Measurement of the radiation dose to the skin of the anterior chest is a reasonable indicator of dose to which structure?

• A. Thyroid dose
• B. Breast dose
• C. Probability of cataracts
• D. Depression of lymphocytes

Answer: (B)

Entrance skin dose to the anterior chest best reflects the dose to the breast because the breast tissue sits directly behind that skin and lies at a shallow depth. The radiation that exits the skin is deposited in surface and near-surface tissues, so the skin dose is a good proxy for the actual dose absorbed by the superficial breast tissue. In contrast, the thyroid is higher up in the neck, the lens of the eye would depend on a different field and geometry, and lymphocyte depression relates to overall body dose rather than a localized superficial structure.