P53 The utility of PET-CT in detecting non-nodal extrathoracic metastases in lung cancer compared to the staging CT

Background NICE Lung Cancer Guidelines 2011 recommend performing a PET-CT in patients being considered for radical treatment after a staging CT of the neck, chest and liver has been performed. If mediastinal lymphadenopathy is detected by CT and the aetiology is determined by intervention, the true value of PET-CT is in the detection of non-nodal extrathoracic metastases. The yield of PET-CT in detecting non-nodal extrathoracic metastases has not previously been reported in comparison to that of reviewing the prior staging CT. Methods 235 consecutive lung cancer patients with no known extrathoracic metastases referred for a staging PET-CT scan prior to radical therapy were included. All patients underwent a contrast-enhanced CT of the neck, chest and liver and a whole body PET-CT. Results The median age at diagnosis was 72 years, 141 men (60%). Patients had stage Ia (16%), Ib (19%), IIa (6%), IIb (7%), IIIa (25%), IIIb (6%) and IV (20%) disease. The median interval between the CT and PET-CT scans was 25 days (IQR, 18 29). 21 (9%) patients had 25 extrathoracic and extra-cerebral metastases. 9 metastases were identified on the CT component of the PET-CT and review of the prior staging CT. 16 metastases were not visible on the staging CT scan; 4 (humeral and pelvic) bone metastases were outside the staging CT field of view, 6 metastases had developed since referral (median scan interval 28 days; IQR, 19 39), and 6 were only identified on PET-CT. Conclusion The addition of pelvic CT in patients referred for PET-CT staging prior to radical therapy may allow for increased detection of extrathoracic metastases. PET-CT detects extrathoracic metastases which were missed or invisible on the staging CT. Lung cancer patients should be offered a contrast-enhanced CT of the neck, chest, abdomen and pelvis at staging. Potentially, an interval CT scan should be performed if a delay of greater than 30 days has occurred prior to the PET-CT scan being performed.