Evolution of imaging findings, laboratory and functional parameters in rheumatoid arthritis patients after one year of treatment with anti-TNF-α agents.

OBJECTIVES: To investigate the efficacy and safety of anti-TNF-α agent treatment compared to non-biologic DMARDs in rheumatoid arthritis patients. METHODS: 82 consecutive patients, 29 males, 53 females, aged 42-79, diagnosed with RA and suitable for anti-TNF-α treatment composed two study groups: 42 with pre-existing rheumatoid arthritis-related interstitial lung disease (RA-ILD) and 40 without RA-ILD. Respective control groups consisted of 44 patients with pre-existing RA-ILD and 44 patients without RA-ILD, treated with non-biologic DMARDs. All patients underwent chest high resolution computed tomography (HRCT), pulmonary function tests (PFTs) and peripheral blood biomarkers at baseline and after one year of treatment. RESULTS: There was a significant decrease of air trapping extent and bronchial wall thickening after treatment in RA-ILD and RA-non ILD study groups (p<0.05). This was accompanied by a statistically significant improvement of maximum mid-expiratory flow (MMEF75-25), RV and RV/TLC in both study groups (p<0.05). In the RA-ILD study group ILD extent scores remained unchanged after anti-TNF-α treatment. None of the RA-non ILD group developed new-onset ILD. In both RA-ILD and RA-non ILD control groups, HRCT findings and PFTs did not differ significantly at the one-year follow-up study. Methotrexate (MTX) regression analysis showed in both RA-ILD study and control groups a negative correlation between MTX dose and ILD extent score at one-year and between MTX dose and air trapping extent at baseline and after one year of treatment. CONCLUSIONS: Anti-TNF-α treatment, in contrast to non-biologic DMARDs, there was an improvement of small airways disease. There was no new-onset ILD or exacerbation of preexisting-ILD, especially in patients treated with anti-TNF-α agents, supporting the efficacy and favourable safety profile of this treatment in RA patients.

MR imaging of spleen in beta-thalassemia major.

PURPOSE: Splenomegaly and splenic siderosis are well-known findings in beta-thalassemia major. We explored the relation between splenic size, splenic and hepatic siderosis in transfusion-dependent beta-thalassemic patients, assessed by MR imaging. MATERIALS AND METHODS: Abdominal MR imaging studies of 47 consecutive thalassemic patients and 10 healthy subjects, used as controls, were retrospectively reviewed. The signal intensity ratios of spleen and liver to the right paraspinous muscle (S/M, L/M, respectively) were calculated on T1, intermediate, and T2*-weighted gradient-echo sequences, splenic volume was estimated on axial images and serum ferritin levels were recorded. RESULTS: Decreased S/M on all MR sequences was displayed in 36 patients. Six patients presented with normal S/M on all MR sequences and 5 patients displayed splenic hypointensity only on T2* sequence. No correlation between S/M and L/M was found whereas both L/M and S/M correlated with serum ferritin (P < 0.03). Splenic volume correlated to L/M (P < 0.05) but not to S/M values. CONCLUSION: In transfusion-dependent patients with beta-thalassemia, iron deposition in spleen cannot be predicted by the degree of hepatic siderosis, whereas splenomegaly relates to liver, but not splenic, iron overload. MR imaging can be a valuable tool in elucidating iron kinetics.

Eye-lens bismuth shielding in paediatric head CT: artefact evaluation and reduction.

