PET/CT in NPC: Is a whole body scanning necessary?

Objectives Explored the yield of “whole-body” FDG PET/CT in nasopharyngeal carcinoma(NPC). The aim of our study is to assess the incidence of distant metastases below diaphragm as an indicator of the contribution of vertex of skull to mid thigh (“whole-body”) FDG PET/CT in NPC imaging.

Methods FDG PET/CT scan reports of histologically proven NPC patients imaged in the department of Nuclear Medicine and PET, Singapore General Hospital, Singapore between 2003 and 2009 were reviewed for the total number of metastases and analyzed for the number of lesions above and below the diaphragm. The lesions below the diaphragm were further analyzed to see if they were solitary or if multiple if any were above the diaphragm.

Results 717 reports were included with 709 total lesions, of which 352of709 (49.6%) were distant metastases, 152of352 (43%) were below the diaphragm and 16of352 (4.5%) had no co-existing distant metastases above the diaphragm. Of the 16 lesions, 12of16 (75%) were solitary (42%liver,50%bones,8%nodes) while 4of16 (25%) had concurrent metastases below the diaphragm. Of the 717 reports 30.3% were staging, 4.9% response, 31.7% recurrence and 33.2% follow up.

Conclusions In our retrospective study 57% of FDG avid metastases in NPC were above the diaphragm. FDG PET/CT from the skull to the diaphragm would have staged 95.5% of cases. A prospective study is required to explore the advisability of limiting FDG PET from the vertex to the diaphragm in NPC as this could reduce the CT radiation burden, scanning time and reporting time but at the cost of missing 4.5% of metastases