4D-treatment with patches and rescanning in proton therapy

The aim of this study, carried out at the Center for Proton Therapy of the Paul Scherrer Institute (Villigen, Switzerland), involves the verification of the possibility of 4D treatments on patients requesting a patch field. This technique is used when the dimensions of the area to be irradiated are greater than 12 cm for the T direction and 20 cm for the U direction. We also went to research the setup that provides a better dose homogeneity, in order to mitigate the tumor's motion during the treatment. Three clinical cases were studied with the motions obtained from the respective 4DCT. Moreover, one of these was analyzed again simulating a motion extrapolated from a 4D-MRI. All 4 cases were analyzed in 9 combinations, 3 possible rescan scenarios (1, 4 and 8 rescan) and 3 different overlapping setups between the two patches (0, 1 and 2 cm of overlap). The values obtained were compared to the 3D plan. The dose homogeneity measures (D5-D95 and V95) showed that in the case of a slight motion (under 2 mm) there was no need to intervene with motion mitigation. For the motions classified of medium intensity (2-10 mm), it was found the need to introduce motion mitigation. In none of the previous cases, a systematic benefit emerged with a certain pattern of patch overlap. It was not possible to fully evaluate the last case, having a large motion (about 20 mm), as it needed an IMPT plan (technique not yet developed for the 4D), but still indications, regarding the benefit of the use of 8 rescan and greater possible overlap, emerged. The experimental measurements obtained at Gantry 2 with the use of a 2D detector (Octavius 1500 XDR), a gating system and a Quasar motion platform, confirmed that there are no problems with the actual dose release. The homogeneity of the dose is also found when there are extreme conditions, such as 2 cm overlap, 8 rescan and 4 patches (for a 4 cm zone receiving 32 rescan) and a strong simulated motion

The FOOT experiment: the associated physics and its acquisition system

According to the World Health Organization (WHO) about 8.8 million of deaths in 2015 were caused by cancer. The treatments for cancer are several: beyond the traditional surgery, chemiotherapy and radiotherapy, also hadrontherapy is developing. The hadrontherapy cures the cancer with ion or proton beams. Every tumor type requires a specific treatment plan called Treatment Planning System (TPS), that it is not complete for hadrontherapy because there is the need of knowing the dose deposition both due to the beam particle ionization and the fragmentation. In this context, the FOOT experiment aims at collecting measurements and data about target or projectile fragmentation cross sections since currently the experimental panorama is rather scarse on the measurements of fragments produced in the interaction of protons or ions with tissue nuclei at the hadrontherapy energies (about 250 MeV for protons and 350 MeV/n for carbon ions). At the moment, the FOOT experiment is at its start and so are the detectors setup and the acquisition system projects. On these bases, this thesis work reports the scientific panorama, highlighting the need of covering the measurement lacks. Moreover, a preliminary example of DAQ system is described with a connected online monitoring system to test the DAQ boards

High Spatial Resolution Silicon Detectors for Independent Quality Assurance in Motion Adaptive Radiotherapy and Charged Particle Radiotherapy Energy Verification

Accurate empirical modelling of the treatment beam is necessary to ensure accurate delivery of dose to the intended target site. Dose calculations within the treatment planning system (TPS) for Stereotactic Radiosurgery (SRS) and Stereotactic Radiotherapy (SRT) treatment rely upon accurate beam data. Inaccuracies within the empirical measurements will propagate as errors throughout calculated patient dose distributions (Tyler, 2013). The necessary empirical measurements for beam commissioning include: percentage depth dose (PDD), output factor (OF) and beam profiles. Thus, especially for the consideration of the afore mentioned small radiation fields, it is important to ensure the most appropriate detector is chosen to conduct measurements of the treatment beams to achieve the highest possible accuracy in measurement of beam parameters. Stereotactic Body Radiation Therapy (SBRT) requires precise delineation of the target using modern imaging modalities (MRI, CT etc.), accurate dosimetry to ensure the planned dose is delivered correctly and effective patient immobilisation. For extracranial sites the treatment accuracy is affected by tumour delineation which identifies the extent of the tumour volume and tumour motion resulting from the physical, biological and physiological processes of the human body. Delivery of radiation using highly conformal and small radiation beams presents challenges for dosimetry and quality assurance (Heydarian, 1996), (Das, 2008). To correctly measure dose in a small field an ideal dosimeter must exhibit properties including: small sensitive volume, near water equivalence, minimal beam perturbation and no dose-rate, energy or directional dependence (Pappas, 2008). Also, treatment planning for dose calculation must be conducted using algorithms which can account for the impact of the heterogeneities found in the abdomen and thoracic cavities to ensure calculation of the dose to tissue in regions with complex scattering conditions is accurate (Rubio, 2013)

