Dosimetry/Bioassay

In order to meet the regulatory requirement to maintain public and occupational radiation doses as low as reasonable achievable (ALARA), Radiation Safety Service (RSS) monitors occupational radiation exposure for individuals working with radioactive materials or radiation-generating machines, and maintains permanent records of all occupational radiation doses at U-M.

Occupational radiation exposure includes:

  • External exposure to ionizing radiation emitted by radioactive materials
  • External exposure from devices that produce x-rays or other forms of ionizing radiation (such as electrons or protons)
  • Internal exposure from inhaled, ingested, or absorbed radioactive materials
External Radiation Exposure

External exposure to ionizing radiation is monitored by wearing a monitoring dosimeter (“badge”).  A dosimeter measures and records the accumulated ionizing radiation dose that an individual receives over a specified amount of time (typically a month or calendar quarter).  It does NOT protect you from radiation. There are two types of dosimeters:

  • Whole-body dosimeter to monitor general whole body dose
  • Ring dosimeter to monitor extremity dose from handling radioactive materials or if the hands are in or near the x-ray beam during a medical or research procedure

The RSS Dosimetry Program provides the appropriate radiation dosimeters, maintains permanent records of all occupational radiation doses, and partners with department liaisons (dosimetry contacts and supervisors) for all matters relating to radiation dosimetry.

Obtaining a Dosimeter

The departmental Dosimetry Contact initiates and submits all requests (to RSS) for new, spare, and replacement dosimeters and notifies RSS of personnel changes (new or terminated personnel, or updated personal information).

At the end of each wear period, current dosimeters are exchanged for new dosimeters per the department’s procedure.  Exchanged dosimeters are due to RSS on the 10th day following the end of the wear period.

Proper Wear of the Dosimeter

To ensure accurate readings from the dosimeter, you must:

  • Wear your own dosimeter – never allow another person to wear your dosimeter and never wear a dosimeter assigned to another individual.
  • Wear your dosimeter for the period of time (wear period) indicated on the dosimeter, starting at the date on the dosimeter.  Dosimeters are designed to monitor radiation exposures for a specific wear period.
  • Wear your dosimeter in the proper location on your body as indicated below:
TYPE OF DOSIMETER WEAR LOCATION ASSIGNED TO
BlackIconChest (black icon)

 

Between the chest and waist Individuals not wearing a protective apron
RedIconCollar (over-apron, red icon)

 

  • Collar of apron or on thyroid shield, nearest to head
  • Outside of apron
Individuals who wear a protective apron (most UMHHC personnel)
YellowIconWaist (under-apron, yellow icon)
  • Under protective apron, between waist and chest
  • Only as a pair with over-apron dosimeter (“double-badge”), never standalone
  • Individuals with higher dose potential
  • Individuals who perform or assist in “fluoroscopic special procedures” (e.g., cardiac catheterization and other interventional fluoroscopy procedures)
FetalIconFetal Under protective apron, on abdomen Declared Pregnant Women
RingIconExtremity (ring)
  • On hand that receives highest exposure (if one ring)
  • With white label/chip facing source of radiation

Preventing Erroneous Readings

To prevent erroneous readings from radiation dosimeters:

  • Ensure the front of the dosimeter is visible (i.e., your name and location icon facing out) when wearing the dosimeter
  • If wearing two dosimeters, always wear the dosimeters in the proper location; do not wear an over-apron dosimeter under the apron
  • Store your dosimeter at work, in an area with low-background radiation and away from radioactive materials and radiation sources when you are not wearing it
  • Do not wear your dosimeter when undergoing medical or dental procedures as a patient
  • Do not store or place dosimeters in an unfavorable environment such as a hot automobile, washer/dryer, or microwave oven
  • Request a replacement if your dosimeter has been run through the washer, dryer or has been damaged, contaminated, or inadvertently exposed to radiation

Supplemental Information

Monitoring Individuals Who Are Pregnant

Additional monitoring is available for pregnant individuals to ensure the occupational radiation dose to the embryo/fetus is kept below the regulatory limit of 500 mrem (for the entire gestation period) and 50 mrem per month.  To initiate monthly fetal monitoring and authorize application of the regulatory dose limit for the embryo/fetus, the individual MUST voluntarily inform U-M of the pregnancy, in writing, using the Pregnancy Declaration Form (RSS-105A).  Declaration of pregnancy requires the individual to provide the estimated due date.

The declaration remains in effect until:

After a signed declaration form has been received by RSS, a fetal dosimeter, instructions for wear, and additional information will be provided to the individual.

If an individual chooses not to declare her pregnancy, her annual occupational dose limit (and that of the embryo/fetus) will remain the same as a normal radiation worker (5,000 mrem per year or 1,250 mrem per quarter, as appropriate).

Supplemental Information

Internal Radiation Exposure

Internal radiation exposure is rare, but it can occur if radioactive materials are inhaled, ingested, or absorbed.  When this occurs, a bioassay is requested from the individual, to measure the amount (activity) of radioactive material in the body.

Bioassays are conducted based on the type of radioactive material involved, as different radionuclides accumulate in various body systems.  For a standard bioassay, the following samples may be collected: urine, blood, saliva, or nasal mucus.  Thyroid bioassays are completed on individuals who have been exposed to volatile radio-iodine, using a sensitive external detector.

Who to Contact If Radiation Exposure Is Suspected

Individuals who have been contaminated by radioactive material or involved in a radioactive material spill should immediately contact their Authorized User (supervisor) and/or RSS at (734) 764-6200.