Radiation Monitoring in Nuclear Medicine

Radiation monitoring

is a cornerstone of radiation safety in nuclear medicine.

patients and staff

Since nuclear medicine involves the use of unsealed radioactive materials (radiopharmaceuticals), both ___ and ____ can be potential sources of exposure.

Radiation monitoring

ensures that doses remain as low as reasonably achievable (ALARA) while still delivering diagnostic and therapeutic benefits.

Radiation exposure 

in nuclear medicine comes from multiple pathways, and understanding these is the foundation of radiation monitoring.

Open Radioactive Sources, Patients, Contaminated Surfaces/Equipment, Airborne Contamination, Sealed Sources

Sources of Exposure (5)

Open Radioactive Sources

These include unsealed radiopharmaceuticals such as Tc 99m vials, syringes, or I-131 capsules. Because these sources are handled directly, they pose risks of external exposure, spills, and contamination

Tc 99m vials, syringes,  I-131 capsules

Open Radioactive Sources:

These include unsealed radiopharmaceuticals such as ___, ___, or___. Because these sources are handled directly, they pose risks of external exposure, spills, and contamination

patient

Once a radiopharmaceutical is administered, the___ themselves becomes a temporary radiation source, emitting gamma rays or positrons. Technologists receive external exposure while assisting, transporting, or imaging patients

Contaminated Surfaces/Equipment

Work areas, counters, injection chairs, and waste bins may accumulate residual radioactivity from spills or droplets.

Airborne Contamination

Volatile isotopes like I-131 can become airborne in the form of vapor or aerosols, posing inhalation risks.

I-131

Airborne Contamination

Volatile isotopes like ___ can become airborne in the form of vapor or aerosols, posing inhalation risks.

Sealed Sources

Calibration sources or brachytherapy seeds are tightly contained, but still emit radiation and require routine monitoring

brachytherapy seeds

Sealed Sources

Calibration sources or ____ are tightly contained, but still emit radiation and require routine monitoring.

external exposure, inhalation, contamination spread, or cumulative occupational dose

Radiation monitoring in nuclear medicine includes four main categories. Each category addresses a unique risk (4)

Source Monitoring

refers to the measurement and verification of radioactive sources before they are administered, stored, or disposed of.

Source Monitoring

In nuclear medicine, this applies to unsealed radiopharmaceuticals (e.g., Tc-99m, I-131, F-18) as well as sealed calibration/check sources (Cs 137, Co-57 flood sources)

Source Monitoring

Its primary purpose is to ensure that the correct activity is administered to the patient, that storage is safe, and that sources remain within regulatory requirements

Source Monitoring

Confirms that sealed sources are intact (no leakage).

Source Monitoring

Verifies activity of radiopharmaceutical doses before patient administration.

Source Monitoring

Ensures safe storage, handling, and disposal of radioactive sources.

Source Monitoring

When is it used:

• During daily constancy checks of dose calibrators.

Source Monitoring

When is it used:

• Before patient injections

Source Monitoring

When is it used:

• Periodic leak testing of sealed sources (I-125, Co-57, Cs-137)

Dose calibrator (ionization chamber)

Measures activity of radiopharmaceutical doses.

Dose Calibrator (ionizing chamber), Well-type scintillation counter, Survey matter

Instruments used in Source monitoring (3)

Well-type scintillation counter

Used for wipe tests of sealed sources.

Survey meter

Checks for leakage or contamination near source storage

Calibration Factor (CF)

is the ratio between the known activity of a radioactive source (in becquerels or curies) and the measured count rate (in counts per second or counts per minute) detected by an instrument.

Calibration Factor (CF)

It provides a conversion factor that allows raw count rates from a detector to be expressed as actual activity.

Calibration Factor (CF)

Applied in wipe tests, contamination surveys, and when quantifying source activity using radiation detectors.

Known Activity (Bq or Ci) / Measured counts per second (cps)

Calibration Factor Formula

200 Bq/cps

A standard source of Technetium-99m (Tc-99m)with an activity of 37 MBq (1 mCi) is measured using a dose calibrator. The detector records a count rate of 185,000 cps. What is the Calibration factor?

