C. Elegans and Microbeam Models in Bystander Effect Research

Radiation induced bystander effects have changed our understanding of the biological effects of ionizing radiations. The original assumption was that biological effects require direct damage to DNA. The bystander effect eliminated that requirement and has become one main stream in radiation research ever since first reported over 20 years ago.

Most bystander studies to date have been carried out by using conventional single cell in vitro systems , 2D cell array and 3D tissue samples, which are useful tools to characterize basic cellular and molecular responses. But to reveal the complexity of radiation responses and cellular communication, live animal models have many advantages. In recent years, models such as C. elegans and Zebrafish have been utilized in bystander effects research. In the Loma Linda/TAMU experiment, a L1 larva C. elegans model was devloped to study the radiation bystander effects by irradiating single intestine cell nuclei with a microbeam of protons.

Due to the stochastic nature of particle interactions with matter and changing stopping power when protons slow down, precise dosimetry in the target nucleus is a difficult problem. This research was undertaken to provide a detailed description of the energy deposition in the targeted and surrounding non-targeted cell nuclei, and to evaluate the probabilities of the non-targeted cell nucleus being irradiated. A low probability is required to exclude the possibility of radiation biological an effect in non-targeted cells is caused by scattered particles. Mathematical models of the microbeam system and the worm body were constructed in this research. Performing Monte Carlo simulations with computer code, Geant 4, this research provided dosimetry data in cell nuclei in different positions and Geant 4, this research provided dosimetry data in cell nuclei in different positions and probabilities of scattering to non-targeted cell nuclei in various microbeam collima- tor configurations. The data provided will be useful for future collimated microbeam design.