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Multicenter Study
. 2023 Nov;50(13):3970-3981.
doi: 10.1007/s00259-023-06371-5. Epub 2023 Aug 11.

Delineation and agreement of FET PET biological volumes in glioblastoma: results of the nuclear medicine credentialing program from the prospective, multi-centre trial evaluating FET PET In Glioblastoma (FIG) study-TROG 18.06

Affiliations
Multicenter Study

Delineation and agreement of FET PET biological volumes in glioblastoma: results of the nuclear medicine credentialing program from the prospective, multi-centre trial evaluating FET PET In Glioblastoma (FIG) study-TROG 18.06

Nathaniel Barry et al. Eur J Nucl Med Mol Imaging. 2023 Nov.

Abstract

Purpose: The O-(2-[18F]-fluoroethyl)-L-tyrosine (FET) PET in Glioblastoma (FIG) trial is an Australian prospective, multi-centre study evaluating FET PET for glioblastoma patient management. FET PET imaging timepoints are pre-chemoradiotherapy (FET1), 1-month post-chemoradiotherapy (FET2), and at suspected progression (FET3). Before participant recruitment, site nuclear medicine physicians (NMPs) underwent credentialing of FET PET delineation and image interpretation.

Methods: Sites were required to complete contouring and dynamic analysis by ≥ 2 NMPs on benchmarking cases (n = 6) assessing biological tumour volume (BTV) delineation (3 × FET1) and image interpretation (3 × FET3). Data was reviewed by experts and violations noted. BTV definition includes tumour-to-background ratio (TBR) threshold of 1.6 with crescent-shaped background contour in the contralateral normal brain. Recurrence/pseudoprogression interpretation (FET3) required assessment of maximum TBR (TBRmax), dynamic analysis (time activity curve [TAC] type, time to peak), and qualitative assessment. Intraclass correlation coefficient (ICC) assessed volume agreement, coefficient of variation (CoV) compared maximum/mean TBR (TBRmax/TBRmean) across cases, and pairwise analysis assessed spatial (Dice similarity coefficient [DSC]) and boundary agreement (Hausdorff distance [HD], mean absolute surface distance [MASD]).

Results: Data was accrued from 21 NMPs (10 centres, n ≥ 2 each) and 20 underwent review. The initial pass rate was 93/119 (78.2%) and 27/30 requested resubmissions were completed. Violations were found in 25/72 (34.7%; 13/12 minor/major) of FET1 and 22/74 (29.7%; 14/8 minor/major) of FET3 reports. The primary reasons for resubmission were as follows: BTV over-contour (15/30, 50.0%), background placement (8/30, 26.7%), TAC classification (9/30, 30.0%), and image interpretation (7/30, 23.3%). CoV median and range for BTV, TBRmax, and TBRmean were 21.53% (12.00-30.10%), 5.89% (5.01-6.68%), and 5.01% (3.37-6.34%), respectively. BTV agreement was moderate to excellent (ICC = 0.82; 95% CI, 0.63-0.97) with good spatial (DSC = 0.84 ± 0.09) and boundary (HD = 15.78 ± 8.30 mm; MASD = 1.47 ± 1.36 mm) agreement.

Conclusion: The FIG study credentialing program has increased expertise across study sites. TBRmax and TBRmean were robust, with considerable variability in BTV delineation and image interpretation observed.

Keywords: Clinical trials; Credentialing; FET PET; Glioblastoma; Inter-observer.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
An overview of NMP credentialing by expert reviewers and their sources of violations of the two key assessments during credentialing: FET1 BTV delineation and FET3 image interpretation. The frequency of acceptable, minor, and major violations is shown for FET1 (a) and FET3 (c), with violations split into initial, first resubmission, and second resubmission. Frequency of FET1 (b) and FET3 (d) violation reasons, accrued from reviewer comments, is shown. Violation reasons are also broken down into reports that requested resubmissions to highlight NMP critical errors
Fig. 2
Fig. 2
Boxplots showing the distribution of NMP BTVs (left), TBRmax (middle), and TBRmean (right) grouped by each nuclear medicine credentialing case
Fig. 3
Fig. 3
Illustration of credentialing image FET1CASE2 that exhibited the best (DSC = 0.88 ± 0.05) agreement amongst NMPs (left) and credentialing image FET3CASE2 that showed the poorest (DSC = 0.77 ± 0.09) agreement (right). Superimposed NMP contours are shown in red. Discrepancy between NMPs when including the additional area of uptake (white arrow) in FET3CASE2 is likely the main source of variability in the pairwise analysis
Fig. 4
Fig. 4
Boxplots visualising the distribution of pairwise Dice similarity coefficient (DSC) of each delineated structure, grouped by case. The biological tumour volume (BTV), GTV0 (volume obtained after threshold is applied), and Static VOI are all generated as part of the delineation process. For each set of credentialing cases, spatial overlap is assessed by calculating the DSC for every pairwise combination of NMP contours

Comment in

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