Room: AAPM ePoster Library
Purpose: We hypothesized that the hypersensitivity response and therapeutic gain observed in Stereotactic Ablative Radiotherapy (SABR) is mediated, at least in part, through the increased production of Reactive Oxygen Species (ROS). In this study we present an improved standard for the absolute absorbed dose to water based on ROS produced in water samples specifically H202 molecule produced post irradiation to ionizing radiation. To investigate this hypothesis, we developed a novel absolute radiation dosimetry approach using fluorometric technique to measure SABR’s potential to generate H202.
Methods: Hydrogen peroxide was quantified using the Resorufin H2O2 Assay following the manufacturer’s guidelines. To measure H2O2 levels after exposure, 100 µl of Ultra Trace water was exposed in a 10 x 10 cm2 field, 100 cm SSD at dmax in solid water phantom. The dose linearity was measured exposing the samples to 10XFFF between 0.05 to 200Gy. Fluorescence was measured using a commercially available fluorometer. The absolute H2O2 was calculated using a standard curve of known H2O2 concentrations.
Results: A linear relationship between Resorufin fluorescence and dose exists within a range 0.05 - 200Gy in 10XFFF. Likewise, H2O2 was linearly related to dose with values between 0.01µM – 24.9µM, yielding a mean value of 0.66µM/Gy, (R2=0.99). Our measured absolute dose for various photon and electron energies was within +/-2% of the absolute dose. The results suggest this assay is sensitive and can detect exposures over a broad dose range.
Conclusion: We developed a sensitive fluorometric technique to measure absolute dose to water by quantifying the H2O2 production. These results show our technique is capable of linearly measuring dose for a broad range of photon and electron energies, dose and dose rates, suggesting this dosimetry method more accurate than conventional methods especially during SABR or Flash therapy. Further research is warranted.