基于MAGNETOM Skyra型磁共振（MRI）设备影像质量测试和分析

目的 探讨检测磁共振影像质量指标的过程,建立磁共振设备影像质量指标的基线值,为完善国家相关标准提供一定的依据。方法 依据国内外现行标准的测试条件,借助SMR 170磁共振影像质量控制模体对新安装的MAGNETOM Skyra型磁共振的信噪比、影像均匀性、层厚、层厚非均匀性、空间分辨力、几何畸变率、低对比度分辨力、共振频率、纵横比等指标进行测试,得到对应的各项指标的基线值,并结合相关材料,探讨影响磁共振影像质量检测的情况。结果 采集图像使用自旋回波序列（SE）、头部线圈、脉冲回波时间为20 ms、脉冲恢复时间为250 ms、视野（FOV）为250 mm×250 mm、采集2次的设置条件,预设层厚分别为5 mm、8 mm和10 mm：测量层厚和非均匀性分别为5.2 mm/1.3%、8.3 mm/2.0%和10.4 mm/3.2%;信噪比和图像均匀性在矩阵为256 mm×256 mm时的结果分别是103.2/98.3%、105.6/96.0%和110.2/96.4%,信噪比在矩阵为512 mm×512 mm时的测量结果分别是102.6、104.8和106.2;空间分辨力在矩阵为256 mm×256 mm时均为1 mm,矩阵为512 mm×512 mm时为0.556 mm、0.556 mm和0.5 mm;低对比度分辨力均为可分辨直径4 mm、孔深0.5 mm的圆孔。几何畸变率在孔径间距为20 mm、40 mm、80 mm和100 mm处的测量结果分别为20.0 mm、40.3 mm、80.5 mm和100.8 mm。结论 应用SMR 170模体检测该型磁共振影像指标的参数设置和建立的基线值可为后续状态检测提供一定的依据;完善MRI影像质量检测指标,研发配套MRI影像质量测试模体,更新相关标准是今后MRI质量控制工作中的重点。     

Improved accuracy of mandible geometry reconstruction at the stage of data processing and modeling

The article presents a comparative study of influence of the Lanczos resampling filter on improving the accuracy of reconstruction of mandible geometries. The research was performed on eight different patients. Digital Imaging and Communications in Medicine data were obtained on the Siemens Somatom Sensation Open 40 scanner. At the stage of reconstruction, the same parameters were utilized, while only slice thickness was changed. Modeling with voxel dimensions of 0.4 mm?×?0.4 mm?×?1.5 mm was chosen as the gold standard over the modeling approach comprising voxel dimensions of 0.4 mm?×?0.4 mm?×?3.0 mm and improved using the Lanczos resampling filter. The influence of the Lanczos resampling filter on the accuracy of reconstruction of mandible geometry is very similar for the eight presented patients. The average results show a distribution with a positive skew and kurtosis. The value of skewness is 0.713 and kurtosis is 4.221 for the model without Lanczos filtering applied. When the Lanczos filtering is applied the value of skewness is 0.542 and kurtosis is 4.313. Based on 95% confidence, changes in layer thickness from 1.5 mm to 3 mm generated errors reconstructing the geometry of the mandible at the value of 0.153 mm?±?1.209 mm. In models improved using the Lanczos resampling filter, the errors generated in reconstructing the geometry of the mandible were minimized at the value of 0.160 mm?±?1.007 mm. The presented research highlights new opportunities to improve the accuracy of reconstruction geometry of the mandible at the stage of data processing.     

The peripheral dose outside the applicator in electron beams of an Elekta linear accelerator

Peripheral doses out of field could have short and long terms biological effects on patients treated with electron beams. In this study, peripheral dose outside the applicator was measured using the 6, 10 and 18 MeV beams of an Elekta synergy linac. For these beams dose profiles were measured using EBT3 film at various depths within a solid water phantom. Measurements were performed using 6?×?6, 10?×?10, 14?×?14 and 20?×?20 cm² applicators at gantryangles of 0°, 10° and 20° and depths of 0, 0.5, 1 cm and depth of Dmax (maximum dose) for each energy. The peripheral dose profiles were normalized to the distance of 2 cm from the edge of each field. The largest peak of the peripheral dose was observed for 18 MeV 3 cm from the outer edge of the applicator. Peak dose increased with increasing energy. Peak dose at 18 MeV electron beam was 1.6% at the surface of phantom and at the distance of 2 cm from the outer edge of the applicator when the applicator of 20?×?20 cm² was used. Peak dose at 6 MeV electron beam was 1.15% at the same distance in the same applicator size. It was found that the peak dose decreased with increasing depth and increased with increase in field size. Also, the peak dose moved towards CAX with increase in gantry angle.In general dose to tissue out of field could be reduced using appropriate shielding for each applicator and beam energy.     

