Two different types of scans side by side

Let’s Talk About Scans: What’s The Difference Between CT Scans And PET Scans?

I’ve read a number of posts on online patient forums lately about scan frequency and types ordered. Many advanced lung cancer patients have CT scans every three months, but others have frequent PET scans as well or instead. What’s the difference between a CT scan and a PET scan? Let me try to clear this up.

What are PET scans?

PET stands for Positron Emission Tomography. According to the National Cancer Institute’s (NCI) dictionary of cancer terms, a PET scan is “a procedure in which a small amount of radioactive glucose (sugar) is injected into a vein, and a scanner is used to make detailed, computerized pictures of areas inside the body where the glucose is taken up. Because cancer cells often take up more glucose than normal cells, the pictures can be used to find cancer cells in the body.”1

PET scans are often used at diagnosis to figure out where the primary site of cancer is located and find any areas of metastasis throughout the body. They are also frequently used to see if a patient might be progressing while on a specific treatment. Some patients I’ve spoken with receive more PET scans than others do because their doctors consider them part of their routine testing protocols.

PET scans are costly

PET scans tend to be significantly more expensive than CT scans, so some insurance companies really balk at covering them. Personally, I’ve only ever had two PET scans in my six years of living with lung cancer — one when I was initially diagnosed and one more recently. The more recent PET scan was actually denied by my insurance company twice before being approved via an appeal process by my oncologist.

What are CT scans?

CT or CAT stands for Computerized Axial Tomography. According to NCI’s dictionary, a CT scan is “a procedure that uses a computer linked to an x-ray machine to make a series of detailed pictures of areas inside the body. The pictures are taken from different angles and are used to create 3-dimensional (3-D) views of tissues and organs. A dye may be injected into a vein or swallowed to help the tissues and organs show up more clearly.”1

CT scans are both quicker and less expensive than PET scans and are usually considered part of routine cancer treatment. While CT scans can show growth and shrinkage of areas of cancer cells in the body when compared to previous CT scans, they cannot determine on their own if new growth is cancerous or whether a remaining, treated mass contains cancer cells or is made up of scar tissue. Oncologists rely on biopsies and/or PET scans to get these more detailed answers.

Based on my experience with CT scans...

Since I was first diagnosed, I have had CT scans (usually without injected dye/contrast) every three months. Upon progression in 2016, a CT scan picked up slight growth even before I experienced any symptoms, which was confirmed with a tissue biopsy.

If you have contrast injected each time you have a CT scan, it might be worth asking if this is completely necessary. Yes, it improves the detail of the pictures created, but might not be needed every time you have a routine CT scan.

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