Verification procedure for isocentric alignment of proton beams

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiosurgery

Background:

• Accurate spatial alignment of proton beams with the gantry mechanical isocenter is critical for effective stereotactic radiosurgery.
• Existing verification methods may lack the required precision or efficiency for routine clinical use.

Purpose of the Study:

• To present a novel technique for verifying proton beam spatial coincidence with the gantry mechanical isocenter.
• To establish a reliable and accurate method for routine alignment testing in proton therapy.

Main Methods:

• Adaptation of the Lutz, Winston, and Maleki test for proton beam verification.
• Utilizing a collimated proton beam, a steel sphere, and a laser tracker measurement system for precise positioning.
• Employing film-based radiation dosimetry (Gafchromic EBT film) and optical image analysis for dose distribution recording.

Main Results:

• The technique clearly identifies the positions of the gantry mechanical and proton beam isocenters.
• Mean proton beam displacement from the gantry mechanical isocenter was 0.22 +/- 0.1 mm.
• Results were well within the accepted maximum deviation of 0.50 mm.

Conclusions:

• The presented film-based dosimetry technique is accurate and efficient for verifying proton beam alignment.
• This method provides a reliable measure of beam alignment with the mechanical isocenter, crucial for patient safety and treatment efficacy.