BACKGROUND: CT scans of the brain, sinuses and petrous bones performed as the initial imaging test for a variety of indications have the potential to expose the eye-lens, considered among the most radiosensitive human tissues, to a radiation dose. There are several studies in adults discussing the reduction of orbital dose resulting from the use of commercially available bismuth-impregnated latex shields during CT examinations of the head. OBJECTIVE: To evaluate bismuth shielding-induced artefacts and to provide suggestions for optimal eye-lens shielding in paediatric head CT. MATERIALS AND METHODS: A bismuth shield was placed over the eyelids of 60 consecutive children undergoing head CT. Images were assessed for the presence and severity of artefacts with regard to eye-shield distance and shield wrinkling. An anthropomorphic paediatric phantom and thermoluminescence dosimeters (TLDs) were used to study the effect of eye lens-to-shield distance on shielding efficiency. RESULTS: Shields were tolerated by 56/60 children. Artefacts were absent in 45% of scans. Artefacts on orbits, not affecting and affecting orbit evaluation were noted in 39% and 14% of scans, respectively. Diagnostically insignificant artefacts on intracranial structures were noted in 1 case (2%) with shield misplacement. Mean eye-lens-to-shield distance was 8.8 mm in scans without artefacts, and 4.3 mm and 2.2 mm in scans with unimportant and diagnostically important artefacts, respectively. Artefacts occurred in 8 out of 9 cases with shield wrinkling. Dose reduction remained unchanged for different shield-to-eye distances. CONCLUSION: Bismuth shielding-related artefacts occurring in paediatric head CT are frequent, superficial and diagnostically insignificant when brain pathology is assessed. Shields should be placed 1 cm above the eyes when orbital pathology is addressed. Shield wrinkling should be avoided.

Energy imparted-based estimates of the effect of z overscanning on adult and pediatric patient effective doses from multi-slice computed tomography.

In the present study effective dose values normalized to computed tomography dose index measured free in air were calculated for adult, newborn, 1, 5, 10 and 15 year old patients regarding scans of the head, chest, abdomen, pelvis, abdomen and pelvis, and trunk, using the energy imparted method. The effect of z overscanning on patient doses was accounted for, and normalized doses are provided for varying beam collimation, pitch and reconstruction slice width values. The contribution of overscanning depends on patient age, anatomic region imaged, acquisition and reconstruction settings. For a head scan it constitutes 15% of the adult effective dose and 24% of the effective dose to a newborn but for an abdomen scan it may be as high as 58% for a newborn and 31% for an adult. The ratios of normalized pediatric doses relative to that for adults for helical scans depend not only on age but also on acquisition and reconstruction parameters, because of variations in the relative distance between the primary beam and the radiosensitive tissues/organs of the body. Regarding scans of the trunk, pediatric doses are up to a factor of 2.5 times higher compared to adult doses (abdominal scans), whereas for scans of the head up to a factor of 1.5. Increasing the pitch value of helical scans while maintaining the same effective mAs setting, and hence noise levels, leads to an increase in patient doses which depends on age, body region, scan and reconstruction parameters. The % difference between doses at pitch 1.5 and pitch 1 is more pronounced in the abdominal region (14% increase for adults) and in young patients (31% in a newborn and 18% in a 10 year old patient) and it is minimal in head scans (4% increase in newborns and 1% in adults). If multiple body regions are to be imaged, doses to adults can be reduced by up to 15% and 36% to children by performing single long-range scans. Scanning adult patients at 100 kVp instead of 120 kVp, results in a 32% reduction in effective dose from head scans and 38% for scans of the torso. The corresponding reduction for a 5 year old patient is 31% for the head and 37% for the trunk. Due to the combined overbeaming and overscanning effect the 24 mm collimation is more dose effective in the head mode and the 12 mm collimation in the body mode. Provided data enable informed design of examination protocols, calculation of effective dose values and familiarization with the technical features of multi-detector technology.

Influence of z overscanning on normalized effective doses calculated for pediatric patients undergoing multidetector CT examinations.

