SU-E-T-94: Proton Characteristics of the NanoDot Dosimeter

Abstract

Purpose: Optically stimulated luminescent detectors (OSLDs) have a number of advantages in radiationdosimetry making them excellent dosimeters for quality assurance and patient dose verification. Although the dosimeters have been investigated in several modalities, relatively little work has been done in examining the dosimeters for use in clinical proton beams. This study examined a number of characteristics needed before the dosimeters should be used clinically in proton beams. Methods: OSLdosimeters from Landauer, Inc. specifically the nanoDot, were investigated. These dosimeters were placed in a special phantom with recesses to fit the dosimeters with minimal air gap. Beams with nominal energies of 160, 200, and 250 MeV were used in the passively‐scattered proton beam at the MD Anderson Cancer Center Proton Therapy Center. SOBP measurements were always done at the center of the SOPB. Results: The dosimeters showed supralinearity with doses above 200 cGy, with 5% supralinearity at 1000 cGy. Field size dependence was measured from sizes 2×2cm2 to 18×18cm2, with no noticeable dependence. Residual signal was measured as a function of cumulative protondose, showing only a small increase up to 800 cGy. Readout signal depletion of the dosimeters after consecutive readings was done for various protondose levels and compared to photons. While the depletion differed slightly for protons, no dose dependence was found. Energy dependence of the dosimeters was examined in the center of various SOBP widths and energies, showing general agreement with ion chamber data with one exception. This exception is being investigated. Conclusion: The nanoDotOSLdosimetercharacteristics were studied in clinical proton beams and found to have dose supralinearity above 200 cGy, and no dependence on field size, or significantly different readout signal depletion with dose. Residual readout signal with cumulative dose did not increase largely with dose.