Estimations of organ doses DT received during computed tomographic examinations are usually performed by applying conversion factors to basic dose indicators like the computed tomography dose index (CTDI) or the dose-length-product (DLP). In addition to the existing conversion factors for beam apertures of 5 mm or 10 mm, we present new DLP-DT conversion factors adapted to high-resolution CT (HRCT) examinations of infants and young children with beam apertures of the order of 1 mm and under consideration of bow tie filtration. Calculations are performed on mathematical MIRD phantoms for an age range from 0, 1, 5, 10, 15 up to (for comparison) 30 years by adapting PCXMC, a Monte Carlo algorithm originally developed by STUK (Helsinki, Finland) for dose reconstructions in projection radiography. For this purpose, each single slice CT examination is approximated by a series of corresponding virtual planar radiographies comprising all focus positions. The transformation of CT exposure parameters into exposure parameters of the series of corresponding planar radiographies is performed by a specially developed algorithm called XCT. The DLP values are evaluated using the EGSRay code. The new method is verified at a beam aperture of 10 mm by comparison with formerly published conversion factors. We show that the higher spatial resolution leads to an enhanced DLP-DT conversion factor if a small organ (e. g. thyroid gland, mammae, uterus, ovaries, testes) is exactly met by the chosen CT slice, while the conversion factor is drastically reduced if the chosen CT slice is positioned above or below the organ. This effect is utilized for dose-saving examinations with only a few single slices instead a full scan, which technique is applied in about 10% of all paediatric chest CT examinations.

The present study has been inspired by the results of earlier dose measurements in tissue-equivalent materials adjacent to thin foils of aluminum, copper, tin, gold, and lead. Large dose enhancements have been observed in low-Z materials near the interface when this ensemble was irradiated with X-rays of qualities known from diagnostic radiology. The excess doses have been attributed to photo-, Compton, and Auger electrons released from the metal surfaces. Correspondingly, high enhancements of biological effects have been observed in single cell layers arranged close to gold surfaces. The objective of the present work is to systematically survey, by calculation, the values of the dose enhancement in low-Z media facing backscattering materials with a variety of atomic numbers and over a large range of photon energies. Further parameters to be varied are the distance of the point of interest from the interface and the kind of the low-Z material. The voluminous calculations have been performed using the PHOTCOEF algorithm, a proven set of interpolation functions fitted to long-established Monte Carlo results, for primary photon energies between 5 and 250 keV and for atomic numbers varying over the periodic system up to Z = 100. The calculated results correlate well with our previous experimental results. It is shown that the values of the dose enhancement (a) vary strongly in dependence upon Z and photon energy; (b) have maxima in the energy region from 40 to 60 keV, determined by the K and L edges of the backscattering materials; and (c) are valued up to about 130 for "International Commission on Radiological Protection (ICRP) soft tissue" (soft tissue composition recommended by the ICRP) as the adjacent low-Z material. Maximum dose enhancement associated with the L edge occurs for materials with atomic numbers between 50 and 60, e.g., barium (Z = 56) and iodine (Z = 53). Such materials typically serve as contrast media in medical X-ray diagnostics. The gradual reduction in the dose enhancement with increasing distance from the material interface, owed to the limited ranges of the emitted secondary electrons, has been documented in detail. The discussion is devoted to practical radiological aspects of the dose enhancement phenomenon. Cytogenetic effects in cell layers closely proximate to surfaces of medium-Z materials might vary over two orders of magnitude, because the dose enhancement is accompanied by the earlier observed about twofold increase in the low-dose RBEM at a tissue-to-gold interface.

Computer tomography (CT) is vital and currently irreplaceable in diagnostic radiology. But CT operates with ionizing radiation which may cause cancer or non-cancer diseases in humans. The degree of radiation impact depends on the dose administered by an investigation. And this is the core issue: Even CT exams executed lege artis, administer doses to patients which by magnitude are far beyond the level of hitherto known doses of conventional film-screen techniques. Patients undergoing one or multiple CT examinations, digital angiographies or interventions will be exposed to effective doses between roughly several mSv and several 100 mSv depending on type and frequency of the diagnostic investigations. From the radiation protection point of view, there is therefore the worldwide problem of formulating firm rules for the control of these high-dose investigations, as dose limits can not be established for reasons of the medical benefit. This makes the difference compared with radiation protection for occupationally exposed persons. What remains is "software", namely "justification" and "optimization". Justification requires balancing the interests between the health benefit and the potential harm of an exam which has to be responsibly executed by the physician himself; therefore the radiologists' associations are in the duty to prepare practicable rules for justification. Optimization again needs a cooperative solution, and that is the establishment of reference doses for diagnostic examinations, to be checked by the technical service of the producers' companies. Experts and authorities have been aware of the high-dose dilemma in diagnostic imaging since long. It is time for the reflection of active solutions and their implementation into practice.

