The use of imaging data for staging of disease, treatment planning, and monitoring of patient response continues to increase. In these types of studies, where comparability between successive scans (often on different scanners) is important, it is crucial to have an understanding of scanner response over time and to be able to relate the quantitative results of different scanners to each to other.
This is especially important in multicenter drug trials, where imaging data from several sites, each using different scanners, are combined to help draw conclusions about drug effectiveness. Such comparability is only possible if all activity calibrators and scanners used in the studies are calibrated against the same standard. Calibrated, traceable phantom sources can be a valuable tool for accomplishing this and can provide a means to accurately quantify and monitor PET system parameters on an absolute basis. We have constructed prototype solid 68Ge phantom sources and have developed a methodology to calibrate their activity content so as to be traceable to national standards.
The first cylindrical prototype sources (figure. 1) were fabricated from poly(methyl methacrylate) and are intended for use in a standard Jaszczak phantom. The active length of all the sources is maintained at nominally 4 cm and the inside diameters are varied to give nominal active volumes of 1, 2, 4, and 6 mL. The wall thickness is 1 mm and the thickness of the bottom is 5 mm. A generalized scheme for preparing and calibrating the phantom sources is given in figure 2.