Patient Skin Dose Research Articles

Validation and Initial Clinical Use of Automatic Peak Skin Dose Localization with Fluoroscopic and Interventional Procedures

To assess the accuracy and initial clinical use of a software tool that automatically maps and records values of skin dose, including peak skin dose (PSD), administered to patients undergoing fluoroscopically guided interventional procedures. In this retrospective study, the institutional review board determined that this HIPAA-compliant study met the criteria as a quality assurance investigation. Informed consent was waived. After the initial validation and accuracy tests, distributed skin dose and PSD estimates were obtained for fluoroscopically guided interventional procedures performed in the radiology, cardiology, and gastroenterology practice areas between January and October 2011. A total of 605 procedures were performed in 520 patients (64% men; age range, 20-95 years). The accuracy of a skin dose tool to estimate patient dose distribution was verified with phantom studies by using an external dosimeter and direct exposure film. PSD distribution, PSD according to procedure type, and PSD for individual physician operators were assessed. Calculated PSD values agreed within ±9% of that measured by using film dosimetry under the condition of matched-phantom geometry. The area receiving the highest dose (greater than 95% of peak) agreed within ±17%. Of 605 patient procedures, 15 demonstrated PSD greater than 2 Gy, with a maximum PSD of 5.6 Gy. Knowledge of the patient skin dose can help direct treatment of patients who were administered relatively high skin dose and may be used to plan future procedures. http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12112295/-/DC1.

Basic imaging properties of an indirect flat-panel detector system employing irradiation side sampling (ISS) technology for chest radiography: comparison with a computed radiographic system

The image quality and potential usefulness for patient skin-dose reduction of a newly developed flat-panel detector (FPD) system employing irradiation side sampling (ISS) were investigated and compared to a conventional computed radiography (CR) system. We used the X-ray beam quality of RQA 9 as noted in the standard evaluation method by the International Electrotechnical Commission 62220-1 to evaluate the image quality of the detector for chest radiography. The presampled modulation transfer function (MTF) of the ISS-FPD system was slightly higher than that of the CR system in the horizontal direction at more than 2.2 cycles/mm. However, the presampled MTF of the ISS-FPD system was slightly lower than that of the CR system in the vertical direction. The Wiener spectrum of the ISS-FPD system showed a 50-65 % lesser noise level than that of the CR system under the same exposure condition. The detective quantum efficiency of the ISS-FPD system was at least twice as great as that of the CR system. We conclude that the ISS-FPD system has the potential to reduce the patient skin dose compared to a conventional CR system for chest radiography.

ICRP PUBLICATION 120: Radiological Protection in Cardiology

Cardiac nuclear medicine, cardiac computed tomography (CT), interventional cardiology procedures, and electrophysiology procedures are increasing in number and account for an important share of patient radiation exposure in medicine. Complex percutaneous coronary interventions and cardiac electrophysiology procedures are associated with high radiation doses. These procedures can result in patient skin doses that are high enough to cause radiation injury and an increased risk of cancer. Treatment of congenital heart disease in children is of particular concern. Additionally, staff1As indicated in the Glossary, the term ‘worker’ is defined by the Commission in Publication 103 (ICRP, 2007b) as ‘any person who is employed, whether full time, part time or temporarily, by an employer, and who has recognised rights and duties in relation to occupational radiological protection’. In a hospital, these persons are part of the staff. The term ‘staff’ is preferred in this report because the intended audience is more familiar with this term.1 in cardiac catheterisation laboratories may receive high doses of radiation if radiological protection tools are not used properly.The Commission provided recommendations for radiological protection during fluoroscopically guided interventions in Publication 85, for radiological protection in CT in Publications 87 and 102, and for training in radiological protection in Publication 113 (ICRP, 2000b,c, 2007a, 2009). This report is focused specifically on cardiology, and brings together information relevant to cardiology from the Commission’s published documents. There is emphasis on those imaging procedures and interventions specific to cardiology. The material and recommendations in the current document have been updated to reflect the most recent recommendations of the Commission.This report provides guidance to assist the cardiologist with justification procedures and optimisation of protection in cardiac CT studies, cardiac nuclear medicine studies, and fluoroscopically guided cardiac interventions. It includes discussions of the biological effects of radiation, principles of radiological protection, protection of staff during fluoroscopically guided interventions, radiological protection training, and establishment of a quality assurance programme for cardiac imaging and intervention.As tissue injury, principally skin injury, is a risk for fluoroscopically guided interventions, particular attention is devoted to clinical examples of radiation-related skin injuries from cardiac interventions, methods to reduce patient radiation dose, training recommendations, and quality assurance programmes for interventional fluoroscopy.