Step-by-Step Methodology (Radiopharmaceutical Dose Check)

1. Turn on dose calibrator and allow to stabilize.

2. Select isotope setting (e.g., Tc-99m).

3. Place dose syringe/vial inside the well chamber.

4. Read displayed activity (Bq or mCi).

5. Compare with prescribed activity and adjust volume/dose as needed.

6. Record results in activity logbook.

Step-by-Step Methodology (Sealed Source Leak Test):

1. Prepare wipe material (cotton swab/filter paper).

2. Wipe around the source capsule or storage container.

3. Insert wipe sample into well counter or gamma counter.

4. Analyze activity– if >185 Bq is detected, source is leaking.

5. Report immediately if leakage is found

tongs, shielding

Handle sources with ___ or ___ to minimize exposure

dose calibrator constancy

Always check ___ before patient work.

lead containers

Store sources in ___ when not in use

leak testing and documentation

Follow regulatory protocols for ____.

Daily Dose Calibrator Check

A technologist measures a Tc-99m syringe before injection

Dose calibrator

confirms activity matches physician’s prescription

Daily Dose Calibrator Check

Technologist role: Adjusts dose volume to ensure correct administration to patient.

Annual Leak Test of Co-57 Flood Source

Technologist wipes around the flood source casing

Well counter detects no activity above background, confirming integrity

Annual Leak Test of Co-57 Flood Source

Instrument role:

Well counter

detects no activity above background, confirming integrity.

Records results and certifies the sealed source is safe for continued use.

Annual Leak Test of Co-57 Flood Source

Technologist role: Records results and certifies the sealed source is safe for continued use.

Airborne Contamination Monitoring

refers to the detection and measurement of radioactive materials (gases, vapors, or aerosols) suspended in the air.

Airborne Contamination Monitoring

This type of monitoring is critical because inhalation is one of the most dangerous routes of internal exposure, and radioactive material that enters the lungs can irradiate tissues for extended periods

Airborne Contamination Monitoring

Ensures that airborne radioactive materials (e.g., iodine-131, xenon-133) are within safe limits.

Airborne Contamination Monitoring

Protects staff and the public from inhalation hazards

Airborne Contamination Monitoring

Detects leaks or spills that may release radionuclides into the air.

Airborne Contamination Monitoring

• When is it used:

During radiopharmaceutical preparation.

Airborne Contamination Monitoring

• When is it used:

After spills, accidents, or potential release of airborne isotopes.

Airborne Contamination Monitoring

• When is it used:

In controlled rooms such as hot labs, isolation wards, or nuclear medicine imaging rooms.

Air Samplers (filter-based), Continuous Air Monitors (CAMs)

Airborne Contamination Monitoring

Instruments:

Continuous Air Monitors (CAMs)

Provide real-time monitoring by drawing air over a detector (scintillation or semiconductor) with alarms for high levels

Air Samplers (filter-based)

Draws a known volume of air through a filter that traps particles. The filter is later counted with a gamma counter

Step-by-Step Methodology (Air Sampler):

1. Prepare the sampler– Ensure calibration, check filters, and set the required airflow rate.

2. Position sampler– Place near potential contamination sources (fume hood, patient room, radiopharmacy).

3. Collect air sample– Run the pump for a pre-set time to capture particulates on the filter

4. Analyze filter– Count using a gamma spectrometer or well counter to identify radionuclides.

5. Interpret results– Convert activity per filter to airborne concentration (Bq/m³) and compare with permissible levels.

Prepare the sampler

Ensure calibration, check filters, and set the required airflow rate.

Position sampler

Place near potential contamination sources (fume hood, patient room, radiopharmacy).

Collect air sample

Run the pump for a pre-set time to capture particulates on the filter

Seal and label filter

After sampling, carefully remove the filter and record time, location, and conditions.

Analyze filter

Count using a gamma spectrometer or well counter to identify radionuclides.

Interpret results

Convert activity per filter to airborne concentration (Bq/m³) and compare with permissible levels

Step-by-Step Methodology (Continuous Air Monitor):

1. Turn on CAM unit and verify background readings.

2. Ensure airflow path is clear (no blockage of intake).

3. Activate continuous sampling– unit automatically draws air and checks for radioactivity.

4. Monitor display/alarms– watch for real-time alerts of rising activity.

5. Record data– log activity levels regularly for regulatory compliance

PPE

Airborne Contamination Monitoring

Safety Measures

Always wear ___ (mask, gloves, lab coat) when handling potentially contaminated areas.

breathing height

Airborne Contamination Monitoring

Safety Measures

Position samplers at ___ (to simulate worker exposure).

evacuate and investigate

Airborne Contamination Monitoring

Safety Measures

Immediately ____ if CAM alarm is triggered.

radio active waste

Airborne Contamination Monitoring

Safety Measures

Dispose of used filters as___

Radiopharmacy Iodine Spill

A technologist spills iodine-131 solution in the preparation room

Stops work, alerts safety officer, initiates decontamination, and documents exposure

Radiopharmacy Iodine Spill

Technologist role:

CAM detects sudden airborne radioactivity.

