Immobilization precision of a modified GTC frame

Area of Science:

• Medical Physics
• Radiation Oncology
• Medical Imaging

Background:

• Proton stereotactic radiosurgery (SRT) requires high precision for patient positioning.
• Traditional immobilization devices can limit treatment angles, particularly for cranial lesions.
• Evaluating immobilization systems is crucial for ensuring treatment accuracy and safety.

Purpose of the Study:

• To assess the interfraction setup reproducibility and intrafraction immobilization precision of a modified GTC frame for proton SRT.
• To quantify the accuracy of patient alignment and imaging systems using simulated shifts and real patient data.
• To determine if the modified GTC frame facilitates a wider range of treatment angles.

Main Methods:

• A cranial skull phantom with simulated shifts was used to measure alignment and imaging system errors.
• Orthogonal kV setup images from 45 proton SRT patients (1002 fractions) were analyzed.
• A modified GTC frame with a radiotransparent carbon cup and molded pillow was employed for immobilization.
• Three implanted 1.5 mm stainless steel fiducials were used for patient and phantom alignment.

Main Results:

• The accuracy of patient positioning and imaging systems was measured at 0.10 ± 0.06 mm, with rotational uncertainty of ±0.07°.
• Interfraction setup reproducibility was 0.13 mm ± 1.8 mm for translations and ±1.07° for rotations.
• Intrafraction immobilization showed translations of 0.19 mm ± 0.66 mm and rotations of ±0.50°.
• The modified frame allowed for a complete range of posterior entrance angles.

Conclusions:

• The modified GTC frame demonstrates high interfraction setup reproducibility and effective intrafraction immobilization for proton SRT.
• The system's accuracy in patient alignment and imaging supports precise radiation delivery.
• The design enables versatile treatment planning by allowing posterior beam angles, beneficial for cranial lesions.