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The aim of this workshop is to provide a platform for young researchers working in the field of prompt gamma imaging in particle therapy.
It will be a workshop in the spirit of previous meetings of the Young Investigators' Workshops series.
We hope to bring together mainly Ph.D. students and post-docs, interested in meeting renowned experts in the field, engaging in open-minded discussions, international networking, and the exchange of novel ideas and concepts.
Hopefully, the established connections will result in better networking and synergy between different projects, boosting their progress.
We encourage the participants to contribute to the Research Topic Prompt Gamma Imaging in Particle Therapy, which will document the output of this conference and present other ongoing developments.
The workshop will be held online, using the MeetAnyway platform. Thanks to the support of the German company offering this product, we can use it free of charge.
Participation in the workshop is free of charge. Optional contribution to the Research Topic Prompt Gamma Imaging in Particle Therapy in Frontiers in Physics is a subject of APC, which may differ for different institutions. For details see Institutional Partnerships.
Particle beams show a unique physical characteristic known as the Bragg-peak, which enables conformal dose delivery to tumor with a lower entrance dose and zero exit dose. This property makes particle therapy highly effective, but accurate prediction of the Bragg-peak is one of the most important techniques to fully utilize the benefits of the expensive particle therapy. Various research has been carried out for the in-vivo dose verification in particle therapy. For this, direct and online measurement of the particle in the patient is essential, but the particle of charged for acceleration is stopped in the patient. The proposed method is to measure the prompt gammas (PG) or positron emission tomography (PET) which is generated by the particle induced nuclear reaction and emitted out of the patient. This study aims to introduce the PG and PET methods, that is, prompt gammas scanning system, in-room PET system, and integrated PG-PET system, carried out in Hanyang University, Mass. General Hospital, and Yonsei University, respectively.
Prompt gamma ray in proton therapy is the product of nuclear reaction between proton and target. The characteristic energies and intensities of prompt gamma lines can be used to determine the types of elements and their amounts in the target. In several previous experiments, it was demonstrated that no matter how complex the reaction cross-section is, once the energy of the incident proton and the irradiated element are determined, there is a definite linear relationship between the element concentration and the number of gamma-ray photons. However, this linear relationship is difficult to apply to medical imaging and the nonlinear behavior of hydrogen has not been investigated so far. In this paper, this linear relationship is extended to mixed elemental materials including nonlinear case such as hydrogen, and a universal mathematical form, which is referred to as the prompt gamma spectroscopy retrieval algorithm (PGSRA), is developed. The basic assumption of the PGSRA is that the PGS of the sample material has a relationship with the molar gamma lines of the elements. For carbon and oxygen, this relationship is linear, while for hydrogen, this relationship is nonlinear. As the 2.23 MeV gamma line originates from neutron absorption radiation, the behavior of hydrogen is carefully investigated. The linear and nonlinear relationships are verified using Monte Carlo simulations with different combinations of carbon, oxygen, and hydrogen, such as PMMA, pentanediol and ethanediol. The PGSRA developed in this work could be the first bridge between PGS and medical imaging.
This work introduces a Positron Enhanced Prompt Gamma Imaging (PEPGI) technique to improve the image reconstruction from a CdZnTe Compton Camera for use in dose reconstruction during proton therapy. PEPGI uses coincidence 511 keV gamma rays emitted from a target to locate the proton beam line using a PEPT-style algorithm, which is then used to improve Compton Camera Prompt Gamma Imaging (PGI) through Distance of Closest Approach (DCA) filtering. This filter eliminates noisy data by removing reconstructed gamma ray events that do not originate close to the proton beam line. The proposed method consists of three CdZnTe detectors configured to combine a dual head Compton Camera with a face to face detector setup in order to detect back-to-back 511 keV gamma ray pairs produced during positron annihilation. In this study, Monte-Carlo simulations,using the Geant4 toolkit, were used to verify the PEPGI process for proton therapy scenarios, in preparation for forthcoming measurements. This method should make image reconstruction more efficient and will require less data to produce.
We are three months from the 20th anniversary of the pioneering proposal to use prompt-gamma (PG) radiation for particle therapy monitoring by Jongen and Stichelbaut at the 39th PTCOG conference. Considerable developments ensued, covering all aspects pertaining exploitation of prompt gammas, from fundamental research to clinical usage of prompt-gamma cameras. Monte Carlo (MC) tools are essential to such a development. This talk will give examples of the type of applications of MC tools in PG monitoring. First, the talk will provide an overview of the research assessing the accuracy of MC simulations for PG emission. This step in PG monitoring research has pitfalls, and the discussion will raise awareness of some of the issues. An overview of the usage of MC tools for PG camera optimization will follow. Finally, the talk will cover several developments in bringing PG monitoring into clinical applications and how MC tools are vital to such a path. These developments range from understanding how to utilize PG radiation in clinical scenarios, namely in adaptive radiation therapy, to creating PG prediction tools that can be integrated into clinical workflows.