The purpose of this study was to evaluate the effect of z overscanning on normalized effective dose for pediatric patients undergoing multidetector-computed tomography (CT) examinations. Five commercially available mathematical anthropomorphic phantoms representing newborn, 1-, 5-, 10-, and 15-year-old patients and the Monte Carlo N-Particle (MCNP, version 4C2) radiation transport code were employed in the current study to simulate pediatric CT exposures. For all phantoms, axial and helical examinations at 120 kV tube voltage were simulated. Scans performed at 80 kV were also simulated. Sex-specific normalized effective doses were estimated for four standard CT examinations i.e., head-neck, chest, abdomen-pelvis, and trunk, for all pediatric phantoms. Data for both axial and helical mode acquisition were obtained. In the helical mode, z overscanning was taken into account. The validity of the Monte Carlo results was verified by comparison with dose data obtained using thermoluminescence dosimetry and a physical pediatric anthropomorphic phantom simulating a 10-year-old child. In all cases normalized effective dose values were found to increase with increasing z overscanning. The percentage differences in normalized data between axial and helical scans may reach 43%, 70%, 36%, and 26% for head-neck, chest, abdomen-pelvis, and trunk studies, respectively. Normalized data for female pediatric patients was in general higher compared to male patients for all ages, examined regions, and z overscanning values. For both male and female children, the normalized effective dose values were reduced as the age was increased. For the same typical exposure conditions, dose values decreased when lower tube voltage was used; for a 1-year-old child, for example, the effective dose was 3.8 times lower when 80 kV instead of 120 kV was used. Normalized data for the estimation of effective dose to pediatric patients undergoing standard axial and helical CT examinations on an multidetector CT system were calculated. This data was found to depend strongly on CT acquisition mode and exposure parameters as well as patient age and sex. The effective dose from a pediatric CT scan performed in axial mode was always considerably lower compared to the corresponding scan performed in helical mode, due to the additional tissue regions exposed to the primary beam in helical examinations as a result of z overscanning.

Magnetic resonance imaging evaluation of small intestinal Crohn's disease.

Imaging evaluation in patients with Crohn's disease is based on morphological abnormalities, traditionally disclosed by barium studies including conventional enteroclysis, and more recently by cross-sectional imaging. A major prerequisite for optimal image quality and a more confident diagnosis is the adequate luminal distension of the bowel, which is usually achieved by administering an intraluminal contrast agent through a nasojejunal catheter. Magnetic resonance enteroclysis is a new technique that combines the advantages of volume challenge with state-of-the-art ultrafast pulse sequences, resulting in an excellent demonstration of the anatomy of the small bowel. Magnetic resonance enteroclysis compares favourably with conventional enteroclysis in detecting, localising and assessing the extent of involved small bowel segments. Luminal narrowing and extramural manifestations or complications of the disease can also be accurately assessed by the technique. Imaging features including the presence of deep ulcers, extensive wall thickening and mesenteric lymph nodes exhibiting marked gadolinium enhancement correlate strongly with disease activity. Although the clinical utility of magnetic resonance enteroclysis in Crohn's disease has been widely recognised, its routine application is currently limited to academic centres. Its clinical indications may include follow-up studies of known disease, the classification of Crohn's disease subtypes, an estimation of disease activity and a determination of the extramucosal extent and spread of the disease process.

Data required for testicular dose calculation during radiotherapy of seminoma.

The purpose of this study was to provide the required data for the direct calculation of testicular dose resulting from radiotherapy in patients with seminoma. Paraortic (PA) treatment fields and dog-leg (DL) portals including paraortic and ipsilateral pelvic nodes were simulated on a male anthropomorphic phantom equipped with an artificial testicle. Anterior and posterior irradiations were performed for five different PA and DL field dimensions. Dose measurements were carried out using a calibrated ionization chamber. The dependence of testicular dose upon the distance separating the testicle from the treatment volume and upon the tissue thickness at the entrance point of the beam was investigated. A clamshell lead shield was used to reduce testicular dose. The scattered dose to testicle was measured in nine patients using thermoluminescent dosimeters. Phantom and patient exposures were generated with a 6 MV x-ray beam. Linear and nonlinear regression analysis was employed to obtain formulas describing the relation between the radiation dose to an unshielded and/or shielded testicle with the field size and the distance from the inferior field edge. Correction factors showing the variation of testicular dose with the patient thickness along beam axis were found. Bland-Altman statistical analysis showed that testicular dose obtained by the proposed calculation method may differ from the measured dose value by less than 25%. The current study presents a method providing reasonable estimations of testicular dose for individual patients undergoing PA or DL radiotherapy.

Estimation of effective doses to adult and pediatric patients from multislice computed tomography: A method based on energy imparted.

