Convection-Enhanced Delivery of an Iodine Tracer Into Rat Brain for Synchrotron Stereotactic Radiotherapy

Abstract

To evaluate direct intracerebral and intratumoral iodine delivery as means to improve iodine distribution for synchrotron stereotactic radiotherapy (SSR) and to evaluate the corresponding X-ray dose distribution. Healthy rats and F98 glioma-bearing rats received an iodinated contrast agent (iopamidol) intracerebrally either by bolus injection (5 microL over approximately 1 min) or by convection-enhanced delivery (infusion volumes of 5, 10, and 20 microL at a rate of 0.5 microL/min). We used synchrotron computed tomography (CT) to determine the iodine distribution after completion of infusion and a Monte Carlo code to compute the resulting radiation dose in SSR. Post-infusion CT imaging revealed high iodine concentrations in the perfused area with both injection methods. The iodine concentration remained elevated, with an exponential decay time constant of approximately 50 min, well suited for SSR treatment. Convection-enhanced delivery was shown to provide more uniform and controlled volumes of distribution than bolus injection and was chosen to evaluate the corresponding X-ray dose distribution. Sharp dose gradients around the target and excellent sparing of the contralateral brain were achievable with low iodine concentrations in the surrounding healthy brain tissues and blood vessels. Convection-enhanced delivery is an effective method to deliver high iodine concentrations and could improve the outcome of iodine-enhanced SSR.