At the SYRMEP (Synchrotron Radiation for MEdical Physics) beamline of Elettra a facility for clinical X-ray phase contrast mammography has been set-up. Over 80 patients have undergone synchrotron radiation (SR) mammography with the aim of resolving questionable diagnosis after the hospital exam. This is so far the only clinical study of this kind. The goal of SYRMA-3D project is to extend the clinical program to breast tomography. The project is based on the collaboration of INFN, Elettra, Azienda Sanitaria Universitaria Integrata di Trieste and University of Trieste.
A general upgrade of the clinical station and control systems is foreseen for the implementation of the new protocol. In order to fulfill all the safety requirements, dedicated systems are designed and implemented, following redundancy criteria and “fail safe” philosophy.
The CT acquisition is done acquiring projections over 180° and exploiting the monochromatic, parallel, coherent, laminar beam available at SYRMEP with typical size of 210x4 mm2 at patient position. The breast will be acquired in several vertical steps. The distance between the source and the patient is about 30 m, and the detector is located about 2 m from the breast. In this geometric configuration, a free space propagation phase-contrast effect is yielded on the acquired projections.
The patient lays prone on a movable support with the breast to be imaged hanging outside of an ergonomically designed aperture. The support has three degrees of freedom: it translates horizontally for breast alignment and moves vertically and rotates during the scan. It will be equipped with an immobilizer to define the breast geometry and position that should be kept fixed during the examination. Its shape acts as a geometrical marker for slice alignment and it also holds references for calibration in linear attenuation coefficients. To have a good balance between the spatial resolution, needed to exploit the phase-contrast effects, and the dose delivered to the patient, a photon counting detector was selected. It is a large area CdTe imaging detector (Pixirad-8), with pixel size of 60 µm and the active area is about 250x25 mm2 suitable for the beam geometry at SYRMEP.
The dosimeter system consists of 2 high-precision ionization chambers placed upstream from the patient support platform. Patient safety will be granted by the “Dose Control” system that ensures the entrance skin dose within some fixed limits and, together with the Safety System, monitors the correct working conditions of all the components before and during a scan. Any kind of alarm status like malfunction of dose monitors, mismatch of monochromator energy, overcome of dose threshold, will result in the exam abort with closing of safety shutters.
At present the breast CT facility is used for the study of test objects and tissue specimens, while the control system for the patient study is under commissioning.