Abstract
The Micromesh Gaseous Structure, or Micromegas, is a technology developed for high count-rate applications in high-energy physics experiments. 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 spatial resolution are presented here. The device was irradiated at the Roberts Proton Therapy Center at the University of Pennsylvania. The system was operated with ionization gains between 10 and 200 and in low and intermediate dose-rate beams, and the digitized signal is found to be reproducible to 0.8%. Spatial resolution is determined to be 1.1 mm (1σ) with a 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. Systems of this type will be extremely useful in future treatment methods involving beams that change rapidly in time and spatial position. The Micromegas design resolves the high dose rate within a proton Bragg peak, and measurements agree with Geant4 simulations to within 5%.
Highlights
At the time of this writing there are 40 hadron therapy facilities in operation worldwide treating cancer patients with hadrons
The steep longitudinal dose gradient that is the motivation behind proton therapy allows for high dose conformity in a third dimension, but detector systems for characterizing 3D dose distributions do not exist
Direct detection of the high beam current used for hadron therapies requires a new generation of dosimetry devices capable of high spatial and time resolution accompanied by good linearity and little to no saturation in the Bragg peak
Summary
At the time of this writing there are 40 hadron therapy facilities in operation worldwide treating cancer patients with hadrons. The depth of the Bragg peak in the patient is controlled by the beam energy, and modern delivery systems allow fast and continuous modulation of beam energy during delivery. Collimation of treatment fields achieves good lateral dose gradients, comparable to X-ray fields, and systems of detectors exist to measure 2D planes of dose distributions. Due to the potential for interplay between the motion of the pencil beam and the respiratory motion of the patient, it is necessary to resolve the time structure of the dose delivery to fully realize the capabilities of hadron therapy, for lung tumors. Direct detection of the high beam current used for hadron therapies requires a new generation of dosimetry devices capable of high spatial and time resolution accompanied by good linearity and little to no saturation in the Bragg peak. New dosimetry technology tailored to hadron therapy will (i) reduce the uncertainties in beam characteristics (position, energy/range, stability), partially addressing the range uncertainty problem and potentially
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