According to AAPM TG-51 recommendations, what quality specifier is used for accelerator photon beams?

The AAPM TG-51 recommendations specify the use of a quality specifier based on the percentage depth dose (PDD) method for accelerator photon beams. When referring to the PDD, it is evaluated under a specific condition which defines the irradiation geometry, including the size of the field and the source-to-skin distance (SSD).

In this case, the correct quality specifier involves a field size of 10x10 cm^2 measured at a standard depth (often at a specific isocenter depth) with an SSD arrangement. This standardized field size is crucial for obtaining consistent and reproducible dose measurements across different treatment setups and linear accelerators.

The PDD for the 10x10 cm^2 field at a fixed SSD serves as an important reference point, ensuring that the measurements taken for calibration are reliable. This consistency enables proper standardization of dose delivery and helps maintain accuracy in treatment planning, which is essential for effective radiation therapy.

Using different field sizes or depth measurements would deviate from the established TG-51 protocol and could lead to inconsistencies in the dosimetric data obtained. Therefore, selecting the PDD (10×10×10, SSD) aligns perfectly with the established guidelines to ensure accurate dos