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Proton beams are promising means for treating tumors. Such charged particles stop at a defined depth, where the ionization density is maximum. As the dose deposit beyond this distal edge is very low, proton therapy minimizes the damage to normal tissue compared to photon therapy. Nevertheless, inherent range uncertainties cast doubts on the irradiation of tumors close to organs at risk and lead to the application of conservative safety margins. This constrains significantly the potential benefits of protons over photons. In this context, several research groups are developing experimental tools for range verification based on the detection of prompt gammas, a nuclear by-product of the proton irradiation. At OncoRay and Helmholtz-Zentrum Dresden-Rossendorf, detector components have been characterized in realistic radiation environments as a step toward a clinical Compton camera. On the one hand, corresponding experimental methods and results obtained during the ENTERVISION training network are reviewed. On the other hand, a novel method based on timing spectroscopy has been proposed as an alternative to collimated imaging systems. The first tests of the timing method at a clinical proton accelerator are summarized, its applicability in a clinical environment for challenging the current safety margins is assessed, and the factors limiting its precision are discussed.

no abstract available

After a first clinical application of a prompt gamma knife-edge slit-camera in double scattering (DS) mode, systematic measurements and quantitative analysis of patient data have been started. To investigate the detection sensitivity of the slit camera for range deviations in DS compared to pencil beam scanning (PBS), phantom measurements in both treatment modes with clinically relevant treatment plans have been performed.

Prompt γ-ray imaging in hadron therapy is a novel approach for range verification. Due to the high energy of prompt γ-rays emitted during therapeutic irradiation in the order of MeV, Compton imaging is a feasible method. In this work, an imaging prototype together with the corresponding data handling and an image reconstruction framework are presented. Data and reconstructed images from laboratory measurements are shown and evaluated. A spatial resolution of 7 mm full width at half maximum in a distance of 7 cm has been achieved. More importantly, current limitations were identified for further work. It has been shown that an assumption on the unknown initial photon energy can considerably improve the imaging result.

Proton therapy facilities are built all around the world for optimized cancer treatments. In order to fully exploit the advantages of this therapy, a proton range verification is mandatory. The most promising advances use either the positron emission tomography (PT-PET) approach or the prompt gamma emissions caused by nuclear reactions (by means of passive collimation, Compton cameras or prompt gamma timing). Gamma ray detectors in this field face unique requirements: Good properties with respect to energy, time and spatial resolution even when operated with high counting rates in rather high background environments. Lutetium Fine Silicate (LFS) is a novel scintillation material which is especially designed for PET applications. Thus, in this work, the characteristics of LFS are determined for energy ranges which match the requirements of the prompt gamma ray monitors (i.e. up to 8 MeV). The usage of different photodetectors (i.e. PMT or Silicon-based read-out), depending on the particular application, is discussed.

A compact high-throughput gamma-ray timing and energy spectrometry systems has been characterized with respect to time and energy resolution at detector loads up to 1.5 Mcps by using 0.1-12.5 MeV bremsstrahlung and a common radioactive source. The detection system, developed for range assessment in particle therapy based on the Prompt Gamma-Ray Timing (PGT) technique, consist of a commercial ⌀2”×1” or ⌀2”×2” CeBr 3 scintillation detector with photomultiplier readout (Scionix), coupled to a digital plug-on spectrometer (U100) by Target Systemelektronik. The excellent time structure of the bremsstrahlung beam at ELBE (HZDR) allowed measuring the system time resolution simultaneously for 0.1-12 MeV photons. Also, the beam current and thus the detector load could be varied in a wide range. The energy resolution was determined in parallel with a 60 Co-source attached to the detector. Source and bremsstrahlung photons were separated by means of cuts in the timing spectra measured against the accelerator RF. The detection system could demonstrate a time resolution of < 260 ps (FWHM) for energies above 3 MeV with the smaller crystal, and an energy resolution of < 3.7% at 1.173 MeV for both crystals, up to detector loads of 1.4 Mcps and a corresponding system throughput of ~ 600 kcps. This fits well with the design goals of the detection system. Corresponding units shall be used for measuring PGT spectra during patients treatments with proton beams, in order to verify the proton beam range for single beam spots in Pencil Beam Scanning (PBS) mode. Range verification is considered a key for reducing margins and for improving precision and health outcome of particle therapy.

