Patient radiation protection covers for head CT scans - a clinical evaluation of their effectiveness.

PURPOSE: Although the use of thyroid shields for patients for head CT examinations is reasonable and even required by German regulations, so far available shields are often not used due to difficult applicability. New shields that are easier to use and therefore may gain wider acceptance and more frequent use are now available. In this work two new patient shields are investigated regarding their dose reduction effectiveness and applicability and compared to a thyroid/sternum shield typically used as a part of personal protective equipment. MATERIALS AND METHODS: The reduction of organ doses for thyroid, sternum and mamma were measured with thermoluminescence detectors in an anthropomorphic female phantom. Additionally, the influence of the length or position of the overview scan at the beginning of the CT examination was taken into account. RESULTS: Depending on the patient shield, a reduction of the organ doses for thyroid of 5 - 24 %, for sternum of 25 - 48 % and for mamma of 25 - 70 % could be found. A shift of 25 mm in the cranial direction for the overview scan resulted in a reduction of these organ doses of 12 - 15 %. CONCLUSION: Patient shields for cranial CT examinations provide a considerable dose reduction. New models are easily applied and no decrease in image quality through reconstruction artifacts could be found. Therefore, it is advised to use shields which are applied upon the patient without the need to be wrapped around the neck and the overview scan should be positioned as close as possible to the examined region. KEY POINTS: • New shields provide a compromise between usability and radiation protection.• Patient shields reduce organ doses even when not directly exposed.• The overview scan contributes considerably to out of field organ doses.• Shielding factors are greatly influenced by the positioning of the examination field.

SU-E-I-107: Suitability of Various Radiation Detectors Used in Radiation Therapy for X-Ray Dosimetry in Computed Tomography.

PURPOSE: Assessment of suitability for X-ray dosimetry in computed tomography of various ionization chambers, diodes and two-dimensional detector arrays primarily used in radiation therapy. METHODS: An Oldelft X-ray simulation unit was used to irradiate PTW 60008, 60012 dosimetry diodes, PTW 23332, 31013, 31010, 31006 axial symmetrical ionization chambers, PTW 23343, 34001 plane parallel ionization chambers and PTW Starcheck and 2D-Array seven29 as well as a prototype Farmer chamber with a copper wall. Peak potential was varied from 50 kV up to 125 kV and beam qualities were quantified through half-value-layer measurements. Energy response was investigated free in air as well as in 2 cm depth in a solid water phantom and refers to a manufacturer calibrated PTW 60004 diode for kV-dosimetry. RESULTS: The thimble ionization chambers PTW 31010, 31013, the uncapsuled diode PTW 60012 and the PTW 2D-Array seven29 exhibit an energy response deviation in the investigated energy region of approximately 10% or lower thus proving good usability in X-ray dosimetry if higher spatial resolution is needed or rotational irradiations occur. CONCLUSIONS: It could be shown that in radiation therapy routinely used detectors are usable in a much lower energy region. The rotational symmetry is of advantage in computed tomography dosimetry and enables dose profile as well as point dose measurements in a suitable phantom for estimation of organ doses. Additional the PTW 2D-Array seven29 can give a quick overview of radiation fields in non-rotating tasks.

SU-E-I-42: Measurement of X-Ray Beam Width and Geometric Efficiency in MDCT Using Radiochromic Films.

PURPOSE: The purpose of this work was to measure the x-ray beam width and geometric efficiency (GE) of a multi detector computed tomography scanner (MDCT) for different beam collimations using radiochromic films. In MDCT, the primary beam width extends the nominal beam collimation to irradiate the active detector elements uniformly (called 'over-beaming') which contributes to increased radiation dose to the patient compared to single detector CT. Therefore, the precise determination of the primary beam width and GE is of value for any CT dose calculation using Monte Carlo or analytical methods. METHODS: Single axial dose profiles free in air were measured for 6 different beam collimations nT for a Siemens SOMATOM Sensation 64 Scanner with Gafchromic XR-QA2 films. The films were calibrated relative to the measured charge of a PTW semiflex ionization chamber (type: 31010) for a single rotation in the CT scanner at the largest available beam collimation of 28.8 mm. The beam energy for all measurements in this work was set to 120 kVp. For every measured dose profile and beam collimation the GEin-air and the full-width-at-half- maximum value (FWHM) as a value for the x-ray beam width was determined. Over-beaming factors FWHM / nT were calculated accordingly. RESULTS: For MDCT beam collimations from 7.2 (12×0.6 mm) to 28.8 (24×1.2 mm) the geometric efficiency was between 58 and 85 %. The over- beaming factor ranged from 1.43 to 1.11. For beam collimations of 1×5 mm and 1×10 mm the GE was 77 % and 84 % respectively. The over-beaming factors were close to 1, as expected. CONCLUSIONS: This work has shown that radiochromic films can be used for accurate x-ray beam width and geometric efficiency measurements due to their high spatial resolution. The measured free-in-air geometric efficiency and the over-beaming factor depend strongly on beam collimation.

