A global calibration model for a-Si EPIDs used for transit dosimetry

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Technology

Background:

• Electronic portal imaging devices (EPIDs) are evolving beyond patient setup verification.
• Their application is expanding into dosimetric verification, particularly for transit dosimetry.
• Amorphous silicon (a-Si) EPIDs offer potential for accurate in-vivo dose measurements.

Purpose of the Study:

• To develop and validate a global calibration model for amorphous silicon EPIDs (a-Si EPIDs).
• To enable accurate dose distribution measurements for transit dosimetry applications.
• To assess the long-term stability and optimize buildup material for a-Si EPIDs.

Main Methods:

• A global calibration model was created, incorporating corrections for ghosting, field size, and energy dependence.
• Long-term stability and additional buildup effects were evaluated.
• Transit dose measurements were compared against ionization chamber data in a water tank using gamma analysis (3%/3mm).

Main Results:

• The calibration model effectively corrected for field size and energy dependence, reducing response variations from 30-40% to under 3%.
• Transit dose distributions consistently met gamma evaluation criteria for various treatment fields and phantoms.
• The developed model demonstrated high accuracy for dosimetric verification across diverse treatment conditions.

Conclusions:

• Amorphous silicon EPIDs can be accurately calibrated for transit dosimetry.
• The proposed global calibration model enhances the reliability of EPID-based dose verification.
• This advancement supports improved quality assurance in radiation therapy.