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

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 cm(2)), aperture (1×1, 2×2, 3×3, 4×4 cm(2)), 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 cm(2) without affecting dosimetry (gamma 2%/1mm) regardless of on- or off-axis placement. For smaller jaw sizes, reduced surface (<2%, 5% for 1×1 cm(2) aperture) and increased Bremsstrahlung (<2%, 10% for 1×1 cm(2) aperture) dose was observed. Configuration (3): Optimal aperture placement was in the corners (order: 1×1, 4×4, 2×2, 3×3 cm(2)) and jaw sizes were 4×4, 4×4, 7×7, and 5×5 cm(2) (apertures: 1×1, 2×2, 3×3, 4×4 cm(2) ). Asymmetric leakage was found from upper and lower jaws. Leakage was generally within 5% with a maximum of 10% observed for the 1×1 cm(2) 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.

Duke Scholars

Author Qiuwen Wu Radiation Oncology