[Is it really not possible to use electronic personal dosimeters in clinical exposure situations?]. / Sind elektronische Personendosimeter in klinischen Expositionssituationen grundsätzlich nicht einsetzbar?

PURPOSE: Due to significant measuring inaccuracies that can occur under certain conditions, the use of electronic personal dosimeters in statutory measurements in X-ray diagnostics is currently legally restricted. The present study investigates the clinically relevant situations in which measurement errors of more then 20 % can be anticipated. MATERIALS AND METHODS: Four series of experiments were made, comparing the results of the electronic personal dosimeter EPD Mk2.3 to those of reference dosimeters (TLDs and diagnostic dosimeters). On the one hand, personal doses have been determined in the routine operation of controlled areas in various departments. On the other hand, measurements on phantoms have been conducted in extreme but realistic situations under radiation protection. Experiments were conducted in unweakened scattered radiation as well as in unattenuated and attenuated direct radiation. RESULTS: The tested electronic personal dosimeter type meets the requirements regarding measurement accuracy for "official" personal dosimeters in all of the examined clinically relevant scattered radiation fields. Only if exposed to radiation directly, an underestimation of the dose can occur and can be greater than 90 %. CONCLUSION: In the range of scattered radiation of diagnostic X-ray equipment, even in pulsed fields, the use of electronic personal dosimeters is reasonable. Considerable measurement errors can only arise in radiation fields that are not realistic under regular conditions and even in connection with most accidents.

[How conservative is routine personal dosimetry monitoring in diagnostic radiology?]. / Wie konservativ ist die Abschätzung der effektiven Dosis durch die amtliche Personendosimetrie für das Personal in der Radiologie?

PURPOSE: Dose values obtained by official personal radiation exposure monitoring are often considered equivalent to the effective dose of a person. This paper provides estimates of the extent of deviation between the two dose concepts under various conditions. MATERIALS AND METHODS: Doses for patients and personnel were measured using thermoluminescence dosimeters for five different geometries at three work settings in a radiology department. Patients and personnel were simulated with anthropomorphic phantoms. Different types of protective clothing as well as permanent protection shields were considered in the calculations. RESULTS: Dose values obtained by official personal dose monitoring are conservative only for specific radiation protection situations. With state-of-the-art personal protective equipment (wrap-around style lead apron with thyroid shield), the ratio between effective dose and personal dose varies between 0.6 and 1.25. Without thyroid protection the official personal dose systematically underestimates the effective dose: for protective clothing with 0.5 mm lead equivalent without thyroid shielding, the effective dose exceeds the personal dose by factors between 1.7 and 3.1. If protective clothing with lead equivalent 0.35 mm is used, this factor varies between 1.1 and 1.82. CONCLUSION: The official exposure monitoring algorithms for estimating the effective dose for occupationally exposed personnel are not always appropriate for typical situations in diagnostic radiology. Improved dose measurement protocols should avoid underestimation of the effective dose. The results presented herein provide an opportunity to derive more realistic effective dose values from personal dosimetry measurements.

A model and reference data for retrospective dose assessment of organ doses (red bone marrow, lymphatic system) in diagnostic radiography and nuclear medicine, 1946-1995.

Retrospective dosimetry for radiologic and nuclear medicine examinations has been a challenge both for individual patients and in epidemiologic studies. Methodological problems include the large range of patient exposures from radiologic examinations, which spans over three orders of magnitude, the considerable dose reduction over time for most types of examinations due to technical advancements, and the increasing concern for radiation protection and quality issues in radiologic practice. A three-step model for retrospective dosimetry for patient exposure is presented that allows determination of organ doses to the red bone marrow and the lymphatic tissue, respectively, for typical examinations over the time period 1946-1995. The model starts from a set of doses assuming ideal technical equipment and radiologic practice. Step II considers the advancement of technical equipment over the different decades since the introduction of medical radiology in the early 1940's. Step III refers to quality in radiologic routine and allows for adjustment for less-than-ideal standards of radiologic practice. Model parameters are derived from contemporary literature and a multitude of historical sources. Tables with reference data are provided that allow a straightforward application of the model in the context of analytic epidemiologic studies. Wherever possible, reference doses are based on dose area product to allow for easy adjustment to different settings and inclusion of prospective data. The model and the results can be readily extended to different countries with different technical advancement and standard of radiologic practice.

[Optimizing staff radiation protection in radiology by minimizing the effective dose]. / Optimierung des Strahlenschutzes für das Personal in der Radiologie auf Grundlage der effektiven Dosis.

