Entrance surface, organ and effective doses for some of the patients undergoing different types of X ray procedures in Bangladesh

Entrance surface doses (ESDs) were measured for the most common types of X ray procedures, such as chest PA, lumber spine AP, lumber spine lateral, skull AP, skull lateral and pelvis AP in four major hospitals of Dhaka, the capital city of Bangladesh. Organ/tissue doses for 29 organs/tissues and effective doses for the patients were also calculated using the entrance surface dose as the input quantity. Organ/tissue doses and effective doses were calculated by using XDOSE software based on the Monte Carlo computation method. It was observed that the fluctuation of the entrance surface dose was too large. The ratio of maximum and minimum ESD values ranged from 4.8 to 35.9. Consequently, variation of organ doses was large even in the same type of X ray examination and in the same facility. Mean effective doses for the above mentioned X ray procedures were also determined and compared with the effective doses of some other countries. In most cases effective doses measured for the different types of X ray procedures were found to be lower than the effective doses of some other countries.     

Microdosimetric characterisation of 28 kVp Mo/Mo,Rh/Rh,Rh/Al,W/Rh and Mo/Rh mammography X ray spectra

Microdosimetric characteristics of 28 kVp mammography X ray spectra were studied for several target/added filtration combinations (Mo/Mo, Rh/Rh, Rh/Al, W/Rh, Mo/Rh). Monte Carlo techniques were used to model X ray production from mammography units and to calculate distributions of absorbed dose and energy imparted in breast tissue. The results show that the dose averaged lineal energy is about 5.0 keV.micron-1, about 25% higher than for general diagnostic imaging X ray spectra. Significant differences in lineal energy between the five X ray qualities were noted, with the highest value for the commonly used Mo/Mo combination. Spectral hardening with depth in the tissues causes a 5% decrease in lineal energy over 5 cm. No significant differences were found for the different tissue compositions.     

Patient dose, image quality and radiographic techniques for common X ray examinations in two Greek hospitals and comparison with European guidelines

The radiographic technique factors and the quality of each radiographic image for three common examinations (chest PA, pelvis AP and lumbar spine LAT) were compared with the European criteria and entrance surface dose (ESD) was measured for each radiograph in two Greek hospitals. The measurements were carried out using calibrated LiF thermoluminescence dosemeters. The patients were selected so that their weight was close to 70 +/- 10 kg and their height to 170 +/- 10 cm. Effective dose values were calculated using a PC-based Monte Carlo program. All four X ray rooms in the survey achieved mean doses well below the European reference doses. However the mean doses in the X ray rooms differed by a factor of about 3.     

Paediatric dose reduction with the introduction of digital fluorography

Fluoroscopy guided examinations in a paediatric X ray department were initially carried out on a unit that used a conventional screen-film combination for spot-films. A new fluoroscopy unit was installed with the facilities of digital fluorography and last image hold. Comparison of equipment performance showed that the dose per image for screen-film and digital fluorography was 3 microGy and 0.4 microGy, respectively. Although the screen-film had superior image quality, the department's radiologist confirmed that digital fluorography provided a diagnostic image. Patient dose measurements showed that introduction of the new unit caused doses to fall by an average of 70%, although fluoroscopy time had not changed significantly. The new unit produced 40% less air kerma during fluoroscopy. The remaining 30% reduction in dose was due to the introduction of digital fluorography and last image hold facilities. It is concluded that the use of digital fluorography can be an effective way of reducing paediatric dose.     

Diagnostic X ray dose profiles in molar teeth using Monte Carlo simulation

The dose profiles in molar teeth from diagnostic X rays was calculated using the Monte Carlo software program MCNP4c2. The information calculated supports needs in EPR retrospective dosimetry to account for diagnostic X ray exposures in teeth. Only tooth positions 6, 7 and 8 were simulated (the three teeth furthest back including the wisdom teeth) using a very detailed model of the pertinent physiology. The lingual and buccal halves of teeth were evaluated as were the crown dentin and roots in tooth position 7. Linear dose profiles through the enamel were also calculated.     

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.     