The purpose of this study is to provide a method and required data for the estimation of effective dose (E) values to adult and pediatric patients from computed tomography (CT) scans of the head, chest abdomen, and pelvis, performed on multi-slice scanners. Mean section radiation dose (dm) to cylindrical water phantoms of varying radius normalized over CT dose index free-in-air (CTDIF) were calculated for the head and body scanning modes of a multislice scanner with use of Monte Carlo techniques. Patients were modeled as equivalent water phantoms and the energy imparted (epsilon) to simulated pediatric and adult patients was calculated on the basis of measured CTDI(F) values. Body region specific energy imparted to effective dose conversion coefficients (E/epsilon) for adult male and female patients were generated from previous data. Effective doses to patients aged newborn to adult were derived for all available helical and axial beam collimations, taking into account age specific patient mass and scanning length. Depending on high voltage, body region, and patient sex, E/epsilon values ranged from 0.008 mSv/mJ for head scans to 0.024 mSv/mJ for chest scans. When scanned with the same technique factors as the adults, pediatric patients absorb as little as 5% of the energy imparted to adults, but corresponding effective dose values are up to a factor of 1.6 higher. On average, pediatric patients absorb 44% less energy per examination but have a 24% higher effective dose, compared with adults. In clinical practice, effective dose values to pediatric patients are 2.5 to 10 times lower than in adults due to the adaptation of tube current. A method is provided for the calculation of effective dose to adult and pediatric patients on the basis of individual patient characteristics such as sex, mass, dimensions, and density of imaged anatomy, and the technical features of modern multislice scanners. It allows the optimum selection of scanning parameters regarding patient doses at CT.

Normalized dose data for upper gastrointestinal tract contrast studies performed to infants.

The aim of the current study was to (a) provide normalized dose data for the estimation of the radiation dose from upper gastrointestinal tract contrast (UGIC) studies carried out to infants and (b) estimate the average patient dose and risks associated with radiation from UGIC examinations performed in our institution. Organ and effective doses, normalized to entrance skin dose (ESD) and dose area product (DAP) were estimated for UGIC procedures utilizing the Monte Carlo N-particle (MCNP) transport code and two mathematical phantoms, one corresponding to the size of a newborn and one to the size of a 1-year-old child. The validity of the MCNP results was verified by comparison with dose data obtained in physical anthropomorphic phantoms simulating a newborn and a 1-year-old infant using thermoluminescence dosimetry (TLD). Data were also collected from 25 consecutive UGIC examinations performed to infants. Study participants were (a) 12 infants aged from 0.5 to 5.9 months (group 1) and (b) 13 infants aged from 6 to 15 months (group 2). For each examination, ESD and dose to comforters were measured using TLD. Patient effective doses were estimated using normalized dose data obtained in the simulation study. The risk for fatal cancer induction was estimated using appropriate coefficients. The results consist of tabulated dose data normalized to ESD or DAP for the estimation of patient dose. Conversion coefficients were estimated for various tube potentials and beam filtration values. The mean total fluoroscopy time was 1.26 and 1.62 min for groups 1 and 2, respectively. The average effective dose was 1.6 mSv for group 1 and 1.9 mSv for group 2. The risk of cancer attributable to the radiation exposure associated with a typical UGIC study was found to be up to 3 per 10 000 infants undergoing an UGIC examination. The mean radiation dose absorbed by the hands of comforters was 47 microGy. In conclusion, estimation of radiation doses associated with UGIC studies performed to infants can be made using the normalized dose data provided in the current study. Radiation dose values associated with UGIC examinations carried out to infants are not low and should be minimized as much as possible.

Scattered dose to thyroid from prophylactic cranial irradiation during childhood: a Monte Carlo study.

The purpose of this study was to estimate the scattered dose to thyroid from prophylactic cranial irradiation during childhood. The MCNP transport code and mathematical phantoms representing the average individual at ages 3, 5, 10, 15 and 18 years old were employed to simulate cranial radiotherapy using two lateral opposed fields. The mean radiation dose received by the thyroid gland was calculated. A 10 cm thick lead block placed on the patient's couch to shield the thyroid was simulated by MCNP code. The Monte Carlo model was validated by measuring the scattered dose to the unshielded and shielded thyroid using three different humanoid phantoms and thermoluminescense dosimetry. For a cranial dose of 18 Gy, the thyroid dose obtained by Monte Carlo calculations varied from 47 to 79 cGy depending upon the age of the child. Appropriate placement of the couch block resulted in a thyroid dose reduction by 39 to 54%. Thyroid dose values at all possible positions of the radiosensitive gland with respect to the inferior field edge at five different patient ages were found. The mean difference between Monte Carlo results and thyroid dose measurements was 9.6%.

