Experiences in calibration with three different types of phantoms

Three types of modular phantom were tested. All can be assembled to fit different geometries and to simulate different body masses. The radionuclide distribution is homogeneous in each module, but uneven distributions in the body can be simulated. The basic modular phantom consisted of flat plastic bottles filled with calibrated radionuclide solutions. An improved version was filled with a solution of plastic monomers, that was polymerised with gamma radiation to form a semi-rigid hydrogel. The third type of phantom is the 'St Petersburg' modular block phantom, consisting of inactive tissue-equivalent plastic blocks into which rods containing known activities of the desired radionuclides are inserted. The precision of assembling the phantoms was very good for all three types. The standard deviation of the mean pulse rate was less than 2% when each phantom was measured repeatedly; the modules were removed and re-assembled between measurements. The accuracy in measuring unknown activities of 134Cs, 137Cs and 60Co was 5% or better. (author)