Can SUVpeak derived from PSF 18F-PET/CT images act as a surrogate for SUVmax derived from EARL compliant reconstructions?

289 Objectives: We explored the possibility of using SUVpeak (defined as a 1mL sphere with the highest average SUV within a lesion/target) derived from 18F-FDG PET/CT images reconstructed with point-spread-function resolution modelling as a surrogate for SUVmax derived from images reconstructed with an EARL compliant protocol. SUVpeak was already suggested as being a better alternative than SUVmax when derived from PSF images1. This assessment was performed using phantom images and clinical data from stage III and IV non-small cell lung cancer (NSCLC) patients. Methods The National Electrical Manufacturers Association (NEMA) image quality phantom was scanned for 5 minutes with a 10:1 sphere-to-background contrast ratio. Additionally, ten stage III and IV NSCLC patients underwent two baseline 18F-FDG PET/CT scans per day at 60min and 90min post injection, at two separate time-points within one week2. All data were reconstructed following two protocols: one compliant with EANM guidelines (EARL multicentre standard) and another with point-spread-function (PSF) resolution modelling. The latter protocol allows for improved lesion detection, but does not provide EARL compliant quantitative results. Patients’ lesions were segmented using a semi-automatic isocontour at SUV=4.0 g/mL. NEMA spheres were manually delineated based on their diameter. The SUVpeak PSF-derived (SUVpeakPSF) was compared with SUVmax EARL-derived (SUVmaxEARL) with Pearson’s correlations, t-tests and Bland-Altman plots. Results For the phantom scans, the mean relative difference between SUVpeakPSF and SUVmaxEARL was -11.0% (SD=15.0%) and showed a correlation ρ=0.95. Considering only the three biggest spheres (volumes larger than 5 mL), the mean relative difference was 1.8% (SD=3.5%). The clinical dataset (total of 21 lesions analysed) presented similar results, with a perfect correlation between SUVpeakPSF and SUVmaxEARL (ρ=1.00) and a mean relative difference of -4.3% (SD=5.2%). This highlights that, overall, SUVpeakPSF values are slightly lower than SUVmaxEARL values. Only two lesions were identified as smaller than 5 mL using the EARL reconstruction, three with PSF. The relative difference between SUV implementations for those small lesions was -7.1% (SD=4.3%). Moreover, uptake time did not affect the differences seen between SUVpeakPSF and SUVmaxEARL, which were -4.2% (SD=5.0%) and -4.3% (SD=5.6%) for the 60 and 90 minutes post-injection data (p=0.89), respectively. Conclusion This pilot study suggests that SUVpeak derived from high resolution PSF reconstructed 18F-FDG PET/CT images might be used as a surrogate for SUVmaxEARL for lesions bigger than 5mL. Conclusions on smaller lesions cannot be substantiated due to limited sample size. Further research using data from different centres and on larger as well as different patient groups is required to fully evaluate the feasibility and clinical impact of using SUVpeakPSF as a surrogate for SUVmaxEARL. References 1. Mansor, S., Pfaehler, E., Heijtel, D., et al. (2017), Impact of PET/CT system, reconstruction protocol, data analysis method, and repositioning on PET/CT precision: An experimental evaluation using an oncology and brain phantom. Med. Phys., 44, 6413-6424. doi:10.1002/mp.12623 2. Kramer, G. M., Frings, V., Hoetjes, N., et al. (2016). Repeatability of quantitative whole-body 18F-FDG PET/CT uptake measures as function of uptake interval and lesion selection in non-small cell lung cancer patients. Journal of Nuclear Medicine, 57(9), 1343-1349. doi:10.2967/jnumed.115.170225.