Automation of the Monte Carlo simulation of medical linear accelerators

La consulta íntegra de la tesi, inclosos els articles no comunicats públicament per drets d'autor, es pot realitzar prèvia petició a l'Arxiu de la UPCThe main result of this thesis is a software system, called PRIMO, which simulates clinical linear accelerators and the subsequent dose distributions using the Monte Carlo method. PRIMO has the following features: (i) it is self- contained, that is, it does not require additional software libraries or coding; (ii) it includes a geometry library with most Varian and Elekta linacs; (iii) it is based on the general-purpose Monte Carlo code PENELOPE; (iv) it provides a suite of variance-reduction techniques and distributed parallel computing to enhance the simulation efficiency; (v) it is graphical user interfaced; and (vi) it is freely distributed through the website http://www.primoproject.net In order to endow PRIMO with these features the following tasks were conducted: - PRIMO was conceived with a layered structure. The topmost layer, named the GLASS, was developed in this thesis. The GLASS implements the GUI, drives all the functions of the system and performs the analysis of results. Lower layers generate geometry files, provide input data and execute the Monte Carlo simulation. - The geometry of Elekta linacs from series SU and MLCi were coded in the PRIMO system. - A geometrical model of the Varian True Beam linear accelerator was developed and validated. This model was created to surmount the limitations of the Varian distributed phase-space files and the absence of released information about the actual geometry of that machine. This geometry model was incorporated into PRIMO. - Two new variance-reduction techniques, named splitting roulette and selective splitting, were developed and validated. In a test made with an Elekta linac it was found that when both techniques are used in conjunction the simulation efficiency improves by a factor of up to 45. - A method to automatically distribute the simulation among the available CPU cores of a computer was implemented. The following investigations were done using PRIMO as a research tool : - The configu ration of the condensed history transport algorithm for charged particles in PENELOPE was optimized for linac simulation. Dose distributions in the patient were found to be particularly sensitive to the values of the transport parameters in the linac target. Use of inadequate values of these parameters may lead to an incorrect determination of the initial beam configuration or to biased dose distributions. - PRIMO was used to simulate phase-space files distributed by Varian for the True Beam linac. The results were compared with experimental data provided by five European radiotherapycenters. It was concluded thatthe latent variance and the accuracy of the phase-space files were adequate for the routine clinical practice. However, for research purposes where low statistical uncertainties are required the phase-space files are not large enough. To the best of our knowledge PRIMO is the only fully Monte Carlo-based linac and dose simulation system , addressed to research and dose verification, that does not require coding tasks from end users and is publicly available.El principal resultado de esta tesis es un sistema informático llamado PRIMO el cual simula aceleradores lineales médicos y las subsecuentes distribuciones de dosis empleando el método de Monte Carlo. PRIMO tiene las siguiente características: (i) es auto contenido, o sea no requiere de librerías de código ni de programación adicional ; (ii) incluye las geometrías de los principales modelos de aceleradores Varían y Elekta; (iii) está basado en el código Monte Carlo de propósitos generales PENELOPE; (iv) contiene un conjunto de técnicas de reducción de varianza y computación paralela distribuida para mejorar la eficiencia de simulación; (v) tiene una interfaz gráfica de usuario; y (vi) se distribuye gratis en el sitio web http://vvww.primoproject.net. Para dotar a PRIMO de esas características, se realizaron las tareas siguientes: - PRIMO se concibió con una estructura de capas. La capa superior, nombrada GLASS, fue desarrollada en esta tesis. GLASS implementa la interfazgráfica de usuario, controla todas las funciones del sistema y realiza el análisis de resultados. Las capas inferiores generan los archivos de geometría y otros datos de entrada y ejecutan la simulación Monte Carlo. - Se codificó en el sistema PRIMO la geometría de los aceleradores Elekta de las series SLi y MLC. - Se desarrolló y validó un modelo geométrico del acelerador TrueBeam de Varian. Este modelo fue creado para superar las limitaciones de los archivos de espacio de fase distribuidos por Varian, así como la ausencia de información sobre la geometría real de esta máquina. Este modelo geométrico fue incorporado en PRIMO. - Fueron desarrolladas y validadas dos nuevas técnicas de reducción de varianza nombradas splitting roulette y selective splitting. En pruebas hechas en un acelerador Elekta se encontró que cuando ambas técnicas se usan en combinación, la eficiencia de simulación mejora 45 veces. - Se implementó un método para distribuir la simulación entre los procesadores disponibles en un ordenador. Las siguientes investigaciones fueron realizadas usando PRIMO como herramienta: - Fue optimizada la configuración del algoritmo de PENELOPE para el transporte de partículas cargadas con historia condensada en la simulación del linac. Se encontró que las distribuciones de dosis en el paciente son particularmente sensibles a los valores de los parámetros de transporte usados para el target del linac. El uso de va lores inadecuados para esos parámetros puede conducir a una incorrecta determinación de la configuración del haz inicial o producir sesgos en las distribuciones de dosis. - Se utilizó PRIMO para simular archivos de espacios de fase distribuidos por Varian para el linac TrueBeam. Los resultados se compararon con datos experimentales aportados por cinco centros de radioterapia europeos. Se concluyó que la varianza latente y la exactitud de estos espacios de fase son adecuadas para la práctica clínica de rutina. Sin embargo estos espacios de fase no son suficientemente grandes para emplearse en investigaciones que requieren alcanzar una baja incertidumbre estadística. Hasta donde conocemos, PRIMO es el único sistema Monte Carlo que simula completamente el acelerador lineal y calcula la dosis absorbida, dirigido a la investigación y la verificación de dosis que no requiere del usuario tareas de codificación y está disponible públicamentePostprint (published version

