I recently had a low-dose CT scan of my chest in a program for the early detection of lung cancer. As I was leaving, I asked how many gray the procedure involved. The tech went into the control room and reported “114”. I asked about the prefix, milli, mega, kilo, etc. She didn’t answer but said “centimeter”, I said “square centimeter”, she said “cubic centimeter”. This left me confused. What was the 114 likely to be, and how much radiation is that?
I’m not sure what she is reporting.
Mostly people care about the volumetric CT Dose Index (CTDIvol), which is usually reported in milliGray (mGy). The goal for Low Dose Chest CT for an average size patient is around or just under 3 mGy, but could be higher in a larger diameter patient.
There is also a Dose-Length Product (DLP) which can be used to estimate exposure (best for populations rather than individuals). This is mGy-cm.
In the hypothetical case of a dose reported to be “114”, this is probably the DLP.
I’m no expert on this, but Google University tells me that the average radiation dose from a CT scan of the abdomen and the pelvis is 14 mGy, so I’m guessing that is more or less what you got and the 114 anything is wrong. (If you had received 144 full Grays, I’m thinking that you wouldn’t be asking this question because of being dead.)
BTW, not out of expected range for a low dose chest CT.
Thanks everyone,
I was in error in stating that the woman I talked with was the tech. The tech had left the room. I never saw him again. This woman came in to wrap up an let me know that the procedure was complete, and she may have said something like 14. My impression was that she was not too knowledgeable.
I was thinking milligrays as well. The radiologist’s report emphasized that the scan was low dose.
A bit of Googling indicates that a low dose scan for early detection of lung cancer is 0.15 mgy, so 0.14 mgy seems right then. That is the same as 0.15 msv. Average inhaled exposure from Radon and its decay products is about 1.25 msv/year, so it looks like I didn’t get fried. Not more than the equivalent of 6 weeks exposure to background.
BTW, I highly recommend anyone who has done any serious smoking and is past 60 or so seriously consider doing this yearly. It will catch cancers of about 5mm
Perhaps she said “point-fourteen” and you heard it as “114.”
I think your calc is off by a decimal.
Dose estimation: Conversion factor for DLP (mGy-cm) to milliSieverts (mSv) for chest CT is 0.014.
See Table 2 on pg 4 of ref below:
http://www.ajronline.org/doi/pdf/10.2214/AJR.09.3462
114 * 0.014 = 1.6 mSv
This is “right” for a low dose chest CT. Regular chest CT would be more.
Computed Tomography (CT)-Chest. 7 mSv
Computed Tomography (CT)-Lung Cancer Screening. 1.5 mSv
Radiography-Chest 0.1 mSv
Taken from:
Thank you Barnacle; that was VERY useful.
Yeah, those decimals will get you every time. It looks like I absorbed about a half a year’s worth of average background in the US. That is not too bad, and it is x-ray radiation, not some radioactive particulate matter which could lodge in my lung and radiate forever.
Just a caveat- I’ve been told that those methods of Dose estimation are more appropriate for populations rather than individuals. So that estimate, especially if combined with estimates from many other cases says more about how much exposure that radiology department is handing out (which, based on the single example seems appropriate) than it does about your individual exposure.
http://www.usa.philips.com/healthcare/product/HCNOCTN193/ingenuity-ct-scanners
indicates that lesser DLP would not be used for lungs, but yeah around 100 cGy cm starts to show the lungs… They are choosing DLP to get the lungs as the subject of the scan.
They use the minimum necessary to show anomalies, but not in great detail. There are side by side comparisons of low dose and regular CT scans online, and the difference is apparent.
Normal lungs are mostly air, containing linear tubes (blood vessels) and hollow tubes (bronchi), plus a bit more airy-fairy tissue and membranes. The is a lot of contrast between nodules and normal lung tissue. Even more so where there is emphysema.
If the chief purpose of the scan is to screen for lung nodules, you can accept more noise, and therefore use less radiation. These noise levels would not be acceptable for a routine chest CT, where everything is on the table.