Identification of residual metabolic-active areas within NSCLC tumours using a pre-radiotherapy FDG-PET-CT scan: a prospective validation

H. Aerts, J. Bussink, W. Oyen, W. van Elmpt, A. Folgering, D. Emans, M. Velders, P. Lambin and D. De Ruysscher

Department of Radiation Oncology (MAASTRO), GROW - School for Oncology and Developmental Biology, Maastricht University Medical Center (MUMC+), Maastricht, The Netherlands.
Jan, 2012



It was recently described that high FDG-uptake areas pre-radiotherapy largely correspond with residual metabolic-active areas post-radiotherapy. Here, an independent prospective validation of these results was performed using an overlap-fraction (OF) calculation of various FDG-uptake based thresholds. Data from twelve patients treated at Radboud University Nijmegen Medical Center with lung cancer were analyzed. All patients underwent two FDG-PET-CT scans, one pre-radiotherapy (pre-RT) and one approximately three months after treatment (post-RT). Of the twelve analyzed patients, eight patients showed residual FDG uptake on the post-RT scan and were included for analysis. One of these patients had a residue that was not clearly distinguishable from the surrounding tissue due to FDG avid inflammation. Therefore, seven patients remained for further analysis. The mean volume of the residual metabolic-active areas post-RT was 14.6±10.0\% (mean±SD) of the mean volume of the gross tumour volume (GTV) pre-RT. The residual metabolic-active areas largely corresponded with the pre-RT GTV (OF=93.7±7.2\%). The pre-RT-scan threshold delineations of 34\%, 40\% and 50\% of the SUV(max) had a large OF with the residual region, 86.9±8.3\%, 77.4±8.1\% and 67.9±6.8\%, respectively. In this independent dataset, we confirmed that the location of residual FDG-uptake areas after radiotherapy corresponds with the high FDG-uptake areas pre-radiotherapy. Therefore, a pre-radiotherapy FDG-PET-CT scan can potentially be used for radiotherapy dose redistribution.