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Directed forgetting (DF) or intentional forgetting can impair the recall of items cued to be forgotten (so-called cost) but can also improve the recall of items cued to be remembered (so-called benefit), following the cost-benefit principle. However, whether the forget cue is the cause of intentional forgetting is doubtful. Several studies suggest that intentional forgetting is extremely hard by introducing a noncue condition, but it is not enough to explain how the cost-benefit principle works without forgetting. Here, two series of experiments are designed to test the voluntary control ability of attentional resource allocation from memory benefits to costs. In the Experiment 1 series, we changed the position and content of cues, replicating the DF effect and the analogous effect without a forget cue. The results showed that precueing can mildly upregulate memory attentional resources to improve performance while incurring memory costs for other items. Since forced remembering can also induce memory costs and benefits, the cost-benefit principle may not be attributed to DF. In the Experiment 2 series, we further demonstrated that memory costs and benefits exist when implicit cues are employed. Overall, when the results of all memory costs in the above experiments are compared with a noncue condition as the baseline in Experiment 2c, there exist no significant differences. The current results indicate that we can voluntarily upregulate our memory performance for certain items but cannot voluntarily downregulate memory encoding, generalizing the selective attentional resource control account to the cost-benefit principle beyond the directed-forgetting effect.

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.

Radionuclides are commonly used as internal radiation sources for diagnostic imaging or external radiation sources for treatment purposes. As most radionuclides have a higher energy level than imaging X-ray tubes, radionuclides are rarely used as a transmission-based external imaging source. In this study, we designed and simulated an imaging model by using 192Ir as an external imaging source to investigate the feasibility of this new imaging method. The goal of this study is to build a portable and flexible dual-function platform that can conduct both imaging and radiation treatment by using a single radiation source. This study uses the Monte Carlo (MC) method to simulate breast fan beam computed tomography (FBCT) and cone beam computed tomography (CBCT) by using 192Ir as an external source. The whole breast phantom is built from a real patient’s chest CT data. We designed an imaging model and embedded it into the Electron Gamma Shower (EGS) simulation environment. CBCT and FBCT data were obtained through EGS simulations. Different image processing techniques were applied to the data. A total of 47 images were reconstructed. Among these images, 16 images have high-density areas (lesions). Comparing with the original CT slices, the lesion volume from both FBCT and CBCT data sets can be identified. CBCT-reconstructed images contain more blurring and noise than FBCT images because of the scattering effects. The 192Ir radionuclide can be used as a possible external radiation source for breast imaging. Considering 192Ir’s therapeutic application and outcomes from its imaging simulation by this study, a new imaging/therapy platform can be potentially created.