RESUMO
The main parameters determining the quality of an electron beam produced by a linear accelerator for medical use were considered in this study, particularly: flatness, symmetry and uniformity. We analyzed and compared several protocols issued by national and international associations (such as the AAPM, IPSM, ICRU, NACP), the software protocol developed for the measurement system we used (Multidata) and the measurement instructions recommended by the accelerator manufacturer (Siemens). The above associations issue quality protocols to ensure system performances suitable for medical use, to increase patient safety and to improve the treatment outcome. Radiation therapy safety and improvement depend on correct dose measurements and dose distribution in the treated volume. Once the dose value per monitor unit ratio (Gy/M.U.) is determined, controls are necessary to be sure that the value does not change in time and that the dose distribution has the same effect in the whole treated volume. Our goal is to point out the differences and the affinities in the definition of the parameters, which change slightly in the different protocols, and to study the origin of the differences found when the experimental results were compared. Another important issue is represented by the frequency of quality controls, which are definitely different from the fast checks which are often performed. In conclusion, some suggestions are provided for the choice of the quality protocol to follow.