Добірка наукової літератури з теми "Radiation dosimetry"

The use of thermoluminescence (TL) as a method for radiation dosimetry of ionizing radiation has been established for many decades and has found many useful applications in various fields, such as personnel and environmental monitoring, retrospective dosimetry, medical dosimetry, space dosimetry, high-dose dosimetry. Method of preparation, studies and applications of thermoluminescence (TL) dosimetric materials are reviewed. Several high sensitivity thermoluminescent dosimeters (TLDs) are now commercially available in different physical forms. These commercial TL dosimeters comply with a set of stringent requirements stipulated by the International Electrotechnical Commission (IEC). Specific features of TL phosphors for thermal neutron, fast neutron and high-energy charged particle (HCP) dosimetry are also considered. Some of the recent developments in the field of optically stimulated luminescence (OSL) and radiophotoluminescence (RPL) are also summarized. Comparative advantages of TL, OSL and RPL dosimeters are given. Results of recent studies of TL in nanosized materials are briefly presented. Future challenges in this field will also be discussed. Contents of Paper

Introduction. Industrial monitoring of pulsed bremsstrahlung radiation is associated with a number of challenges. Russia produces only three dosimeters that can be used for measuring pulsed bremsstrahlung radiation with a pulse duration of less than 10 gs. These dosimeters, in addition to being rather expensive, have a number of significant restrictions on the energy range (10 MeV) and the minimum pulse duration (10 ns). The DKG-RM1621 dosimeter with a Geiger-Muller counter can be used for dosimetry of photon radiation with energies up to 20 MeV. However, this device is not intended for dosimetry of pulsed radiation.Aim. Development of a methodology for conducting radiation monitoring of pulsed bremsstrahlung radiation sources using dosimeters with Geiger-Muller counters.Materials and methods. In 2021, measurements of the dose rate of pulsed bremsstrahlung radiation with a maximum energy of 3.0 MeV at pulse repetition rates of 50, 100, 150, 200, 250, 300, and 400 Hz were carried out using DKS- AT1123 (as a reference) and MKS-AT117M dosimeters with a Geiger-Muller counter.Results. A technique was developed for correcting the results of measuring the dose rate of pulsed bremsstrahlung radiation by a dosimeter equipped with a Geiger-Muller counter, which allows the dose rate of pulsed bremsstrahlung radiation to be measured with an additional error of less than 15 % in a practically significant range of dose rates. For the MKS- AT117M dosimeter at a pulse repetition rate of 400 Hz, this value was 320 gSv/h, which is sufficient for most practical tasks in radiation monitoring.Conclusion. The feasibility and possibility of successful application of dosimeters with Geiger-Muller counters for dosimetry of pulsed bremsstrahlung radiation using the proposed measurement technique with a limitation on the maximum measured dose rate is shown.

AbstractBackgroundOptically stimulated luminescence dosimeters (OSLDs) have a number of advantages in radiation dosimetry making them an excellent dosimeter for in vivo dosimetry. The study aimed to study the dosimetric characteristics of a commercial optically stimulated luminescence (OSL) system by Landauer Inc., before using it for routine clinical practice for in vivo dosimetry in radiotherapy. Further, this study also aimed to investigate the cause of variability found in the literature in a few dosimetric parameters of carbon-doped aluminium oxide (Al2O3:C).Materials and methodsThe commercial OSLD system uses Al2O3:C nanoDotTM as an active radiation detector and InLightTM microStar® as a readout assembly. Inter-detector response, energy, dose rate, field size and depth dependency of the detector response were evaluated for all available clinical range of photon beam energies in radiotherapy.ResultsInter-detector variation in OSLD response was found within 3·44%. After single light exposure for the OSL readout, detector reading decreased by 0·29% per reading. The dose linearity was investigated between dose range 50–400 cGy. The dose response curve was found to be linear until 250 cGy, after this dose, the dose response curve was found to be supra-linear in nature. OSLD response was found to be energy independent for Co60 to 10 MV photon energies.ConclusionsThe cause of variability found in the literature for some dosimetric characteristics of Al2O3:C is due to the difference in general geometry, construction of dosimeter, geometric condition of irradiation, phantom material and geometry, beam energy. In addition, the irradiation history of detector used and difference in readout methodologies had varying degree of uncertainties in measurements. However, the large surface area of the detector placed in the phantom with sufficient build-up and backscatter irradiated perpendicularly to incident radiation in Co60 beam is a good method of choice for the calibration of a dosimeter. Understanding the OSLD response with all dosimetric parameters may help us in estimation of accurate dose delivered to patient during radiotherapy treatment.

