A method to improve dose gradient for robotic radiosurgery.

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiosurgery

Background:

• Large collimators in robotic radiosurgery minimize treatment time but can compromise dose gradients.
• Substantial target volumes in radiosurgery often necessitate large collimators, leading to potential adverse effects on surrounding healthy tissues.
• Existing methods may not optimally balance treatment efficiency with precise dose delivery for large targets.

Purpose of the Study:

• To implement and evaluate an inner-shell planning method for robotic radiosurgery.
• To enhance the dose gradient and reduce radiation dose to normal tissues.
• To improve treatment planning for large planning target volumes (PTVs) in radiosurgery.

Main Methods:

• A novel inner-shell planning approach was developed, splitting the planning target volume (PTV) into a core and a 5 mm outer shell.
• The 7.5 mm Iris collimator was exclusively used for the inner shell, with other collimators applied to the core.
• Ten patients with PTVs > 2 cm³ previously treated with CyberKnife M6 were retrospectively analyzed, comparing new plans to clinical plans.

Main Results:

• The inner-shell method demonstrated significant volume reduction at 12 Gy, 9 Gy, and 5 Gy dose levels compared to clinical plans.
• Mean absolute dose-volume reductions were 5.6 cm³ (12 Gy), 9.8 cm³ (9 Gy), and 24.8 cm³ (5 Gy).
• A mean gradient index (GI) reduction of 12.6% (p=0.0014) was observed, with a mean treatment time increase of 7.0 minutes.

Conclusions:

• The inner-shell planning method substantially improves the dose gradient in robotic radiosurgery for large targets.
• This technique effectively reduces radiation dose to normal tissues while maintaining target coverage and conformity.
• The method offers a promising approach to enhance treatment precision and efficacy in complex radiosurgery cases.