Feasibility of real-time monitoring for administered activity during Lu-177 infusion by imaging the administration site using a pinhole gamma camera: a Monte Carlo study.

Using personalized treatment with Lu-177-labeled radiopharmaceuticals, rather than using a fixed activity of 7.4 GBq, the administered radioactivity is adjusted in each patient. Achieving precise control of the administered activity would be possible during Lu-177 infusion if real-time monitoring techniques were possible. However, these techniques are not currently available. In this study, we used Monte Carlo simulations to simulate imaging of the administration site in an arm phantom with a pinhole gamma camera to explore the feasibility of achieving real-time monitoring and control of the administered activity during infusion. We used the Geant4 toolkit to simulate a compact gamma camera. We simulated the basic performance of the camera within an energy window of 208 keV ± 10% and the imaging of an arm phantom to evaluate the feasibility of visualizing and quantifying the inflow of Lu-177-labeled radiopharmaceutical activity. The spatial resolution with the 1.0-mm pinhole collimator for Lu-177 was 1.8 mm full width at half maximum (FWHM) at 50 mm, whereas it was 1.2 mm FWHM for the 0.5-mm pinhole collimator. Our gamma camera captured the activity of Lu-177 in a 3.0-mm diameter vessel within the arm phantom, achieving measurements in only 1 min. The maximum values among the mean estimation errors of the administered activity were 0.73% and -3.53% for the 1.0 and 0.5-mm pinhole collimators, respectively, both occurring within the initial 1 min. Monte Carlo simulations demonstrated the feasibility of real-time monitoring of administered activity during Lu-177 infusion by imaging the administration site with our pinhole gamma camera.