A Review: Photonic Devices Used for Dosimetry in Medical Radiation.

Numerous instruments such as ionization chambers, hand-held and pocket dosimeters of various types, film badges, thermoluminescent dosimeters (TLDs) and optically stimulated luminescence dosimeters (OSLDs) are used to measure and monitor radiation in medical applications. Of recent, photonic devices have also been adopted. This article evaluates recent research and advancements in the applications of photonic devices in medical radiation detection primarily focusing on four types; photodiodes - including light-emitting diodes (LEDs), phototransistors-including metal oxide semiconductor field effect transistors (MOSFETs), photovoltaic sensors/solar cells, and charge coupled devices/charge metal oxide semiconductors (CCD/CMOS) cameras. A comprehensive analysis of the operating principles and recent technologies of these devices is performed. Further, critical evaluation and comparison of their benefits and limitations as dosimeters is done based on the available studies. Common factors barring photonic devices from being used as radiation detectors are also discussed; with suggestions on possible solutions to overcome these barriers. Finally, the potentials of these devices and the challenges of realizing their applications as quintessential dosimeters are highlighted for future research and improvements.

Long-term fade study of the DT-702 LiF: Mg,Cu,P TLD.

LiF thermoluminescent dosemeters (TLDs) are used by the US Navy to record radiation exposure of personnel. The Model DT-648 LiF:Mg,Ti TLD has been replaced by a new Model DT-702 LiF:Mg,Cu,P TLD. The DT-648 was used for many years and has undergone extensive testing to identify its pre- and post-irradiation fade operating characteristics. Studies have shown that the addition of copper increases the thermoluminesence sensitivity of the TLD for improved low-level radiation monitoring. This study evaluates various fading characteristics of the new copper-doped dosemeter using current equipment for processing of TLDs and calibrating to a National Institute of Standards and Technology standard source. The 57-week study took place at the Naval Dosimetry Center, Bethesda, MD, USA. TLDs were stored for various lengths of time before and after being exposed to a National Institute of Standards and Technology calibrated radiation sources. TLDs were then processed using current US Navy instructions and the resulting dose compared with the calibrated exposure. Both loss of signal and loss of sensitivity were evaluated. The results of this study have shown that the DT-702 TLD has no statistically significant change in sensitivity or change in signal with up to 57 weeks of pre- or post-irradiation time. The results of this study will increase the accuracy of exposure record keeping for the Navy and will allow longer issue periods. This will increase flexibility with international and domestic shipping procedures, as well as reduce workload requirements for dosimetry processing.

Some developments in neutron and charged particle dosimetry.

There is an increasing need for dosimetry of neutrons and charged particles. Increasing exposure levels are reported in the nuclear industry, deriving from more frequent in-service entries at commercial nuclear power plants, and from increased plant decommissioning and refurbishment activities. Another need stems from the compliance with requirements of the regulations and standards. The European Council directive 96/29 requires dosimetric precautions if the effective dose exceeds 1 mSv a(-1). On average, aircrew members exceed this value. Further, there is a trend of increasing use of charged particles in radiotherapy. The present situation is that we have reasonably good photon dosemeters, but neutron and charged particle dosemeters are still in need of improvements. This work highlights some of the developments in this field. It is mainly concentrated on some developments in passive dosimetry, in particular thermally and optically stimulated luminescent detectors, indicating the direction of ongoing research. It shows that passive dosemeters are still a very active field. Active dosemeters will not be discussed with the exception of new developments in microdosimetric measurements [new types of tissue equivalent proportional counters (TEPCs)]. The TEPC is unique in its ability to provide a simultaneous determination of neutron / charged particle / gamma ray doses, or dose equivalents using a single detector.

Theories of TL systems: failures, successes, conflicts, trends: insights into possible future materials and techniques.

In this paper some of the many theoretical models dealing with characteristics of TL materials are discussed. Special attention is given to some of the models dealing with the effects of ionisation density, that is Modified Track Structure Theory (MTST) and Microdosimetric Track Structure Theory (MTT) for the calculation of Heavy Charged Particle relative TL efficiencies, as well as solid-state models based on conduction band/valence band theory. Failures, successes, conflicts and trends are highlighted as well as a peek into future avenues of research for dosimetric TL materials.

