Poster - Thurs Eve-11: Quantitative imaging of 213Bi alpha-emitter with a beta-imager

Targeted alpha-particle emitter therapy is emerging as a promising approach for treating metastatic cancer. An understanding of the biodistribution of targeted alpha-emitters at the cell level is important in evaluating potential efficacy and toxicity. This is best accomplished by autoradiography of tissue samples, ex vivo. We have investigated the feasibility of using a high resolution, quantitative beta-imager (Biospace Mesures β-Imager) to detect the short-lived alpha-particle emitter, Bismuth-213 (213Bi). The advantages of this detector include: shorter acquisition time than film-based autoradiography, which is critical for an isotope with such a short half-life; high resolution; and data acquisition in list mode. While our interest in 213Bi lies in the α, the decay chain includes high energy β^- particles, enabling this study. Published studies using the β-Imager show predominantly qualitative results, with the quantitative depending on long exposure time or direct comparisons. At low count rate the detector auto-regulates by varying the HV, directly affecting the results. We imaged a phantom prepared from 213Bi in 5% gelatin. We plot only the results in a narrow HV range and fit an exponential decay function to obtain a half-life close to the expected value. We plot the ratio of the exponential fit to the measured count rate value against HV for all count rates and find a functional correlation between HV and count rate. A similar correction for gas flow ratio variations is also applied. As the remaining fluctuations conform to Gaussian statistics, this suggests that we have successfully calibrated 213Bi for future studies.