A new imaging/therapy platform by using external radionuclide (192Ir) part 2: data acquisition and analysis for breast imaging

Abstract

Radionuclides with various types of radiation are frequently used for brachytherapy. For example, iridium-192 (192Ir) has been widely used as high-dose rate (HDR) brachytherapy source, housed in a remote after-loading unit. With its average energy of 380 keV, the photons emitted from 192Ir are generally considered unsuitable for usage as transmission-based external imaging sources. Using Monte Carlo simulations, we have previously showed that 192Ir indeed can be used as an external source to image the breast in the forms of fan-beam computed tomography (FBCT) and cone-beam computer tomography (CBCT). In this study, we designed and built an imaging assembly in a physical laboratory setting to prove and validate this new imaging method. The goal of this study is to demonstrate the feasibility of building a robust dual-function platform that can carry out both image-guided target localization and radiation treatment through a single HDR source. In this study, a microSelectron HDR 192Ir source was used as the external imaging source and the amorphous-silicon imaging panel on a Simulix Evolution™ radiotherapy simulator as the imaging detector. A breast phantom with cystic lesions was situated on a custom-made rotary stage whose center was aligned along the pathway between the radiation source and the center of the imaging panel. Plain radiographic images were obtained at every 3° intervals from 0° to 360° around the center of the rotary stage. The CBCT images were subsequently reconstructed. A 3D data set of 192Ir CBCT images was reconstructed. Compared with the images obtained from a conventional thin-slice CT scanner, the cystic lesions inside the breast phantom can be clearly identified. Despite multiple sources of scattering and resultant noise, the quality of images demonstrated sufficient clarity for the purpose of target localization. The 192Ir radionuclide can be used as a possible external radiation source for breast imaging. This study provides the evidence that building a new imaging/therapy dual-function platform using a single 192Ir source is feasible.