Different measurements of depth-dose curves and dose profiles were performed in heterogeneous phantoms and compared to dose distributions calculated by a Monte Carlo code. These heterogeneous phantoms consisted of lung and/or bone heterogeneities. Irradiations and simulations were carried out for an 18 MeV electron beam and a 12 MV photon beam. Depth-dose curves were measured with Fricke dosimeters and with plane and cylindrical ionization chambers. Dose profiles were measured with a small cylindrical ionization chamber at different depths. The LINAC was modelled using the PENELOPE code and phase space files were used as input data for the calculations of the dose distributions in every simulation. The detectors (Fricke dosimeters and ionization chambers) were not modelled in the geometry. There is generally a good agreement between the measurements and PENELOPE. Some discrepancies exist, near interfaces, between the ionization chamber and PENELOPE due to the attenuation of the lower energy electrons by the wall of the ionization chamber.

Purpose: From IEC 976 and 977, the dose distributions quality for x‐rays beams from LINAC gets through the fulfilment of four parameters. This work is aimed at replacing these dosimetric tests by one parameter (gamma index) and using this concept to validate Monte Carlo simulated beams. Method and Materials: From measurements of a 12 MV beam of a medical LINAC, analytical functions have been set to fit reference depth‐dose and profile distributions. Then, those 1D distributions have been altered to reach the admissible limits of the IEC standard criteria. The peculiar tolerance criteria of the gamma index have been determined by comparing altered and reference distributions. This 12 MV beam have been simulated with the Monte Carlo code PENELOPE for different incident electron configurations at the target. The simulations have been fitted with polynomial functions to get better resolution before being compared to measurements using the gamma index to avoid false positives or false negatives due to a lack of spatial resolution in these simulations. Results: The tolerance criteria for the gamma index have been determined experimentally by comparison with the IEC standard requirements. They are more restrictive by nature than the IEC criteria. This unified concept of dosimetric tests by the systematic use of the gamma index enabled us to select effectively the parameters for the beam simulation. Conclusion: This work shows the possibility of using only one test for all the measurements required for x‐rays beam QA and its Monte Carlo simulations. In the future, this work will lead to the implementation of a set of simulations in order to replace measurements required for the quality control of the Treatment Planning System. Evaluation tests should be based on the calculation of the 3D gamma index to simplify test processes.