A subset of solid state materials have long been used as integrating dosimeters because they store energy deposited as a result of their interactions with ionizing radiation and then, when stimulated appropriately, release a proportionate amount of visible or near-visible light. During the 1960s, thermoluminescent dosimeters (TLDs), for which heat is used to extract the stored dosimetric signal, began to replace the photographic film as occupational dosimeters of record and for medical dosimetry. At the end of the twentieth century, a viable optically stimulated luminescent (OSL) material was developed which is now gaining in popularity as both an occupational and medical dosimeter. This paper reviews the related stored luminescence processes, presenting a simple conceptual model for optical absorption transitions in OSL materials along with a basic mathematical model for delayed luminescence. The approaches for extracting signal from the OSLs are enumerated.

Purpose The purpose of this paper is to study the effect of gamma-rays on murexide (Mx) dye and its possible use as radiation dosimeters in two different dosimetry systems. The first system depends on the Mx dye as a liquid dosimeter. The second dosimetry system depends also on the same dye but as in a gel form, which is more sensitive to gamma-rays. Design/methodology/approach The prepared Mx (solutions/gels) have a considerable two peaks at 324 and 521 nm that upon irradiation, the intensity of these peaks decreases with the increasing radiation dose. Findings The gamma-ray absorbed dose for these dosimeters was found to be up to 2 kGy for the solution samples and 40 Gy for the gels. Radiation chemical yield, dose response function, radiation sensitivity and before and after-irradiation stability under various conditions were discussed and studied. Practical implications It is expected that the radiolysis of the Mx dye can be used as radiation dosimeters in two different dosimetry systems; liquid and gel dosimeters. This can be applied in a wide range of gamma radiation practical industrial applications in water treatment, food irradiation dosimeters, radiotherapy and fresh food irradiation and seed production. Originality/value Both of the prepared Mx dyes, either as solutions or gel samples, can be facilely prepared from commercially, cheap, safe, available chemicals and suitable for useful applied Mx solutions and gels radiation dosimeters.

Abstract As the utilizing of porphyrins and metalloporphyrins in high dose dosimetry becomes more prevalent, research on structural effects of these molecules on dosimetric characteristics and physicochemical properties of their film dosimeters becomes more and more essential. The present study emphasizes dosimetry (measuring radiolytic bleaching of two novel film dosimeters with spectrophotometric methods against 60Co γ-rays exposure in dose range of 0–100 kGy) and evaluating substituent effects on the radiation response of the film dosimeters (role of organic groups and changing the metal core of porphyrins). With casting of solutions of polycarbonate (PC) containing 0.5 wt.% 5,10,15,20-Tetrakis(2,4,6-trimethoxyphenyl) porphyrin (TTMPP) and 5,10,15,20-Tetraphenyl-21H,23H-porphine manganese (III) chloride (Mn-TPP), two novel radiochromic films with the thickness of 20 μm were fabricated. The presence of porphyrin fragments has been observed in the UV–Vis spectra after γ radiation. Due to the changes of the metal core and substituents of the dye ring, meaningful shifts of maximum absorbance of Soret bands of porphyrins and different radiation response of film-dosimeters were observed. The results were compared with the other polycarbonate/porphyrin film dosimeters. The results indicate that the radiation-induced decoloration of PC/Porphyrin films can be reliably tuned and used in high dose dosimetry.

