A Determination of a Correction Factor from ⁶⁰Co to ¹⁹²Ir Obtained by a Monte Carlo Simulation

Radiation dosimetry is an integral part of the radiation therapy process. The ultimate goal of radiation dosimetry is to determine the dose delivered to the tumour and to the normal tissues in a patient undergoing radiotherapy. The importance of HDR ¹⁹²Ir brachytherapy as the main mode of treatment calls for an accurate dosimetry standard. A dosimetry standard for the direct measurement of absolute dose to water in ¹⁹²Ir sources is not available. In this work, we proposed an absorbed dose conversion by determination of a beam quality factor (k_Q) with an ionization chamber. Ideally, the k_Q should be measured directly for each chamber at the same quality as the user beam. However, this is not achievable in most standards laboratories. When no experimental data are available, or it is difficult to measure kQ directly to realistic beams, in many cases the correction factors can be calculated theoretically with Monte Carlo method.