Dosimetric evidence confirms computational model for magnetic field induced dose distortions of therapeutic proton beams

Given the sensitivity of proton therapy to anatomical variations, this cancer treatment modality is expected to benefit greatly from integration with magnetic resonance (MR) imaging. One of the obstacles hindering such an integration are strong magnetic field induced dose distortions. These have been predicted in simulation studies, but no experimental validation has been performed so far. Here we show the first measurement of planar distributions of dose deposited by therapeutic proton pencil beams traversing a one-Tesla transversal magnetic field while depositing energy in a tissue-like phantom using film dosimetry. The lateral beam deflection ranges from one millimeter to one centimeter for 80 to 180 MeV beams. Simulated and measured deflection agree within one millimeter for all studied energies. These results proof that the magnetic field induced proton beam deflection is both measurable and accurately predictable. This demonstrates the feasibility of accurate dose measurement and hence validates dose predictions for the framework of MR-integrated proton therapy

An Underappreciated Radiation Hazard from High Voltage Electrodes in Vacuum

The use of high voltage (HV) electrodes in vacuum is commonplace in physics laboratories. In such systems, it has long been known that electron emission from an HV cathode can lead to bremsstrahlung X-rays; indeed, this is the basic principle behind the operation of standard X-ray sources. However, in laboratory setups where X-ray production is not the goal and no electron source is deliberately introduced, field-emitted electrons accelerated by HV can produce X-rays as an unintended hazardous byproduct. Both the level of hazard and the safe operating regimes for HV vacuum electrode systems are not widely appreciated, at least in university laboratories. A reinforced awareness of the radiation hazards associated with vacuum HV setups would be beneficial. We present a case study of a HV vacuum electrode device operated in a university atomic physics laboratory. We describe the characterisation of the observed X-ray radiation, its relation to the observed leakage current in the device, the steps taken to contain and mitigate the radiation hazard, and suggest safety guidelines.Comment: Submitted to Health Physic

MRI- γ Detector Hybrid System

The medical imaging field can be divided in 2 imaging modalities: those generating the imaging information from outside the body (basically all x-ray combinations) and ones sending the image information from inside the body (nuclear medicine, US and MRI). The advantage of the latest is that they are able to give functional information (better contrast), however they lack of image resolution compared with CT, for example. The combination of resolution and functional information can be found in hybrid equipment like PET/CT, widely extended commercially. Recent advances in MRI have achieved spatial resolution close those possible with CT, while maintaining superior contrast and functional information. This has promoted its use as hybrid technique, like PET/MR or SPECT/MR. The handicap of these equipment is the influence of the magnetic field, on the γ detection system, whose solution implies high cost and sophisticated electronics . In the current study, we propose the use of MR implementing a dosimetric gel to obtain the functional image. Then it is possible to adapt the γ detector to any clinical MRI. As a result, a low cost and versatil hybrid MRI-γ detector is presented.El campo de la imagen médica se puede dividir en 2 modalidades: las que generan información desde fuera del cuerpo (básicamente todas las combinaciones de rayos x) y los que envían la información de la imagen desde interior del cuerpo (medicina nuclear, US, PET y la RM). La ventaja de las últimas es que tienen la capacidad de ofrecer información funcional (mejor contraste), sin embargo; carecen de buena resolución de imagen en comparación con la CT, por ejemplo. La combinación de resolución e información funcional se puede encontrar en equipos híbridos como la PET/CT, ampliamente comercializado. Recientemente, el gran avance en RM ha sido lograr una resolución espacial cercana a la del CT, manteniendo el mejor contraste y la información funcional. Esto ha promovido su uso en equipos híbridos como la PET/MR o SPECT/MR. El mayor inconveniente de estos es la influencia del campo magnético en el sistema de detección γ , cuya solución implica altos costos y una electrónica sofisticada. En el presente estudio, se propone utilizar RM adaptando el uso de gel dosimétrico para la obtención de la imagen funcional. De esta manera es posible adaptar cada componente a un equipo de RM clínico como una alternativa versátil y de bajo costo para la obtención de imágenes con información anatómica y funcional.COLCIENCIASDesign and development of a low field MRI prototype for nuclear medicineDoctorad

The Interface and characterization of an LFESR spectrometer and preliminary study to detect ultrasound induced radicals by LFESR spectroscopy