To safeguard the safety and well-being of interventional cardiology healthcare workers, monitoring their occupational radiation exposure is crucial. This study evaluates the radiation dose of interventional cardiologists using the Swiss Ordinance for personal dosimetry approach. Its primary aim is to estimate the radiation dose for each operator engaged in interventional cardiology procedures to protect from dangerous levels of radiation. Additionally, this study assesses the correlation between under-apron and over-apron dosimeters. Notably, no previous studies in Sri Lanka have specifically assessed radiation dose in this context, making this research vital in shedding light on radiation exposure in an interventional cardiology environment. Two cardiologists conducted a total of 108 interventional cardiology procedures, including coronary angiograms and percutaneous coronary interventions for a month at the cardiac catheterization laboratory of Sri Jayewardenepura General Hospital, Sri Lanka. Active dosimeters were utilized to measure dose values using a two-dosimeter approach where one dosimeter was positioned above the thyroid collar and the other beneath the lead apron on the left side of the waist. The effective doses (E) were determined using the Swiss Ordinance algorithm. Furthermore, this study also examined the relationship between under and over-apron dose values. The Swiss Ordinance algorithm estimated the mean annual E values for each cardiologist, resulting in 3.0397 mSv/year and 0.9697 mSv/year, respectively showing that the estimated annual occupational doses remained well below the annual dose limit (20 mSv/year). The accuracy of the algorithm in interventional ionising radiation scenarios was also highlighted. A strong positive correlation (R2 = 0.9500) was observed between over-apron and under-apron dose values. Applying the Swiss Ordinance for personal dosimetry and studying the link between over and under-apron dosimeters in interventional cardiology improve our grasp of radiation dosimetry. Emphasizing precise dose estimation for the safety of cardiologists, this study enhances the radiation safety practices in interventional cardiology.

Introduction: Ionizing radiation is applied in various fields, and dosimetric control guarantees the quality and safety of products during the irradiation process. There is a need for dosimetric calibration procedures in industrial irradiation plants, specifically for self-shielded irradiation systems. Objective: To implement high dose dosimetry in the routine control of irradiated materials within a self-shielded irradiator. Methods: We worked with 32 dosimeters; we divided the dose range used into 8 points and used four RED Perspex dosimeters per point. We measured the specific absorbance for each dosimeter; plotted these values against dose and produced a third-degree polynomial fit as a calibration curve. Results: We obtained the calibration curve with an r2 of 0,9997. The uncertainties due to the dispersion of the dosimeters and the calibration curve were 1,39% and 0,22%, respectively, for a total uncertainty of 4,80%. This uncertainty includes dose determination with a factor coverage (k) equal to 2 for a 95% confidence interval. Conclusion: Perspex RED dosimeters can be used for routine control of irradiated products in a self-shielded irradiator system.

Selecting the proper dosimeter and methodology is crucial for accurate dose measurement, especially since the requirements are different for clinical and retrospective dosimetry. Regardless of the field-radiotherapy, X-ray diagnostic radiology or nuclear medicineefforts are continuously being made to improve radiation measurement accuracy through the development of new dosimeters, accurate calibration of instrumentation, training of staff, proper quality control and enhancement of radiation safety procedures. For instance, for retrospective dose estimation during radiation accidents, the selection of the appropriate material and knowledge of the intrinsic background signal of the selected material are crucial. In both clinical and retrospective dosimetry it is important to have adequate protocols as well as expertise in possible uncertainties, discussed here based on the authors own research.

Diamond has long been considered as a suitable material for the fabrication of radiation detectors due to its outstanding physical properties. Even more so in the specific case of radiation therapy dosimetry applications, where the near-tissue equivalence radiation absorption, good spatial resolution and radiation hardness are required. Recently, a synthetic single crystal diamond dosimeter was developed at “Tor Vergata” University in cooperation with PTW-Freiburg, showing excellent dosimetric properties. Such a device was thus commercialized (microDiamondTM, PTW-type 60019) and widely accepted by the medical physics community, due to its reproducibility, reliability, accuracy and versatility. In this work, a novel diamond based dosimeter for in vivo application developed in our laboratories is presented. A basic dosimetric characterization of detector performances was performed under irradiation with 60Co and 6 MV photon beams. Response stability, short and long term reproducibility, fading effect, linearity with dose, dose rate dependence, and temperature dependence were investigated. The detector response was found to be reproducible and dose rate independent in the range between 0.5 and 5 Gy/min. Its temperature dependence was within 0.5% between 25 and 38 ◦C, and negligible fading effect was observed. The obtained results indicate the proposed novel diamond device as a promising candidate for in vivo dosimetry in radiation therapy application.

