Proton Tracks Research Articles

WE‐H‐BRA‐01: BEST IN PHYSICS (THERAPY): Nano‐Dosimetric Kinetic Model for Variable Relative Biological Effectiveness of Proton and Ion Beams

Purpose:Recent clonogenic cell survival and γH2AX studies suggest proton relative biological effectiveness (RBE) may be a non‐linear function of linear energy transfer (LET) in the distal edge of the Bragg peak and beyond. We sought to develop a multiscale model to account for non‐linear response phenomena to aid in the optimization of intensity‐modulated proton therapy.Methods:The model is based on first‐principle simulations of proton track structures, including secondary ions, and an analytical derivation of the dependence on particle LET of the linear‐quadratic (LQ) model parameters α and β. The derived formulas are an extension of the microdosimetric kinetic (MK) model that captures dissipative track structures and non‐Poissonian distribution of DNA damage at the distal edge of the Bragg peak and beyond. Monte Carlo simulations were performed to confirm the non‐linear dose‐response characteristics arising from the non‐Poisson distribution of initial DNA damage.Results:In contrast to low LET segments of the proton depth dose, from the beam entrance to the Bragg peak, strong deviations from non‐dissipative track structures and Poisson distribution in the ionization events in the Bragg peak distal edge govern the non‐linear cell response and result in the transformation α=(1+c_1 L) α_x+2(c_0 L+c_2 L^2)(1+c_1 L) β_x and β=(1+c_1 L)^2 β_x. Here L is the charged particle LET, and c_0,c_1, and c_2 are functions of microscopic parameters and can be served as fitting parameters to the cell‐survival data. In the low LET limit c_1, and c_2 are negligible hence the linear model proposed and used by Wilkins‐Oelfke for the proton treatment planning system can be retrieved. The present model fits well the recent clonogenic survival data measured recently in our group in MDACC.Conclusion:The present hybrid method provides higher accuracy in calculating the RBE‐weighted dose in the target and normal tissues.

TH-CD-201-07: Experimentally Investigating Proton Energy Deposition On the Microscopic Scale Using Fluorescence Nuclear Track Detectors

Purpose: In order to further understand the interplay between proton physics and radiobiology it is necessary to consider proton energy deposition on the microscopic scale. In this work we used Fluorescent Nuclear Track Detectors (FNTDs) to experimentally investigate proton energy deposition, track-by-track. Methods: We irradiated 8×4×0.5mm3 FNTD chips (Landauer Inc) at seven water depths along a pristine proton Bragg peak with range=12cm. After irradiation, the FNTDs were scanned using a confocal microscope (FV1200, Olympus) with a high-power red laser and an oil-immersion objective lens (UPLSAPO60XO, NA=1.35). 10 slice image stacks were acquired with a slice-thickness of 2µm at multiple positions across each FNTD. Image-based analyses of track radius and track “mass” (integrated signal intensity) were performed using trackpy. For comparison, Monte Carlo simulated data were obtained using TOPAS and TOPAS-nBio. Results: Excellent correlation was observed between median track mass and TOPAS dose-averaged linear energy transfer. The resolution of the imaging system was determined insufficient to detect a relationship between track radius and exposure depth. Histograms of track mass (i) displayed strong repeatability across positions within an FNTD and (ii) varied in peak position and shape as a function of depth. TOPAS-nBio simulations implemented on the nanometer scale using physics lists from GEANT4-DNA yielded energy deposition distributions for individual protons and electrons scored within a virtual FNTD. Good agreement was found between these simulated datasets and the FNTD track mass distributions. Conclusion: Robust experimental measurements of the integral energy deposited by individual proton tracks can be performed using FNTDs. Monte Carlo simulations offer an exceedingly powerful approach to the quantification of proton energy deposition on the microscopic scale, but whilst they have been well validated at the macroscopic level, their microscopic validation is far from complete. Our results demonstrate that FNTD-based study can play an important role in addressing this deficit. Tracy Underwood gratefully acknowledges the support of the European Commission under an FP7 Marie Curie International Outgoing Fellowship for Career Development (#630064).

