Setup error with and without image guidance using two canine intracranial positioning systems for radiation therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Daily image guidance is crucial for reducing patient positioning errors in intracranial radiation therapy.
• However, residual setup errors can persist due to limitations in detecting and correcting small positioning inaccuracies.
• The pre-image guidance accuracy of positioning systems may influence the final residual setup error.

Purpose of the Study:

• To compare the setup accuracy of a novel head positioning system (HPS) against a standard positioning system (SPS) before and after image guidance (megavoltage and cone-beam CT).
• To evaluate the impact of initial positioning accuracy on residual setup errors after image guidance in intracranial radiation therapy.

Main Methods:

• Six dog cadavers were positioned 24 times using the HPS in a head repositioner.
• Fiducial marker coordinates were measured before and after image-guided correction (MV and CBCT).
• Setup accuracy, quantified by the mean three-dimensional distance vector (3DDV), was compared between HPS and SPS.

Main Results:

• The HPS demonstrated significantly lower mean 3DDV than the SPS before image guidance (P = .019).
• After MV guidance, the HPS also showed a significantly lower mean 3DDV than the SPS (P = .027).
• No significant difference in mean 3DDV was observed between HPS and SPS after CBCT guidance (P = .231).
• The 95th percentile setup errors were lower for HPS (2.1 mm MV, 2.9 mm CBCT) than SPS (2.8 mm MV, 3.6 mm CBCT).
• A more accurate pre-image guidance position correlated with lower residual setup error after MV guidance.

Conclusions:

• The head positioning system (HPS) offers improved setup accuracy over the standard positioning system (SPS) for intracranial radiation therapy, particularly before and after MV image guidance.
• Initial positioning accuracy is a critical factor influencing residual setup errors, highlighting the importance of precise patient setup prior to image guidance.
• The findings suggest that optimizing the positioning system can enhance the overall accuracy and effectiveness of image-guided radiation therapy for intracranial treatments.