Comments on 'Increasing film-focus distance (FFD) reduces radiation dose for X-ray examinations' by P.C. Brennan, S. McDonnell and D. O'Leary

Sir, Comments on ‘Increasing film-focus distance (FFD) reducesradiation dose for X-ray examinations’ by P.C. Brennan,S. McDonnell and D. O'Leary. In a recent publication, Brennan et al.⁽¹⁾ claim that increasingthe film-focus distance (FFD) from 100 to 130 cm will reduceeffective doses (E) by 33% for a pelvic X-ray examination. Thisconclusion is based on a reported 33% reduction in the entrancesurface dose (ESD), by the use of the same effective dose perunit ESD conversion coefficient (E/ESD) at both FFD values.However, E/ESD values are only valid for the specific     

Patient-size-dependent radiation dose optimisation technique for abdominal CT examinations

Since patient doses from computed tomography (CT) are relatively high, risk-benefit analysis requires dose to patients and image quality be optimised. The aim of this study was to develop a patient-dependent optimisation technique that uses patient diameter to select a combination of CT scanning parameters that minimise dose delivered to patients undergoing abdominal CT examinations. The study was performed using cylindrical phantoms of diameters ranging from 16 to 40 cm in order to establish the relationship between image degradation, CT scanning techniques, patient dose and patient size from two CT scanners. These relationships were established by scanning the phantoms using standard scanning technique followed by selected combinations of scanning parameters. The image noises through phantom images were determined using region of interest software available in both scanners. The energy depositions to the X-ray detector through phantoms were determined from measurements of CT dose index in air corrected for attenuation of the phantom materials. The results demonstrate that exposure settings (milliampere seconds) could be reduced by up to 82 % for smaller phantom relative to standard milliampere seconds, while detector signal could be reduced by up to 93 % for smaller phantom relative to energy depositions required when scanned using standard scanning protocols. It was further revealed that the use of the object-specific scanning parameters on studies performed with phantom of different diameters could reduce the incident radiation to small size object by up to 86 % to obtain the same image quality required for standard adult object. In view of the earlier mentioned fact, substantial dose saving from small-sized adults and children patients undergoing abdomen CT examinations could be achieved through optimal adjustment of CT scanning technique based on the patient transverse diameter.     

Patient dose estimation for multi-detector-row CT examinations

The spread of Multi-detector-row computed tomography (MDCT) has been remarkable. Here, various organ and tissue doses were evaluated with six types of MDCT scanners in common use in Japan; using thermoluminescence dosimeters and anthropomorphic phantoms under condition of routine clinical examinations of the chest in adult and child, of the head in child and of the abdomen-pelvis in adult. Estimated lung doses and averaged effective dose in chest examinations were 19.2 +/- 2.03 mGy and 9.54 +/- 0.90 mSv for the adult and 15.7 +/- 1.88 mGy and 7.42 +/- 0.82 mSv for the child phantom, respectively. The numerical difference between effective dose and organ or tissue doses was about 2-2.5 times. For the adult abdomen-pelvis examinations, averaged effective dose was 13.0 +/- 3.72 mSv. Averaged effective dose for the child head examinations was 2.6 +/- 1.32 mSv. In one case, the dose approached 80 mGy for the brain in the head examination, giving a difference from the effective dose of 10 times or more.     

Monte Carlo calculation of radiation dose in CT examinations using phantom and patient tomographic models

By using a voxel-based Monte Carlo simulation technique, we developed and validated a method to calculate radiation-absorbed dose in the computed tomography (CT) examinations from the images of phantoms and patients. The ionising radiation transport was simulated using the EGS4 code system. The geometry of the X-ray beam (focus-to-axis distance, field of view, collimation, and primary and beam-shaper filtration) and the X-ray spectral distribution (HiSpeed LX/i) were included in the simulation. Each axial CT image was reduced to a 256 x 256 matrix and stacked in a volume. The patient images were segmented before the simulation of radiation transport by using four categories of materials, such as air, lung, muscle and bone. To test the voxel-based method, the values of the radiation dose derived from a simulated CT exposure were calculated and compared with those obtained from the measurements performed within the dosimetry phantoms. To complete the scope of the work, series of CT scans of the trunk of an anthropomorphic phantom and patients were simulated to calculate the average dose in each 1-cm-wide transverse slice (ADS). The comparison between the simulated and measured dose data for the CT indices showed a difference of <5% in all the cases. The estimated mean values of ADS from the chest, abdomen and pelvis of the anthropomorphic phantom were approximately 1.7-2 times the weighted CT dose index (CTDI(w)) value, whereas the mean ADS values for these anatomical areas were 1.3-2 times the CTDI(w) of patients. The voxel-based simulation method provided a technique for estimating the individual patient doses in the CT examinations.     

