Beta camera and pinhole SPECT imaging for dosimetry applications

Animals inoculated with gliomas in the brain treated with intratumoral injection of ²⁰¹Tl have previously shown promising results concerning survival. This study undertaken to investigate methods for estimating dosimetry in these animals. Two high resolution techniques were used, Beta-camera and pinhole SPECT. Pinhole SPECT was used for detection of the administered ²⁰¹Tl activity in vivo. After sacrifice, the sliced rat brain was imaged with the Beta-camera. Histopathological examinations of the brain slices were compared to the Beta-camera images. Treated animals survived several days longer than the controls. Necrosis was found in all the ²⁰¹ Tl-treated brain tumors and tumor sizes decreased. In some cases the tumors had totally disappeared. Biokinetics of the activity in the tumor gave the cumulated activity. The Beta-camera activity distribution matrix was used as input for calculating the absorbed dose rate. The authors have shown that these techniques are useful for determining the dosimetry in small laboratory animals undergoing radionuclide therapy