Investigation of the prostate edema dose effects in brachytherapy treatment using Monte Carlo method

In this study, edema effect, which is not taken into account in clinical applications, in permanent source brachytherapy method is which radiation is used in cancer treatment is examined. With this effect, which is effective in a certain period of the treatment period, a volumetric change occurs in the prostate gland. In line with clinical data, the time dependent behavior of this change is defined by the isotropic edema model and mathematical functions. Although the dynamic behavior model is known, the initial conditions that will determine which parameter pair will be in before the effect occurs have not yet been discovered. In clinical practice, the treatment dose difference created by the effect can be obtained by finding the parameter pairs with the anatomical images taken at certain times. Dynamic dose distribution calculation method was created in this study to examine the effect of prostate swelling on the treatment dose. Samples taken on the time axis are carried out with BrachyDose software. With the conventional static dose distribution calculation, for an edema with a half-life of 14 days and a volume change of 50%, a dose reduction of 6.3% and 22.6%, respectively, occurs in sources containing 125I and 103Pd at D90. This difference increases as the numerical values of the payment parameters increase. It was investigated when the difference between the static dose distribution in the control shot and the dynamic dose distribution in which the total treatment was calculated was the least. In line with the calculations made in the study, it is recommended that the control shooting be done between 15-20 days and 35-40 days, respectively, for sources containing 125I and 103Pd. Methods that can be used in future treatment planning systems were developed in these calculations, which included the internal structures of radioactive sources. Dynamic behavior and locations of sources in each sample were calculated using the isotropic edema model. In the volumetric change caused by edema, two different models of dynamic change in which the density and mass remain constant were examined, and it was revealed that mass and density are two parameters that should be taken into account in calculations based on payment. Another innovation is the time projection method, developed by sampling according to volumetric variation. Thus, the simulation results for a single edema behavior were made available to other edema parameter pairs.