Focus-skin Distance Research Articles

The impact of 3D stereoscopic visualisation on performance in electron skin apposition techniques using VERT

Abstract Introduction: The Virtual Environment for Radiotherapy Training (VERT) is a simulator used to train radiotherapy students cost-effectively with limited risk. VERT is available as a two-dimensional (2D) and a more costly three-dimensional (3D) stereoscopic resource. This study aimed to identify the specific benefits afforded by stereoscopic visualisation for student training in skin apposition techniques. Method: Eight participants completed six electron skin apposition setups in both 2D and 3D views of VERT using a 7 cm × 10 cm rectangular applicator setup to 100 cm focus skin distance (FSD). The standard deviation (SD) of the mean distance from each corner of the applicator to the virtual patient’s skin surface [which we define as apposition precision (AP)] was measured along with the time taken to achieve each setup. Participants then completed a four-question Likert-style questionnaire concerning their preferences and perceptions of the 2D and 3D views. Results: There was little difference in mean setup times with 218·43 seconds for 2D and 211·29 seconds for 3D (3·3% difference). There was a similarly small difference in AP with a mean SD of 5·61 mm for 2D and 5·79 mm for 3D (3·2% difference) between views. The questionnaire results showed no preference for the 3D view over the 2D. Conclusion: These findings suggest that the 2D and 3D views result in similar setup times and precision, with no user preference for the 3D view. It is recommended that the 2D version of VERT could be utilised in similar situations with a reduced logistical and financial impact.

Dose evaluation in paediatric patients undergoing skull examinations

The purpose of this study was to estimate the kerma-area product (KAP) and incident air kerma of radiographic skull examinations in a large paediatric hospital in Brazil. In addition, the influence of thickness on patient parameters and radiographic technique was verified. A total of 125 paediatric patients (69 males and 56 females) were evaluated, and 294 radiographs (125 projections in anteroposterior/posteroanterior and 123 in lateral, and 46 in Towne) were performed. To analyse the results, the patients were divided into age groups: 0–1 year, 1–5 years, 5–10 years, and 10–15 years. Anthropometric data of the patient (weight, height and thickness) and radiographic technique data (voltage, product current time and focus skin distance) were collected. The analysis of patients' thicknesses and other characteristics which can be used to determine radiographic protocols showed that thickness can be estimated from the patient's age, height, or weight with an uncertainty higher than 15%. The age groups, which are usually used to compare radiographic techniques, are not appropriate for data-oriented decisions. For practical purposes, we suggest the following groups with fixed radiographic protocols; age: <0.5 year, 0.5–1 year, and >1 year; height: 40–60 cm, 60–80 cm, and >80 cm; weight: <5 kg, 5–10 kg and >10 kg. There was a very small correlation between the patient dose and thickness, with a difference of up to 20-fold in dose for patients of the same thickness. If radiological protocols were to be standardized, it should be possible to keep the dose below ∼0.9 mGy. The correlation between the KAP and the patient's thickness is clearer; however, the dispersion of the KAP values is even greater, especially for anteroposterior/posteroanterior projection.

Estimation of Radiation Dose from Most Common Pediatrics Radiographic Examinations within Main Central Hospitals in Najaf City, Iraq

In this study the Entrance Surface Dose (ESD) received by pediatrics patients undergoing chest, abdomen and skull X-ray examinations was estimated. The study was conducted in two hospitals in Najaf city where three radiographic systems were considered. The study participants were classified into four age groups 0-1 , 1-5 , 5-10 and 10-15 years. Calculations were performed using exposure factors, kVp, mAs and focal-skin distance, together with patient data age. The ESD was calculated for the involved patients who underwent an Antero-posterior (AP) chest, abdomen and skull X-ray examination. The resulted data were analyzed and compared with international dose references. For all studied radiographic examinations and all X-ray machines, the ESD increases with age. The lowest recorded radiation dose was from hospital 1 machine 2. In this facility ESD ranged from 19.93 µGy to 67.66 µGy for chest X-ray, from 39.03 µGy to 82.63 µGy for abdomen (AP), and from 35.47 µGy to 94.27 µGy for skull (AP). In contrast the highest dose levels are recorded from hospital 2 machine 1; the minimum ESD for chest X-ray is 247.51 µGy and the maximum is 2393.12 µGy; for abdomen X-ray the lowest ESD is 269.05 µGy and the highest value is 5106.15 µGy; and for skull X-ray minimum values is 430.96 µGy and the maximum value is 3072.77 µGy. In conclusion, for the considered pediatrics examinations, most of ESD values are within the international acceptable level and some are higher &gt;100% .

