153 Dose monitoring in synchrotron radiation breast computed tomography with radiochromic films

Purpose To measure the dose distribution in a phantom during a synchrotron radiation (SR) computed tomography (CT) scan using radiochromic films, for procedure assessment and for offline dose monitoring in SR breast CT. Methods We used XR-QA2 radiochromic films (calibrated in terms of free air kerma) and a 14-cm PMMA cylindrical phantom. Measurements were performed at the SYRMEP beamline of ELETTRA facility, within the SYRMA-3D project for phase-contrast breast CT [1] . The phantom was positioned at isocenter, pending from the patient bed. Measurements were performed at 38 keV, beam size of 3 mm × 150 mm (H × W), at an air kerma corresponding to a mean glandular dose of 5 mGy in a 14-cm diameter 50% glandular breast. The phantom was irradiated over 360° first with a film at the mid-plane, and then with film strips wrapped on its surface. Additional tests were made over 180° with an axial scan pitch of 1, 0.8 or 0.5. Results Results show a dose map at mid-plane the phantom, indicating the cup-shaped horizontal profile due to primary and scatter dose. Analogous maps were recorded with the films at the periphery of the phantom, representing the surface dose maps. Conclusions We performed measurements of the dose distribution in a phantom during a SR CT scan with different irradiation geometries. This technique produces evidence for selecting the suitable scan procedure. Moreover, as an offline monitor system, a piece of calibrated radiochromic film wrapped on a suitable holder around the breast could record the history of the organ irradiation.