A Compton camera prototype for the position-sensitive detection of prompt γ rays from nuclear reactions between proton (or ion) beams and organic targets is being commissioned in Garching. The detector system is designed to allow for reconstructing the γ-source position from the Compton scattering kinematics of the primary photon as well as from tracking the Compton-scattered electron trajectory. The camera consists of a monolithic LaBr3(Ce) scintillation absorber crystal, read out by a 256-fold segmented multi-anode PMT and preceded by a stacked array of 6 double-sided silicon strip detectors acting as scatterers. The detector system has been calibrated and characterized in the laboratory as well as at different accelerator facilities, including clinical proton beams. Results from online commissioning runs will be presented, demonstrating excellent agreement between experimental prompt-γ spectra and Monte-Carlo simulations. Particular effort was dedicated to characterize the spatial resolution achievable with the monolithic LaBr 3 (Ce) scintillator when targeting the primary photon interaction position. Intense, tightly collimated 137Cs and 60Co sources were used for 2D irradiation scans as prerequisite for studying the performance of the “k-Nearest Neighbour”-algorithm developed in Delft and extending its applicability into the energy range beyond 511 keV. Systematic results of the monolithic scintillator’s spatial resolution will be presented as a function of the k-NN parameters (e.g. events per irradiation position) and the PMT segmentation, resulting in the realization of the presently optimum spatial resolution (3.8(2) mm @1.3 MeV) already for a reduced PMT segmentation (8x8). An outline of ongoing and planned further experimental activities and upgrade plans will be presented. This work is supported by the DFG Cluster of Excellence MAP (Munich-Centre for Advanced Photonics).

(1) Purpose In order to guarantee the best outcome of a therapeutic irradiation with protons and other light ions a non-invasive in-vivo range verification is desired. One approach in this field is Prompt y-ray Imaging (PGI). A possible detection system for the prompt y-rays is the Compton camera. Several groups have been working on the construction of Compton camera prototypes (Kormoll et al., 2011; Llosá et al., 2013; Thirolf et al., 2014; Hueso-González et al., 2014). Up to now, Compton cameras have not been used in clinical practice for the monitoring of particle therapy. Therefore, by means of Geant4 simulations, we performed an end-to-end test to evaluate the clinical applicability of a Compton camera detection system and to determine the requirements regarding hardware and image reconstruction. (2) Materials/methods First, a treatment plan for a therapeutic proton irradiation for the head-neck region was prepared using XiO (Electa AB, Sweden). Based on this treatment plan, the y-ray emissions from the patient's tissue were simulated with Geant4. As a next step, the detector response was modelled, also with Geant4, for two large Compton cameras arranged around the patient in an angle of 90 degrees. Large-area detectors were already recommended (McCleskey et al., 2015). Each camera was built up from a scatter layer (CdZnTe) of dimension 10 × 10 × 0.5 cm3 and an absorber layer (LuSiO) of size 20 × 20 × 2 cm3. In practice, these cameras would be replaced by several smaller camera modules. For the simulation of the detector response a total number of previously simulated y-ray emissions were used as input corresponding to an applied dose of 1 Gy, i.e. a common dose of one field of one treatment session. After extracting the resulting coincident events, the image was reconstructed using a 3D MLEM algorithm (Schoene et al., 2015). The impact of the number of events as well as background on the image quality was also studied. (3) Results Figure 1 shows the images for the planned dose, the distribution of the y-ray emissions and the reconstructed image obtained with 128 iterations of the MLEM algorithm. For the considered number of events and the chosen voxels of 5 mm3 the runtime of the reconstruction was about two days on a cluster. (4) Conclusions For the considered large camera system and the realistic patient scenario with a dose of 1 Gy adequate images are obtained, which certainly could be applied to detect range deviations in the range of centimeters. Thus, this study demonstrates in principle the clinical applicability. The reconstruction algorithm still has potential for improvements with respect to performance. Furthermore, in practice, the costs of this complex detection system could lead to the preference of simpler methods of PGI.

