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Diagnostic Reference Levels to be Implemented (posted 6/6/2017)
The Radiation Safety Section has decided to proceed with the use of Diagnostic Reference Levels (DRL) to compare patient exposures measured during routine inspections. DRLs are non-regulatory levels meant to alert a facility if they are using exposures higher than seen in most other facilities. We will begin moving to DRLs the week of June 12, 2017. More information on DRLs may be found on our web page under Patient Radiation Exposure Information.
On April 18, 2017, a GovDelivery message was sent describing our proposal to use DRLs and to solicit concerns or comments. Some of the comments we received and our response to those comments follow:
Comment: We request that the RSS make available on its website the measurement methodology used (e.g., geometry, attenuator material and thickness, distance to detector, etc.) to obtain and report the doses for specific projections. This is needed so that Michigan registrants can replicate and investigate any reported values exceeding the RL or AD. It has added significance because the radiology projections do not differentiate between CR and DR unlike the dental.
Response: Radiation Safety will describe the measurement methodology on the Patient Radiation Exposure Information page on our website.
Comment: Using one value for each exam ignores that CR is much less radiation-sensitive than DR. Most CR systems operated at “speed” targets of 200, which required twice the dose we used with screen-film. Newer DR systems typically operate at doses much lower that screen-film, and substantially lower than CR. It may be wise to wait until more data are gathered with these newer DR systems, or separate the recommended DRLs into detector type (CR vs DR vs film).
Response: The graphs that will be posted on the website will show the 75th percentile for CR, DR and film, but the DRLs will be at the 75th percentile of the aggregate. Although data from CR and film will drive the aggregate higher, use of the aggregate is from NCRP Report 172 which says “The DRLs recommended in this Report for routine chest, abdomen and spine radiography are based on all of the data from the randomly selected population at the time of the survey”. The data reflects the way radiography is currently being performed in the state. Facilities may wish to compare their exposures to the 75th percentile for their imaging type. We expect to re-evaluate the DRLs 5 years from now.
Comment: Do the diagnostic reference levels pertain to exposure received by radiography personnel involved in taking x-rays or do they pertain to exposures to patients?
Response: The diagnostic reference levels pertain to patients undergoing a radiographic exam, not doses to the worker performing the exam.