A novel procedure to monitor multi-field hadrontherapy treatments with in-beam PET: proof of concept on PMMA phantoms (#2476)
V. Ferrero1, 2
1 University of Torino, Physics, Torino, Italy
Positron Emission Tomography (PET) monitoring in hadrontherapy is a reliable imaging technique for treatment quality assessment. Because of physiological washout effects and short isotope decay time, in-vivo monitoring is recommended. In December 2016, the INSIDE in-beam PET monitored the treatment of a patient for the first time at the synchrotron hadrontherapy facility in Pavia, Italy. Given the promising results, the scanner prototype will be upgraded so as to monitor a wider set of patients and their different beam fields. To this date, there are no relevant results about the monitoring of multiple beam fields, mainly because of washout and residual activity background from previous irradiations. In-beam monitoring minimizes physiological effects, and residual activity can be removed to a certain degree through data analysis, giving the opportunity to validate not just the first irradiation, but the treatment in its whole. A preliminary test on PMMA phantoms with a proton and carbon ion treatment plan comprising two beam fields each was carried out for this purpose. In both cases, the second beam field was discriminated from the first irradiation residual activity and compared to a prior image. Results demonstrated qualitative and quantitative agreement between the second field acquisition and the prior 3-dimensional activity distributions. This first attempt pose very promising prospects for multiple field in-vivo monitoring. The INSIDE in-beam PET will soon be tested on more patients to monitor and validate their whole treatment sessions.
Keywords: hadrontherapy, in-vivo imaging, in-beam PET, multi-field treatment plan
Dose Reconstruction from PET Images in Carbon Ion Therapy: A Deconvolution Approach Using an Evolutionary Algorithm (#2055)
T. Hofmann1, A. Fochi1, M. Pinto1, A. Mohammadi2, M. Nitta2, F. Nishikido2, Y. Iwao2, H. Tashima2, E. Yoshida2, M. Safavi-Naeini3, A. Chacon3, A. Rosenfeld3, T. Yamaya2, K. Parodi1
1 Ludwig-Maximilians-Universität München, Department for Medical Physics, Garching, Bavaria, Germany
Dose monitoring and range verification are important tools in carbon ion therapy. For their implementation, positron emission tomography (PET) can be used to image the β+-activation of tissue during treatment. Predictions of these β+-activity distributions are usually obtained from Monte Carlo simulations, which demands high computational time and thus limits the applicability of this technique in clinical scenario. Nevertheless, it is desirable to explore faster approaches able to give such a prediction, since only its comparison with the measured distributions allows a definite assessment of potential range deviations from the planned treatment.
For the first time, we present an approach to perform deconvolution from PET data in carbon ion therapy and reconstruct the dose. A filtering method is used to predict positron emitter profiles from dose profiles in short time. In order to reverse the convolution and estimate a dose distribution from a positron emitter distribution, we apply an evolutionary algorithm. Filters are obtained from either a library or are created in advance for a specific problem, assuming that a prediction of the positron emitter distribution is available. To perform the latter method and find the best filter for a specific problem, we use another evolutionary algorithm, hence optimizing the filter on-the-fly for the given treatment scheme. The application of our method is shown for dose and positron emitter distributions in homogeneous phantoms using simulated and newly measured online PET data. Carbon ion ranges can be predicted within 1.5 mm and the shape of the dose distribution is reconstructed with an overall promising agreement.
This work was supported by PROSALMU, the DFG Cluster of Excellence MAP, and the NIRS International Open Laboratory.
Keywords: Carbon Ion Therapy, Dose Monitoring, Range Verification, Nuclear Imaging (PET), Inverse Methods, Evolutionary Algorithm
Radioactive Primary Beams for Treatment Delivery in Heavy Ion Therapy (#2840)
A. Chacon1, 2, M. Safavi-Naeini1, 2, D. Bolst1, S. Guatelli1, A. Mohammadi3, T. Yamaya3, M. - C. Gregoire2, A. Rosenfeld1
1 University of Wollongong, Centre for Medical Radiation Physics, Wollongong, NSW, Australia
The use of in-beam positron emission tomography (PET) for quality assurance (QA) in heavy ion therapy is under development at several facilities. During 12C therapy, several positron-emitting radionuclide species are produced through fragmentation of the primary particle beam and target atoms. As these radio nuclei decay, the spatial distribution of the resulting positron-annihilation photons can be imaged using a PET scanner. A large number of these annihilation photons must be detected to obtain a sufficiently high quality PET image for QA. The use of positron-emitting radioactive nuclei for the heavy ion beam itself is expected to significantly increase the number of annihilation photons produced during the delivery of a therapeutic dose, with the majority surviving to decay via positron emission at their stopping point, corresponding to the location of the Bragg peak. In this study, we compare the positron yield profiles, resulting from positron-emitting radioactive ion beams versus non-radioactive ion beams, and evaluates the correlation between positron yield profile and the dose map while delivering the same biological effective dose to the treatment region. Monte Carlo simulations of heavy ion therapy using positron-emitting radioactive pencil beams were undertaken using Geant4 toolkit, estimating the spatio-temporal positron distribution using beams of 10C, 11C, 12C, 15O, 16O with a range of energies and phantoms.The radiobiological effectiveness (RBE10) of each beam was calculated for each phantom/energy using the modified microdosimetric kinetic model. The RBE10 of the radioactive ion beams was estimated to be within 4% of the corresponding non-radioactive ion beams for all energies and targets, indicating that the therapeutic efficacy of such beams is comparable to beams of the non-radioactive counterpart ion, while leading to a significant increase in the quantity of positron-emitting nuclei stopping in the vicinity of the target region.