Past and future application of solid-state detectors in manned spaceflight.

The radiation exposure in space missions can be reduced by careful mission planning and appropriate measures, such as provision of a radiation shelter, but it cannot be eliminated. The reason for that is the high penetration capability of the radiation components owing to their high energies. Radiation is therefore an acknowledged primary concern for manned spaceflight and is a potentially limiting factor for long-term orbital and interplanetary missions. The radiation environment is a complex mixture of charged particles of solar and galactic origin and of the radiation belts, as well as of secondary particles produced in interactions of the galactic cosmic particles with the nuclei of atmosphere of the earth. The complexity even increases by placing a spacecraft into this environment owing to the interaction of the radiation components with the shielding material. Therefore it is a challenge to provide for appropriate measurements in this radiation field, coping with the limited resources on experiment power and mass. Solid-state dosemeters were already chosen for measurements in the first manned flights. Thermoluminescence dosemeters (TLDs) and plastic nuclear track detectors (PNTD) especially found a preferred application because they are light-weighted, need no power supply and they are tissue-equivalent. Most of the data available until 1996 were gathered by using these passive detectors; this especially holds for heavy ion particle spectra. The systems, supplemented by converter foils or fission detectors and bubble detectors, provide information on dose, particle flux-, energy- and linear energy transfer spectra of the ionising radiation and neutron fluxes and doses. From 1989, silicon detectors were used for dose and flux measurements and later on for particle spectrometry. Silicon detectors were demonstrated as a powerful tool for the description of space radiation environment. Optical simulated luminescence (OSL) detectors have now been introduced as a new system in space research. Both, OSL and superheated drop detectors are candidates for personal dosimetry systems. The article will summarise past results, and results of measurements performed recently on the ISS, and conclude with future aspects.

The application of LiF:Mg,Cu,P to large scale personnel dosimetry: current status and future directions.

LiF:Mg,Cu,P is starting to replace LiF:Mg,Ti in a variety of personnel dosimetry applications. LiF:Mg,Cu,P has superior characteristics as compared to LiF:Mg,Ti including, higher sensitivity, improved energy response for photons, lack of supralinearity and insignificant fading. The use of LiF:Mg,Cu,P in large scale dosimetry programs is of particular interest due to the extreme sensitivity of this material to the maximum readout temperature, and the variety of different dosimetry aspects and details that must be considered for a successful implementation in routine dosimetry. Here we discuss and explain the various aspects of large scale LiF:Mg,Cu,P based dosimetry programs including the properties of the TL material, new generation of TLD readers, calibration methodologies, a new generation of dose calculation algorithms based on the use of artificial neural networks and the overall uncertainty of the dose measurement. The United States Navy (USN) will be the first US dosimetry processor who will use this new material for routine applications. Until June 2002, the Navy used two types of thermoluminescent materials for personnel dosimetry, CaF2:Mn and LiF:Mg,Ti. A program to upgrade the system and to implement LiF:Mg,Cu,P, started in the mid 1990s and was recently concluded. In 2002, the new system replaced the LiF:Mg,Ti and is scheduled to start replacing the CaF2:Mn system in 2006. A pilot study to determine the dosimetric performance of the new LiF:Mg,Cu,P based dosimetry system was recently completed, and the results show the new system to be as good or better than the current system in all areas tested. As a result, LiF:Mg,Cu,P is scheduled to become the primary personnel dosimeter for the entire US Navy in 2006.

Diagnostic radiology dosimetry: Status and trends.

Since 1970s the expression of protection standards shifted from a dose -to a risk-based approach, with dose limits established to yield risks to medical radiation workers. Worldwide interest in patient dose measurement was stimulated by the publication of Patient Dose Reduction in Diagnostic Radiology by the UK National Radiological Protection Board (NRPB). This has resulted in the development of new dosimetric measuring instruments, techniques and terminologies which present challenges to those working in the clinic al environment and those supporting them in calibration facilities. In this sense, thermoluminescent dosimetry (TLD) has been actively developed in the past last 3 decades thanks to their successful applications in diagnostic radiology. The present work analyzes current status and future trends of diagnostic radiology dosimetry using thermoluminescence phenomena.