Durch die Einführung von Synchrozyklotronen und Laser-Teilchenbeschleunigern, entwickelt mit dem Ziel günstigere und kompaktere Protonentherapieanlagen bereitzustellen, werden stark gepulste Strahlenfelder möglicherweise Anwendung in der Teletherapie finden. Darüber hinaus bergen stark gepulste Strahlenfelder das Potential klinischer Vorteile durch eine bessere Schonung gesunden Gewebes oder die verbesserte Behandlung bewegter Tumore. Allerdings ergeben sich neue Herausforderungen im Bereich der Dosimetrie, der Grundlage für eine präzise therapeutische Anwendung ionisierender Strahlung. Diese Herausforderungen betreffen sowohl den Bereich der klinischen Dosimetrie für die unmittelbare Strahlenanwendung als auch die Strahlenschutzdosimetrie zum Schutz von Umwelt und Personal. Luftgefüllte Ionisationskammern, die primären Messinstrumente der klinischen Dosimetrie, sind von einem zunehmenden Signalverlust aufgrund von Volumenrekombination betroffen, da stark gepulste Strahlenfelder eine hohe Ionisationsdichte innerhalb eines sehr kurzen Zeitraums erzeugen. Beschreibungen für diese Effekte sind zwar gut etabliert für die moderat gepulsten Felder im gegenwärtigen klinischen Einsatz (Boags Theorie), allerdings sind die dafür nötigen Näherung höchst wahrscheinlich unzureichend für die stark gepulsten Strahlenfelder zukünftiger Beschleuniger. Ferner sind Dosisleistungsmessgeräte, welche im Strahlenschutz als fest installierte oder mobile Überwachungsdosimeter eingesetzt werden, nur für kontinuierliche Strahlenfelder geprüft und bauartzugelassen, was Zweifel an ihrer Eignung für die Messung gepulster Felder eröffnet. In dieser Arbeit wurden beide Bereiche der Dosimetrie, sowohl Strahlenschutz als auch klinische Dosimetrie, untersucht, um die medizinische Anwendung stark gepulster Strahlung zu ermöglichen. Für ein möglichst umfassendes Verständnis wurden dabei experimentelle Untersuchungen mit theoretischen Überlegungen und Entwicklungen verzahnt. Mit dem ELBE-Forschungsbeschleuniger wurde ein gepulster 20 MeV Elektronenstrahl und somit ein gepulstes Strahlungsfeld erzeugt, welches eine systematische Untersuchung in einem großen Bereich in Bezug auf Pulsdosis und Pulsdauer erlaubte. Ionisationskammern für den klinischen Einsatz wurden mit diesem Elektronenstrahl direkt bestrahlt und ein Faraday-Becher diente als unabhängige Referenzmessung. Dosisleistungsmessgeräte hingegen wurden im, durch den Elektronenstrahl im Faraday-Becher erzeugten, Bremsstrahlungsfeld bestrahlt. Dabei fungierte die Ionisationskammer vor dem Faraday-Becher als Strahlmonitor und diente zur Bestimmung der Referenzdosis des Bremsstrahlungsfeldes über eine Querkalibrierung mit Thermolumineszenzdosimetern. Es wurden drei Dosisleistungsmessgeräte basierend auf unterschiedlichen Messprinzipien untersucht, die damit einen großen Teil der im Strahlenschutz eingesetzten Messprinzipien abdecken: Die Ionisationskammer RamION, das Proportionalzählrohr LB1236-H10 und der Szintillationsdetektor AD-b. Für die klinische Dosimetrie wurden zwei verbreitete Ionisationskammergeometrien untersucht: die Advanced Markus Kammer als Flachkammer und die PinPoint Kammer als Kompaktkammer. Zusätzlich zu der üblichen Luftfüllung wurde außerdem eine Füllung mit reinem Stickstoff und zwei Flüssigionisationskammern mit Isooctan und Tetramethylsilan untersucht. Ferner wurde eine numerische Berechnung der Volumenrekombination in Ionisationskammern durch die Beschreibung der Prozesse von Ladungsfreisetzung, Ladungstransport und Reaktion entwickelt, um eine Beschreibung zu erhalten, die ohne die für Boags Theorie notwendigen Näherungen auskommt. Insbesondere berücksichtigt diese Berechnung den Einfluss der freigesetzten Ladungen auf das elektrische Feld, der in Boags Theorie vernachlässigt wird. Von den drei untersuchten Dosisleistungsmessgeräten zeigte nur das RamION Messungen innerhalb der gegebenen Toleranzen in den untersuchten Strahlungsfeldern. Die unerwartet schlechte Präzision des AD-b Szintillationsdetektors, der keinen prinzipiellen Beschränkungen in gepulsten Feldern unterliegen sollte, wurde auf die Signalverarbeitung im Messgerät zurückgeführt, welche das prinzipielle Problem einer unbekannten Signalverarbeitung in kommerziellen Geräten hervorhebt. Das LB 1236-H10 Proportionalzählrohr andererseits maß den Erwartungen entsprechend. Dies unterstützt zwar die in DIN IEC/TS 62743 dargelegten Erwartungen für zählende Dosimeter, zeigt allerdings zugleich die allgemeine Unzulänglichkeit solcher Instrumente für die Messung stark gepulster Felder und demonstriert die Notwendigkeit für weitere normative Bestrebungen, um einheitliche Bedingungen für die Untersuchung nicht-zählender Dosimeter (wie das RamION) zu schaffen. Durch die Aufnahme dieser Ergebnisse in die Literatur der Strahlenschutzkommission wurde hier der Grundstein für eine solche Entwicklung gelegt. Die Untersuchung der Ionisationskammern für klinische Dosimetrie zeigte z.T. starke Abweichungen zwischen Boags Theorie und experimentellen Beobachtungen. Boags Theorie beschreibt Volumenrekombination hinreichend genau lediglich für die zwei Flüssigionisationskammern. Im Falle sämtlicher gasgefüllter Kammern waren effektive Parameter notwendig, deren Wert kaum einen Zusammenhang mit der ursprünglichen Definition besaß. Doch auch dieser Ansatz versagt jedoch für die Advanced Markus-Kammer bei Sammelspannungen ≥ 300 V und Pulsdosen ab ca. 100 mGy. Das entwickelte numerische Berechnungsverfahren lieferte eine deutlich passendere Berechnung der Volumenrekombination und ermöglichte es, die Ursache für die Unterschiede zu Boags Theorie in dem Einfluss der freigesetzten Ladungen auf das elektrische Feld zu identifizieren. Eine aufgrund der erhöhten Pulsdosis erhöhte positive Raumladung verlangsamt die Sammlung der normalerweise schnellen freien Elektronen, welche von Volumenrekombination zunächst unbeeinträchtigt sind. Aufgrund der längeren Verweildauer im Kammervolumen, lagert sich jedoch ein höherer Anteil der Elektronen an und bildet negative Ionen. Der daraus resultierende höhere Anteil an Ladungen die Volumenrekombination ausgesetzt sind, zusätzlich zu der erhöhten Ladungsmenge, bedingt eine Erhöhung der Volumenrekombination mit der Pulsdosis, die sich nicht durch Boags Theorie beschreiben lässt. Insbesondere von Bedeutung ist dieser Effekt bei hohen elektrischen Feldstärken und kleinen Elektrodenabständen, die in einem hohen Anteil freier Elektronen resultieren. Des Weiteren erlaubt das numerische Verfahren die Berechnung für beliebige Pulsdauern, wohingegen Boags Theorie auf verschwindend geringe Pulsdauern beschränkt ist. Im Allgemeinen ergab das numerische Berechnungsverfahren Ergebnisse in guter Übereinstimmung mit den experimentellen Beobachtungen für die sehr verschiedenartigen Füllungen von Luft, Stickstoff und Flüssigkeiten. Auch die geometrisch komplexere Kompaktkammer konnte prinzipiell damit beschrieben werden, wobei sich jedoch für die untersuchte PinPoint-Kammer einige Diskrepanzen zu den experimentellen Beobachtungen ergaben. Eine vielversprechende Weiterentwicklung der Berechnung wäre die verbesserte Beschreibung der Sammelspannungsabhängigkeit der Volumenrekombination. In ihrer derzeitigen Form erfordert die Berechnung eine Charakterisierung jeder Kammer und Spannung, was durch eine Weiterentwicklung der Berechnung möglicherweise eliminiert werden könnte. Nichtsdestotrotz stellt die entwickelte numerische Berechnung eine deutliche Verbesserung gegenüber Boag's Theorie durch die korrekte Beschreibung der Pulsdosis- und Pulsdauerabhängigkeit der Volumenrekombination in stark gepulsten Felder dar, was prinzipiell eine absolute Dosimetrie dieser Felder ermöglichen sollte