The finite range of a proton beam in tissue opens new vistas for the delivery of a highly conformal dose distribution in radiotherapy. However, the actual particle range, and therefore the accurate dose deposition, is sensitive to the tissue composition in the proton path. Range uncertainties, resulting from limited knowledge of this tissue composition or positioning errors, are accounted for in the form of safety margins. Thus, the unverified particle range constrains the principle benefit of proton therapy. Detecting prompt gamma-rays, a side product of proton-tissue interaction, aims at an on-line and non-invasive monitoring of the particle range, and therefore towards exploiting the potential of proton therapy. Compton imaging of the spatial prompt gamma-ray emission is a promising measurement approach. Prompt gamma-rays exhibit emission energies of several MeV. Hence, common radioactive sources cannot provide the energy range a prompt gamma-ray imaging device must be designed for. In this work a benchmark measurement-setup for the production of a localized, monoenergetic 4.44MeV gamma-ray source is introduced. At the Tandetron accelerator at the HZDR, the proton-capture resonance reaction 15N(p , alpha gamma4.439)12C is utilized. This reaction provides the same nuclear de-excitation (and gamma-ray emission) occurrent as an intense prompt gamma-ray line in proton therapy. The emission yield is quantitatively described. A two-stage Compton imaging device, dedicated for prompt gamma-ray imaging, is tested at the setup exemplarily. Besides successful imaging tests, the detection efficiency of the prototype at 4.44MeV is derived from the measured data. Combining this efficiency with the emission yield for prompt gamma-rays, the number of valid Compton events, induced by gamma-rays in the energy region around 4.44MeV, is estimated for the prototype being implemented in a therapeutic treatment scenario. As a consequence, the detection efficiency turns out to be a key parameter for prompt gamma-ray Compton imaging limiting the applicability of the prototype in its current realization.

Prompt γ-ray imaging with a knife-edge shaped slit camera provides the possibility of verifying proton beam range in tumor therapy. Dedicated experiments regarding the characterization of the camera system have been performed previously. Now, we aim at implementing the prototype into clinical application of monitoring patient treatments. Focused on this goal of translation into clinical operation, we systematically addressed remaining challenges and questions. We developed a robust energy calibration routine and corresponding quality assurance protocols. Furthermore, with dedicated experiments, we determined the positioning precision of the system to 1.1 mm (2σ). For the first time, we demonstrated the application of the slit camera, which was intentionally developed for pencil beam scanning, to double scattered proton beams. Systematic experiments with increasing complexity were performed. It was possible to visualize proton range shifts of 2 - 5 mm with the camera system in phantom experiments in passive scattered fields. Moreover, prompt γ-ray profiles for single iso-energy layers were acquired by synchronizing time resolved measurements to the rotation of the range modulator wheel of the treatment system. Thus, a mapping of the acquired profiles to different anatomical regions along the beam path is feasible and additional information on the source of potential range shifts can be obtained. With the work presented here, we show that an application of the slit camera in clinical treatments is possible and of potential benefit.

In der Radioonkologie gewinnt die Bestrahlung mit Protonen zunehmend an Bedeutung. Um die vorteilhaften strahlenphysikalischen Eigenschaften jedoch voll ausschöpfen zu können, ist eine Verifizierung der Protonenreichweite notwendig. Hierfür gibt es verschiedene Ansätze, wobei das Prompt Gamma Imaging (PGI) eine vielversprechende Methode ist. Eine Schlitzkamera, welche eine mögliche technische Realisierung für das PGI darstellt, ermöglicht die tiefenaufgelöste Messung von protoneninduzierten Prompt-Gamma-Emissionen und erlaubt Aussagen über die tatsächliche Reichweite der applizierten Protonen. An der Universitätsprotonentherapie Dresden (UPTD) wird in naher Zukunft eine klinische Studie zur Nutzung einer solchen Schlitzkamera im Patientenbetrieb beginnen. Hierfür erfolgen gegenwärtig die Vorbereitung der klinischen Implementierung sowie die systematische Charakterisierung des Kamerasystems.

