Assessment of absorbed dose in deformed breast tissue by Monte Carlo simulation

The main concern in radiotherapy of the breast is covering the target volume and increasing the dose absorbed by tumor cells. The aim is intended to provide a pertinent moldable perspective to the currently utilized methods of calculating Kerma value (KV) as a function of distance from nipple. The KV in the breast deformed for two shapes, such as cylindrical-conical (CC) and cubic-rectangular (CR), was simulated using Monte Carlo method with appropriate assumptions and a 2 MeV X-ray system. The source was positioned near the right breast. Simulation results demonstrated that decreasing height of CR shape reduced the absorption and scattering cross-sections as well as the KV. Relative accumulated dose for a CR-shaped breast was 96.89% lower than that for CC-shaped breast. The KV in the breast decreased with increasing distance from the nipple (depth) for both shapes, but for right and left breasts in CR form was independent from depth with no change between breasts as depth increased. The relative difference in KV between the breasts was significant for CR shape, in which the KV was high at low depths and decreased linearly with increasing depth. Tumors are often differentiable in the breast form; hence, the normal breast should be deformed into CR shape to improve the degree of tissue protection in adjuvant radiotherapy. It is expected that the dose absorbed by the gland will be more strongly increased for CC shape rather than for CR shape in radiation therapy.