Improving the quality of reconstructed X-ray CT images of polymer gel dosimeters: zero-scan coupled with adaptive mean filtering

This study evaluated the feasibility of combining the ‘zero-scan’ (ZS) X-ray computed tomography (CT) based polymer gel dosimeter (PGD) readout with adaptive mean (AM) filtering for improving the signal to noise ratio (SNR), and to compare these results with available average scan (AS) X-ray CT readout techniques. NIPAM PGD were manufactured, irradiated with 6 MV photons, CT imaged and processed in Matlab. AM filter for two iterations, with 3 × 3 and 5 × 5 pixels (kernel size), was used in two scenarios (a) the CT images were subjected to AM filtering (pre-processing) and these were further employed to generate AS and ZS gel images, and (b) the AS and ZS images were first reconstructed from the CT images and then AM filtering was carried out (post-processing). SNR was computed in an ROI of 30 × 30 for different pre and post processing cases. Results showed that the ZS technique combined with AM filtering resulted in improved SNR. Using the previously-recommended 25 images for reconstruction the ZS pre-processed protocol can give an increase of 44% and 80% in SNR for 3 × 3 and 5 × 5 kernel sizes respectively. However, post processing using both techniques and filter sizes introduced blur and a reduction in the spatial resolution. Based on this work, it is possible to recommend that the ZS method may be combined with pre-processed AM filtering using appropriate kernel size, to produce a large increase in the SNR of the reconstructed PGD images.     

MRI distortion: considerations for MRI based radiotherapy treatment planning

Distortion in magnetic resonance images needs to be taken into account for the purposes of radiotherapy treatment planning (RTP). A commercial MRI grid phantom was scanned on four different MRI scanners with multiple sequences to assess variations in the geometric distortion. The distortions present across the field of view were then determined. The effect of varying bandwidth on image distortion and signal to noise was also investigated. Distortion maps were created and these were compared to the location of patient anatomy within the scanner bore to estimate the magnitude and distribution of distortions located within specific clinical regions. Distortion magnitude and patterns varied between MRI sequence protocols and scanners. The magnitude of the distortions increased with increasing distance from the isocentre of the scanner within a 2D imaging plane. Average distortion across the phantom generally remained below 2.0 mm, although towards the edge of the phantom for a turbo spin echo sequence, the distortion increased to a maximum value of 4.1 mm. Application of correction algorithms supplied by each vendor reduced but did not completely remove distortions. Increasing the bandwidth of the acquisition sequence decreased the amount of distortion at the expense of a reduction in signal-to-noise ratio of 13.5 across measured bandwidths. Imaging protocol parameters including bandwidth, slice thickness and phase encoding direction, should be noted for distortion investigations in RTP since each can influence the distortion. The magnitude of distortion varies across different clinical sites.     

Effect of voxel size when calculating patient specific radionuclide dosimetry estimates using direct Monte Carlo simulation

The scalable XCAT voxelised phantom was used with the GATE Monte Carlo toolkit to investigate the effect of voxel size on dosimetry estimates of internally distributed radionuclide calculated using direct Monte Carlo simulation. A uniformly distributed Fluorine-18 source was simulated in the Kidneys of the XCAT phantom with the organ self dose (kidney ← kidney) and organ cross dose (liver ← kidney) being calculated for a number of organ and voxel sizes. Patient specific dose factors (DF) from a clinically acquired FDG PET/CT study have also been calculated for kidney self dose and liver ← kidney cross dose. Using the XCAT phantom it was found that significantly small voxel sizes are required to achieve accurate calculation of organ self dose. It has also been used to show that a voxel size of 2 mm or less is suitable for accurate calculations of organ cross dose. To compensate for insufficient voxel sampling a correction factor is proposed. This correction factor is applied to the patient specific dose factors calculated with the native voxel size of the PET/CT study.     

