Characterization of nanoDot optically stimulated luminescence detectors and high‐sensitivity MCP ‐N thermoluminescent detectors in the 40–300 kV p energy range

Purpose To investigate empirically the energy dependence of the detector response of two in vivo luminescence detectors, LiF:Mg,Cu,P ( MCP ‐N) high‐sensitivity TLD s and Al 2 O 3 :C OSLD s, in the 40–300‐ kV p energy range in the context of in vivo surface dose measurement. As these detectors become more prevalent in clinical and preclinical in vivo measurements, knowledge of the variation in the empirical dependence of the measured response of these detectors across a wide spectrum of beam qualities is important. Method We characterized a large range of beam qualities of three different kilovoltage x‐ray units: an Xstrahl 300 Orthovoltage unit, a Precision x‐Ray X‐ RAD 320ix biological irradiator, and a Varian On‐Board Imaging x‐ray unit. The dose to water was measured in air according to the AAPM 's Task Group 61 protocol. The OSLD s and TLD s were irradiated under reference conditions on the surface of a water phantom to provide full backscatter conditions. To assess the change in sensitivity in the long term, we separated the in vivo dosimeters of each type into an experimental and a reference group. The experimental dosimeters were irradiated using the kilovoltage x‐ray units at each beam quality used in this investigation, while the reference group received a constant 10  cG y irradiation at 6  MV from a Varian clinical linear accelerator. The individual calibration of each detector was verified in cycles where both groups received a 10  cG y irradiation at 6 MV. Results The nanoDot OSLD s were highly reproducible, with ±1.5% variation in response following >40 measurement cycles. The TLD s lost ~20% of their signal sensitivity over the course of the study. The relative light output per unit dose to water of the MCP ‐N TLD s did not vary with beam quality for beam qualities with effective energies <50 keV (~150  kV p/6 mm Al). At higher energies, they showed a reduced (~75–85%) light output per unit dose relative to 6  MV x rays. The nanoDot OSLD s exhibited a very strong (120–408%) dependency of the light output relative to 6 MV x rays. Variations up to 15% between different x‐ray units with equivalent effective energies were also observed. Conclusions While convenient for clinical use, nanoDot OSLD s exhibit a strong variation in their measured light output per unit dose relative to 6  MV in the 40–300  kV x‐ray range. This variability differs unit‐to‐unit, limiting their effective use for in vivo dosimetry applications in the kilovoltage x‐ray energy range. MCP ‐N TLD s offer a much more stable response, but suffer from variations in sensitivity over time dependent on radiation history, which requires careful experimental handling.