# Two scans, days apart. Might one be superfluous? **URL:** \ **Category:** Factual Questions\ **Created:** [August 23, 2008, 9:12pm UTC](https://boards.straightdope.com/t/two-scans-days-apart-might-one-be-superfluous/461047 "2008-08-23T21:12:52Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![BarnOwl](https://avatars.discourse-cdn.com/v4/letter/b/e95f7d/32.png) [@BarnOwl](https://boards.straightdope.com/u/BarnOwl)\ **Post date:** [August 23, 2008, 9:12pm UTC](https://boards.straightdope.com/t/two-scans-days-apart-might-one-be-superfluous/461047/1 "2008-08-23T21:12:52Z")
Had chemo and radiation therapy April-May for CA, lung Chem doctor scheduled a CAT Scan for 9/5, Rad doctor scheduled a PET SCan for 9/9. Do you think I need both? I know you’re not my doctor, so I’m just asking. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [August 23, 2008, 9:51pm UTC](https://boards.straightdope.com/t/two-scans-days-apart-might-one-be-superfluous/461047/2 "2008-08-23T21:51:03Z")
I really don’t have the answer to your question, but my thought would be to call the Chem doctor and ask them if a PET scan would work, and/or call the rad doctor and ask them if a CAT scan would work. Which ever one says it would work, I would make sure they make any adjustments to the order so they can see what they need to see. ---
**Author:** ![yoyodyne](https://avatars.discourse-cdn.com/v4/letter/y/a9a28c/32.png) [@yoyodyne](https://boards.straightdope.com/u/yoyodyne)\ **Post date:** [August 24, 2008, 1:12am UTC](https://boards.straightdope.com/t/two-scans-days-apart-might-one-be-superfluous/461047/3 "2008-08-24T01:12:29Z")
They are different types of scans and image different things. There is no reason to think one is superfluous. ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [August 24, 2008, 1:26am UTC](https://boards.straightdope.com/t/two-scans-days-apart-might-one-be-superfluous/461047/4 "2008-08-24T01:26:33Z")
Actually, superfluous scans can potentially be a problem. Since both CAT and PET have a radiological aspect, and this person has already had radiation therapy this year, both doctors should be informed of both scheduled scans. There is _probably_ not a problem, but there have been a few cases where people got more radiation than they should have. Can’t hurt to tell the docs, and it might be a good thing you did. ---
**Author:** ![yoyodyne](https://avatars.discourse-cdn.com/v4/letter/y/a9a28c/32.png) [@yoyodyne](https://boards.straightdope.com/u/yoyodyne)\ **Post date:** [August 24, 2008, 1:37am UTC](https://boards.straightdope.com/t/two-scans-days-apart-might-one-be-superfluous/461047/5 "2008-08-24T01:37:04Z")
The health risk of PET and CT radiation doses is miniscule in comparison to radiation therapy, and is far outweighed by the benefit the scans provide. There is really no rational reason for concern. ---
**Author:** ![BarnOwl](https://avatars.discourse-cdn.com/v4/letter/b/e95f7d/32.png) [@BarnOwl](https://boards.straightdope.com/u/BarnOwl)\ **Post date:** [August 24, 2008, 2:40am UTC](https://boards.straightdope.com/t/two-scans-days-apart-might-one-be-superfluous/461047/6 "2008-08-24T02:40:04Z")
In any event, I’ll call my chemo doctor on Monday. Thanks for your inputs. ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [August 24, 2008, 3:20am UTC](https://boards.straightdope.com/t/two-scans-days-apart-might-one-be-superfluous/461047/7 "2008-08-24T03:20:57Z")
[QUOTE=yoyodyne] The health risk of PET and CT radiation doses is miniscule in comparison to radiation therapy, and is far outweighed by the benefit the scans provide. There is really no rational reason for concern. [/QUOTE] It’s not so much the individual tests but the cumulative doses. Enough scans in a short enough period of time can be of concern, which is precisely why all doctors should be made aware of all exposure to radiation (be it x-ray or other). CAT scans expose people to less radiation than radiotherapy, but the dose with a CAT scan is still considerable in comparison to, say, normal background radiation or a single chest x-ray. Better safe than sorry. ---
