Answer to Question #14995 Submitted to "Ask the Experts"

One of our patients was recently treated with tiny needles covered with radium-224 (²²⁴Ra) inserted into the pancreas with an endoscope. Some of the ²²⁴Ra was detected in the facial area (around the mouth, nose, and eyes) with an alpha detector. The lower limit for radioactivity contamination in Canada is 0.3 Becquerel per square centimeter (Bq cm^-2) for low-energy alpha emitters. (This value is not related to the patient’s exposure but provides context.) The measured Bqcm^-2 over those facial areas of the patient was at least twice that level. I am wondering about the risk and potential consequences (if any) for a patient with that level of ²²⁴Ra in those areas.  

This is an excellent and timely question, as new radioactive material treatments using alpha-emitting radionuclides such as ²²⁴Ra are becoming increasingly popular. Based on the information you have provided, the amount of radiation exposure from this scenario is minimal and is not a major concern for your patient's overall health.

One may view this scenario from both skin contamination exposure and accidental intake exposure perspectives.

Using your provided contamination estimate (approximately 0.6 Bq cm^-2), a safety factor of 10, and a standard assumption of a 10 cm² contamination area, the total skin contamination value would be approximately 60 Bq per10 cm^-, rounded up to 100 Bq per10 cm² to be conservative. The isotope ²²⁴Ra decays via a six-step decay chain, emitting both alpha and beta particles and relatively high energy photons along the way. While alpha particles do not deliver a significant skin dose, beta particles and photons may, depending upon the amount. Using commercially available software (Varskin v6.2.1) to estimate skin dose, and data from the International Commission on Radiation Protection (ICRP) Report 107, the calculated skin dose estimate for this event would be 5 milligray (mGy, a unit of radiation absorbed dose). The International Atomic Energy Agency (IAEA) indicates that neither skin reddening (erythema) nor any other type of radiation effect on the skin would be observable below a dose of 2,000 mGy.

While this is a patient-related issue, data provided for occupational workers may be used as the foundation of a discussion on internal exposure. If one assumes that same 100 Bq (the conservative approximation from skin contamination) was also ingested by the patient, a second calculation can be made. ²²⁴Ra will circulate within the body, delivering small amounts of dose to the whole body, while concentrating mainly on the bone surfaces. Using the annual limit of intake (ALI) table values provided by the United States Nuclear Regulatory Commission (US NRC), one would expect approximately 0.01 millisieverts (mSv, a unit of equivalent dose, that is the same as mGy for beta particles and photons) "whole body" dose per 100 Bq from this type of intake, with a slightly higher 0.2 mSv per 100 Bq to bone surfaces. Not only are these values significantly below levels at which documentable biological effects have been observed, they are also well below levels received from natural background radiation from the Earth over the course of a year.

In summary, the amount of radiation exposure received in this scenario, from both skin and internal perspectives, is exceptionally low. The associated risk from this event is negligible and should not be of concern to your patient.

Brian Serencsits, CHP