What is the cancer risk associated with Technetium-99m (Tc-99m) ibis?

Cancer Risk Associated with Technetium-99m (Tc-99m) in Medical Imaging

The cancer risk from Tc-99m radiopharmaceuticals used in diagnostic nuclear medicine procedures is extremely low, with effective radiation doses typically ranging from 0.2 to 16 mSv depending on the specific protocol—well below the threshold for detectable cancer risk and comparable to or less than natural background radiation exposure. 1, 2

Radiation Dose Context

The radiation exposure from Tc-99m imaging procedures must be understood in the context of established safety thresholds:

• Effective doses for common Tc-99m procedures range from 0.048 mSv to 16.3 mSv, with most diagnostic studies falling in the lower range 1, 2
• Current scientific consensus indicates that non-cancer health effects are not detectable below 50 mSv, and deterministic effects (malformations, growth retardation) do not occur below 100-200 mSv 1
• For comparison, average annual background radiation exposure is approximately 3.1 mSv 3

Specific Tc-99m Procedure Doses

Cardiac Imaging

• Tc-99m sestamibi or tetrofosmin for myocardial perfusion imaging delivers 9.8 to 16.3 mSv for a 1-day rest-stress protocol 2
• Single injection doses range from 20-30 mCi for cardiac studies, with imaging acquisition taking approximately 40 minutes 1, 2

Sentinel Node Procedures

• Administered activities range from 15 MBq (same-day) to 120 MBq (2-day procedure), with effective doses around 0.048-0.2 mSv 1
• These doses are orders of magnitude below the 100-200 mSv threshold for deterministic effects 1

Pediatric Considerations

• Pediatric doses are weight-adjusted, typically 0.15 mCi/kg for Tc-99m sestamibi with a minimum of 2 mCi and maximum of 10 mCi 1
• Children are at inherently higher risk from radiation due to organ sensitivity and longer life expectancy, necessitating dose optimization 1

Special Population Safety

Pregnancy and Fetal Exposure

• Maximum fetal absorbed dose following injection of 18.5 MBq Tc-99m is calculated at 0.013 mSv—equivalent to one day of natural background radiation in the USA 1
• This dose is orders of magnitude below the threshold for fetal harm 1

Lactation

• Breastfeeding discontinuation is advised following Tc-99m procedures, though the radiopharmaceutical can be used in lactating women 1

Occupational Exposure Context

Healthcare workers handling Tc-99m face minimal risk:

• Mean annual occupational exposure for nuclear medicine personnel is 100-140 mrem (1-1.4 mSv)—significantly below maximum permissible doses 1
• Tc-99m has a 6-hour physical half-life and emits monochromatic 140 keV photons without beta radiation, minimizing radiation damage 4

Clinical Risk-Benefit Assessment

The radiation risk from Tc-99m diagnostic procedures is considered negligible compared to the clinical benefit of accurate diagnosis. 1 The key principle is that these procedures should only be performed when clinically indicated, as the diagnostic information gained far outweighs the theoretical cancer risk at these low dose levels.

Important Caveats:

• Tc-99m procedures should not be performed routinely without clinical indication 1
• Dose optimization techniques should always be employed, particularly in pediatric patients 1
• The linear no-threshold model suggests any radiation carries theoretical risk, but at doses below 50 mSv, cancer risk increases are not detectable above background rates 1