The use of ionising radiation in medicine is the single largest man-made source of population exposure. Individual and collective doses to patients arising from the medical use of ionising radiations continue to rise significantly year on year. This is due to the increasing use of medical imaging procedures in modern healthcare systems as well as the continued development of new high dose techniques. This paper reviews the scientific basis for the principles of radiation protection as defined by the International Commission on Radiological Protection. These principles attempt to include exposures arising from both medical and non-medical applications within a common framework and have evolved over many years and changing socioeconomic considerations. In particular, the concepts of justification and ALARA (doses should be as low as reasonably achievable), which underpin the principles for medical exposures are assessed in terms of their applicability to the scientific process and relevance to a rapidly changing technologically-led healthcare system. Radiation protection is an integral component of patient safety in medical practices and needs to be evidence based and amenable to the scientific process. The limitations imposed by the existing philosophy of radiation protection to the development of a quantitative framework for adequately assessing the performance of medical imaging systems are highlighted. In particular, medical practitioners will require quantitative guidance as to the risk-benefits arising from modern X-ray imaging methods if they are to make rational judgements as to the applicability of modern high-dose techniques to particular diagnostic and therapeutic tasks. At present such guidance is variable due to the lack of a rational framework for assessing the clinical impact of medical imaging techniques. The possible integration of radiation protection concepts into fundamental bio-medical imaging research activities is discussed.

OBJECTIVE:Little is known about the long-term effects of exposure to diagnostic ionizing radiation in childhood. Current estimates are made with models derived mainly from studies of atomic bomb survivors, a population that differs from today's patients in many respects.MATERIALS AND METHODS:We analyzed the cancer incidence among children who underwent diagnostic x-ray exposures between 1976 and 2003 in a large German university hospital. We reconstructed individual radiation doses for each examination and sorted results by groups of referral criteria for all cancers combined, solid tumors, and leukemia and lymphoma combined.RESULTS:A total of 68 incidence cancer cases between 1980 and 2006 were identified in a 78,527-patient cohort in the German childhood cancer registry: 28 leukemia, nine lymphoma, six tumors of the CNS, and 25 other tumors. The standardized incidence ratio for all cancers was 0.97 (95% CI, 0.75-1.23). Dose-response relations were analyzed by multivariable Poisson regression. Although the cancer incidence risk differed by initial referral criterion for radiographic examination, a positive dose-response relation was observed in five patients with endocrine or metabolic disease.CONCLUSION:Overall, we observed no increase in cancer risk among children and youths with very low radiation doses from diagnostic radiation, which is compatible with model calculations. The growing use of CT warrants further studies to assess associated cancer risk. Our work is an early contribution of epidemiologic data for quantifying these risks among young patients.

Radiation exposure due to medical imaging is a topic of emerging importance. In Europe this topic has been dealt with for a long time and in other countries it is getting more and more important and it gets an aspect of public interest in the latest years. This is mainly true due to the fact that the average dose per person in developed countries is increasing rapidly since threedimensional imaging is getting more and more available and useful for diagnosis. This paper introduces the most common dose quantities used in medical radiation exposure characterization, discusses usual ways for determination of such quantities as well as some considerations how these values are linked to radiation risk estimation. For this last aspect the paper will refer to the linear non threshold theory for an imaging application.