Keywords: Heavy ion therapy, Positron emission tomography, in-beam quality assurance, Radioactive primary beam, Geant4 simulation
Range verification in proton therapy by prompt gamma-ray timing (PGT): Steps towards clinical implementation (#1876)
T. Werner1, 2, J. Berthold2, 3, W. Enghardt1, 2, F. Hueso Gonzalez1, 7, T. Kögler1, 2, J. Petzoldt2, 5, C. Richter1, 2, A. Rinscheid2, 4, K. Roemer8, K. Ruhnau6, J. Smeets5, J. Stein6, A. Straessner3, A. Wolf6, G. Pausch1, 2
1 Helmholtz-Zentrum Dresden - Rossendorf, Institute of Radiooncology, Dresden, Saxony, Germany
In-situ range verification of ion beams during dose delivery is a key for further improving the precision and reducing side effects of radiotherapy with particle beams. The detection and analysis of prompt gamma rays with respect to their emission points, emission time, and emission energy can provide corresponding means. Prompt gamma-ray imaging (PGI) has already been used for range verification in patient treatments with proton beams. The prompt gamma-ray timing (PGT) technique promises range verification at lower hardware expense with simpler detection systems superseding heavy collimators. After proving the principle, this technique is now being translated to the treatment room. The paper presents latest experimental results obtained with clinically applicable PGT hardware in irradiations of plexiglass targets in pencil beam scanning (PBS) mode with proton beams at clinical dose rates. The data were acquired with multiple PGT detection units while the distal layer of an artificial 1 Gy dose cube treatment plan was repeatedly delivered to a solid PMMA target that sometimes comprised a cylindrical air cavity of 5, 10, or 20 mm depth. The corresponding local range shifts were clearly detected and visualized by analyzing position or variance of the prompt gamma-ray timing peaks in PGT spectra assigned to the individual PBS spots. In this context, a major challenge concerning all prompt-gamma based techniques is examined and discussed: collecting the event statistics that is needed for range verification of single pencil beam spots at an accuracy level of a few millimeters.
Keywords: Particle therapy; proton therapy; treatment verification; range verification; prompt gamma rays; prompt gamma imaging; prompt gamma timing; gamma spectroscopy; throughput;
Improving MACACO, a Compton Telescope for Treatment Monitoring in Hadron Therapy (#3509)
J. Barrio1, A. Etxebeste1, L. Granado1, C. Lacasta1, E. Muñoz1, J. F. Oliver1, A. Ros1, C. Solaz1, G. Llosá1
1 IFIC (UV/CSIC), Valencia, Spain
The IRIS group of IFIC-Valencia has developed and fully characterized a first version of MACACO (Medical Applications CompAct Compton camera), a three-layer Compton telescope based on LaBr3 crystals and SiPMs. Laboratory and beam tests showed very promising results, demonstrating the feasibility of the proposed technology. The limitations of this first version of MACACO have been identified, being the energy resolution the most critical parameter in detector performance. For this reason, an improved version of the detectors employing the Hamamatsu MPPC array S13361-3050AE-08 has been assembled. The MPPC array consists of 64 (8x8) elements of 3 x 3 mm2, covering an area of 25.8 x 25.8 mm2. This new model provides higher photon detection efficiency, higher uniformity and lower noise, as well as a significant reduction of the dead space between SiPM elements with respect to the previous version employed. A full characterization of a detector mounted with a LaBr3 crystal has been carried out in order to maximize energy resolution. A complete study of the configuration parameters has been performed. The best energy resolution obtained is 5.9% FWHM at 511 keV. This value significantly improves the energy resolution obtained with the previous version of the detector. Coincidence tests have been carried out with new detectors placed in the first two planes of the telescope and operated in time coincidence. One and two point-like sources simultaneously and a 22Na array of 37 point-like sources separated 10 mm from one another have been imaged. Tests with the new detectors show results better than those obtained with the previous version of the system. In addition, alternatives to LaBr3 are being considered in order to explore more affordable scintillator crystals. In this sense, tests with CeBr3 crystals have been performed with the aim of comparing its performance with LaBr3 crystals and assess its suitability for the Compton telescope. Tests in beam are planned.
Keywords: hadron therapy, SiPM, LaBr3, CeBr3, continuous crystals, Compton telescope, Compton camera
Imaging of a monochromatic beam by measuring secondary electron bremsstrahlung for carbon-ion therapy (#1295)
M. Yamaguchi1, Y. Nagao1, K. Ando2, S. Yamamoto2, M. Sakai3, R. K. Parajuli3, K. Arakawa1, 3, N. Kawachi1
1 National Institutes for Quantum and Radiological Science and Technology (QST), Takasaki Advanced Radiation Research Institute, Quantum Beam Science Research Directorate, Takasaki, Gunma, Japan
A feasibility study on an imaging of a monochromatic carbon-ion beam for carbon-ion therapy using a pinhole camera for X-rays by measuring secondary electron bremsstrahlung (SEB) was performed by means of a Monte Carlo simulation and a beam-irradiation experiment. From the simulation, it was found that the trajectory of the carbon-ion beam having the injection energies of 290 MeV/u in a water phantom were clearly imaged by measuring the SEB having energies from 30 to 60 keV by the pinhole camera. The range position was found to be coincident with the position where the ratio of the count of SEB acquisition to the maximum count was 0.191. For the experimental result, we evaluated whether the expected range position coincide with the estimated range position where the ratio of the count to the maximum count coincided with the ratio 0.191, which was deduced from the simulation. As a result, the estimated range from the experimental result was 16.02 ± 0.14 cm and slightly shorter than the expected range, 16.46 cm.
Keywords: carbon-ion therapy, beam-trajectory imaging, range estimation, secondary electron bremsstrahlung, Monte Carlo simulation, pinhole camera