29 research outputs found
Reassessment of stopping power ratio uncertainties caused by mean excitation energies using a water‐based formalism
No full textPURPOSE: In proton therapy planning, the accuracy of the Stopping Power Ratios (SPR) calculated in the stoichiometric CT calibration is affected by, among others, uncertainties on the mean excitation energies (I-values) of human tissues and water. Traditionally, the contribution of these uncertainties on the SPR has been conservatively estimated of the order of 1% or more for a reference tissue of known composition. This study provides a methodology that enables a finer estimation of this uncertainty, eventually showing that the traditional estimates of the uncertainty are too conservative. METHODS: Since human tissues contain water, a correlation exists between the I-values of tissues and water. As the SPR is the ratio of the tissue stopping power to that of water, this correlation decreases the uncertainty of the SPR. Our formalism considers this by expressing the I-value of the tissue as a function of the water weight fraction and the I-value of water, while applying Bragg's additivity rule only to the nonaqueous mixture of the tissue. For 22 reference tissue compositions, the SPR uncertainty was estimated by randomly sampling Gaussian distributions, based on ICRU data, for the I-values of water and the nonaqueous mixture, as well as for the water weight fraction. RESULTS: The relative standard deviation of the SPR, estimated at 150 MeV, is in the range of 0.1%-0.3% for soft tissues with an average water weight percentage of at least 60%. For tissues with a low water content (e.g., adipose and bones), this uncertainty is in the range of 0.5%-0.7%. CONCLUSION: Uncertainties on the I-values of human tissues and water appear to have a significantly lower impact on the SPR uncertainty than traditionally expected. In the future, this may provide a rationale for using smaller distal and proximal margins on the target volume, provided that all other range uncertainty components are correctly estimated too.sponsorship: This work has been supported by a research grant from IBA S.A. (Belgium). Dr. Labarbe and Mr. Vander Stappen are employees of IBA S.A. (IBA S.A. (Belgium))status: Publishe
First acquisitions of realistic Proton Therapy treatments delivered on an anthropomorphic phantom with a prompt gamma camera
No full textProton Therapy treatments are affected by uncertainties on the penetration depth of the beam within the patient. For this reason, real-time range control is highly desirable to deliver safer treatments. Real-time range control can be performed by imaging prompt gammas emitted along the proton tracks in the patient. Our approach uses a knife-edge slit collimator to obtain a 1-dimensional projection of the beam path on a gamma camera. The energy spectrum of prompt gammas includes energy events up to 10 MeV and the event rate on a 500 cm3 scintillator is tens of MHz. Standard SPECT and PET modules are not suitable for the purpose and a dedicated gamma camera was designed. The camera features a 3 cm thick LYSO crystal segmented in two rows of 20 slabs with a width of 4 mm and a height of 10 cm. The crystal is coupled to arrays of Silicon Photomultipliers, read out by dedicated electronics boards to perform both spectra acquisition at low rates and photon counting at high rates for profile reconstruction. The prototype was aimed at reaching clinical requirements. The camera was tested in the Proton Therapy Center in Prague using an anthropomorphic phantom on which realistic treatment plans were delivered in pencil beam scanning mode. For each layer of the treatment, acquired profiles corresponding to the single spots were compared to simulated profiles and the shift was retrieved. The study demonstrated that the system is actually suitable for patient treatment monitoring
Prompt gamma imaging with a slit camera for real-time range control in proton therapy: Experimental validation up to 230 MeV with HICAM and development of a new prototype
No full textTreatments delivered by proton therapy are affected by uncertainties on the range of the beam within the patient. To reduce these margins and deliver safer treatments, different projects are currently investigating real-time range control by imaging prompt gammas emitted along the proton tracks in the patient. This study reports on the development and test of a prompt gamma camera using a slit collimator to obtain a 1-dimensional projection of the beam path on a scintillator detector. A first prototype slit camera using the HICAM gamma detector, originally developed for low-energy gamma-ray imaging in nuclear medicine and modified for this purpose, was tested successfully up to 230 MeV beam energy. Results now confirm the potential of this concept for real-time range monitoring with millimeter accuracy in pencil beam scanning mode for the whole range of clinical energies. With the experience gained, a new prototype is under study for clinical beam currents. In this work, we present both the profiles obtained at 230 MeV using HICAM and the description of the new gamma camera prototype design
PO-0914: Adjustment of CT calibration in presence of titanium implants by pencil beam proton radiography
No full text
Prompt gamma imaging of proton pencil beams at clinical dose rate