Dosimeter for real-time monitoring of nuclear radiation energy (dose) using a metal-gas-insulator-semiconductor structure

A new type of semiconducting dosimeter is proposed for real-time monitoring of nuclear radiation energy (dose). This dosimeter produces an electrical output signal directly proportional to the incident radiation dose (and not its intensity) and its sensitivity to this radiation dose can be controlled. Pis’ma Zh. Tekh. Fiz. 24, 64–69 (November 26, 1998)     

Comparison of full field digital (FFD) and computed radiography (CR) mammography systems in Greece

The purpose of this study is to evaluate and compare the performance of 52 full field digital (FFD) and computed radiography (CR) mammography systems checked by the Greek Atomic Energy Commission with respect to dose and image quality. Entrance surface air kerma (ESAK) was measured and average glandular dose (AGD) was calculated according to the European protocol on dosimetry in mammography. The exposures were performed using the clinical protocol of each laboratory. The image quality was assessed by the total score of resolved phantom structures incorporated in an American College of Radiology accreditation phantom. The mean ESAK values for FFD and CR systems were 4.59 ± 1.93 and 5.0 ± 1.78 mGy, respectively, whereas the AGD yielded a mean value of 1.06 ± 0.36 mGy for the FFD and 1.04 ± 0.35 mGy for the CR systems. Considering image quality, FFD systems indicated a mean total score of 13.04 ± 0.89, whereas CR systems a mean total score of 11.54 ± 1.06.     

Comparison of patient radiation dose from chest and lumbar spine X-ray examinations in 10 hospitals in Ghana

This study estimated the patient dose in chest and lumbar spine radiographic examinations in 10 hospitals in Ghana. Dose estimations were done on 1045 patients (aged, 39.6 ± 10.6 y; range 18-85 y) involving 501 (47.9%) males and 544 (52.1%) females for a total of 1495 individual projections. The entrance surface dose (ESD) for the patients was assessed by an indirect method, using the patient's anatomical data and exposure parameters utilised for the specific examination and a Quality Assurance Dose Database software developed by Integrated Radiological Services Ltd in Liverpool, UK. The study showed variations in the ESDs for chest examinations with five of the hospitals having values above the internationally recommended levels. ESDs for lumbar spine anterior-posterior and lateral projections were within acceptable limits. Diagnostic reference levels proposed by the International Commission on Radiological Protection based on patient dose data are imperative to the current Ghanaian situation and will lead to a reduction of the radiation dose.     

Towards dose reduction in CT: patient radiation dose assessment for CT examinations at university health center in Canada and comparison with national diagnostic reference levels

Dose indicators such as the computed tomography dose index (CTDI) and dose-length product (DLP) were gathered for all routine abdomen-pelvis, chest and head examinations performed on all computed tomography (CT) scanners at a University Health Center (UHC) in Canada. These indicators were analysed and compared with the range of diagnostic reference levels (DRLs) suggested by Health Canada and with DRLs in other countries. Mean DLP values varied from one scanner to another, but mean values at the UHC (750 mGy cm(-1) for abdomen-pelvis CT, 349 mGy cm(-1) for chest CT and 1181 mGy cm(-1) for head CT) were all below the upper limit of the range of DRLs suggested by Health Canada. Local DRLs at the UHC were set to 810 mGy cm(-1) for abdomen-pelvis CT, 345 mGy cm(-1) for chest CT and 1205 mGy cm(-1) for head CT. Results, however, show the need for protocols revisions, since some scanners exhibit mean DLP values slightly below or above the upper limit of the range of DRLs suggested by Health Canada.     

A method of estimating exposure dose for a scanning x-ray beam

Translated from Izmeritel'naya Tekhnika, No. 10, pp. 53–54, October, 1991.     

