Evaluation of organs at risk dose in the left breast IOERT procedures whit and without shielding disc using monte carlo simulation

Introduction: One of the treatment choices in breast cancer is Intra operative electron beam radiation therapy (IOERT). Due to high dose delivery in this procedure, shielding disk is used to protect organs at risk (OARs). In this study, we evaluate the OARs dose in the breast IOERT using Monte Carlo simulation with and without shielding disk in RANDO phantom. Material and Methods: Simulation of dedicated IOERT linear accelerator (LIAC) head with 5cm diameter applicator was performed using BEAMnrc Monte Carlo simulation cod. Three phase-space files for each nominal electron beam energies (6,8,10,12 MeV) produced in the end of the applicator, after 2 cm tissue in the end of applicator. The last phase-space was created after disk. These phase- space were used in DOSXYZnrc for irradiation of RANDO phantom. Both lungs and heart were considered as OARs in the IOERT of the left breast irradiation. For each energy, the 3ddose files, as an output of DOSXYZnrc and contoured organs in the RANDO phantom imported to CERR software. 12Gy was considered as a normalized value in the target. Then dose-volume- histogram (DVH) data were extracted for analysis. Results: The mean and maximum dose for each OAR in all energies with and without disk and with consideration of 2 cm tissue as a target were extracted from DVH data. For all nominal energies, the right lung dose was zero. The maximum and mean dose range in the left lung without disk were 11.5-13.9 and 0.15-0.5 Gy, respectively. These values for heart were 0-2.9 and 0-0.16Gy. The mean dose of heart and the left lung were un-remarkable with applying 2cm tissue and disk. Conclusion: With the increase of the electron beam energy in the IOERT, an increase of OARs dose was seen with and without shielding disk application. On the other hand, application of shielding disk in breast IOERT reduces OARs dose significantly