In fact, it is one of the few imaging tools for which the Medicare system imposes limits — currently, three follow-up PET scans per person, even when doctors only order them after spotting something on a computed tomography (CT) scan or other medical image.
The specific amounts patients pay vary according to their insurance coverage. Medicare limits the number of PET scans following initial cancer treatment to three per patient. (More could be covered if deemed necessary by the doctor.) “These are good scans and appropriate in many situations,” Healy says.
This low dose of radiation has not been shown to cause harm. For children or for other people who need multiple PET scans, CT scans, and x-rays, there may be a small potential increased risk of cancer in the future. Doctors can use lower dose scans or limit the areas that need to be scanned.
"In other words, if you want to do more than three, you will have to justify it," says Rathan Subramaniam, MD, PhD, MPH, an associate professor of radiology and radiological science, oncology, head, and neck surgery, and health policy and management at Johns Hopkins Medicine Division of Nuclear Medicine in Baltimore.
In a patient who is in good physical shape, I do this every three months with the advice to come in sooner if you have any worries. In practice, many doctors do CT scans of the body and pelvis every few months; others do nuclear medicine tests such as PET scans or bone scans. Many patients also demand them.
Not all cancers show up on a PET scan. PET scan results are often used with other imaging and lab test results. Other tests are often needed to find out whether an area that collected a lot of radioactive material is non-cancerous (benign) or cancerous (malignant).
A PET scan can help to: show up a cancer. find out how big it is and whether it has spread (stage a cancer) show whether a lump is cancer or not.
There is no recommended limit on how many computed tomography (CT) scans you can have.
Will I be radioactive? Because we use a radioactive tracer, you will be slightly radioactive for the next 24 hours after your scan. After 24 hours all the radioactivity will be gone. Once you leave the imaging center, you may resume all normal activities including holding children.
Temporary side effects – The iodine-based contrast dye used in a PET CT scan can cause temporary side effects. Some PET scan side effects are diarrhea, nausea, etc., which eventually fade within a day.
PET scanning can give false results if chemical balances within the body are not normal. Specifically, test results of diabetic patients or patients who have eaten within a few hours prior to the examination can be adversely affected because of altered blood sugar or blood insulin levels.
If it looks as though there are still swollen (enlarged) lymph nodes after treatment, a PET-CT scan can help show if this is due to scar tissue or there are still active lymphoma cells.
If a PET scan is not funded by Medicare, patients have to pay between $800 and $1000.
Patients who remained clinically equivocal after multidisciplinary review of post-treatment imaging and clinical exam findings were ordered a repeat PET/CT, typically 1–4 months following the patient's initial post-treatment imaging. Repeat PET/CT imaging was assessed in the same way as initial post-treatment imaging.
This type of scan help determine whether a smaller spot is cancerous or benign, as cancerous lesions are much more likely to light up on a PET scan than benign spots or scar tissue.
A CT scan of the abdomen (belly) and pelvis exposes a person to about 10 mSv. A PET/CT exposes you to about 25 mSv of radiation. This is equal to about 8 years of average background radiation exposure.
After a PET-CT scan
After the PET-CT scan, you can return to your usual diet and activities. This includes driving. Drink lots of water. It helps wash any leftover radioactive substance and dye out of your body.
Newer scanners will adjust the radiation exposure automatically and reduce the exposure. Repeated CT scans should be avoided, and certainly if the scans are being repeated only because the physician does not have access to the images from a recent CT scan.
Follow-up appointments are often scheduled at 4 and 12 weeks after your radiation treatments are done. You may be asked to have a scan (CT, PET, or MRI) before this visit. Your provider will see how you are doing and give you information on continued follow-up care.
“There's a risk of developing a tumor if you have a lot of CT scans, but that doesn't usually happen unless you have a very serious life-threatening medical condition,” says Dianna Cody, Ph. D., professor of Imaging Physics at MD Anderson.
Cancer cells tend to be more active than normal cells because they are growing and multiplying faster than normal, so they take in more sugar and give off more positrons and gamma rays. This causes them to glow brighter than normal cells on a PET-CT scan.
Not all that lights up on a PET scan can or should be considered malignancy, and clinical context can become even more pertinent. Inflammatory cells, sarcoidosis, and other thoracic etiologies such as silicone-induced granuloma, can cause PET scans to light up, giving false positives [3,4,5].
PET has been reported to have a sensitivity of 97–100% and a specificity of 62–100% in the detection of recurrent tumours. Scans are most reliable 6 months to 1 year after completion of therapy. Before that time, hypermetabolic inflammatory changes may result in false-positive studies.