Evaluation of radiation dose in pediatric radiological exams

Abstract Background Pediatric patients are in a phase of high anatomical and physiological development, whose characteristics make them more radiosensitive to certain radiation exposures. Exposure to doses of radiation can lead to the occurrence of biological effects, including cancer. Objectives To analyze radiation exposures resulting from pediatric radiological examinations and to perform an optimization process, with the purpose to adequate use of the principles of radiological protection. Methods The analysis of radiation doses was performed using the technical parameters of the tests (voltage, current, exposure time and focus-skin distance), the patient's parameters (age, weight and thickness), the calculation of the radiation dose, using the output of the X-ray tube, all recorded at the time of the examination. The results were classified into 4 age groups and 5 weight groups. Results The results were classified according to the patient's age and weight, taking into account the radiation dose received. The data were also separated by gender, as the analysis showed that female patients are slightly smaller than male patients, and as a consequence, the doses received by this gender were lower. Examinations of the chest, abdomen, pelvis, skull and sinuses were analyzed and some groups received higher doses compared to other studies and international dose reference levels (DRL). Conclusions An optimization study must be carried out to verify the possible cause of such values, readjusting the values of the technical parameters and performing a new radiation dose analysis.

Calculating organ and effective doses in paediatric interventional cardiac radiology based on DICOM structured reports – Is detailed examination data critical to dose estimates?

PurposeTo estimate effective dose (E), equivalent organ doses (HT) and associated conversion coefficients (CCE:KAP = E/KAP, CCHT:KAP = HT/KAP; KAP = Kerma-area product) in paediatric cardiac interventions, using detailed exposure data from radiation dose structured reports (RDSR). These “RDSR dose estimations” have been compared with estimations performed using the approach currently implemented in the clinic that is based on a simplified assumptions method (SAM). MethodsThe Monte Carlo system PCXMC, incorporated into a previously developed framework, was used to calculate E and HT for 202 children. The calculations were performed with input values from RDSR, and also using simplified assumptions, including fixed nominal values for the focus-skin distance, collimated beam size, irradiation geometry and patient size (age, weight and height). ResultsMean HT to critical organs were: 5–25 mSv (lungs), 5–8 mSv (breasts) and 5–22 mSv (heart), with the lower and upper end of the doses associated with the neonatal and 15 years group, respectively. The associated mean CCHT:KAP for the different age groups were: 9.4–1.6 mSv/Gycm2 (lungs), 8.9–0.54 mSv/Gycm2 (breasts) and 9.3–1.4 mSv/Gycm2 (heart). ConclusionsThe extension of the concept of a conversion coefficient for HT is introduced and CCHT:KAP values for paediatric cardiac interventions divided in age groups are presented. This method of linking the KAP to HT is intended for use in epidemiological/cohort studies or in clinics that do not have access to RDSR. Further, the population-averaged conversion coefficients for the critical organs estimated from RDSR, displayed no statistically significant difference compared with the SAM approach.

P116] Transition of the patient dose by the diagnostic X-ray examinations in the area of the local-area survey by the novel patient dose calculation system

Purpose The diagnostic reference level (DRLs) was proposed to a patient dose as a tool for optimization by diagnostic X-ray examination. The purpose of this study was to estimate the entrance surface dose for the different types of X-ray examinations of the hospital. In this study, a novel calculation system was developed for estimating the entrance surface doses and the result of the local survey about the patient dose of the local area was reanalyzed. Methods The entrance surface dose by novel calculation system (call estimation patient dose calculation system: EPD) is calculated using the parameter of an X-ray output (tube voltage, current time product, filtration, focus-skin distance, field size, etc.). The coefficient which standardized the output in each conditions based on the measurement result of a standard air kerma is used for this calculation system. Although the standard body thickness according to types of X-ray examination, exposure field size, etc. are used in initial setting, modification is also possible respectively. The entrance surface dose by means of survey continuously conducted by the Ibaraki Association of Radiologic Technologists from 1988 to the hospital in Ibaraki Prefecture was re-analyzed using this calculation system. Results As for the calculation result, a maximum of +20% of difference was confirmed to the measurement result of an ionization chamber type dosimeter (DC300: Wellhofer). However, it is proper as an estimate to the survey for attaining rationalization of a dose. There is a limit in accurate dose estimate by the range of 40–150 kV tube voltage, the difference in filtration, etc. Although the dose was a decline tendency on the whole in the re-analysis result of the patient dose by the novel dose calculation system, transition is trifling in recent years. Conclusions A novel calculation system was developed for estimating the entrance surface dose and the result of the local survey about the patient dose of the area was reanalyzed. The accuracy of dose estimation was investigated and the usefulness was confirmed. The transition of the level of the patient doses in a local area has been grasped.

