High accuracy dosimetry with small pieces of Gafchromic films

Publication date: March–April 2018
Source:Reports of Practical Oncology & Radiotherapy, Volume 23, Issue 2
Author(s): Ryszard Dąbrowski, Izabela Drozdyk, Paweł Kukołowicz
AimTo investigate the influence of several factors on the accuracy of dose measurements and feasibility of application of small Gafchromic detectors for postal audit.BackgroundOur experience showed that precision of dose measurements with small pieces of Gafchromic films may be significantly improved.Materials and methodsGafchromic films with dimensions of 1×1, 2×2 and 3×3cm² were exposed to 6MV X-rays at dose levels of 50cGy-210cGy. The single- and multichannel methods (MM) were used for dose measurements. Detectors were scanned with an Epson V750PRO flatbed colour scanner. For 1×1 and larger detector sizes, separate calibration curves were established. The influence of the following factors was investigated: the heterogeneity of Gafchromic detectors group for single- and MM, ambient thermal detector conditions, the dose delivered on the measurement accuracy, application of two separate calibration curves for the smallest and larger pieces of films.ResultsThe MM improves significantly the precision of dose measurement. The uncertainty attributed to detector active layer differences and scanner instabilities was about 1cGy (1 StDev) regardless of dose and detector size. The ambient temperature of the environment in which films were stored after irradiation influenced the dose reading. Significant difference of transmission for detectors sized 1×1 and 2×2cm² was observed. The maximal difference between applied dose and dose reading performed was 1.1%.ConclusionsThe MM with a scaling protocol leads to a very high precision of dose measurements. The ambient thermal detector environment causes significant changes of measured signal. The detector size has relevant impact on dose reading.



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