Synchrocyclotrons and laser based particle accelerators, developed with the goal to enable more compact particle therapy facilities, may bring highly pulsed radiation field to external beam radiation therapy. In addition, such highly pulsed fields may be desirable due to their potential clinical benefits regarding better healthy tissue sparing or improved gating for moving tumors. However, they pose new challenges for dosimetry, the corner stone of any application of ionizing radiation. These challenges affect both clinical and radiation protection dosimetry. Air-filled ionization chambers, which dominate clinical dosimetry, face the problem of increased signal loss due to volume recombination when a highly pulsed field liberates a large amount of charge in a short time in the chamber. While well established descriptions exist for this volume recombination for the moderately pulsed fields in current use (Boag's formulas), the assumptions on which those descriptions are based will most likely not hold in the prospective, highly pulsed fields of future accelerators. Furthermore, ambient dose rate meters used in radiation protection dosimetry as survey meters or fixed installations are generally only tested for continuous fields, casting doubt on their suitability to measure pulsed fields. This thesis investigated both these aspects of dosimetry - clinical as well as radiation protection - to enable the medical application of highly pulsed radiation fields. For a comprehensive understanding, experimental investigations were coupled with theoretical considerations and developments. Pulsed fields, varying in both dose-per-pulse and pulse duration over a wide range, were generated with the ELBE research accelerator, providing a 20 MeV pulsed electron beam. Ionization chambers for clinical dosimetry were investigated using this electron beam directly, with an aluminium Faraday cup providing the reference measurement. Whereas the dose rate meters were irradiated in the photon field generated from stopping the electron beam in the Faraday cup. In those measurements, the reference was calculated from the ionization chamber, then serving a an electron beam monitor, cross-calibrated to the photon field with thermoluminescent dosimeters. Three dose rate meters based on different operating principles were investigated, covering a large portion of the operating principles used in radiation protection: the ionization chamber based RamION, the proportional counter LB 1236-H10 and the scintillation detector AD-b. Regarding clinical dosimetry, measurements of two prominent ionization chamber geometries, plane-parallel (Advanced Markus chamber) and thimble type (PinPoint chamber), were performed. In addition to common air-filled chambers, chambers filled with pure nitrogen and two non-polar liquids, tetramethylsilane and isooctane, were investigated. In conjunction with the experiments, a numerical solution of the charge liberation, transport, and recombination processes in the ionization chamber was developed to calculate the volume recombination independent of the assumptions necessary to derive Boag's formulas. Most importantly, the influence of the liberated charges in the ionization chamber on the electric field, which is neglected in Boag's formulas, is included in the developed calculation. Out of the three investigated dose rate meters only the RamION could be identified as an instrument truly capable of measuring a pulsed field. The AD-b performed below expectations (principally, a scintillator is not limited in detecting pulsed radiation), which was attributed to the signal processing, emphasizing the problem of a typical black-box signal processing in commercial instruments. The LB 1236-H10, on the other hand, performed as expected of a counting detector. While this supports the recent effort to formalize these expectations and standardize testing for counting dosimeters in DIN IEC/TS 62743, it also highlights the insufficiency of counting detectors for highly pulsed fields in general and shows the need for additional normative work to establish requirements for dose rate meters not based on a counting signal (such as the RamION), for which no framework currently exists. With these results recognized by the German radiation protection commission (SSK) the first steps towards such a framework are taken. The investigation of the ionization chambers used in radiation therapy showed severe discrepancies between Boag's formulas and the experimentally observed volume recombination. Boag's formulas describe volume recombination truly correctly only in the two liquid-filled chambers. All the gas-filled chambers required the use of effective parameters, resulting in values for those parameters with little to no relation to their original meaning. Even this approach, however, failed in the case of the Advanced Markus chamber for collection voltages ≥ 300 V and beyond a dose-per-pulse of about 100 mGy. The developed numerical model enabled a much better calculation of volume recombination and allowed the identification of the root of the differences to Boag's formulas as the influence of the liberated charges on the electric field. Increased positive space charge due to increased dose-per-pulse slows the collection and reduces the fraction of fast, free electrons, which are unaffected by volume recombination. The resultant increase in the fraction of charge undergoing volume recombination, in addition to the increase in the total amount of charge, results in an increase in volume recombination with dose-per-pulse that is impossible to describe with Boag's formulas. It is particularly relevant in the case of high electric fields and small electrode distances, where the free electron fraction is large. In addition, the numerical calculation allows for arbitrary pulse durations, while Boag's formulas apply only to very short pulses. In general, the numerical calculation worked well for plane-parallel chambers, including those filled with the very diverse media of liquids, nitrogen and air. Despite its increased complexity, the thimble geometry could be implemented as well, although, in the case of the PinPoint chamber, some discrepancies to the experimental data remained, probably due to the required geometrical approximations. A possible future development of the numerical calculation would be an improved description of the voltage dependence of the volume recombination. At the moment it requires characterizing a chamber at each desired collection voltage, which could be eliminated by an improved modeling of the volume recombination's dependence on collection voltage. Nevertheless, the developed numerical calculation presents a marked improvement over Boag's formulas to describe the dose-per-pulse dependence and pulse duration dependence of volume recombination in ionization chambers, in principle enabling the application of ionization chambers in the absolute dosimetry of highly pulsed fields