A modular low frequency electron spin resonance (LFESR) spectrometer has been interfaced, characterized, and applied in a test to detect ultrasound-induced free radicals with low frequency ESR spectroscopy The modular system, which operates at -250 MHz, was interfaced with a 486DX2 66 MHz PC, using a multifunction PC compatible interface board to facilitate integrated software control of the modular components. The operating software was programmed in Microsoft Visual C++ to execute in the Windows operating environment. Computer control of the magnet was calibrated, using the 2,5-di-tert-butyl parabenzosemiquinone anion radical as a gfactor and hyperfine splitting standard. Preparation of the semiquinone standard from 2,5-di-tert-butylhydroquinone is described. The spectrometer was characterized, using an aqueous solution of potassium peroxylamine disulfonate [K2N0(S03)2], (Fremy\u27s salt) in 10% sodium hydroxide, as a spin standard. The optimized spectrometer was found to have a line width dependent detection limit of 4.52 x 10^21 spins T^-1 A study was carried out to test the ability of the LFESR spectrometer to detect free radicals spin trap adducts generated from the 20 kHz, 120 watt / cm sonication of aqueous solutions of the nitrone spin trap, 5, 5 -dimethyl- 1-pyroline Noxide, (DMPO). No radicals were detected in the tests. Fricke dosimetric solutions were used to confirm the generation of radicals. Attempts to measure the optical absorbance of DMPO-OH were unsuccessful in confirming the formation of DMPOOH radical adducts. Future variations of this study, utilizing integrated ultrasoundsample probe assemblies are suggested to achieve detectable steady state concentrations of DMPO-H and DMPO-OH spin trap adducts, since rapid decay of the adducts to undetectable concentrations by bimolecular and unimolecular processes seem to be the principle problem to deal with at the conclusion of the present study

Antenna Development for Radio Frequency Hyperthermia Applications

This thesis deals with the design steps, development and validation of an applicator for radio frequency hyperthermia cancer therapy. An applicator design to enhance targeted energy coupling is a key enabler for preferential temperature increments in tumour regions. A single-element, near-field approach requires a miniaturised solution, that addresses ergonomic needs and is tolerant to patient anatomy. The antenna war-field rriodality and the high-dielectric patient loading introduce significant analytical and computational resource challenges. The antenna input impedance has to be sufficiently insensitive to in-band resonant cletuning and the fields in the tissue can he targeted to selected areas in the patient. An introduction to the medical and biological background of hyperthermia is presented. The design requirements of antennas for medical and in particular for hyperthermia applications are highlighted. Starting from a conventional circular patch, the antenna evolved into a compact circular patch with a concentric annular ring and slotted groundplane, operating at the 434 MHz Industrial Scientific and Medical frequency band. Feed point location is optimized for an energy deposition pattern aligned with the antenna centre. The applicator is assessed with other published approaches and clinically used loop, dipole and square patch antennas. The antennas are evaluated for the unloaded condition and when loaded with a tri-layer body tissue numerical model. This model comprises skin, fat and transverse fiber of muscle of variable thicknesses to account for different body locations and patient. anatomy. A waterbolus containing de-ionized water is added at the skin interface for superficial tissue cooling aud antelina matching. The proposed applicator achieves a penetration depth that supersedes other approaches while remaining compact and an ergonomic fit to tumour areas on the body. To consider the inner and peripheral complex shapes of human bodies, the full human body numerical model developed by Remcom is used. This model was segmented from 1 mm step computed tomography (CT) and magnetic resonance imaging (MRI) cross-sections through and adult male and it comprises twenty-three tissue types with thermal and frequency-dependent dielectric properties. The applicator performance is evaluated at three anatomical body areas of the model to assess its suitability for treatment of tumours at different locations. These three anatomical regions present different aperture coupling and tissue composition. \u27Different conformal waterbolus and air gap thickness values are evaluated. The models used in this work are validated with measurements performed in a phantom containing a lossy liquid with dielectric properties representative of homogeneous human body tissue. The dosimetric assessment system (DASY) is used to evaluaxe the specific absorption rate (SAR) generated for the antenna into the liquid. The measurement setup with the antenna, phantom and liquid are simulated. Simulated and measured results in terrms of specific absorption rate and return loss are evaluated

Microwave dosimetry in biological exposure studies and in practical safety evaluations

