SSTR PET-CT for neuroendocrine tumours | Super Sahyog Nuclear 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

Neuroendocrine tumours (NETs) are relatively uncommon type of tumours that can occur anywhere in the body, but are most commonly found in the intestines, pancreas and lungs. More aggressive forms of NETs that would have spread (metastasized) to distant sites in the body or show potential to do so are called neuroendocrine 'carcinomas' (NECs).

Most NET cells express a type of protein called somatostatin receptor (SSTR) on their surface.

'Octreotide' is a synthetic molecule that mimics somatostatin, and causes inhibition of function as well as growth of NET / NEC cells.

'DOTA' is a bifunctional chelator that connects the radioactive fluorine-18 (¹⁸F) with octreotide. When such a radiopharmaceutical (RP) is injected into the blood, the octreotide component binds to the SSTR on NET / NEC cells, and the ¹⁸F component emits gamma (annihilation) photons that can be detected by the PET detector.

Likewise, when DOTA-octreotide complex is combined with beta-emitters like lutetium-177, it can kill the NET / NEC cells expressing SSTR. This mode of treatment is known as 'peptide receptor radionuclide therapy' (PRRT).

Indications (conditions in which advised)

Initial staging.
Localizing the primary tumour in those with confirmed metastasis of neuroendocrine carcinoma.
Selection of patients for PRRT.
Evaluating response to PRRT.
Staging before surgery.
Evaluation in cases wherein NET is suspected, but biopsy is not possible and/or difficult.
Monitoring in cases where CT and/or MRI would have missed abnormalities found on DOTA PET.
When there is suspicion of NET based on symptoms and/or blood tests, but wherein other diagnostic procedures (e.g., CT, MRI or endoscopy) could not identify the tumour.
When there is suspicion of progression based on symptoms and/or blood tests, but other diagnostic procedures (e.g., CT or MRI) do not show corresponding progression.
When a new abnormality is detected on CT or MRI, but is not clear whether it represents NET.
Follow-up after surgery with curative intent.
Selection of patients for treatment with somatostatin-analogues like octreotide (e.g.,Sandostatin®).

Considerations / steps before procedure

Prior appointment is a must as the RP spontaneously decays, and is not readily available at the diagnostic facility.
Recent (within past 7 days) serum creatinine level must be known.
Patient must not be pregnant.
If breast feeding, please inform the staff for further directions.
Short-acting forms of octreotide must be stopped at least 12 hours before the appointment in consultation with your referring doctor. Long-acting forms of octreotide or lanreotide should be preferably stopped for 3 to 4 weeks before the scheduled procedure. For certain patients stopping these drugs might not be feasible because of fear of unacceptably severe symptoms. In such cases, it is more important to perform the treatment response and follow-up scans under similar condition. E.g,. if octreotide is not stopped for the pre-treatment scan, then it should preferably not be stopped for post-treatment scan as well.
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 ~1 hour (± 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.

DOTA PET-CT for neuroendocrine tumours

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