Characterisation and evaluation of a novel transmission detector for intra-fraction monitoring of radiotherapy.

The goal of this thesis was to characterise a novel transmission detector in the context of signal prediction. This was to eliminate the need to collect a baseline signal for the device before treatment. This not only saves time, but, by independently generating the baseline signal, the process is less prone to missing errors. A simple analytical algorithm was designed and was found to be capable of detecting gross errors, however, it was shown not to be accurate enough to detect MLC position errors that could have a clinical effect on the delivery. MU check software was commissioned, however the fluence distribution it produced lacked the complexity for accurate signal prediction. A Monte Carlo model of a linac was built and validated then used to demonstrate that the detector could be modelled as two slabs of Perspex; the signal being proportional to the dose measured in the air between them. Two Monte Carlo models were then made using different systems, these were both evaluated by comparing predicted signals to measured signals for VMAT plans. Both models performed well and were capable of detecting leaf errors ~1mm; the merits of both are discussed with regard to error detection and ease of use

On the development of a novel detector for simultaneous imaging and dosimetry in radiotherapy

Radiotherapy uses x-ray beams to deliver prescribed radiation doses that conform to target anatomy and minimise exposure of healthy tissue. Accuracy of dose delivery is essential, thus verification of dose distributions in vivo is desirable to monitor treatments and prevent errors from compromising patient outcomes. Electronic portal imaging devices (EPIDs) are commonly used x-ray imagers, however their non water-equivalent response complicates use for dosimetry. In this thesis, a Monte Carlo (MC) model of a standard EPID was developed and extended to novel water-equivalent configurations based on prototypes in which the high atomic number components were replaced with an array of plastic scintillator fibres. The model verified that full simulation of optical transport is not necessary to predict the standard EPID dose response, which can be accurately quantified from energy deposited in the phosphor screen. By incorporating computed tomography images into the model, its capacity to predict portal dose images of humanoid anatomy was also demonstrated. The prototype EPID’s water-equivalent dose response was characterised experimentally and with the MC model. Despite exhibiting lower spatial resolution and contrast-to-noise ratio relative to the standard EPID, its image quality was sufficient to discern gross anatomical structures of an anthropomorphic phantom. Opportunities to improve imaging performance while maintaining a water-equivalent dose response were identified using the model. Longer fibres increased efficiency and use of an extra-mural absorber maximised spatial resolution. Optical coupling between the scintillator fibres and the imaging panel may further improve performance. This thesis demonstrates the feasibility of developing a next-generation EPID for simultaneous imaging and dosimetry in radiotherapy. Such a detector could monitor treatment deliveries in vivo and thereby facilitate adaptations to treatment plans in order to improve patient outcomes

On the development of a novel detector for simultaneous imaging and dosimetry in radiotherapy

