Positron Emission Tomography CT (PET-CT)
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www.rcr.ac.uk Recommendations for cross-sectional imaging in cancer management, Second edition Positron emission tomography CT (PET-CT) Faculty of Clinical Radiology www.rcr.ac.uk Contents Positron emission tomography CT (PET-CT) 3 Scanning 5 Patient preparation 3 Standardised uptake value (SUV) 5 Hyperglycaemia 4 Radiation protection 5 Injection site 5 References 8 3 www.rcr.ac.uk Positron emission tomography CT (PET-CT) Derangement in chemical processes is one of the be attending for their appointment at which point first indicators of cancer and this precedes the importance of arriving on time should be changes in morphology. PET-CT provides unique stressed. The information sheet should request information about metabolic processes within that patients inform the department if they are tissue and precisely identifies where areas of diabetic, claustrophobic, pregnant, breast deranged metabolism are occurring. The majority feeding, have difficulty lying flat on their back for of cancers have increased glucose metabolism at least 30 minutes or if they are scheduled for compared with normal tissue. In clinical practice, any other hospital appointments on the same day 18Fluorine fluoro-deoxyglucose (FDG) is the most as their PET-CT scan. At the time of booking, widely used radiotracer with PET-CT in clinical patients should also be advised that it is practice. FDG PET-CT identifies the difference recommended that they have minimal close and increase in glucose metabolism of cancer contact with pregnant women or young children cells compared with normal cells. FDG PET-CT is for the remainder of the day following their scan. now recognised as a key investigation for For patients who are claustrophobic or have optimum management in an increasing number difficulty lying down it is recommended that they of malignancies. Depending on the tumour type, visit the department prior to their appointment to FDG PET-CT can be highly effective for primary look at the scanner and discuss whether they tumour staging, assessing treatment response think they will be able to tolerate the scan. and for detecting disease recurrence.1 These Depending on the referral indication and local applications of FDG PET-CT have been shown to experience, imaging protocols will vary slightly alter patient management in approximately one- and specific information should be provided third of patients with cancer. The current where possible. document makes reference to the use of FDG PET-CT in specific tumours where best evidence Patients are asked to abstain from food and supports its use in routine clinical practice and its drink, other than water, for at least four to six limitations in other tumours are also addressed in hours before the scan. Patients should be the appropriate disease sections. encouraged to drink plenty of water but should be told that they can void as often as required and Drawing from new evidence, the use of FDG do not need to have a full bladder. Insulin- PET-CT in our cancer patients continues to be dependent diabetic patients should not be asked refined and expanded. The role of FDG PET-CT to fast and should be instructed to eat and take for radiotherapy planning and monitoring early their medication as usual. Their appointment response to neoadjuvant chemotherapy should be scheduled so that their FDG injection treatment are two areas which are currently is given as long after their last meal as possible, attracting considerable research attention. while preserving their normal routine. For patients Radiotracers other than FDG are being studied; with poorly controlled diabetes, a discussion included are fluoro-thymidine which provides an between the Administration of Radioactive index of cell proliferation and fluoro-ethyl and Substances Advisory Committee (ARSAC) fluro-methyl choline which measure cell certificate holder and the patient’s referrer prior to membrane turnover. booking will reduce the likelihood of an uninterpretable scan. Patient preparation Patients with stomas following bowel surgery All patients should receive written confirmation should be asked to bring fresh stoma bags with regarding the timing of their appointment along them so that, if required, the bag can be changed with information about what the scan involves, immediately prior to scanning. how long it will take and how the results will be communicated to their clinician. To reduce the To reduce the risk of false-positive or false- risk of wasted FDG and appointment times, negative results, when scheduling the patient’s patients should be asked to confirm that they will appointment, consideration should be given to 4 www.rcr.ac.uk the timing of the appointment in relation to Hyperglycaemia concurrent or recently completed chemo and radiotherapy. Guidance should be sought from All patients must have their blood glucose the ARSAC certificate holder as to the optimal measured and recorded prior to FDG injection. time for scanning. The finger prick blood