Health Sense : A new technique to see cancer inside your body

New technology: PET/CT (Positron Emission Tomography + Computed Tomography) scan uses gamma rays from radioactive glucose, the basic energy source of all living tissues in the body. Courtesy of Raymond NgehEveryone has heard of CTs, MRIs, ultrasounds and bone scans — the imaging techniques to see structures inside the body.

Computed Tomography (CT) uses X-Rays, Magnetic Resonance Imaging (MRI) uses radio-waves and magnetic fields, and ultrasounds uses sound-waves. All these techniques are very commonly used, but they see only differences in density within structures inside the body.

Bone Scan uses gamma rays and it has been around for many years. Unlike the other techniques, it sees differences in activity (not density) inside bones. It can detect cancer cells inside bones as small as 1 millimeter, if very active, when no other technique can see it. So it is very widely used in cancer diagnosis.

Similarly, the new PET/CT (Positron Emission Tomography + Computed Tomography) scan uses gamma rays from radioactive glucose, the basic energy source of all living tissues in the body.

PET/CT sees differences in activity of all structures in the body, including bones and soft tissues. It can detect cancer cells as small as 1 mm if the cancer is very active, not only in bones, but in all hard and soft tissues in the body. It is, at present, the most sensitive and accurate method of detecting cancer inside the body and all reputable cancer centers in the world are using it for cancer diagnosis and treatment, replacing all the other techniques, including the Bone Scan. Large hospitals in Singapore that have PET/CT include Mount Elizabeth Hospital, Singapore General Hospital and the National University Hospital.

Like the Bone Scan, PET/CT scan is a “whole-body” scan, whereas the other imaging techniques usually see only one part of the body. Of course, they can be used to see the whole body, but that would take a very long time (by scanning separately the different segments of the body) and would cost a lot of money. A whole-body PET/CT can take as little as 15 minutes, and the cost, although still high, is coming down recently due to competition.

Ask for a PET/CT scan when there is suspicion of cancer or an unknown primary cancer, either from clinical symptoms or lab tests. It is also useful for fever of unknown origins.

Before cancer treatment starts, the scan is very useful to determine the “baseline” for future comparison and for staging. Very often, the PET/CT scan changes the staging done by other imaging techniques (upstage or downstage).

After treatment, PET/CT can determine if it has been effective. For treatments that take a long time to complete like chemotherapy and radiotherapy, it can give an indication on their effectiveness. Currently, it plays a big role in the testing of new cancer drugs.

When treatment has been effective, cancer recurrence is common, so regular PET/CT scans can be able to detect the earliest recurrence.

It is good for almost all cancers, especially for bone metastases, and it should replace the well established Bone Scan.

Since the cost of a whole-body PET/CT is now the same or lower than a whole-body MRI or CT, and radiation received is no more than a normal CT scan, it should be the scan used for diagnosis and management of cancer. PET/CT’s radiation is low because the CT used is low-dose and the radioactive glucose has very short half-life.

Dr. Raymond Ngeh has a medical degree from the University of Strasbourg and operates two PET/CT centers in Johor Bahru and Kuala Lumpur.