Study of the scattered x-ray distributions around a mammography unit

Purpose: To measure the distribution of scattered radiation in a mammography unit for shielding design purposes. Methods and Materials: Measurements were carried out with an anthropomorphic phantom used to simulate a body from one adult patient. The dose rate for scattered radiation was recorded by placing a solid state sensor (Unfors Xi Survey Detector) every 10 degrees at 1 m distance from the FOV centre, in the axial and coronal planes of the breast. The scattered radiation distribution was treated as isodose curves, specifying the amount of radiation that will be delivered to a specific point in the room around the equipment (GE Senographe DMR). More than 50 exposures were made with a tube voltage of 30 kVp, anode-filter combination Mo/Mo and large focus. Results: In the axial plane, results show that the scattered radiation is absorbed up to 73% on the back of the anthropomorphic phantom, at the potter bucky plane height. In the coronal plane, the scattered radiation significantly increases with the angle due to backscattering effect. Assuming the direction of the incidence beam is 0 degree, results show that the scattered radiation is 86% higher at 160 degrees than at 90 degrees. Conclusion: The type of mammographic view and the patient´s body strongly influence the distribution of scattered x-ray radiation. These results can be used to improve the shielding design of a mammographic unit with less resources and less spending on shielding barriers