PT - JOURNAL ARTICLE AU - Mattias Sandstrom AU - Anders Sundin AU - Mark Lubberink TI - Intrinsic or extrinsic uniformity maps using <sup>177</sup>Lu on a GE Discovery 870 CZT gamma camera<strong/> DP - 2019 May 01 TA - Journal of Nuclear Medicine PG - 1363--1363 VI - 60 IP - supplement 1 4099 - http://jnm.snmjournals.org/content/60/supplement_1/1363.short 4100 - http://jnm.snmjournals.org/content/60/supplement_1/1363.full SO - J Nucl Med2019 May 01; 60 AB - 1363Objectives: Fractionated therapy with 177Lu-octreotate is an effective treatment option for patients with generalized neuroendocrine tumors. The most frequent protocol in therapy with 177Lu-octreotate is to give all patients 4 cycles of 7.4 GBq, but more and more centers individualize treatments basted on patient-specific absorbed dose calculations. To do absorbed dose calculations, quantitative imaging with a gamma camera is needed. The main aim of this work was to study SPECT imaging capabilities in terms of uniformity, image contrast and attenuation correction accuracy of 177Lu on a GE Discovery 870 CZT using intrinsic and extrinsic uniformity maps. Secondary aim was to compare the best CZT imaging SPECT technique to SPECT imaging on a conventional GE Discovery 670 PRO. Methods: To accurately investigate the system performance, good statistics in the SPECT images was highly warranted (as is used in an ordinary planar uniformity test). Because of this, imaging was performed with 120 angles (60 for each detector), using a 128 matrix and 360 s per angle. An MEHR collimator was used for all measurements on the CZT system using an energy window of 208 keV ± 6%, whereas an MEGP collimator was used with for the PRO system with an energy setting of 208 keV ± 10%. Low dose CT was done for attenuation correction and images were reconstructed using OSEM (8 iterations, 8 subsets). In case of the 870 CZT, images were reconstructed using both intrinsic and extrinsic uniformity maps. To investigate SPECT uniformity, a cylindrical phantom with 20 cm diameter filled with about 500 MBq 177Lu was used. Uniformity of the SPECT images was calculated as an integral uniformity in a ROI at 80% of the phantom diameter (16 cm), mean of five slices. Comparing 870 CZT with 670 PRO two measurements were performed. The first was with a NEMA NU2-2001 Image Quality phantom, where the spheres were filled with a concentration that was 8 times higher than the background. Percent contrast of the concentration in the spheres was calculated for the two measurements. The second was a PET attenuation correction phantom described in NEMA NU 2-1994. Results and Discussion: 870 CZT SPECT uniformity was about 14 % with severe ring artifacts when intrinsic uniformity correction was used. Using uniformity correction collected extrinsic the SPECT uniformity was better than 5 % with no visible artefacts, and hence only extrinsic maps were used for the other two measurements. The percent contrast in the image quality phantom measurements for the smallest to the largest sphere was for the PRO system 5, 6, 11, 18, 28 and 34 % while it was 5, 12, 19, 31, 42 and 55 % using the CZT system. The attenuation correction phantom measurement gave similar results for both scanners. It should be noted that the reconstruction of the images for both scanners was done with the same settings and that these are optimized for the PRO system. These seem to work well for the CZT system but could be further optimized. Conclusions: As opposed to the 670 PRO, extrinsic uniformity maps should be used for the 870 CZT system to ensure sufficient image uniformity. Use of intrinsic maps resulted in severe ring artifacts and should be avoided. Using extrinsic uniformity maps, image contrast was considerably improved for the 870 CZT system compared to the 670 PRO.