Dosimetric evaluation in brachytherapy and teletherapy for prostate cancer using Monte Carlo simulation and anatomically realistic virtual anthropomorphic phantom

The benefits that radiotherapy provides to the patient are unquestionable. However, there is growing concern about the increased risk of radiation-induced secondary cancer and the late damage to organs and tissues associated with the treatment. In this sense, the main objective of this study was to determine the radiation doses in the organs and tissues of the prostate cancer patient for two radiotherapy options, using the Monte Carlo code MCNPx2.7.0. The patient was represented by the ICRP 110 reference virtual anthropomorphic phantom and underwent brachytherapy with a192Ir source, Nucletron Microselectron V2 model, and alternatively, conventional 3D-CRT radiotherapy with an 18 MV X-ray beam from a Varian 2100c medical linear accelerator with 4-field planning (anteroposterior, 0 degrees; posteroanterior, 180 degrees; left lateral, 90 degrees; and right lateral, 270 degrees). A set of conversion factors (CF) for equivalent and effective dose were determined. The obtained results showed that in the more distant organs related to the prostate, such as the lung, brain, and salivary glands, the contribution of scattered radiation decreases, especially when brachytherapy is used. Comparing the two treatment modalities, the CF for effective dose per therapeutic dose was 42% lower when 192Ir was chosen as the main form of treatment. The CF values for photon equivalent doses calculated in 3D-CRT 4-fields are among one and two orders of magnitude higher than 192Ir therapy. These differences are even higher when the neutron equivalent dose in 3D-CRT is considered. In this way, the tools and methodology presented significantly improve the previously used to accurately estimate the equivalent doses in organs and tissues, which is the best quantity to assess the risk of inducing secondary cancer of healthy organs and tissues of patients undergoing treatment with radiotherapy.