Answer to Question #10723 Submitted to "Ask the Experts"

Category: Medical and Dental Patient Issues — Diagnostic X Ray and CT

The following question was answered by an expert in the appropriate field:

Q

I am a 33-year-old male (six foot two and 230 pounds) and am interested in having children; however, I received a pelvic CT (computerized tomography) scan. I did not know the consequences of CT scans until I started researching it after the fact, and now have a bit of anxiety about it. I am having a hard time understanding the relationship between CTDIvol, DLP, and overall cancer and genetic mutation risk. With and without contrast, my total CTDIvol was 40 mGy, and DLP was 1,400 mGy; 120 kVp and mAs were about 500 without contrast and 250 with. Also, I had a sperm analysis done about three months after the scan, and my count was okay but most of my sperm were immobile.  

  1. Could these numbers have caused temporary infertility based on the dose to the testes?
  2. What is the relationship between effective dose (which, according to a calculator using the DLP, was 26 mSv) and dose to the specific organ (i.e., testes)?
  3. Is it now too risky to have children at this dose, based on sperm mutations?
  4. Why was this dose so much higher than the average pelvic CT of 6 mSv?

Thank you so much in advance for your time and expertise. This is a very stressful situation for me.

A

In order to calculate a more accurate dose, much more information would be necessary such as the make and model of the scanner and a variety of image acquisition parameters. However, to answer your main questions, the information you provided will suffice. Note that I am assuming that the dose length product (DLP) you reported of 1,400 mGy was in fact 1,400 mGy-cm because the DLP (as its name implies) is the dose times the scan length.  

  1. Could these numbers have caused temporary infertility based on dose to the testes?
    Answer: No. The threshold (i.e., <1% incidence in a clinically significant decrease) for temporary infertility is ~100 mGy which would appear three to nine weeks after the exposure. The maximum dose to the testes you likely received was lss than 50 mGy.
  2. What is the relationship between effective dose (which, according to a calculator using the DLP, was 26 mSv) and dose to the specific organ (i.e., testes)? 
    Answer: The same absorbed dose to different organs (measured in units of milligray (mGy) may result in different risks of cancer and hereditary effects depending on the relative sensitivity of the organs exposed to those clinical endpoints. The effective dose is a rough correction of the absorbed dose to account for those differences and is expressed in units of millisieverts (mSv) which can be used to compare the approximate radiation-induced risk of one type of imaging exam with x rays to another. This is done by multiplying the risk factor for each exposed organ times the absorbed dose (in mGy) to that organ and then adding them all up. So the effective dose (in mSv) applies to the whole person, but has no meaning for an individual organ or tissue. 
  3. Is it now too risky to have children at this dose based on sperm mutations?
    Answer: No. Despite numerous studies, there is little to no convincing or consistent evidence to suggest that one would expect an excess of heritable genetic mutations among the offspring of exposed parents, even if the dose was much higher than the dose you received.
  4. Why was this dose so much higher than the average pelvic CT of 6 mSv?
    Answer: I cannot be sure what calculator you were using but a DLP of 1,400 mGy-cm would be more like 20 mSv or about 10 mSv average per exam. Without much more information it's difficult to tell but 6 mSv is on the low end of effective doses for one pelvic CT which for large adults is typically more on the order of 8–10 mSv per exam. So while the dose you report is on the high side, it is not out of the range of normal.

Jerrold T. Bushberg, PhD, DABMP, FAAPM
Clinical Professor, Radiology and Radiation Oncology

Ask the Experts is posting information using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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