Bilio-cutaneous fistula formation after percutaneous liver mass biopsy: embolization of the tract with a gelatin matrix.

We report an unusual complication of ultrasound-guided percutaneous liver biopsy, in the form of a persisting iatrogenic bilio-cutaneous fistula. A patient with liver hilar tumor and malignant obstructive jaundice was initially treated by successful placement of bilateral metallic stents and did well until mass biopsy was decided. The fistula created decreased patient's quality of life, and because the patient refused further interventions, fistula catheterization for embolization was proposed. We injected a gelatin matrix into the extrahepatic portion of the fistula and embolized the tract successfully.

Hepatic artery aneurysm presenting with hemobilia in a patient with Behçet's disease: treatment with percutaneous transcatheteral embolization.

We herein report a case of hemobilia caused by a hepatic artery aneurysm. A 40-year-old male patient with a history of Behçet's disease with a thrombus hanging out of the papilla of Vater had a large hepatic aneurysm in angiography. The hepatic artery feeding the aneurysm was embolized. Endovascular treatment can treat patients with hepatic artery aneurysms caused by Behçet's disease.

Reduction of eye lens radiation dose by orbital bismuth shielding in pediatric patients undergoing CT of the head: a Monte Carlo study.

Our aim in the study was to assess the eye lens dose reduction resulting from the use of radioprotective bismuth garments to shield the eyes of pediatric patients undergoing head CT. The Monte Carlo N-particle transport code and mathematical humanoid phantoms representing the average individual at different ages were used to determine eye lens dose reduction accomplished with bismuth shielding of the eye in the following simulated CT scans: (a) scanning of the orbits, (b) scanning of the whole head, and (c) 20 degrees angled scanning of the brain excluding the orbits. The effect of bismuth shielding on the eye lens dose was also investigated using an anthropomorphic phantom and thermoluminescence dosimetry (TLD). Eye lens dose reduction achieved by bismuth shielding was measured in 16 patients undergoing multiphase CT scanning of the head. The patient's scans were divided in the following: CT examinations where the eye globes were entirely included (n=5), partly included (n=6) and excluded (n=5) from the scanned region. The eye lens dose reduction depended mainly on the scan boundaries set by an operator. The average eye lens dose reduction determined by Monte Carlo simulation was 38.2%, 33.0% and <1% for CT scans of the orbits, whole head, and brain with an angled gantry, respectively. The difference between the Monte Carlo derived eye lens dose reduction factor values and corresponding values determined directly by using the anthropomorphic phantom head was found less than 5%. The mean eye lens dose reduction achieved by bismuth shielding in pediatric patients were 34%, 20% and <2% when eye globes were entirely included, partly included and excluded from the scanned region, respectively. A significant reduction in eye lens dose may be achieved by using superficial orbital bismuth shielding during pediatric head CT scans. However, bismuth garments should not be used in children when the eyes are excluded from the primarily exposed region.

Magnetic resonance enteroclysis.

MR enteroclysis (MRE) is an emerging technique for the evaluation of small intestinal diseases. Administration of an iso-osmotic water solution through a nasojejunal catheter can guarantee adequate luminal distention, and in combination with ultrafast sequences, such as single shot TSE, true FISP, HASTE and 3D FLASH, results in excellent anatomic demonstration of the small intestine. MR fluoroscopy can be performed during MRE examination to monitor the filling process and might be useful in studying low-grade stenosis or motility related disorders. MRE is a very promising technique for the detection and characterization of involved small bowel segments in patients with Crohn's disease while its diagnostic performance in disclosing lumen narrowing and extramural manifestations and complications of the disease is outstanding. Initial experience shows that MRE is very efficient in the diagnosis of small bowel tumors and can be used in the evaluation of small bowel obstruction.

Testicular dose and associated risk from inverted-Y field irradiation in patients with Hodgkin's disease.