PURPOSE: In the present study the optimization of radiation protection devices is achieved by minimizing the effective dose of the staff members since the stochastic radiation effects correlate to the effective dose. MATERIALS AND METHODS: Radiation exposure dosimetry was performed with TLD measurements using one Alderson Phantom in the patient position and a second phantom in the typical position of the personnel. Various types of protective clothing as well as fixed shields were considered in the calculations. RESULTS: It was shown that the doses of the unshielded organs (thyroid, parts of the active bone marrow) contribute significantly to the effective dose of the staff. Therefore, there is no linear relationship between the shielding factors for protective garments and the effective dose. An additional thyroid protection collar reduces the effective dose by a factor of 1.7 - 3.0. X-ray protective clothing with a 0.35 mm lead equivalent and an additional thyroid protection collar provides better protection against radiation than an apron with a 0.5 mm lead equivalent but no collar. CONCLUSION: The use of thyroid protection collars is an effective preventive measure against exceeding occupational organ dose limits, and a thyroid shield also considerably reduces the effective dose. Therefore, thyroid protection collars should be a required component of anti-X protection.

Estimation of x ray overexposure in a childhood leukaemia cluster by means of chromosome aberration analysis.

Only multiple X ray diagnostics could be identified as a common risk factor in a leukaemia cluster that appeared between 1985-1989 in the municipality of Sittensen in northern Germany. In order to judge if the effect could be explained by irradiation dose, estimates were done in two of the leukaemia cases and seven former patients of a practice where some of the leukaemia cases had been treated for orthopaedic reasons. The methods used for the reconstruction of doses were physical simulation and biological dosimetry by dicentric chromosomes in peripheral lymphocytes. Compared to the Bremen laboratory control the mean frequency of dicentric chromosomes in the lymphocytes of the seven volunteers was significantly elevated. An overexposure of about 12-fold could be derived compared to state of the art X raying. At least two cases of the leukaemia cluster in Sittensen can therefore be correlated to an overexposure by diagnostic X rays.

[Radiation exposure in diagnostic radiation: a quantification model for analytic epidemiological studies]. / Strahlenexposition in der Röntgendiagnostik: Ein Quantifizierungsmodell für analytische epidemiologische Studien.

The present paper introduces a model for retrospective assessment of radiation exposure to patients undergoing conventional diagnostic radiography. The model allows for the quantification of relevant organ doses as well as the effective dose from exposures in the time period between 1946 and 1995. The assessment procedure consists of three consecutive steps. The first step uses a set of ideal doses that were measured under optimum conditions. In the second step, we account for the state of radiological technology available at the time of a given exposure. The third step, finally, considers the prevailing standard of radiological practice. Model parameters are derived from a compilation of data from the contemporary radiologic literature as well as from a multitude of historic sources. The three-dimensional matrix of ideal doses and respective correction factors presented here can be readily implemented in the context of analytic epidemiological studies.

[Thoracic radiography in intensive care units. Comparison of an asymmetric film-screen-grid combination with an L-film]. / Thoraxaufnahmen auf der Intensivstation. Vergleich einer asymmetrischen Film-Folien-Raster-Kombination mit einem L-Film.

PURPOSE: Using an asymmetrical screen-film-grid combination with an ITC-VHC special grid (Kodak), the effect of the individual components was evaluated with regard to detail in the lungs and mediastinum as well as patient dose. MATERIALS AND METHODS: The system was compared with the Curix Ortho screen film system (Agfa L-film) using phantoms and 62 patients in an intensive care unit. The results were analysed by three independent observers. Dose measurements on phantoms were carried out with a WD 10 (Wellhoefer) dosimeter and with a thermoluminescence dosimeter for patients. RESULTS: Both phantom and patient images showed improved demonstration of mediastinal structures with similar details of lung structure. Details in the peripheral lungs are significantly better shown with the ITC-VHC system with the special grid than they are without the grid. However, there is an increase about three to four times in radiation dose when using the grid. CONCLUSION: Our trial shows that the use of the ITC-VHC grid system is to be recommended for routine clinical use because of the better demonstration of details, but one must be aware of the increased radiation dose to the patient.

[A versatile phantom for hemodynamic measurements with ultrasound Doppler equipment]. / Ein vielseitiges Phantom für hämodynamische Messungen mit Ultraschall-Doppler-Geräten.

The test object described comprises a blood simulating liquid pumped through tubes embedded in tissue-mimicking material. The main components of the system can be realised in different ways. They are largely exchangeable with each other. Water, reticulated foam or silicone rubber is used as bulk background material, blood vessels are simulated using latex or silicone tubes or heat-shrink sleeving; in the artificial blood, sephadex particles or silicone emulsion were used as scatterers. The suspension of scattering particles is driven by a roller pump or a membrane dosage pump. The features of the components are described and the applications of the different phantoms discussed.