The iMPACT project tracker and calorimeter

In recent years the use of hadrons for cancer radiation treatment has grown in importance, and many facilities are currently operational or under construction worldwide. To fully exploit the therapeutic advantages offered by hadron therapy, precise body imaging for accurate beam delivery is decisive. While traditional X-ray Computed Tomography (xCT) fails in providing 3D images with the precision required for hadrons treatment guidance, Proton Computer Tomography (pCT) scanners, currently in their R&D phase, can. A pCT scanner consists of a tracker system, to track protons, and of a calorimeter, to measure their residual energy. In this paper we will present the iMPACT project, which foresees a novel proton tracking detector with higher scanning speed, better spatial resolution and lower material budget with respect to present state-of-the-art detectors, leading to enhanced performances. The tracker will be matched to a fast, highly segmented proton range calorimeter.

A comparison of two prompt gamma imaging techniques with collimator-based cameras for range verification in proton therapy

In vivo range verification plays an important role in proton therapy to fully utilize the benefits of the Bragg peak (BP) for delivering high radiation dose to tumor, while sparing the normal tissue. For accurately locating the position of BP, camera equipped with collimators (multi-slit and knife-edge collimator) to image prompt gamma (PG) emitted along the proton tracks in the patient have been proposed for range verification. The aim of the work is to compare the performance of multi-slit collimator and knife-edge collimator for non-invasive proton beam range verification. PG imaging was simulated by a validated GATE/GEANT4 Monte Carlo code to model the spot-scanning proton therapy and cylindrical PMMA phantom in detail. For each spot, 108 protons were simulated. To investigate the correlation between the acquired PG profile and the proton range, the falloff regions of PG profiles were fitted with a 3-line-segment curve function as the range estimate. Factors including the energy window setting, proton energy, phantom size, and phantom shift that may influence the accuracy of detecting range were studied. Results indicated that both collimator systems achieve reasonable accuracy and good response to the phantom shift. The accuracy of range predicted by multi-slit collimator system is less affected by the proton energy, while knife-edge collimator system can achieve higher detection efficiency that lead to a smaller deviation in predicting range. We conclude that both collimator systems have potentials for accurately range monitoring in proton therapy. It is noted that neutron contamination has a marked impact on range prediction of the two systems, especially in multi-slit system. Therefore, a neutron reduction technique for improving the accuracy of range verification of proton therapy is needed.

Nanoscale measurements of proton tracks using fluorescent nuclear track detectors.

The authors describe a method in which fluorescence nuclear track detectors (FNTDs), novel track detectors with nanoscale spatial resolution, are used to determine the linear energy transfer (LET) of individual proton tracks from proton therapy beams by allowing visualization and 3D reconstruction of such tracks. FNTDs were exposed to proton therapy beams with nominal energies ranging from 100 to 250 MeV. Proton track images were then recorded by confocal microscopy of the FNTDs. Proton tracks in the FNTD images were fit by using a Gaussian function to extract fluorescence amplitudes. Histograms of fluorescence amplitudes were then compared with LET spectra. The authors successfully used FNTDs to register individual proton tracks from high-energy proton therapy beams, allowing reconstruction of 3D images of proton tracks along with delta rays. The track amplitudes from FNTDs could be used to parameterize LET spectra, allowing the LET of individual proton tracks from therapeutic proton beams to be determined. FNTDs can be used to directly visualize proton tracks and their delta rays at the nanoscale level. Because the track intensities in the FNTDs correlate with LET, they could be used further to measure LET of individual proton tracks. This method may be useful for measuring nanoscale radiation quantities and for measuring the LET of individual proton tracks in radiation biology experiments.

Time-Lapse Monitoring of DNA Damage Colocalized With Particle Tracks in Single Living Cells

Understanding the DNA damage and repair induced by hadron therapy (HT) beams is crucial for developing novel strategies to maximize the use of HT beams to treat cancer patients. However, spatiotemporal studies of DNA damage and repair for beam energies relevant to HT have been challenging. We report a technique that enables spatiotemporal measurement of radiation-induced damage in live cells and colocalization of this damage with charged particle tracks over a broad range of clinically relevant beam energies. The technique uses novel fluorescence nuclear track detectors with fluorescence confocal laser scanning microscopy in the beam line to visualize particle track traversals within the subcellular compartments of live cells within seconds after injury. We designed and built a portable fluorescence confocal laser scanning microscope for use in the beam path, coated fluorescence nuclear track detectors with fluorescent-tagged live cells (HT1080 expressing enhanced green fluorescent protein tagged to XRCC1, a single-strand break repair protein), placed the entire assembly into a proton therapy beam line, and irradiated the cells with a fluence of ∼1×10(6) protons/cm(2). We successfully obtained confocal images of proton tracks and foci of DNA single-strand breaks immediately after irradiation. This technique represents an innovative method for analyzing biological responses in any HT beam line at energies and dose rates relevant to therapy. It allows precise determination of the number of tracks traversing a subcellular compartment and monitoring the cellular damage therein, and has the potential to measure the linear energy transfer of each track from therapeutic beams.