This study aims to estimate testicular dose and the associated risks for infertility and hereditary effects from inverted-Y field irradiation Radiotherapy was simulated on a humanoid phantom using a 6 MV photon beam. Testicular dose was measured for various field sizes and tissue thicknesses along beam axis using an ionization chamber. Gonadal dose was reduced by placing lead cups around the testes supplemented by a field edge block. For a tumor dose of 40 Gy, testicular dose was 0.56-6.52 Gy depending upon the field size and the distance from the inferior field edge. The corresponding dose to shielded testes was 0.12-1.96 Gy. The increase of tissue thickness in reased the testicular dose up to 40%. An excess risk of hereditary disorders of (7-391) per 10000 births was calculated. The treatment parameters, the presence of gonad shield and the somatometric characteristics determine whether testicular dose can exceed 1 Gy which allows a complete recovery of spermatogenesis.

Discriminatory ability of magnetic resonance T2* measurements in a sample of postmenopausal women with low-energy fractures: a comparison with phalangeal speed of sound and dual x-ray absorptiometry.

RATIONALE AND OBJECTIVES: We sought to assess the ability of magnetic resonance T2* measurements to discriminate between patients with and without osteoporotic fracture and compare the results with the discriminatory ability of speed of sound (SOS) measured at the phalanx and axial bone mineral density (BMD). MATERIALS AND METHODS: T2* measurements of lumbar spine were obtained at 1.5 T in 26 postmenopausal women with osteoporotic fractures and 28 age-matched healthy control subjects. A multiecho gradient echo (MEGRE) pulse train sequence was used with echo times of 2.70-74.93 milliseconds using 2.33-millisecond interecho intervals. BMD measurements were made in the axial skeleton. SOS also was measured at the finger phalanges. RESULTS: The in vivo short-term reproducibility for T2* was 1.85%. T2*, spinal BMD, total hip BMD, and SOS measurements were found to give comparable discrimination between normal and osteoporotic women with odds ratios of 2.6, 2.6, 3.2, and 2.2, respectively. CONCLUSIONS: T2* measurements of lumbar spine are reproducible and capable of differentiating between postmenopausal women with and those without osteoporotic fractures.

Ultrasound velocity through the cortex of phalanges, radius, and tibia in normal and osteoporotic postmenopausal women using a new multisite quantitative ultrasound device.

RATIONALE AND OBJECTIVES: To assess a new multisite quantitative ultrasound (QUS) device (Sunlight Omnisense 7000 S) suitable for the measurement of speed of sound (SOS) in the phalanges, radius, and tibia. METHODS: The study group consisted of 270 healthy Caucasian postmenopausal patients (mean age: 60.0 +/- 7.6 years) and 53 Caucasian postmenopausal patients (mean age: 67.2 +/- 7.4 years) with osteoporotic fractures. Measurements of SOS and bone mineral density (BMD) were carried out in all subjects. RESULTS: Intraobserver in vivo short-term precision was on average 0.76% for the radius, 0.47% for the tibia, and 1.54% for the phalanges. The interobserver precision ranged from 0.77% to 2.39%. Measurements of SOS at the 3 skeletal sites were significantly correlated (r = 0.28-0.44; P < 0.001). Significant correlations were found between SOS at all sites and BMD (r = 0.21-0.41; P < 0.001). The odds ratio for fracture prediction for SOS was 1.47 for tibia, 1.69 for radius, and 2.69 for phalanx. The corresponding odds ratios for BMD at the lumbar spine, femoral neck, and total hip ranged from 2.08 to 3.26. The area under the receiver operating characteristic curve ranged from 0.611 to 0.741 for SOS measurements and from 0.745 to 0.797 for BMD measurements. CONCLUSIONS: The Omnisense multisite QUS device exhibits reproducible performance. Among the QUS variables, the phalangeal SOS provides the best discrimination of fracture patients.

Comparison of four methods for assessing patient effective dose from radiological examinations.

