AbstractID: 7975 Title: Biological Effects of Low Dose Ionizing Radiation in Human
Subjects Undergoing Radiotherapy: Accuracy of Monte Carlo Dose Calculations in
Peripheral Regions of Radiotherapy Beams
Assessing human health risk of low dose ionizing radiation (LDIR) is important for setting national standards of acceptable and safe exposure. Our research is focused on assessing effects of LDIR on gene expression in vivo in human subjects undergoing radiotherapy. Monte Carlo simulations are used to predict where to collect tissue biopsy samples, in order to obtain tissues at specific dose levels, ranging from 1-10 cGy. During irradiation, thermoluminescent dosimeters are used to verify the dose near the tissuesample location. Gene expression profiles are determined in superficial biopsy samples, obtained after irradiation. Here we report on the validation of Monte Carlo simulations used to predict dose in the low dose region outside of radiotherapy fields modified by jaws, blocks and jaws plus blocks. Peripheral dose measurements were taken using film, a Farmer chamber, and an IC-10 ion chamber for a
Varian Clinac 2100, 18 MeV beam. Monte Carlo calculations were used to estimate dose outside the field edge. Measurements and simulations agreed to within 10-15% for a 10x10 cm
2
field at 100 cm SSD, and suggested that the most stable (smallest dose-gradient) region for sample collection is on the exit surface of the patient, in an area covered by several centimeters of tissue-equivalent material.
Funded by DOE-OBER grant #DE-FG03-01ER6323