Purpose: To construct and characterize a transportable phantom that maintains the desired hypoxic level for up to two weeks.
Methods: A round nearly tissue equivalent polycarbonate phantom (ρ = 1.19 g/cc), was used in this study. Each phantom had a diameter of 35 mm and a height of 3 mm, with a 5 mm diameter by 1 mm depth cylindrical cavity for the placement of the DNA sample. To measure the percent oxygen in the phantom cavity solution, a 2×2 mm² optical sensor (FireSting-O2, PyroScience, Inc.) was glued to the bottom of the cavities. Prior to preparing the samples, the phantoms were placed in a vinyl anaerobic chamber (Coy Laboratory Products, Inc.) and were left in the chamber for 24 hours to deplete them of residual oxygen. A 6 uL 10 mM Tris-HCl (pH 7.6) and 20 mM potassium phosphate solution was pipetted into each phantom cavity and allowed to reach ~0.15% oxygen in the anaerobic chamber. An aluminum induction seal was used to seal the solution inside the cavity, and the entire phantom was vacuumed sealed inside a 3 mil transparent bag (Doug Care Equipment, Inc.), that was itself sealed in a 5.25 mil mylar vacuum bag (Azure Market, Inc.). The oxygen levels in the phantoms were optically measured in triplicate as a function of time using the FireSting-O2 system and tested for their ability to retain the desired hypoxia level stored at ~21 °C, and -20 ℃.
Results: The partial pressures of oxygen were 0.19% and 0.17% when stored at -20° C and ~21°C, respectively, and plateaued to 0.61% and 0.76% after 6 hours, respectively.
Conclusion: We have constructed and characterized a phantom to maintain hypoxic DNA samples that can be transported to collaborators for irradiations irrespective of temperature.