Spine SBRT With Halcyon™: Plan Quality, Modulation Complexity, Delivery Accuracy, and Speed.

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Technology

Background:

• Spine SBRT demands precise radiation delivery with steep dose gradients and strict spinal cord dose limits.
• The Halcyon™ platform features a new dual-layer staggered 1-cm MLC, offering potential improvements over existing MLC technologies.

Purpose of the Study:

• To evaluate the impact of four different multi-leaf collimator (MLC) designs on treatment plan quality for spine SBRT.
• To compare the dosimetric and delivery characteristics of Halcyon™ MLCs against TrueBeam MLCs for spine SBRT.

Main Methods:

• Re-planning of 15 previously treated spine SBRT patients using NRG-BR-002 guidelines (3000 cGy/3 fractions).
• Utilized a 3-arc VMAT technique with 6xFFF, 800 MU/min, and manually optimized planning objectives for each MLC design.
• Assessed plan quality using conformity index, homogeneity index, gradient measure, global point dose maximum, delivery accuracy, modulation complexity, and delivery time.

Main Results:

• All evaluated MLC designs successfully achieved adequate target coverage and met NRG-BR-002 dosimetric constraints.
• Halcyon™ dual-layer MLC plans showed comparable quality to TrueBeam plans, with noted differences in dose fall-off and conformity.
• MLC leaf width influenced organ at risk maximum dose and overall plan quality.

Conclusions:

• The Halcyon™ dual-layer MLC is capable of producing clinically equivalent spine SBRT plans compared to TrueBeam.
• While MLC leaf width affects dose fall-off and conformity, it does not preclude the generation of acceptable spine SBRT treatment plans.