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Characteristics of a Compact Tabletop Alanine EPR System for Clinical Dosimetry

B Smith*, W Culberson, University of Wisconsin Madison, School of Medicine and Public Health, Department of Medical Physics, Madison, WI

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: Alanine is an attractive dosimeter for radiotherapy since the measured signal is fundamentally related to tissue damage from free radicals. However, performing alanine dosimetry is impractical outside a dedicated lab due to the specialized equipment. Recently, compact tabletop spectrometers have been developed tailored towards chemical spectrometry. Therefore, it was the purpose of this work to independently assess the viability of a compact spectrometer as an economical option to alanine dosimetry.


Methods: Alanine electron paramagnetic resonance (EPR) spectrometry was performed using a Magnettech MiniScope MS 5000X spectrometer and ruby reference crystal. The field modulation width and microwave power were optimized for the alanine-ruby EPR system’s SNR and then later used to characterize the system. All measured spectra were background subtracted, corrected for baseline trends, and underwent alanine and ruby peak-to-peak spectral quantification. Numerous measurements were performed using pellets irradiated with well-known doses to assess measurement repeatability, reproducibility, ruby stability, and EPR signal linearity.


Results: Measurement repeatability was largely dependent on the alanine spectra SNR and dose level ranging from 2-6% at 10 Gy and 0.05-0.1% at 1000 Gy. The reproducibility of the pellet dwell position within the resonator cavity was within 0.5%, which is on the order of the alanine pellet’s angular and orientation dependence within the chamber. The ruby was found to be stable to within 0.05% over the course of measurements spanning several days. Signal linearity was well-maintained between 1 Gy and 1000 Gy.


Conclusion: Tabletop EPR spectrometers may offer a new vehicle for personalized alanine dosimetry that can feasibly be performed in a clinical setting. For intermediate and high doses, conventional alanine analysis techniques demonstrated in this study appear to provide sufficient measurement precision to be clinically useful. However, there are several challenges that still present before the precision and accuracy for lower doses are clinically acceptable.

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Keywords

Dosimetry, Chemical Dosimetry

Taxonomy

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

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