Characterization of a plastic dosimeter based on organic semiconductor photodiodes and scintillator. (April 2020)

• Record Type: Journal Article
• Authors: Posar, Jessie A.; Davis, Jeremy; Brace, Owen; Sellin, Paul; Griffith, Matthew J.; Dhez, Olivier; Wilkinson, Dean; Lerch, Michael L.F.; Rosenfeld, Anatoly; Petasecca, Marco
• Is Part Of: Physics and imaging in radiation oncology. Volume 14(2020)
• Page Start: 48
• Page End: 52
• Publication Date: 2020-04
• Subjects: Organic semiconductor -- Plastic scintillator -- Radiotherapy -- Radiation detection -- Radiation damage; Radiotherapy -- Periodicals; Radiation dosimetry -- Periodicals; Cancer -- Imaging -- Periodicals; Oncology -- Periodicals; 615.842
• DOI: 10.1016/j.phro.2020.05.007
• Languages: English
• ISSNs: 2405-6316

Abstract

Highlights: Degradation of light sensitivity stabilized to 65% after exposure to 40 kGy. Uniform dose rate dependence for indirect detection of ionising radiation. Percentage depth dose curves within ±3% in comparison to an Ionisation Chamber. Response to keV energies is only dependent on the coupled plastic scintillator. Abstract: Background and purpose: Measurement of dose delivery is essential to guarantee the safety of patients undergoing medical radiation imaging or treatment procedures. This study aimed to evaluate the ability of organic semiconductors, 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-irradiated and pre-irradiated photodiode biased at −2 V. The response was independent of the dose-per-pulse between 0.031 and 0.34 mGy/pulse. An energy dependence was found for low keV energies, explained by the energy 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 range of 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 semiconducting materials deteriorate sensor response but can be stabilized.