[The AMBER thoracic imaging system in routine diagnosis]. / Das AMBER-Thoraxaufnahmesystem in der Routinediagnostik.

After installation of an Amber lung x-ray imaging system the range of application of this technique was registered for two months. Additionally the image quality for structures of the lung parenchyma and mediastinum were proved and dose measurements were performed. 50.6% (772) patients from a total of 1525 could be x-rayed by the Amber imaging system. Related to all people able to stand 73.6% from 1049 patients were examined with the Amber system. Most of the imaging figures of merit specified by the German national physician board were accomplished, besides the fact that 1/3 of the p.a. radiographs were cut off at the side because of the small size of the film. The excellent image of pleuro-mediastinal structures was proofed quantitatively by counting the pleuro-mediastinal lines and comparing the results with standard radiographs. Measuring the exposure at entrance point we obtained nearly the same values for the Amber system using a screen-film combination with a speed of 400 and conventional radiographs (40-120 mu Gy; 21 pat.).

[The determination of the surface and organ doses in the AMBER system. Advanced Multiple Beam Equalization Radiography]. / Bestimmung von Oberflächen- und Organdosen am AMBER-System.

Surface and organ doses were determined by means of thermoluminescence dosimetry with the Alderson-Rando phantom and the patient, for the AMBER thoracic imaging system, sensitivity class 400, and the conventional grid screen stand, sensitivity class 200. The dose on entering the body, which varied according to object-dependent modulation of x-ray intensity, was 140 microGy for the mediastinum and 96 microGy for the lung in p.a. AMBER takes, and hence was comparable with the entrance dose of 132 microGy with the conventional grid screen stand. In lateral takes the entrance doses were lower with the AMBER system (302 microGy) than with conventional takes (593 microGy). Exposure of the gonads at the AMBER system for p.a. thoracic takes was lower than at the screen grid stand in females (4-6 microGy). More unfavourable values were measured for the gonad exposure in males (2-0.8 micrograms).

[The findings of color Doppler sonography in breast tumors]. / Befunde der Farb-Doppler-Sonographie bei Tumoren der Brustdrüse.

UNLABELLED: 72 histologically confirmed tumours of the breast--37 carcinomas and 35 benign tumours--for which mammograms were also available were examined by colour Doppler sonography. Vascularisation of benign processes showed at most 2 vessels (with the exception of 3 sarcoma phylloides and one proliferative mastopathy). Vascularisation clearly in excess of benign processes was observed in only 15 of the 37 carcinomas. In 33 of the carcinomas there was no doubt concerning the diagnosis preoperatively, in the remaining 4 the high vascularity was taken as an indication for surgery. CONCLUSION: In rare cases colour Doppler sonography can provide additional information in the presence of 'vascular' tumours. It is not possible to differentiate between poorly vascularised carcinomas and benign tumours.

[Color-coded Doppler sonographic studies of the morphology and hemodynamics of the pelvic and leg arteries in normal subjects]. / Farbcodierte doppler-sonographische Untersuchungen zur Morphologie und Hämodynamik der Arterien des Beckens und der Beine bei gesunden Probanden.

An attempt has been made to demonstrate the morphology and haemodynamics of the arteries in the pelvis and lower limbs by means of angiodynography in 20 normal individuals. Problem areas for morphological evaluation are the pelvic vessels, the vessels in the distal adductor canal and the fibular artery in the calf. Haemodynamic studies are successful if the morphology can be adequately shown, but for flow measurements this is true only in the thigh. The results of quantitative haemodynamic analyses are detailed in tabular form (systolic flow -, late systolic reverse and diastolic flow velocity; deceleration; pulsation index; flow values).

[Phantom measurements of blood flow using color-coded Doppler sonography (Quantum Angiodynograph): accuracy and sources of error]. / Phantommessung des Blutflusses mit der farbkodierten Doppler-Sonographie (Quantum Angiodynograph): Genauigkeit und Fehlerquellen.

Flow measurements were carried out on a phantom simulating tissue, using systematic variations of various parameters and of relevant geometric factors. The effect of imaging and flow parameters on the accuracy of the measurements is described and the conditions are defined which are necessary for obtaining a high degree of accuracy. Large errors are introduced by measurements carried out with large Doppler angles or if the delimiters used for automatic vessel measurements have not been set up accurately.

Contributions to depth discrimination gamma-gamma-coincidence methods in scintigraphy.

Two problems in the gamma-gamma-coincidence method for depth discrimination in scintigraphy are discussed. Firstly, the FW (1/e)M of the distribution function of time differences between 'coincident' pulses is calculated to be the optimum resolving time for measurement of true coincidences. Secondly, the improvement of time resolution of such an apparatus by substituting a large volume NaI(TI) crystal by an array of many small ones is analysed. It is shown that such arrays will have no practical advantage since the loss in efficiency is of the same order of magnitude as the gain in time resolution.