The AKS of a brachytherapy source is defined as what?

The Air Kerma Strength (AKS) of a brachytherapy source is defined as the air kerma rate in free space. This term is critical in the context of brachytherapy as it quantifies the radiation output of the source, providing a reliable measure of its strength.

Air kerma is a physical quantity that indicates the energy transferred from ionizing radiation to air. When assessing brachytherapy sources, the air kerma rate is essential for calculating dosimetry, ensuring that the correct dose is delivered to the treatment area while minimizing exposure to surrounding healthy tissues. Knowing the AKS allows dosimetrists to adjust and calculate the appropriate dose distributions for patient-specific treatment plans.

In contrast, the other options deal with different aspects of radiation measurement but do not specifically define AKS. For instance, the absorbed dose at a distance does not directly represent the source strength in the same way. Similarly, exposure rate or radial dose distribution pertains to different parameters and measurements that, while relevant in the field, do not align with the specific definition of AKS. Thus, understanding the AKS as the air kerma rate in free space is vital for proper dosimetry and treatment planning in brachytherapy.