Monte Carlo model of the scanning beam digital x-ray (SBDX) source

The scanning-beam digital x-ray (SBDX) system has been developed for fluoroscopic imaging using an inverse x-ray imaging geometry. The SBDX system consists of a large-area x-ray source with a multihole collimator and a small detector. The goal of this study was to build a Monte Carlo (MC) model of the SBDX source as a useful tool for optimization of the SBDX imaging system in terms of its hardware components and imaging parameters. The MC model of the source was built in the EGSnrc/BEAMnrc code and validated using the DOSXYZnrc code and Gafchromic film measurements for 80, 100, and 120 kV x-ray source voltages. The MC simulated depth dose curves agreed with measurements to within 5%, and beam profiles at three selected depths generally agreed within 5%. Exposure rates and half-value layers for three voltages were also calculated from the MC simulations. Patient skin-dose per unit detector-dose was quantified as a function of patient size for all three x-ray source voltages. The skin-dose to detector-dose ratio ranged from 5–10 for a 20 cm thick patient to 1 × 103–1 × 105 for a 50 cm patient for the 120 and 80 kV beams, respectively. Simulations of imaging dose for a prostate patient using common imaging parameters revealed that skin-dose per frame was as low as 0.2 mGy.

Skin dose in longitudinal and transverse linac‐MRIs using Monte Carlo and realistic 3D MRI field models

The magnetic fields of linac-MR systems modify the path of contaminant electrons in photon beams, which alters patient skin dose. To accurately quantify the magnitude of changes in skin dose, the authors use Monte Carlo calculations that incorporate realistic 3D magnetic field models of longitudinal and transverse linac-MR systems. Finite element method (FEM) is used to generate complete 3D magnetic field maps for 0.56 T longitudinal and transverse linac-MR magnet assemblies, as well as for representative 0.5 and 1.0 T Helmholtz MRI systems. EGSnrc simulations implementing these 3D magnetic fields are performed. The geometry for the BEAMnrc simulations incorporates the Varian 600C 6 MV linac, magnet poles, the yoke, and the magnetic shields of the linac-MRIs. Resulting phase-space files are used to calculate the central axis percent depth-doses in a water phantom and 2D skin dose distributions for 70 μm entrance and exit layers using DOSXYZnrc. For comparison, skin doses are also calculated in the absence of magnetic field, and using a 1D magnetic field with an unrealistically large fringe field. The effects of photon field size, air gap (longitudinal configuration), and angle of obliquity (transverse configuration) are also investigated. Realistic modeling of the 3D magnetic fields shows that fringe fields decay rapidly and have a very small magnitude at the linac head. As a result, longitudinal linac-MR systems mostly confine contaminant electrons that are generated in the air gap and have an insignificant effect on electrons produced further upstream. The increase in the skin dose for the longitudinal configuration compared to the zero B-field case varies from ∼1% to ∼14% for air gaps of 5-31 cm, respectively. (All dose changes are reported as a % of D(max).) The increase is also field-size dependent, ranging from ∼3% at 20 × 20 cm(2) to ∼11% at 5 × 5 cm(2). The small changes in skin dose are in contrast to significant increases that are calculated for the unrealistic 1D magnetic field. For the transverse configuration, the entrance skin dose is equal or smaller than that of the zero B-field case for perpendicular beams. For a 10 × 10 cm(2) oblique beam the transverse magnetic field decreases the entry skin dose for oblique angles less than ±20° and increases it by no more than 10% for larger angles up to ±45°. The exit skin dose is increased by 42% for a 10 × 10 cm(2) perpendicular beam, but appreciably drops and approaches the zero B-field case for large oblique angles of incidence. For longitudinal linac-MR systems only a small increase in the entrance skin dose is predicted, due to the rapid decay of the realistic magnetic fringe fields. For transverse linac-MR systems, changes to the entrance skin dose are small for most scenarios. For the same geometry, on the exit side a fairly large increase is observed for perpendicular beams, but significantly drops for large oblique angles of incidence. The observed effects on skin dose are not expected to limit the application of linac-MR systems in either the longitudinal or transverse configuration.

