Sci-Thurs PM: Delivery-11: Image guidance for prostate IMRT using low dose cone beam CT

Area of Science:

• Medical Physics
• Radiation Oncology
• Image Guidance

Background:

• Linac-mounted cone beam computed tomography (CBCT) delivers high imaging doses and lacks automated clinical target volume (CTV) registration.
• Frequent treatment corrections in prostate intensity modulated radiation therapy (IMRT) are hindered by current CBCT limitations.

Purpose of the Study:

• To develop and evaluate automatic image guidance strategies to reduce imaging dose and improve CTV registration for prostate IMRT.
• To enable frequent treatment corrections during IMRT by addressing CBCT dose and registration issues.

Main Methods:

• Acquired low-dose CBCT images for patient setup verification.
• Implemented and compared two automatic image guidance strategies: 'global' (couch correction) and 'local' (treatment re-optimization).
• Evaluated techniques using an anthropomorphic male pelvis phantom, assessing registration error and treatment doses.

Main Results:

• The 'global' technique showed a registration error of 3.6 ± 1.3 mm but resulted in high bladder and rectal doses with motion.
• The 'local' technique achieved a reduced registration error of 2.3 ± 0.8 mm at 15% of the default OBI dose.
• The 'local' method consistently yielded clinically acceptable treatment doses.

Conclusions:

• The automatic 'local' image guidance technique effectively reduces imaging dose during prostate IMRT.
• This approach demonstrates sufficient accuracy and robustness for clinical application, enabling precise treatment adjustments.
• The 'local' method corrects treatment to match patient setup, improving safety and efficacy.