On the use of LiF:Mg,Ti thermoluminescence dosemeters in space--a critical review.

The use of LiF:Mg,Ti thermoluminescence dosemeters (TLDs) in space radiation fields is reviewed. It is demonstrated in the context of modified track structure theory and microdosimetric track structure theory that there is no unique correlation between the relative thermoluminescence (TL) efficiency of heavy charged particles, neutrons of all energies and linear energy transfer (LET). Many experimental measurements dating back more than two decades also demonstrate the multivalued, non-universal, relationship between relative TL efficiency and LET. It is further demonstrated that the relative intensities of the dosimetric peaks and especially the high-temperature structure are dependent on a large number of variables, some controllable, some not. It is concluded that TL techniques employing the concept of LET (e.g. measurement of total dose, the high-temperature ratio (HTR) methods and other combinations of the relative TL efficiency of the various peaks used to estimate average Q or simulate Q-LET relationships) should be regarded as lacking a sound theoretical basis, highly prone to error and, as well, lack of reproducibility/universality due to the absence of a standardised experimental protocol essential to reliable experimental methodology.

[Thermoluminescence Slab Dosimeter].

In 1953 F. Daniels et al. used the property of thermoluminescence in dosimetry for the first time. Since then, numerous TLD have been developed. 2D TLD was investigated for the first time in 1972 by P Broadhead. However, due to excessive fading, difficulties with handling and the time required for measurements, development stalled. At the current time, the majority of TLD are used in small scale, localized dosimetry with a wide dynamic range and personal dosimeters for exposure management. Urushiyama et. al. have taken advantage of the commoditization of CCD cameras in recent years--making large area, high resolution imaging easier--to introduce and develop a 2D TLD. It is expected that these developments will give rise to a new generation of applications for 2D TL dosimetry. This paper introduces the "TL Slab Dosimeter" developed jointly by Urushiyama et. al. and our team, its measurement system and several typical usage scenarios.

Postal dose audits for radiotherapy centers in Latin America and the Caribbean: trends in 1969-2003.

Since 1969 the International Atomic Energy Agency and the World Health Organization (along with the Pan American Health Organization, working with countries in Latin America and the Caribbean) have operated postal dosimetry audits based on thermoluminescent dosimetry (TLD) for radiotherapy centers. The purpose of these audits is to provide an independent dosimetry check of radiation beams used to treat cancer patients. The success of radiotherapy treatment depends on accurate dosimetry. Over the period of 1969 through 2003 the calibration of approximately 5,200 photon beams in over 1,300 radiotherapy centers in 115 countries worldwide was checked. Of these audits, 36% were performed in Latin America and the Caribbean, with results improving greatly over the years. Unfortunately, in several instances large TLD deviations have confirmed clinical observations of inadequate dosimetry practices in hospitals in various parts of the world or even accidents in radiotherapy, such as the one that occurred in Costa Rica in 1996. Hospitals or centers that operate radiotherapy services without qualified medical physicists or without dosimetry equipment have poorer results than do hospitals or centers that are properly staffed and equipped. When centers have poor TLD results, a follow-up program can help them improve their dosimetry status. However, to achieve audit results that are comparable to those for centers in industrialized countries, additional strengthening of the radiotherapy infrastructure in Latin America and the Caribbean is needed.

