Fig. 57.--Loading radioactive beads TABLE 31. Sample : Location Statistics oF Cs®? MicROSPHERES | No. of INO. O beads | - n | & min Top 100 58 10 Top 20 10 13 100 10 Top Middle Bottom 10 100 9 11 ° | i raeee , i 2 The usefulness of a phantomis solely dependent : S.D. 11,930 + 180 x? | | 11,850 + 179 6 12,070 + 218 10 12,690 + 140 10 ANALYSIS 12,450 + 240 | 1634 346 201 155 523 n = No. of samples counted. i = mean counting time per sample. About 25 radioelements are available from the 3M Companyin microsphere form. For short-lived isotopes, it would seem entirely feasible to load the nylon beads with any desired stable element and produce the desired activity in situ by neutron irradiation. We have not investigated this possibility in detail as yet. its imitating the relevant dimensions and shape body and of the radioactive organ, and on co) locating one within the other. Obviously, the de (customarily a single or multiple Nal erystal possibly collimated) must be placed identically respect to the body and the phantom. If we ar cerned with calculating the burdenof a single indi with precision, the uncertainties arising from n variations in size and location must all be recog dependent as these are upon the patient’s age race, and habitus. But these considerations are con to any calibration procedure. As a preliminary to studyingthe statistical pro} of many sources, an analysis was attempted « minimum number and optimum spatial positi discrete beads that are required to simulate a unif active organ to any stated degree of accuracy