 



Following the success achieved^ in the replacement of bone marrow in 

 mice receiving whole-body irradiation, it seemed natural to attempt the 

 same replacement in larger animals, such as the rabbit. Since, however, 

 whole-body irradiation at the dose levels required to destroy the rabbit's 

 own bone marrow produces in the rabbit fatal radiation damage to other 

 organs-, it becomes necessary to find some more selective way of irradiating 

 the haemopoietic tissue. Radio-active isotopes appeared to offer a possible 

 solution to this problem and it was therefore decided to investigate their 

 suitability as a means of producing selective irradiation to the bone marrow 

 and other haemopoietic organs. 



Ionic radio-phosphorus, ^-P, and colloidal radio-gold, ^^*Au, were 

 chosen for preliminary investigation, for reasons which we now discuss 

 briefly. Both are readily available. Apart from some Brehmsstrahlung y 

 radiation from the pure ^ emitter ^^P and the relatively weakly ionizing y 

 radiation from the ^, y emitter ^^^Au, both these isotopes irradiate tissue 

 only within a range of one or two mm of the site of their deposition. Hence, 

 if selective distribution of isotope can be achieved, corresponding selective 

 irradiation of tissue can also be achieved. As regards selective distribution 

 of isotope, ^-P was considered because it is a bone-seeking element and it 

 has already been used in the control of polycythaemia vera and leukaemia^. 

 Intravenously injected colloidal ^^^Au was considered because it is known 

 to be selectively taken up in the liver, spleen and bone marrow*. 



Preliminary experiments were undertaken on a series of guinea-pigs in 

 order to get some estimate of the order of magnitude of the specific curie 

 dosej level required to produce aplasia of the bone marrow. The isotopic 

 material was injected via the intracardiac route and it was found that 

 specific dose levels of the order of 2 mC/kg for ^^P or ^^*Au produced com- 

 plete aplasia. The animals died, presumably of anaemia, in two to three 

 weeks. Autopsy revealed gross petechial haemorrhage in all cases. The liver 

 and other organs of the animals were examined for changes that could be 

 attributed to the direct effects of radiation and in no case was any such 

 change observed. 



In the main investigation with rabbits, we chose colloidal ^^^Au as the 



* Institute of Child Health, Royal Alexandra Hospital for Children, Camperdown. N.S.W. 

 j" By 'specific curie dose', or simply 'specific dose', we refer to the quantity of radio- 

 activity administered per unit body-weight. 



56 



