Journal
PHYSICS IN MEDICINE AND BIOLOGY
Volume 61, Issue 20, Pages 7484-7506Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0031-9155/61/20/7484
Keywords
optically stimulated luminescence; pixel bleeding; galvo distortion; laser scanning; image reconstruction; 2D dosimetry; aluminum oxide
Funding
- Alexander von Humboldt Foundation
- Landauer, Inc.
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The objective of this work was to develop an image reconstruction algorithm for 2D dosimetry using Al2O3: C and Al2O3: C, Mg optically stimulated luminescence (OSL) films imaged using a laser scanning system. The algorithm takes into account parameters associated with detector properties and the readout system. Pieces of Al2O3: C films (similar to 8 mm x 8 mm x 125 mu m) were irradiated and used to simulate dose distributions with extreme dose gradients (zero and non-zero dose regions). The OSLD film pieces were scanned using a custom-built laser-scanning OSL reader and the data obtained were used to develop and demonstrate a dose reconstruction algorithm. The algorithm includes corrections for: (a) galvo hysteresis, (b) photomultiplier tube (PMT) linearity, (c) phosphorescence, (d) 'pixel bleeding' caused by the 35 ms luminescence lifetime of F-centers in Al2O3, (e) geometrical distortion inherent to Galvo scanning system, and (f) position dependence of the light collection efficiency. The algorithm was also applied to 6.0 cm x 6.0 cm x 125 mu m or 10.0 cm x 10.0 cm x 125 mu m Al2O3: C and Al2O3: C, Mg films exposed to megavoltage x-rays (6 MV) and C-12 beams (430 MeV u(-1)). The results obtained using pieces of irradiated films show the ability of the image reconstruction algorithm to correct for pixel bleeding even in the presence of extremely sharp dose gradients. Corrections for geometric distortion and position dependence of light collection efficiency were shown to minimize characteristic limitations of this system design. We also exemplify the application of the algorithm to more clinically relevant 6 MV x-ray beam and a C-12 pencil beam, demonstrating the potential for small field dosimetry. The image reconstruction algorithm described here provides the foundation for laser-scanned OSL applied to 2D dosimetry.
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