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Angular dependence of the nanoDot OSL dosimeter
James R Kerns1, Stephen F Kry, Narayan Sahoo
1Department of Radiation Physics, UT MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030, USA. jrkerns@mdanderson.org
Medical Physics
|August 24, 2011
Summary
The nanoDot optically stimulated luminescent dosimeter (OSLD) shows a 3-4% lower response in photon beams when irradiated parallel versus normal to its plane. This angular dependence, not seen in proton beams, may impact dose accuracy in varied radiation directions.
Area of Science:
- Medical Physics
- Radiation Dosimetry
- Radiotherapy Physics
Background:
- Optically stimulated luminescent detectors (OSLDs) are increasingly used for radiation dosimetry in clinical settings.
- Accurate dose assessment requires thorough characterization of OSLDs, including their response to various physical factors.
- The Landauer InLight/OSL system, particularly the nanoDot dosimeter, is widely adopted in medical applications.
Purpose of the Study:
- To investigate the angular dependence of the nanoDot OSLD response.
- To assess the impact of incident radiation angle on dosimeter readings in photon and proton beams.
- To provide crucial data for accurate use of nanoDot dosimeters in radiotherapy.
Main Methods:
- Relative dosimeter response measurements were performed at multiple angles in 6 and 18 MV photon beams and a clinical proton beam.
- Measurements were conducted within a phantom at a depth beyond the build-up region.
- Monte Carlo simulations using MCNPX were employed to verify experimental findings and explore underlying mechanisms.
Main Results:
- A non-trivial angular dependence was observed for the nanoDot dosimeter in photon beams.
- The dosimeter response was 4% lower at 6 MV and 3% lower at 18 MV when irradiated parallel to its plane compared to normal incidence.
- No significant angular dependence was found in the clinical proton beam, and Monte Carlo simulations supported these experimental results, suggesting partial volume irradiation as a cause.
Conclusions:
- The nanoDot OSLD exhibits a measurable angular dependence in photon beams, with reduced sensitivity when irradiated parallel to the dosimeter's plane.
- This angular effect, potentially due to partial volume irradiation, must be considered for precise dose calculations in radiotherapy when beams originate from diverse angles.
- The findings highlight the importance of characterizing angular response for OSLDs used in clinical dosimetry, especially in photon therapy.
