Functional imaging of interstitial brachytherapy in pancreatic carcinoma xenografts using spectral CT: how does iodine concentration correlate with standardized uptake value of 18FDG-PET-CT?

Objective: This study aimed to investigate the correlation between iodine concentration (IC) for the quantitative analysis of spectral CT and maximum standardized uptake value (SUVmax) of 18 fludeoxyglucose positron emission tomography-CT ((18)FDG PET-CT) as an indicator of therapeutic response to interstitial brachytherapy in transplanted human pancreatic carcinomas in BALB/c-nu mice. Methods: Xenograft models were created by subcutaneous injection of SW1990 human pancreatic cancer cell suspensions into immunodeficient BALB/c-nu mice. 30 mice bearing SW1990 human pancreatic cancer cell xenografts were randomly separated into two groups: experimental (n=15; 1.0 mCi) and control (n=15, 0 mCi). After 2 weeks of treatment, spectral CT and (18)FDG microPET-CT scan were performed. IC values and SUVmax in the lesions were measured. IC normalized to the muscle tissue is indicated as nIC. The relationships between the nIC and SUVmax of the transplantation tumours were analysed. Results: 2 weeks after treatment, the nIC in three-phase scans and SUVmax of the experimental group were significantly lower than those of the control group. The nIC values of the three-phase scans have certain positive correlation with the SUVmax values (r=0.69, p<0.05; r=0.73 and p<0.05; r=0.80, p<0.05 in the 10-, 25- and 60-s phase, respectively). Conclusion: Spectral CT could serve as a valuable imaging modality, as our results suggest that nIC correlates with SUVmax of (18)FDG PET-CT for evaluating the therapeutic effect of I-125 interstitial brachytherapy in a pancreatic carcinoma xenograft. Advances in knowledge: Spectral CT offers opportunities to assess the therapeutic response of pancreatic cancer. This study supports the conclusion that nIC values in spectral CT could also serve as a valuable functional imaging parameter for early monitoring and evaluation of the therapeutic response of I-125 interstitial brachytherapy mouse models because the nIC correlates with the SUVmax of (18)FDG PET-CT.