[Evaluation of positioning reproducibility using a re-locatable head frame for stereotactic radiotherapy]

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiosurgery

Background:

• Accurate patient positioning is critical for fractionated stereotactic radiotherapy (SRT).
• The Gill-Thomas-Cosman (GTC) re-locatable stereotactic frame is used for patient immobilization.
• Current depth helmet measurements may not account for rotational head displacement, potentially affecting isocenter accuracy.

Purpose of the Study:

• To evaluate the precision of patient relocation reproducibility using the GTC frame.
• To compare depth helmet measurements with CT-based anatomical position displacement.
• To assess the clinical acceptability of relocation errors in SRT.

Main Methods:

• Analysis of 21 patient setups (8 patients) using the GTC frame for SRT between June 2001 and June 2003.
• Comparison of GTC frame setup reproducibility using depth helmet measurements and CT imaging.
• Evaluation of average discrepancy and standard deviation for both measurement methods.

Main Results:

• The average discrepancy for the GTC frame setup measured by depth helmet was 0.6 mm (SD 0.3 mm).
• The average discrepancy measured by CT was 0.7 mm (SD 0.4 mm).
• Relocation accuracy within 1.0 mm was considered clinically acceptable.

Conclusions:

• The GTC frame demonstrates good reproducibility for patient immobilization in SRT.
• CT imaging provides a more comprehensive evaluation of relocation accuracy by detecting rotational displacement missed by depth helmets.
• Utilizing CT imaging is recommended for a more thorough assessment of patient repositioning accuracy in SRT.