Ion beam therapy promises enhanced tumour coverage compared to conventional radiotherapy, but particle range uncertainties significantly blunt the achievable precision. Experimental tools for range verification in real-time are not yet available in clinical routine. The prompt gamma ray timing method has been recently proposed as an alternative to collimated imaging systems. The detection times of prompt gamma rays encode essential information about the depth-dose profile thanks to the measurable transit time of ions through matter. In a collaboration between OncoRay, Helmholtz-Zentrum Dresden - Rossendorf and IBA, the first test at a clinical proton accelerator (Westdeutsches Protonentherapiezentrum Essen, Germany) with several detectors and phantoms is performed. The robustness of the method against background and stability of the beam bunch time profile is explored, and the bunch time spread is characterized for different proton energies. For a beam spot with hundred million protons and a single detector, range differences of five millimetres in defined heterogeneous targets are identified by numerical comparison of the spectrum shape. For higher statistics, range shifts down to two millimetres are detectable. A proton bunch monitor, higher detector throughput and quantitative range retrieval are the upcoming steps towards a clinically applicable prototype. In conclusion, the experimental results highlight the prospects of this straightforward verification method at a clinical pencil beam and settle this novel approach as a promising alternative in the field of in vivo dosimetry.

No abstract available

A primary subject of the present research in particle therapy is to ensure the precise irradiation of the target volume. The prompt gamma timing (PGT) method provides one possibility for in vivo range verification during the irradiation of patients. Prompt gamma rays with high energies are emitted promptly due to nuclear reactions of protons with tissue. The arrival time of these gammas to the detector reflects the stopping process of the primary protons in tissue and are directly correlated to the range. Due to the time resolution of the detector and the proton bunch time spread, as well as drifts of the bunch phase with respect to the accelerator frequency, timing spectra are smeared out and compromise the accuracy of range information intended for future clinical applications. Nevertheless, counteracting this limitation and recovering range information from the PGT measured spectra, corrections using a phase beam monitor can be performed. A first prototype of phase beam monitor was tested at GSI Darmstadt, where measurements of the energy profile of the ion bunches were performed. At the ELBE accelerator Helmholtz-Zentrum Dresden-Rossendorf (HZDR), set up to provide bremsstrahlung photons in very short pulses, a constant fraction algorithm for the incoming digital signals was evaluated, which is for optimizing the time resolution. Studies of scattering experiments with different thin targets and detector positions are accomplished at Oncoray Dresden, where a clinical proton beam is available. These experiments allow a basic characterization of the proton bunch structure and the detected yield.

In proton therapy, high dose conformality and the finite range of the projectiles are exploited to reduce the dosage to healthy tissue while increasing the dose inside the tumor volume compared to conventional radiotherapy. However, those benefits can be diminished by range uncertainties. An online range verification and in-vivo dosimetry is therefore highly desired. The prompt gamma ray timing (PGT) method utilizes the detection time of high energetic photons emitted during treatment. The time distribution of the gamma rays contains essential information about the range of the protons. However, PGT spectra are smeared by the time spread of the proton bunches. Knowledge about this time spread would help to disentangle the PGT data and to give better input parameters to simulation procedures. At the UniversitaetsProtonenTherapieDresden (Dresden, Germany), a dedicated experiment was realized to measure the time spread of a clinical proton pencil beam created by a Cyclone 230 fixed energy cyclotron from Ion Beam Applications. Two phoswich detectors each made out of plastic scintillator and BGO were placed under 90 degrees to detect coincident protons originating from elastic pp-scattering at a thin slice of PMMA. The time spread was measured for incident proton energies between 70 MeV and 225 MeV as well as for several positions of the momentum limiting slits of the energy selection system. Additionally, the absolute transmission of protons from point of extraction to beam exit was determined. Summarizing, the measured data will help to create reasonable range verification procedures using the PGT method in clinical routine.