Validation of a radiotherapy treatment planning system using an anthropomorphic phantom and MTS-N thermoluminescent detectors

A treatment planning system (TPS) was validated in conditions of simulated radiotherapy (RT) of an anthropomorphic tissue-equivalent phantom. Individually calibrated solid MTS-N (LiF:Mg,Ti) detectors were placed within the treatment volume in this phantom which was then repeatedly irradiated by external 60Co or 6 MV X ray beams. On the basis of TLD-measured depth-dose curves for the two beams, the relative accuracy of determining dose (of the order of 1 Gy) at live depths in a water phantom is about 0.4-0.6%. In the volume of interest representing the target volume, the relative standard difference between the calculated and measured dose values ranged between 1.3% and 2.2% for the 60Co and 6 MV X ray beams, respectively. The TPS-calculated uniformity of irradiation of that volume is within 1%. While fraction-to-fraction repeatability was within 1-2%, systematic underexposure around the reference point, by 2-3%, was found in two consecutive exposures by sets of both beams.     

Measurements of X ray absorbed doses to dental patients in two dental X ray units in Nigeria

Measurements of absorbed doses from radiographic examinations to various anatomical sites in the head and neck of patients with an average age of 45 years using intra-oral dental radiography have been carried out. LiF (TLD-100) dosemeters were used for the measurements of the absorbed dose. The measured absorbed doses to the various anatomical sites in the two units are reported, discussed and compared with results from the literature. Quality control measurements were also performed using a Victoreen quality control test device on the X ray units. The tube voltage accuracies for the two units were found to be within acceptable limits (less than +/- 10%). On the other hand the exposure time accuracies for these units have large deviations (>20%). These results and those that have been reported in the literature may be an indication that high patient doses are common in most dental X ray centres and countries. As a result of this, regular compliance and performance checks of dental diagnostic X ray equipment are essential in order to ensure proper performance and to minimise unnecessary patient and operator doses.     

Induction of chromosome aberration in human lymphocytes and its dependence on X ray energy

The variations of dose response with X ray energy observed with the human lymphocyte dicentric assay is examined. In order to determine reliably the initial slopes (RBEm) many cells need to be analysed at low doses. Insufficient analysis may explain some reported interlaboratory differences in fitted dose-response coefficients. One such discrepancy at 150 kVp, E = 70 keV is examined. Data are also presented for an X ray spectrum of 80 kVp, E = 58 keV. Over the photon energy range 20 keV X rays to 1.25 MeV gamma rays RBEm varies by about a factor of 5, with the lower energies being more effective. This is consistent with microdosimetric theory. By contrast, in radiological protection a radiation weighting factor of 1.0 is assumed for all photons when assessing the risk of inducing cancer at low doses. The measured variations of biological effect with photon energy have led to suggestions that the lower energies, as used for some diagnostic radiology, carry a greater risk per unit dose than is normally assumed by those involved in radiological protection. Interpretation of the data reported in this paper does not support this view.     

Local diagnostic reference levels in standard X-ray examinations

The national diagnostic reference levels (NDRLs) form an efficient, concise and powerful standard for optimising radiation protection of a patient. However, in a large hospital, where many radiological departments are present, it is also possible to calculate and define lower dose values as local diagnostic reference levels (LDRLs). In our hospital there are eight radiological departments; in each of these, the entrance skin dose (ESD) distributions were determined for 10 standard projections (AP Abdomen, PA and LAT Chest, AP and LAT Lumbar Spine, LAT Lumbo-Sacral Joint, AP Pelvis, PA and LAT Skull and AP Urinary tract) and then the ESDs were compared with data previously published and with Italian NDRLs. All ESD values were below the corresponding NDRLs. The maximum/minimum ratio of ESDs ranged from 3.9 (LAT Skull) to 34.3 (AP Abdomen) for individual adult patients and from 2.1 (PA Skull) to 6.5 (Urinary tract) across the mean values of the radiological departments. Finally, it is shown how LDRLs can be proposed to obtain a more fully optimised radiation protection of patients.     

Dose estimation by EPR spectroscopy of tooth enamel in Chinese medical diagnostic X-ray workers

Individual accumulated doses were determined by electron paramagnetic resonance spectroscopy of tooth enamel in Chinese medical diagnostic X-ray workers. Dose determination was performed using a specially developed automatic spectrum processing procedure. The determined dose values owing to X rays for the three workers with entry year (the year they began their career as medical diagnostic X-ray workers) in the 1950s ranged from 435 to 903 mGy, the converted effective doses ranged from 91 to 190 mSv.     

