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Penumbra and Depth Dose Measurements with a DNA Dosimeter

B Bui*, K McConnell , M Obeidat , N Papanikolaou , E Shim , N Kirby , Ut Health San Antonio, San Antonio, TX


(Sunday, 7/29/2018) 1:00 PM - 1:55 PM

Room: Davidson Ballroom A

Purpose: A DNA dosimeter (DNAD) that can measure double-stranded breaks (DSBs) was developed to introduce more biologically relevant radiation measurements compared to conventional dosimeters. The goal is to provide a proof-of-principle test for using the DNAD to measure penumbra and percent depth dose (PDD) with a radiation beam.

Methods: The DNAD consists of four kilobase pair, double-stranded DNA strands which are labeled with fluorescein at one end and biotin at the other end. These are attached to streptavidin magnetic beads and suspended in phosphate-buffered saline as the working dosimeter. Irradiation of the DNAD creates DSBs, which cause the fluorescein to float free from the bead. The broken and unbroken strands are magnetically separated and used to determine the probability of DSB (PDSB). Experiments were conducted with convention dosimeters for comparison. For all radiation experiments, a Varian600C was used with 6 MV photons. The DNAD was irradiated to known doses, and a calibration table was created to determine dose from the measured PDSB. Solid water was used to obtain PDD measurements for a 10 x 10 cm field at depths of 0.5, 1.0, 1.5 and 10 cm with the DNAD, optically stimulated luminescent (OSL) dosimeters, an ion chamber, and a diode. To obtain penumbra measurements at 1.5 cm depth, the DNAD was plated in a 384-microplate and simultaneously irradiated with EBT3 film.

Results: The DNAD produced PDD measurements that were consistent with the conventional dosimeters. For the penumbra measurements, the differences between film and the DNAD were on average 3.0 % in the low-gradient dose regions. These differences were 18% in the high-gradient region, but this difference equates to a 1.5 mm distance to agreement.

Conclusion: Based on the positional alignment accuracy of the setup and the variability of the DNAD these measurements are consistent with those made by conventional dosimeters.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by the following grants: SABER IRACDA K12 (K12GM111726) CPRIT RTA (RP 170345)


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