Die Erfindung betrifft Verfahren und Einrichtungen zur Kontrolle der Reichweite einer Partikelstrahlung in der Strahlentherapie über die Messung prompter Gammastrahlung mit wenigstens einem einzelne Gammaquanten nachweisenden Detektor und mindestens einem Analysator, die sich insbesondere durch ihre einfache und robuste Realisierung sowie eine durch stark reduzierte Messzeit auszeichnen, die eine Reichweitekontrolle in Echtzeit erlaubt. Dazu werden mit Hilfe des Detektors und des Analysators unter Verwendung eines Referenzsignals der Bestrahlungseinrichtung oder eines separaten Partikeldetektors Zeitverteilungen gemessen, die statistische Verteilungen der Flugzeiten von Therapiepartikeln bis zur Emission eines prompten Gammaquants, ergänzt um die Flugzeit des entsprechenden Gammaquants zum Detektor, widerspiegeln. Informationen über die Reichweite der Therapiepartikel werden im Wesentlichen aus diesen Zeitverteilungen abgeleitet.

Offenbart wird die Kontaktierung eines quaderförmigen CZT-Kristalls zur Detektierung von Gammastrahlung in einer Compton-Kamera, wobei der CZT-Kristall eine der einfallenden Strahlung zugewandte, vollflächige Vorderseitenelektrode und auf der der Vorderseite gegenüberliegenden Rückseite mehrere, voneinander beabstandete rechteckige und als Elektroden ausgeführte Pixelflächen aufweist, wobei die zu den Pixelflächen komplementären Anschlussflächen eines oder mehrerer Flachbandkabel mit diesen Pixelflächen elektrisch leitfähig mittels eines leitfähigen Klebstoffs verbunden sind.

The characteristic dose profile of accelerated ions has opened up new horizons in the context of cancer treatment. However, particle range uncertainties strongly constrain the potential of ion beam therapy. Despite of worldwide efforts, a detector system for range and dose delivery assessment in real-time is not yet available for clinical routine. Complementary to the active- and passively collimated prompt gamma ray imaging systems for range assessment under development in several research centers, the prompt gamma ray timing method has been recently proposed. Based on the measurable transit time of ions through matter, the emission times of prompt gamma rays encode essential information about the depth-dose profile. In a collaboration between OncoRay, Helmholtz-Zentrum Dresden-Rossendorf and IBA, the prompt gamma ray timing method was tested for the first time at a clinical proton accelerator (Westdeutsches Protonentherapiezentrum Essen) with different phantoms. Several fast scintillation detectors were used to acquire prompt gamma ray timing distributions at various geometries and proton energies. From the resulting distributions, particle range differences of around 5 millimeters in heterogeneous phantoms were observed. In conclusion, we proved the feasibility of the prompt gamma ray timing method for range verification in a clinical radiation environment and realistic phantoms, which reassures this novel approach as a promising alternative in the field of prompt gamma based in vivo dosimetry.

kein Abstract verfügbar.

Proton therapy is, due to the well defined penetration depth, advantageous compared to classical radiation therapy in oncology. But range uncertainties can arise easily and have to be corrected for, preferably immediately during irradiation. Prompt gammas are a good means of instantaneous determination of the dose deposition. Detection systems have to cope with the high counting rates, energy region of up to several MeV and increased background due to secondary emissions, while providing reliable information on energy, timing and location of the detected gamma ray. Various concepts utilize these prompt gammas for dose verification like collimated systems, Compton cameras or prompt gamma timing. The digital silicon photomultiplier (dSiPM), as a favorable alternative to PMTs because of good timing performances and no requirement of further electronics, has been modelled in order to understand the complex behavior when working with monolithic scintillation crystals. Especially, the selection of trigger- and validation-parameters may lead to different spectrum shapes. This model will be helpful for finding best parameter settings for the required task, because it determines the photons lost in various processes, the trigger timing information and the spatial map. Comparison of modelled spectra and measured spectra are presented.

Characterization of Scintillators with respect to their Application in Prompt Gamma Imaging Systems.

