What warning should be posted when a patient is treated with Iodine 131?

When a patient is treated with Iodine 131, the appropriate warning to post is "Caution: radioactive materials." This warning is necessary because Iodine 131 is a radioactive isotope used in the treatment of certain thyroid conditions, including hyperthyroidism and thyroid cancer. It emits both beta and gamma radiation, so isolating the patient and ensuring that staff and other individuals are aware of the potential radiation risk is crucial for safety.

The phrase "Caution: radioactive materials" effectively communicates the presence of radioactive substances, alerting those who enter the area to potential exposure risks and the need for protective measures such as maintaining distance or wearing protective equipment, if necessary. This warning is informative and appropriate for the context of a medical facility where radioisotopes are handled.

Reflecting on the other options, "High radiation- grave danger" would imply a more immediate and severe risk than what is typical for Iodine 131 in a controlled patient treatment setting. "Caution: high dose radiation" might suggest that the radiation levels are consistently high or pose an immediate danger, which is not the case in most therapeutic scenarios. "Do not enter: radiation at excessive levels" may convey an overly prohibitive stance, potentially causing unnecessary alarm.