Room: Exhibit Hall
Purpose: To explore observed dose discrepancies between photon and electron irradiated OSLDs and determine the optimum procedure for creating and using linear and nonlinear microSTARii calibration files based on specific dose range and energy source of clinical relevance.
Methods: Commercial dosimeters (Landauer screened nanoDots) were irradiated according to manufacturerâ€™s recommended dose range (5 â€“ 1300 cGy) at 6 MV to create clinic specific calibration sets of OSLDs. A quality control (QC) set was created with photon (6MV) and electron (6MeV/12 MeV) beams for purposes of testing calibrations at typical therapeutic dose range. Scatter conditions, depth, and doses for typical treatments were approximated. Calibration files (linear and nonlinear) were created in microSTARii software using 6 MV irradiated nanoDots and tested with QC dosimeters.
Results: Electron irradiated OSLDs consistently read 7% lower than actual exposure in clinically relevant dose range of 200 â€“ 350 cGy. Photon irradiated OSLDs, however, are well within the expected +/- 5%. On average, linear calibration read photon exposed OSLDs between 4% and 9% above exposed dose from 250 â€“ 350 cGy. Nonlinear calibration read the same OSLDs within +/-2%. The same procedure was used to read electron irradiated OSLDs. A correction factor of 1.07 was multiplied by the readings to adjust for observed -7% error in electrons. After adjustment, linear calibration read between 7 and 12% higher than exposure. Nonlinear read the same OSLDs within +/- 1%.
Conclusion: While it is reported that OSL behaves linearly up to 300 cGy, we observed that nonlinear calibration is potentially more accurate as low as 200 cGy. Therefore, tests should be performed to determine usability of each type of calibration according to dose. When using OSLD for electrons, clinics should ascertain consistent error percentage and consider using a correction factor, the factor being +7% in our clinic.