High-dose MVCT image guidance for stereotactic body radiation therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Medical Imaging

Background:

• Stereotactic body radiation therapy (SBRT) requires precise tumor localization for effective treatment.
• Tomotherapy, combining helical intensity-modulated radiation therapy (IMRT) with onboard megavoltage CT (MVCT), is suitable for SBRT.
• Standard MVCT has limitations in soft tissue contrast and image noise compared to kilovoltage CT.

Purpose of the Study:

• To investigate the impact of increased imaging doses on tomotherapy machines.
• To enhance image quality for SBRT image guidance.
• To assess if higher imaging doses can overcome MVCT limitations.

Main Methods:

• Developed two high-dose imaging modes by increasing the linear accelerator (LINAC) pulse rate (160 Hz and 300 Hz).
• Measured weighted CT dose indexes (wCTDIs) in phantoms for standard and high-dose modes.
• Assessed image quality using metrics like contrast-to-noise ratios (CNRs) and spatial resolution in phantoms and patient scans.

Main Results:

• wCTDI values increased with dose, reaching 8.5 cGy in the high-dose mode.
• Contrast-to-noise ratios (CNRs) improved with increasing dose.
• Image uniformity improved, and percent noise decreased with higher imaging doses.
• Patient images showed notable decreases in image noise with high-dose scans.

Conclusions:

• High-dose imaging modes are feasible on clinical tomotherapy by adjusting LINAC pulse rate.
• Increased imaging dose significantly improves CNRs, aiding visualization of low-contrast structures.
• The tested high-dose levels are acceptable for SBRT delivered in 3-5 fractions.