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Radiobiological Impact of the Static Magnetic Field During MRI-Guided HDR Brachytherapy

E Brescia1*, G Pang2 , L Liu1 , G Mardirossian4 , M Tambasco1 , (1) San Diego State Univ, San Diego, CA, (2) Sunnybrook Health Sciences Centre, Toronto, ON, (3) Genesis Healthcare Partners, San Diego, CA,


(Sunday, 7/14/2019) 1:00 PM - 2:00 PM

Room: 301

Purpose: To quantify the effect of a strong static magnetic field (SMF) on DNA damage during MRI-guided HDR brachytherapy using plasmid DNA irradiation.

Methods: A commercial plasmid DNA, pBR322 (Thermo Fisher Scientific), was loaded into a millimeter scale well that was 3-D printed with biocompatible tissue equivalent material. The phantom contained an upper and lower pathway through which an HDR transfer tube was inserted for irradiation with an Ir-192 HDR brachytherapy source, using a Nucletron microSelectron™ afterloader (Elekta). A GE BrightSpeed 16 CT scanner was used to scan the phantom with 1 mm thick slices to construct a treatment plan using Oncentra™ by Elekta. The plan was designed to deliver 50 Gy (±2%) to four separate samples, with and without the presence of a 1.5 T SMF produced by a bipolar magnet (SES Instruments Pvt Ltd). Agarose gel electrophoresis was used to provide separation of the DNA into supercoiled, open circular, and linear bands corresponding to no strand breaks, single strand break (SSB), and double strand break (DSB) damage, respectively. ImageJ (National Institutes of Health) was used to analyze the intensity of the DNA bands, and relative yields of each band were computed with respect to the sum of all band intensities per lane to quantify the SSBs and DSBs.

Results: The average yield of irradiated DNA with SSBs in the presence and absence of the SMF was 0.845±0.097 and 0.830±0.051, respectively. The average yield of irradiated DNA with DSBs in the presence and absence of the SMF was 0.041±0.008 and 0.040±0.003, respectively.

Conclusion: HDR irradiation in the presence of the SMF indicated a small increase in SSB damage; however, no difference in DSB damage was observed. Our data will be expanded to include more samples to verify the statistical significance of these findings.


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