PC-Assisted Dose Assessment in Clinical TL Dosimetry and QA Programmes

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Abstract
TL dosimetry with LiF:Mg,Ti (TLD-100) detectors suffers from the limited reproducibility of the thermal procedures mandatory for detector readout and annealing. Further, changes of transmittance and reflectivity in the optical pathway as well as of the PMT sensitivity may affect the dosimetric precision. A PC software has been developed that overcomes these drawbacks and hence contributes significantly to improve TL precision in routine clinical dosimetry. The software allows computation of individual calibration factors, correction for systematic changes and assessment of unknown doses respecting, additionally, supralinearity and beam quality. Feasibility of a statistical data analysis and full data documentation is implemented. As a result relative standard deviations of 0.2% <SD <0.5% were achieved, as found from repeated measurements with individual LiF:Mg,Ti chips under laboratory conditions for an absorbed dose level of 1 Gy. Results of blind tests show comparable precision also for the assessment of unknown doses. These results were obtained with data files of commercially available TL equipment using unselected LiF:Mg,Ti samples. The PC-assisted TL dosimetry may be very valuable for therapy level dosimetry and quality assurance programmes at medical accelerators.

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