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cat scan or pet scan

horsepad's picture
horsepad
Posts: 147
Joined: Apr 2012

A good friend of mine was recently diagnosed.  The doctor is recommending a CT scan and not a pet scan.  I am an eight year survivor of stage 4 anal cancer.  Is it normal for a CT scan instead of a pet scan to stage her?  I had a pet scan.  What is the normal protocol?  She doesn't have a clue what questions to ask.  I want to be there for her.  Help her understand her cancer and ask the right questions.  She said she needs surgery to remove the tumor but that is all she knows  

 

Any insight to what she can expect is appreciated.

abrub's picture
abrub
Posts: 2131
Joined: Mar 2010

I've only had CTs and MRIs for my Appendix Cancer, over the past 13 years.  They see different aspects of the cancer, and in different detail.

Trubrit's picture
Trubrit
Posts: 5192
Joined: Jan 2013

I think the CT is the first line they take, as allot of insurance comanies balk at paying up for a PET. 

If she is heading into surgery, they may think a CT is good enough. They will probably stage her after surgery, as allot depends on what they see when they get inside.  They will remove a bunch of lymph nodes, to see if it has spread to them, as that is an indicator of movement. 

Congratulations on being eight years out. That is fantastic! 

It would be wonderful if your friend could join us here, but of course, having you by her side will be a great help. 

Tru

 

Bellesouth
Posts: 24
Joined: Feb 2017

"The pictures from a PET scan provide information different from that uncovered by other types of scans, such as computerized tomography (CT) or magnetic resonance imaging (MRI). A PET scan or a combined CT-PET scan enables your doctor to better diagnose illness and assess your condition."

 

Not sure if it helps or answers your question. I had both PET and CT in the beginning. I have since learned that colorectal tumors often are not detected in CT. Mine was not. I guess they had already established in the biopsy that it was malignant and did the CT and PET to see how widespread it was because the original tumor was so large, it had obviously been hanging out there awhile. Sure enough, my torso lit up like a Christmas tree in the PET. Uh. 

annie4145
Posts: 182
Joined: Jul 2018

I had anal cancer and did a CT scan and then a PET scan.  The PET scan picked up a spread to the lymph node that the CT did not, but now my current doctor likes CT scans better and says that they are better for soft tissue, so I don't know which is better.  I think perhaps PET, but my current doctor doesn't necessarily agree. 

zx10guy
Posts: 266
Joined: Dec 2013

CTs and PETs are two different scanning technologies.  CTs go about imaging what's inside of you.  PETs do not image.  When you have a combined PET/CT, the CT is done to create a "rough" image of your internal body to overlay the output from a PET scan.  Both scanning technologies use ionizing radiation.  The way PETs work is to measure metabolic activity.  Cancer cells are hypermetabolic which means their energy consumption is much higher than surrounding normal cells.  All cells uptake glucose/sugars for energy.  With a PET scan, a radioactive glucose tracer is injected into your body.  Because of the hypermetabolic nature of cancer cells, these cells will uptake more of this radioactive glucose.  This concentration is picked up by the PET scan.  The amount of uptake is measured in SUV.  The higher the number the more concentration of the radioactive glucose and therefore the higher the supposed metabolic activity.  This is why you're requried to follow a strict diet before your exam and to limit your physical activity.  It is also why you have to wait about 45 minutes to an hour after the tracer injection before you have the scan so the tracer has had ample time to circulate through your body.

Some reasons why PETs are not used as a first line scan for cancer treatment are as follows.  First, PET scans expose your body to the most radiation of any type of medical diagnostic technique.  Radiation exposure is cummulative over your life time.  Your doctor has to weigh the benefits to the long term risks of using a PET scan.  Second, as mentioned, PET scans are expensive.  Many insurance companies will not pay for a PET scan unless there have been other tests done or diagnostics which lead to needing a PET scan to confirm or rule out a diagnosis.  Third, PET scans are not infallible.  There can be false positives (and some false negatives).  Any major inflammation can trigger a false positive.  There are areas of your body which will always have higher than normal SUV readings.  These are your kidneys (as they're filtering out the tracer from your blood stream), bladder (where all the waste from your kidneys collect), and your brain as brain cells require higher amounts of glucose to function.

I'm going on 8 years since my initial diagnosis.  I've had 4 PET scans, 2 MRIs, and a ton of CTs which I lose count.  The PETs were always ordered to rule out potential metastisis picked up from a CT or abnormal blood work.  The use of any imaging technique is always patient dependent as my situation is very different from someone else's.

A word about staging.  There are two types of staging: clinical and pathelogical.  Clinical is done from only a scan.  These are typically for rectal cancers.  Pathelogical staging is from actually examining tumor tissue to determine the level of invasiveness in the particular organ and surrounding tissue.  Pathelogical staging is the final gold standard as to what you are.  A surgeon will not tell you what your staging is by just looking around in the area of surgery.  The exception to this is if there is clear evidence of cancer spread which at this point you're automatically stage 4.  But for other staging such as stage 0 to 3, there is no way a surgeon can tell you if you're anyone of those without having a lab do a full pathology work up on the removed tissue.

Trubrit's picture
Trubrit
Posts: 5192
Joined: Jan 2013

If I didn't have chemo brain, I'm sure I would memorize this, as you are always SO GOOD to post it when the question of CT vrs. PET comes up. 

Tru

zx10guy
Posts: 266
Joined: Dec 2013

You're welcome.

horsepad's picture
horsepad
Posts: 147
Joined: Apr 2012

Thank you for the information.  A CT scan was done and she is also going to get an MRI next week.  She said she was told it is non invasive.  She asked me to go to her next appointment with the oncologist.  She would like me to ask the necessary questions and take notes for her.  If anyone has suggestions on questions we should ask, let me know.  I appreciate everyone's input.

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