Background and purpose:
Measurement of dose delivery is essential to guarantee the safety of patients under-going medical radiation imaging or treatment procedures. This study aimed to evaluate the ability of organic semi conductors, coupled with a plastic scintillator, to measure photon dose in clinically relevant conditions, and establish its radiation hardness. Thereby, proving organic devices are capable of being a water-equivalent, mechanically flexible, real-time dosimeter.
Materials and methods:
The shelf-life of an organic photodiode was analyzed to 40 kGy by comparison of the charge-collection-efficiency of a 520 nm light emitting diode. A non-irradiated and pre-irradiated photodiode was coupled to a plastic scintillator and their response to 6 MV photons was investigated. The dose linearity,dose-per-pulse dependence and energy dependence was characterized. Finally, the percentage depth dose (PDD)between 0.5 and 20 cm was compared with ionization chamber measurements.Results:Sensitivity to 6 MV photons was (190 ± 0.28) pC/cGy and (170 ± 0.11) pC/cGy for the non-irra-diated and pre-irradiated photodiode biased at −2 V. The response was independent of the dose-per-pulsebetween 0.031 and 0.34 mGy/pulse. An energy dependence was found for low keV energies, explained by theenergy dependence of the scintillator which plateaued between 70 keV and 1.2 MeV. The PDD was within ± 3%of the ionization chamber.
Conclusion:
Coupling an organic photodiode with a plastic scintillator provided reliable measurement of a rangeof photon energies. Dose-per-pulse and energy independence advocate their use as a dosimeter, specifically image-guided treatment without beam-quality correction factors. Degradation effects of organic semi conducting materials deteriorate sensor response but can be stabilized
