Technical evaluation of TomoTherapy automatic roll correction.

Area of Science:

• Medical Physics
• Radiation Oncology
• Image-Guided Radiation Therapy

Background:

• Image guidance is crucial for accurate radiation therapy.
• Rotational misalignment can compromise treatment efficacy and safety.
• The TomoTherapy Hi·Art System offers rotational correction capabilities.

Purpose of the Study:

• To develop and evaluate a custom method for end-to-end testing of the TomoTherapy Hi·Art roll correction feature.
• To assess the accuracy of roll corrections and the automatic registration's ability to detect induced roll.
• To determine the sensitivity of the evaluation method and the effectiveness of the roll correction feature.

Main Methods:

• Designed a roll-sensitive treatment plan delivered to a solid water phantom with induced rotations.
• Measured dose to targets and avoidance structures using film dosimetry.
• Performed gamma analysis and compared measured vs. induced roll using MVCT images.

Main Results:

• Statistically significant deviations from baseline observed beyond 0.3° induced rotation.
• Gamma pass rates dropped below 90% at ~0.5° (3%/3 mm) and 0.2°-0.3° (2%/2 mm).
• Roll correction maintained dose measurements indistinguishable from baseline with >96% gamma pass rates (3%/3 mm).

Conclusions:

• The TomoTherapy automatic registration system accurately detects induced rotations.
• The presented evaluation method is sensitive to sub-degree rotations and easily implemented.
• The TomoTherapy Hi·Art roll correction feature effectively corrects rotational misalignments within this level of uncertainty.