The proton therapy in oncology requires instantaneous and reliable particle range verification, which can be done using prompt gamma emissions. The characteristic requirements of prompt gamma detection include the energy range of up to several MeV, increased background due to secondary emissions and high counting rates. Different concepts make use of these prompt gammas for dose verification like collimated systems or Compton cameras. Additionally to prompt gamma imaging, the prompt gamma timing method has been proposed, utilizing the proton time-of-flight inside the body. Those approaches imply different needs on energy-, spatial- or timing-resolution of the detection system. Various scintillator materials with multiple shapes have been characterized with respect to those requirements using classical photomultiplier tubes (PMT) and different experimental setups and locations. The light output, non-linearity and energy resolution were measured using gamma sources. The timing was characterized at the ELBE facility at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), using the bremsstrahlung beam with photons up to 12.5 MeV. Planned measurements at the 3 MV Tandetron accelerator at HZDR will provide information at the energy resolution at therapy relevant energies of 4.4 MeV.

The characteristic dose profile of accelerated ions has opened up new horizons in the context of cancer treatment. However, particle range uncertainties strongly constrain the potentialities of ion beam therapy. Despite of worldwide efforts, a detector system for range and dose delivery assessment in real-time is not yet available for clinical routine. Complementary to the active- and passively collimated prompt gamma ray imaging systems for range assessment, the prompt gamma ray timing method has been recently proposed and tested at a research accelerator. Based on the measurable transit time of ions through matter, the emission times of prompt gamma rays encode essential information about the depth-dose profile. In a collaboration between OncoRay, Helmholtz-Zentrum Dresden-Rossendorf and IBA, the prompt gamma ray timing method was tested for the first time at a clinical proton accelerator (Westdeutsches Protonentherapiezentrum Essen) with different phantoms. Several fast scintillation detectors were used to acquire prompt gamma ray timing distributions at various geometries and proton energies. From the resulting distributions, particle range differences of around 5 millimetres in heterogeneous phantoms were observed by simple qualitative inspection. In conclusion, our preliminary analysis points out that the prompt gamma ray timing method for range verification is feasible in a clinical radiation environment and realistic phantoms, which reassures this novel approach as a promising alternative in the field of prompt gamma based in vivo dosimetry.

We present a novel approach for real time range verification in particle therapy based on prompt gamma ray timing (PGT) spectroscopy. The measurement approach relies on the fact that high-energy particles need, dependent on their range, a varying transit time through the irradiated material. This transit time is about 1-2 ns in the case of protons with a range of 5-20 cm. Timing spectroscopy of promptly emitted gamma rays, measured with an arrangement resembling a typical time-of-flight (TOF) setup, encode these transit times and thus give a real time access to the particle range. We show that statistical momenta of PGT distributions such as the center of gravity and the variance incorporate the information on the particle range with a millimeter precision, although measurement uncertainties may cover the described effect at first sight. Typical uncertainties are limited by the detector time resolution and the particle bunch spread, and are finally determined by the spectrum stability. In contrast to other prompt gamma imaging techniques, the PGT method is based on straight timing spectroscopy with a single scintillation detector. Therefore, neither passive nor electronic collimation is required. The proposed idea is verified by an analysis of experimental data taken during proton irradiation experiments at the AGOR facility at KVI-CART in Groningen (The Netherlands). The measurement results are in excellent agreement with Monte Carlo based modeling of the experimental setup. We conclude that precise range assessment is feasible within a few seconds of irradiation due to the direct measurement method.

Proton and ion beams open up new vistas for the curative treatment of tumors, but adequate technologies for monitoring the compliance of dose delivery with treatment plans in real time are still missing. Range assessment, meaning the monitoring of therapy-particle ranges in tissue during dose delivery (treatment), is a continuous challenge considered a key for tapping the full potential of particle therapies. In this context the paper introduces an unconventional concept of range assessment by prompt-gamma timing (PGT), which is based on an elementary physical effect not considered so far: therapy particles penetrating tissue move very fast, but still need a finite transit time—about 1–2 ns in case of protons with a 5–20 cm range—from entering the patient’s body until stopping in the target volume. The transit time increases with the particle range. This causes measurable effects in PGT spectra, usable for range verification. The concept was verified by proton irradiation experiments at the AGOR cyclotron, KVICART, University of Groningen. Based on the presented kinematical relations, we describe model calculations that very precisely reproduce the experimental results. As the clinical treatment conditions entail measurement constraints (e.g. limited treatment time), we propose a setup, based on clinical irradiation conditions, capable of determining proton range deviations within a few seconds of irradiation, thus allowing for a fast safety survey. Range variations of 2 mm are expected to be clearly detectable.

