Determining optimal transit dosimetry gamma parameter values for the detection of failure modes using receiver...

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Transit dosimetry software like PerFRACTION is crucial for verifying radiotherapy dose delivery accuracy.
• Identifying potential failure modes in external beam radiotherapy is essential for patient safety.
• Optimizing gamma criteria is key to maximizing the sensitivity and specificity of these checks.

Purpose of the Study:

• To determine the optimal gamma criteria for the PerFRACTION transit dosimetry software.
• To maximize sensitivity and specificity in detecting various failure modes in external beam radiotherapy.
• To evaluate the performance of different gamma criteria under simulated radiotherapy incidents.

Main Methods:

• Simulated five failure modes: Linac hardware, breathing management, patient identification, planning CT selection, and bolus positioning errors.
• Utilized VMAT and 4D-CT data for head and neck, lung, and breast cancer treatment plans.
• Compared transit images using seven global and local gamma criteria, generating ROC curves based on PTV mean dose changes (5%, 10%, 20%).

Main Results:

• The global gamma criterion γ(10%/1 mm) demonstrated maximum sensitivity and specificity for detecting dose changes exceeding 10%.
• The standard global gamma criterion, γ(3%/3 mm), was optimal for identifying deviations greater than 5% in the PTV mean dose.
• Specific gamma criteria effectively distinguished between different magnitudes of dose errors.

Conclusions:

• A 10%/1 mm global gamma criterion is recommended for identifying significant erroneous radiotherapy deliveries (≥10% dose difference).
• Standard gamma criteria (e.g., 3%/3 mm) are suitable for detecting smaller dose deviations (≥5%).
• Optimized gamma criteria enhance the reliability of transit dosimetry for quality assurance in radiotherapy.