Electron beam therapy planning and custom electron bolus design were identified as areas in which improvements in equipment and techniques could lead to significant improvements in treatment delivery and patient outcomes. The electron pencil beam algorithms used in conventional Treatment Planning Systems do not accurately model the dose distribution in irregularly shaped objects, near oblique surfaces or in inhomogeneous media. For this reason, at Christchurch Oncology Centre the TPS is not relied on for planning electron beam treatments. This project is an initial study of ways to improve the design of custom electron bolus, the planning of electron beam therapy, and other radiation therapy simulation tasks, by developing a system for the accurate assessment of dose distributions under irregular contours in clinically relevant situations. A shaped water phantom system and a diode array have been developed and tested. The design and construction of this water phantom dosimetry system are described, and its capabilities and limitations discussed. An EGS/BEAM Monte Carlo simulation system has been installed, and models of the Christchurch Oncology Centre linacs in 6MeV and 9MeV electron beam modes have been built and commissioned. A test was run comparing the EGS/BEAM Monte Carlo system and the CMS Xio conventional treatment planning system with the experimental measurement technique using the water phantom and the diode array. This test was successful as a proof of the concept of the experimental technique. At the conclusion of this project, the main limitation of the diode array system was the lack of data processing software. The array produces a large volume of raw data, but not enough processed data was produced during this project to match the spatial resolution of the computer models. An automated data processing system will be needed for clinical use of the array. It has been confirmed that Monte Carlo and pencil-beam algorithms predict significantly different dose distributions for an irregularly shaped object irradiated with megavoltage electron beams. The results from the diode array were consistent with the theoretical models. This project was an initial investigation. At the time of writing, the diode array and the water phantom systems were still at an early stage of development. The work reported here was performed to build, test and commission the equipment. Additional work will be needed to produce an instrument for clinical use. Research into electron beam therapy could be continued, or the equipment used to expand research into new areas.

