E-S Koh, R J Francis, G Ninatti, I Ruisi, M A Ebert, E Lau, A Whitehead, J Descallar, E H Barnes, S T Lee, E L Thomas, M B Pinkham, M Back, S P Ng, N Bucknell, H K Gan, O Cook, R Dykyj, A Moore, S Porter, Patricia Banyer, F E Scott, D L Bailey, N Barry, T Akhurst, R Alipour, A Bece, C Bettingdon, S Beuzeville, J H Chang, B Chua, C Clark, J Croker, S Gill, P Gorayski, E Hsiao, K Jung, S Khan, D Krishna, I Kirkwood, H Le, P Lin, T Ly, M McGuiness, S Ngai, D A Pattison, C Phillips, A P Pullar, G Schembri, J Sia, F Syed, P Thomas, W Vallat, M Wada, D Wong, J Yap, T C Yeow, A K Nowak, F Foroudi, M Rosenthal, P Roach, L Adda, R De Abreu Lourenco, B A Moffat, C Brighi, A Lasocki, L Holloway, M Fay, A M Scott
FET-PET differed significantly from MRI-based GTV delineation, with its incorporation leading to a clinically meaningful change in GTV in the majority of participants.
BACKGROUND: The FET-PET in Glioblastoma (FIG) study (TROG 18.06) assessed the impact of adding FET-PET to MRI on radiotherapy gross tumor volume delineation in newly diagnosed glioblastoma.
METHODS: This multicenter prospective phase 2 study evaluated participants with newly diagnosed glioblastoma IDH-wildtype undergoing post-operative MRI and FET-PET imaging before adjuvant radiotherapy, delivered according to standard MRI-based planning. The FET-PET-positive biological tumor volume (BTV) was used to derive the Hybrid (FET-PET+MRI) gross tumor volume (Hybrid-GTV). Primary outcomes were: 1) BTV excluded from the GTV defined on MRI alone (MR-GTV); 2) Hybrid-GTV excluded from the MR-GTV with both comparisons analyzed by non-overlap volume (cm3 and %), dosimetry (D98 and V95) and spatial similarity metrics; 3) clinically meaningful change in GTV non-overlap percentage volume with the addition of FET-PET.
RESULTS: There were 172 participants recruited, n = 140 evaluable. Median BTV was 23.1 cm3, median MR-GTV was 32.1 cm3, and median Hybrid-GTV was 46.0 cm3. Hybrid-GTV was significantly larger than the MR-GTV (p < 0.001), with a larger Hybrid-GTV observed in 83% of cases. Comparing BTV to MR-GTV, median non-overlap volume was 10.1 cm3 and non-overlap percentage volume 53.5%. Comparing Hybrid-GTV to MR-GTV, median non-overlap volume was 14.9 cm3 and non-overlap percentage volume 33.9%. D98 and V95 were lower for the Hybrid-GTV than for the MR-GTV, suggesting lower dose coverage. Applying a > 20% non-overlap percentage volume threshold, 76% of participants had a meaningful change in GTV with the addition of FET-PET.
CONCLUSION: FET-PET differed significantly from MRI-based GTV delineation, with its incorporation leading to a clinically meaningful change in GTV in the majority of participants.