Improving proton therapy by metal-containing nanoparticles: nanoscale insights.

The use of nanoparticles to enhance the effect of radiation-based cancer treatments is a growing field of study and recently, even nanoparticle-induced improvement of proton therapy performance has been investigated. Aiming at a clinical implementation of this approach, it is essential to characterize the mechanisms underlying the synergistic effects of nanoparticles combined with proton irradiation. In this study, we investigated the effect of platinum- and gadolinium-based nanoparticles on the nanoscale damage induced by a proton beam of therapeutically relevant energy (150 MeV) using plasmid DNA molecular probe. Two conditions of irradiation (0.44 and 3.6 keV/μm) were considered to mimic the beam properties at the entrance and at the end of the proton track. We demonstrate that the two metal-containing nanoparticles amplify, in particular, the induction of nanosize damages (>2 nm) which are most lethal for cells. More importantly, this effect is even more pronounced at the end of the proton track. This work gives a new insight into the underlying mechanisms on the nanoscale and indicates that the addition of metal-based nanoparticles is a promising strategy not only to increase the cell killing action of fast protons, but also to improve tumor targeting.

A new silicon tracker for proton imaging and dosimetry

For many years, silicon micro-strip detectors have been successfully used as tracking detectors for particle and nuclear physics experiments. A new application of this technology is to the field of particle therapy where radiotherapy is carried out by use of charged particles such as protons or carbon ions. Such a treatment has been shown to have advantages over standard x-ray radiotherapy and as a result of this, many new centres offering particle therapy are currently under construction around the world today. The Proton Radiotherapy, Verification and Dosimetry Applications (PRaVDA) consortium are developing instrumentation for particle therapy based upon technology from high-energy physics.The characteristics of a new silicon micro-strip tracker for particle therapy will be presented. The array uses specifically designed, large area sensors with technology choices that follow closely those taken for the ATLAS experiment at the HL-LHC. These detectors will be arranged into four units each with three layers in an x–u–v configuration to be suitable for fast proton tracking with minimal ambiguities.The sensors will form a tracker capable of tracing the path of ~200MeV protons entering and exiting a patient allowing a new mode of imaging known as proton computed tomography (pCT). This will aid the accurate delivery of treatment doses and in addition, the tracker will also be used to monitor the beam profile and total dose delivered during the high fluences used for treatment.We present here details of the design, construction and assembly of one of the four units that will make up the complete tracker along with its characterisation using radiation tests carried out using a 90Sr source in the laboratory and a 60MeV proton beam at the Clatterbridge Cancer Centre.

136 - Monte Carlo simulation of prompt-γ emission in proton therapy using a track length estimator

Purpose: Online in vivo control of the ion range in a patient during proton therapy is a major challenge for quality assurance of treatments. After measurements showed that prompt-γ emission is correlated to the ion range (Min et al 2006, Testa et al 2008), prompt-γ imaging emerged as apromising method (Verburg et al 2013). Fast methods are required to compute accurate prompt-γ emission maps to design and predict the camera response from treatment plans. An analytic computation method based on the structure of the dose calculation engines in treatment planning system has recently been proposed (Sterpin et al 2015). An alternative technique based on variance reduction in Monte Carlo (MC) calculations is developed here for computing prompt-γ emission maps in proton therapy.Materials/Methods: The track length estimator (TLE) method is a standard variance reduction technique in voxel-based dose computation in the kerma approximation (Williamson 1987), and similar approaches have also been developed for positron emitter distributions in proton therapy (Parodi et al 2007). A specific track length estimator has been developed here to design a continuous process along the proton track that locally deposits the expected value of the prompt-γ emission (induced by proton inelastic scattering) that would have occurred if a large number of protons with the same incident energy had followed the same step (i.e. track element). First an elemental database of prompt-γ emission spectra is established in the clinical energy range of incident protons for all elements in the composition of human tissues. This database of the prompt-γ spectra is built offline with high statistics. Regarding the implementation of the prompt-γ TLE MC tally, each proton deposits along its track the expectation of the prompt-γ spectra from the database according to the proton kinetic energy and the local material density and composition. All software developments have been carried out with the Gate/Geant4 toolkit.Results: A detailed statistical analysis is reported to characterize the dependency of the variance reduction on the geometrical (track length distribution) and physical (linear prompt-γ spectrum database) parameters. Benchmarking of the proposed technique with respect to an analogous MC technique is carried out. A large relative efficiency gain is reported, ca. 105. Such an efficiency gain could reduce the MC computing time of a full treatment from some weeks to less than one hour. Implementation issues are also addressed.Conclusions: This MC-based technique makes it possible to deal with complex situations such as heterogeneities for which proton straggling and secondary protons may have a decisive contribution. When considering translation to clinic, measurements for the prompt-γ s pectrum d atabase, or at least a sound calibration protocol of the simulated prompt-γ spectra, will have to be carried out.

