Measuring the diffusion length of radon-220 in cancerous tissues

  Guy Heger  ,  Maayan Vatarescu  ,  Ishay Luz  ,  Tomer Cooks  ,  Lior Arazi  
Ben-Gurion University

Diffusing alpha-emitters Radiation Therapy (DaRT) is a new method used for treating solid tumors with alpha radiation, wherein the DaRT source, carrying a low activity of radium-224, is inserted into a tumor and begins releasing into the tumor its alpha-emitting daughter atoms. These then spread in the tumor by diffusion, delivering a lethal dose to the tumor through their alpha decay. Characterizing the diffusion process inside the cancerous tissue is essential in order to produce accurate and viable predictions, and a necessary step on the way of turning DaRT into an acceptable and useful cancer treatment. Two of the key parameters needed for DaRT treatment planning are the diffusion lengths of lead-212 and radon-220, as they determine the lethal dose radius around a DaRT source. The values of lead-212 diffusion length for various cell lines and tumor masses will be reported in a different contribution. Here, we present the first-ever results for Rn diffusion length, measured for several cancerous cell-lines and tumor masses. These measurements were done using the iQID system - a new-generation autoradiography system, which utilizes a high-speed CMOS censor and the computing power of modern graphics cards in order to analyze acquired images in real-time, thereby avoiding optical blurring and providing images with significantly higher resolution compared with older-generation machines. In addition, the iQID provides a time-stamp for each alpha particle measured, allowing for time-based analyses of the measured tissues. For example – it is possible to estimate the level of radium-224 leakage from the DaRT source into the tumor by fitting the decay function of the residual tissue radioactivity – analysis that was not possible in older-generation autoradiography systems.