Two-dimensional in vivo dose verification using portal imaging and correlation ratios

Area of Science:

• Medical Physics
• Radiation Oncology
• Diagnostic Imaging

Background:

• The electronic portal imaging device (EPID) offers potential for in vivo dosimetry in radiation therapy.
• Existing methods allow for isocenter dose calculation using EPID transit images.

Purpose of the Study:

• To extend EPID-based dosimetry for calculating 2D dose maps at the isocenter depth.
• To validate this extended method for clinical treatment plans.

Main Methods:

• Extended an existing EPID dosimetry method to generate 2D dose maps.
• Quantified EPID signal-to-dose variability in Solid Water phantoms.
• Developed a field edge dose calculation correction.
• Validated the method on an anthropomorphic phantom with realistic treatment plans.

Main Results:

• Achieved good agreement (≥96.5% with 3%/3mm gamma) for whole brain and brain primary plans.
• The algorithm overestimated dose by 7%-9% in the presence of lung tissue.
• Demonstrated the feasibility of 2D dose map calculation using EPID transit images.

Conclusions:

• The 2D EPID-based in vivo dosimetry method provides reliable post-treatment dose verification.
• This technique enhances the safety and quality of patient radiation treatments.
• Future work could enable real-time dose monitoring and prevention of delivery errors.