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Purpose: To evaluate the performance and safety of a radiation therapy positioning system (RealEye) based on tracking a radioactive marker (Tracer) implanted in patients with localized prostate cancer., Methods and Materials: We performed a single-arm multi-institutional trial in 20 patients. The iridium-192 ((192)Ir)-containing Tracer was implanted in the patient together with 4 standard gold seed fiducials. Patient prostate-related symptoms were evaluated with the International Prostate Symptom Score (IPSS) questionnaire. Computed tomography (CT) was performed for treatment planning, during treatment, and after treatment to evaluate the migration stability of the Tracer. At 5 treatment sessions, cone beam CT was performed to test the positioning accuracy of the RealEye., Results: The Tracer was successfully implanted in all patients. No device or procedure-related adverse events occurred. Changes in IPSS scores were limited. The difference between the mean change in Tracer-fiducial distance and the mean change in fiducial-fiducial distance was -0.39 mm (95% confidence interval [CI] upper boundary, -0.22 mm). The adjusted mean difference between Tracer position according to RealEye and the Tracer position on the CBCT for all patients was 1.34 mm (95% CI upper boundary, 1.41 mm)., Conclusions: Implantation of the Tracer is feasible and safe. Migration stability of the Tracer is good. Prostate patients can be positioned and monitored accurately by using RealEye., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Purpose: To investigate in a three-dimensional framework the effectiveness and reproducibility of reducing the respiratory motion of liver tumors using abdominal compression in a stereotactic body frame., Methods and Materials: A total of 12 patients with liver tumors, who were treated with stereotactic body radiotherapy, were included in this study. These patients had three gold fiducial markers implanted in the healthy liver tissue surrounding the tumor. Fluoroscopic videos were acquired on the planning day and before each treatment fraction to visualize the motion of the fiducial markers during free breathing and varying levels of abdominal compression. Software was developed to track the fiducial markers and measure their excursions., Results: Abdominal compression reduced the patient group median excursion by 62% in the craniocaudal and 38% in the anteroposterior direction with respect to the median free-breathing excursions. In the left-right direction, the median excursion increased 15% (maximal increase 1.6 mm). The median residual excursion was 4.1 mm in the craniocaudal, 2.4 mm in the anteroposterior, and 1.8 mm in the left-right direction. The mean excursions were reduced by compression to <5 mm in all patients and all directions, with two exceptions (craniocaudal excursion reduction of 20.5 mm to 7.4 mm and of 21.1 mm to 5.9 mm). The residual excursions reproduced well during the treatment course, and the craniocaudal excursions measured on the treatment days were never significantly (alpha = 0.05) greater than on the planning days. Fine tuning the compression did not considerably change the excursion on the treatment days., Conclusions: Abdominal compression effectively reduced liver tumor motion, yielding small and reproducible excursions in three dimensions. The compression level established at planning could have been safely used on the treatment days.