New approach to evaluate the exit dose quality for high radioprotection and radiotherapy efficiency

For safety and radioprotection reasons in radiotherapy treatment, the exit dose is evaluated with irradiation field size and photon beam energy. The objective of this study is to introduce an empirical law for predicting the delivered dose at the other side of patient while radiotherapy treatment of cancer . In this study, the exit dose is the delivered dose out of the phantom on beam central axis. The measurements of percentage depth dose were done as a function of irradiation field size with an uncertainty of 2 % as recommended by IAEA protocols for two photon beam energies 6 and 18 M V . For high radioprotection quality inside radiotherapy department, an empirical law is elaborated with a reliability of 97 %. Thereafter, it consists a basic law that should be used theoretically to know the delivered dose variation with field size at the exit dose point for knowing the behavior of dose outside of radiotherapy treatment region . The medical physicists and physicians should take this law in radiotherapy treatment of the cancer. Keywords: dose build-up, radiotherapy, photon beam, dosimetry, radiotherapy quality