Correcting scan-to-scan response variability for a radiochromic film-based reference dosimetry system

Area of Science:

• Medical Physics
• Radiological Dosimetry

Background:

• Radiochromic film dosimetry systems commonly use CCD-based flatbed scanners for dose measurements.
• Scan-to-scan response variability in these systems can lead to significant uncertainties in dose determination.

Purpose of the Study:

• To investigate factors contributing to scan-to-scan response variability in radiochromic film dosimetry.
• To quantify the impact of these factors on dose measurement uncertainty.

Main Methods:

• Repetitive scanning of EBT3 radiochromic films at various doses using flatbed document scanners.
• Evaluation of scanner lid open/closed conditions, temperature effects (9°C vs. 22°C), and film-to-light source distance variations.
• Use of neutral density and blue optical filters to assess response under different conditions.

Main Results:

• Standard deviation of response measurements for EBT3 films was low (0.09%-0.17%) under controlled conditions.
• Opening/closing the scanner lid increased average scan-to-scan differences from 0.12% to 0.27%.
• Temperature changes affected RGB response (-0.05% to -0.17%/°C), while reduced film-to-light distance increased response (1.1% to 1.4%/mm).
• Film flatness issues were observed, with potential for significant dose uncertainty (>5%) due to variations in film-to-light source distance.

Conclusions:

• Factors like scanner lid operation, temperature, and film flatness can introduce dose uncertainties greater than 2%.
• Film-to-light source distance variations, particularly due to film curl, pose a substantial risk for dose uncertainty (>5%).
• Implementing a transparent sheet over the film and including a reference film in scans can eliminate these uncertainties.