Getting to know your scans

What is a PET scan and is there difference between a PET scan and a CT scan?

PET scan stands for Positron Emission Tomography. A PET scan allows doctors to see inside the body beyond the organs and structures down to the biochemistry on a cellular level. It looks at the biological structures of tissue, showing whether it is alive; dead or dying. Because cancer cells grow much faster than normal cells, they have a much higher biological activity when actively growing, which a PET scan will identify.

On the other hand a CT scan (Computerised Tomography) shows detailed images of the body’s internal anatomy and accurately outlines organs and bone structures. It is able to detect changes in tissue structures and hence details of anatomy – its size; shape and location. This makes it a useful screening diagnostic test for suspected tumor, disease or injury.

When done separately they show two totally different points of view (see pictures above) but when they are combined in one procedure then it gives a 3D visualisation of what is happening in the body. It is capable of showing the structure, size and location of the cancer, or its metastases’ and then shows whether the tumor is alive (active), or dead. Because a PET scan looks at disorders on a cellular level an oncologist can pick up abnormalities very early on – before the anatomic changes seen on a CT scan can be detected.

Is a PET scan only used in oncology?

While PET scans are used extensively and effectively around the world in the detection and monitoring of cancer, it is also used in the fields of neurology, cardiology and psychiatry. It looks specifically at how the tissue is functioning metabolically, or responding to treatment. For example, in a patient who has had a stroke a PET scan would be able to pick up whether the affected tissue is alive; dead or dying.

When used in conjunction with MRi scans and ultrasounds a CT scan is used to detect injuries, damage and abnormalities of body structures.

How is a PET scan done?

Living cells absorb glucose very easily, so when doing a PET scan the technologist injects a glucose based radioactive tracer. The glucose tracer is then collected by the body through all the living cells. Usually a CT scan is done as the initial portion of the exam. This produces the images of the body’s internal structure. Then the PET scan portion is done. The scanner picks up the gamma (radioactive) rays given off by the glucose tracer in the body. Cancer cells absorb far more glucose than any other tissue in the body so this would mean the tracer would show up brighter in the living cancerous cells in the body while dead cancer cells would be darker than the surrounding tissue. When you put the two scans together it provides a very clear view of what is happening from a structural, as well as a cellular level.

Why would my oncologist want to do a PET scan?

Unfortunately, not all cancers are detectable by a PET scan. Certain cancer cells do not absorb the glucose-based tracer well and so this test is not of use.  It is therefore important that both local and international guidelines are followed by the referring doctor in order not to waste costs

If the particular cancer is detectable using this test then the indications for PET scan are classified into four categories:

• Diagnosis

• Staging

• Treatment response

• Re-staging

Diagnosis: PET scans can be used to diagnose the size and extent of cancerous growths which might assist a doctor to plan the most appropriate treatment approach in managing the cancer.

Staging: It is important to understand the extent and spread of cancers in newly diagnosed patients. This is important to determine the primary disease site and if there is any spread to other organs. This helps the oncologist decide on the appropriate treatment to be initiated for a specific cancer and patient.

Treatment Response: Chemotherapy leads to changes in the cellular activity of the cancer. A PET scan can measure these changes before they can be visualised on a CT scan. This might assist the doctor to evaluate treatment response earlier and, if needed, modifications to the treatment. However, it has never been proven to facilitate improved long-term outcomes, and the cost implications might not justify the theoretical benefit.

Re-Staging:  After treatment is complete PET scans can pick up if the mass seen on a CT scan is the “dead”left over of the previous cancer, or if it is a recurrence. It can also highlight tumors that might, otherwise have been missed because it is obscured by scar tissue from previous surgery or radiation.

How much does a PET scan cost and does my medical aid cover it?

Compared to CT scans that range between R3 000- R12 000 each, a PET scan costs between R20 000- R24 000.

While most medical aids do cover PET scans under certain guidelines set out by the Radiology Society of South Africa – and in terms of specific option and scheme rules defined in the Medical Aid’s protocols – they are not always covered from the oncology benefits allocated to you. When a CT or MRi scan is done it is usually authorised and paid through the oncology benefit as a Prescribed Medical Banefit (PMB) with no co-payments. This is because CT scans and MRi’s are available to all patients in a State hospital. PET scans are, however not routinely available because of the costs and hence not considered as PMB level of care. Keeping this in mind, your medical aid might authorise it from the Specialised Radiology family benefit limit and this may incur a co-payment, as well as you being liable for any shortfalls.

Are there any risks involved in having a PET scan?

As with all tests, there are always risks and dangers involved. There is the risk of reaction to the radioactive tracer that is injected before the scan. It is recommended that pregnant women do not have PET scans. Although minimal, there is always the risk of exposure to radiation.  Because the tracer used is glucose based, abnormal blood sugar readings or patients suffering from diabetes can have errors in their scan reports.

In short, while PET scans are very effective tools in the management and monitoring of some cancers, they can be very costly, not only to your medical aid but also to you and your family, due to short falls in payment and co-payments. Always discuss all your options with your Oncologist. A PET scan, or any other test always has an alternative. If the alternative investigations leave questions that can’t be answered and have a material impact on your treatment strategy, then with motivation most Medical Aids will look at funding PET scans as long as it falls within your benefit structure; the guidelines and the Medical Aids’ protocols.

When you are not sure read your membership guide. It is sent to you yearly to keep you informed of your benefits and limits that you have available to you. If you are still not clear then call your Oncology authorisations department and discuss it with them. They are there to help you and advise you in a way best suited to you while taking into account your benefits and requirements.

If you are still not happy with the answer, or decision made you have a right to appeal the decision with the scheme involved.

Written by Gillian Warren