18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography–Based Radiotherapy Target Volume Definition in Non–Small-Cell Lung Cancer: Delineation by Radiation Oncologists vs. Joint Outlining With a PET Radiologist?

Purpose: 18F-Fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) has benefits in target volume (TV) definition in radiotherapy treatment planning (RTP) for non–small-cell lung cancer (NSCLC); however, an optimal protocol for TV delineation has not been determined. We investigate volumetric and positional variation in gross tumor volume (GTV) delineation using a planning PET/CT among three radiation oncologists and a PET radiologist. Methods and Materials: RTP PET/CT scans were performed on 28 NSCLC patients (Stage IA–IIIB) of which 14 patients received prior induction chemotherapy. Three radiation oncologists and one PET radiologist working with a fourth radiation oncologist independently delineated the GTV on CT alone (GTVCT) and on fused PET/CT images (GTVPETCT). The mean percentage volume change (PVC) between GTVCT and GTVPETCT for the radiation oncologists and the PVC between GTVCT and GTVPETCT for the PET radiologist were compared using the Wilcoxon signed-rank test. Concordance index (CI) was used to assess both positional and volume change between GTVCT and GTVPETCT in a single measurement. Results: For all patients, a significant difference in PVC from GTVCT to GTVPETCT exists between the radiation oncologist (median, 5.9%), and the PET radiologist (median, -0.4%, p = 0.001). However, no significant difference in median concordance index (comparing GTVCT and GTVFUSED for individual cases) was observed (PET radiologist = 0.73; radiation oncologists = 0.66; p = 0.088). Conclusions: Percentage volume changes from GTVCT to GTVPETCT were lower for the PET radiologist than for the radiation oncologists, suggesting a lower impact of PET/CT in TV delineation for the PET radiologist than for the oncologists. Guidelines are needed to standardize the use of PET/CT for TV delineation in RTP. [Copyright &y& Elsevier]