Development and multi-institutional evaluation of a new phantom for verifying beam-positioning errors at...

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Single-isocenter stereotactic radiotherapy is essential for treating multiple brain metastases.
• Accurate delivery at off-isocenter positions is critical for treatment efficacy and patient safety.

Purpose of the Study:

• To verify beam-positioning errors at off-isocenter locations using a novel phantom.
• To assess the accuracy and reproducibility of treatment delivery in single-isocenter stereotactic radiotherapy.

Main Methods:

• A phantom with five stainless-steel balls was designed to evaluate off-isocenter beam positioning.
• Phantom rotations (0° and 90°) and multi-institutional testing on eight linacs were performed.
• Reproducibility was assessed via standard deviation (SD) at a single institution.

Main Results:

• The phantom setup and image acquisition took approximately 20 minutes.
• Reproducibility tests showed a standard deviation of 0.41 mm for beam-positioning errors.
• Multi-institutional evaluation revealed errors within 1.00 mm of tolerance at the isocenter, with the largest error (1.36 mm) observed 7.5 cm off-isocenter.

Conclusions:

• The developed phantom is a valuable tool for establishing beam-positioning errors in single-isocenter stereotactic radiotherapy.
• It facilitates accurate assessment of off-isocenter treatment delivery, enhancing safety for patients with brain metastases.