PURPOSE:Although the carcinogenic effect of ionizing radiation is well known, knowledge gaps persist on the health effects of low-dose radiation, especially in children. The cancer incidence rate in a cohort of 92,957 children diagnosed using X-rays in the years 1976 - 2003 in the radiology department of a large university clinic was studied.MATERIALS AND METHODS:Individual radiation doses per examination were reconstructed using an algorithm taking into account the dose area product and other exposure parameters together with conversion factors computed specifically for the equipment and protocols used in the radiology department. Incident cancer cases in the period 1980 - 2006 were identified via record linkage to the German Childhood Cancer Registry using pseudonymized data.RESULTS:A total of 87 cancers occurred in the cohort between 1980 and 2006: 33 leukemia, 13 lymphoma, 10 brain tumors, and 31 other tumors. The standardized incidence ratio (SIR) for all cancers was 0.99 (95 % CI: 0.79 1.22). A dose-response relationship was not observed for all cancers, leukemia and lymphoma or solid tumors. The cancer risks for boys and girls did not differ.CONCLUSION:No increase in the cancer incidence risk in relation to very low doses of diagnostic ionizing radiation was observed in this study. However, the results are compatible with a broad range of risk estimates.

Purpose: Calculation of conversion coefficients for the reconstruction of organ doses from entrance doses for thoracoabdominal babygrams of premature neonates with a gestational age of 23 and 27 weeks and of mature neonates. Materials und Methods: Using the commercially available personal computer program PCXMC developed by the Finnish Centre for Radiation and Nuclear Safety (Sateilyturvakeskus STUK), conversion coefficients for conventional thoracoabdominal babygrams were calculated with Monte Carlo simulations in mathematical hermaphrodite phantom models describing patients of different ages. Results: Conversion coefficients for the reconstruction of organ doses in approximately 40 organs and tissues of the human body from measured entrance doses during thoracoabdominal babygrams were calculated for the standard sagittal beam projections and the standard focus film distance of 100 cm. Conclusion: The conversion coefficients presented in this paper may be used for organ dose assessments from entrance doses measured during thoracoabdominal babygrams especially in patients in special care baby units.

Imaging plates commonly replace analogue film in radiography, yet not in individual monitoring. One reason for this is the temporal instability of the optically stimulated luminescence signal over prolonged storage time, termed ‘fading’. The present investigation comprises measurements of noncommercially available imaging plate prototypes of the BaFBr:Eu type in order to test their applicability to individual monitoring. Results are included for relative luminescence yield, reusability, dose response, photon energy-dependence of response, and fading.

Technical progress in computed tomography (CT) has substantially increased the clinical efficacy of CT procedures and offered promising new applications in diagnostic imaging. On the other hand, data from various national surveys have confirmed, as a general pattern, the growing impact of CT as a major source of patient and population exposure. From a radiation-hygienic point of view, it is thus necessary to optimize the medical benefit of CT examinations to patients, while strictly controlling and reducing their risk from the radiation exposure. It is the purpose of this chapter to summarize relevant dosimetric concepts for dose assessment in CT, to give an overview on the specific factors determining radiation exposure to patients in MSCT, and to provide suggestions for the optimization of MSCT protocols to balance patient exposure against image quality.

ESR spectroscopy using amino acid alanine as sensor material has developed ability, in the recent past, for outstanding and versatile dosimetry. Physically the method makes use of the radiation induced generation of free radicals in alanine: ESR spectroscopy serves for identification of the free radical type and for quantification of its concentration which corresponds linearly to the given radiation dose, in a wide dose range. Alanine/ESR dosimetry has reached acceptance as a leading technology in high-dose standardisation, world-wide. Currently it is high-ranking in therapy level dosimetry for clinical applications and used for reference metrology in postal dose intercomparisons aiming at both high energy photon and electron radiation. Alanine/ESR dosimetry has qualified to compete Fricke dosimetry and complement ionization chamber dosimetry, with respect to high reliability, low uncertainty, small size and easy handling. The present review reports on the evolution of alanine/ESR dosimetry and on its established dosimetric properties up to the current state-of-the-art. The review has an eye also on international reports and recommendations dealing with alanine/ESR dosimetry, e.g. published by ICRU, ISO, IAEA.

