What is the recommended depth for photon beam calibration in accelerators?

The recommended depth for photon beam calibration in accelerators is typically at 10 cm in a water or equivalent medium. This depth is chosen because it corresponds to the build-up region of the beam where the dose delivered is sufficiently stabilized for accurate measurements. At this depth, the dose is representative of the clinical treatment conditions, allowing for reliable calibration of the photon beams.

Calibrating at 10 cm ensures that the measurements account for the changes in dose distribution that occur as the beam penetrates tissue. This standard depth is widely accepted in protocols such as those set by the American Association of Physicists in Medicine (AAPM) and is crucial for maintaining consistency and accuracy across different treatment planning systems and clinical practices. By targeting this specific depth, dosimetrists can ensure that the calculations and measurements reflect the actual delivery of radiation therapy to patients, optimizing treatment effectiveness and safety.