Intensity modulated proton arc therapy via geometry-based energy selection for ependymoma

Area of Science:

• Radiation Oncology
• Medical Physics
• Cancer Treatment

Background:

• Intensity-modulated proton therapy (IMPT) is a precise radiation technique.
• Optimizing treatment plans for complex tumor geometries, like ependymoma, remains a challenge.
• Novel planning strategies are needed to enhance dosimetric outcomes and biological effectiveness.

Purpose of the Study:

• To develop and evaluate a novel method for intensity modulated proton arc therapy (IMPAT) planning.
• To assess if IMPAT planning offers dosimetric advantages over conventional IMPT for ependymoma.
• To compare the computational resources required for IMPAT and IMPT planning.

Main Methods:

• A geometry-based energy selection module was developed, utilizing ray-tracing and Gaussian approximation for spot contributions.
• The module identifies a minimal set of energy layers per gantry angle to ensure target coverage.
• IMPAT plans were generated using robust optimization in a commercial treatment planning system and compared to reference IMPT plans for four ependymoma patients.

Main Results:

• IMPAT plans achieved comparable plan robustness and similar maximum doses to the brainstem as IMPT plans.
• IMPAT plans demonstrated superior homogeneity and conformity of the dose distribution within the clinical target volume (CTV).
• IMPAT plans showed increased relative biological effectiveness (RBE) enhancement in the CTV and, in most cases, the brainstem.

Conclusions:

• The proposed IMPAT planning method is efficient and shows potential for treating ependymoma and tumors near critical organs.
• IMPAT planning can provide dosimetric benefits, including enhanced RBE, due to increased linear energy transfer (LET).
• This technique may improve treatment efficacy and reduce toxicity for specific patient populations.