The main advantage of proton therapy over conventional radiotherapy is the scheme of dose deposition: unlike X-rays, protons are fully stopped in patient’s tissues with a distinct maximum at the end of their range: the Bragg peak. Such a distribution allows for a precise coverage of a tumor volume while sparing the nearby healthy tissues. However, accurate control of the proton beam range is still considered a challenge. The SiFi-CC (SiPM and scintillation Fiber based Compton Camera) project aims to develop a method of in vivo proton range monitoring with the use of a Compton camera. Such a detector exploits the Compton effect and can register prompt gamma rays produced when protons interact with the nuclei of the tissues. We propose a design which is a trade-off between the camera performance and its cost, dependent on the number of channels. In our approach, both detector modules (scatterer and absorber) will consist of multiple layers of scintillation fibers with dual readout via silicon photomultipliers. The scintillation material and fiber coating were chosen based on an extensive study of the fiber properties. Our simulation studies have shown that such a solution is feasible and appropriate for online range monitoring in proton therapy. I am going to present the idea and overview of the SiFi-CC project and elaborate on the single module of a Compton camera that has recently been tested with a proton beam in Heidelberg Ion Beam Therapy Center. I will present a preliminary analysis of the data from these tests. I will also discuss preliminary results of a comparison of several data acquisition systems that we considered to use in the Compton camera detector.
Range uncertainty is a main limitation to fully exploiting the benefits of proton therapy. Its reduction will improve treatment effectiveness by increasing both dose conformality in the tumor and normal tissue sparing.
We present a proof of principle investigation of a range verification approach based on the detection of prompt gammas (PG), whose production is artificially enhanced with a non-radioactive element transported selectively to the tumor with a drug carrier. Nuclear interactions of this element with protons generate a signature PG spectrum, from which both the absolute proton range and the tumor position can be reconstructed by exploiting the existing PG Spectroscopy (PGS) methods.
Combining experimental data and calculations obtained both with TALYS and TOPAS Monte Carlo code, we selected three stable elements: 31-Phosporous ($^{31}$P), 63-Copper ($^{63}$Cu), and 89-Yttrium ($^{89}$Y). We measured signature PG energy lines emitted by solutions of water and the candidate materials (CuSO$_4$+H$_2$O, NaH$_2$PO$_4$+H$_2$O and Y(NO$_3$)$_3$+H$_2$O) when exposed to clinical proton beams. From measurements, we evaluated that, at a realistic element concentration in the tumor of 0.4 mM, 10$^9$ protons for an iso-energy slice, and an advanced detection system, the produced PG signature is large enough to be distinguished from the normal tissue background. In addition, using the $^{31}$P label, we experimentally proved that the proposed methodology predicts the absolute proton range with a 2 mm accuracy on a simplified patient geometry.
Range assessment is not the only feature of PGS. Paulo Martins et al. Sci Rep (2020) demonstrated that it is possible to determine the elemental composition of the target from the energies and intensities of the measured gamma lines. In this work, we studied with TOPAS MC the impact of tumor heterogeneity on element uptake ditribution in a real patient's geometry. By detecting the inter-fraction variations in element concentration, it could be possible to assess the biological response of the tumor to the radiation.
The presented approach can open a new avenue of improvement for monitoring the proton range and the tumor response at the same time.
Starting from a look back at the performance demonstrated by the first prompt gamma cameras, we propose to make one jump ahead of time and discuss the potential roles of prompt gamma imaging with the next generation proton therapy system. We will tentatively anticipate requirements, synergies, redundancies and/or incompatibilities with the other proton therapy features under research and/or development. Insights from the workshop participants are wished during the presentation.
The purpose of this talk is to review the development and use of Compton Imaging for the evaluation and verification of particle beams used for cancer treatment. First, the history of Compton Imaging and its initial applications in nuclear imaging and radiotherapy will be briefly reviewed. This will be followed by a discussion of applications of Compton cameras (CC) to image secondary prompt gammas (PG) emitted during particle therapy beam delivery for the purpose of verifying the position and range of the beam in vivo. This includes the capabilities for Compton cameras to produce 3-dimensional images and spectroscopic images of PGs emitted from elements of interest (e.g. oxygen) in healthy tissues and tumors. Finally, the barriers to clinical application of CCs for range verification will be discussed, as well as new frontiers in CC research that have the potential to overcome these barriers. The overall goal for this talk is to provide the viewer with an understanding of how CC based PG imaging works, as well as an introduction of emerging areas of research into their application in the radiotherapy treatment process.
