Development and application of a dose verification tool using a small field model for TomoTherapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Helical TomoTherapy uses small fields for precise dose delivery.
• Quality assurance is crucial for accurate radiation therapy.
• Small field dosimetry presents unique challenges due to source effects and disequilibrium.

Purpose of the Study:

• To develop and validate a dose verification tool for Helical TomoTherapy.
• To assess the impact of small field characteristics on dose distribution.
• To evaluate the tool's efficacy in quality assurance programs.

Main Methods:

• Implementation of a small field model considering source shape and lateral charged particle equilibrium (CPE).
• Development of a dose verification tool for tomotherapy systems.
• Comparison of measured and calculated output factors and dose profiles.

Main Results:

• The tool demonstrated good agreement between measured and calculated values within 2%/2mm gamma criteria.
• Systematic and random variations did not lead to failed gamma scores (3%/3mm).
• The model accurately predicts dose distributions in small fields relevant to tomotherapy.

Conclusions:

• The developed dose verification tool is effective for Helical TomoTherapy quality assurance.
• The small field model accurately accounts for key physical phenomena.
• This tool enhances the evaluation of radiation delivery performance in tomotherapy units.