What is measured precisely at 1 m from the perpendicular bisector of the source in brachytherapy?

In brachytherapy, the air kerma rate is a critical measurement taken at a standardized distance, specifically at 1 meter from the perpendicular bisector of the radiation source. This measurement is important because it allows for the standardized evaluation of the radiation output from the source, facilitating comparisons between different sources and treatment plans.

Measuring the air kerma rate at this specific distance helps to quantify the strength of the radioactive source, which can then be used to calculate the dose delivered to the target tissue and surrounding structures. This value is essential for determining the appropriate treatment plan, ensuring the delivered dose is both effective and safe for the patient.

On the other hand, exposure time refers to the duration a patient is exposed to the radiation and does not directly measure the source characteristics at a specific distance. Dose distribution encompasses how the dose varies in the treatment area but is not limited to a specific measurement point. Source weight does not relate to radiation output or dosimetry. Therefore, air kerma rate is the primary and most relevant measurement in this context.