RT Journal Article SR Electronic T1 Correlation of lesional uptake parameters and ratios with miPSMA score and estimating normal physiological concentration: an exploratory analysis in mCRPC patients with 68Ga-PSMA-11 PET-CT JF Journal of Nuclear Medicine Technology JO J. Nucl. Med. Technol. FD Society of Nuclear Medicine SP jnmt.120.261289 DO 10.2967/jnmt.120.261289 A1 Ashwini Kalshetty A1 Biju Menon A1 Sutapa Rakshit A1 Atanu Bhattacharjee A1 Sandip Basu YR 2021 UL http://tech.snmjournals.org/content/early/2021/07/09/jnmt.120.261289.abstract AB Background and Aim: The employment of prostate-specific membrane antigen (PSMA)-based PET-CT imaging has grown rapidly over the recent years. The aim of the present study was to estimate the lesional uptake across the different levels of molecular imaging PSMA (miPSMA) expression score along with normal physiological concentration of 68Ga-PSMA-11 in a cohort of mCRPC patients including their temporal variation on delayed imaging. Materials and Methods: Fifty patients of mCRPC who were being evaluated for 177Lu-PSMA PRLT, and underwent 68Ga-PSMA-11 PET-CT for evaluation of disease status, were retrospectively evaluated. The mean age of the patients undergoing the scan was 67.5 ± 8 years (52-84 years) with an average serum PSA level of 401 ± 1353 ng/ml (0.098-9235.13 ng/ml) at the time of scanning. All patients underwent standard 68Ga-PSMA-11 PET-CT at 65 minutes post-injection on an average (60-90 mins). Tumoral analysis (n = 50) was undertaken to see their correlation with miPSMA expression score and their uptake values. The physiological tracer distribution was estimated by placing a spherical VOI of fixed diameter of 1 cm for smaller organs (in the regions of submandibular glands, parotid glands, lacrimal glands, tubarial glands, renal cortices, blood pool and bowel) and 3 cm for larger organs (liver and spleen). Standardised uptake value maximum (SUVmax) and mean (SUVmean) were estimated for each of the regions. Tumor-to-spleen (T/S), tumor-to-liver (T/L) and tumor-to-parotid (T/P) ratios were calculated for each lesion. A subgroup of 16 patients underwent a delayed scan at 135 mins post injection on average (120 – 150 mins), for whom an additional analysis was performed to evaluate the effect of delayed imaging on uptake values and ratios. Results: The maximum uptake was observed in renal cortices followed by salivary glands, bowel, spleen, liver, lacrimal glands and blood pool in the descending order. The average SUVmax with SD of the organs are as: 37.7 ±22.1 for renal cortices, 15.4 ±7.3 for submandibular glands, 14.4 ± 7.1 for parotid glands, 9.4± 4.9 for spleen, 6.2 ± 3.7 for lacrimal glands, 5.9± 2.3 for liver, 5.3 ± 1.41 for tubarial glands, 13.8 ±7.6 for bowel, and 2.4 ±1.9 for blood pool. The average SUVmax of miPSMA expression score 2 was 10.33 ± 3.27 (6.46 - 17) and 38.21 ± 25.9 (7.68 – 119.08) for score 3. The average tumor-to-spleen (T/S) and tumor-to-parotid (T/P) ratios for score 2 lesions were 1.21 ± 0.44 (0.48 – 2.04) and 0.6 ± 0.18 (0.39- 0.87) respectively. The average T/S and T/P ratios for score 3 lesions were 5.05 ± 4.46 (1.25 – 20.89) and 3.15 ± 2.09 (1.06 – 9.45) respectively. The average SUVmax of index score 3 lesions was 18.85 which increased to 26.24 on delayed imaging with statistically significant difference (P = 0.0001). However, the T/L, T/S and T/P ratios did not show any significant change. The temporal variation of normal organs showed that the SUVmax was significantly increased in delayed scan in salivary (submandibular and parotid) and lacrimal glands, and renal cortices, while the SUVmean significantly increased in spleen and liver, parotid, tubarial and lacrimal glands and not significant in other organs. Conclusion: Thus, the reference ranges of normal organs (physiological uptake) and tumor lesions for uptake and ratios for miPSMA score 2 and score 3 were documented and established in the present study, based upon which a consensus on standard reference range can be proposed for all quantitative assessment values on 68Ga-PSMA-11 PET-CT. The temporal variation trends of the lesions and reference organs should be kept in mind for delayed acquisitions, the T/S, T/Lor T/P ratios could serve as better markers for such scenarios.