A novel compound 6D-offset simulating phantom and quality assurance program for stereotactic image-guided radiation...

Area of Science:

• Medical Physics
• Radiation Oncology
• Quality Assurance

Background:

• Image-guided radiation therapy (IGRT) systems are crucial for precise radiation delivery.
• Commissioning and routine testing of 6D IGRT systems require robust quality assurance (QA) methods.
• Existing QA protocols may not fully address the complexities of 6D IGRT systems.

Purpose of the Study:

• To develop and evaluate a comprehensive QA device and program for commissioning and routine testing of 6D IGRT systems.
• To assess the performance of a BrainLAB ExacTrac X-ray IGRT system integrated with a Varian Clinac.
• To establish system characteristics and validate the precision of the 6D IGRT system for stereotactic radiotherapy.

Main Methods:

• Development and fabrication of a novel compound 6D-offset simulating phantom.
• Implementation of a QA program generating random 6D offset values for phantom setup and shifts.
• Automated detection and correction of phantom offsets by the BrainLAB IGRT system via a robotic couch.
• Analysis of detection errors, correction errors, and their correlations from routine QA data.

Main Results:

• The 6D IGRT system demonstrated high precision, with component detection and correction errors within ±1 mm and ±1°.
• Translational and rotational resultant errors were found to be 0.50 ± 0.27 mm and 0.54 ± 0.23°, respectively.
• Individual component errors were largely independent of their initial offset values, indicating system stability.

Conclusions:

• The developed QA methodology is competent in assuring the overall integrity of 6D IGRT systems.
• The BrainLAB 6D IGRT system, when added to a standard linear accelerator, is sufficiently precise for stereotactic radiotherapy.
• Annual comprehensive analyses are recommended for maintaining local system consistency and enabling external cross-comparison. A 1.5 mm 3D margin from CTV to PTV is confirmed for this IGRT system.