Beam-Port Design of a Radiobiological Dosimetry Experiment for {sup 10}B-Enhanced {sup 252}Cf Brachytherapy

It has been previously suggested that the incorporation of {sup 10}B-labeled drugs into tumor cells might significantly increase the dose to the peripheral tumor cells in {sup 252}Cf brachytherapy. The dose enhancement comes from the thermal neutron capture reactions of {sup 10}B(n, {alpha}){sup 7}Li. As a new cancer treatment modality, this so-called {sup 10}{und B}-{und E}nhanced {sup 252}{und C}f {und B}rachy{und t}herapy (BECBT) is currently being commercialized by Isotron. One of the challenges for implementing BECBT has been to determine the maximum tolerable dose (MTD) to the normal tissue surrounding a tumor. Because the relative biological effectiveness for the {sup 10}B(n, {alpha}){sup 7}Li reaction products is greater than that for fission neutrons, the MTD should decrease as {sup 10}B concentration increases for BECBT. To more precisely determine the MTD for BECBT, we intend to conduct both in vitro (cell culture) and in vivo (rat) experiments with a 50-mg {sup 252}Cf source. We will use cell survival fraction and normal brain necrosis as the biological end points for the cell-culture experiments and rat experiments, respectively. To carry out these experiments, the neutron field to which the samples are exposed must contain a significant portion of thermal neutrons. The rat experiments furthermore » require the use of a very small and well-collimated neutron beam to effectively irradiate the rat brain while minimizing the dose to its whole body. This paper discusses the design criteria for the experimental neutron beam port and the computational work leading to its optimal configuration.« less