Comparison of MCNPX and MIRDcell in assessing self-dose and cross-dose delivered to cell nuclei and the development of a realistic geometric model

摘要

Purpose:This study aims to provide a comparison between MCNPX and MIRDcell calculations for self-dose and cross-dose for three therapeutic isotopes used in internal radiotherapy (Lu-177, I-131 and Y-90) and to develop a multi-cellular geometric model to simulate anin vitroscenario. Materials and Methods:The self- and cross-dose to individual cell nuclei were assessed by Monte Carlo N-Particle eXtended (MCNPX). A close-packed cubic cell arrangement was assumed with the same amount of radioactivity per cell. Various cell sizes and subcellular distributions of radioactivity (nucleus, cytoplasm and cell membrane) were simulated. S values were obtained by MIRDcell for comparison. A Python 3.4 program was used to generate random cell coordinates in order to build a complex model that takes certain real conditions (cell size and cluster size) into account. Results:The relative differences of MCNPX versus MIRD S values (S-self) ranged from 2.88 to 10.10% for Lu-177; from 0 to 8.41% for I-131 and from 2.80 to 9.58% for Y-90. The relative differences of MCNPX versus MIRDcell cross-dose S values were 3.6%-15.7% for a sphere. The ratio ofS(cross)max toS(self)decreased for Lu-177 and I-131 with increasing cell size. The source localization within the cells had no significant impact on the cross-dosing. For single cells, the subcellular location of the source had an effect onS(self). Conclusions:MCNPX and MIRD cell-calculated S values showed good agreement. The model provided could be used to predict the biological effect caused by emitted radiation from therapeutic radionuclides at the cellular level.