D Brivio¹*, A Liles^1,2, M Gagne², E Sajo², P Zygmanski¹, (1) Brigham and Women's Hospital, Boston, MA, (2) University of Massachusetts Lowell, Lowell, MA

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  D Brivio

WE-D-BRA-6 (Wednesday, 7/13/2022) 10:15 AM - 11:15 AM [Eastern Time (GMT-4)]

Ballroom A

Purpose: The use of electron beams has been rekindled by the advent of high-dose rate radiotherapy (FLASH) and very high energy electrons (VHEE) as exciting novel modalities in external beam radiotherapy. In this work we explore the potential of a multi-layer nanoporous aerogel High-Energy-Current (HEC) detector as a dosimeter for electron beam using standard dose rates and energies before applying it for FLASH and VHEE. The purpose was to understand detector response to electron energy and residual range.

Methods: Multilayer HEC detectors were constructed using 1x-10x basic modules of Aluminum(Al)_aerogel(A)_Tantalum(Ta) with 10μm-70μm layer thicknesses. Signal was collected from all electrodes (3-21, depending on module multiplicity) with zero external voltage bias. Measurements were acquired as a function of depth(z) in solid water using Varian TrueBeam for energies E=6,9,12,15MeV (SDD=105cm, 6x6cone, 1000MU/min). Computational simulations of identical detector geometries were performed using the 1D deterministic code CEPXS/ONEDANT. Additionally, percent-depth-doses PDD(z), measured in water with ion chamber, were used to explore the response of HEC for various energies and residual ranges.

Results: The current measured from Ta electrodes is proportional to the derivative dPDD(z,E)/dz corrected for contribution from photon contamination. The signal is positive on the surface, and it decreases with depth reaching a negative local minimum at z=R50 (depth at which PDD(z)=50%), before increasing again, reaching zero at about the practical range z=Rp. In contrast, the signal from Al electrodes is shaped like the electron PDD(z) shape but with lower signal at the surface and higher bremsstrahlung tail.

Conclusion: Multi-layer HEC sensors exhibit characteristic response to electron beams that are unlike ion chambers. Since this sensor structure is sensitive to electronic disequilibrium, Ta electrodes give a signal proportional to the derivative of PDD(z). The detector does not suffer from radiation damage or signal saturation, making it suitable for very high dose rate applications.

Keywords

Electron Therapy, Dosimetry, Quality Assurance

Taxonomy

TH- External Beam- Electrons: Development (new technology and techniques)

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