SU-E-T-402: Coordinate Transformation after Stereotactic Frame Reapplication in Gamma Knife Radiosurgery

Area of Science:

• Neurosurgery
• Medical Imaging
• Radiotherapy Physics

Background:

• Gamma Knife (GK) radiosurgery requires stereotactic frame reapplication for some treatments.
• Frame reapplication can necessitate repeat invasive angiography and treatment re-planning, particularly for vascular lesions.
• This process is burdensome for both physicians and patients.

Purpose of the Study:

• To develop a mathematical coordinate transformation method to avoid repeat angiography and reduce re-planning time in GK radiosurgery.
• To correlate pre- and post-frame reapplication stereotactic images using Affine transformation.
• To minimize Root Mean Square (RMS) error in coordinate transformation using a genetic algorithm.

Main Methods:

• Affine transformation was used to correlate pre- and post-frame reapplication MR or CT images.
• A genetic algorithm determined transformation parameters minimizing RMS error.
• The algorithm was verified using CT skull phantom studies and clinically evaluated with MR images from five patients undergoing multiple GK procedures.

Main Results:

• The RMS error for coordinate transformation was 0.3 mm for skull phantoms and 0.6 mm for clinical images.
• Treatment lesions (0.2–14.1 cc) showed 3% RMS error in irradiation time and 11% in target coverage.
• Deeply-located lesions had a 3% RMS error in conformity index, outperforming superficial lesions.

Conclusions:

• A coordinate transformation method successfully generated new treatment plans post-frame reapplication.
• Converted plans maintained original plan quality with minimal dose distribution changes, primarily due to head rotation.
• This approach effectively reduces the need for repeat procedures and planning time in GK radiosurgery.