When to Get a Scan?

[azgirl]

My mom is getting her last chemo. treatment on 17th (hurray!) and is scheduled to get a PET scan on the 20th. My brother's friend, who is a doctor, has informed us that this is too soon to get a PET scan because the chemo. needs to be out of her body for the PET scan to be accurate. My mom asked her nurse about this, but she was unsure. I thought I would post this here and see if anyone knows about the timing of a PET scan. I would appreciate any feedback. Thank you.

[Connie B]

My Onc told me many moons ago, that chemo is out of your system in 72 hours. If you want a professional answer I suggest you ask our Dr. West.

[Bruce u]

I have an appointment with my onc. and that was 1 of the questions I am asking. I'll let you know his answer.

[cat127]

if she were taking radiation also, then i can promise you it would be too soon. the radiation itself can cause inflammation, this would show up as hypermetabolic areas on the PET and be confounding in the results. the recommendation is to wait 8 weeks after radiation. we are in that 8 week waiting period with my sister, with the PET scheduled for next monday.

if she has only had chemotherapy, then it is less clear. though the drugs themselves, including the premedication drugs, can cause a false negative therefore it is not recommended that for staging of a disease you do this right after chemo, again a 6-8 week period is best. but it is used a lot as a follow-up for monitoring the chemo and done right after the end of chemo, when the patient has already had a baseline PET down for the staging. here is a comment that i found on the web:

However, more and more PET-CT scans are being utilized in the more immediate post-chemotherapy setting to monitor effectiveness of the type of chemotherapy used. The guidelines for recommended timing of PET-CT scan "chemotherapy monitoring" have yet to be determined, but is being investigated worldwide.

i would ask the doctor if waiting a bit may be more informative, but it isn't a clear cut, "she should not have a PET yet", as it would be if she had taken radiation. which i guess i'm guessing she hasn't since you don't mention it.

[azgirl]

She had whole brain radiation in Aug. but that is all.

[cat127]

yeah, i saw the WBR in your profile after i posted. i would say if she had radiation to the lungs, then she shouldn't have a PET for 2 months after the last dose of radiation. I'm nost sure though about the issue of whether there would be residual inflammation in the brain after WBR that would then mask the results of the PET on looking at any brain mets. that is something worth asking the dr though. you sure don't want to get any false positives.

[Guest hearrean]

How about CT Scans?

I'm having weekly chemo treatments & my Onc at MD Anderson wants me back there on 12/28 for testing (Blood work, Chest X-Ray & CT Scan) to check results to see how my tumor + nodes are responding. The day before that (12/27) I will have had my 4th treatment. Does this mean that when I do the tests (the next day), they quite possibly could be inaccurate?

I would have thought the Onc would have thought of that.

Ken

[recce101]

As far as I know (and cat127 or someone will correct me if I'm wrong) the delay applies mainly, perhaps exclusively, to PET scans. That's because PET measures metabolic activity in the organs/tissues, which can be caused by things other than cancer, such as inflammation from radiation treatment or infection or heavy exertion or whatever. So you want all those types of things at a minimum to avoid too many false positives. A CT scan very accurately displays the size, shape, and density of the various body parts but not their activity.

Some newer machines can give a CT and PET in the same session and the images are overlaid for viewing, the best of both worlds, so a combination CT/PET might be delayed for the same reasons as above. But if, as in your case, the size/shape/density of the tumor and nodes are to be measured to determine response, that would probably be done on a regular CT machine and no delay would be needed.

Aloha,

Ned

[cat127]

correct, the main issue is with PET scans because of what they measure. most oncs i think do a CT scan midway through chemo treatments to assess how things are going, that is perfectly fine and normal. when taking radiation, at the end of it they would likely want to wait a bit before doing a CT but for different reasons. with the PET it is the fear of false positives from inflammed tissues. with the CT, it is due to the fact that the radiation will keep working for a bit after you are done taking treatments, so a more accurate measure of the size of the tumor being irradiated would be from a CT taken maybe a month after radiation.

and yes most PETs are a CT/PET combo. i can only say that at my job, we don't consider that CT to be an accurate measure of the tumor response, we would require a dedicated CT. the CT with the PET is not the same as when you have a regular CT done, however i can't really say why as i'm not that involved in that aspect. i'm just speaking from the response i hear when that is discussed at my office.

but to the poster above, it is fine that the dr wants a CT while you are in the middle of chemo, it is not problematic, it is advisable as it will show them how you are responding. i think my profile states how after 2 cycles (6 weekly doses) my sister had a CT and we had a nearly 60% reduction in the tumor. i will tell you this, i think hearing that made it much easier for my sister to endure the needles and the radiation, which she started after the CT showed that response. it helps to be told what you are doing is having a good effect. good luck to you on your CT!