Proton Radiography With Timepix Based Time Projection Chambers.

The development of a proton radiography system to improve the imaging of patients in proton beam therapy is described. The system comprises gridpix based time projection chambers, which are based on the Timepix chip designed by the Medipix collaboration, for tracking the protons. This type of detector was chosen to have minimal impact on the actual determination of the proton tracks by the tracking detectors. To determine the residual energy of the protons, a BaF 2 crystal with a photomultiplier tube is used. We present data taken in a feasibility experiment with phantoms that represent tissue equivalent materials found in the human body. The obtained experimental results show a good agreement with the performed simulations.

Databank of proton tracks in polyallyldiglycol carbonate (PADC) solid-state nuclear track detector for neutron energy spectrometry

A computer program for studying etched proton tracks in the polyallyldiglycol carbonate (PADC) solid-state nuclear track detector was prepared. The program provided visualization of track appearance as seen under the optical microscope in the transmission mode. Measurable track parameters were also determined and displayed and written in a data file. Three-dimensional representation of tracks was also enabled. Application of this software in neutron dosimetry for energy up to 11MeV was demonstrated through the creation of a databank with a large number of tracks, which would be used to compare real-life tracks obtained in the PADC detector upon neutron irradiation. One problem was identified, viz., very similar tracks were obtained from protons with very different energies and incident angles, and strategies to solve this were proposed.

Energy dependent track structure parametrisations for protons and carbon ions based on nanometric simulations

The BioQuaRT project within the European Metrology Research Programme aims at correlating ion track structure characteristics with the biological effects of radiation and develops measurement and simulation techniques for determining ion track structure on different length scales from about 2 nm to about 10 μm. Within this framework, we investigate methods to translate track-structure quantities derived on a nanometre scale to macroscopic dimensions. Input data sets were generated by simulations of ion tracks of protons and carbon ions in liquid water using the Geant 4 Monte Carlo toolkit with the Geant4-DNA processes. Based on the energy transfer points — recorded with nanometre resolution — we investigated parametrisations of overall properties of ion track structure. Three different track structure parametrisations have been developed using the distances to the 10 next neighbouring ionisations, the radial energy distribution and ionisation cluster size distributions. These parametrisations of nanometric track structure build a basis for deriving biologically relevant mean values which are essential in the clinical situation where each voxel is exposed to a mixed radiation field.

Design of a neutron-TPC prototype and its performance evaluation based on an alpha-particle test

A neutron-TPC (nTPC) is being developed for use as a fast neutron spectrometer in the fields of nuclear physics, nuclear reactor operation monitoring, and thermo-nuclear fusion plasma diagnostics. An nTPC prototype based on a GEM-TPC (Time Projection Chamber with Gas Electron Multiplier amplification) has been assembled and tested using argon-hydrocarbon mixture as the working gas. By measuring the energy deposition of the recoil proton in the sensitive volume and the angle of the proton track, the incident neutron energy can be deduced. A Monte Carlo simulation was carried out to analyze the parameters affecting the energy resolution of the nTPC, and gave an optimized resolution under ideal conditions. An alpha particle experiment was performed to verify its feasibility, and to characterize its performance, including energy resolution and spatial resolution. Based on the experimental measurement and analysis, the energy resolution (FWHM) of the nTPC prototype is predicted to be better than 3.2% for 5 MeV incident neutrons, meeting the performance requirement (FWHM<5%) for the nTPC prototype.