Estudio dosimétrico de la embolización endovascular de varicocele en pacientes pediátricos / Paediatric varicocele embolization dosimetric study

Introducción y objetivos: El varicocele es una anomalía benigna que se detecta generalmente en pacientes jóvenes, y para cuyo tratamiento existen técnicas quirúrgicas. La embolización endovascular es un procedimiento terapéutico alternativo mínimamente invasivo, pero con un riesgo radiológico asociado que resulta esencial conocer para valorar el método de tratamiento más adecuado. El objetivo del trabajo es determinar niveles locales de dosis recibidas en embolizaciones de varicocele en pacientes pediátricos y minimizarlas, estimando el riesgo radiológico. Material y métodos: El estudio se ha realizado en dos fases; una retrospectiva para 15 embolizaciones en pacientes con edades comprendidas entre 10 y 18 años, sin intervención previa en el método de trabajo, y otra prospectiva para 10pacientes de 10 a 16 años de edad, utilizando algunas técnicas de reducción de dosis implementadas en el equipo. Se conocía el tiempo de es copia y el valor del producto dosis-área de cada intervención. Además, en la fase prospectiva, se han utilizado dosímetros termoluminescentes para la evaluación de la dosis máxima de entrada en piel, y películas radiográficas para verificar la zona irradiada. Resultados: La dosis efectiva media estimada en el estudio retrospectivo fue de 8.8 mSv. El riesgo total medio de inducción de cáncer fatal en cualquier localización fue un 0.16%, siendo un 0.0007% para los efectos hereditarios. La dosis máxima de entrada en piel fue de 250 mGy, siendo 2 Gy el umbral de dosis para la aparición de efectos deterministas en piel. Para los pacientes del estudio prospectivo, las dosis y el riesgo radiológico se redujeron en más de un 70%. Conclusiones: La estimación de riesgo radiológico estocástico es relativamente elevada comparada con el riesgo de complicaciones severas en las intervenciones quirúrgicas de varicocele, excepto para el caso de efectos hereditarios. Son descartables los efectos de tipo determinista, salvo en complicaciones del procedimiento. La exposición a la radiación debe ser optimizada. Es necesario que los clínicos prescriptores e intervencionistas conozcan los riesgos radiológicos asociados a la intervención e informen a sus pacientes (AU)

Introduction and objectives: Varicocele is a benign condition, often asymptomatic, that appears among young men with a normal life expectancy. The endovascular embolization is a minimally invasive therapeutic procedure indicated for varicocele treatment, although there are safe surgical alternatives. It is essential to know the radiological risk associated with the procedure. The aim of this work is to determine local dose levels in paediatric varicocele embolization, in order to minimize and to estimate the radiological risk. Material and methods: In the retrospective study, 15 cases were analyzed, all of which were paediatric patients (10-18 years). The screening time and the dose-area product were known, as provided by the X-ray equipment. In the prospective study, dose optimization techniques were implemented, and in addition, radiographic films were used in order to verify the radiated zone and termoluminiscense dosimeters in order to evaluate gonad dose and maximum skin dose for10 paediatric patients (10-16 years). Results: In the retrospective group, the average effective dose was 8.8 mSv. The total average risk of a fatal cancer induction in any location was 0.16%, and 0.0007% for hereditary effects. The maximum skin dose was 250 mGy, which is far from the threshold for deterministic effects (2 Gy). In the prospective group, dose and radiological risk decreased by more than 70%.Conclusions: Hereditary effects were very low in contrast to the fatal cancer risk estimation. According to the results we can discard deterministic effects, unless complications appear in the procedure. Radiation exposure must be optimized. It is necessary that medical staff know the radiological risks associated with the intervention, and inform the patients about them (AU)

Postal dose audits for radiotherapy centers in Latin America and the Caribbean: trends in 1969-2003 / Auditorías de las dosis usadas en centros de radioterapia en América Latina y el Caribe: tendencias observadas en el período de 1969­2003