COMPARING MEASURED AND CALCULATED DOSES IN INTERVENTIONAL CARDIOLOGY PROCEDURES.

Interventional cardiology requires complex procedures and can result in high doses and dose rates to the patient and medical staff. The many variables that influence the dose to the patient and staff include the beam position and angle, beam size, kVp, filtration, kerma-area product and focus-skin distance. A number of studies using the Monte Carlo method have been undertaken to obtain prospective dose assessments. In this paper, detailed irradiation scenarios were simulated mathematically and the resulting dose estimates were compared with real measurements made previously under very similar irradiation conditions and geometries. The real measurements and the calculated doses were carried out using or simulating an interventional cardiology system with a flat monoplane detector installed in a dedicated room with an Alderson phantom placed on the procedure table. The X-ray spectra, beam angles, focus-skin distance, measured kerma-area product and filtration were simulated, and the real dose measurements and calculated doses were compared. It was shown that the Monte Carlo method was capable of reproducing the real dose measurements within acceptable levels of uncertainty.

Justification and good practice in using handheld portable dental X-ray equipment: a position paper prepared by the European Academy of DentoMaxilloFacial Radiology (EADMFR).

Handheld portable X-ray devices are increasingly used for intraoral radiography. This development introduces new challenges to staff and patient safety, for which new or revised risk assessments must be made and acted upon prior to use. Major issues might be: difficulties in using rectangular collimation with beam aiming devices, more complex matching of exposure settings to the X-ray receptor used (e.g. longer exposure times), movements owing to the units' weight, protection of the operator and third persons, and the use in uncontrolled environments. These problems may result in violation of the "as low as reasonably achievable'', that is, ALARA principle by an increase in (re)exposures compared with the other available intraoral X-ray devices. Hence, the use of handheld portable X-ray devices should be considered only after careful and documented evaluation (which might be performed based on medical physics support), when there is evidence that handheld operation has benefits over traditional modalities and when no new risks to the operators and/or third parties are caused. It is expected that the use of handheld portable X-ray devices will be very exceptional, and for justified situations only. Special attention should be drawn to beam-aiming devices, rectangular collimation, the section of the X-ray receptor, focus-skin distance, and backscatter shielding, and that the unit delivers reproducible dose over the full set of environmental conditions (e.g. battery status and temperature).

Estimation of absorbed organ doses and effective dose based on body mass index in digital radiography

With the introduction of digital radiography, patients undergoing radiographic procedures are subject to being overexposed to radiation. Therefore, it is necessary to estimate the absorbed organ dose and the effective dose, which are significant for patient health, along with body type. During chest radiographic examinations conducted in 899 patients for screening, the absorbed dose of the 13 major organs, the average whole-body dose, and two effective doses weighted by factors published in ICRP 60 and ICRP 103 were calculated on the basis of patient information such as height, weight and examination condition, including kilovolt potential, focus-skin distance and entrance surface dose (ESD), using a PC-based Monte Carlo program simulation. It was found that dose per unit ESD had a tendency to decrease with body mass index (BMI). In particular, the absorbed dose for most organs was larger at high voltages (140 kVp) than at low voltages (120 kVp, 100 kVp). In addition, the effective dose which was based on ICRP 60 and ICRP 103 also represented the same tendency in respect of BMI and tube voltage.

