Final answer:
A gonad shield should be used in radiographic procedures whenever the edge of the radiation field is within 5 cm of the gonads to protect reproductive health.
Step-by-step explanation:
The student's question relates to the use of gonad shields during imaging procedures that involve exposure to a radiation field. A gonad shield is a protective barrier designed to reduce the exposure of the reproductive organs to ionizing radiation during diagnostic radiographic procedures. It is particularly important for protecting patients' reproductive viability during x-rays that penetrate the pelvic region. According to health and safety guidelines, a gonad shield should be used whenever the edge of the radiation field is within 5 cm of the gonads. Therefore, the correct answer is a. 5 cm.