Radiopharmacy Iodine Spill

Instrument role: 

Patient Therapy Isolation Ward

A patient receiving iodine-131 therapy exhales radioactive iodine.

Air sampler measures airborne activity in the ward.

Patient Therapy Isolation Ward

Instrument role:

Monitors air samples, ensures ventilation is adequate, and confirms staff are not overexposed.

Patient Therapy Isolation Ward

Technologist role: 

Surface Contamination Monitoring

detects radioactive residues deposited on work surfaces, equipment, floors, PPE, or even the skin

Surface Contamination Monitoring

This is vital in nuclear medicine because technologists handle unsealed radiopharmaceuticals that can spill or drip, leading to the spread of contamination

Surface Contamination Monitoring

Ensures contamination does not spread outside controlled areas

Surface Contamination Monitoring

Identifies spills, leaks, or poor handling practices.

Surface Contamination Monitoring

Provides assurance before releasing equipment or rooms for general use.

Surface Contamination Monitoring

When used:

After patient therapy administration

Surface Contamination Monitoring

When used:

During routine daily/weekly surveys in nuclear medicine labs.

Geiger-Müller (GM) survey meter, Scintillation survey meter, Wipe test with well counter

Surface Contamination Monitoring

Instruments:

Scintillation survey meter

More sensitive for low-energy gamma contamination

Wipe test with well counter

Indirect check by wiping surfaces and analyzing collected contamination

Geiger-Müller (GM) survey meter

Detects beta/gamma contamination directly.

calibrated; known standard source

Surface Contamination Monitoring

Step-by-Step Methodology for Using GM Counter

1. Preparation

Ensure the GM counter is ___ using a___

battery; functionality

Surface Contamination Monitoring

Step-by-Step Methodology for Using GM Counter

1. Preparation

Check the___ and ___ of the instrument

lowest

Surface Contamination Monitoring

Step-by-Step Methodology for Using GM Counter

1. Preparation

Set the scale/range to an appropriate sensitivity level (usually the ___ for contamination checks).

clean area

Surface Contamination Monitoring

Step-by-Step Methodology for Using GM Counter

2. Background Measurement

Measure background radiation in a ___ and record it.

subtracted

Surface Contamination Monitoring

Step-by-Step Methodology for Using GM Counter

2. Background Measurement

This will be ___ from actual surface readings

1 cm

Surface Contamination Monitoring

Step-by-Step Methodology for Using GM Counter

3. Survey Technique

Hold the GM probe about ___ from the surface without touching it (to avoid contaminating the detector).

slowly (~2–5 cm per second)

Surface Contamination Monitoring

Step-by-Step Methodology for Using GM Counter

3. Survey Technique

Move the probe ___ (____) to avoid missing small contaminated spots.

all areas

Surface Contamination Monitoring

Step-by-Step Methodology for Using GM Counter

3. Survey Technique

Survey ___ systematically: benches, floors, protective clothing, equipment handles, door handles, etc.

CPM or µSv/hr

Surface Contamination Monitoring

Step-by-Step Methodology for Using GM Counter

4. Recording Results

Record readings in ___ for each location.

net contamination counts

Surface Contamination Monitoring

Step-by-Step Methodology for Using GM Counter

4. Recording Results

Subtract background to obtain ___

contaminated

Surface Contamination Monitoring

Step-by-Step Methodology for Using GM Counter

4. Recording Results

If the reading is above permissible limits, label the area as “____.”

Mark, restrict access

Surface Contamination Monitoring

Step-by-Step Methodology for Using GM Counter

5. Decontamination(if contamination is found)

___ and ____ to the contaminated area

Laboratory Bench Monitoring

After a nuclear medicine procedure involving Tc-99m, a technologist surveys the workbench with a GM counter

GM counter ; within permissible limits

Surface Contamination Monitoring

Step-by-Step Methodology for Using GM Counter

5. Decontamination(if contamination is found)

Re-survey the area with the ___until levels are ___

Surface Contamination Monitoring

Step-by-Step Methodology (Wipe Test):

1. Prepare filter paper or swab.

2. Wipe surface with consistent pressure over a 100 cm² area.

3. Seal wipe in vial and label properly.

4. Measure activity in a well counter or gamma counter.

5. Compare results against permissible limits.