To derive the absorbed dose to water from a standard of absorbed dose to graphite, the metrology laboratories which apply such a method usually make use of cavity ionization chambers as transfer instruments. In addition, the BNM-LPRI has tested, as such instruments, two types of Fricke dosimeter in its cobalt-60 beam. The two procedures are compared and their results are found to be in good agreement (the difference is less than 0.1%). Both procedures are then taken into account for the calculation of the reference value of absorbed dose to water.

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.

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