Lifetime extension of optically stimulated luminescent dosimeters above 10 Gy

Background: Optically stimulated luminescent dosimeters (OSLDs) are used in clinical radiation dosimetry, but their sensitivity changes with the accumulated dose, limiting their reusability. Different studies have reported inconsistent results regarding the changes in sensitivity at different accumulated doses, and the reasons for this inconsistency remain unclear. In addition, the extent to which the OSLD linearity and element sensitivity correction factor (k(s,i)) change with the accumulated dose has not been well established. Purpose: We sought to characterize how the individual ks, i and dose non-linearity correction factor (k(L)) change with accumulated dose and how such changes affect the measurement of the dose to water (D-w). Determining the extent to which these parameters change with the accumulated dose can help clinics, institutions, and the Imaging and Radiation Oncology Core (IROC) at MD Anderson extend the OSLD accumulated dose limit above 10 Gy and thus increase the efficiency of use of these detectors, including for the remote audit output audits run by IROC for the National Clinical Trials Network. Methods: 95 nanoDot OSLDs were individually irradiated in 4-Gy cycles with 90 cGy used to determine sensitivity, irradiated between 0.25- to 3-Gy to determine linearity, and then irradiated to return all dosimeters to the same total dose history. Repeated measurements between 10 and 23 Gy were performed with the same batch (N = 129) and with a different batch (batch 2, N = 130). Dosimeters were read with a microSTARii system 5-8 h following each irradiation, and each OSLD was bleached for 24 h in the IROC bleaching box prior to every irradiation. A combination of single-factor ANOVA, Levene tests, and linear regressions was used to quantify changes in OSLD characteristics as a function of accumulated dose. The Dw was calculated using Equation (1)in the American Association of Physicists in Medicine Task Group 191 report. Results: The signal response of the OSLDs showed stability within 1% up to an accumulated dose of 23 Gy before decreasing with dose. The k(s,i) remained the same, while linearity changed with accumulated dose but did so in a linear and predictable manner. Conclusion: Our findings improve our understanding of accumulated dose and could help improve overall process efficiency by extending the reusability of OSLDs.