Three methods of indirect effective dose estimation were reviewed and compared to a direct effective dose determination method. An anthropomorphic phantom and thermoluminescence dosimetry were used to obtain dosimetric data associated with anterior-posterior (AP) abdominal radiography, posterior-anterior (PA) chest radiography, PA head radiography, and AP heart fluoroscopy. Effective dose was determined using: (i) organ specific dose values directly determined by thermoluminescence dosimeters, (ii) data published by National Radiological Protection Board (NRPB) and entrance surface dose (ESD), (iii) NRPB data and dose area product (DAP), (iv) energy imparted derived from DAP. The effective dose values estimated from the Rando phantom measurements were 161, 32.3, and 8.4 microSv/projection for the abdomen, chest, and head radiographs, respectively. Cardiac fluoroscopy yielded an effective dose value of 111 microSv/min. The effective dose values obtained indirectly using NRPB data and DAP were in good agreement with directly assessed values in all simulated exposures (difference <8%). The effective doses using NRPB data and ESD values differed from directly assessed values by less than 15% for the radiographic exposures and 60% for heart fluoroscopy. The energy imparted method yielded 136, 31, and 6.6 microSv/projection for the abdomen, chest, and head radiographs, respectively, and 111 microSv/min for heart fluoroscopy. Indirect patient effective dose determination using the NRPB dosimetric data and the measured value of incident radiation allows for reliable patient effective dose estimates. The use of DAP rather than ESD is recommended because it yields accurate results even for complex radiologic exposures involving fluoroscopy. The value of energy imparted may be used for the accurate determination of patient effective dose, especially when specific organ dose values are not of interest. The calculation of energy imparted with the use of EAP provides a reliable starting point for estimation of effective dose from radiologic examinations for which dosimetric data are not provided by NRPB.

Influence of initial electron beam parameters on Monte Carlo calculated absorbed dose distributions for radiotherapy photon beams.

Our aim in the present study was to investigate the effects of initial electron beam characteristics on Monte Carlo calculated absorbed dose distribution for a linac 6 MV photon beam. Moreover, the range of values of these parameters was derived, so that the resulted differences between measured and calculated doses were less than 1%. Mean energy, radial intensity distribution and energy spread of the initial electron beam, were studied. The method is based on absorbed dose comparisons of measured and calculated depth-dose and dose-profile curves. All comparisons were performed at 10.0 cm depth, in the umbral region for dose-profile and for depths past maximum for depth-dose curves. Depth-dose and dose-profile curves were considerably affected by the mean energy of electron beam, with dose profiles to be more sensitive on that parameter. The depth-dose curves were unaffected by the radial intensity of electron beam. In contrast, dose-profile curves were affected by the radial intensity of initial electron beam for a large field size. No influence was observed in dose-profile or depth-dose curves with respect to energy spread variations of electron beam. Conclusively, simulating the radiation source of a photon beam, two of the examined parameters (mean energy and radial intensity) of the electron beam should be tuned accurately, so that the resulting absorbed doses are within acceptable precision. The suggested method of evaluating these crucial but often poorly specified parameters may be of value in the Monte Carlo simulation of linear accelerator photon beams.

Normalized conceptus doses for abdominal radiographic examinations calculated using a Monte Carlo technique.

The aim of the present study was to develop a reliable method for estimating conceptus radiation doses resulting from abdominal radiographic examinations for all trimesters of pregnancy. The method is based on normalized conceptus doses estimated using Monte Carlo modeling. The Monte Carlo N-Particle (MCNP) radiation transport code was employed in the current study. The validity of the MCNP computational approach was verified by comparison with dose data obtained in anthropomorphic phantoms simulating pregnancy at the three trimesters of gestation using thermoluminescence dosimetry (TLD). The results consist of radiation doses normalized to air kerma so that conceptus dose from any technique and x-ray unit used for abdominal radiography can be easily calculated. Normalized conceptus doses are presented for the first, second, and third trimesters of gestation for various kVp and total beam filtration values. Data apply to radiographic systems equipped with high frequency or 3 phase 12 pulse generators. A very good agreement was observed between the normalized conceptus doses estimated by TLD measurements and the MCNP simulation for all periods of gestation (maximum difference 8.1%). The results of MCNP procedures were compared to published data obtained by TLD measurements. Normalized conceptus dose values agree well, with most differences being lower than 10%. The normalized doses obtained in the current study are dependent on field size. However, for small changes in the size of the x-ray field, the change in normalized doses is not considerable. Accurate estimation of conceptus doses due to abdominal conventional x-ray examinations can be made using the dose data provided in the current study.