####Introduction Historically, the provision of positron emission tomography (PET) in the UK has lagged behind Western Europe and the USA. In 2003, for example, the population served per PET scanner in Belgium was 0.54 million, while in the UK it was 8.6 million. It is estimated that, on current evidence, 800 PET scans per million population are required per annum. With a population of approximately 5 million in Scotland this equates to 4,000 scans per annum. Each scanner is expected to perform 2,000 scans per year, but this does not take into account research into new applications for PET imaging or the geographical considerations which limit the distances patients can travel and the distances over which the radioactive isotopes can be transported. Oncology accounts for 85–90% of the use of PET imaging, with a smaller number of scans requested for neurological or cardiac patients. Recent developments have allowed co-registration of computerised tomography (CT) and PET images (PET/CT). With this type of scanner, anatomical and functional images can be acquired in a single examination. This has been shown to increase the accuracy over PET alone. For the majority of oncological studies the fluorine-labelled glucose analogue 18F-fluoro-deoxyglucose (FDG) is used. This is based on the predominantly glycolytic metabolism found in most solid tumours. The UK Government and Department of Health believe that every cancer network within the UK should have access to PET scanning. Within the USA, the Center for Medicare and Medicaid Services will reimburse for PET imaging in lung cancer, lymphoma, colorectal cancer, melanoma, oesophageal cancer and head and neck cancer. The evidence of benefit is strongest in non-small cell lung cancer, Hodgkin’s and non-Hodgkin’s lymphoma and colorectal carcinoma, and these are currently the tumours where the routine use of PET is accepted in the UK. ####Non-small-cell lung carcinoma (NSCLC) A quantification of FDG uptake by calculation of the standardised uptake value (SUV) at initial staging is of prognostic value in NSCLC. While several studies have reported an improved survival with a low initial SUV, the cut-off value that accurately predicts prognosis has still to be determined.[1,2] In a retrospective study of 96 patients with NSCLC whose staging included FDG PET, a high FDG uptake was associated with reduced overall survival and disease-free survival.[2] The median survival was significantly longer in patients with a lower (SUVmax ≤ 7.8) FDG uptake (127 months vs 69 months, p=0.001). Disease-free survival was also significantly better for lower metabolic tumours: 96.1 months vs 87.7 months (p=0.01). 18F-fluoro-deoxyglucose PET has been used to predict the long-term prognosis after induction treatment prior to resection and, in patients with locally advanced and advanced stages of NSCLC, has been shown to be predictive for clinical outcome at an early stage of treatment. ####Hodgkin’s and non-Hodgkin’s lymphoma Computerised tomography has until recently been the gold standard for staging lymphoma, but is limited by its ability to assess only structural information. The addition of FDG-PET to staging protocols using standard imaging has been reported to alter management in 18–60% of patients.[3] Following treatment, PET has the ability to distinguish between post-treatment fibrosis and viable tumour cells. A recent meta-analysis found FDG-PET/CT to be superior to CT alone or PET alone in the initial staging and restaging of malignant lymphoma.[4] Isohashi et al. reported the diagnostic accuracy of FDG-PET for staging and restaging, evaluating treatment response and screening for recurrence in patients with malignant lymphoma.[5] A total of 156 FDG-PET examinations for which the corresponding CT/magnetic resonance imaging (MRI) scans was also available were evaluated in 59 patients. The accuracy of FDG-PET compared with CT/MRI was 92% vs 84% (p=0.06) for staging/restaging, 84% vs 50% (p< 0.05) for the evaluation of the treatment response, and 83% vs 72% (p= 0.21) for the screening of recurrence. Where disagreement existed between FDG-PET and CT/MRI (n=122), FDG-PET was more accurate than CT/MRI (76% vs 24%), especially for the evaluation of treatment response. ####Colorectal carcinoma Positron emission tomography has not yet been established as part of routine staging in patients with colorectal carcinoma (CRC). A recent study evaluated the impact on management of the addition of FDG-PET to conventional imaging in the initial staging of patients with CRC.[6] In 104 patients, FDG-PET identified undetected disease in 19.2% and changed the stage in 13.46%. This had a significant impact on surgical management. Its main application is in the detection of recurrent disease and in the selection of patients with potentially operable metastatic disease. A recent meta-analysis of 27 studies evaluating FDG-PET in recurrent CRC reported a sensitivity and specificity for detecting distant metastasis or whole body involvement of 0.91 (95% confidence interval (CI) 0.88–0.92) and 0.83 (95% CI 0.79–0.87), respectively.[7] Sensitivity and specificity in detecting hepatic metastasis were 0.97 (95% CI 0.95–0.98) and 0.98 (95% CI 0.97–0.99) and for pelvic metastasis or local regional recurrence were 0.94 (95% CI 0.91–0.97) and 0.94 (95% CI 0.92–0.96). 18F-fluoro-deoxyglucose PET appears to have great potential in monitoring the success of local ablative therapies soon after intervention and in the prediction and evaluation of response to radiotherapy, systemic therapy and combinations thereof. In patients with advanced CRC receiving chemotherapy, the degree of change in tumour FDG uptake was predictive for overall patient survival and progression-free survival.[8] ####Other tumour systems The use of PET/CT is currently under review in oesophageal, gynaecological and head and neck cancer. The evidence for routine PET/CT in staging oesophageal cancer is limited due to the lack of large trials and conflicting results reported from existing case series. The PET Advisory Group is considering its role in staging patients with potentially operable disease on CT imaging. As regards cervical cancer, PET/CT is indicated in patients with stage 1B or 2A disease (greater than 2 cm on MRI imaging) who are being considered for radical hysterectomy and pelvic lymph node dissection (RHND). In patients with suspected relapse after RHND and who are being considered for concomitant chemoradiation therapy (CCRT), PET/CT is required for restaging. Patients considered for CCRT with localised disease are recommended to undergo PET/CT to exclude extra-pelvic disease. In head and neck cancer a PET/CT is indicated in patients with suspected disease recurrence and negative CT or MRI. It is also of use in patients with metastatic cervical lymphadenopathy from an unknown primary and in whom CT and MRI have failed to identify the primary lesion. In thyroid cancer, patients with suspected recurrence after treatment of a differentiated tumour with a negative I-131 scan and rising thyroglobulin are recommended to undergo PET/CT, as are those patients with treated medullary cancer with a raised calcitonin level and normal conventional imaging. #####Further reading * [NHS24](http://www.nhs24.com/content/default.asp?page=s5_4&articleID=427&sectionID=1) * [CancerHelp UK](http://www.cancerhelp.org.uk/help/default.asp?page=26428) * Department of Health. [A framework for the development of Positron Emission Tomography (PET) services in England.](http://www.dh.gov.uk/en/Publicationsandstatistics/Publications/PublicationsPolicyAndGuidance/DH_4121029) 2009-05-15T15:01:38Z None declared. 108 2009-05-15T00:00:00Z 2009-05-28T09:48:10Z positron-emission-tomography-pet-scanning 2009-05-28T09:48:10Z

The past five years have seen a large investment in positron emission tomography and computerised tomography equipment in the UK. Most scans are performed on oncology patients, and there are clear recommendations for their use in non-small cell lung cancer, Hodgkin’s and non-Hodgkin’s lymphoma and colorectal carcinoma. A lack of evidence currently exists on other tumour types. Mr Graeme Couper, Consultant Surgeon at the Royal Infirmary of Edinburgh, explains the most common uses of this technology.

2009-05-28T09:48:10Z