Room: Exhibit Hall | Forum 7
Purpose: A dosimeter was created to measure DNA double-strand breaks (DSB) and potentially provides a more biologically relevant measurement of radiation than the commercially available dosimeters. The goal here is to investigate the energy and directional dependence of this dosimeter.
Methods: The dosimeter has four kilo-base pair DNA double strands (labelled on one endwith biotin and on the other one with fluorescein) attached to streptavidin magnetic beads andsuspended in phosphate-buffered saline. For both experiments, we calibrated linacs to deliver known doses using an ion chamber. The energy dependence experiment was performed three times using two different linacs (Elekta Versa HD and Varian Clinac 23EX). For each energy experiment, five DNA dosimeters were irradiated for each photon energy (6, 10, and 18 MV) and dose (25, 50, and 100 Gy). For the directional dependence experiment, we used a Varian Clinac 600 C to deliver 50 Gy using 6 MV photons to five DNA dosimeters for each of the four cardinal gantry angles in a MiniPhantom.
Results: For the energy dependence experiment, the probability of DSB did not show a clear energy dependence. For the directional dependence experiment, the probability of DSB for the DNA dosimeter at 50 Gy was 12.2, 12.2, 11.1, and 12.3% for gantry angles 0, 90, 180, and 270Â°, respectively.
Conclusion: The dosimeter did not exhibit an energy dependence, but did show directional dependence. Gravity causes the bead-connected DNA strands to settle at the bottom of the encapsulation volume. This creates an asymmetry for a particular orientation relative to the sample, which affected the response when irradiated with the same direction as gravitational force.