PRDC--a software package for personnel radiation dose calculation

To determine effective dose, we usually need to use a very complicated human body model and a sophisticated computer code to transport radiations in the body model and surrounding medium, which is not very easy to practicing health physicists in the field. This study develops and tests a software package, called PRDC (Personnel Radiation Dose Calculation), which calculates effective dose and radiation doses to various organs/tissues and personal dosemeters based on a series of interpolations.     

Assessment of annual effective dose due to natural gamma radiation in Zanjan (Iran)

The outdoor and indoor measurement of natural gamma radiation in Zanjan province (Iran) was made using a Geiger-Muller dosemeter. The average outdoor and indoor dose rates were determined as 127 +/- 20 and 135 +/- 23 nSv h(-1), respectively. The average annual effective dose was calculated as 0.82 mSv, which is more than the same value worldwide.     

A compton polarimeter for synchrotron radiation in the x-ray energy range

A polarimeter for synchrotron radiation in the energy range E ? 15 keV is described. It utilizes 90° Compton scattering by low Z atoms in a thin organic foil. The effect of double scattering on the analyzing power is calculated. The instrument can be used for continuously monitoring the intensity and the polarization of a photon beam during an experiment.     

电子产品检测中电气间隙和爬电距离的确定

不同的安全标准对电气间隙和爬电距离有不同要求,其限值的求法和结果不尽相同.今以一开关电源电路为例,介绍在不同标准下如何根据工作电压情况对最小电气间隙和爬电距离值进行确定.     

New semiconductor devices based on a special metal-insulator-semiconductor structure for measuring the energy (dose) of electromagnetic and nuclear radiation

This article describes and studies a new type of device for quantitative measurements of radiation energy. Pis’ma Zh. Tekh. Fiz. 23, 23–29 (February 26, 1997)     

立体定向放射治疗计划输出剂量的验证

本文简单介绍对加速器的立体定向治疗计划的输出剂量进行的验证测量，其测量结果和治疗计划预制输出剂量在-1．1％内吻合。并利用胶片法测量了立体定向治疗计划的输出剂量的分布，其测量结果与治疗计划输出剂量分布的80％等剂量曲线面积重合率为94％，得到较满意的结果。     

Improvements in extremity dose assessment for ionising radiation medical applications

This study aims at testing the INTE ring dosemeter based on MCP-Ns and TLD-100 detectors on users from the field of medical applications, namely radiopharmacists, personnel at a cyclotron facility with corresponding FDG synthesis cells, interventional radiology technologists and radiologists. These users were chosen due to the fact that they have a significantly high risk of exposure to their hands. Following previous results, MCP-Ns TL thin material was used for radiology measurements, whereas TLD-100 was preferred for other applications. The dosemeters were tested to make sure that they were waterproof and that they could be sterilised properly prior to use. Results confirm the need to implement finger dosimetry, mainly for interventional radiologists as finger dose can be >50 times higher than whole-body dose and 3 times higher than wrist dose.     

立体定向放射治疗计划输出剂量的验证

本文简单介绍对加速器的立体定向治疗计划的输出剂量进行的验证测量,其测量结果和治疗计划预制输出剂量在-1 1%内吻合。并利用胶片法测量了立体定向治疗计划的输出剂量的分布,其测量结果与治疗计划输出剂量分布的80%等剂量曲线面积重合率为94%,得到较满意的结果。     

Patient dose variation investigated in four Irish hospitals for barium meal and barium enema examinations

Four hospitals have been studied, intra- and inter-hospital variations examined and the mean DAP values recorded for barium enemas and barium meals. Mean DAP values for barium meals and barium enemas at 11.4 Gy x cm2 and 20.1 Gy x cm2 respectively have been shown. Differences between individual examinations for barium meals varied by up to a factor of 185 and for barium enemas, up to a factor of 19, with hospital means for barium meal and enema examinations each differing by up to a factor of 3. The data provided by this study have suggested that large variations in patient dose do exist in Ireland for barium meal and barium enema examinations. Fluoroscopy time was shown to be a major contributor to the variations reported, with number of images playing a minor role. Results have demonstrated the need for standardisation of technique throughout the country for these examinations.