Dosimetric accuracy of Gafchromic EBT2 and EBT3 film for in vivo dosimetry

Radiochromic film has the potential to provide accurate in vivo dosimetry measurements. However, it is not known whether small film pieces can still provide accurate dosimetric results. The use of small film pieces is of particular interest in regions of interest (ROIs) such as the eye, or where the patient’s contour changes rapidly. This study examines the dosimetric accuracy of Gafchromic EBT2 and EBT3 models of radiochromic film and its dependence on film size, ROI size, and height above the scan bed for 6 MV photons and 9 MeV electrons. Films cut to sizes of 5.0 × 5.0, 10.0 × 10.0, 20.0 × 20.0, and 40.0 × 40.0 mm² were tested and it was found that there was no increase in uncertainty of dose when even the smallest film sizes were used. For a film 5.0 × 5.0 mm², ROIs of 1.4 × 1.4, 2.1 × 2.1 and 3.5 × 3.5 mm² were tested and it was found that the ROI size of 2.1 × 2.1 mm² was the most accurate. The standard deviation of the EBT3 placed on the glass (2.1 %) was larger than the standard deviation of the EBT3 film raised above the glass (1.2 %), therefore it is recommended that film is scanned raised above the scan bed. The general dosimetric performance of EBT3 was comparable to EBT2. We conclude that film pieces as small as 5.0 × 5.0 mm² could be used for the purpose of in vivo dosimetry of radiotherapy treatments.     

An Electrochemical Approach to Simultaneous Determination of Acetaminophen and Ofloxacin

This study presents a simple electrochemical approach for preparing a poly(l-serine) film-modified glassy carbon electrode, which responds quickly and sensitively during the simultaneous determination of acetaminophen and ofloxacin in prepared, environmental, and pharmaceutical samples. The prepared electrode exhibited catalytic activities and promoted the oxidation of acetaminophen and ofloxacin. Acetaminophen and ofloxacin showed linear responses between 1.0 × 10^?5 and 1.0 × 10^?4 mol/L and their limits of detection were 1.2 × 10^?7 and 1.6 × 10^?7 mol/L, respectively. The average recoveries (±relative standard deviations) of acetaminophen and ofloxacin were 96.8 ± 3.5 % and 97.6 ± 3.2 %, respectively, indicating that the prepared electrode and detection method are very accurate and reproducible for the simultaneous determination of acetaminophen and ofloxacin.     

Intensity modulated radiation therapy (IMRT) surface dose measurements using a PTW advanced Markus chamber

A new PTW advanced Markus ionization chamber has been implemented in IMRT fields, to measure surface dose at ICRU and ICRP reference depth of 0.07 mm [ICRU Report 39, Determination of dose equivalents resulting from external radiation sources, 1985; ICRP Publication 60, 1990 recommendations of the International Commission on Radiological Protection, 1991]. This chamber has a small radius with a revised guard ring design, therefore less prone to surface over-response effects. The over response correction for advanced Markus chamber is 3.3%, which is significantly smaller than 10.1% which was the original Markus chamber over response. After over response correction, the surface dose can be accurately measured by either data extrapolation or by adding one layer of plastic sheet protector to the top of Markus chamber. The surface dose measurements for small fields, e.g 3 × 3 cm, the polarity effect of advanced Markus chamber is 12%, which is significantly higher than the 5% polarity effect of the original Markus. For a 12 × 12 cm field size, surface dose (at 0.07 mm) measured by advanced Markus chamber is 19.8% for open field and 19.2% for an unmodulated step-and-shoot IMRT field. The variation in surface dose due to intensity modulated IMRT fields has also been investigated. For an intensity modulated, step-wedge IMRT field, surface dose varies from 15.7 ± 1% for the highest intensity segment to 26.9 ± 1% for the lowest intensity segment. The results of chamber measurements have been compared against EBT type GAFCHROMIC^® film results.     

The influence of leaflet skin friction and stiffness on the performance of bioprosthetic aortic valves

Leaflet skin friction and stiffness were found to have a significant influence on the systolic performance of a 19 mm diameter bioprosthetic aortic valve based on fluid–structure interaction simulations at a heart rate of 72 bpm. Four different leaflet skin friction coefficients (0.0, 9.2 × 10^?4, 4.8 × 10^?2 and 4.8 × 10^?1) were simulated along with three different leaflet elastic moduli (3.0 × 10⁶, 3.5 × 10⁶, 4.0 × 10⁶ N m^?2). Higher leaflet skin friction was found to increase the magnitude of the systolic transvalvular pressure gradient and the peak velocity through the valve, as well as decrease the valve orifice area. The results for the leaflet opening and closing kinematics also showed that higher leaflet skin friction combined with higher leaflet stiffness produces longer rapid valve opening, closing and ejection times, as well as smaller valve orifice areas. These results are consistent with clinical findings for calcified aortic valves and suggest that valve performance under stenotic conditions is strongly influenced by the combined effect of increasing leaflet stiffness and surface roughness caused by calcification.     