Since 1969 the International Atomic Energy Agency and the World Health Organization (along with the Pan American Health Organization, working with countries in Latin America and the Caribbean) have operated postal dosimetry audits based on thermoluminescent dosimetry (TLD) for radiotherapy centers. The purpose of these audits is to provide an independent dosimetry check of radiation beams used to treat cancer patients. The success of radiotherapy treatment depends on accurate dosimetry. Over the period of 1969 through 2003 the calibration of approximately 5 200 photon beams in over 1 300 radiotherapy centers in 115 countries worldwide was checked. Of these audits, 36 percent were performed in Latin America and the Caribbean, with results improving greatly over the years. Unfortunately, in several instances large TLD deviations have confirmed clinical observations of inadequate dosimetry practices in hospitals in various parts of the world or even accidents in radiotherapy, such as the one that occurred in Costa Rica in 1996. Hospitals or centers that operate radiotherapy services without qualified medical physicists or without dosimetry equipment have poorer results than do hospitals or centers that are properly staffed and equipped. When centers have poor TLD results, a follow-up program can help them improve their dosimetry status. However, to achieve audit results that are comparable to those for centers in industrialized countries, additional strengthening of the radiotherapy infrastructure in Latin America and the Caribbean is needed.

Estimación del riesgo radiológico asociado a la dilatación endourológica de la estenosis pieloureteral congénita en pacientes pediátricos / Evaluation of radiological risk associated tod pieloureteral surgery in paediatric patients

Introducción y objetivos. El uso de radiaciones ionizantes (RI),como instrumento útil en determinadas intervenciones quirúrgicas, hace conveniente la evaluación de los riesgos radiológicos derivados de su empleo. Este riesgo es especialmente relevante en el caso de pacientes pediátricos, debido a su mayor radiosensibilidad y esperanza de vida. El objetivo de este trabajo es, descartados los efectos deterministas, estimarlos riesgos probabilísticos inducidos por las RI en la dilatación endourológica de la estenosis píelo-ureteral (EPU), así como establecer niveles de referencia de dosis en este tipo de cirugía. Material y métodos. El estudio se ha realizado para 20 pacientes pediátricos de ambos sexos, con edades comprendidas entre 2 meses y 9 años, sometidos a intervenciones de dilatación endourológica dela EPU congénita durante los años 2006 y 2007. Se conocen el tiempo de escopia y el valor proporcionado por el equipo de radiodiagnóstico del producto dosis-área. Además se han utilizado dosímetros termoluminescentes para la evaluación de la dosis máxima de entrada en piel y películas radiográficas para verificar la zona irradiada y la dosis. Resultados. La dosis efectiva media por minuto para pacientes menores de 5 años es 0,36mSv, y 0,43mSv para pacientes mayores de esta edad, resultados inferiores a los publicados en la bibliografía para este tipo de intervenciones. El riesgo total medio de inducción de un cáncer fatal en cualquier localización, incluyendo todos los grupos de edad, es un 0,012%. La dosis máxima de entrada en piel es 19.81mGy,siendo 2Gy el umbral de dosis para la aparición de efectos deterministas en piel. Conclusiones. A pesar de que el riesgo de efectos probabilísticos es pequeño, es recomendable el uso de todos los métodos de protección radiológica disponibles y una coordinación más estrecha entre los diferentes colectivos implicados, para la correcta optimización de las dosis (AU)

Introduction. Because of the application of ionising radiation in surgical procedures, it is necessary to perform an evaluation of the radiological risks. Potential hazards are of greater influence in paediatric patients, due to their longer life expectancy and greater radio sensibility. The aim of this paper was, with the exception of deterministic injuries, trying to evaluate patient doses and stochastic risks induced by ionising radiations in paediatric pieloureteral surgery. Material and methods. Twenty paediatric patients of both sexes, from 2 months to 9 years, were included in the study. All the procedures were performed in 2006 and 2007. The X-Ray equipment shows fluoroscopy time and dose area product in each procedure, thermoluminiscent dosimeters (TLD’s) measure patient´s skin dose and non screen films verify the radiated field and dose. Results. The average effective dose per minute was 0.36mSv for patients under 5 year old and 0.43mSv for over 5. These figures were lower than previously published results for this kind of surgery. The average total risk of fatal cancer induction in any location, for each study group, was 0.012%. Maximum skin dose was 19.81mGy, which is well below the threshold for deterministic injuries (2 Gy).Conclusions. Although stochastic risks were small, it´s highly recommended to employ all the available methods and techniques developed for patient radiological protection. A strong coordination between team members is advisable for improving the dose optimization (AU)