Scripting a planning avoidance structure to perform simultaneous integrated boost breast on Halcyon linear...

Area of Science:

• * Radiation Oncology
• * Medical Physics
• * Cancer Treatment

Background:

• * Simultaneous integrated boost (SIB) in breast radiotherapy often utilizes an oblique anterior field for tumor bed targeting.
• * The Eclipse software's 'fixed jaw' option is unavailable on Halcyon linear accelerators, posing challenges for precise beam collimation.
• * Halcyon accelerators lack jaw collimators, relying solely on multileaf collimators (MLCs), which can lead to unintended irradiation of organs at risk.

Observation:

• * The absence of jaw collimators on Halcyon systems prevents the 'fixed jaw' optimization technique used in other Varian systems.
• * Without intervention, the optimizer may open MLCs over critical structures like the heart or spinal cord on the oblique anterior field.
• * A workaround was needed to ensure MLCs remained closed over organs at risk during treatment planning.

Findings:

• * An avoidance structure was developed using the Eclipse Scripting Application Programming Interface (ESAPI) to overcome Halcyon's limitations.
• * This structure, representing the patient's entire body minus beam paths, guided the optimizer to close MLCs appropriately.
• * Planning for six breast cancer patients demonstrated that this ESAPI-generated avoidance structure effectively met all dosimetric constraints, fully closing MLCs outside the planning target volume (PTV).

Implications:

• * This ESAPI-based approach provides a viable solution for precise radiation delivery in SIB breast treatments on Halcyon accelerators.
• * It ensures the protection of critical organs at risk by preventing unintended irradiation.
• * The method offers a pathway for adapting advanced radiotherapy techniques to newer accelerator technologies.