Abstract
ObjectivesTo propose an easily applicable segmentation method (perPET-RT) for delineation of tumour volume during radiotherapy on interim fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in patients with non-small cell lung cancer (NSCLC).Material and methodsSixty-seven patients (51 primary tumours, 60 lymph nodes), from 4 prospective studies, underwent an FDG PET/CT scan during the fifth week of radiation therapy, using different generations of PET/CT. Per-therapeutic PET/CT scans were delineated in consensus by two experienced physicians leading to the gold standard threshold to be applied. The mathematical expression of Thopt, the optimal threshold to be applied as a function of the maximum standard uptake value (SUVmax), was determined. The performance of this method (perPET-RT) was assessed by computing the DICE similarity coefficient (DSC) and was compared with 8 fixed threshold values and 3 adaptive thresholding methods.ResultsThopt verified the following expression: Thopt = A.ln(1/SUVmax) + B where A and B were 2 constants. A and B were independent from the generation of PET/CT, but depended on the type of lesions (primary lung tumours vs. lymph nodes). PerPET-RT showed good to very good agreement in comparison to the gold standard. The mean and standard deviation of DSC value was 0.81 ± 0.13 for lung lesions and 0.78 ± 0.15 for lymph nodes. PerPET-RT showed a significant better agreement than the other segmentation methods (p < 0.001), except for one of the adaptive thresholding method ADT (p = 0.11).ConclusionOn the database used, perPET-RT has proven its reliability and accuracy for tumour delineation on per-therapeutic FDG PET/CT using only SUVmax measurement. This method may be used to delineate tumour volume for dose-escalation planning.Trial registrationNCT01261598, NCT01261585, NCT01576796.
Highlights
Non-Small Cell Lung Cancer (NSCLC) represents a leading cause of death by cancer in the world, especially in Europe and North America
In the case of NSCLC, pre-therapeutic FDG positron emission tomography/computed tomography (PET/CT) allows the delineation of the metabolic tumour volume (MTV), the exclusion of non-tumoral abnormalities and improves inter and intra observers reproducibility [6, 7], which are one of the main limitations when delineating on CT modality alone
Aerts et al [9] and Calais et al [10] showed that high FDG uptake areas on pre-therapeutic FDG PET/CT scans were highly correlated to the sites of local relapse or persistent abnormalities on post-therapeutic scans
Summary
Non-Small Cell Lung Cancer (NSCLC) represents a leading cause of death by cancer in the world, especially in Europe and North America. Aerts et al [9] and Calais et al [10] showed that high FDG uptake areas on pre-therapeutic FDG PET/CT scans were highly correlated to the sites of local relapse or persistent abnormalities on post-therapeutic scans. These findings lead to consider the idea of dose-escalation on a smaller volume, allowing a better local control of the disease and minimising in parallel early and late toxicity
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