WE-E-BRB-06: Monte Carlo Calculations of the Skin Dose for Longitudinal Linac-MR System Using Realistic Three-Dimensional Magnetic Field Modeling.

This study quantifies the effects of the magnetic field of a longitudinal linac-MR system (B-field parallel to beam direction) on skin dose due to the confinement of contaminant electrons, using Monte Carlo calculations and realistic 3-D models of the magnetic field. The complete realistic 3-D magnetic fields generated by the bi-planar Linac-MR magnet assembly are calculated with the finite element method using Opera- 3D. EGSnrc simulations are performed in the presence of ∼0.6T and IT MRI fields that have realistic rapid fall-off of the fringe field. The simulation geometry includes a Varian 600C 6MV linac, the yoke and magnetic shields of the MRIs, and features an isocentre distance of 126 cm. Phase spaces at the surface of a water phantom are scored using BEAMnrc; DOSXYZnrc is used to score the resulting CAX percent depth-doses in the phantom and the 2D skin dose distributions in the first 70 urn layer. For comparison, skin doses are also calculated in the absence of magnetic field and using a 1-D magnetic field with an unrealistic fringe field. The effects of field size and air gap (between phantom surface and magnet pole) are also examined. Analysis of the phase-space and dose distributions reveals that significant containment of electrons occurs primarily close to the uniform magnetic field region. The increase in skin dose due to the magnetic field depends on the air gap, varying from 1% to 13% for air gaps of 5 to 31 cm, respectively. The increase is also field-size dependent, varying from 3% at 20×20 cm2 to 11% at 5×5 cm2. Calculations based on various realistic MRI 3D magnetic-field maps that appropriately account for the rapid decay of the fringe field show that the increase in the patient skin dose of a longitudinal Linac-MR system is clinically insignificant.

The potential of attenuation-based dynamic CT beam-shaping filter modulation as a new method for radiation dose reduction in MDCT: Evaluation by Monte-Carlo simulation of spatial dose distribution

Ziele: MDCT beam-shaping filters modulate X-ray beam intensity across the fan, compensating for decreasing absorption due to shorter X-ray path lengths through patient body periphery compared to its center. The effect of replacing static MDCT beam-shaping filter geometry by filter geometry dynamically adapted to elliptical specimen in dependence of projection angle has been evaluated with regard to its potential for radiation exposure reduction. Methode: Using a Compton spectrometer, primary MDCT X-ray spectra (120kVp) have been measured at different angular distance (0°-21°) from the central ray of the fan. These have been used to calculate the geometrical shape of the bowtie filter. In addition, a theoretical model of beam-shaping filtration that can be dynamically adapted to elliptical subject geometries has been developed. Both bowtie models were implemented in a Geant4 MC simulation of MDCT, and spatial distributions of dose deposited in an elliptical water phantom (16.0cm semimajor, 12.5cm semiminor axes) were simulated for projections in steps of 15° (10^7 photons/proj., 120kVp-spectrum). Comprehensive spatial dose distributions within the phantom were reconstructed and used to evaluate relative dose reduction achievable by dynamic beam-shaping in CT. Ergebnis: Projection-angle dependent spatial distribution of dose deposition around the center of the beam created by dynamic filtration minimizes dose contributions to more peripheral voxels, leading to relative patient skin dose reductions of ~50% a.p. or ~30% lateral. Compared to a CT acquisition without any beam-shaping filter, measured static and proposed dynamic beam-shaping filter allow reducing total deposited dose by 33% and 48%, resp.. Thus, an additional radiation exposure reduction by 15% can be achieved with a filter dynamically adapted to subject shape. Schlussfolgerung: The results of the simulation study indicate that replacing static by dynamic beam shaping filtration allows for significant additional radiation exposure reduction in MDCT.

