(18)F-FDG avid volumes on pre-radiotherapy FDG PET as boost target delineation in non-small cell lung cancer

Background: To investigate whether during/post-radiotherapy FDG uptake locations within tumors is likely identified using a pre-radiotherapy scan for non-small cell lung cancer (NSCLC), ultimately enabling confirm that a suitable metabolically active sub-volume pre-radiotherapy of the primary tumor for radiation boosting target.

Methods: Patients with a pathologically proven inoperable stage II-III NSCLC were enrolled. For each patient, one pre-radiotherapy (pre-RT) plus one following 40Gy during-radiotherapy (during-RT) or post-radiotherapy (post-RT) FDG PET/CT scans were available. On pre-RT scan, the high FDG uptake region were auto-delineated using several percentage of the maximal standardized uptake value (SUVmax) thresholds, varying from 40% to 70%. On during-RT scan, FDG uptake region is delineated by 40% SUVmax, manual method respectively. With the FDG-positive areas on post-RT images is defined as 80% SUVmax. The overlap fractions (OFs) were calculated between pre-RT scan and during-RT or post-RT scan. Semi-quantitative assessment was used to determine SUVmax and metabolic tumor volume (MTV). The SUVmax changes during-RT representing the radiotherapy (RT) early metabolic response is attainable. Then, a spearman correlation was used to analysis the correlation between percentage changes in SUVmax during-RT and SUVmax-threshold definition volume pre-RT.

Results: Of those 7 patients, a total of 16 FDG-PET scans were acquired. 5 patients were received pre-RT and during-RT scan, while 2 of these 5 patients underwent both post-RT scan. 2 patients were received FDG-PET/CT scan pre-RT and post-RT. The pre-RT scan threshold delineations of 50% SUVmax had a large OF with the 40% SUVmax threshold and manual method delineation on the during-RT scan, 74.3% and 84.4%, respectively. Comparably, the 80% SUVmax on the post-RT scan also largely corresponded (OF > 72%) with the 50% SUVmax threshold and the volume was small compared to the gross tumor volume (GTV), accounting for 29.4%. However, the 50% SUVmax threshold was not correlate with the percentage change in SUVmax (P > 0.05).

Conclusions: A pre-RT FDG-PET scan allows for the identification of during- and post-RT FDG uptake locations. The volume defined by 50% SUVmax may be a suitable threshold for dose escalation.