A study of Winston–Lutz test on two different electronic portal imaging devices and with low energy imaging

Stereotactic radiosurgery requires sub-millimetre accuracy in patient positioning and target localization. Therefore, verification of the linear accelerator (linac) isocentre and the laser alignment to the isocentre is performed in some clinics prior to the treatment using the Winston–Lutz (W–L) test with films and more recently with images obtained using the electronic portal imaging devices (EPID). The W–L test is performed by acquiring EPID images of a radio-opaque ball of 6 mm diameter (the W–L phantom) placed at the isocentre of the linac at various gantry and table angles, with a predefined small square or circular radiation beam. In this study, the W–L test was performed on two linacs having EPIDs of different size and resolution, viz, a TrueBeam? linac with aS1000 EPID of size 40 × 30 cm² with 1024 × 768 pixel resolution and an EDGE? linac having an EPID of size 43 × 43 cm² with pixel resolution of 1280 × 1280. In order to determine the displacement of the radio-opaque ball centre from the radiation beam centre of the W–L test, an in-house MATLAB? image processing code was developed using morphological operations. The displacement in radiation beam centre at each gantry and couch position was obtained by determining the distance between the radiation field centre and the radio-opaque ball centre for every image. Since the MATLAB code was based on image processing that was dependent on the image contrast and resolution, the W–L test was also compared for images obtained with different beam energies. The W–L tests were performed for 6 and 8 MV beams on the TrueBeam? linac and for 2.5 and 6 MV beams on the EDGE? linac with a higher resolution EPID. It was observed that the images obtained with the EPID of higher resolution resulted in same accuracy in the determination of the displacement between the centres of the radio-opaque ball and the radiation beam, and significant difference was not observed with images acquired with different energies. It is concluded that the software based on morphological operations provided an accurate estimation of the displacement of the ball centre from the radiation beam center.     

The Pediatric Symptom Checklist: Comparison of symptom profiles using three factor structures between pediatric gastroenterology and general pediatric patients

This study evaluated and compared three different factor structures of the Pediatric Symptom Checklist (PSC) in a gastroenterology (GI) and a general pediatrics (GP) sample. Parents of GP (n = 169) and GI (n = 177) patients completed the PSC. Each structure includes internalizing, externalizing, and attention problems. Only one structure includes school problems. Hierarchical regression analyses revealed higher internalizing symptoms for GI patients across factor structures. The relationship between internalizing symptoms and age was moderated by group. The PSC seems sensitive to internalizing difficulties in GI patients regardless of factor structure. Older pediatric GI patients may be at increased risk for internalizing symptoms.     

Imaging techniques for measuring adipose-tissue distribution--a comparison between computed tomography and 1.5-T magnetic resonance

We developed a method for calculating adipose-tissue areas from transverse body scans by magnetic-resonance imaging (MRI). The method is based on an inversion recovery experiment (repetition time 820 ms, inversion delay time 300 ms, and echo time 20 ms). Total-fat areas and subcutaneous-fat areas were calculated by this method and by computed tomography (CT) from abdominal scans taken in seven male volunteers. The SEE ranged from 4.4 cm2 (CV 4.4%) for subcutaneous-fat areas to 8.3 cm2 (CV 12.8%) for visceral-fat areas. The reproducibility of measuring fat areas with MRI was assessed in seven other volunteers (four males, three females). The average errors of the method for different fat areas were 5.4%, 10.6%, and 10.1% for total-, visceral-, and subcutaneous-fat areas, respectively. We conclude that CT and MRI may yield different absolute values of fat areas (especially visceral fat) but that the ranking of individuals on the basis of their fat areas will be similar by both methods.     

