Local failure after radical radiotherapy of non-small cell lung cancer in relation to the planning FDG-PET/CT

<p><b>Objectives:</b> Local recurrence (rec) in lung cancer is associated with poor survival. This study examined whether the pattern of failure is associated with the most PET avid volume in the planning-FDG-PET/CT scan (p-PET/CT).</p> <p><b>Methods:</b> 162 consecutive inoperable NSCLC patients (pts) receiving radiotherapy between January 2012 and April 2014 were reviewed. Radiotherapy was delivered in 2 Gy/fraction (5f/week) to a total dose of 60–66 Gy. Pts were followed with CT scans every third month. Patients with local rec as first event were analyzed. For the primary tumor (T) the overlap-fraction (OF) between 50% of SUV<sub>peak</sub> on p-PET/CT and the volume of T-rec was calculated: OF = (SUV<sub>p50</sub>∩T-rec)/min(SUV<sub>p50</sub>, T-rec). Similarly for the GTV on the p-CT: OF = (GTV∩T-rec)/min(GTV, T-rec). OF was based on a rigid registration between p-PET/CT and rec-CT with PET guided delineation of T- rec. For lymph nodes (LN), the correlation between the location of treated-LN and the location of recurrence-LN was evaluated.</p> <p><b>Results:</b> 67 patients developed local rec. 51 pts had rec in T-site, 45 pts in LN-site. Due to anatomical changes, reliable registration between p-CT and rec-CT was only obtained in 26 pts with T-rec. The median OF<sub>SUVp50</sub> was 52, 8% [range 26; 100%] and the median OF<sub>GTV</sub> was 80.5% [19.7; 100%]. Eleven pts had higher OF<sub>SUVp50</sub> than OF<sub>GTV</sub>. LN-rec predominantly occurred in the station 2R (32%), 4R (46%), 7 (46%) and right hilum (36%). Pts with malignant LNs in station 4R or 7 on p-CT had a high risk of rec in these stations; 4R (55%) and 7 (83%).</p> <p><b>Conclusions:</b> This study indicates that the most PET active volume on p-PET-CT is a driver for rec at T-site. LN-recurrences predominantly appear in station 2R, 4R, 7 and right hilum. Additional confirmatory studies regarding lymph node mapping and selective lymph node irradiation is needed.</p>