Exploring the gamma surface: A new method for visualising modulated radiotherapy quality assurance results

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Patient-specific quality assurance (QA) is crucial for verifying the accuracy of modulated radiotherapy treatment plans.
• Current methods for evaluating QA results can be insufficient for identifying subtle plan deviations or comparing performance across different clinical settings.

Purpose of the Study:

• To present a novel visualization technique, the "gamma surface", for analyzing patient-specific QA results in modulated radiotherapy.
• To improve the comparison of borderline and failing QA plans.
• To enhance the inter-departmental comparison of patient-specific QA outcomes.

Main Methods:

• Developed a method to create three-dimensional gamma surface plots using gamma pass rates.
• Generated plots by mapping gamma pass rates against dose difference and distance-to-agreement on a grid.
• Calculated 100x100 gamma pass rates for treatment plan comparisons against measurement data.

Main Results:

• Gamma surface plots enabled rapid evaluation of QA criteria and clearly distinguished between well-modeled and poorly delivered plans.
• Identified large-scale features in the plots, suggesting potential issues like over-modulation, systematic dose errors, or areas of disagreement.
• Facilitated quick assessment of plan quality and identification of deviations.

Conclusions:

• Gamma surface plots are effective for investigating radiotherapy QA failures and borderline results.
• This visualization tool provides valuable insights into treatment plan QA performance that might otherwise be overlooked.
• Offers a new approach for detailed analysis of radiotherapy QA data.