Answer to Question #14797 Submitted to "Ask the Experts"
Category: Medical and Dental Patient Issues
The following question was answered by an expert in the appropriate field:
What is the difference between DLP and effective dose, and why is there some hesitation about the use of effective dose?
Dose-length product (DLP), in units of milliGy–centimeters (mGy·cm) is a metric related to the amount of radiation a patient has received. When a correction factor is used, you can convert DLP to effective dose. See ATE Q/A 11118.
You asked why there is hesitation to use effective dose when talking about patient exposures. Effective dose was never meant to be used to calculate individual patient risk from radiation exposure. The factors used in the effective dose calculation are based on epidemiology data from radiation workers (like x-ray technologists) and it was developed to be used to establish and assess worker radiation exposure limits.
While it is possible to calculate an effective dose value for an individual patient, the effective dose concept was not designed for individual risk assessments or to assess patient exposures. Calculating a cancer risk from effective dose can be done using a factor corresponding to a hypothetical risk. This is by no means an exact science. Keeping in mind that about 40% of people will develop cancer in their lifetime scientists estimate that the increased risk of developing cancer from receiving 100 mSv of radiation is about 0.5%. See the American Cancer Society website.
Therefore, if a person is exposed to 100 mSv, their lifetime risk of developing a cancer is approximately 40.5%. Most scientists agree that the potential effects of cumulative doses less than 50 mSv are so low they are considered negligible.
Linda Kroger, MS