Assessment of tumour response after stereotactic ablative radiation therapy for lung cancer: A prospective quantitative hybrid ¹⁸F‐fluorodeoxyglucose‐positron emission tomography and CT perfusion study

Abstract

Introduction: Stereotactic ablative radiotherapy (SABR) is a guideline-recommended treatment for inoperable stage I non-small cell lung cancer (NSCLC), but imaging assessment of response after SABR is difficult. The goal of this study was to evaluate imaging-based biomarkers of tumour response using dynamic 18 F-FDG-PET and CT perfusion (CTP). Methods: Thirty-one patients with early-stage NSCLC participated in this prospective correlative study. Each underwent dynamic 18 F-FDG-PET/CTP studies on a PET/CT scanner pre-and 8 weeks post-SABR. The dynamic 18 F-FDG-PET measured the tumour SUV max , SUV mean and the following parameters: K 1 , k 2 , k 3 , k 4 and K i , all using the Johnson-Wilson-Lee kinetic model. CTP quantitatively mapped BF, BV, MTT and PS in tumours and measured largest tumour diameter. Since free-breathing was allowed during CTP scanning, non-rigid image registration of CT images was applied to minimize misregistration before generating the CTP functional maps. Differences between pre-and post-SABR imaging-based parameters were compared. Results: Tumour size changed only slightly after SABR (median 26 mm pre-SABR vs. 23 mm post-SABR; P = 0.01). However, dynamic 18 F-FDG-PET and CTP study showed substantial and significant changes in SUV max , SUV mean , k 3 , k 4 and K i . Significant decreases were evident in SUV max (median 6.1 vs. 2.6; P < 0.001), SUV mean (median 2.5 vs. 1.5; P < 0.001), k 3 (relative decrease of 52%; P = 0.002), K i (relative decrease of 27%; P = 0.03), whereas there was an increase in k 4 (+367%; P < 0.001). Conclusions: Hybrid 18 F-FDG-PET/CTP allowed the response of NSCLC to SABR to be assessed regarding metabolic and functional parameters. Future studies are needed, with correlation with long-term outcomes, to evaluate these findings as potential imaging biomarkers of response.

Plasma radio–metabolite analysis of PET tracers for dynamic PET imaging: TLC and autoradiography

“…In this study, we established an alternate method to HPLC to determine the fraction of radio-labeled parent The effect of not correctly accounting for blood radio-metabolite was investigated with computer simulation using a previously published kinetics model (16). For all parameter sets listed in Table 1, the fitting to the Additional simulations were performed to investigate how intersubject variability in parent tracer fractions over time would affect the accuracy of the estimated kinetic parameters.…”

Plasma Radio–Metabolite Analysis of PET Tracers for Dynamic PET Imaging: TLC and Autoradiography

“…The effect of not correctly accounting for blood radio-metabolite was investigated with computer simulation using a previously published kinetics model (14). For all parameter sets listed in Table 1 (22) with the use of solid phase extraction and HPLC.…”

“…A simulation study was performed to observe the effect of blood plasma radio-metabolites in the estimation of kinetic parameters. For simulating the tissue TAC, our in-house flow modified two compartment (F2TC) model (14) that models the bi-directional permeation of the endothelial barrier during the transit time of the tracer through blood vessels, was utilized. The flow scaled impulse residue function (IRF F (t)) for the model is expressed as:…”

Kinetic Analysis of Dominant Intraprostatic Lesion of Prostate Cancer Using Quantitative Dynamic [18F]DCFPyL-PET: Comparison to [18F]fluorocholine-PET

“…TACs for DIL and benign tissue were obtained by nding the area-weighted average of the mean activity in each DIL and benign ROI for all slices. The dynamic TACs of both tracers were analyzed using the ow modi ed two r tissue compartment model (F2TCM), as described in a previous publication [19]. This model accounts for the combined effects of the three tracer uptake processes: tracer delivery via blood ow; bidirectional permeation of the blood-tissue barrier during tracer transit through vessels; and binding to and dissociation from the target.…”