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Dynamic Electron Arc Radiotherapy (DEAR): A Feasibility Study

A Rodrigues

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

TU-E-108-2 Tuesday 2:00PM - 3:50PM Room: 108

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. DEAR utilizes modulation in gantry rotation, dose rate, and intensity to create desirable dose distributions. This study investigates the feasibility of DEAR in terms of deliverability and dosimetry.

Methods: DEAR plans were designed and delivered across various energies, doses, and dose rates on a cylindrical phantom. Deliverability was evaluated by verifying the accuracy of the MU, gantry, and couch axes: The agreement between planned and actual axes values recorded in the trajectory log during delivery was quantified by the root mean square error (RMSE). Subsequently, couch, gantry, and collimator velocities were derived and evaluated. Maximum velocities were verified by delivering 10 MU at 1000 MU/min while an axis covered a large distance/rotation, thus forcing a dose rate drop resulting in maximum velocity. Dosimetry was evaluated with radiographic film for static and DEAR plans by comparing in-plane and cross-plane beam penumbra (20-80%) to those calculated with the eMC algorithm in Eclipse v10. Dose homogeneity within target region was evaluated.

Results: Trajectory log analysis of planned and actual axes values for DEAR plans had small RMSE (<0.1 MU, <0.1⁰ gantry, <0.1 cm couch positions). Velocities for couch lateral, vertical, and gantry ranged from 0.1-1.1cm/s, 0.1-1.7cm/s, and 0.3-6⁰/s, respectively. Maximum velocities agreed with manufacturer's specifications and were 3.8, 2, and 7.4cm/s for couch lateral, vertical, and longitudinal, respectively; and 2.9, 5.9, and 14.2⁰/s for couch rotational, gantry, and collimator, respectively. Dosimetric evaluation showed good agreement for the penumbrae (within 1 mm). Further, dose homogeneity was within ±2% of the mean dose.

Conclusion: Preliminary findings show that DEAR has the potential to deliver electron beam therapy with high accuracy and dose homogeneity.

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