Dose Volume Distribution in Digital Breast Tomosynthesis: A Phantom Study

Monte Carlo (MC) calculations for breast dosimetry in digital breast tomosynthesis (DBT) require experimental validations. We measured the 3-D dose distribution in breast phantoms, using XR-QA2 radiochromic films, compared to dose maps obtained with a previously validated MC code. Film sheets were positioned at the entrance surface, at the bottom surface as well as at four depths between adjacent slabs in the fiveslabs 50-mm-thick phantoms simulating a compressed breast. We employed a homogeneous PMMA phantom, for the method validation, and a heterogeneous (BR 50/50) phantom for a preliminary study in a complex breast phantom. Irradiations were made at 40 kV at ±25° and 0° in craniocaudal view. A continuous scan over 15° was carried out for the homogeneous phantom. In the direction of the beam axis the dose decreases down to 12% of the entrance value. In the transverse planes, the dose varies up to 17%; in the heterogeneous phantom, it decreases to 25% in the direction of the beam axis. In transverse planes the maximum dose variations are up to 18% at θ = 0°, whereas the dose varies up to 22% in angular views. The simulations agreed with the measured values within the measurement uncertainties.