A Monte Carlo based three-dimensional dose reconstruction method derived from portal dose images

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Intensity-modulated radiation therapy (IMRT) requires rigorous quality control for accurate patient treatment.
• Pretreatment verification is crucial to identify discrepancies between planned and delivered radiation doses.
• Existing methods may not fully capture the complexities of 3-D dose distribution in IMRT.

Purpose of the Study:

• To develop and validate a novel 3-D dose verification method for IMRT.
• To accurately reconstruct the delivered radiation dose distribution within a phantom.
• To assess the accuracy of the reconstruction method against established measurement techniques.

Main Methods:

• A 3-D dose reconstruction algorithm combining portal dose images from an electronic portal imaging device (EPID) and Monte Carlo dose calculations.
• Portal images were converted to energy fluence, and lateral scatter was subtracted.
• Phase-space distributions were sampled for 3-D dose calculation in a phantom.

Main Results:

• Depth dose curves and off-axis profiles were reconstructed with high accuracy (typically <1% error for depth dose, <2% for profiles).
• Absolute dose values were reconstructed within 1.5% for various field sizes.
• For an IMRT plan, 99% of pixels passed a gamma evaluation (3% dose, 3 mm distance) compared to film measurements.

Conclusions:

• The developed dose reconstruction algorithm accurately predicts 3-D dose distributions in phantoms.
• Combining EPID portal dosimetry with Monte Carlo calculations provides a reliable method for IMRT pretreatment verification.
• This approach enhances radiation therapy quality control by ensuring accurate dose delivery.