PURPOSE:Calculation of conversion coefficients for the reconstruction of organ doses from entrance doses for abdomen radiographs of 0, 1, 5, 10, 15, and 30-year-old patients in conventional pediatric radiology for the radiographic settings recommended by the German and European guidelines for quality management in diagnostic radiology. MATERIALS UND METHOD: Using the commercially available personal computer program PCXMC developed by the Finnish Center for Radiation and Nuclear Safety (Säteilyturvakeskus STUK), conversion coefficients for conventional abdomen radiographs were calculated performing Monte Carlo simulations in mathematical hermaphrodite phantom models describing patients of different ages. The possible clinical variation of beam collimation was taken into consideration by defining optimal and suboptimal radiation fields on the phantoms' surfaces. RESULTS:Conversion coefficients for the reconstruction of organ doses in about 40 organs and tissues of the human body from measured entrance doses during abdomen radiographs for 0, 1, 5, 10, 15, and 30-year-old pediatric patients were calculated for the standard sagittal and lateral beam projections and the standard focus film distances of 100 cm and 115 cm. CONCLUSION:The conversion coefficients presented in this paper may be used for organ dose assessments from entrance doses measured during abdomen radiographs of patients of all age groups and all beam collimations within the optimal and suboptimal standard beam collimations.

Ionizing radiation is an established cause of cancer, yet little is known about the health effects of doses from diagnostic examinations in children. The risk of childhood cancer was studied in a cohort of 92.957 children who had been examined with diagnostic X rays in a large German hospital during 1976-2003. Radiation doses were reconstructed using the individual dose area product and other exposure parameters, together with conversion coefficients developed specifically for the medical devices and standards used at the radiology department. Newly diagnosed cancers occurring between 1980 and 2006 were determined through record linkage to the German Childhood Cancer Registry. The median radiation dose was 7 mu Sv. Eight-seven incident cases were found in the cohort: 33 leukemia, 13 lymphoma, 10 central nervous system tumors, and 31 other tumors. The standardized incidence ratio (SIR) for all cancers was 0.99 (95% CI: 0.79-1.22). No trend in the incidence of total cancer, leukemia or solid tumors with increasing radiation dose was observed in the SIR analysis or in the multivariate Poisson regression. Risk did not differ significantly in girls and boys. Overall, while no increase in cancer risk with diagnostic radiation was observed, the results are compatible with a broad range of risk estimates. (C) 2009 by Radiation Research Society

X-ray imaging in diagnostic radiology is recognized worldwide as an outstanding tool for the early recognition and prevention of diseases. The reverse side is that radiography contributes essentially to the exposure of the public. Mean effective doses, averaged over patients and non-patients, are reaching or exceeding the level of natural radiation. This is particularly the case when digital imaging techniques are utilized, such as CT, coronary angiography and interventional radiology. Individual effective doses for a patient may occur between several mSv and several hundred mSv by one examination or a series of examinations, while individual organ doses of a patient may reach equivalent doses even up to several Sv, such as for the skin. The purpose of this review is to provide information on effective dose levels occuring in diagnostic radiology as compared with individual effective doses achieved from environmental radiation, radiation at workplaces and after major radiation incidents.

Ziele: Rontgendiagnostische Untersuchungen von Kindern bedurfen der besonderen Aufmerksamkeit, nicht zuletzt in Anbetracht des erhohten kindlichen Strahlenrisikos. Dabei kann die Kollektivdosis in der Rontgendiagnostik als ein Mas fur das stochastische Strahlenrisiko der Patienten aufgefasst werden. Dargestellt werden die im Rahmen der konventionellen Rontgendiagnostik an einer Universitats-Kinderklinik bei Kindern aller Altersstufen applizierten Kollektivdosen. Methode: In der Abteilung Radiologie im Dr. von Haunerschen Kinderspital werden seit 1976 die im klinischen Routinebetrieb anfallenden Rontgenexpositionsdaten einschlieslich der gemessenen Dosisflachenprodukte in elektronischen Datenbanksystemen dokumentiert. Anhand von Monte-Carlo-Simulationen an den mathematischen padiatrischen MIRD-Phantomen von Tapiovara & Servomaa wurden unter Berucksichtigung samtlicher Standard-Untersuchungsverfahren der padiatrischen Radiologie die in der Abteilung Radiologie im Dr. von Haunerschen Kinderspital bei einem Kollektiv von weit uber 100.000 Patienten aller Altersstufen uber einen Zeitraum von nahezu 30 Jahren applizierten Kollektivdosen abgeschatzt. Ergebnis: Es konnte gezeigt werden, dass vor allem die zwar vergleichsweise selten durchgefuhrten, jedoch mit vergleichsweise hohem Dosisbedarf assoziierten Durchleuchtungsverfahren wesentlich zum iatrogenen stochastischen Strahlenrisiko von Kindern beitragen. Schlussfolgerung: Wie die dosimetrischen Analysen zeigen, ist das iatrogene stochastische Strahlenrisiko beim Kind im wesentlichen mit der im Rahmen von Durchleuchtungsuntersuchungen applizierten Strahlendosis assoziiert. Eine Reduktion dieser Strahlendosis kann neben dem vermehrten Einsatz der gepulsten Durchleuchtung vor allem durch eine besonders sorgfaltige Indikationsstellung zu Durchleuchtungsuntersuchungen bei Kindern erreicht werden. Korrespondierender Autor: Seidenbusch M Dr. von Haunersches Kinderspital Munchen, Abteilung Radiologie, Lindwurmstr. 4, 80337 Munchen E-Mail: adressems@aol.com

