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Description
Purpose: To quantify the effect of a strong static magnetic field (SMF) on DNA damage and electron transport during Iridium-192 irradiation. Methods: A commercial plasmid DNA was loaded into a small well phantom that was 3-D printed with biocompatible tissue equivalent material. The phantom contained two pathways through which a transfer tube was inserted for irradiation with an Ir-192 HDR brachytherapy source. A CT scanner was used to scan the phantom with 1 mm thick slices to construct a treatment plan designed to deliver 50 Gy (±4%) to ten samples each in the presence and absence of a 1.5 Tesla (T) SMF. Agarose gel electrophoresis was used to separate the DNA into bands corresponding to single strand breaks (SSBs) and double strand breaks (DSBs). The intensities of the DNA bands were analyzed, and the relative yields of SSBs and DSBs were computed. Triplicate radiochromic film measurements were performed in two other phantoms and irradiated to 5 Gy in the presence and absence of a 1.5 T magnetic field. The films were scanned, and the 2-D dose distribution in two planes (sagittal and coronal), and in a small region of interest at the center of the films were analyzed. Results: The average yield of irradiated DNA with SSBs in the presence and absence of the SMF was 0.833±0.027 and 0.804±0.014, respectively. The average yield of irradiated DNA with DSBs in the presence and absence of the SMF was 0.062±0.013 and 0.077±0.008, respectively. Statistical analysis comparing the average yields of DNA suggest a statistically significant difference between the yields (p<0.005). The dose distributions from the analyzed films in the presence of the magnetic field agreed within the uncertainty of the measurements. Conclusions: HDR irradiation in the presence of the SMF indicated a small difference in SSB and DSB damage. However, the yields were characterized by high uncertainties, suggesting that more studies are needed to definitively conclude that the differences observed are real. The expected lack of significant changes in electron transport, due to the relatively low Ir-192 energies, was measured and confirmed by the films.
