Final answer:
The personal dosimeter should be worn under the lead apron to accurately measure occupational exposure to ionizing radiation.
Step-by-step explanation:
When wearing a lead apron as a protective measure against radiation during medical procedures, the personal dosimeter should be worn under the apron. This placement ensures that the dosimeter can measure the dose of radiation that actually reaches the body through the protective lead barrier. Wearing it under the apron provides a more accurate representation of the occupational exposure to ionizing radiation that the health practitioner receives.