Electron contamination modeling and skin dose in 6 MV longitudinal field MRIgRT: Impact of the MRI and MRI fringe field

In recent times, longitudinal field MRI-linac systems have been proposed for 6 MV MRI-guided radiotherapy (MRIgRT). The magnetic field is parallel with the beam axis and so will alter the transport properties of any electron contamination particles. The purpose of this work is to provide a first investigation into the potential effects of the MR and fringe magnetic fields on the electron contamination as it is transported toward a phantom, in turn, providing an estimate of the expected patient skin dose changes in such a modality. Geant4 Monte Carlo simulations of a water phantom exposed to a 6 MV x-ray beam were performed. Longitudinal magnetic fields of strengths between 0 and 3 T were applied to a 30 × 30 × 20 cm(3) phantom. Surrounding the phantom there is a region where the magnetic field is at full MRI strength, consistent with clinical MRI systems. Beyond this the fringe magnetic field entering the collimation system is also modeled. The MRI-coil thickness, fringe field properties, and isocentric distance are varied and investigated. Beam field sizes of 5 × 5, 10 × 10, 15 × 15 and 20 × 20 cm(2) were simulated. Central axis dose, 2D virtual entry skin dose films, and 70 μm skin depth doses were calculated using high resolution scoring voxels. In the presence of a longitudinal magnetic field, electron contamination from the linear accelerator is encouraged to travel almost directly toward the patient surface with minimal lateral spread. This results in a concentration of electron contamination within the x-ray beam outline. This concentration is particularly encouraged if the fringe field encompasses the collimation system. Skin dose increases of up to 1000% were observed for certain configurations and increases above Dmax were common. In nonmagnetically shielded cases, electron contamination generated from the jaw faces and air column is trapped and propagated almost directly to the phantom entry region, giving rise to intense dose hot spots inside the x-ray treatment field. These range up to 1000% or more of Dmax at the CAX, depending on field size, isocenter, and coil thickness. In the case of a fully magnetically shielded collimation system and the lowest MRI field of 0.25 T, the entry skin dose is expected to increase to at least 40%, 50%, 65%, and 80% of Dmax for 5 × 5, 10 × 10, 15 × 15, and 20 × 20 cm(2), respectively. Electron contamination from the linac head and air column may cause considerable skin dose increases or hot spots at the beam central axis on the entry side of a phantom or patient in longitudinal field 6 MV MRIgRT. This depends heavily on the properties of the magnetic fringe field entering the linac beam collimation system. The skin dose increase is also related to the MRI-coil thickness, the fringe field, and the isocenter distance of the linac. The results of this work indicate that the properties of the MRI fringe field, electron contamination production, and transport must be considered carefully during the design stage of a longitudinal MRI-linac system.

진단방사선촬영에서 광자극형광선량계의 에너지의존성에 대한 보정인자

이 연구의 목적은 진단방사선촬영에서 환자의 피부선량을 측정하는 나노도트선량계의 에너지의존성에 대한 보정인자들을 구하는 것이다. 보정인자들은 랜다우어사에서 제공한 팬텀 정에 관한 X-선에 상대적인 선량계의 에너지반응그래프와 로사도 등이 발표한 IEC의 RQR 표준방사선 품질들에 대한 평균에너지 값들을 사용하여 구하였다. 결과들은 관전압 40-150 kVp에서 1-1.33의 보정인자들을 나타냈다. 얻어진 보정인자들은 각 관전압에서 정확한 피부선량 측정을 위하여 임상에 사용하는데 유용할 것으로 생각된다. The purpose of this study is to calculate correction factors for energy dependence of a nanoDotdosimeter to measure patient's skin dose in diagnostic radiography. The correction factors were calculated by using the values of mean energy for the RQR standard radiation qualities of IEC publicated by Rosado et al. and the energy response graph of dosimeter relative X-ray on phantom calibration provided by landaur corporation. Results showed the correction factors of 1-1.33 over the tube voltage range of 40-50 kVp. Acquired correction factors are considered to be useful in the clinics for the measurement of accurate skin dose at each tube voltage.

