Page 18 - 18F-FDG PET as biomarker in aggressive lymphoma; technical and clinical validation

Chapter 1
Baseline metabolic tumor volume
More recently several publications report that, apart from the level of maximum [18F]FDG uptake, the so‐called metabolic tumor volume (MTV ) may also harbor prognostic value in DLBCL [44,45]. In lung cancer it was demonstrated that test-retest variability of metabolic volume was high compared to SUV, thus careful optimization of imaging and delineation method parameters is needed when using metabolic volume as a prognostic parameter [46]. A more recent study in gastro-intestinal malignancies showed high feasibility of 96% and repeatability for MTV measured with a 50% threshold of mean SUV of a sphere of 12mm with highest local intensity and recommended this method for multicenter [18F] FDG PET studies [47]. However, for lymphoma the optimal method in terms of interobserver agreement (fast, robust and reliable) is not yet fully investigated and determined. Therefore, technical standardization and validation is needed before implementation of MTV as prognostic factor in trials and possible future clinical use.
PETRA Consortium
It is clear that no single study is able to collect enough evidence to determine the optimal timing, response criteria and treatment effect of interim [18F]FDG PET. Therefore, collaboration with national and international experts in lymphoma (hematologists) and PET imaging (nuclear medicine specialists) was needed. This idea was pitched by prof.dr. Josée Zijlstra (hematologist), prof.dr. Otto Hoekstra (nuclear medicine specialist), prof.dr.ir. H.C.W. de Vet (epidemiologist) and prof.dr. R. Boellaard (medical physicist) in the international lymphoma conference in Menton in 2011. Experts from HOVON, London and from a large German randomized trial group (PETAL) already intended to join before a formal collaboration was started. Other researchers involved in interim [18F] FDG PET studies in DLBCL were identified by a systematic literature searches and were invited to join the consortium. Our research group successfully set up a collaboration with principal investigators from these major international interim [18F]FDG PET studies in DLBCL by organizing meetings, development of policy documents and protocols, and solving several legal and practical issues. Finally, a shared database was established with imaging and clinical data of these studies, called PETRA [48]. PETRA is an abbreviation of PET Re-Analysis. For the
16