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Dynamic Electron Arc Radiotherapy (DEAR): A Planning Study

A Rodrigues

A Rodrigues*, F Yin, Q Wu, Duke University Medical Center, Durham, NC

SU-E-T-602 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Electron beam therapy is under-utilized in radiation treatment of cancer and has remained practically unchanged for decades. We propose a new technique, Dynamic Electron Arc Radiotherapy (DEAR) with synchronized couch motion. In DEAR, gantry rotation, dose rate, and intensities are modulated to create desirable dose distributions free of hot and/or cold spots, with high homogeneity, and narrow penumbra. This study demonstrates the potential of DEAR in improving dose distributions.

Methods: Dose distributions for single-field and two-field were compared to DEAR with equal and optimized beam weights on a 32 cm diameter cylindrical phantom. Plans were designed to irradiate equivalent field size on the phantom surface, with the target dimension extending from 315⁰-45⁰ in radial angle and target depth at 1 cm (6 MeV) or 2 cm (9 MeV). Penumbra (20-80%), dose homogeneity, and dose area histogram (DAH) were evaluated at target depths. Plans were calculated with the eMC algorithm in Eclipse v10.

Results: In-plane (longitudinal direction) penumbra was comparable across all plans as expected. Cross-plane (along curved surface) penumbra was 5.0, 1.5, and 2.0 cm (6 MeV) and 5.6, 1.7, and 2.1 (9 MeV), for single-field, two-field, and DEAR, respectively. While the two-field penumbra was better, it exhibited a hot spot 60% higher than the target mean at the beam junction covering approximately 20% of the target. DEAR plans displayed homogenous dose distributions with variations of less than ±1.5%. DAH of the single-field failed to achieve optimal coverage, while the two-field displayed a high-dose tail (>100%). 90% of the target receives at least 95% (two-field) and 88% (DEAR) of the target dose.

Conclusion: Preliminary findings show that DEAR can produce homogenous dose distributions over large and curved targets without hot and/or cold spots while maintaining narrow penumbra. Future work includes planning for various target shapes and desired dose distributions.

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