Radiotherapy uses x-ray beams to deliver prescribed radiation doses that conform to target anatomy and minimise exposure of healthy tissue. Accuracy of dose delivery is essential, thus verification of dose distributions in vivo is desirable to monitor treatments and prevent errors from compromising patient outcomes. Electronic portal imaging devices (EPIDs) are commonly used x-ray imagers, however their non water-equivalent response complicates use for dosimetry. In this thesis, a Monte Carlo (MC) model of a standard EPID was developed and extended to novel water-equivalent configurations based on prototypes in which the high atomic number components were replaced with an array of plastic scintillator fibres. The model verified that full simulation of optical transport is not necessary to predict the standard EPID dose response, which can be accurately quantified from energy deposited in the phosphor screen. By incorporating computed tomography images into the model, its capacity to predict portal dose images of humanoid anatomy was also demonstrated. The prototype EPID’s water-equivalent dose response was characterised experimentally and with the MC model. Despite exhibiting lower spatial resolution and contrast-to-noise ratio relative to the standard EPID, its image quality was sufficient to discern gross anatomical structures of an anthropomorphic phantom. Opportunities to improve imaging performance while maintaining a water-equivalent dose response were identified using the model. Longer fibres increased efficiency and use of an extra-mural absorber maximised spatial resolution. Optical coupling between the scintillator fibres and the imaging panel may further improve performance. This thesis demonstrates the feasibility of developing a next-generation EPID for simultaneous imaging and dosimetry in radiotherapy. Such a detector could monitor treatment deliveries in vivo and thereby facilitate adaptations to treatment plans in order to improve patient outcomes

Monte Carlo Simulations of Chemical Vapour Deposition Diamond Detectors

Chemical Vapour Deposition (CVD) diamond detectors were modelled for dosimetry of radiotherapy beams. This was achieved by employing the EGSnrc Monte Carlo (MC) method to investigate certain properties of the detector, such as size, shape and electrode materials. Simulations were carried out for a broad 6 MV photon beam, and water phantoms with both uniform and non-uniform voxel dimensions. A number of critical MC parameters were investigated for the development of a model that can simulate very small voxels. For a given number of histories (100 million), combinations of the following parameters were analyzed: cross section data, boundary crossing algorithm and the HOWFARLESS option, with the rest of the transport parameters being kept at default values. The MC model obtained with the optimized parameters was successfully validated against published data for a 1.25 MeV photon beam and CVD diamond detector with silver/carbon/silver structure with thicknesses of 0.07/0.2/0.07 cm for the electrode/detector/electrode, respectively. The interface phenomena were investigated for a 6 MV beam by simulating different electrode materials: aluminium, silver, copper and gold for perpendicular and parallel detector orientation with regards to the beam. The smallest interface phenomena were observed for parallel detector orientation with electrodes made of the lowest atomic number material, which was aluminium. The simulated percentage depth dose and beam profiles were compared with experimental data. The best agreement between simulation and measurement was achieved for the detector in parallel orientation and aluminium electrodes, with differences of approximately 1%. In summary, investigations related to the CVD diamond detector modelling revealed that the EGSnrc MC code is suitable for simulation of small size detectors. The simulation results are in good agreement with experimental data and the model can now be used to assist with the design and construction of prototype diamond detectors for clinical dosimetry. Future work will include investigating the detector response for different energies, small field sizes, different orientations other than perpendicular and parallel to the beam, and the influence of each electrode on the absorbed dose

Application of Dynamic Monte Carlo Technique in Proton Beam Radiotherapy using Geant4 Simulation Toolkit

Monte Carlo method has been successfully applied in simulating the particles transport problems. Most of the Monte Carlo simulation tools are static and they can only be used to perform the static simulations for the problems with fixed physics and geometry settings. Proton therapy is a dynamic treatment technique in the clinical application. In this research, we developed a method to perform the dynamic Monte Carlo simulation of proton therapy using Geant4 simulation toolkit. A passive-scattering treatment nozzle equipped with a rotating range modulation wheel was modeled in this research. One important application of the Monte Carlo simulation is to predict the spatial dose distribution in the target geometry. For simplification, a mathematical model of a human body is usually used as the target, but only the average dose over the whole organ or tissue can be obtained rather than the accurate spatial dose distribution. In this research, we developed a method using MATLAB to convert the medical images of a patient from CT scanning into the patient voxel geometry. Hence, if the patient voxel geometry is used as the target in the Monte Carlo simulation, the accurate spatial dose distribution in the target can be obtained. A data analysis tool?root was used to score the simulation results during a Geant4 simulation and to analyze the data and plot results after simulation. Finally, we successfully obtained the accurate spatial dose distribution in part of a human body after treating a patient with prostate cancer using proton therapy