Volume staging for arteriovenous malformation SRS treatment using VMAT

Area of Science:

• Radiation Oncology
• Medical Physics
• Neurosurgery

Background:

• Volume staging (VS) divides large targets into smaller segments for radiation treatment.
• Stereotactic radiosurgery (SRS) delivers high-dose radiation to small targets with steep dose falloff.
• Volumetric Modulated Arc Therapy (VMAT) is an advanced radiation delivery technique.

Purpose of the Study:

• To investigate the feasibility of volume-staged stereotactic radiosurgery (VS-SRS) using VMAT on a linear accelerator.
• To compare VMAT-based VS-SRS plans with Gamma Knife (GK) VS-SRS plans.
• To evaluate the impact of planning target volume (PTV) margins on normal brain (NB) dose.

Main Methods:

• Ten patients with arteriovenous malformations (AVMs) previously treated with hypofractionated radiotherapy were selected.
• VS-SRS plans were created using VMAT on a TrueBeam STx linear accelerator with two target divisions (AVM and PTV).
• Plans were compared to literature GK VS-SRS data, and end-to-end testing with film dosimetry was performed.

Main Results:

• VMAT-based VS-SRS plans achieved median target dose coverage of 97.5% and conformity index of 0.8.
• The average normal brain V12Gy increased by 48.9% with a 1 mm PTV margin compared to the AVM target alone.
• Point-dose measurements showed excellent agreement (-0.6%) with treatment planning system calculations; gamma analysis passing rates exceeded 90%.

Conclusions:

• VMAT is capable of producing VS-SRS plans with dose falloff characteristics similar to Gamma Knife.
• Normal brain dose is significantly influenced by the planning target volume margin size.
• Two-stage treatment setups for VS-SRS do not appear to introduce additional uncertainty in treatment delivery.