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.

This paper shows that reliable measurements with TLDs in complex energy spectra require a study of the detector dose response with the radiation quality and specific calibration methodologies which model accurately the experimental conditions where the detectors will be used. The authors have developed and studied a method with highly sensitive TLDs and contributed to its validation by comparison with results from the literature. This methodology can be used to provide direct estimates of the absorbed dose rate in water for irradiations with HDR (192)Ir brachytherapy sources.

The devices and methods applied for the LNE–LNHB primary standards in terms of reference air-kerma and absorbed dose to water for low dose-rate brachytherapy sources are described. Both standards are based on ionometric measurements, using a circular-shaped free-in-air ionization chamber, and Monte Carlo calculated conversion factors. Results for an IBt Bebig 125I source are presented and used here to assess the dose-rate constant. Uncertainties of 1.5% and 1.6% (with k = 1) were found for the air-kerma rate and the absorbed dose to water rate estimated with the new primary standards. Good agreement was found between our values and the AAPM published dose-rate constants. Comparisons with other primary standards are in progress.

The purpose of this work was to develop a procedure to directly estimate the spatial distribution of the absorbed dose rate to water, , around an HDR 192Ir brachytherapy source. The methodology developed was based on Monte Carlo calculations and measurements in air and in water with thermoluminescent detectors. Variations in detector positioning had a significant influence near the brachytherapy source (20% at 1 cm). The method leads to a mean difference of about 7% with the CLRP TG-43 Parameter Database when the absorbed dose to water is characterized along the transverse plane to the source (from 1 cm to about 11 cm). This mean difference, however, is within an uncertainty of 7.7% over all distances. This method therefore can be used to provide direct estimates of the absorbed dose rate to water for HDR brachytherapy source irradiations which are more realistic than those which use other phantom materials. In addition, measurements are indicative of the source geometry and material composition.