Skin dose mapping for fluoroscopically guided interventions

To introduce a new skin dose mapping software system for interventional fluoroscopy dose assessment and to analyze the benefits and limitations of patient-phantom matching. In this study, a new software system was developed for visualizing patient skin dose during interventional fluoroscopy procedures. The system works by translating the reference point air kerma to the location of the patient's skin, which is represented by a computational model. In order to orient the model with the x-ray source, geometric parameters found within the radiation dose structured report (RDSR) are used along with a limited number of in-clinic measurements. The output of the system is a visual indication of skin dose mapped onto an anthropomorphic model at a resolution of 5 mm. In order to determine if patient-dependent and patient-sculpted models increase accuracy, peak skin dose was calculated for each of 26 patient-specific models and compared with doses calculated using an elliptical stylized model, a reference hybrid model, a matched patient-dependent model and one patient-sculpted model. Results were analyzed in terms of a percent difference using the doses calculated using the patient-specific model as the true standard. Anthropometric matching, including the use of both patient-dependent and patient-sculpted phantoms, was shown most beneficial for left lateral and anterior-posterior projections. In these cases, the percent difference using a reference model was between 8 and 20%, using a patient-dependent model between 7 and 15%, and using a patient-sculpted model between 3 and 7%. Under the table tube configurations produced errors less than 5% in most situations due to the flattening affects of the table and pad, and the fact that table height is the main determination of source-to-skin distance for these configurations. In addition to these results, several skin dose maps were produced and a prototype display system was placed on the in-clinic monitor of an interventional fluoroscopy system. The skin dose mapping program developed in this work represents a new tool that, as the RDSR becomes available through automated export or real-time streaming, can provide the interventional physician information needed to modify behavior when clinically appropriate. The program is nonproprietary and transferable, and also functions independent to the software systems already installed on the control room workstation. The next step will be clinical implementation where the workflow will be optimized along with further analysis of real-time capabilities.

Visual and numerical methods to measure patient skin doses in interventional procedures using radiochromic XR-RV2 films

Radiochromic XR-RV2 films are considered as one of the best dosemeters to measure patient skin doses in fluoroscopy-guided interventional procedures. To fulfil this purpose, they need to be calibrated with diagnostic energies and doses beyond several Gray. The vendor provides a visual calibration strip to estimate the absorbed dose. Differences between visual dose estimation versus film digitisation were investigated. The influence of backscatter radiation on film sensitivity was also investigated and the sources of uncertainty were analysed when skin doses were measured with these films. When based on the visual comparison with the strip, the estimation of the dose resulted in an error of 50 % (2 Gy in the region around 4 Gy). However, when using numerical methods after film digitisation, the uncertainty in dose measurement fell to 7-14 % in the dose range of interest. Calibration under backscatter conditions demonstrates that the 'in air' calibration underestimates the doses by 7 %. When the dose was measured with a calibration method based on 16 bits grey digitisation, uncertainty was twice higher than when the red channel from red, green, blue digitised images was used.

Dosimetry using Gafchromic XR-RV2 radiochromic films in interventional radiology

Patient dose measurements of local entrance dose to the skin have been carried out using radiochromic film (Gafchromic XR-RV2) in a sample of interventional procedures. The major aim of the work was to measure patient entrance dose from such examinations using Gafchromic XR-RV2. Forty-five various interventional procedures (including nefrostomies and urinary stenting, biliary stenting and percutaneous transhepatic biliary drainage (PTBD) and aorta stent grafting) were evaluated. Maximum entrance doses were 537 ± 119 mGy in nephrostomies, 943 ± 631 mGy in biliary stenting and PTBD and 2425 ± 569 mGy in aorta stent grafting. Results indicate that all patients undergoing aorta stent grafting received skin dose above 1500 mGy, which means that there is an increasing potential to suffer radiation-induced skin injuries. The film provides dose mapping, the position of the skin area with highest dose and can be used for immediate qualitative and as well as for quantitative assessment of patient skin dose.