Successful use of radiotherapy for radiation-induced basal cell carcinoma of the scalp

Conflict of interest: none declared. In an interesting contribution published in Clinical and Experimental Dermatology,1 a case of basal cell carcinoma (BCC) of the scalp arising after radiotherapy for tinea capitis and successfully treated with radiotherapy was described. In the same article, the question about the management of patients with radiation‐induced skin malignancies was discussed, with considerations we fully share. The authors, however, stated that they were not able to find ‘published reports of successful treatment of radiation‐induced skin cancers with radiotherapy’. Therefore, we think it useful to report that we treated with radiotherapy two women with BCCs of the scalp, which appeared, respectively, 52 and 76 years after end of radiation therapy received for tinea capitis.2 The lesions were treated with contact X‐ray therapy (dose per fraction 5 Gy twice/week, giving a total dose 55 Gy). For the two women, the size of the irradiation fields was 10 and 35 mm, respectively, focus skin distance 15 and 50 mm, half‐value depth 2 and 12 mm, voltage 55 and 60 kV, and current was 4 mA for both. Both lesions are in complete remission 24 and 54 months, respectively, after the end of radiotherapy. To date, the cosmetic result has been judged as good in both lesions.

An assessment of the characteristics of n-type diodes for use in electron beam radiotherapy

Diodes are now commercially available for use in electron beams. This paper aims to assess their response and limitations under different clinical conditions. Parameters considered were applicator factors, focus skin distance (FSD), angle of incidence, and temperature dependence. The beam perturbation was also measured. The beam energies used varied from 5 to 17 MeV. Applicator factors, measured at the surface of a phantom, differed by up to 7% compared with ion chamber measurements at D max. Similarly, large differences were found in FSD dependence. The temperature dependence was found to be approximately double the manufacturer’s specification at 0.7% per degree Centigrade and the angular dependence was within the specification of ± 2% for angles of ± 30°. The beam perturbation was measured as a maximum of 25% for 5-MeV electrons. The measurements were compared to other published data but this is highly dependent on the methodology employed. It was concluded that the diodes could be used in some circumstances, but only if used with extreme caution. An extensive set of commissioning measurements would be required before introducing the diodes into use clinically.

254 poster Correlation between pelvic patient movement derived from electronic portal images and external focus-skin distance measurements

254 poster Correlation between pelvic patient movement derived from electronic portal images and external focus-skin distance measurements

Clinical application and dosimetric calibration procedure of the superficial and orthovoltage therapy unit Therapax DXT300.

The aim of this study was to configure a new superficial and orthovoltage therapy unit for clinical use and discuss the clinical indications for this kind of energy. There is renewed interest in radiotherapy using photon beams in the range from 40 to 300 kVp, in particular for the treatment of non-neoplastic diseases and superficial lesions. This is due to the fact that the latest units are of good quality, relatively cheap and reliable in comparison with alternative equipment. It is therefore necessary to document the steps involved in the clinical application of this therapeutic equipment. The calibration procedure for a new superficial/orthovoltage therapy unit, Therapax DXT300 (Pantak, USA), installed at the Radiotherapy Department of the Mauriziano Hospital in Turin, was carried out by measurement of beam quality (half-value layer, HVL), percentage depth dose (PDD), profiles, internal dosimetry system, dose rate calibration and output factors. The Therapax DXT300 can be programmed to stop treatment either by time or dose, like a linear accelerator. It is equipped with one adjustable collimator (2 x 2 divided by 20 x 20 cm2) for orthovoltage therapy (focus skin distance, FSD = 50 cm) and six fixed applicators for superficial and orthovoltage therapy (FSD = 30 and 50 cm, respectively). Up to eight combinations of generating potential, tube current and added beam filter can be set. In the range of accelerating potentials from 40 to 300 kVp the Therapax provides beams with HVL ranging from 1.48 mm Al to 3.68 mm Cu. As regards the PDD curves, a slight difference between PDD values has been observed with potentials ranging from 200 to 300 kVp. The beam symmetry and flatness are almost the same in Y and X plane directions for accelerating potentials of less than 200 kVp. At higher kVp values these parameters are significantly worse in the anode-cathode axis direction, because the useful X-ray beam is extracted perpendicular to the anode-cathode axis direction: as the energy increases, the bremsstrahlung becomes more forward directed, resulting in a higher dose rate on the anode side. The present paper suggests a methodological approach for the clinical application of an orthovoltage/superficial therapy unit and discusses its current indications. It is necessary to maintain the performance of the equipment within predefined limits in order to meet the requirements of an efficient quality assurance program. This unit is particularly useful in the treatment of superficial lesions and non-neoplastic diseases and in palliative care (eg for bone metastases).

