Thermoluminescence dosimetry for quality assurance in radiation therapy

A methodology based on thermoluminescence dosimetry was developed to check the output of teletherapy units and the given doses. It was applied in a hospital as a part of an extemal quality audit programme. Over a 7 year period the mean ratios of the output doses measured by TLDs calibrated free-in-air to the doses measured at the hospital in a 6 MV X ray and in a 60Co unit were 1.000 +/- 0.024 (n = 86) and 0.997 +/- 0.027 (n=61), respectively. TLDs in capsules were attached to the patient's body or to a phantom to assess entrance, exit and midline doses and transmission. Factors were determined experimentally to relate the doses measured with TLDs in capsules and inside the body. The accuracy in given doses with pelvic and tangential breast fields and assessed via 752 in vivo measurements, was considered to be adequately good, taking into account the limitations of the equipment available in the hospital.     

Quantities and units in radiation protection

In its Publication No. 60, the International Commission on Radiological Protection (ICRP) introduced a new quantity, the equivalent dose in tissue, HT = sigma R WR DT.R where DT.R is the absorbed dose averaged over the tissue or organ, T, and WR is the radiation weighting factor. The latter depends on the incident radiation, i.e., the type and energy, but is independent of the tissue. On the other hand, a customarily defined quantity, the 'dose equivalent' is maintained (in particular the operational dose-equivalent quantities introduced in ICRU Report 39), but the relationship between the quality factor Q(L) and the linear energy transfer, L, has been redefined. In the case of neutrons, this procedure gives rise to an increase of the corresponding fluence to dose-equivalent conversion factors. The reasons for introducing these and the new tissue-weighting factor changes are discussed.     

Microdosimetry of neutron field for boron neutron capture therapy at Kyoto university reactor

Microdosimetric single event spectrum in a human body simulated by an acrylic phantom has been measured for the clinical BNCT field at the Kyoto University Reactor (KUR). The recoil particles resulting from the initial reaction and subsequent interactions, namely protons, electrons, alpha particles and carbon nuclei are identified in the microdosimetric spectrum. The relative contributions to the neutron dose from proton, alpha particles and carbon are estimated to be about 0.9, 0.07 and 0.3, respectively, four depths between 5 and 41 mm. We estimate that the dose averaged lineal energy, yD decreased with depth from 64 to 46 keV microm(-1). Relative biological effectiveness (RBE) of this neutron field using a response function for the microdosimetric spectrum was estimated to decrease from 3.6 to 2.9 with increasing depth.     

Medical radiation protection in next decade

Interest in medical radiation protection today is the same as what it would have been almost a century ago. After many decades of relatively safe application of radiation in medicine, the recent spurt in over exposures, over-use of imaging and accidental exposures has created the need for stakeholders to join hands and contribute towards increasing radiation safety levels. Whether it be the need for technological developments to achieve sub-mSv CT scans, tracking of patient exposure history, accounting for repeated exposures of the same patient, specific consideration of requests for radiological examinations that deliver few mSv of dose, or utilization of regulatory approaches, radiological equipment will need to alert users whenever the radiation dose to the patient is above a defined value. The current decade will focus increasingly on carcinogenic effects in patients.     

Occupational radiation protection dosimetry in Nigeria

The general features of occupational radiation protection dosimetry in Nigeria within the period 1990-1999 have been summarised. About 640 personnel, representing about 25% of the estimated number of radiation workers in Nigeria, were monitored by the TL dosimetry technique during the period, with the majority being the personnel of the teaching hospitals across the country. Most private establishments, especially the X ray diagnostic centres, operate without dosimetry coverage or supervision by a regulatory authority. The weighted mean of the annual effective dose ranged between 0 and 28.97 mSv with the upper limit of collective effective dose being 18.47 man.Sv per year. The individual risk estimate due to this is about 1.5 x 10(-3) per year and this was among the medical personnel. The value could be more if all radiation workers in the country were monitored.     

Dose quantities in radiation protection and dosemeter calibration

Dosimetric concepts and the definition of dose quantities for use in radiation protection were defined by the ICRP and the ICRU. Three types of quantities are of relevance for radiation protection purposes: basic physical quantities, protection quantities, and operational quantities. The physical quantities are universally accepted for the characterisation of radiation fields. These are defined in any point of the field, and the units are directly obtained by primary standards. The protection quantities form the basis for dose limitation. These quantities are not directly measurable. A set of measurable operational quantities provides, in general, a conservative estimate of the protection quantities. These operational quantities are recommended in routine monitoring of occupational exposure. The relation between these different types of quantities is discussed. In addition, the calibration procedure for dosemeters in terms of the operational quantities, including the use of calibration phantoms, is summarised.     

Classical microdosimetry in radiation protection dosimetry and monitoring

Classical microdosimetry concerns the measurement and analysis of the spectrum of radiation energy deposition events in simulated microscopic tissue-equivalent sites. Over the past three decades, classical microdosimetry has been extensively applied for the direct measurement of dosimetric quantities, such as the ambient dose equivalent, and for the spectroscopic properties of tissue-equivalent proportional counters that have led to methods of mixed-field analysis and particle identification. This paper reviews some of the special applications of classical microdosimetry such as the determination of kerma coefficients, differential dosimetry and aviation dosimetry. Also reviewed are some of the technological innovations related to the application of microdosimetry in operational health physics and in particular the development of multi-element proportional counters and detectors based on gas microstrip technology.     

