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A New Technology for Fast Two-Dimensional Detection of Proton Therapy Beams

D Dolney

R Hollebeek1, M Newcomer1, G Mayers1, B Delgado1, G Shukla1, R Maughan2, D Dolney2*, (1) Department of Physics, University of Pennsylvania, Philadelphia, PA, (2) Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA

TU-C-108-12 Tuesday 10:30AM - 12:30PM Room: 108

Purpose: The authors have developed a novel detector technology for proton therapy dosimetry
with fine spatial and time resolution. New dosimetry technology tailored to proton therapy will
reduce the uncertainties in beam characteristics, assist in the development of new and more
advanced therapy-supporting technologies, facilitate more rapid delivery and commissioning of
new particle therapy facilities, and allow more comprehensive Quality Assurance measurements.

Methods: The Micromesh Gaseous Structure, or Micromegas, is a technology developed for high
count-rate applications in high-energy physics experiments. Presented here are tests using a
Micromegas chamber and specially designed amplifiers and readout electronics adapted to the
requirements of the proton therapy environment and providing both excellent time and high spa-
tial resolution. Several iterations of Micromegas prototypes have been fabricated and assembled.
Data has been collected with these prototypes in proton therapy beams to demonstrate the capa-
bilities and limitations of this new technology.

Results: The digitized ionization signal from the chamber is found to be reproducible to better
than 0.8%. Spatial resolution is determined to be 1.1 mm (1σ) at 1 ms time resolution. We resolve
the range modulator wheel rotational frequency and the thicknesses of its segments and show
that this information can be quickly measured owing to the high time resolution of the system. Our
system resolves the high dose rate within a proton Bragg peak and measurements agree with a
parallel-plate ionization chamber (PTW 34070) to better than 1%.

Conclusion: We have demonstrated an adaptation of Micromegas as a beam monitor for proton
therapy, and the data indicates that Micromegas holds promise as a high spatial and time resolu-
tion measurement device. Systems of this type will be useful in future treatment methods involving
beams that change rapidly in time and spatial position.

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