CT Stone protocol - radiation exposure

[Adcadet]

Hey gang. In a discussion the concept of the "CT stone protocol" was discussed. As an MS4 in the ED, I've frequently ordered it to confirm nephrolithiasis. The major advantage, as far as I can tell from the ED, is that it's quick. I also know that many primary care clinics are also moving towards CT to confirm nephrolithiasis, and again, I've ordered them from a primary care clinic. In both settings (ED, primary care office) I've usually been pretty sure that the patient had a stone based on the symptomatology - they were both classic presentations. In the primary care clinic on one occasion, the patient was ~65 years of age and a smoker with less clear symptoms, so I did want some reassurance that the hematuria wasn't a malignancy. In retrospect, I'm now wondering about radiation exposure. In the past I've always been pretty cavalier about dismissing concerns about radiation, since I've always been pretty convinced the data obtained was crucial to the patients health (CT angio for the dyspnic patient who may have a PE, CXR in the older smoker who might have a simple pneumonia vs. a nasty malignancy, head CT in trauma patients, etc). But in the case of kidney stones, I'm wondering if the radiation dose always or usually warrants the study in patients who you strongly suspect a stone but have no personal history (if a patient says that the pain is just like the previous stone, and they don't have any red flags, I've been happy to give them a UA to r/o infection, a narcotic, some sympathy, and sometimes tamsulosin). And then there's the question of repeating the study to confirm that the stone is moving, which again in a primary care setting I've also done. If my web references are correct, a CT stone protocol involves about 500 mrem. If I recall, that's a fairly substantial dose. Maybe it's no big deal in an 70 year old person who doesn't otherwise get scanned ever, but in a younger person who then gets the scan repeated to monitor stone progression, I'm starting to wonder if the radiation dose is worth it. I'm hoping some of my radiology colleagues can help me put this radiation exposure in context to help me recommend for or against this very cool test for a surprisingly common and painful problem.

Thanks,
Adcadet

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[Flankstripe]

Here's the current FDA table looking at radiation doses for several tests.

http://www.fda.gov/cdrh/ct/risks.html

On their listing, a CT abd has the effective dose equivalent of 500 PA CXR's. Measuring CT doses is difficult, with a myriad of confounding factors, but the point is that CT is a monumental step up in dose relative to most plain radiographs. We get stone patients rolling through the ER who often have 5-10 abdomen/pelvis CT's to their credit.

Pump that number up significantly for the recurrent drug seekers in the ED with "flank pain" who receive that CT just so that "we can call them normal and dispo them." It's staggering to think how many studies they may have had at all the other outside hospitals they've "rounded on."

Would you feel comfortable disclosing to these patients that they've literally had the equivalent of thousands of CXR's?

Unfortunately, the wide availability of CT, and the rapidity of reads means that we are scanning more and more patients each day, and the indications get more dubious on an incremental level. We also seem to be scanning more and more kids and young adults, and their long-term risk from this radiation is completely unknown.

On a totally different note, if you order a CT scan both with and without IV contrast to "make sure that you covered all your bases", as seems to be the norm for many less-knowledgeable health care providers, you've just doubled the amount of radiation, as the techs will scan the patient non-contrast, then administer IV contrast and re-scan them.

We radiologists are pretty aggressive with the techs to protocol all these studies correctly to minimize this, but some of these orders still do fall through.

Outside of selected indications, scanning both with and without IV contrast often doesn't add significantly more clinically-relevant information, certainly not enough to justify doubling the radiation dose.

 

[f_w]

The major advantage, as far as I can tell from the ED, is that it's quick.

AND the definitive test for rocks. So, while you can do the IVP, the plain films and an ultrasound, in the end you still have a chance of relatively radiolucent or small stones getting missed.

I've ordered them from a primary care clinic. In both settings (ED, primary care office) I've usually been pretty sure that the patient had a stone based on the symptomatology - they were both classic presentations.

I have seen leaking AAA (with concomittant UTI), retroperitoneal hematoma, Burkitts and renal cell present with the 'classic' history. And again, the CT will give you the best 'rule-out' for all these mimickers compared with the other modalities involved.

so I did want some reassurance that the hematuria wasn't a malignancy.

Unfortunately, the non-contrast CT hasn't ruled that out yet. You will need a study to look at the upper tract lumen (IVP, retrograde or CT-urogram), a study to look at renal parenchyma (US or contrast CT) and typically a cysto to truly know that it is not malignancy.

In retrospect, I'm now wondering about radiation exposure. In the past I've always been pretty cavalier about dismissing concerns about radiation, since I've always been pretty convinced the data obtained was crucial to the patients health

You are asking the right question. If I think the patients life depends on it, I will gladly radiate until the skin turns red. If I think a study is ordered for BS-CYA reasons, the administration of any amount of radiation is battery.

But in the case of kidney stones, I'm wondering if the radiation dose always or usually warrants the study in patients who you strongly suspect a stone but have no personal history

You can try to get your answers by means that incur less radiation. E.g. a KUB and an Ultrasound, if no obstruction on US an IVP. The urologist will still order the CT to decide whether the lithotripter is going to crack that nut or whether he needs escalate things.

And then there's the question of repeating the study to confirm that the stone is moving, which again in a primary care setting I've also done.

If you are concerned about monitoring progression of a rock and radiation dose (and your patients wallet), getting KUBs ($40 a pop, 40CXR equivalent) is going to be a better deal than repeated CTs ($500 a pop, 500CXR equivalents)

I'm starting to wonder if the radiation dose is worth it.

At least you are wondering.

