A flexible, relatively flat and thin patch, optionally made of biodegradable material, substantially attenuates ionizing radiation from normal but sensitive anatomy during radio-therapy, particularly breast brachytherapy. The patch is of such a thickness as to substantially attenuate radiation by distance or consists of a material that has been formulated with radio-attenuating filler or is of radio-attenuating material. An alternative version consists of a thin patch that is coated with radio-attenuating material.