In modern linacs monitor units should be defined in water at 10 cm depth rather than at dmax
VAN DEN HEUVEL F., Wu Q., Cai J.
Thanks to the widely adopted guidelines such as AAPM TG‐511 and IAEA TRS‐3982, linac calibration has become more consistent and accurate around the globe than previously. Modern linac photon beams are often calibrated in water at 10 cm depth, and configured such that 1 monitor unit (MU) corresponds to 1 cGy at the depth of maximum dose, (dmax). However, such configuration is not without limitations. Some think it is unnecessarily complex and prone to errors, and believe that defining MU at 10 cm is more appropriate. Others think that change in MU definition can cause confusion and possibly serious consequences without any real benefit. This is the premise debated in this month's Point/Counterpoint.