SU‐E‐I‐80: Dose Metrics, the Relationship, and Reduction Strategies for Interventional Procedures

Purpose: Interventional Radiological (IR) procedures result in the highest individual doses in most radiology practices. Recently FDA unveiled initiative to reduce unnecessary radiation exposure from medical imaging. To achieve this goal, the understanding of dose metrics and their relationships from IR procedures is a must. This study aims to summarize dose metrics, investigate the relationship and develop strategies for IR dose reduction and overdose alert. Methods: A Rando phantom was used to investigate entrance skin dose (ESD) in two Siemens flat panel fluoroscopy systems (Artis and Atris Biplane) using typical protocols for neuro, chest and abdominal interventional procedures. Fluoroscopy time, dose‐area product (DAP), and reference dose were recorded from consoles. Exposure rate and cumulative dose at different surface (skin) locations of the imaged areas were measured with a RadCal dosimeter and a Unfors Patient Skin Dosimeter (PSD, with 4 sensors). The relationships among dose metrics were then analyzed for different clinical settings and dose reduction/overdose alert strategies were discussed. Results: Linear relationships among different dose metrics are observed for fixed clinical setting (SID, image area, fluoroscopy mode, etc). With changes in clinical settings, the linear relationship changes accordingly, which causes difficulty in directly predicting ESD by any single dose metric. However, combining different settings may give a reasonable estimation of patient skin dose during IR procedure. Conclusions: Considering different clinical settings, ESD can be estimated from dose metrics in the current fluoroscopy systems and used as indicator of patient dose during IR procedures. This information and related strategies may potentially reduce the risk of patient overdose.

SU-E-I-188: Potential for Dose Reduction in An Indirect Flat Panel Detector System Employing Irradiation Side Sampling

Purpose: To investigate possibility of dose reduction for a newly developed indirect flat panel detector(FPD)system employing irradiation side sampling (ISS), physical imaging properties were measured and compared with those of a conventional computed radiography(CR)system. Method and Materials:The FPDsystem employing ISS (CALNEO MT, Fuji Film) and the CRsystem (FCR PROFECT CS, Fuji Film) including the imaging plate (ST‐VI, Fuji Film) were used in this study. The Wiener spectrum (WS), the presampled modulation transfer function(MTF), and the detective quantum efficiency (DQE) for both systems were measured. To evaluate image quality of the detector for chest radiography, the RQA 9 in the International Electrotechnical Commission (IEC) 62220‐1 was used. Results: The WS of the FPDsystem showed considerably lower than that of the CRsystem at every spatial frequency. The WS of the FPDsystem with a 50 % dose reduction of the CRsystem was almost identical to that of the CRsystem. The presampled MTF of the FPDsystem was comparable to that of the CRsystem. The DQE of the FPDsystem obtained at zero spatial frequency was almost twice than that of the CRsystem. Conclusion: The radiographic noise property and the detection efficiency of the new ISS FPD were significantly superior to those of the conventional CRsystem. It is expected that the use of the new ISS FPDsystem for chest radiography can reduce the patient skin dose by 50 % compared with the conventional CRsystem.

MO-D-110-02: Calculating Patient-Specific Skin Dose

Records of radiation exposure with fluoroscopic guided interventional (FGI) exposures commonly include fluoroscopy duration, KAP, cumulative AK at the RP but may or may not include fluoroscopic exposure location information. Newer equipment use DICOM Radiation Dose SR (RDSR) which if coupled with simulation tools can re‐create an entire exposure history to calculate patient skin dose distributions and locate the regions of peak skin dose (PSD). A software tool will be described that automatically captures RDSR data to a database. A separate physicist screen (web enabled or laptop) provides prompts to set up a new or upgraded FGI lab. This task would be similair to acceptance testing a complex imaging device. This activity permits corrections for vendor specified AK at the RP, inclusion of backscatter factors, table and pad attenuation, specifying distance from the x‐ray tube, field size corrections, patient positioning (supine or prone, left or right sided, head or feet first), table movement, patient location on the table and field shape. Other fields that address QA are set by the physicist and include the list of authorized users, email alerts and action levels. A separate technologist web screen is used for each patient to choose a correct simulated patient size, positioning on the table and the individuals performing the procedure. At the end of the procedure the technologist receives a record of skin dose mapping, including an Alert if the reference values are exceeded. As the data are stored in the DICOM Tracker database, a number of QA tools can be applied including the ability monitor individual types of procedures and fluoroscopists comparative values. For legacy FGI equipment (having some, but not all of the required DICOM fields) it is possible to estimate PSD by making assumptions about the proportion of fluoroscopic exposure relative to acquistions (digital spots and cine).