A novel optical calorimetry approach is proposed for the dosimetry of therapeutic radiation, based on the optical technique of Digital Holographic Interferometry (DHI). This detector determines the radiation absorbed dose to water by measurement of the refractive index variations arising from radiation induced temperature increases. The output consists of a time series of high resolution, two dimensional images of the spatial distribution of the projected dose map across the water sample. This absorbed dose to water is measured directly, independently of radiation type, dose rate and energy, and without perturbation of the beam. These are key features which make DHI a promising technique for radiation dosimetry. A prototype DHI detector was developed, with the aim of providing proof-of-principle of the approach. The detector consists of an optical laser interferometer based on a lensless Fourier transform digital holography (LFTDH) system, and the associated mathematical reconstruction of the absorbed dose. The conceptual basis was introduced, and a full framework was established for the measurement and analysis of the results. Methods were developed for mathematical correction of the distortions introduced by heat di usion within the system. Pilot studies of the dosimetry of a high dose rate Ir-192 brachytherapy source and a small eld proton beam were conducted in order to investigate the dosimetric potential of the technique. Results were validated against independent models of the expected radiation dose distributions. Initial measurements of absorbed dose demonstrated the ability of the DHI detector to resolve the minuscule temperature changes produced by radiation in water to within experimental uncertainty. Spatial resolution of approximately 0.03 mm/pixel was achieved, and the dose distribution around the brachytherapy source was accurately measured for short irradiation times, to within the experimental uncertainty. The experimental noise for the prototype detector was relatively large and combined with the occurrence of heat di usion, means that the method is predominantly suitable for high dose rate applications. The initial proof-of-principle results con rm that DHI dosimetry is a promising technique, with a range of potential bene ts. Further development of the technique is warranted, to improve on the limitations of the current prototype. A comprehensive analysis of the system was conducted to determine key requirements for future development of the DHI detector to be a useful contribution to the dosimetric toolbox of a range of current and emerging applications. The sources of measurement uncertainty are considered, and methods suggested to mitigate these. Improvement of the signal-to-noise ratio, and further development of the heat transport corrections for high dose gradient regions are key areas of focus highlighted for future development.

