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摘要
Indium 111 SPECT allows one to determine the activity distribution of tracers used in radioimmunotherapy, such as Zevalin (R) labeled with yttrium 90. Using computer simulations and phantom models, we assessed various processing schemes to identify a clinically feasible protocol to estimate the tracer concentrations from (111)In SPECT images. The SPECT acquisition of a cylindrical phantom containing spheres was simulated. Several processing protocols that all included corrections for scatter, attenuation, and partial volume effect were compared using the simulated data. The protocol yielding the most accurate estimates of activity concentrations in the spheres was identified. This protocol was then applied to the experimental SPECT acquisitions of the cylindrical phantom and of an anthropomorphic phantom. Using the experimental data, the impact of the delineation and location of the volumes of interest (VOI) used for the measurements was also studied. The algorithm yielding the most accurate activity estimates included a dual energy window scatter subtraction, nonuniform attenuation correction in OSEM, and partial volume effect correction using recovery coefficients. With this protocol, errors in activity estimates were less than 9% in spheres greater than 15 mm in diameter for the simulated and the experimental data of the cylindrical phantom. Realistic errors in volume delineation increased the errors in activity estimates up to 23% for these spheres. Using the anthropomorphic phantom, errors in activity estimates using realistic VOI were less than 20% in all organs and tumors. Appropriate processing of (111)In SPECT images yielded clinically useful activity estimates that were accurate within +/- 20%. It is therefore possible to use these activity values as an input for radiation-absorbed dose calculations in targeted radiotherapy.
- 出版日期2010-6
