Monte Carlo investigation on precise dosimetry of HDR breast brachytherapy with Accuboost

Introduction: Accuboost is a HDR brachytherapy system in early stages breast cancer treatment. This device provides a completely noninvasive procedure with parallel-opposed radiation from two immobilizing peripheral applicators that caused it a preferred option of modalities to choose. In most commercial treatment planning systems, tissues are considered as a simple water phantom. Inaccuracies arised from geometry and compositions can lead to deviations in interested dose distribution. This study intends to simulate HDR breast brachytherapy with Accuboost device in order to consider requirement corrections to have an accurate treatment dosimetry. Materials and Methods: MCNP5 simulation is employed to model phantoms in dosimetric measurements. We tried to take geometrical corrections into account in three phantoms. Dose distributions as dose volume histogram parameters and isodose plots obtained from these phantoms are compared to those of water. Corrections are included using real breast tissue with ICRU-44 breast composition, chest defined with an air cavity as lung and a curved surface to introduce a more realistic contour for breast skin. Accuboost is simulated with radiations from eighteen HDR 192-Ir sources on each applicator with appropriate tungsten shields. Results: Differences in most regions with less than 1% to water and maximum value about 5 % have been observed in phantom with ICRU-44 breast material compared to the water. Lung presence have increased deviations a few percent but it has not significantly differed. In phantom with all corrections maximum differences are almost the same as both earlier and deviations with about 5-7% are found near the chest and around the breast skin not in contact to applicators. Conclusion: Based on the results, although discrepancies between corrected phantom and water phantom are in areas near the skin the main differences are in clinical accepted uncertainties and other points of tissue have shown accommodatian. Therefore essential correction may be not needed.