CT dosimetry considerations in non typical conditions: The effect of scan field of view and table height selection

Purpose To experimentally investigate the effect of the scan field of view (SFOV) selection and table height settings on the Computed Tomography Dose Index (CTDI) and the implications concerning patient effective and skin dose. Methods Air-kerma length product (AKLP) measurements were carried out in a helical CT scanner using a pencil type dosimeter positioned in air and inside the holes of a head and a body phantom, using all available SFOV selections and different table height settings. Furthermore, using radiotherapy verification films placed on the CT table surface, the entrance surface air kerma (ESAK) profiles were derived with different SFOV and table height selections, both with and without a phantom on top of the films. Results The AKLP is strongly dependent on the SFOV selection and the table height settings. Different SFOV selections correspond to the selection of different bowtie filters that shape the X-ray beam intensity, resulting in different ESAK values at the isocenter and at the other points within the scanning plane. With the off-center positioning the calculated CTDI values within the center and the periphery of the phantom change also, as a result of the different intensity and width of the X-ray beam to which are exposed to. Conclusions The existing protocols for calculating effective dose are limited to only two patient anatomy-SFOV combinations and cannot account for off-center positioning. Therefore, more work will be required to estimate the effective and skin dose for non-standard SFOV-patient anatomy combinations and off-center patient positioning.

Calibration of GafChromic XR‐RV3 radiochromic film for skin dose measurement using standardized x‐ray spectra and a commercial flatbed scanner

In this study, newly formulated XR-RV3 GafChromic film was calibrated with National Institute of Standards and Technology (NIST) traceability for measurement of patient skin dose during fluoroscopically guided interventional procedures. The film was calibrated free-in-air to air kerma levels between 15 and 1100 cGy using four moderately filtered x-ray beam qualities (60, 80, 100, and 120 kVp). The calibration films were scanned with a commercial flatbed document scanner. Film reflective density-to-air kerma calibration curves were constructed for each beam quality, with both the orange and white sides facing the x-ray source. A method to correct for nonuniformity in scanner response (up to 25% depending on position) was developed to enable dose measurement with large films. The response of XR-RV3 film under patient backscattering conditions was examined using on-phantom film exposures and Monte Carlo simulations. The response of XR-RV3 film to a given air kerma depended on kVp and film orientation. For a 200 cGy air kerma exposure with the orange side of the film facing the source, the film response increased by 20% from 60 to 120 kVp. At 500 cGy, the increase was 12%. When 500 cGy exposures were performed with the white side facing the x-ray source, the film response increased by 4.0% (60 kVp) to 9.9% (120 kVp) compared to the orange-facing orientation. On-phantom film measurements and Monte Carlo simulations show that using a NIST-traceable free-in-air calibration curve to determine air kerma in the presence of backscatter results in an error from 2% up to 8% depending on beam quality. The combined uncertainty in the air kerma measurement from the calibration curves and scanner nonuniformity correction was +/- 7.1% (95% C.I.). The film showed notable stability. Calibrations of film and scanner separated by 1 yr differed by 1.0%. XR-RV3 radiochromic film response to a given air kerma shows dependence on beam quality and film orientation. The presence of backscatter slightly modifies the x-ray energy spectrum; however, the increase in film response can be attributed primarily to the increase in total photon fluence at the sensitive layer. Film calibration curves created under free-in-air conditions may be used to measure dose from fluoroscopic quality x-ray beams, including patient backscatter with an error less than the uncertainty of the calibration in most cases.