Radiation protection in interventional radiology.

Introduction Furthermore, this information is usually displayed at the operator’s console where it cannot be seen In recent years there has been an increase in by the interventionalist undertaking the examinthe number, type and complexity of interventional ation. Unfortunately, total elapsed fluoroscopy radiology procedures. The impetus behind this time does not correlate very well with maximum rapid and continuing expansion has been the desire skin entrance dose. The latter quantity being for improved, more cost-effective medicine, in dependent on the automatic dose-rate control setwhich the patient can look forward to an improved ting selected, patient’s size, focus–skin distance and prognosis. Often patients having interventional the period of time that the area of skin was radiology procedures are treated as either outirradiated. Equipment developments are required patients or day cases, whereas the alternative surgito enable the interventionalist to be provided with cal technique would require hospitalization. This an on-line display which provides a better indiexpansion in interventional radiology has occurred cation of the potential onset of deterministic effects. in many countries worldwide, irrespective of the Extended fluoroscopy times, sometimes coupled type of system for health care delivery, because of with higher than average fluoroscopy currents can the many benefits. lead to an increased risk of non-deterministic In the main, interventional procedures are characeffects such as leukaemia in which the probability terized by having extended fluoroscopy times, and of the effect is proportional to the dose. The risk sometimes requiring many radiographic images to of inducing a hypothetical cancer at some time in be taken. As a consequence, developments in interthe future from interventional radiology correlates ventional radiology have a number of profound reasonably well with dose–area product. radiation protection implications for both patients Dose–area product is a quantity which may be and staff. In particular, the application of the conmeasured using a large area ionization chamber cept of justification to these procedures is different placed at the output port of the X-ray tube or than to other radiological examinations, as both inferred from a knowledge of X-ray technique deterministic and non-deterministic effects on the factors and the field size. Measurement of dose– patient have to be considered. area product is also recommended in the National Patient Dosimetry Protocol [1]. Patient dose The maximum skin entrance dose can be deduced from the dose–area product if the field For the patient, long fluoroscopy times lead to size and focus–skin distance are known. higher radiation doses, sometimes limited to a Instrumentation that is able to accomplish this is small area of the patient’s skin surface. This in in an early developmental stage. The display of turn leads to the potential for deterministic effects, total dose–area product and the estimated maxisuch as skin erythema, to be seen in patients who mum skin entrance dose on the interventionalist’s have had interventional radiology procedures. television monitor would provide information Physicians treating patients who have had an about the two types of radiation effect. interventional radiology procedure need to be It is also important to minimize patient doses aware of this possibility. whenever possible. One method of trying to achieve The potential induction of deterministic effects patient dose reductions would be to provide the in the skin is compounded by the lack of approinterventionalist with online dose rate information. priate patient dosimetry information available to The interventionalist could then select techniques the interventionalist during the procedure. At prewhich resulted in a lower patient dose, if desired. sent, fluoroscopy units used for interventional radiology are only required to be fitted with an Staff dose indication of total elapsed fluoroscopy time.

Effective Doses for Different Techniques Used for PA Chest Radiography

A survey of X ray units, used for diagnostic chest examinations in the Leiden region, showed considerable variation in exposure conditions and techniques (conventional radiography, mobile unit, lung-shaped filters). Varying the exposure conditions, including focus-skin distance (FSD) and beam quality, as employed in PA chest radiography according to the survey, effective dose (E) was calculated by Monte Carlo simulation of radiation transport. Adult male and female patients were simulated with the mathematical phantoms ADAM and EVA, respectively. For a typical exit dose of 4 µGy, E ranges from 7 to 17 µSv. Thus, proper choice of technique parameters allows a 2.5-fold dose reduction. For similar conditions, E for EVA may differ up to 28% from its value for ADAM. Varying FSD only, differences in E may reach 34%. Lowest doses were found for ADAM at medium FSD, for EVA at small FSD. A small vertical shift (5 cm) in beam position results in a 10% change in E. Best beam quality for radiation protection is offered by large-HVL beams or, for ADAM, small-HVL beams plus lung filters.

