Diversity studies in the interaction between the anthracnose fungus Colletotrichum gloeosporioides and its host plant Stylosanthes spp. in Mexico

Pests 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

Detection of mixed-range proton pencil beams with a prompt gamma slit camera

With increasing availability of proton and particle therapy centers for tumor treatment, the need for in vivo range verification methods comes more into the focus. Imaging of prompt gamma rays emitted during the treatment is one of the possibilities currently under investigation. A knife-edge shaped slit camera was recently proposed for this task and measurements proved the feasibility of range deviation detection in homogeneous and inhomogeneous targets. In the present paper, we concentrate on laterally inhomogeneous materials, which lead to range mixing situations when crossed by one pencil beam: different sections of the beam have different ranges. We chose exemplative cases from clinical irradiation and assembled idealized tissue equivalent targets. One-dimensional emission profiles were obtained by measuring the prompt gamma emission with the slit camera. It could be shown that the resulting range deviations can be detected by evaluation of the measured data with a previously developed range deviation detection algorithm. The retrieved value, however, strongly depends on the target composition, and is not necessarily in direct relation to the ranges of both parts of the beam. By combining the range deviation detection with an analysis of the slope of the distal edge of the measured prompt gamma profile, the origin of the detected range deviation, i.e. the mixed range of the beam, is also identified. It could be demonstrated that range mixed prompt gamma profiles exhibit less steep distal slopes than profiles from beams traversing laterally homogeneous material. For future application of the slit camera to patient irradiation with double scattered proton beams, situations similar to the range mixing cases are present and results could possibly apply

Measurement of prompt gamma profiles in inhomogeneous targets with a knife-edge slit camera during proton irradiation

Proton and ion beam therapies become increasingly relevant in radiation therapy. To fully exploit the potential of this irradiation technique and to achieve maximum target volume conformality, the verification of particle ranges is highly desirable. Many research activities focus on the measurement of the spatial distributions of prompt gamma rays emitted during irradiation. A passively collimating knife-edge slit camera is a promising option to perform such measurements. In former publications, the feasibility of accurate detection of proton range shifts in homogeneous targets could be shown with such a camera. We present slit camera measurements of prompt gamma depth profiles in inhomogeneous targets. From real treatment plans and their underlying CTs, representative beam paths are selected and assembled as one-dimensional inhomogeneous targets built from tissue equivalent materials. These phantoms have been irradiated with monoenergetic proton pencil beams. The accuracy of range deviation estimation as well as the detectability of range shifts is investigated in different scenarios. In most cases, range deviations can be detected within less than 2 mm. In close vicinity to low-density regions, range detection is challenging. In particular, a minimum beam penetration depth of 7 mm beyond a cavity is required for reliable detection of a cavity filling with the present setup. Dedicated data post-processing methods may be capable of overcoming this limitation

Prompt gamma imaging of proton pencil beams at clinical dose rate

In 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

Impact of machine log-files uncertainties on the quality assurance of proton pencil beam scanning treatment delivery

Irradiation log-files store useful information about the plan delivery, and together with independent Monte Carlo dose engine calculations can be used to reduce the time needed for patient-specific quality assurance (PSQA). Nonetheless, machine log-files carry an uncertainty associated to the measurement of the spot position and intensity that can influence the correct evaluation of the quality of the treatment delivery. This work addresses the problem of the inclusion of these uncertainties for the final verification of the treatment delivery. Dedicated measurements performed in an IBA Proteus Plus gantry with a pencil beam scanning (PBS) dedicated nozzle have been carried out to build a 'room-dependent' model of the spot position uncertainties. The model has been obtained through interpolation of the look-up tables describing the systematic and random uncertainties, and it has been tested for a clinical case of a brain cancer patient irradiated in a dry-run. The delivered dose has been compared with the planned dose with the inclusion of the errors obtained applying the model. Our results suggest that the accuracy of the treatment delivery is higher than the spot position uncertainties obtained from the log-file records. The comparison in terms of DVHs shows that the log-reconstructed dose is compatible with the planned dose within the 95% confidence interval obtained applying our model. The initial mean dose difference between the calculated dose to the patient based on the plan and recorded data is around 1%. The difference is essentially due to the log-file uncertainties and it can be removed with a correct treatment of these errors. In conclusion our new PSQA protocol allows for a fast verification of the dose delivered after every treatment fraction through the use of machine log-files and an independent Monte Carlo dose engine. Moreover, the inclusion of log-file uncertainties in the dose calculation allows for a correct evaluation of the quality of the treatment plan delivery.status: publishe

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

Treatments 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

First acquisitions of realistic Proton Therapy treatments delivered on an anthropomorphic phantom with a prompt gamma camera

Proton 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