Answer to Question #11118 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:


I had a CT (computerized tomography) scan of neck, chest, and abdomen done on myself today. I was hoping to get accurate dosage information on my report in mSv as I am concerned about the amount of radiation I would receive through this test. The report does not have any dosage information on it. What it has is CTDI(vol) and DLP information for the tests. For example, the CT Abdomen test result says CTDI(vol) is 23.01 and DLP is 1,153. I am not sure how to convert this information to mSv as it is important for me to keep track of the amount of radiation I receive.


The term CTDI(vol), in the unit of milligray (mGy), is a reference value used for the measurement of radiation dose in a plastic cylinder. DLP stands for dose-length product. DLP is the CTDI(vol) multiplied by the scan length in centimeters and is given in units of mGy–cm. Both CTDI(vol) and DLP are machine parameters and do not reflect your radiation dose. Nonetheless, your radiation dose can be estimated using DLP.    
I recommend that you go to the x-ray risk calculator website which provides both an estimate of the CT dose and the corresponding increase in the cancer risk. For example, after selecting CT scans on the second page, select "Abdomen CT" and "Standard." I entered the age of 50 and the DLP of 1,153 mGy–cm that you gave. The effective dose is 20.7 mSv. Again, this is a rough estimate, and not exactly the dose you received.  
I hope this information helps.
John Jacobus, MS
Certified Health Physicist
Editor's Note: The cancer risks calculated on the website referred to above are population risks, not individual risks. The website gives a baseline cancer risk of 44.9 percent, i.e., the risk of getting cancer from all sources. You don't have a 44.9 percent risk of cancer. Instead, in a group of 1,000 random people, 449 are expected to get cancer. It's a subtle but important distinction. Think about it this way: your neighbor smokes tobacco products and works in a coal mine. You exercise and eat broccoli and blueberries every day. The two of you don't have the same cancer risk, but you both are in the group of 1,000 people from which there will be 449 cancers.

Answer posted on 7 January 2015. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.