In the context of ion beam therapy, particle range verification is a major challenge for the quality assurance of the treatment. One approach is the measurement of the prompt gamma rays resulting from the tissue irradiation. A Compton camera based on several position sensitive gamma ray detectors, together with an imaging algorithm, is expected to reconstruct the prompt gamma ray emission density map, which is correlated with the dose distribution. At OncoRay and Helmholtz-Zentrum Dresden-Rossendorf (HZDR), a Compton camera setup is being developed consisting of two scatter planes: two CdZnTe (CZT) cross strip detectors, and an absorber consisting of one Lu2SiO5 (LSO) block detector. The data acquisition is based on VME electronics and handled by software developed on the ROOT framework. The setup has been tested at the linear electron accelerator ELBE at HZDR, which is used in this experiment to produce bunched bremsstrahlung photons with up to 12.5 MeV energy and a repetition rate of 13 MHz. Their spectrum has similarities with the shape expected from prompt gamma rays in the clinical environment, and the flux is also bunched with the accelerator frequency. The charge sharing effect of the CZT detector is studied qualitatively for different energy ranges. The LSO detector pixel discrimination resolution is analyzed and it shows a trend to improve for high energy depositions. The time correlation between the pulsed prompt photons and the measured detector signals, to be used for background suppression, exhibits a time resolution of 3 ns FWHM for the CZT detector and of 2 ns for the LSO detector. A time walk correction and pixel-wise calibration is applied for the LSO detector, whose resolution improves up to 630 ps. In conclusion, the detector setup is suitable for time-resolved background suppression in pulsed clinical particle accelerators. Ongoing tasks are the quantitative comparison with simulations and the test of imaging algorithms. Experiments at proton accelerators have also been performed and are currently under analysis.

To test the validity and reliability of a new tool for assessing residents' competence in ophthalmic surgery. Changing paradigms of ophthalmic education in the United States have influenced worldwide ophthalmic education and necessitated new methods of assessing resident competence. Accordingly, a new tool for assessing residents' competence in ophthalmic surgery (phacoemulsification) that could be applicable internationally was developed. We hypothesize that this instrument is valid and reliable.A panel of six international content experts adapted a previously published tool for assessing phacoemulsification. The tool (called the International Council of Ophthalmology's Ophthalmology Surgical Competency Assessment Rubric, or ICO-OSCAR:phaco) was reviewed by 12 international content experts for their constructive comments, which were incorporated to ensure content validity. Ten expert cataract surgery teachers then graded six recorded phacoemulsification surgeries with the ICO-OSCAR:phaco to investigate inter-rater reliability.The coefficient alpha statistic (a measure of reliability/internal consistency) for the ICO-OSCAR:phaco as a whole was 0.92, and 17 of its 20 dimensions had alpha coefficients greater than 0.70.The ICO-OSCAR:phaco is a valid and reliable assessment tool that could be applied internationally to satisfy the global need of new instruments to comply with emerging trends in ophthalmic education. A toolbox of similar surgical competency assessment tools is being developed.

International audience; The ENVISION-WP3 collaboration aims at designing and constructing innovative imaging devices able to control the Bragg peak position in vivo during ion therapy

Radiation therapy is an important treatment modality in cancer therapy. New radiation species, like protons and light ions have the potential to increase tumor conformality of irradiation and to decrease normal tissue dose. Such high precision radiotherapy treatment requires efficient quality assurance techniques. Therefore, a dose monitoring system is highly desirable. Between 1997 and 2008, the in-beam Positron Emission Tomography (PET) method was used at the GSI Helmholtzzentrum fr Schwerionenforschung, Darmstadt, Germany, for monitoring the dose delivered by 12C beams. The spatial distribution of positron emitters generated via nuclear interactions is measured during and shortly after the irradiation. By means of a comparison between measured and simulated activity distribution conclusions on the accuracy of the dose deposition can be drawn. Different modalities of PET, i.e. measuring during the irradiation versus taking data after the treatment have been compared. Recent investigation and limits of the PET method used for in-vivo dose monitoring at ion beams will be presented and discussed. Due to inherent physical restrictions of this method, a direct quantification of the delivered dose is not feasible. Therefore, another approach based on dose monitoring by detection of prompt gamma rays is currently under investigation. In contrast to PET this method relies on the detection of prompt gamma rays between 0 and 10 MeV emitted almost instantaneously during the therapeutic irradiation. To measure these photons a Compton camera design was evaluated with respect to the special requirements and conditions that arise from this application. Different concepts were compared by means of simulation. The complete chain from simulation based on the treatment plan to the iterative reconstruction of the data was developed and is now under optimization. First measurements have been successfully performed with radioactive sources and ion beams.

