Influence of breast tissue composition on dosimetric characteristics of therapeutic low energy X-rays

Abstract

Intraoperative radiotherapy using low energy X-rays (low-kV IORT) is a candidate modality for early-stage breast cancer irradiation. The patient treatment planning in this type of radiotherapy is based on the acquired dosimetry data inside the water, while the difference of breast tissue composition respect to the water may change the dosimetric characteristics of employed low energy X-rays. The impact of different breast tissue compositions on dosimetric characteristics of low energy X-rays was assessed through Monte Carlo (MC) simulation in the current study.A validated MC model of INTRABEAM machine along with 2.5 and 5 cm diameter applicator, based on the GEANT4 MC Toolkit, was used to calculate the percentage depth dose (PDD) curves of the bare probe and mentioned applicator diameters inside different breast compositions of 30% and 70% glandular weight as well as the calcified breast. Finally, obtained PDD results were quantitatively compared with corresponding data inside the water.The results showed that the 70% glandular breast composition has the best accordance to the water so that the mean difference between the acquired PDDs for the bare probe, 2.5, and 5 cm diameter applicator respect to the water was obtained as 5.6%, 4.1%, and 4.9%, respectively. On the other hand, the calcified breast substantially changes the dosimetric features of low energy X-rays, so that the mean difference between the PDD data respect to the water can reach to about 78%.Based on the findings, it can be concluded that the breast tissue composition can affect the employed dosimetry data for patient treatment planning in the low-kV IORT method, especially in the case of calcified breast. Considering the variations of breast tissue composition can improve the accuracy of the delivered dose to the patient.