test is, as a rule, avoided and instead a drop of blood is taken during For patients who will be receiving contrast media cannulation. as part of their PET-CT scan, please refer to the information provided in the CT section of this Considerations for a non-diabetic patient with document. high blood glucose The patient’s blood glucose is usually high On arrival in the department, it is important that because they have not fasted as instructed. If so, the procedure is clearly explained to the patient the patient is invited to drink 3–4 glasses of water and that the patient is allowed an opportunity to and the blood glucose is repeated about two ask questions so that they are as relaxed as hours later. The blood glucose is then ordinarily possible. It is important to take a clear clinical normal. history from the patient including details regarding recent treatment and to measure and If the blood glucose remains high, it is usually record the patient’s height and weight. Where due to a concurrent infection. If this is the case appropriate, last menstrual period (LMP) dates most centres would consider postponing the scan should be requested and recorded and, if and inviting the patient to visit their GP. necessary, pregnancy status should be established with local protocols followed ensuring Considerations for a diabetic patient compliance with The Ionising Radiations Tablet controlled: The patient is usually 2 . Regulations 1999 and the Ionising Radiation invited to attend an early morning 3 (Medical Exposure) Regulations 2000. For these appointment and asked to refrain from reasons appointment times should ideally include breakfast and their diabetic medication, or a pre-injection period of at least 20 minutes. invited to attend a middle of the day appointment having eaten a light breakfast at The patient should be comfortably warm before 6 am and taken all their medication including the scan to aid relaxation and reduce normal diabetic medication at the time of breakfast. physiological muscle and brown fat FDG uptake. Insulin controlled: In general, the patient is It is important to diminish physiological uptake by . invited to attend a middle of the day brown fat and muscle because this can lead to appointment having eaten a light breakfast at errors in interpretation of the scan. 6 am and taken all their medication at the time of breakfast, including their insulin injection. Normal physiological uptake of FDG into the However, each patient is advised on an intrinsic laryngeal muscles is demonstrated in individual basis and factors such as the time patients who speak before, during or after tracer of the insulin injection will influence their injection and this can cause confusion. For this appointment. reason, it is recommended that patients, and especially those with conditions involving the Patients with diabetes mellitus (DM) are asked to head and neck, such as head and neck cancer, drink plenty of water in the six hours leading up to observe a silence protocol with no talking for 20 the scan appointment (about a litre). Depending minutes prior to the injection, during the injection on the nature of the DM and the preparation period and for the majority of the uptake period instructions that have been given, they are (the first 30 minutes after injection being the most advised to bring their food/tablets/insulin with important period). These patients should, them to be taken immediately after their scan. therefore, be asked to arrive for their appointment Advice given is guided by the patient’s recent at least 40 minutes before their scheduled blood glucose levels and, for follow-up FDG PET- injection time. CTs, advice is also influenced by the blood glucose level of previous scans. In patients with blood glucose of more than 12 mmol/litre, it is 5 www.rcr.ac.uk usually appropriate to consider deferring the FDG Depending on local practice, some centres PET-CT, as it can result in false-negative results. routinely include the cranial cavity and others However, each patient is advised on an individual start scanning from the skull base. With modern basis and with all relevant factors taken into scanners, it usually takes about 30 minutes to consideration. obtain an FDG PET-CT from skull base to mid- thighs. Injection site Most centres in the UK do not give IV contrast as It is advisable to allow the patient to relax for a part of the FDG PET-CT examination. If IV couple of minutes between the cannulation and contrast CT is required, this is usually obtained the administration of the FDG. This also ensures immediately after the PET-CT applying standard that the integrity of the line can be adequately CT technique and in the same scanner. checked and will reduce the risk of extravasation. It is critical that the member of staff performing Standardised uptake value (SUV) the cannulation and injection (usually the nuclear medicine technologist or radiographer) is well The maximum SUV (SUVmax) of a lesion is the trained and well practised as a precise technique most commonly used measure of FDG uptake is critical.