RJ32-2106P和AT1123两种Χ-γ剂量率仪响应时间性能研究

目的 探讨国内医用X射线诊断工作场所放射防护检测中存在的问题，试验比较国产和进口两款X-γ剂量率仪响应时间性能，评估其在医用X射线诊断工作场所放射防护检测中的适用性。方法 在一台医用X射线摄影机上，使用固定的管电压（70 kV），分别设定不同的管电流获取高中低三档剂量，曝光时间从10 ms递增至1 000 ms，记录不同曝光时间下两种X-γ剂量率仪的周围剂量当量率读数。结果 国产RJ32-2106P型X-γ剂量率仪在3档剂量水平的X射线中，低剂量档时间响应为160 ms，中、高剂量档对应的响应时间为50~64 ms；AT1123的响应时间在3个剂量档均稳定在80~100 ms左右。结论 在医用X射线诊断机房防护检测时，应根据X射线辐射场，选择能够测量短时间出束和脉冲辐射场的设备进行测量。RJ32-2106P和AT1123X-γ剂量率仪在不同剂量水平下时间响应在200 ms以内，适用于医用X射线诊断机房的放射防护检测。     

Spatio-temporal analysis of auditory cortex activation as detected with silent event related fMRI

Functional magnetic resonance imaging (fMRI) allows neuroscientists to assess brain function by evaluating haemodynamic activity (blood flow) when a stimulus is present or absent. In clinical practice, the hearing levels of individuals are determined using an audiometer that allows presentation of a pure-tone of specific intensity and frequency. Functional images of the auditory nervous system have been obtained using stimuli such as pure-tone, speech, noise, etc. However, the observed activation evoked by the stimulus is confounded with the neuronal response evoked by scanner noise generated during imaging. Hence, researchers have been developing fMRI techniques to overcome the inadvertent effect of scanner noise on fMRI studies of the auditory cortex. Silent event related fMRI is a recently reported fMRI technique diminishing the confounding effects of background scanner noise. A drawback of sfMRI is that it requires long acquisition times (30-40 min) to achieve statistically significant activation. An additional complication associated with all fMRI data is that measurements obtained at consecutive times tend to exhibit substantial temporal correlation. Such correlation structure complicates the identification of brain locations (voxels) demonstrating statistically significant activation. We propose an approach for detecting activation with high statistical power and low false-positive rate. To accomplish these goals of high power and low type I error rate in sfMRI with shorter acquisition times, we describe a statistical model that accounts for the spatial and temporal correlation structure of the haemodynamic response. Temporal dependence within each voxel's measurements is modelled, and a regional measurement-error-free kriging predictor is used to combine information from neighbouring voxels when assessing voxel activation. Instead of simply applying a post hoc smoothing to thevoxelwise test statistics (e.g. t statistics), we attempt to make optimal use of information in the locality of each voxel when estimating the voxel's mean, variance, and temporal dependence parameters. The primary advantage to this spatial modelling approach is that the degree to which voxel parameters are smoothed is driven by the data. Thus, we are not subjectively smoothing noisy data, but objectively estimating the noise-free version of the spatial processes associated with the response. The resulting voxel activation maps exhibit substantially more spatial continuity than other currently used approaches, while exhibiting desirable inferential properties including a lower false-positive rate and high power for detection of activated regions. Minimal computational resources are necessary to carry out the approach, which yielded voxel activation maps for our experiment in only minutes.     

Interzonal airflow rates for use in near-field far-field workplace concentration modeling

Interzonal air flow rates (β) for a workspace above a table were measured in 12 indoor air spaces using an experimental apparatus simulating a vapor release into an occupied near zone. The near field was modeled as a 0.32 m³ rectangular cube volume 0.60 m high above the 0.60 m × 0.90 m table. A total of 74 experimental measurements of β were made. The apparatus consisted of photoionization detectors measuring concentrations of acetone around an evaporating liquid surface with a robot arm simulating worker motion in the near field. The vapor release rate and the resulting concentrations were used in a near-field far-field (NF-FF) model to calculate β. Measures of mixing within the near-field supported the assumption of the NF-FF model that the near field is well-mixed. Measured values of β ranged from 0.4–19 m³/min with an average of 4.8 m³/min. This corresponds to 1.2–59 air changes per minute in the near field and an average of 15 air changes per minute. The values of β were log normally distributed with a geometric mean of 3.4 m³/min and a geometric standard deviation of 2.3. The 95% confidence interval on the geometric mean of β was 2.8–4.2 m³/min. The product of the random air speed in the room and one half of the near-field free surface area was shown to be a good method of determining β. There was a slight correlation seen between room volume and β, but the effect size was small. Room air change rate was not found to be correlated with β. The observed distribution of β will be helpful in selecting values for interzonal airflow rate in NF-FF modeling of worker exposures.     

