The AKS of a brachytherapy source is 15 U. This refers to an AKS of which of the following?

In the context of brachytherapy, the term AKS stands for "Air Kerma Strength," which quantifies the strength of a radioisotope source used in treatment. The unit "U" in this case represents a standard for measuring air kerma strength, specifically defined as 1 U = 1 cGy cm² h⁻¹ at a distance of 1 meter.

When the AKS is noted as 15 U, this directly correlates to 15 cGy cm² h⁻¹. This measurement is crucial in determining the dose delivered to the treatment volume, as it represents the rate of energy deposited by the radiation per unit mass in air, impacting dosimetry calculations in brachytherapy.

The other options refer to different measurement units that do not correlate directly to AKS in the same way. For instance, muGy m² h⁻¹ and Gy cm² h⁻¹ are not the standard units for air kerma strength, and cGy m² h⁻¹ represents a different relationship in dose measurement that does not apply in this context. Therefore, the choice of 15 cGy cm² h⁻¹ as the correct answer accurately reflects the accepted definition and measurement for AK