In order to observe impact of PET/CT on precise and accurate radiotherapy (PAR) planning of patients with non-small cell lung cancer (NSCLC)

21 patients with NSCLC had CT and FDG-hybrid PET examinations prospectively in radiation treatment position.Five radiation oncologists delineated independently the GTV including positive lymph nodes of 21 lung cancer patients on CT.The same observers delineated the GTV of the 21 patients on matched PET/CT scans.The size of GTV and coefficient of variation were used to assess inter-observer variability.The results show that all patients’ GTVCT differed from their GTVPET/CT

and the variability in the contouring of GTVCT among different physicians was statistically significant (F=9.25

P<0.001)

but less significant in the contouring of GTVPET/CT.The mean coefficient of variation for GTV based on PET/CT was significantly smaller (t=-7.46

P<0.001) than that for CT data only.It van be concluded that PET/CT may have notable impact on clinical staging of NSCLC and on its PAR planning

and will result in a reduction in this variation of the contouring of GTVs among different radiation oncologists.