Institutional experience with SRS VMAT planning for multiple cranial metastases

Area of Science:

• Radiation Oncology
• Medical Physics
• Neurosurgery

Background:

• Cranial stereotactic radiosurgery (SRS) is a key treatment for brain lesions.
• Volumetric modulated arc therapy (VMAT) is an advanced radiotherapy technique.

Purpose of the Study:

• To summarize the institutional procedure for cranial SRS using VMAT.
• To evaluate the efficacy and efficiency of VMAT for treating multiple cranial metastases.

Main Methods:

• VMAT plans were created using Eclipse software for 40 patients with 188 lesions on a TrueBeam STx system.
• Multiple isocenters were used due to lesion distribution and beam model limitations.
• Conformity Index (CI), Gradient Index (GI), and Heterogeneity Index (HI) were calculated for each lesion.

Main Results:

• Lesion volumes varied, with a median of 0.77 cm³.
• Dosimetric parameters showed favorable results: median HI of 1.3, CI of 1.2, and GI of 4.4.
• A predictive formula for GI (GI = 4/PTV^0.2) was developed and implemented.
• Median treatment time was 61 minutes, with brain V7Gy at a median of 42 cm³.

Conclusions:

• VMAT enables precise dose delivery with steep gradients and low critical structure dose for cranial SRS.
• VMAT treatment times are shorter than conventional methods.
• Improvements in VMAT planning, particularly dose modeling in treatment planning systems, are needed to further optimize efficiency for multiple cranial metastases.