Therapeutic irradiation with ions and protons is superior to a treatment with gammas with respect to tumour conformity of dose and damage of normal tissue. On the other hand, mispositioning of the patient or density changes in the treated volume may easily compromise the success of treatment. For this reason, non-invasive, in-situ dose verification is necessary. The only clinically proven method up to now is Positron Emission Tomography [Eng04]. This method does not allow direct dose quantification due to limited angle artefacts and washout in the patient. Another promising approach is in-beam SPECT: the detection of prompt gamma-rays following nuclear interaction between the ions and the atoms of the penetrated tissue. Detection systems based on Compton-scattering and pair-conversion are now under investigation. So far, Compton-cameras have been used for diagnostic imaging in nuclear medicine and astronomy. In telescopes also pair-creation cameras are established [Zog04]. In contrast to this, in-beam dose verification systems have to manage the specific energy range and low count rates due to the patient dose. A prototype of a Compton-camera is under construction at OncoRay [Kor10, Fie11, Kor11]. It consists of a scatter layer made from CZT and an absorption layer (LSO). From the energy deposited in the detector planes a cone surface of all possible directions of the incident photon can be reconstructed [Sch11]. The expected energy distribution of the prompt gammas is calculated by means of simulations based on treatment plan data [Fie11]. To optimize the setup simulations are required. Therefore, the Monte-Carlo framework GEANT4 is used for: (1) Analysis of the efficiency in dependence of the geometry; (2) Study of background caused by backscattered photons and other secondary particles; (3) Development of filters for event selection; (4) Study parameters influencing the spatial resolution of the reconstructed image (multiple Compton-scattering inside a detector layer, escape of energy, intrinsic radioactivity of the detector material, Doppler-broadening); (5) Creation of test data sets as input for the reconstruction. For photon energies above 7 MeV the pair production is the dominant electromagnetic process in CZT. To use these events the Compton-camera might be combined with a pair-conversion camera by adding thin silicon layers in between to track the path of the electron and the positron produced during pair conversion. Exploiting this information the direction of the incident photon can be deduced. Unfortunately, the angular resolution is heavily degraded especially for photons with rather low incident energies by small-angle scattering of the secondary particles and by the recoil of the nuclei when a pair production takes place [Gol11]. Both effects were studied whereas the latter is not included in the GEANT4 code version 9.3. This simulation serves as basis for the development of an iterative reconstruction algorithm dedicated to in-beam SPECT with a pair production camera. Apart from the analysis of efficiency, angular resolution and noise, the combination of a pair production and a Compton-camera is a challenging task. Results on simulations for optimizing the setup and the refinement of the reconstruction algorithm for a clinical dose verification system will be presented. [Eng04] W. Enghardt et al., Nucl. Instr. and Meth. A 525 (2004) [Fie11] F. Fiedler et al., Nucl. Sci. Symp. IEEE (2011), accepted [Gol11] C. Golnik et al., Nucl. Sci. Symp. IEEE (2011), accepted [Kor10] T. Kormoll et al., Nucl. Instr. and Meth. A (2010) [Kor11] T. Kormoll et al., Nucl. Sci. Symp. IEEE (2011), accepted [Ric10] M.-H. Richard et al., IEEE Transactions on Nuclear Science (2010) [Sch11] S. Schöne et al., Proc. Fully 3D Meeting (2011) [Zog04] A. Zoglauer et al., Nucl. Sci. Symp. Conf. Rec. IEEE (2004)