This thesis considers the risk evaluation of microwaves from two important points of view. First, the methodology of the exposure studies elucidating the health effects of mobile phones is considered starting from the general aspects of designing setups and proceeding to the assessment of the exposure level (dosimetry) and practical execution of the experiments. Second, the exposure assessment in practical safety evaluations of fixed radio transmitters, such as mobile phone base stations, is studied. The dosimetry and the exposure setup design are critical for the success of exposure studies since the biological results are worthless if the used exposure level is not known. Furthermore, the experiments with test animals or human volunteers are always very challenging in practice. This work aimed to design, implement and analyse setups for four separate biological experiments. The first experiment related to a novel study of the effects of mobile phone (GSM) radiation in human skin in vivo. In the second experiment the brain functions of domestic pigs exposed to high level GSM type radiation were studied. The third setup was used for long term exposure of over 200 unrestrained rats. The rat setup was further utilised in another experiment searching the effects of microwave radiation on central nervous system of juvenile rats. The dosimetric analysis was performed by means of numerical simulations in all cases. The simulations were validated by measurements and the uncertainty of achieved results was analysed. The functionality of the setups was proven in practice; all experiments were successfully executed and the results of both methodological and biological studies were reported in peer reviewed journals. The need for microwave safety evaluations has increased quickly during the last decade. The number of base station (BS) antennas has increased rapidly and they are often placed on roof tops etc. where various professionals have to work. Hence, efficient methods for assessing the compliance with exposure limits are needed. The scope of the work, presented in this thesis, was to study the near field exposure caused by real commercial BS models. Experimental measurements were utilised to achieve a set of specific absorption rate (SAR) and electric field data in the near field of six commonly used antenna models. Moreover, one of the antennas was studied in more detail by numerical simulations. The results were further analysed to compare the different methods for checking the compliance of an antenna installation with the exposure limits and to find out how significant the local exposure is as compared to the whole body average at different distances. These results provide useful information for the future revisions of the exposure limits and related measurement standards

Establishment of the Physical and Technical Prerequisites for the Determination of the Relative Biological Effectiveness of Low-energy Monochromatic X-rays

A superconducting electron linear accelerator of high brilliance and low emittance (ELBE) is under operation at Forschungszentrum Rossendorf since January 2003. The first stage of ELBE is based on an electron energy of 20 MeV, whereas in the future a 40 MeV beam will be provided. The relativistic electron beam is used to drive various kinds of secondary radiation sources. Among all, X-rays in a wide energy range can be obtained. One method for production of intensive, quasi-monochromatic Xrays in the energy range 10 - 100 keV, tunable in photon energy, is by channeling of relativistic electrons in a perfect crystal. This unconventional photon source with variable time structure will be optimised and used for radiobiological studies. Its first test operation was in October 2003. This thesis is part of the first radiobiological project – the determination of relative biological effectiveness (RBE) of the X-rays in this energy range. The most important aspects of medical application of low-energy X-rays are imaging and radiation therapy, but they can also be helpful in the study of radiation effects in living matter. However, the RBE depends on the photon energy, dose range, cell line and biological endpoint. Up to now no definitive conclusions can be made about their biological effectiveness due to the large spread of the published data. Therefore, in order to precisely determine the RBE, studies have to be performed at an intensive, tunable photon source, for several practically relevant cell lines and biological endpoints. The possibility of using channeling radiation (CR) for medical applications has been widely discussed in the literature, but building and optimisation of a dedicated source is for the first time performed at the ELBE accelerator

Interaction of antenna systems with human body

The research investigates the influence on the human body on a communication system. To understand this, the effect of hands free kit (HFK) on energy absorption in the body was investigated when operating a smart phone at 2G. Findings on the research are given in the thesis report. Also, the influence of the way in which a phone is held on a phone s received power was investigated. The result was compared to that obtained using a hand phantom acquired from SPEAG. This was to check if the hand phantom best represents the human hand when using it in experiments. The setup for the experiment was in an anechoic chamber at Loughborough University. The mobile phone transmitted in the 2G system. In further experiments carried out on the body, two antennas were attached to the body in six different orientations to receive power from a source creating a Single Input Multiple Output (SIMO) system. The antennas used were monopoles mounted on a circular ground plane. These antennas were designed and constructed with the influence of the body taken into consideration. The use of diversity techniques to improve transmission to an on-body system is investigated with the antennas on the body. For each alignment, the transmission to the on-body was compared with the transmission to the corresponding off-body (free space). Experiments for this work were carried out in three environments

A Patch Antenna Design for Application in a Phased-Array Head and Neck Hyperthermia Applicator

In this paper, we describe a specifically designed patch antenna that can be used as the basis antenna element of a clinical phased-array head and neck hyperthermia applicator. Using electromagnetic simulations we optimized the dimensions of a probe-fed patch antenna design for operation at 433 MHz. By several optimization steps we could converge to a theoretical reflection of -38 dB and a bandwidth (-15 dB) of 20 MHz (4.6%). Theoretically, the electrical performance of the antenna was satisfactory over a temperature range of 15 C–35 C, and stable for patient-antenna distances to as low as 4 cm. In an experimental cylindrical setup using six elements of the final patch design, we measured the impedance characteristics of the antenna 1) to establish its performance in the applicator and 2) to validate the simulations. For this experimental setup we simulated and measured comparable values: -21 dB reflection at 433 MHz and a bandwidth of 18.5 MHz. On the basis of this study, we anticipate good central interference of the fields of multiple antennas and conclude that this patch antenna design is very suitable for the clinical antenna array. In future research we will verify the electrical performance in a prototype applicator