Evaluating the impact of FET PET on radiotherapy target volume delineation: Results of the radiation oncology credentialing program from the prospective, multi-centre trial evaluating FET PET in glioblastoma (FIG) study – TROG 18.06

Background and purpose The [18]F-fluoroethyl-L-tyrosine (FET) PET in Glioblastoma (FIG) study is an Australian prospective, multi-centre trial evaluating FET PET for newly diagnosed glioblastoma management. The Radiation Oncology credentialing program aimed to assess the feasibility in Radiation Oncologist (RO) derivation of standard-of-care (MR) and hybrid (MR + FET) target volumes, which incorporated pre-defined FET PET biological tumour volumes (BTVs). Materials and methods Central review and analysis of MR-derived target volumes (TVMR) and hybrid target volumes (TVMR+FET) was undertaken across three benchmarking cases. Associated BTVs were pre-defined by a sole nuclear medicine expert. Intraclass correlation coefficient (ICC) evaluated volume agreement. RO contour spatial and boundary agreement were evaluated (Dice similarity coefficient [DSC], Jaccard index [JAC], overlap volume [OV], Hausdorff distance [HD] and mean absolute surface distance [MASD]). Dose plan generation, involving one case per site, was also assessed. Results Data from 19 ROs across 10 trial sites (54 initial submissions, 8 resubmissions requested, 4 conditional passes) was assessed with an initial pass rate of 77.8 %, with all resubmissions passed. TVMR+FET were significantly larger than TVMR (p < 0.001) for all cases. Between ROs, volume agreement was moderate-to-excellent for GTVMR (ICC = 0.910; 95 % CI, 0.708–0.997) and good-to-excellent for GTVMR+FET (ICC = 0.965; 95 % CI, 0.871–0.999). Across all cases, GTVMR+FET showed greater spatial overlap and boundary agreement between ROs compared to GTVMR. CTVMR+FET showed lower average boundary agreement versus CTVMR (MASD: 1.73 mm vs. 1.61 mm, p = 0.042). All ten sites passed the planning case exercise. Conclusion The national FIG study credentialing program demonstrated feasibility in successful credentialing of 19 ROs across 10 study sites, resulting in increased expertise in TVMR+FET delineation.