Is Obesity Contagious by Way of Body Image? A Study on Japanese Female Students in the United States

Although it has been suggested that obesity is ‘contagious’ within the social network, direct cause of this spread of obesity remains unclear. This study hypothesized that Body Image (BI), the perception of one’s own body size, may play a role in this obesity spread, since a high prevalence of obesity could shift people’s perception of ‘what is normal’. Young Japanese females (n = 53) were interviewed within 1 month after moving to New York City, where the prevalence of obesity is substantially higher than that of their home country, Japan. Each participant was examined for her BI in terms of current body size (CBS) and ideal body size (IBS). They were interviewed again 2 months after the first examination. Between the two interviews, the participants’ CBS was decreased (having thinner self-image), while the IBS increased (having fatter ideal-image), leading to less dissatisfaction (smaller CBS–IBS) with their body size. These results suggest that one’s BI could change in a period as short as 2 months, possibly because of being surrounded by more obese people. The IBS change was positively associated with BMI change (increased by 0.4 ± 0.6 kg/m²), warranting further study on the role of BI in the spread of obesity.     

HPLC Method Development and Validation of Chromafenozide in Paddy

A simple and efficient HPLC–UV method was developed and validated for determination of chromafenozide in paddy as there was no previous report on record in this regard. The residue analysis method of chromafenozide, its dissipation and final residue in paddy along with soil were also studied after field treatment. Residues of chromafenozide were extracted and purified from paddy and soil followed by liquid/liquid partitioning, chromatographic column and determination by HPLC equipped with PDA detector. The separation was performed on a Phenomenex Luna RP C₁₈ (250 × 4.6 mm i.d, 5 μm particle size) column at room temperature. The mean accuracy of analytical method were 94.92 %, 95.38 %, 94.67 % and 96.90 % in straw, grain, soil and field water respectively. The precision (repeatability) was found in the range of 1.30 %–9.25 % for straw/grain, 1.27 %–11.19 % in soil; 1.0 %–9.25 % in field water. The precision (reproducibility) in straw/grain was ranging from 2.2 % to 12.1 %, in soil it from 2.0 % to 11.7 %. The minimum detectable concentration was 0.01 mg kg^?1. The degradation of chromafenozide formulation in rice, soil and water was determined and results showed that chromafenozide as wettable powder formulation degraded with the half-lives of about 4.4 and 2.9 days in paddy plant and soil respectively for double recommended dose. The results indicated that the developed method is easier and faster then could meet the requirements for determination of chromafenozide in paddy.     

A study on the use of Gafchromic™ EBT3 film for output factor measurements in kilovoltage X-ray beams

Relative output factors are used in radiation therapy for treatment planning purposes including treatments using kilovoltage X-ray beams. The output factor is the relative dose output for a particular applicator relative to a reference applicator. Due to the differences in the scatter contribution from the inside of an applicator, it is more accurate if output factors are measured for all combinations of X-ray beam energy and applicator. Previously published papers and various kilovoltage X-ray beam dosimetry protocols have discussed the validity of using various cylindrical and parallel plate ionization chambers for relative output factor measurements. In this work, we evaluated the suitability of Gafchromic? EBT3 film for the determination of output factors for kilovoltage X-ray beams. Output factors were measured with Gafchromic? EBT3 film for beam qualities of 50, 75, 100 and 125 kVp and applicator sizes of 2, 3, 4 cm diameter, 8 × 8 and 12 × 12 cm² square applicators. The film read out was performed with a flatbed EPSON Expression 10000XL scanner. The measured data was compared with benchmark data from measurements using an Advanced Markus ionisation chamber as well as comparing with ratios of published backscatter factor values. The agreement between output factors measured with EBT3 film and the ionisation chamber was generally better than 2 %, with the largest difference of 3.3 % occurring for the 2 cm diameter field with the 50 kVp X-ray beam. These differences were consistent with the estimated total uncertainty in the measurements as calculated by the ISO GUM. The agreement between the output factors measured with film and the published BSFs was generally better than 5 % but differences of up to 12 % occurred for the smallest field size. The results demonstrate that Gafchromic? EBT3 film is a suitable dosimeter for output factor measurements of kilovoltage X-ray beams.