TILDA-V: A full-differential code for proton tracking in biological matter

SynopsisMonte Carlo track structure codes are commonly used for predicting the radio-induced biological damages at the cellular scale. However most of them are based on semi-empirical cross sections as well as the use of water as surrogate of the biological matter. The aim of this work is to present our home-made Monte Carlo code, called TILDA-V, based on a quantum-mechanical cross section data base able to model all the proton- and secondary electron-induced collisions in both water and DNA.

Simulation of the secondary electrons energy deposition produced by proton beams in PMMA: influence of the target electronic excitation description

We have studied the radial dependence of the energy deposition of the secondary electron generated by swift proton beams incident with energies T = 50 keV–5 MeV on poly(methylmethacrylate) (PMMA). Two different approaches have been used to model the electronic excitation spectrum of PMMA through its energy loss function (ELF), namely the extended-Drude ELF and the Mermin ELF. The singly differential cross section and the total cross section for ionization, as well as the average energy of the generated secondary electrons, show sizeable differences at T ⩽ 0.1 MeV when evaluated with these two ELF models. In order to know the radial distribution around the proton track of the energy deposited by the cascade of secondary electrons, a simulation has been performed that follows the motion of the electrons through the target taking into account both the inelastic interactions (via electronic ionizations and excitations as well as electron-phonon and electron trapping by polaron creation) and the elastic interactions. The radial distribution of the energy deposited by the secondary electrons around the proton track shows notable differences between the simulations performed with the extended-Drude ELF or the Mermin ELF, being the former more spread out (and, therefore, less peaked) than the latter. The highest intensity and sharpness of the deposited energy distributions takes place for proton beams incident with T ~ 0.1–1 MeV. We have also studied the influence in the radial distribution of deposited energy of using a full energy distribution of secondary electrons generated by proton impact or using a single value (namely, the average value of the distribution); our results show that differences between both simulations become important for proton energies larger than ~0.1 MeV. The results presented in this work have potential applications in materials science, as well as hadron therapy (due to the use of PMMA as a tissue phantom) in order to properly consider the generation of electrons by proton beams and their subsequent transport and energy deposition through the target in nanometric scales.

SU‐E‐T‐581: On the Value of LET as a Radiation Quality Descriptor for RBE

Purpose:To investigate the relationship between linear energy transfer (LET) and relative biological effectiveness (RBE) for protons and light ions, and the corresponding role of LET as a descriptor of radiation quality of hadron therapy.Methods:Monte Carlo (MC) proton and light ion (He, Li, C) tracks with LET &lt; 30 eV nm‐1 were generated in an event‐by‐event mode. They were overlaid on a cell nucleus model containing 6×109 nucleotide base pairs using an isotropic irradiation procedure that provides electronic equilibrium. Strand breaks (sbs) were scored in the DNA sugar‐phosphate groups and further sub‐classified into single or double sbs (ssbs or dsbs). Distributions of ssbs and dsbs for 2 Gy fractions were calculated to estimate RBE for the induction of initial dsbs with reference to 60Co. Additionally, sbs were classified based on their complexity (i.e. the number of sbs in each cluster).Results:An increase in LET for light ions of the same atomic number or a decrease in atomic number for ions of the same LET resulted in a lower kinetic energy of emitted secondary electrons. The clustering of DNA damage was more pronounced as reflected by the increase in proton RBE from ∼ 1.75 to 4 for LET values of 7 to 28 eV nm‐1. A significant RBE decrease between protons, He, Li and C ions of the same LET was also noticed as function of the atomic number. Significant differences in ssbs and dsbs complexities were also seen for particles with the same LET, potentially supporting a clustering‐based radiation quality descriptor.Conclusion:The LET‐RBE relationships were simulated for proton and light ions and exhibited expected trends, including different RBEs for particles with the same LET but different atomic numbers. A complexity based radiation quality descriptor may allow better differentiation of RBE between radiation fields of similar LET.We would like to acknowledge support from the Fonds de recherche du Quebec Sante (FRQS), from the CREATE Medical Physics Research Training Network grant (number 432290) of NSERC, support from NSERC under grants RGPIN 397711‐11 and RGPIN‐2014‐06475 and support from CIHR under grants MOP‐114910, MOP‐136774 and MOP‐102550.

