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Verification of Monte Carlo simulations for dosimetry in radiation therapy


Monte Carlo calculations enable the simulation of electron and photon transport through matter. Based on the simulations, among others, the (mean) energy can be determined which is deposited within a certain volume during the passage of the particles. In the field of radiation therapy, the correctness of such Monte Carlo simulations is particularly important, since they provide the possibility of determining the dose for treatment planning more accurately.

Monte Carlo programs provide standardized results such as, e.g., the dose per incident electron or the dose per incident fluence. Since such standardized values usually cannot be achieved experimentally, the experiments and the simulation results are usually compared at a relative level. Statements which are based on relative comparisons can, however, not be fully applied to absolute values. Also, the calculation results have been compared with theoretically known results. The latter are, however, not always applicable in practice, since these considerations are based on unrealistic (idealised) conditions.

Within the scope of a doctoral thesis in cooperation with the Ilmenau University of Technology, experimental measurements in high-energy photon radiation fields will be compared for the first time with Monte Carlo simulation calculations in an absolute way. Thus, the simulations can be verified directly. The corresponding benchmark experiment will be, as far as possible and sensible, based on the conditions of clinical radiation therapy. The possibilities provided by the new research accelerator located in the Richard Glocker building at PTB are exploited. The accelerator’s electron beam can be very accurately characterized by means of beam current monitors and spectrometers. The Monte Carlo simulations are performed using the software EGSnrc.

Figure : The benchmark experiment is to be simulated in EGSnrc. An example of a component in the experiment is a cavity ionization chamber for dose measurement (upper picture). The chamber was modelled using the geometry package egspp which is included in EGSnrc. The bottom picture depicts a cross section of the chamber model.