Determining optimal spot delivery pattern using log file Derived dose discrepancy factor in pencil beam scanning...

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Spatial uncertainties in spot positioning during reference dosimetry measurements of pencil beam scanning systems cause fluctuations in the reference dosimetry curve.
• Accurate reference dosimetry is crucial for ensuring effective and safe radiation therapy.

Purpose of the Study:

• To develop a method for determining the optimal delivery pattern for reference dosimetry measurements.
• To quantify the expected dose discrepancy caused by spot positioning errors using log file information.

Main Methods:

• Delivered 7 different delivery patterns five times each, collecting log files for each delivery.
• Introduced a dose discrepancy factor (DDF) calculated using a pencil beam algorithm and actual spot positions from log files.
• Quantified Type A and B uncertainties of DDF to identify the most optimal delivery pattern.

Main Results:

• Relative dose differences of up to 2% were observed with certain delivery patterns.
• A moderate correlation (R²=0.56) was found between DDF and measured dose ratio.
• Delivery patterns with repainting and X fast scan (50MU) showed the lowest average uncertainty, while Y fast scan (50MU) was identified as the most optimal pattern with the least discrepancy.

Conclusions:

• Delivery patterns significantly impact reference dosimetry measurements.
• A log file-based approach can determine optimal delivery patterns to minimize spot positioning errors.
• This method enhances the accuracy and reliability of reference dosimetry in pencil beam scanning systems.