In April 2007, the American College of Radiology released the "White Paper on Radiation Dose in Medicine". The Blue Ribbon panel members included private practice and academic diagnostic radiologists, medical physicists, representatives of industry and regulatory groups, and a patient advocate. The panel concluded that the expanding use of imaging modalities using ionizing radiations such as CT and nuclear medicine may result in an increased incidence of radiation-related cancer in the exposed population in the not-too-distant future, and this problem can likely be minimized by preventing the inappropriate use of such imaging and by optimizing studies that are performed to obtain the best image quality with the lowest radiation dose. The White Paper set forth practical suggestions to minimize radiation risk, including education for all stakeholders in the principles of radiation safety and preferential use of alternative (non-ionizing) imaging techniques, such as MRI and ultrasound. These recommendations are especially relevant for cardiologists, who prescribe and/or practice medical imaging examinations accounting for at least 50% of the total effective dose by radiation medicine, which amounts to an equivalent of about 160 chest x-rays per head per year in US. Were they be enacted, these simple recommendations would determine a revolution in the contemporary way of teaching, learning and practising cardiology.

Patients are exposed to X rays when undergoing medical examinations in diagnostic radiology. Exposure data acquired and assessed in Germany for the year 1997 resulted in a mean annual effective dose of 2 +/- 0.5 mSv per head of the population, thereby reaching or exceeding the average level of environmental radiation in many cases. The underlying frequency of medical X-ray examinations was approximately 136 million, i.e. approximately 1.7 examinations annually per head of the population. For comparison, corresponding data of other countries were extracted from the UNSCEAR 2000 report or originate from the literature. Data analysis shows significant differences in national radiological practices and a very uneven distribution of patient doses amongst the world population. The mean annual effective dose per head of the population varies by up to a factor of 60 between health care level I and IV countries, and still by a factor of approximately 6 within health care level I countries. While projection radiography has succeeded in reducing dose consumption, computed tomography and radiological interventions have given rise to a significant growth of patient exposure, and interventional radiology can even exceed thresholds for deterministic radiation effects. Patient exposure is further shown to result from misadministration and retakes of X-ray examinations, usually not registered, as well as from technical failures of X-ray facilities, which can cause significantly enhanced exposure times. Corresponding data are presented and comments are made on the international situation of non-harmonised data collection on patient exposure as well as of parameters affecting the assessment of exposure and risk.

In individual voxel phantoms, which were segmented from whole-body computed tomography (CT) scans, S-values were calculated for (131)I using the EGS4 Monte Carlo code and compared to Medical Internal Radiation Dose (MIRD) S-values, which were derived from transport calculations in idealized mathematical phantoms. The individually calculated S-values agree very well with the MIRD values for organs, which are source and target simultaneously, when individual organ-mass corrections are applied to the MIRD values. For different source-target combinations, large deviations up to 184% were found. The contribution of the gamma-absorbed fractions to the total dose, however, is small ( approximately 4%). We conclude, therefore, that individual transport calculations in radionuclide-targeted therapies are not necessary for macroscopic dose estimates. Reliable dosimetry is reduced to the problem of accurate activity determination in vivo.