How is the SAR obtained?

The correct method for obtaining Specific Absorption Rate (SAR) is through the process of comparing the Tissue-Air Ratio (TAR) of a specified field to the zero field TAR. By subtracting the zero field TAR from the TAR of the given field, one can isolate the contribution of the radiation from the treatment field itself while accounting for any ambient conditions that may affect the measurement. This approach allows for a more accurate representation of how much radiation is being absorbed in a specific area, which is particularly important in medical dosimetry for ensuring proper dose delivery and patient safety.

In this context, measuring the total absorbed dose, while related to overall dose assessment, doesn't directly provide a method for deriving SAR. Simply averaging multiple dose measurements lacks the precision needed for a detailed understanding of how field characteristics affect absorption rates. An algorithmic approach could assist in calculations or modeling but does not replace the fundamental measurement methodology outlined in the correct choice.