The thesis gives an overview on the preclinical results in Microbeam Radiation Therapy (MRT), a novel radiation therapy using microscopically small beams. In the first chapter preclinical results and biological observations after Microbeam Radiation Therapy are presented, in particular the normal tissue tolerance is highlighted. A chapter based on theoretical Monte Carlo dose calculations is summarizing a set of data on peak to valley dose ratios (PVDR) and relative dose distributions for various parameter settings, providing some guideline for preclinical studies. The main part of the thesis is focusing on the experimental dosimetry, on one side to measure the high dose rate in the homogenous field proposing the necessary corrections to be applied for absolute dose measurements and on the other side, to measure peak and valley dose. For the high resolution dose measurements of the spatially fractionated beam, results using several types of detectors are presented and discussed. Various results using Gafchromic film dosimetry in combination with a microdensitometer show slightly higher (~10-15 %) valley dose than the MC calculated values. Results of theoretical calculations of output factors and their experimental verification are in very good agreement. The great potential of interlaced Microbeams in an anthropomorphic phantom with one single high dose delivery is discussed, including the technical challenges to be mastered in the future.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, September 2003.
Thesis advisor(s): Todd R. Weatherford, Andrew A. Parker. Includes bibliographical references (p. 39). Also available online.

A new generation of Alkaline earth sulfides (MgS, CaS, and BaS) doped with rare-earth ions have been identified by the University of Montpellier as the very high sensitivity of these phosphors, the short time constant of the luminescence and the perfectly separated spectra enable many applications in real time and online dosimetry. The online detecting technology of optically stimulated luminescent (OSL) radiation dosimeter main make use of the OSL characteristics of doping the alkaline-earth metal sulphides, makes the material into the thin films for storing energy from Ionizing radiation, the excitation light through optical fibers reached the where under radiation-field, with a sensitive detection device to read out the radiation dose from storing the OSL material, obtains a novel technology of radiation dose measurement. In the previous works, the dosimeter benefits from a printed circuit board mount. Both the sensor and the electronics are exposed to radiation, the problem of the radiation induced damage is supposedly being addressed. In both cases, the use of optical fibers can provide an elegant solution. Optical fibers offer a unique capability for remote monitoring of radiation in difficult-to-access and hazardous locations. Optical fiber can be located in radiation hazardous areas and optically interrogated from a safe distance. Hence, optical fiber dosemeters are immune to electrical and radio-frequency interference that can seriously degrade the performance of remote electronic dosimeters. In this paper, a novel remote optical fiber radiation dosimeter is described. The optical fiber dosimeter takes advantage of the charge trapping materials CaS:Ce, Sm and SrS:Eu, Sm that exhibit optically stimulated luminescence (OSL). The range of the dosimeter is from 0.01 to 1000Gy. The optically stimulated luminescent (OSL) radiation dosimeter technically surveys a wide dynamic measurement range and a high sensitivity. The equipment is relatively simple and small in size, and has low power consumption. This device is suitable for measuring the space radiation dose; it also can be used in high radiation dose condition and other dangerous radiation occasions.