SU‐E‐T‐344: Dynamic Electron Beam Therapy Using Multiple Apertures in a Single Cut‐Out

Abstract

Purpose:Few leaf electron collimators (FLEC) or electron MLCs (eMLC) are highly desirable for dynamic electron beam therapies as they produce multiple apertures within a single delivery to achieve conformal dose distributions. However, their clinical implementation has been challenging. Alternatively, multiple small apertures in a single cut‐out with variable jaw sizes could be utilized in a single dynamic delivery. In this study, we investigate dosimetric characteristics of such arrangement.Methods:Monte Carlo (EGSnrc/BEAMnrc/DOSXYnrc) simulations utilized validated Varian TrueBeam phase spaces. Investigated quantities included: Energy (6 MeV), jaw size (1×1 to 22×22 cm 2; centered to aperture), applicator/cut‐out (15×15 cm2), aperture (1×1, 2×2, 3×3, 4×4 cm2), and aperture placement (on/off central axis). Three configurations were assessed: (1) single aperture on‐axis, (2) single aperture off‐axis, and (3) multiple apertures. Reference was configuration (1) with standard jaw size. Aperture placement and jaw size were optimized to maintain reference dosimetry and minimize leakage through unused apertures to <5%. Comparison metrics included depth dose and orthogonal profiles.Results:Configuration (1) and (2): Jaw openings were reduced to 10×10 cm2 without affecting dosimetry (gamma 2%/1mm) regardless of on‐ or off‐axis placement. For smaller jaw sizes, reduced surface (<2%, 5% for 1×1 cm2 aperture) and increased Bremsstrahlung (<2%, 10% for 1×1 cm2 aperture) dose was observed. Configuration (3): Optimal aperture placement was in the corners (order: 1×1, 4×4, 2×2, 3×3 cm2) and jaw sizes were 4×4, 4×4, 7×7, and 5×5 cm2 (apertures: 1×1, 2×2, 3×3, 4×4 cm2 ). Asymmetric leakage was found from upper and lower jaws. Leakage was generally within 5% with a maximum of 10% observed for the 1×1 cm2 aperture irradiation.Conclusion:Multiple apertures in a single cut‐out with variable jaw size can be used in a single dynamic delivery, providing a practical alternative to FLEC or eMLC. Future simulations will expand on all variables.