Validating plastic scintillation detectors for photon dosimetry in the radiologic energy range
- 10 August 2012
- journal article
- research article
- Published by Wiley in Medical Physics
- Vol. 39 (9), 5308-5316
- https://doi.org/10.1118/1.4738964
Abstract
Purpose: Photondosimetry in the kilovolt (kV) energy range represents a major challenge for diagnostic and interventional radiology and superficial therapy. Plastic scintillation detectors(PSDs) are potentially good candidates for this task. This study proposes a simple way to obtain accurate correction factors to compensate for the response of PSDs to photon energies between 80 and 150 kVp. The performance of PSDs is also investigated to determine their potential usefulness in the diagnostic energy range. Methods: A 1-mm-diameter, 10-mm-long PSD was irradiated by a Therapax SXT 150 unit using five different beam qualities made of tube potentials ranging from 80 to 150 kVp and filtration thickness ranging from 0.8 to 0.2 mmAl + 1.0 mmCu. The light emitted by the detector was collected using an 8-m-long optical fiber and a polychromatic photodiode, which converted the scintillation photons to an electrical current. The PSD response was compared with the reference free air dose rate measured with a calibrated Farmer NE2571 ionization chamber.PSD measurements were corrected using spectra-weighted corrections, accounting for mass energy-absorption coefficient differences between the sensitive volumes of the ionization chamber and the PSD, as suggested by large cavity theory (LCT). Beam spectra were obtained from x-ray simulation software and validated experimentally using a CdTe spectrometer. Correction factors were also obtained using Monte Carlo(MC) simulations. Percent depth dose (PDD) measurements were compensated for beam hardening using the LCT correction method. These PDD measurements were compared with uncorrected PSD data, PDD measurements obtained using Gafchromic films, Monte Carlo simulations, and previous data. Results: For each beam quality used, the authors observed an increase of the energy response with effective energy when no correction was applied to the PSD response. Using the LCT correction, the PSD response was almost energy independent, with a residual 2.1% coefficient of variation (COV) over the 80–150-kVp energy range. Monte Carlo corrections reduced the COV to 1.4% over this energy range. All PDD measurements were in good agreement with one another except for the uncorrected PSD data, in which an over-response was observed with depth (13% at 10 cm with a 100 kVp beam), showing that beam hardening had a non-negligible effect on the PSD response. A correction based on LCT compensated very well for this effect, reducing the over-response to 3%. Conclusion: In the diagnostic energy range, PSDs show high-energy dependence, which can be corrected using spectra-weighted mass energy-absorption coefficients, showing no considerable sign of quenching between these energies. Correction factors obtained by Monte Carlo simulations confirm that the approximations made by LCT corrections are valid. Thus, PSDs could be useful for real-time dosimetry in radiology applications.Keywords
Funding Information
- Natural Sciences and Engineering Research Council of Canada (262105)
- National Institutes of Health (CA016672)
This publication has 28 references indexed in Scilit:
- Fiber-coupled radioluminescence dosimetry with saturated Al 2 O 3 :C crystals: Characterization in 6 and 18 MV photon beamsRadiation Measurements, 2011
- A prototype scintillation dosimeter customized for small and dynamic megavoltage radiation fieldsPhysics in Medicine & Biology, 2010
- Characterization of a water‐equivalent fiber‐optic coupled dosimeter for use in diagnostic radiologyMedical Physics, 2009
- Measurement accuracy and Cerenkov removal for high performance, high spatial resolution scintillation dosimetryMedical Physics, 2005
- Spectral discrimination of Čerenkov radiation in scintillating dosimetersMedical Physics, 2005
- Scintillating fiber dosimeter for radiation therapy acceleratorIEEE Transactions on Nuclear Science, 2002
- A miniature "scintillator-fiberoptic-PMT" detector system for the dosimetry of small fields in stereotactic radiosurgeryIEEE Transactions on Nuclear Science, 2001
- Water-equivalent plastic scintillation detectors for high-energy beam dosimetry: I. Physical characteristics and theoretical considerationsPhysics in Medicine & Biology, 1992
- Water-equivalent plastic scintillation detectors for high-energy beam dosimetry: II. Properties and measurementsPhysics in Medicine & Biology, 1992
- Introduction to Radiological Physics and Radiation DosimetryPublished by Wiley ,1986