40k 10 CASES 14 CASES O= OVER 20 YEARS AT INITIAL EXPOSURE ™x=UNDER 20 YEARS AT INITIAL EXPOSURE 30 z oO we 4) 20h a ty x a|” ee <5 o £|2 wrap ma x 10 N O9F a 0 ec OBE ee oa O7 Z O6F x I5 *YEARS OLD x Oo O5o4be ose tb 2 4 tt 6 8 td 10 [2 4 16 18 dd 20 22 24 26 2B 30 dt 32 34 36 td 38 40 42 44 46 48 YEARS CARRIED gle intra- Fic. 44.—Difference in concentration of ?*Ra in persons exposed before and after age 20 Figure 45 shows the results obtained by Sears et to al.) in the vertebrae of high-level radium dogs which E were sacrificed serially at different times after injec- tion. There would appearto be nosignificant difference ' in the rate of fall of the hotspots and the diffuse activity. Likewise, two other studies in dogs with *Ra™ aud Ca failed to show any significant difference between the loss from the hotspots and from thediffuse | lubel of the cortex of the tibia between one month and ane year after injection. However, the loss in the whole-body retention between these two times was less > x = |OE - 5 = Oo a values shown here suggest a lower rate of loss of ac| tivity from the hotspots compared with the diffuse. Between 3 days and 100 days the loss in activity was | ubouta faetor of 4 for the hotspots and a factor of 10 ‘es 45- # for the diffuse. Figure 47 gives the best values we have leon able to obtain for the human data. Here the loss ut the in the hotspot activity over a period of 25 years is a re two; factor of 3.6, while that for the diffuse is a factor of 10 ths as ( over the same period for the mid-cortex of the tibia. comThe values plotted for the hotspots at short times after ‘owth, beling ¥ mn] ection were calculated from the injected dose assume two ing that the hotspots in the bone were formed at the luate Z “ame concentration as the 228Ra/g Ca in the blood. This ptake § Ws found to be true for dogs.'#) Recently, the diffuse luhcl was shown to be 0.48 and 0.35 of the uniform label Average Hotspot ¥=.74517-247 *% 5 ONE E Average Diffuse xy Y=-0781~-159 0 pe than 40%. Figure 46 shows a similar plot for Ca as observed | for hotspots and diffuse uptake for rabbits." The x Kx F < <t a © Maximum Hotspot 0.0! Lj 10 Litiuul TL toil 100 1,000 jtft 10,000 DAYS Fic, 45—Diminution of “Ra in canine vertebrae in two radium cases studied at 140 days and 400 days after injection of radium, compared to an average value of 0.43 found for about 20 cases at 25 years after injection.'®) This suggests that the diffuse level in the tibial cortex divided by the uniform label for the whole skeleton does not change appreciably with time. There would appear to be some doubt as to whether the diffuse label and the hotspot levels vary between different bones. All the animal work: * ® would sug- gest that the diffuse level found in the vertebrae is about a faetor of two higher than that found in the mid-shaft of the tibia at short times after injection.