If the gonads are properly shielded with 0.5 mm lead equivalent, approximately what percent of the incident primary beam radiation dose can the gonads still receive from internal scatter?

• A. 5%
• B. 10%
• C. 20%
• D. 30%

Answer: (A)

Internal scatter is created inside the patient and can still reach the gonads even when shielding is in place. A 0.5 mm lead equivalent shield greatly reduces the dose, but it cannot block all scatter. The remaining dose from internal scatter to the gonads is typically about 5% of the incident primary beam. This small residual amount reflects that scatter is lower energy and spread in many directions, so most of it is absorbed or diverted, leaving a minor fraction that reaches the gonads. The exact value can vary with technique, field size, and patient factors, but around 5% is a commonly cited approximate figure.