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22 March 2010

Answer to Question #5885 Submitted to "Ask the Experts"

Category: Doses and Dose Calculations — Doses from medical sources

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

Is there is another reliable method of calculating effective dose for CT (computerized tomography) scans without the use of TLDs and phantoms, that is, software?

One way to obtain an estimate of the effective dose from a CT scan is the following:

Most state-of-the-art CT scanners provide an estimate of the DLP (dose-length product) on the scanner console before the scan begins. The DLP is obtained by multiplying the CTDIvol in mGy by the length of the patient being scanned in cm. (CTDI stands for computed tomography dose index and the volume CTDI is also provided on the scanner console when the scan parameters are chosen.)
To get the effective dose in mSv, multiply the DLP in mGy-cm by a factor supplied in a table from the European Guidelines on Quality Criteria for Computed Tomography. (See Table 2 in Appendix I of Chapter 1.) The choice of the most appropriate factor depends on the part of the body being scanned.

Note that the factors for the head and neck are significantly lower than the others, reflecting the fact that there are fewer organs at risk for cancer induction (or other end points) in the head than in the chest, abdomen, or pelvis.

Lawrence N. Rothenberg, PhD, Fellow HPS

Answer posted on 17 October 2006. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of 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 specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.