FET-PET for malignant glioma treatment planning

Background and purpose The aim of this study was to compare MRI-based morphological gross tumour volumes (GTVs) to biological tumour volumes (BTVs), defined by the pathological radiotracer uptake in positron emission tomography (PET) imaging with 18 F-fluoroethyltyrosine (FET), subsequently clinical target volumes (CTVs) and finally planning target volumes (PTVs) for radiotherapy planning of glioblastoma. Patients and methods Seventeen patients with glioblastoma were included into a retrospective protocol. Treatment-planning was performed using clinical target volume (CTV=BTV+20mm or CTV=GTV+20mm+inclusion of the edema) and planning target volume (PTV=CTV+5mm). Image fusion and target volume delineation were performed with OTP-Masterplan®. Initial gross tumour volume (GTV) definition was based on MRI data only or FET–PET data only (BTV), secondarily both data sets were used to define a common CTV. Results FET based BTVs (median 43.9cm 3 ) were larger than corresponding GTVs (median 34.1cm 3 , p =0.028), in 11 of 17 cases there were major differences between GTV/BTV. To evaluate the conformity of both planning methods, the index (CTV MRT ∩CTV FET )/(CTV MRT ∪CTV FET ) was quantified which was significantly different from 1 (0.73±0.03, p Conclusion With FET–PET-CT planning, the size and geometrical location of GTVs/BTVs differed in a majority of patients. It remains open whether FET–PET-based target definition has a relevant clinical impact for treatment planning.