Program Information
Dynamic Electron Beam Therapy Using Multiple Apertures in a Single Cut-Out
A Rodrigues1,2*, F Yin1,2 , Q Wu1,2 , (1) Duke University Medical Center, Durham, NC, (2) Medical Physics Graduate Program, Duke University Medical Center, Durham, NC
Presentations
SU-E-T-344 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
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 (1x1 to 22x22 cm²; centered to aperture), applicator/cut-out (15x15 cm²), aperture (1x1, 2x2, 3x3, 4x4 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 10x10 cm² without affecting dosimetry (gamma 2%/1mm) regardless of on- or off-axis placement. For smaller jaw sizes, reduced surface (<2%, 5% for 1x1 cm² aperture) and increased Bremsstrahlung (<2%, 10% for 1x1 cm² aperture) dose was observed. Configuration (3): Optimal aperture placement was in the corners (order: 1x1, 4x4, 2x2, 3x3 cm²) and jaw sizes were 4x4, 4x4, 7x7, and 5x5 cm² (apertures: 1x1, 2x2, 3x3, 4x4 cm²). Asymmetric leakage was found from upper and lower jaws. Leakage was generally within 5% with a maximum of 10% observed for the 1x1 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.
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