Electron Streaming Effect Associated With the Elekta Unity Anterior Imaging Coil
Powers, Marcus, and Baines, John (2022) Electron Streaming Effect Associated With the Elekta Unity Anterior Imaging Coil. Frontiers in Physics, 10. 880121.
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Abstract
The presence of the static field in magnetic resonance guided radiation therapy (MRgRT) systems, such as the Elekta Unity MR-Linac (MRL), influences charged particle motion due to the Lorentz force in and around patients. Consequently, for the Unity, changes to out-of-field dose (OFD) relative to conventional linacs occur due to the electron streaming effect (ESE) and spiraling contaminant electrons (SCE). This work investigates OFD associated with irradiation of the anterior MR imaging coil, which is in situ for all treatments on the Unity. Film measurements and Monaco simulations were performed to quantify the magnitude of OFD at the superior and inferior ends of the coil as a function of coil tilt relative to the beam direction. The dependence of OFD on field size and the relative electron density (RED) assigned to the coil and surrounding air are reported. The doses at both coil ends were clinically significant, with nearly 23.0% of the D-max dose to water being recorded for the largest field (8.0 x 22.0 cm(2)) and 6.8% for the smallest field (3.0 x 3.0 cm(2)). Monaco simulations of OFD agreed with film within 5.0%, when appropriate calculation conditions were set. OFD decreases as coil tilt is reduced, and there is no evidence of ESE when the coil is horizontal. Clinically, the potential magnitude of cranio-caudal streaming dose from a tilted coil necessitates the use of appropriate shielding. A clinical case involving coil-induced ESE during treatment of a lesion in the right angle is presented. The planning-based investigation revealed that ESE doses associated with the coil and an immobilization vacuum bag can be clinically significant.
| Item ID: | 74362 |
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| Item Type: | Article (Research - C1) |
| ISSN: | 2296-424X |
| Keywords: | Elekta Unity, electron streaming effect, anterior coil, monaco unity, MRgRT, out-of-field dose, spiraling contaminant electrons |
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| Copyright Information: | Copyright © 2022 Powers and Baines. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. |
| Date Deposited: | 01 Jun 2022 08:01 |
| FoR Codes: | 51 PHYSICAL SCIENCES > 5105 Medical and biological physics > 510502 Medical physics @ 100% |
| SEO Codes: | 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280120 Expanding knowledge in the physical sciences @ 50% 20 HEALTH > 2002 Evaluation of health and support services > 200206 Health system performance (incl. effectiveness of programs) @ 50% |
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