SU‐E‐T‐494: Influence of Proton Track‐Cell Nucleus Incidence Angle On Relative Biological Effectiveness

Purpose:To explain a Monte Carlo (MC) simulation artifact whereby differences in relative biological effectiveness (RBE) in the induction of initial double strand breaks are observed as a function of the proton track incidence angles in a geometric cell nucleus model. Secondly, to offer an alternative isotropic irradiation procedure to mitigate this effect.Methods:MC tracks of 1 MeV protons were generated in an event‐by‐event mode. They were overlaid on a cylindrical model of a cell nucleus containing 6×109 nucleotide base pairs. The tracks incidence angle θ with respect to the cell nucleus's axis was varied in 10 degrees intervals, each time generating one hundred fractions of ∼2 Gy. Strand breaks were scored in the modeled DNA sugar‐phosphate groups and further sub‐classified into single or double strand breaks (ssbs or dsbs). For each angle, an RBE for the induction of initial dsbs with reference to Co‐60 was calculated.Results:Our results show significant angular dependencies of RBE, with maximum values for incidence angles parallel to the nucleus central axis. Further examination shows that the higher cross‐sections for the creation of dsbs is due to the preferential alignment of tracks with geometrical sub‐parts of the cell nucleus model, especially the nucleosomes containing the sugar‐phosphate groups. To alleviate the impact of this simulation artifact, an average RBE was calculated with a procedure based on a weighted sampling of the angular data.Conclusion:This work demonstrates a possible numerical artifact in estimated RBE if the influence of the particle incidence angle is not correctly taken into account. A correction procedure is presented to better conform the simulations to real‐life experimental conditions.We would like to acknowledge support from the Fonds de recherche du Quebec Sante (FRQS), from the CREATE Medical Physics Research Training Network grant (number 432290) of NSERC, support from NSERC under grants RGPIN 397711‐11 and RGPIN‐2014‐06475 and support from the CIHR under grants MOP‐114910, MOP‐136774 and MOP‐102550.

CMOS Active Pixel Sensors as energy-range detectors for proton Computed Tomography

Since the first proof of concept in the early 70s, a number of technologies has been proposed to perform proton CT (pCT), as a means of mapping tissue stopping power for accurate treatment planning in proton therapy. Previous prototypes of energy-range detectors for pCT have been mainly based on the use of scintillator-based calorimeters, to measure proton residual energy after passing through the patient. However, such an approach is limited by the need for only a single proton passing through the energy-range detector in a read-out cycle. A novel approach to this problem could be the use of pixelated detectors, where the independent read-out of each pixel allows to measure simultaneously the residual energy of a number of protons in the same read-out cycle, facilitating a faster and more efficient pCT scan.This paper investigates the suitability of CMOS Active Pixel Sensors (APSs) to track individual protons as they go through a number of CMOS layers, forming an energy-range telescope. Measurements performed at the iThemba Laboratories will be presented and analysed in terms of correlation, to confirm capability of proton tracking for CMOS APSs.

Treatment planning aspects and Monte Carlo methods in proton therapy

Over the last years, the interest in proton radiotherapy is rapidly increasing. Protons provide superior physical properties compared with conventional radiotherapy using photons. These properties result in depth dose curves with a large dose peak at the end of the proton track and the finite proton range allows sparing the distally located healthy tissue. These properties offer an increased flexibility in proton radiotherapy, but also increase the demand in accurate dose estimations. To carry out accurate dose calculations, first an accurate and detailed characterization of the physical proton beam exiting the treatment head is necessary for both currently available delivery techniques: scattered and scanned proton beams. Since Monte Carlo (MC) methods follow the particle track simulating the interactions from first principles, this technique is perfectly suited to accurately model the treatment head. Nevertheless, careful validation of these MC models is necessary. While for the dose estimation pencil beam algorithms provide the advantage of fast computations, they are limited in accuracy. In contrast, MC dose calculation algorithms overcome these limitations and due to recent improvements in efficiency, these algorithms are expected to improve the accuracy of the calculated dose distributions and to be introduced in clinical routine in the near future.

Expected proton signal sizes in the PRaVDA Range Telescope for proton Computed Tomography

Proton radiotherapy has demonstrated benefits in the treatment of certain cancers. Accurate measurements of the proton stopping powers in body tissues are required in order to fully optimise the delivery of such treaments. The PRaVDA Consortium is developing a novel, fully solid state device to measure these stopping powers. The PRaVDA Range Telescope (RT), uses a stack of 24 CMOS Active Pixel Sensors (APS) to measure the residual proton energy after the patient. We present here the ability of the CMOS sensors to detect changes in the signal sizes as the proton traverses the RT, compare the results with theory, and discuss the implications of these results on the reconstruction of proton tracks.