Medical radiation usage and exposures from medical X ray diagnosis in Shandong province of China

Shandong province is situated in the eastern part of China with a population of 88 million. A collaborative survey was conducted in 1999 to investigate the medical radiation usage and the patients' exposures from medical X ray diagnosis in this province. There were three stages in this survey: general survey, sampling survey and dose survey. Patients' entrance surface doses (ESD) were measured using thermoluminescence dosemeters (TLDs) attached to the patient's skin. All the hospitals in this province and 2153 patients were included in this survey. The frequencies of tele- and brachytherapy were 1.450 and 1.685 per 1000 population in 1996 and 1998 respectively. The frequency of diagnostic nuclear medicine was 0.325 and 0.412 per 1000 population in 1996 and 1998 respectively; for therapeutic nuclear medicine, it was 0.015 and 0.021. The total annual frequencies of every type of X ray examination and interventional radiology (IVR) in 1996 and 1998 were 179.8 and 200.0 per 1000 population respectively. The main type of X ray examination was chest fluoroscopy, which made up about 39% of the total. The average entrance surface doses were comparatively high for the examinations of CT, gastrointestinal tract, lumbarspine, urography, angiography, hip and cerebral angiography.     

Filtered X ray beam dosimetry from 10(-3) to 10(2) Gy dose range by using phototransistors

Low-cost, commercially available phototransistor-type semiconductor devices have been tested for monitoring filtered X ray beam dose. A Pantak X-ray unit was used to generate aluminium filtered X ray beams from 60 to 120 kV potentials. The analysis of the radiation detection behaviour as a function of the X ray tube parameters (peak kilovoltage and electrical current) are presented. The changes of the phototransistor electronic parameters have been evaluated and the results indicate that phototransistors can be used as X ray detectors for dose estimation in two different ways: electrical current read-out from 1 to 100 mGy dose range, and the changing of the radiation detection sensitivity in the dose range from 0.1 to 100 Gy. In addition, the devices show high reliability with no sign of substantial performance degradation with use and, in certain dose ranges, the cumulative dose evaluations could be performed up to 10,000 times with no need for re-calibration.     

Neonatal doses from X ray examinations by birth weight in a neonatal intensive care unit

The aim of this study was to investigate the frequency and type of X ray examinations performed on neonates classified according to their birth weight in a neonatal intensive care unit (NICU). In this study, the radiology records of 2408 neonates who were admitted to the NICU of Oita Prefectural Hospital between January 1994 and September 1999 were investigated. This study revealed that the neonates with earlier gestational ages and lower birth weights required longer NICU stays and more frequent X ray examinations made using a mobile X ray unit. The average number of X ray examinations performed on neonates of less than 750 g birth weight was 26 films per neonate. In regard to computed tomography and fluoroscopy, no significant relationship was found between the birth weight and number of X rays. This study revealed that the entrance-surface dose per neonate was dependent upon the birth weight, while the maximum dose was not dependent upon the birth weight. The average neonatal dose in the NICU was predominantly from computed tomography and fluoroscopy. The individual dose varied widely among neonates.     

Radiation exposure to patients during paediatric cardiac catheterisation

Radiation doses were investigated for 18 infants and children undergoing cardiac catheterisation procedures with thermoluminescence dosemeters. The range of integrated current values used during cardiac catheterisation procedure was wide, from 12.2 to 1195.8 mA.min (mean 604.9). The average was 22.9 mA.min for fluoroscopy, and 616.1 mA.min for cineangiography, and the ratio of cineangiography to fluoroscopy ranged from 10.5 to 89.5 with an average of 34.0. The cineangiographic contribution was estimated to be 90% of the total doses. The entrance surface doses and thyroid doses varied widely. The ratio of maximum to minimum for entrance surface doses was 98.5, for left and right thyroid it was 59.8 and 104.4, respectively. The analysis of the entrance surface doses in three age groups showed that there was no significant difference among them. There was a weak inverse relation between the thyroid dose and the weight of the patient, while no correlation was found between the thyroid dose and the entrance surface dose. The average of entrance surface doses to the patients was 847.3 mGy, which was 1-2 orders of magnitude higher than common X ray examinations.     

