Personnel Dosimetry: Monitoring Devices, Dose Limits, and Record Keeping

Why Personnel Dosimetry Matters

Radiation workers receive small doses repeatedly over a career. Because the health effects of low-level chronic exposure accumulate over time, the industry tracks every worker's dose carefully. Personnel dosimetry is the system of devices, records, and limits that protects you, your coworkers, and your patients. As a limited radiologic technologist, you are legally and professionally required to wear your assigned dosimeter correctly and to understand what the numbers on your dose report mean.

Types of Personnel Dosimeters

Film Badge

The film badge was the standard monitoring device for decades. It contains a small piece of photographic film inside a plastic holder fitted with filters made of different materials (aluminum, copper, and open windows). When ionizing radiation strikes the film, it creates a latent image. The badge is sent to a processing laboratory, where the film is developed and the degree of darkening (optical density) is measured to estimate dose. Film badges are inexpensive and provide a permanent record, but they are sensitive to heat and humidity, can fog if accidentally exposed to light, and must be replaced on a regular cycle (often monthly). They are largely being phased out in favor of newer technologies.

Thermoluminescent Dosimeter (TLD)

A TLD contains crystals—commonly lithium fluoride—that trap electrons in higher-energy states when exposed to radiation. When the badge is returned to the laboratory, the crystals are heated. As the electrons return to their ground state they release light, which is measured by a photomultiplier tube. The amount of light is proportional to the radiation dose received. TLDs are more accurate than film badges, are not affected by humidity, and can measure a wide range of doses. They can be read multiple times if needed (though repeated readings release the stored energy), and the crystals can be reused after being fully annealed.

Optically Stimulated Luminescence Dosimeter (OSL)

The OSL dosimeter, such as the Luxel+ badge, contains aluminum oxide crystals. Radiation traps electrons in the crystal in a manner similar to the TLD. To read the dose, a laser stimulates the crystal with light rather than heat. The released luminescence is measured and converted to a dose value. OSL dosimeters are highly sensitive (they can detect very low doses), do not require heating, and the same crystal can be re-read multiple times without losing accuracy. This re-readability is a significant advantage for verifying or auditing dose records. OSL badges are the most widely used dosimeter in US radiology departments today.

Comparison Summary

| Device | Detection Mechanism | Reading Frequency | Advantages | Limitations |

|---|---|---|---|---|

| Film badge | Optical density of photographic film | Monthly | Inexpensive; permanent record | Sensitive to heat, humidity; fogs |

| TLD | Thermoluminescence from heated crystals | Quarterly or monthly | Accurate; reusable crystals | Single reliable read; requires heating |

| OSL | Optically stimulated luminescence | Quarterly or monthly | Very sensitive; re-readable; stable | Requires specialized laser reader |

Wearing Your Dosimeter Correctly

Wear your whole-body dosimeter at collar level (outside the lead apron if one is worn) unless instructed otherwise by your radiation safety officer. A separate ring dosimeter is worn on the dominant hand if you regularly hold patients or image receptors near the primary beam. Never leave your dosimeter in a high-radiation area when you are not present; store it in a low-background area (away from X-ray rooms). Do not share dosimeters. Improper wear invalidates your dose record and removes a key safety safeguard.

Reading an Occupational Dose Report

Dose reports typically list dose in millisieverts (mSv) or millirem (mrem). Know the conversion: 1 mSv = 100 mrem. Reports show dose for each monitoring period (monthly or quarterly), a running year-to-date (YTD) total, and often a lifetime cumulative total. Look for any single-period value that seems unusually high—this may indicate a dosimeter was misplaced, an exposure incident occurred, or the badge was accidentally irradiated. Compare the YTD total against established limits. Report any unexpected readings to your radiation safety officer (RSO) promptly.

NCRP Recommended Annual Dose Limits

The National Council on Radiation Protection and Measurements (NCRP) publishes recommendations that form the basis for US regulatory limits. Current recommended annual occupational dose limits include:

• Whole body (effective dose): 50 mSv (5 rem) per year
• Lens of the eye: 150 mSv (15 rem) per year
• Skin and extremities: 500 mSv (50 rem) per year
• Members of the public (frequent exposure): 1 mSv (0.1 rem) per year

Different limits exist because tissues differ in radiation sensitivity and in practical likelihood of exposure. The lens of the eye is more radiosensitive than skin; therefore its limit is lower. Extremities (hands, feet) can receive higher local doses without the same whole-body systemic risk, so their limit is higher. The public limit is far lower than the occupational limit because members of the public have not chosen to work with radiation and receive no occupational benefit from it.

The guiding principle behind all dosimetry is ALARA—As Low As Reasonably Achievable. Meeting the limit is not the goal; the goal is keeping every worker's dose as far below the limit as practical.

Record-Keeping Requirements

Employers must maintain occupational dose records and make them available to workers upon request. Workers who change jobs can request their dose history from previous employers or from the dosimetry company. Accurate, complete records protect both the worker and the employer. Falsifying or discarding dose records is a serious regulatory violation.