Linn Mielke$^{1}$, François Campioni$^{1}$, Michelle Dombeu$^{1}$, Alexander Fenger$^{1}$, Ronja Hetzel$^{1}$, Jonas Kasper$^{1}$, Magdalena Kołodziej$^{2}$, Magdalena Rafecas$^{3}$, Katarzyna Rusiecka$^{2}$, Achim Stahl$^{1}$, Vitalii Urbanevych$^{2}$, Mark Wong$^{2}$, Aleksandra Wrońska$^{2}$
The SiPM and scintillating Fiber based Compton Camera (SiFi-CC) project is a collaboration between the Jagiellonian University, University of Lübeck, and the RWTH Aachen University for online monitoring of proton therapy. The Compton camera detects prompt gamma radiation which originates from nuclear interactions of the protons. As the prompt gamma radiation impinges on the camera material, the hits are recorded and Compton hits identified. In this way, the origin of a single prompt gamma can be narrowed down to a cone surface. With enough of these cones, the Bragg peak position in the patient can be traced back and, if necessary, the beam can be adjusted. To this end, the collaboration not only needs to construct the Compton camera, but also plan out the analysis. A simulation of the Compton camera, which is currently under construction, is used to test out different scenarios and feed further analysis steps, such as neural networks. The simulation itself consists of multiple steps to mirror each part of the process and is based on the Geant4 framework as well as specialized code made by collaboration members for this use case. To ensure the simulation’s accuracy, it is validated against measurements and and adjusted to changes in the Compton camera design. All steps of the project are connected and will be covered in the presentation, with focus on the simulation.
$^{1}$ RWTH Aachen University
$^{2}$ Jagiellonian University, Kraków
$^{3}$ University of Lübeck
Among the various techniques that are being proposed for particle range monitoring, Prompt Gamma Timing (PGT) potentially offers considerable advantages.
In PGT, the existing correlation between the incident ion path and the overall ion-plus-PG Time-Of-Flight (TOF) can be exploited to simply measure the ion range, or to retrieve a spatial information on tissue heterogeneities within the patient. The detection principle is trivial, requiring lighter and more compact detectors than other techniques, as no collimation system is necessary. The consequent higher detection efficiency and limited neutron background typical of PGT-based systems are expected to favourably impact on the technique sensitivity.
However, numerous limitations/challenges still remain to be addressed to fully exploit PGT potential, some of which are inherent to the technique while others are currently being overcome by different research groups.
In this talk, I will give a review on TOF based PG detection: starting from the first proof of principle experiments, I will then present the efforts that are being made to improve the detection systems (in terms of time resolution, synchronisation, background rejection…) as well as the novel data reconstruction algorithms that are being proposed to increase the technique sensitivity.
Being a promising candidate for proton treatment verification, Prompt Gamma-ray Timing (PGT) currently undergoes translation into clinical application. Presently, PGT is being extensively investigated under preclinical conditions. For that, a realistic dosimetric head phantom is irradiated with clinically relevant treatment plans. Global and local range deviations are studied with eight 2-inch CeBr3 scintillators. Moreover, the PGT system’s behavior in ensuing conditions (extreme changes in the detector load between beam-on and beam-off phases, gain instabilities, time non-linearities, etc.) is being explored as to improve the system’s characteristics. The most recent results of the study will be presented, the main challenges of the PGT method will be addressed, and the future plans and prospects will be outlined.
The high sensitivity of proton therapy to anatomical deviations implies improved treatment outcomes are achievable with real-time range monitoring. To this end, the NOVO project was initiated with the goal of developing a multi-particle imaging system for proton therapy. In this work, we characterize a novel organic glass scintillator (OGS) and investigate its potential for such a system, where range monitoring will be based on the simultaneous imaging of both secondary prompt gamma-rays and fast neutrons produced in patient tissues during treatment. The neutron vs. gamma-ray pulse-shape discrimination (PSD), light output, and energy resolution of a 10 × 10 × 200 mm3 bar of OGS were evaluated using time-of-flight methods. Additional measurements with a 10×10×100 mm3
OGS bar and radioactive emitters were made to investigate the coincident time, depth-of-interaction reconstruction, and energy resolution of the detector. The tested samples exhibited PSD figure-of-merits > 1 above 250 keVee (corresponding to recoil protons > 550 keV). Additionally, above 400 keVee an energy resolution < 10 %, coincident time resolution < 500 ps, and a position resolution < 10 mm was achieved. This work demonstrates that OGS is a promising candidate for particle therapy range verification using both neutrons and gamma-rays.