154 



BENSTED, BLACKETT, COURTENAY, AND LAMERTON 



This finding suggests that gross histological damage exemplified by 

 fibrosis and epiphyseal plate damage could be an important factor in the 

 production of bone tumours by radiation. However, some other experiments 



Mortality with time of appearance of bone tumours 



X-rays 140lcVp to one hind limb 

 3000 r 



■3x|000r at 

 2 -week intervals 



^ I Bone tumour 



10 15 



Months 



25 



Fig. 3. Comparison of bone-tumour incidence with single (3,000 r) and repeated (3 X 1,000 r) 

 doses of 140 kVp X-radiation to one hind limb. 



have not confirmed this suggestion. Figure 4 shows results for localized 

 irradiation with 230 kVp radiation to both hind limbs where six doses of 

 500 r were given at 0, 1, 4, 5, 6 and 7 weeks. Here 7 out of 17 animals (that is, 



Mortality with time of appearance of bone tumours 



20 



a 

 o 



E 



-7 



10 



X-rays: 230kVp to both hind limbs 

 6x500r 



X Bone tumours 



I I I I 



_J 1 1 : \ 1 I 







10 15 



Months 



20 



25 



Fig. 4. Bone-tumour incidence with repeated (6 x 500 r) doses of 230 kVp X-radiation to 

 one hind limb. 



7 out of 34 irradiated hind limbs) developed bone tumours between ten and 

 fifteen months. This incidence is more than half that observed after a single 

 dose of 3,000 r at 140 kVp, yet there was very little evidence indeed, in the 



