Can't answer this clinical question

[salih]

Hi all,

I hope you can help me with answering this question regarding a clinical question. I've tried to search the whole internet and medical databases but can't seem to find an answer. I'm currently in my 5th year of my study (medicine).

Let's say you are a doctor and a pregnant woman arrives with symptoms of an pulmonary embolism(PE). The only way to see if she truly as a PE is to do a ventilation-perfusion scan or a CT scan. We all know that these scans do have a negative influence on the foetus.
Because the woman is pregnant the breast tissue is proliferating and that means that these scans also may have a negative influence.

The question that I am trying to solve is: is there a increased chance of developing breast cancer when a pregnant patient is getting a CT or a ventilation-perfusion scan?

Can anyone help me with this question? Thank you very much!!

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[colbgw02]

The conventional wisdom is that stochastic radiation effects follow a linear-no threshold model. That means the short answer to your question is "yes".

Determining the exact increase risk is very difficult to do. Numbers are out there (Google "BEIR VII"), but a lot of the science is iffy. Suffice it to say, the risk of any single examination is almost always outweighed by the clinical concern, which means the study typically gets done.

I've spoken with a well-known radiology physicist about fetal dose in V/Q versus CT pulmonary angiogram, and his calculations come out essentially even. Obviously, the dose to the breast will be much higher with CT, even if you use shielding. I think the best bet is probably to do perfusion scanning first, and then stop if it's normal. That will produce the least overall, fetal, and breast dose while still answering the question. Of course, if you use xenon for ventiliation, like my hospital does, this route goes out the window. There are also the practical considerations, to wit, V/Q scans are time and labor intensive as compared to CT.

Hope that helps.

 

[salih]

I've spoken with a well-known radiology physicist about fetal dose in V/Q versus CT pulmonary angiogram, and his calculations come out essentially even. Obviously, the dose to the breast will be much higher with CT, even if you use shielding. I think the best bet is probably to do perfusion scanning first, and then stop if it's normal. That will produce the least overall, fetal, and breast dose while still answering the question. Of course, if you use xenon for ventiliation, like my hospital does, this route goes out the window. There are also the practical considerations, to wit, V/Q scans are time and labor intensive as compared to CT.

Hope that helps.

Thnx for the info!! I found out that a single CT scan uses alot less radiation then VP scan. (source: Diagnosing pulmonary embolism in pregnancy: rationalizing
1fetal radiation exposure in radiological procedures. M.NIJKEUTER)
The CT uses 0.026 mSv and a VPscan uses 0.11-0.20 mSv. but this doens't really answer my main question.

Anyone else with tips?

 

[shark2000]

As colbgw02 said the best way is to start with V/Q scan and ideally you have to be do a perfusion scan and if negative stop it. But if you use xenon for ventilation it should be administered before the perfusion. Most places use xenon because it is more cost-efficient.

CTA has one advantage and one disadvantage.
It is coned down on the mother's chest and the scattered dose to the fetus is less. On the other hand for V/Q scan the scattered dose to the baby is much higher. The expected dose to the fetus in a CT is less than 50 uSV. Also on the third trimester the baby is usually in the pelvis and many times the head is located inferiorly, so most of the dose to the fetus is to his buttocks.
On the other hand, for an optimal CTA for PE, the patient should be in expiratory phase. In pregnancy for many reasons it is more difficult to obtain and the false positives are higher.
There are a lot of controversy on this issue and it is institution by institution. At our facility we do CT.