Validation of a rotating camera based SPECT system for dosimetry applications

The authors have evaluated the quantitative properties of a rotating camera based SPECT system using three isotopes commonly used clinically (Tc-99m, In-111, and I-123 contaminated with I-124). The isotopes were chosen due to their different imaging characteristics. The Alderson body phantom was used with 'hot' spheres, with and without background activity, to determine system sensitivity and linearity. An analytic post processing attenuation correction routine was implemented which increased system linearity with respect to position in the phantom and was used throughout the study. Up to four organ phantoms were placed in the body phantom and imaged in two ways. First, a two view planar technique, and second, a circular rotation SPECT acquisition. The two view planar technique uses a combination arithmetic and geometric mean with correction for attenuation. The planar technique showed good correlation to actual activity in absence of background (slope .98; R .99), and slightly degraded accuracy with background (slope .91; R .97). However, it was only able to quantitate activity when no overlying or underlying organs were present. The SPECT system, though, was clearly able to distinguish regions of activity in transverse section for which accurate quantitation was possible. Very good correlation between SPECT activity and measuredmore » activity was observed both with (slope .98; R .98), and without (slope 1.02; R .99) background activity present. Accurate quantitation of total organ activity is very useful not only for dosimetry applications, but also for radiotherapy planning and monitoring of treatment.« less