CT's versus MRI's

[Eugene]

In my understanding the effect of radiation therapy is separate and unrelated to the baseline risk, which would make it additive. So were talking up to 45% risk for lifetime development of a new malignancy depending on which numbers you use.
Of course the later in life the radiation is received the less time you have to develop something due to it.

Cumulative dose certainly matters too but I think it's more usefull in looking at non stochastic / deterministic effects e.g. Skin burns, radiation cataracts or bone marrow suppression.

CT doses are nowhere near therapeutic radiation. (10mGy for Abd CT vs 25-30Gy). Risk will definitely be less. Unfortunately no data as to what it actually is exists. In the practice at the medical center where I work we stop worrying about radiation risk for a non cancer patient after the age of 60 roughly.
Anything more than 1 CT in 6 months in any patient under 60 is concerning. That is assuming there is any other options. Kinda like you can follow renal cysts with US instead of CT. Obviously someone with say lung CA is going to benefit more from the CTs and radiation is a secondary risk given expected survival.

-E

[CW406]

In my understanding the effect of radiation therapy is separate and unrelated to the baseline risk, which would make it additive.

Ok, gotcha on that one, it was a matter of semantics.

I'm pretty interested in this whole subject myself. I'm 25 and so far the only CT I've had was for my diagnostic workup (only 3 months out so no followup CT yet). So if I can head off an unneeded risk, then I'd be all for it. The literature that I've read always seems to simply cite cost and availability (and, implicitly, tradition) as the reason for CTs being used over MRIs. Pretty weak in my book. I mean, as a lay person and as an engineer, I'd think the limitations here would be governed by physics, not biology. Either the MRI can resolve the structures in question to the appropriate level or it can't!

My oncologist is an MD/PhD with a research background and is a pretty smart guy who knows the literature and keeps up to date with the latest studies. I also have a relative who is a radiologist with 20+ years experience. I'd not thought to bring this specific matter up yet, but I think I will inquire and see what their respective opinions are on the topic.

[Eugene]

We're in the same boat. I'm a little older but same ballpark. I ve got a vested interest in lowering radiation since I'm going to get radiation while working. MRI definitely has the resolution to see retroperitoneal nodes. Question is do just abdomen or abdomen pelvis. Each one is about 45 mins.

I saw a case once of a patient who had seminoma cme back as an inguinal mass with vascular involvement. Don't wanna miss that one!!

I have an MD/PhD, but the PhD is in cardiac physiology, kinda makes me wish I did it in radiation physics instead

Let me know what you find out..


Cheers,
-E

[Aegean]

Except you don't add the two, based on what you stated, you multiply them, then add. A 10-15% INCREASE in a 20-35% baseline risk is a 2% to 5.25% increase in overall risk.

Also, I'm not an expert on radiation effects, but does radiation from a short period of high-intensity exposures (such as the radiotherapy to which you were referring) truly equate to a number of low-dosage exposures over a long period? That is, is it really only cumulative dose that matters? I'd think, instinctively, that the intensity would play a role as well, and CTs would be less intense than radiotherapy, right?

Much like accounting at public companies, I think the numbers are a matter of interpretation. In a general sense, the number of gy's sustained over a 10 year surveillance schedule for stage 1 seminoma is far less(a fraction) than the 25 to 35 gy for adjuvant radiation, given over a rather short period.

Further, I think it is interesting how in the medical community, certain experts are divided as to the actual possible effects of these CT scans we all fear. Thus my alluding to accounting at public companies and how the same set of numbers represents a "buy" for one analyst and a "hold" for another. I have yet to see a study that has gained universal head nodding in the community, and I have searched. What really sucks in my mind is that having had one cancer doesn't necessarily reduce the odds of another primary of some other sort further down the road, and thus that is why surveillance, even with the possible risk of CT's, is a very valid option as in many cases of TC you can save the radiation and chemo if needed when older.

Realistically, avoiding radiation is good... can only be good, but you are now in a situation where you need to either do 1 or 2 shots of carbo and have fewer CT's or not CT's but longer MRI's, if you want to reduce exposure. Either way you have to chose.

[Aegean]

Thought I would pre-empt this report talking about CT Scans and extreme radiation, at least the title does. It seems to me that the body of the report dwells on financial considerations just as heavily and is light on any real scientific fact. What I keyed in on is the word "unnecessary". Unfortunately as a cancer survivor, these scans are a necessary evil, until at least MRI's and/or new protocols with the CT machines are adopted.

[Redlight]

In a period of 14 months, I had 10 CT scans of my abdomen and pelvis and 4 CT scans of my chest and I know many people have had significantly more. However, my oncologist just switched me to MRI scans as of my last one. As a personal preference, I enjoy them better. Even though the scan takes significantly longer, I don't have to wait around while I drink bottle after bottle of contrast dye. It takes hours to get ready for a CT-scan, at least at MD Anderson.

Additionally, I think that MRI's do a pretty good job of picking things up. I have a residual 0.7 cm node that is stable after chemo and several cysts on my liver that were found with no problems. I think I might be on an MRI schedule for a while.

[Aegean]

I believe the type of cancer (even the type of TC specifically) may play into the effectiveness of MRI versus CT.

[Paul54]

Here is a recently published study that indicates no or nil association between TC surveillance CT's and secondary cancers. Note the median follow-up was only 11 years with a max of 14. That leaves open the door for longer term increase of risk.

http://jco.ascopubs.org/content/early/2011/06/13/JCO.2011.34.6379.short?rss=1