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Direct Measurement of a Change in Biological Damage Between Low and High Energy X-Ray Beams Using a Novel DNA Dosimeter

K McConnell

K McConnell1*, X Li1 , M Obeidat1 , N Kirby2 , E Shim1 , (1) UT Health San Antonio, San Antonio, TX, (2) University of Texas HSC SA, San Antonio, TX


MO-AB-FS4-3 (Monday, July 31, 2017) 7:30 AM - 9:30 AM Room: Four Seasons 4

Purpose: Published data indicates that low energy x-rays, as compared with higher energy x-rays, have higher relative biological effectiveness (RBE). Conventional detectors for radiotherapy dosimetry are incapable of directly measuring this increase in biological damage. By using a novel DNA dosimeter that uses DNA double-strand breaks (DSB) as the mechanism for dose detection, an RBE was directly measured between a low and high energy x-ray beam. Additionally, a mouse neural stem cell line (mNS-5) was used as a biological RBE reference.

Methods: A DNA dosimeter consisting of magnetic streptavidin beads attached to 4 kilobase pair DNA strands labeled with biotin and fluorescein amidite on opposing ends was created. mNS-5 cells were passaged and cultured in RHB-A media. Both were irradiated over a range of doses in low (160 kVp) and high (6 MV) energy x-ray beams. A RaySafe XI R/F detector was used to verify the dose in the low energy (Faxitron Model 43855F), and OSLD measurements were used to verify dose in the high energy (Varian 600 C/D). Probability of DSB (PDSB) was measured by DNA dosimeters and survival fraction was computed for the mNS-5 cells. Doses corresponding to the same level of damage (PDSB or SF) between the low and high energy beams were identified and used to calculate RBE.

Results: For the DNA dosimeter, 6 Gy in the low energy beam produced the same PDSB as 7.2 Gy in the high energy beam, yielding an RBE of 1.20±0.16. For the mNS-5 cells, 6 Gy in the low energy beam produced the same SF as 7.62 Gy in the high energy beam, yielding an RBE of 1.27±0.12.

Conclusion: Given the RBE agreement, the DNA dosimeter potentially has the capability to directly measure the biological effect of radiation. More refinement and measurements will be performed to confirm these results.

Funding Support, Disclosures, and Conflict of Interest: This research was funded in part by CPRIT RP140105 and RP170345.

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