A predictive model for Gamma Knife intermediate dose spill: R50%_Analytic-GK

Area of Science:

• Medical Physics
• Radiation Oncology
• Neurosurgery

Background:

• Minimizing intermediate dose spill is critical in brain stereotactic radiosurgery (SRS) to reduce the risk of radionecrosis.
• R50% is a key metric for quantifying intermediate dose spill.
• A predictive model, R50%Analytic, exists for VMAT-delivered SRS.

Purpose of the Study:

• To extend the R50%Analytic model to Gamma Knife (GK) delivered SRS, creating the R50%Analytic-GK model.
• To predict intermediate dose spill in GK Icon treatments.
• To provide a benchmark for assessing SRS treatment plans.

Main Methods:

• Developed the R50%Analytic-GK model using phantom calculations on spherical targets (0.001–44 cm³).
• Validated the model against clinical data from 18 brain metastasis cases treated with GK Icon.
• Analyzed 35 targets (0.011–27.4 cm³) comparing predicted R50%Analytic-GK with clinically achieved R50%Clinical.

Main Results:

• R50%Analytic-GK generally predicted a lower bound for R50%Clinical.
• The median difference (R50%Clinical - R50%Analytic-GK) was 0.92, confirming the lower bound nature.
• The model accurately reflected intermediate dose spill characteristics in clinical cases, with outliers attributed to planning complexities.

Conclusions:

• The R50%Analytic-GK model successfully extends the R50%Analytic framework to GK-delivered SRS.
• It offers a reliable method for predicting intermediate dose spill in GK Icon treatments.
• The model serves as a valuable tool for evaluating SRS treatment plan quality.