Calibration Test of PET Scanners in a Multi-Centre Clinical Trial on Breast Cancer Therapy Monitoring Using 18F-FLT

Abstract

A multi-centre trial using PET requires the analysis of images acquired on different systems We designed a multi-centre trial to estimate the value of 18F-FLT-PET to predict response to neoadjuvant chemotherapy in patients with newly diagnosed breast cancer. A calibration check of each PET-CT and of its peripheral devices was performed to evaluate the reliability of the results.Material and Methods11 centres were investigated. Dose calibrators were assessed by repeated measurements of a 68Ge certified source. The differences between the clocks associated with the dose calibrators and inherent to the PET systems were registered. The calibration of PET-CT was assessed with an homogeneous cylindrical phantom by comparing the activities per unit of volume calculated from the dose calibrator measurements with that measured on 15 Regions of Interest (ROIs) drawn on 15 consecutive slices of reconstructed filtered back-projection (FBP) images. Both repeatability of activity concentration based upon the 15 ROIs (ANOVA-test) and its accuracy were evaluated.ResultsThere was no significant difference for dose calibrator measurements (median of difference −0.04%; min = −4.65%; max = +5.63%). Mismatches between the clocks were less than 2 min in all sites and thus did not require any correction, regarding the half life of 18F. For all the PET systems, ANOVA revealed no significant difference between the activity concentrations estimated from the 15 ROIs (median of difference −0.69%; min = −9.97%; max = +9.60%).ConclusionNo major difference between the 11 centres with respect to calibration and cross-calibration was observed. The reliability of our 18F-FLT multi-centre clinical trial was therefore confirmed from the physical point of view. This type of procedure may be useful for any clinical trial involving different PET systems.

The 68 Ge phantom-based FDG-PET site qualification program for clinical trials adopted by FIL (Italian Foundation on Lymphoma)

“…The experience with the 68 Ge phantom prompted us to require a re-calibration in case of an observed BAC variability higher than 3-5%. In this study we did not ship a radionuclide calibrator source along with 68 Ge phantom differently from Bouchet et al [49], who, by combining a radionuclide activity calibration check and a 18 F-filled uniform phantom, demonstrated an interscanner variability of the 11 PET/CT scanners lower than 10%. Therefore, within our experimental framework it was not possible to separate the bias coming from an inaccurate radionuclide calibrator with respect to the bias due to the whole calibration process.…”

For avid glucose tumors, the SUV peak is the most reliable parameter for [18F]FDG-PET/CT quantification, regardless of acquisition time

“…For all tumor SUVs, maximal fluctuations were observed between the shortest replay (R 1.5 or R 2 ) and R 10 . Considering a maximum fluctuation of 10 % as an acceptable level of variation for tumor SUV [ 11 ], the number of patients with tumor SUV fluctuations >10 % (compared to R 10 ) was noted. R 1.5 and R 2 were the replays in which the higher number of patients with SUV fluctuations >10 % was observed, whatever the type of SUV.…”

“…Using a reference time of 15 min, Lodge et al [ 20 ] reported similar results with a significant lower bias for the SUV peak compared to the SUV max for the 1-, 2-, 3-, and 4-min images. In our study, large SUV max variations up to 58 % (R 1.5 versus R 10 ) were observed for the same tumor in the same patient, which is obviously unacceptable for response-monitoring purposes, particularly when accumulated to other sources of bias [ 11 , 21 ] and if a threshold value is applied to determine treatment response as with PERCIST criteria [ 3 ]. As previously reported [ 2 , 4 , 22 ], we noted that fluctuations of SUV max also affected threshold method SUV since the VOI was determined by selecting pixel values equal to 41 % of the maximum pixel value.…”

Combined morphologic and metabolic pipeline for Positron emission tomography/computed tomography based radiotherapy response evaluation in locally advanced pancreatic adenocarcinoma

“…However, the use of multiple PET/CT scanners may have led to some inconsistency in metabolic metric calculations despite our best effort to calibrate these scanners to be consistent. A calibration comparison study on 11 regularly maintained PET/CT scanners observed good reproducibility and accuracy of all dose calibrators and reported no major deviation across different PET calibration systems [29]. Nevertheless, many quantitative descriptors draw from GTVs, for instance, textural features, have been reported to have limited robustness against multiscanners [30].…”