Effective Doses for Different Techniques Used for PA Chest Radiography

A survey of X ray units, used for diagnostic chest examinations in the Leiden region, showed considerable variation in exposure conditions and techniques (conventional radiography, mobile unit, lung-shaped filters). Varying the exposure conditions, including focus-skin distance (FSD) and beam quality, as employed in PA chest radiography according to the survey, effective dose (E) was calculated by Monte Carlo simulation of radiation transport. Adult male and female patients were simulated with the mathematical phantoms ADAM and EVA, respectively. For a typical exit dose of 4 µGy, E ranges from 7 to 17 µSv. Thus, proper choice of technique parameters allows a 2.5-fold dose reduction. For similar conditions, E for EVA may differ up to 28% from its value for ADAM. Varying FSD only, differences in E may reach 34%. Lowest doses were found for ADAM at medium FSD, for EVA at small FSD. A small vertical shift (5 cm) in beam position results in a 10% change in E. Best beam quality for radiation protection is offered by large-HVL beams or, for ADAM, small-HVL beams plus lung filters.

Beam characteristics of the Therapax DXT300 orthovoltage therapy unit

The operating performance and beam characteristics of a new orthovoltage unit, the Therapax DXT300, have been evaluated. Percentage depth-dose and backscatter tables are presented for several applicator sizes, at 30 cm and 50 cm focal skin distances (FSDS) and for multiple X-ray beam qualities with the tube operating between 100 and 300 kVp accelerating potential. The unit has been found to provide beam characteristics similar to those reported for other orthovoltage therapy machines. The linearity and short- and longterm stability/reproducibility of the unit's internal dosimetry system have also been studied, and results indicate a very stable beam output of better than 1% standard deviation. The data presented in this work should provide the basis for comparison with other units and act as a reference for clinics commissioning the Therapax DXT300 in the future.

Zur Bestimmung der Ovarialdosis bei der Defäkographie an einem digitalen C-Bogen

When using defaecography as a radiological tool for diagnosing the anorectal function in female patients, the ovaries are inevitably directly exposed. With the aim of minimising the ovarian dose applied both the area-dose product and the surface dose above the ovaries were measured during investigations of female patients with a digital C-arm unit. These values were converted into ovarian doses using tissue-air ratios. From the surface dose measured with TLD-100 a mean ovarian dose of 15.6 +/- 8.6 mGy was derived. The contributions of screening and film exposures were similar. A reduction of screening time by 10 seconds or omission of 60 film exposures results in a decrease of ovarian dose by values between 0.7 and 2 mGy. Employing a greater focus-skin distance during defaecography, however, made it possible to reduce the ovarian dose by 26%.

Organ absorbed doses in intraoral dental radiography

A dental radiography unit operating at 70 kV (nominal) and 20 cm focus-skin distance was used to irradiate an anthropomorphic phantom loaded with lithium fluoride thermoluminescent dosemeters, in order to assess the variation in organ absorbed dose with intraoral periapical radiographic view. 14 views using the bisecting-angle technique and four views using the paralleling technique were studied. The results are presented and the doses and dose distributions examined. Doses for the paralleling and bisecting-angle techniques are compared, and the effects of focus-skin distance and beam collimation upon patient dosimetry discussed. Sources of uncertainty in dental dosimetry studies using phantoms are also considered.

Absorbed dose to organs in the head and neck from bitewing radiography.

Dose measurements were carried out to estimate the absorbed dose to organs at risk from bitewing radiography under exposure conditions similar to those found in general dental practice in The Netherlands. The measurements were carried out in the head and neck of a Rando phantom using TLD-100 ribbons. Three different X-ray machines were used simulating 10 different exposure conditions to determine the effects of beam energy, beam size and focus-skin distance on the absorbed dose. The absorbed dose in the primary beam, close to the focal spot, decreased as the beam energy increased, while behind the film plane it increased with the beam energy. Outside the primary beam, at short distances from the skin surface, the absorbed dose decreased as the energy increased, while behind the film plane and at greater distances from the primary beam the absorbed dose increased as the beam energy increased. The absorbed dose was significantly lower for smaller beam sizes and for larger focus-skin distances, independent of beam energy.