Tolerance levels of CT number to electron density table for photon beam in radiotherapy treatment planning system

The accuracy of computed tomography number to electron density ( CT ‐ ED ) calibration is a key component for dose calculations in an inhomogeneous medium. In a previous work, it was shown that the tolerance levels of CT ‐ ED calibration became stricter with an increase in tissue thickness and decrease in the effective energy of a photon beam. For the last decade, a low effective energy photon beam (e.g., flattening‐filter‐free ( FFF )) has been...