Multiple Brain Metastases Radiosurgery with CyberKnife Device: Dosimetric Comparison between Fixed/Iris and Multileaf...

Area of Science:

• Medical Physics
• Radiation Oncology
• Neurosurgery

Background:

• Stereotactic radiosurgery (SRS) is a key treatment for brain metastases.
• The CyberKnife (CK) device is commonly used for SRS, employing fixed/Iris collimators.
• Evaluating alternative collimator technologies like multileaf collimator (MLC) is crucial for optimizing treatment delivery.

Purpose of the Study:

• To compare the dosimetric quality of CyberKnife (CK) multileaf collimator (MLC) plans versus fixed/Iris collimator plans for multiple brain metastases.
• To assess if MLC plans can achieve comparable or superior dosimetric quality to fixed/Iris plans.
• To evaluate treatment efficiency and normal tissue complication probability (NTCP) differences between the two collimator types.

Main Methods:

• Nineteen existing fixed/Iris CK treatment plans were recalculated using MLC technology.
• MLC plans were re-optimized and re-normalized to match the minimum dose of the total planning target volume (PTVtot).
• Dosimetric metrics including conformation number (CN), homogeneity index (HI), dose gradient index (DGI), integral dose (ID), and V12 (volume receiving 12 Gy) were analyzed. Normal tissue complication probability (NTCP) for brain radionecrosis was calculated.

Main Results:

• MLC plans resulted in significantly shorter treatment times (-18.4%), fewer monitor units (-33.3%), beams (-46.0%), and nodes (-21.3%).
• Fixed/Iris plans demonstrated superior dosimetric quality with higher CN (+8.6%), HI (+2.2%), DGI (+44.0%), and lower ID (-35.9%).
• Fixed/Iris plans showed lower NTCP for PTVtot volumes below the median (2.58cc), indicating a reduced risk of brain radionecrosis for smaller targets.

Conclusions:

• CK-MLC plans offer significant advantages in treatment duration for stereotactic radiosurgery of brain metastases.
• However, fixed/Iris collimators provide better dosimetric quality and lower NTCP for smaller target volumes.
• MLC plans may be more appropriate for patients with larger PTVtot to mitigate the increased risk of brain radionecrosis.