It is a great test, but like any test that can kill the patient it should be used judiciously. If a 16 year old girl (who got drunk at the county fair 5 days ago) presents with +++WBCs, fever and flank-pain, she has honeymooners cystitis/pyelonephritis and not that occult 'obstructed infected stone vs appendicitis' that we seem to hunt down all too often. Talking to your patients, getting the whole story and a fair amount of clinical judgement go a long way. Unfortunately, these things seem to go lost in the teaching of emergency medicine these days.

 

[Adcadet]

If you are concerned about monitoring progression of a rock and radiation dose (and your patients wallet), getting KUBs ($40 a pop, 40CXR equivalent) is going to be a better deal than repeated CTs ($500 a pop, 500CXR equivalents)

If after the initial CT you know the stone is radio-opaque, the patient is doing well except for some pain and maybe hematuria (no additional reason to worry about an infection), is it reasonable to follow progression with a KUB? Again, I'm wondering about the young patient with a big history of stones in whom you want to minimize radiation exposure since you foresee many future CTs to confirm a stone.

 

[f_w]

If after the initial CT you know the stone is radio-opaque, the patient is doing well except for some pain and maybe hematuria (no additional reason to worry about an infection), is it reasonable to follow progression with a KUB?

That is exactly the scenario where a KUB is the right test. Also, after litho it is a pretty good way to follow the fragments.

Again, I'm wondering about the young patient with a big history of stones in whom you want to minimize radiation exposure since you foresee many future CTs to confirm a stone.

Chances are, for every episode of stone disease you will need at least 1 CT.

 

[Adcadet]

F_W - thanks for your thoughts. It seems that that in the young, frequent stone patient in whom you want to minimize radiation, an initial CT (stone protocol) followed by a KUB to monitor progression if needed, is a reasonable approach as long as the patient remains non-infected or obstructed clinically. In my limited experience, this patient gets multiple CTs for any stone that takes more than a week to pass, which I recently thought was perhaps not a good thing.

 

[f_w]

In my limited experience, this patient gets multiple CTs for any stone that takes more than a week to pass, which I recently thought was perhaps not a good thing.

With any test you order, you have to ask yourself: Will I rush this patient to the OR based on the result ? If the question is: 'only a weekly CT will tell me whether this patient will need litho, stents, percs this week', then the weekly CT is justified. If you are not ready to pull that trigger, there is no point to it.

 

[bosky]

I understand their position, but ER people and my medicine co-interns need to at least pause before blasting young people with radiation. CT of the abdomen is ~ 10 milliSieverts, that is equivalent to 500 CXR or 3.3 years of background radiation that all occurs in < 5 seconds.

Based on your interpretation of the results from a 60-year followup study comparing lifetime solid tumor risk to estimates of radiation exposure for survivors of Hiroshima and Nagasaki, where approximately 10000 survivors were in the dose range of CT radiation exposure, a single CT may increase your lifetime risk of solid tumors from 0.1 to 0.5% (given that normal lifetime risk is 20% already). This risk is worse for radiation exposure to females or younger patients (the latter because they live long enough to get the tumors). See http://www.rerf.or.jr and papers from that study. The FDA estimates risk at 0.05% but I'm unsure why the lower estimate - politics, $$?.

I extrapolated off the RERF study curves and estimated CT radiation exposures that the newly popular head-to-toe CT from a trauma may be equivalent solid tumor risk to being ~ 1.5-2 miles from the hypocenter of Hiroshima when the bomb went off and surviving.

 

[Whisker Barrel Cortex]

I agree that limiting the number of these scans performed, especially on younger patients, is important. It is, without a doubt, the most accurate and versatile study for the evaluation of renal colic. I think the first time someone presents with these symptoms, a non con CT is the correct first choice.

On repeat visits, there are viable alternatives. These will not be as good as CT. If the symptoms are pretty classic and they have known renal calculi, an abdominal radiograph to evaluate for change in the location of the stones and/or and ultrasound to evaluate for hydronephrosis would be another option. IVP is not a viable alternative, in my opinion, b/c it doesn't really decrease radiation dose much compared to CT.

If the patient's symptoms do not pass after a couple of days and no stone passes in the urine, follow up with US or a CT could be considered, especially if urologic intervention is being considered.

 

[f_w]

Based on your interpretation of the results from a 60-year followup study comparing lifetime solid tumor risk to estimates of radiation exposure for survivors of Hiroshima and Nagasaki, where approximately 10000 survivors were in the dose range of CT radiation exposure,

I am allways very skeptical about atom bomb survivor studies. These people
- where often malnourished
- incorporated good stuff like I131 and Cs137.
- where exposed to a city burning down

None of the studies used to calculate threshold doses really deals with a population in any way similar to todays circumstances.

 

[bosky]

I totally agree, the other thing is the controls were people from more than 3 miles away so there may be a rural vs urban risk difference bias as well. But, it is the best information we have. There will never be a prospective double-blinded study on healthy people to sort this out.

Just another argument for ALARA in my opinon.

 

[f_w]

Just another argument for ALARA in my opinon.

I am all for ALARA. It just irks me if people take 60 year old data that is hardly comparable to make pronouncements such as:

By doing this CT you incur a 1:1000 chance of this patient dying from cancer !!!

If this nonsense is kept up, we will have a huge avalance of frivolous lawsuits down the line.

Reality is: We don't know whether and how much damage a CT or any other low-dose exposure does (low-dose compared to lets say clearing debris of the roof of the Chernobyl reactor or working on a soviet attack submarine). And as long as we don't know, we should use this tool judiciously.