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Purpose: [C]Choline has been established as a PET tracer for imaging prostate cancer. The aim of this study was to determine whether [C]choline can be used for monitoring the effects of therapy in a prostate cancer mouse xenograft model. Methods: The androgen-independent human prostate cancer cell line PC-3 was implanted subcutaneously into the flanks of 13 NMRI (nu/nu) mice. All mice were injected 4–6 weeks after xenograft implantation with 37 MBq [C]choline via a tail vein. Dynamic imaging was performed for 60 min with a small-animal PET/CT scanner (Siemens Medical Solutions). Six mice were subsequently injected intravenously with docetaxel twice (days 1 and 5) at a dose of 3 mg/kg body weight. Seven mice were treated with PBS as a control. [C]Choline imaging was performed prior to and 1, 2 and 3 weeks after treatment. To determine choline uptake the images were analysed in terms of tumour-to-muscle (T/M) ratios. Every week the size of the implanted tumour was determined with a sliding calliper. Results: The PC-3 tumours could be visualized by [C]choline PET. Before treatment the T/M ratio was 1.6±0.5 in the control group and 1.8±0.4 in the docetaxel-treated group ( p=0.65). There was a reduction in the mean [C]choline uptake after docetaxel treatment as early as 1 week after initiation of therapy (T/M ratio 1.8±0.4 before treatment, 0.9±0.3 after 1 week, 1.1±0.3 after 2 weeks and 0.8±0.2 after 3 weeks). There were no decrease in [C]choline uptake in the control group following treatment (T/M ratio 1.6±0.5 before treatment, 1.7±0.4 after 1 week, 1.8±0.7 after 2 weeks and 1.7±0.4 after 3 weeks). For analysis of the dynamic data, a generalized estimation equation model revealed a significant decrease in the T/M ratios 1 week after docetaxel treatment, and the ratio remained at that level through week 3 (mean change −0.93±0.24, p<0.001, after 1 week; −0.78±0.21, p<0.001, after 2 weeks; −1.08±0.26, p<0.001, after 3 weeks). In the control group there was no significant decrease in the T/M ratios (mean change 0.085±0.39, p=0.83, after 1 week; 0.31±0.48, p=0.52, after 2 weeks; 0.11±0.30, p=0.72, after 3 weeks). Metabolic changes occurred 1 week after therapy and preceded morphological changes of tumour size during therapy. Conclusion: Our results demonstrate that [C]choline has the potential for use in the early monitoring of the therapeutic effect of docetaxel in a prostate cancer xenograft animal model. The results also indicate that PET with radioactively labelled choline derivatives might be a useful tool for monitoring responses to taxane-based chemotherapy in patients with advanced prostate cancer. [ABSTRACT FROM AUTHOR]

In this study an evaluation of the performance of the Philips MOSAIC small animal PET scanner is presented, with special emphasis on the ability of the system to provide quantitatively accurate PET images. The performance evaluation was structured according to NEMA-like procedures. The transaxial spatial resolution of the system (radial component) ranged between 2.7 mm FWHM at the centre and 3.2 mm FWHM at a radial offset of 45 mm from the centre. The axial spatial resolution of the system ranged between 3.4 mm FWHM at the centre and 5.8 mm FWHM at a radial offset of 45 mm from the centre. The scatter fraction was determined for a mouse- as well as for a rat-sized phantom, and the values obtained were 9.6% and 16.8%, respectively. For the mouse phantom, the maximum count rate measured was 560 kcps at 93 MBq; the maximum NEC rate equalled 308 kcps at 1.7 MBq/ml. For the rat phantom, these values were 400 kcps at 100 MBq and 129 kcps at 0.24 MBq/ml, respectively. The sensitivity of the system was derived to be 0.65%. An energy window between 410 and 665 keV was used in all experiments. The MOSAIC system exhibits moderate spatial resolution and sensitivity values, but good NEC performance. In combination with its relatively large field of view, the system allows for high-throughput whole-body imaging of mice and rats. The accurate measurement of relative changes in radiotracer distributions is feasible. [ABSTRACT FROM AUTHOR]