F-DOPA whole-body PET-CT for tumour imaging

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For most essential points to best prepare for the procedure, please download the patient information brochure (PDF).
For a more elaborate explanation of the procedure and related points, please continue to read ahead.

Brief introduction

Principle

Amino acids are the building blocks of proteins. Neurotransmitters are signalling molecules synthesized and released by neurons (nerve cells) that stimulate or inhibit other neurons and some other organs (e.g., muscles, sweat glands, etc.).

The human body can use an amino acid called L-3,4-dihydroxyphenylalanine (L-DOPA or 'levodopa') to synthesize 3 different neurotransmitters: 'dopamine', 'epinephrine' and 'norepinephrine'. These are all very important neurotransmitters, and their function depends on the site of their release.

¹⁸F-DOPA is the radiopharmaceutical (RP), which is taken up by the same cells that also take up L-DOPA. Most remarkably, it is taken up by cells of basal ganglia in the brain (discussed in the article on F-DOPA brain PET) and certain tumour cells (mentioned below).

Many relatively well differentiated (less aggressive) tumours do not take up FDG very avidly, and hence they are difficult to identify using FDG PET-CT. Some of these tumours belonging to the neuroendocrine family take up F-DOPA, and hence can be detected using F-DOPA PET-CT. Salient examples of such tumours are:

Neuroendocrine tumours (NETs)
Pheochromocytoma and paraganglioma
Medullary carcinoma of thyroid
Congenital hyperinsulinism (not a tumour)
Tumours of the brain like glioma and metastases from other organs

Indications (conditions in which advised)

Detection, staging, treatment response evaluation and follow up of aforementioned tumours / conditions.

Considerations / steps before procedure

Prior appointment is a must as the RP spontaneously decays, and is not readily available at the diagnostic facility.
Patient must not be pregnant.
If breast feeding, please inform the staff for further directions.
Recent (within past 7 days) serum creatinine level must be known.
4 hours’ fasting before scan.
Please let the staff know at the time of appointment if the patient is unable to lie still for ~20 min, has breathing difficulty, or might need special medical attention for the duration of visit.
Have at least 1/2 litre water within an hour before reporting for the scan. There is no need to hold urine.
Wear loose-fitting but warm clothes.
Do not bring expensive jewellery or accessories along with you for the scan.
Proof of doctor's request is necessary for starting the procedure.
The patient must be accompanied by a responsible carer.

What to expect as part of procedure?

Important steps

Patient registration and consent.
Handing over medical documents to the staff.
Oral contrast (typically 500 to 1,000 mL) to be had over next 45 min to 1 hour.
Intravenous (IV) access is established (in form of cannula).
RP is injected through the cannula.
Waiting time of ~75 min (± 15 min) to allow sufficient time for RP to be taken up and eliminated by all organs. Pass urine just before the scan, and also before that (if needed).
‘Whole-body’ procedure typically includes scanning from head to upper thigh as the patient lies still on their back. IV contrast is injected through the cannula. Time taken on the scanning table is ~15 min. Patient may have to hold breath for few seconds.
Scan is briefly reviewed for adequacy and quality. Occasionally, a scan may be repeated or scanning of additional body parts may be considered. If everything is to staff’s satisfaction, then the patient may leave.

Discomfort / risks during procedure

Pain during IV cannula insertion.
There is risk of extravasation at the time of IV cannula insertion, RP injection or injection of iodinated IV contrast. [Extravasation means that blood leaks through the walls of vein punctured by cannula’s needle].
Iodinated contrast is injected in relatively large volumes and at a high flow rate. This can cause sensation of warmth and pain at the injection site. Rarely, patients develop allergic reaction to the contrast in form of skin rash, breathing difficulty, dizziness, or loss of consciousness. IV contrast also mildly and transiently suppresses kidney function, but it usually recovers completely by itself, and patients do not experience any corresponding discomfort.
RP does not cause any discomfort. It is injected in very minute quantity, so it does not alter function of any organ.

Time taken for the entire patient visit

Typical: 3.5 hours.
Be prepared for: 5 hours (can be further prolonged in case of unforeseen events like malfunctioning of scanner, delayed delivery of RP, etc.).

What to expect after procedure?

Precautions / special care

Maintain at least 1 metre-distance from pregnant ladies and children (below 10 years) for at least 5 hours after the scan.
Drink plenty of water throughout the day (3 to 4 litres).
Pass urine as frequently as possible.

Discomfort / risks

Because of IV contrast, some patients experience headache or heaviness of head, which resolve within a day.
Oral contrast can cause watery motions or loose stools. This typically resolves by itself within a day.
Both RP and X-rays expose the patient to ionizing radiation. However, radiation dose received as part of the entire procedure is not expected to cause any obvious harmful effect. Additionally, benefit from information received through the procedure greatly outweighs any theoretical risk associated with this radiation exposure.

Time taken for report generation

Typical (for self-paying patients): 12 hours.
Be prepared for: 36 hours (especially if some patient data or past scan data are missing).
Credit patients will receive their reports from the respective referring hospitals.

Additional reading

For additional information, please visit the following links.

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