[18]F-fluoroethyl-l-tyrosine positron emission tomography for radiotherapy target delineation: Results from a...

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 target volumes (TV_MR) and hybrid target volumes (TV_MR+FET) incorporating pre-defined FET PET biological tumour volumes (BTVs).

Central review and analysis of TV_MR and TV_MR+FET was undertaken across three benchmarking cases. BTVs were pre-defined by a sole nuclear medicine expert. Intraclass correlation coefficient (ICC) confidence intervals (CIs) 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 (one case per site) was assessed.

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 %; all resubmissions passed. TV_MR+FET were significantly larger than TV_MR (p < 0.001) for all cases. RO gross tumour volume (GTV) agreement was moderate-to-excellent for GTV_MR (ICC = 0.910; 95 % CI, 0.708-0.997) and good-to-excellent for GTV_MR+FET (ICC = 0.965; 95 % CI, 0.871-0.999). GTV_MR+FET showed greater spatial overlap and boundary agreement compared to GTV_MR. For the clinical target volume (CTV), CTV_MR+FET showed lower average boundary agreement versus CTV_MR (MASD: 1.73 mm vs. 1.61 mm, p = 0.042). All sites passed the planning exercise.

The credentialing program demonstrated feasibility in successful credentialing of 19 ROs across 10 sites, increasing national expertise in TV_MR+FET delineation.