No full textIn this work, we present experimental results of a prompt gamma camera for real-time proton beam range verification. The detection system features a pixelated Cerium doped lutetium based scintillation crystal, coupled to Silicon PhotoMultiplier arrays, read out by dedicated electronics. The prompt gamma camera uses a knife-edge slit collimator to produce a 1D projection of the beam path in the target on the scintillation detector. We designed the detector to provide high counting statistics and high photo-detection efficiency for prompt gamma rays of several MeV. The slit design favours the counting statistics and could be advantageous in terms of simplicity, reduced cost and limited footprint. We present the description of the realized gamma camera, as well as the results of the characterization of the camera itself in terms of imaging performance. We also present the results of experiments in which a polymethyl methacrylate phantom was irradiated with proton pencil beams in a proton therapy center. A tungsten slit collimator was used and prompt gamma rays were acquired in the 3–6 MeV energy range. The acquisitions were performed with the beam operated at 100 MeV, 160 MeV and 230 MeV, with beam currents at the nozzle exit of several nA. Measured prompt gamma profiles are consistent with the simulations and we reached a precision (2σ) in shift retrieval of 4 mm with 0.5 × 108, 1.4 × 108 and 3.4 × 108 protons at 100, 160 and 230 MeV, respectively. We conclude that the acquisition of prompt gamma profiles for in vivo range verification of proton beam with the developed gamma camera and a slit collimator is feasible in clinical conditions. The compact design of the camera allows its integration in a proton therapy treatment room and further studies will be undertaken to validate the use of this detection system during treatment of real patients
Quality prediction of bakery products in the initial phase of process design
No full textThe development of food production processes is facilitated by tools which explore the interaction between process design, operation
conditions and product characteristics. In this work an approach how to set-up a simulation model is presented for the phenomena and
transformations which occur during baking and which fix the product quality. The simulation model has three consecutive parts: mass and heat
transport in the product, transformations concerning starch state transition and color, and the formation of quality attributes (color, softness,
crispness and staling). The model for mass and heat transfer is based on laws of conservation and expressed in partial differential equations for
spatial products. The starch state transition and color formation are a mixture of qualitative and quantitative information, while the product
quality model is mainly based on qualitative information. The model is applied to three bakery products: bread, biscuit and a cake-type. The
results show that the model estimates the product quality and its transformations as a function of dough composition, baking and storage
condition. The results fit well to observed changes of properties and product quality during baking
Diversity studies in the interaction between the anthracnose fungus Colletotrichum gloeosporioides and its host plant Stylosanthes spp. in Mexico
No full textPests and diseases are important constraints to production in both traditional and modern agricultural systems. It is widely accepted that crop diversity, mainly through use of resistance and tolerance genes, is an important asset in reducing the risk of crop losses related to pests and diseases. However, little is known about the effect of the natural pathogen diversity on the occurrence and severity of phytopathological infestations. This publication summarizes the results of the multidisciplinary project ‘Genetic diversity studies in the interaction between the anthracnose fungus Colletotrichum gloeosporioides and its host plant Stylosanthes spp.’ The legume Stylosanthes is an important forage crop worldwide and Colletotrichum gloeosporioides is its most important pathogen. This project was a multidisciplinary bi-national effort centred in Mexico, a centre of origin of the host plant, which focused on characterizing both the host plant and the pathogen using different characterization techniques, from macro-morphological through molecular. As anthracnosis is reducing Stylosanthes yields from Africa to Australia, an increased knowledge and understanding of the co-existence of crop and pathogen diversity will benefit stakeholders outside the study area as well. A team of international researchers undertook a coordinated effort to increase the inclusion of information on host and pathogen diversity in areas where the crop and its pathogen are native. The Unité de Phytopathologie de l’Université catholique de Louvain, Louvain-la-Neuve, Belgium (UCL) focused on the characterization of C. gloeosporioides and other Colletotrichum species associated with wild Stylosanthes species in Mexico, while Stylosanthes diversity and taxonomy were studied by the Laboratorio de Recursos Naturales, Unidad de Biología, Tecnología y Prototipos, Facultad de Estudios Superiores Iztacala de la Universidad Nacional Autónoma de México (UNAM) at the morphological level and by the Laboratory of Gene Technology, Katholieke Universiteit Leuven, Belgium (KUL) that studied the material at the molecular level. The Mexican partner, UNAM, was responsible for the collection of materials, both host plant and pathogen, while the Belgian partners, UCL and KUL, carried out the molecular analysis. This study is a clear example of how a collaborative, multidisciplinary effort, including the exchange of plant material, allows for the optimal use of existing synergies between different research centres, leading to a better understanding of a complex theme such as host-pathogen diversity. This will permit a better use of the crop’s genetic diversity, and the corresponding resistance genes available, as well as the application of better screening methods for pest or disease resistance, based on a more extensive pathogen diversity. Bioversity International, formerly known as IPGRI, and its Regional Office for the Americas in Cali, Colombia is honoured that it was allowed to coordinate this project
