Biological target volume based on fluorine-18-fluorode-oxyglucose positron emission tomography/computed tomography imaging: a spurious proposition?

Purpose To assess whether the high metabolic region of fluorine-18-fluorode-oxyglucose ( 18 F-FDG) in the primary lesion is the crux for recurrence in patients with nasopharyngeal carcinoma (NPC), to assess the feasibility and rationale for use of biological target volume (BTV) based on 18 F-FDG positron emission tomography/computed tomography ( 18 F-FDG-PET/CT). Methods The retrospective study included 33 patients with NPC who underwent 18 F-FDG-PET/CT at the time of initial diagnosis as well as the time of diagnosis of local recurrence. Paired 18 F-FDG-PET/CT images for primary and recurrent lesion were matched by deformation coregistration method to determine the cross-failure rate between two lesions. Results The median volume of the V pri (primary tumor volume using the SUV thresholds of 2.5), the V high (the volume of high FDG uptake using the SUV50%max isocontour), and the V recur (the recurrent tumor volume using the SUV thresholds of 2.5) were 22.85, 5.57, and 9.98 cm 3 , respectively. The cross-failure rate of V recur∩high showed that 82.82% (27/33) of local recurrent lesions had < 50% overlap volume with the region of high FDG uptake. The cross-failure rate of V recur∩pri showed that 96.97% (32/33) of local recurrent lesions had > 20% overlap volume with the primary tumor lesions and the median cross rate was up to 71.74%. Conclusion 18 F-FDG-PET/CT may be a powerful tool for automatic target volume delineation, but it may not be the optimal imaging modality for dose escalation radiotherapy based on applicable isocontour. The combination of other functional imaging could delineate the BTV more accurately.