Risks Associated with Medical Events

The term “medical event” may sound alarming when used in nuclear medicine and radiation 

therapy. But it may not mean a patient has been harmed. It means there may have been a problem in a 

medical facility’s use of radioactive 

materials. 

These materials can help to 

diagnose and treat illnesses or be used 

in medical research. Small amounts can

allow doctors to see certain organs. 

Images created using radioactive 

materials can help to find, identify and 

measure tumors, or view problems in an 

organ’s structure or function. 

Radioactive materials can also kill 

cancerous tissue, shrink a tumor or 

reduce pain.

NRC regulations aim to assure radioactive materials are used properly. This is also true when 

they are used in medical diagnosis, treatment or research. The rules protect the safety of patients, 

medical workers, the public and the environment. They define “medical event” in very specific terms.

A “medical event” involving radioactive materials occurs if BOTH: 

(1) The dose given is not what was prescribed, and the difference meets the NRC’s reporting 

requirements, AND

(2) One or more of the following incidents occur:

• the dose given is off by at least 20 percent from 

the prescribed dose, either too high or too low,

• the wrong drug is used,

• the drug is given by the wrong route,

• the wrong individual receives the dose,

• a dose is administered to the wrong part of the 

body and exceeds by 50 percent or more the dose 

that area should have received, or

• a sealed source used in the treatment leaks.

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Yttrium-90 microspheres deliver radiation directly to tumors

Gamma knife focuses tiny beams of radiation on a tumor
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The NRC requires reporting because a medical 

event shows the licensee had a problem in 

administering the doctor’s prescription. The problem 

may have been technical, or may be a quality assurance 

issue. Dose errors may be a sign of problems in the 

medical facility’s operations. But there is no scientific 

basis to conclude that such an error results in harm to a 

patient.

To know if a patient has been harmed, the 

doctor must do more analysis. Harm may come from 

too high a dose. But it could also result from 

inadequate treatment when a dose is too low. 

The NRC also analyzes each event to see if further action is 

needed. If there is a violation of the regulations, the NRC might take 

enforcement action. 

The agency will also look for trends to see if something in 

NRC regulations or guidance may need to be clarified. 

Severe events are rare. An example would be a dose error 

that is well over 20 percent too high or too low. In severe events, an 

independent medical consultant will assess the patient’s risk of harm. 

In all cases, a “medical event” indicates potential problems in 

a facility’s use of radioactive materials. It does not necessarily result 

in harm to a patient. But the NRC’s rules are designed so events are 

reported to the NRC and the public. Even when there is harm to a 

patient, the NRC protects the public health and safety.

July 2022

Shielding and syringe holder used to protect medical 

workers as the load a syringe from a bulk vial of a 

radiopharmaceutical containing fluorine-18

Leaded shields for radiopharmaceutical 

syringes model PSV (Courtesy of 

COMECER S.P.A)