Radiation doses to paediatric patients and comforters undergoing chest X rays

Pneumonia is an important cause of hospital admission among children in the developed world and it is estimated to be responsible for 3-18 % of all paediatric admissions. Chest X ray is an important examination for pneumonia diagnosis and for evaluation of complications. This study aims to determine the entrance surface dose (ESD), organ, effective doses and propose a local diagnostic reference level. The study was carried out at the university hospital of Larissa, Greece. Patients were divided into three groups: organ and effective doses were estimated using National Radiological Protection Board software. The ESD was determined by thermoluminescent dosemeters for 132 children and 76 comforters. The average ESD value was 55 ± 8 μGy. The effective dose for patients was 11.2 ± 5 μSv. The mean radiation dose for comforter is 22 ± 3 μGy. The radiation dose to the patients is well within dose constraint, in the light of the current practice.     

Targeted Gold Nanocluster‐Enhanced Radiotherapy of Prostate Cancer

For over a hundred years, X‐rays have been a main component of the radiotherapeutic approaches to treat cancer. Yet, to date, no radiosensitizer has been developed to selectively target prostate cancer. Gold has excellent X‐ray absorptivity and is used as a radiotherapy enhancing material. In this work, ultrasmall Au₂₅ nanoclusters (NCs) are developed for selective prostate cancer targeting, radiotherapy enhancement, and rapid clearance from the body. Targeted‐Au₂₅ NCs are rapidly and selectively taken up by prostate cancer in vitro and in vivo and also have fast renal clearance. When combined with X‐ray irradiation of the targeted cancer tissues, radiotherapy is significantly enhanced. The selective targeting and rapid clearance of the nanoclusters may allow reductions in radiation dose, decreasing exposure to healthy tissue and making them highly attractive for clinical translation.     

Development of a real-time hand dose monitor for personnel in interventional radiology

Medical procedures denoted as interventional radiology require operation near an X ray beam, which brings high dose exposures to the operators' hands. For the effectual control of their extremity doses, a prototype of a real-time wrist dosemeter has been developed, hand dose monitor (HDM), based on a single silicon detector. Experiments were performed to test its response to diagnostic X rays. The HDM was highly sensitive and showed a linear response down to doses of a few tens of microsieverts. Though dose rate, energy and angular dependence of the response were observed in some extreme conditions, the HDM was proved to be of practical use if it was appropriately calibrated. Since an HDM enables personnel to check their hand doses on a real-time basis, it would enable medical staff to control the exposure themselves.     

A motion-based approach to abdominal clutter reduction

In ultrasound images, clutter is a noise artifact most easily observed in anechoic or hypoechoic regions. It appears as diffuse echoes overlying anatomical structures of diagnostic importance, obscuring tissue borders and reducing image contrast. A novel clutter reduction method for abdominal images is proposed, wherein the abdominal wall is displaced during successive-frame image acquisitions. A region of clutter distal to the abdominal wall was observed to move with the abdominal wall, and finite impulse response (FIR) and blind source separation (BSS) motion filters were implemented to reduce this clutter. The proposed clutter reduction method was tested in simulated and phantom data and applied to fundamental and harmonic in vivo bladder and liver images from 2 volunteers. Results show clutter reductions ranging from 0 to 18 dB in FIR-filtered images and 9 to 27 dB in BSS-filtered images. The contrast-to-noise ratio was improved by 21 to 68% and 44 to 108% in FIR- and BSS-filtered images, respectively. Improvements in contrast ranged from 4 to 12 dB. The method shows promise for reducing clutter in other abdominal images.     

The calibration of dosimetry instruments used in interventional radiology

No general agreement about the definition of the patient dose exists. As regards the radiation health risk, the doses to specific organs, Hi, are the ultimate measures for a patient dose. Values of the calibration measured, Hi, are provided only by calculational means. Out of the whole process of patient dose determination, the instruments to measure X ray spectra, FSD, field dimensions and Ka can be calibrated, X ray quality is derived from the total filtration and kV value. The actual dynamic and X ray quality ranges shall be considered when air kerma and DAP meters are calibrated. A DAP meter measurement averages the uniform radiation field specific for the X ray tube assembly used and for the beam shaping technique performed. Therefore, a DAP meter calibrated on site is preferable for patient dosimetry in interventional radiology.