Combined Fluoroscopy- and CT-Guided Transthoracic Needle Biopsy Using a C-Arm Cone-Beam CT System: Comparison with Fluoroscopy-Guided Biopsy

ObjectiveThe aim of this study was to evaluate the usefulness of combined fluoroscopy- and CT-guided transthoracic needle biopsy (FC-TNB) using a cone beam CT system in comparison to fluoroscopy-guided TNB (F-TNB).Materials and MethodsWe retrospectively evaluated 74 FC-TNB cases (group A) and 97 F-TNB cases (group B) to compare their respective diagnostic accuracies according to the size and depth of the lesion, as well as complications, procedure time, and radiation dose.ResultsThe sensitivity for malignancy and diagnostic accuracy for small (< 30 mm in size) and deep (≥ 50 mm in depth) lesions were higher in group A (91% and 94%, 92% and 94%) than in group B (73% and 81%, 84% and 88%), however not statistically significant (p > 0.05). Concerning lesions ≥ 30 mm in size and < 50 mm in depth, both groups displayed similar results (group A, 91% and 92%, 80% and 87%; group B, 90% and 92%, 86% and 90%). Pneumothorax occurred 26% of the time in group A and 14% for group B. The mean procedure time and patient skin dose were significantly higher in group A (13.6 ± 4.0 minutes, 157.1 ± 76.5 mGy) than in group B (9.0 ± 3.5 minutes, 21.9 ± 15.2 mGy) (p < 0.05).ConclusionCombined fluoroscopy- and CT-guided TNB allows the biopsy of small (< 30 mm) and deep lesions (≥ 50 mm) with high diagnostic accuracy and short procedure times, whereas F-TNB is still a useful method for large and superficial lesions with a low radiation dose.

Reduction of the effect of non-uniform backscatter from an E-type support arm of a Varian a-Si EPID used for dosimetry

Backscatter from the metallic components in the support arm is one of the sources of inaccuracy in dosimetry with Varian amorphous silicon electronic portal imaging devices (a-Si EPIDs). In this study, the non-uniform arm backscatter is blocked by adding lead sheets between the EPID and an E-type support arm. By comparing the EPID responses on and off the arm, with and without lead and considering the extra weight on the imager, 2 mm of lead was determined as the optimum thickness for both 6 and 18 MV beam energies. The arm backscatter at the central axis with the 2 mm lead in place decreased to 0.1% and 0.2% for the largest field size of 30 × 30 cm2 using 6 and 18 MV beams, from 2.3% and 1.3% without lead. Changes in the source–to-detector distance (SDD) did not affect the backscatter component more than 1%. The symmetry of the in-plane profiles improved for all field sizes for both beam energies. The addition of lead decreased the contrast-to-noise ratio and resolution by 1.3% and 0.84% for images taken in 6 MV and by 0.5% and 0.38% for those in 18 MV beams. The displacement of the EPID central pixel was measured during a 360° gantry rotation with and without lead which was 1 pixel different. While the backscatter reduces with increasing lead thickness, a 2 mm lead sheet seems sufficient for acceptable dosimetry results without any major degradation to the routine performance of the imager. No increase in patient skin dose was detected.

Patient skin dose measurements during coronary interventional procedures usingGafchromic film

Interventional cardiology (IC) procedures are known to give high radiation doses to patientsand cardiologists as they involve long fluoroscopy times and several cine runs. Patients’dose measurements were carried out at the cardiology department in a local hospital inPenang, Malaysia, using Gafchromic XR-RV2 films. The dosimetric properties of theGafchromic film were first characterised. The film was energy and dose rate independentbut dose dependent for the clinically used values. The film had reproducibility within ± 3% when irradiated on three different days and hence the same XR-RV2 dose–responsecalibration curve can be used to obtain patient entrance skin dose on different days. Theincrease in the response of the film post-irradiation was less than 4% over a periodof 35 days. For patient dose measurements, the films were placed on the tableunderneath the patient for an under-couch tube position. This study included atotal of 44 patients. Values of 35–2442 mGy for peak skin dose (PSD) and 10.9–344.4 Gy cm2 for dose–area product (DAP) were obtained. DAP was found to be a poorindicator of PSD for PTCA procedures but there was a better correlation (R2 = 0.7344) forCA + PTCA procedures. The highest PSD value in this study exceeded the threshold dose value of 2 Gyfor early transient skin injury recommended by the Food and Drug Administration.