**Author:** ![Ragiel](https://avatars.discourse-cdn.com/v4/letter/r/6de8d8/32.png) [@Ragiel](https://boards.straightdope.com/u/Ragiel)\ **Post date:** [August 24, 2008, 3:26pm UTC](https://boards.straightdope.com/t/two-scans-days-apart-might-one-be-superfluous/461047/8 "2008-08-24T15:26:49Z")
The CAT scan, like an X-ray in three dimensions, will show volume and position of the structures (e.g. a tumor). The PET is measuring cellular activity, by intake and use of radiolabeled glucose molecules. They’re not the same, but comparing the two would give the added benefit of distinguishing active tissue from “dead” tissue. Meanwhile, the MRI scan measures tissue density and might be used to demonstrate what type is being imaged. If they need that information, they would order MRI also. (Take-home message from a continuing education course “Imaging for Psychiatrists” that I took last year. I’ll take the updated course in November. It’s always interesting.) ---
**Author:** ![BarnOwl](https://avatars.discourse-cdn.com/v4/letter/b/e95f7d/32.png) [@BarnOwl](https://boards.straightdope.com/u/BarnOwl)\ **Post date:** [August 24, 2008, 4:59pm UTC](https://boards.straightdope.com/t/two-scans-days-apart-might-one-be-superfluous/461047/9 "2008-08-24T16:59:42Z")
All of you were kind enough to advise me, so I’l let you know what happens when I call my doctors tomorrow. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [August 24, 2008, 6:10pm UTC](https://boards.straightdope.com/t/two-scans-days-apart-might-one-be-superfluous/461047/10 "2008-08-24T18:10:45Z")
[QUOTE=Broomstick] CAT scans expose people to less radiation than radiotherapy, but the dose with a CAT scan is still considerable in comparison to, say, normal background radiation or a single chest x-ray. [/QUOTE] Indeed. I’ve inserted a table that gives typical expsoures for common imaging procedures. Note that a CT of the chest gives the equivalent exposure as about 400 chest x-rays or almost four years of natural background radiation - impressive figures, but still considered safe. ```auto Diagnostic Typical effective Equiv. no. of Approx. equiv. period procedure dose (mSv) chest x-rays of natural background radiation single arm, leg, hand, or foot less than 0.01 less than 0.5 less than 1.5 days Chest (single PA film) 0.02 1 3 days Skull 0.06 3 9 days Thoracic spine 0.07 35 4 months Lumbar spine 1.0 50 5 months Hip 0.4 20 2 months Pelvis 0.7 35 4 months Abdomen 0.7 35 4 months IVU/IVP 2.4 120 14 months Barium swallow 1.5 75 8 months Barium meal 2.6 130 15 months Bariumfollow-through 3 150 16 months Barium enema 7.2 360 3.2 years CT head 2.0 100 10 months CT chest 8 400 3.6 years CT abdomen or pelvis 10 500 4.5 years ``` ---
**Author:** ![yoyodyne](https://avatars.discourse-cdn.com/v4/letter/y/a9a28c/32.png) [@yoyodyne](https://boards.straightdope.com/u/yoyodyne)\ **Post date:** [August 24, 2008, 8:06pm UTC](https://boards.straightdope.com/t/two-scans-days-apart-might-one-be-superfluous/461047/11 "2008-08-24T20:06:16Z")
[QUOTE=KarlGauss] Indeed. [/QUOTE] How many superfluous CTs of cancer patients do you suppose are ordered? ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [August 24, 2008, 8:15pm UTC](https://boards.straightdope.com/t/two-scans-days-apart-might-one-be-superfluous/461047/12 "2008-08-24T20:15:01Z")
[QUOTE=yoyodyne] How many superfluous CTs of cancer patients do you suppose are ordered? [/QUOTE] **KG** can probably provide actual data on the topic, but as a doctor who has many patients getting treated for cancer, I can say that it does happen. Usually when multiple doctors are involved, and they’re not always fully aware of what the other doc has ordered, frankly. I’ve seen CT scans ordered and performed on more than one occasion because the ordering MD didn’t have the access to or knowledge of a scan done just days ago. Coordination of care can be a challenge, especially in the setting I practice in. ---
**Author:** ![ivylass](https://avatars.discourse-cdn.com/v4/letter/i/9de053/32.png) [@ivylass](https://boards.straightdope.com/u/ivylass)\ **Post date:** [August 24, 2008, 8:30pm UTC](https://boards.straightdope.com/t/two-scans-days-apart-might-one-be-superfluous/461047/13 "2008-08-24T20:30:11Z")
Prior to my lumpectomy, my chemo doctor ordered a whole slew of scans…a PET scan, a CAT scan, a bone scan, and a Muga scan. He wanted to make sure the rest of my body was healthy before he started chemo. ---
**Author:** ![BarnOwl](https://avatars.discourse-cdn.com/v4/letter/b/e95f7d/32.png) [@BarnOwl](https://boards.straightdope.com/u/BarnOwl)\ **Post date:** [August 24, 2008, 10:18pm UTC](https://boards.straightdope.com/t/two-scans-days-apart-might-one-be-superfluous/461047/14 "2008-08-24T22:18:00Z")
[QUOTE=ivylass] Prior to my lumpectomy, my chemo doctor ordered a whole slew of scans…a PET scan, a CAT scan, a bone scan, and a Muga scan. He wanted to make sure the rest of my body was healthy before he started chemo. [/QUOTE] How have you fared - from the radiation and the surgery? Well, I hope!