Optimization of the gafchromic EBT protocol for IMRT QA.

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Dosimetry

Background:

• External beam radiotherapy (EBT) quality assurance necessitates specialized tools.
• Gafchromic EBT (G-EBT) films offer high spatial resolution suitable for radiotherapy dose distribution measurements, particularly for intensity-modulated radiation therapy (IMRT).

Purpose of the Study:

• To provide a comprehensive evaluation of G-EBT film characteristics for practical IMRT verification.
• To develop and optimize a protocol for IMRT quality assurance (QA) using G-EBT films and a flatbed scanner.

Main Methods:

• Investigated G-EBT film characteristics including batch constancy, optical density (OD) versus dose relationship (1.4–8.4 Gy), dose rate dependence (55–441 MU/min), energy dependence (50kV, 6 MV), tissue equivalency, and post-irradiation effects.
• Evaluated scanner characteristics (inhomogeneity, software effects) and film-scanner interactions (OD variation with scanning parameters).
• Optimized an IMRT QA protocol balancing compound error minimization and evaluation time.

Main Results:

• The study determined key G-EBT film and EPSON-Expression 1680 pro flatbed scanner characteristics relevant to IMRT QA.
• An optimized protocol achieved a compound error of approximately 2% for a quality-driven approach and up to 5.5% for a time-driven approach.
• The quality-driven approach is suitable for individual patient QA, while the time-driven approach is appropriate for preliminary measurements.

Conclusions:

• A comprehensive evaluation and optimized protocol for G-EBT films significantly improve IMRT QA accuracy.
• The developed protocol offers flexibility, allowing for either high accuracy or reduced evaluation time depending on QA needs.
• This work provides a robust methodology for enhancing the reliability of radiotherapy dose verification using radiochromic films.