Calculation of portal dose using the convolution/superposition method

Area of Science:

• Medical Physics
• Radiation Oncology
• Image Processing

Background:

• Accurate dose prediction is crucial for radiation therapy verification.
• Portal imaging is used to confirm patient setup and beam configuration.
• Distinguishing scatter from primary dose in portal images is challenging.

Purpose of the Study:

• To validate the convolution/superposition method for predicting dose in extended volumes including phantoms and portal imaging devices.
• To assess the accuracy of the method by comparing calculated portal dose images with measured ones.
• To utilize the method for enhancing megavoltage portal images by removing scatter.

Main Methods:

• Applied the convolution/superposition method to calculate dose distributions in extended volumes (phantoms and portal imaging devices).
• Compared calculated portal dose images with measurements using film and electronic portal imaging devices.
• Determined scatter and primary dose contributions using dose deposition kernels.
• Extracted primary dose and primary energy fluence from portal images.

Main Results:

• Calculated portal dose images showed agreement within 4% of measured images in central field regions.
• The method successfully determined primary and scatter dose contributions.
• Enhancement of megavoltage portal images by removing scatter blurring was achieved.
• Estimated relative primary energy fluence with improved contrast was obtained.

Conclusions:

• The convolution/superposition method is accurate for predicting dose in extended volumes for radiation therapy verification.
• The method provides a means to enhance portal images, improving their utility for quantitative analysis and dose modeling.
• This technique offers potential for improved quality assurance in radiation oncology.