Dose quantities in radiation protection and their limitations

For more than 50 years the quantity absorbed dose has been the basic physical quantity in the medical applications of ionising radiation as well as radiological protection against harm from ionising radiation. In radiotherapy relatively high doses are applied (to a part of the human body) within a short period and the absorbed dose is mainly correlated with deterministic effects such as cell killing and tissue damage. In contrast, in radiological protection one is dealing with low doses and low dose rates and long-term stochastic effects in tissue such as cancer induction. The dose quantity (absorbed dose) is considered to be correlated with the probability of cancer incidence and thus risk induced by exposure. ICRP has developed specific dosimetric quantities for radiological protection that allow the extent of exposure to ionising radiation from whole and partial body external radiation as well as from intakes of radionuclides to be taken into account by one quantity. Moreover, radiological protection quantities are designed to provide a correlation with risk of radiation induced cancer. In addition, operational dose quantities have been defined for use in measurements of external radiation exposure and practical applications. The paper describes the concept and considerations underlying the actual system of dose quantities, and discusses the advantage as well as the limitations of applicability of such a system. For example, absorbed dose is a non-stochastic quantity defined at any point in matter. All dose quantities in use are based on an averaging procedure. Stochastic effects and microscopic biological and energy deposition structures are not considered in the definition. Absorbed dose is correlated to the initial very short phase of the radiation interaction with tissue while the radiation induced biological reactions of the tissue may last for minutes or hours or even longer. There are many parameters other than absorbed dose that influence the process of cancer induction, which may influence the consideration of cells and/or tissues at risk which are most important for radiological protection.     

Accreditation in radiation protection for cardiologists and interventionalists

Training in radiation protection is widely recognised as one of the basic components of optimisation programmes for medical exposures. Occupational and patient radiation risks in interventional radiology can be quite high and international bodies have shown concern on this item. Following recommendations of the International Commission on Radiological Protection and in accordance with the European Directive on medical exposures, some initiatives for training in radiation protection took place in Spain and Luxembourg. These provided practitioners of interventional radiology adequate theoretical and practical training in radiation protection. The main outcome of the pilot courses organised to this end is discussed, concluding its suitability to implement the European Directive in practice.     

Adaptation of the present concept of dosimetric radiation protection quantities for external radiation to radiation protection practice

The present concept of dosimetric radiation protection quantities for external radiation is reviewed. For everyday application of the concept some adaptations are recommended. The check of the compliance with dose limits should be performed either by the comparison with values of the respective operational quantities directly or by the calculation of the protection quantity by means of the operational quantity, the appertaining conversion coefficient and additional information of the radiation field. Only four operational quantities are regarded to be sufficient for most applications in radiation protection practice. The term equivalent should be used in the connection dose equivalent only. Proposals are made for names of frequently used operational quantities which are denoted up to now by symbols only.     

Regulatory aspects of radiation protection

The paper introduces the projects launched by the European Community to foster prospects in dosimetry, radiation protection and best use of equipment in the medical field. These projects are put in perspective with the European legal framework for radiation protection, in particular, the Basic Safety Standards Directive, the Medical Exposures Directive and the Directive on High-Activity Sealed Sources. A summary is given of the overall mission statements of the commission services in the field of radiation protection, including the field of research, and how they relate to other actions in the overall health policy of the EU. In conclusion, a number of priority areas for future work in the medical field are highlighted.     

Neutron spectrometry for radiation protection

The various instruments used for neutron spectrometry can be divided into four categories. Within each of these categories, the underlying measurement principle for all devices is essentially the same. The applications of the instruments within each group to spectrometry for radiation protection are reviewed.     

International standards for radiation protection

International standards for radiation protection are issued by many bodies. These bodies differ to a large extent in their organisation, in the way the members are designated and in the way the international standards are authorised by the issuing body. Large differences also exist in the relevance of the international standards. One extreme is that the international standards are mandatory in the sense that no conflicting national standard may exist, the other extreme is that national and international standards conflict and there is no need to resolve that conflict. Between these extremes there are some standards or documents of relevance, which are not binding by any formal law or contract but are de facto binding due to the scientific reputation of the issuing body. This paper gives, for radiation protection, an overview of the main standards issuing bodies, the international standards or documents of relevance issued by them and the relevance of these documents.     

Response of radiation protection dosemeters in mixed high-energy photon and electron radiation fields

The response of radiation protection dosemeters in terms of the phantom-related operational quantities Hp(10) and H'(10.0 degrees) was measured for personal and area monitoring systems in mixed high-energy electron and photon radiation fields with energies up to 7 MeV. Using mixed radiation fields composed of different fractions of charged particle and photon fluence, three conditions were produced at the point of measurement: charged particle equilibrium (CPE) (a), a lack (b) and an excess (c) of charged particles relative to the conditions of CPE. Personal and area dosemeters of different types were investigated under conditions (a)-(c). A large variability of the response of the different dosemeter types was observed. The results are presented and discussed.     

Global view on radiation protection in medicine

When planning good management of ionising radiation in medicine, key factors such as ensuring that health professionals work together and convincing them that radiation protection (RP) represents a substantial part of the quality management system in their clinical practice are of utmost importance. The United Nations Scientific Committee on the Effects of Atomic Radiation has decided that one of the thematic priorities will be medical radiation exposure of patients. The International Commission on Radiological Protection has recently updated the report on RP in medicine and continues to work on focused documents centred on specific areas where advice is needed. The roles of the International Atomic Energy Agency, World Health Organization and the European Commission, in the area of RP in medicine, are described in the present document. The industry, the standardisation organisations as well as many scientific and professional societies are also dedicating significant effort to radiation safety aspects in medicine. Some of the efforts and priorities contemplated in RP in medicine over the coming years are suggested. The best outcome will be accomplished when all the actors, i.e. medical doctors, other health professionals, regulators, health authorities and the industry manage to work together.