Physician scatter dose in interventional CT fluoroscopy

To quantify operator dose in interventional CT fluoroscopy (CTF) procedures and compare to catheterization laboratory and interventional radiology procedures.Fifteen studies quantifying operator scatter dose for c‐arm fluoroscopy and CTF were reviewed from a literature survey. The dose provided in each study was normalized to skin entrance air kerma and air kerma rate including backscatter. The average air kerma rate and exposure duration were calculated and compared between c‐arm fluoroscopy and CTF. To enable operator scatter dose calculations in CTF procedures, a model was created which scaled the dose from a reference condition.Our literature survey indicated that for CTF relative to c‐arm fluoroscopy: (1) the mean air kerma rate is 3.5 times higher, while (2) the mean exposure duration is 31.6 times lower. On average, a physician would have to perform 9.1 times (i.e., 31.6/3.5) more CTF procedures relative to c‐arm fluoroscopy procedure to receive equal operator scatter doses. Our own experimental measurements provided scaling factors allowing physician scatter dose to be obtained at any rotation time, tube current, beam collimation, or beam energy.Our results shed light onto a currently mis‐understood issue in radiology. Namely, that physicians receive more dose from CT relative to c‐arm fluoroscopy motivating them to retreat from the room during interventional exposures. Our literature review and experimental measurements indicate the opposite it true; interventional CT produces on average nine times less physician dose relative to c‐arm procedures. Our method allows for prospective/retrospective determination of an individual's dose.

performed, improved patient safety, and increased procedure speed.A particularly notable advancement was the development of slip ring helical CT which directly led to the introduction of CT fluoroscopy (CTF). 2 CTF can be performed in both continuous mode (cCTF) and intermittent mode (iCTF).Concerns over high radiation doses with cCTF combined with the realization that real-time imaging was rarely necessary led to the more recent introduction of intermittent CTF (iCTF), also known as "step-and-shoot," "tap mode," or "quick check" (e.g., SUREFLUORO for Canon Medical Systems USA, smartstep for GE Healthcare, i-Fluoro for Siemens Healthineers).In iCTF, a single pedal tap results in a single tube rotation, a limited volume of images, and low radiation doses.However, confusion between the two CTF methods, inconsistent use of CT parameters (particularly beam collimation and mAs), and confusing radiation reporting nomenclature have led to a wide range of misconceptions related to CTF radiation exposure. 3Physician radiation dose is particularly complicated to capture without the use of highly sensitive real-time radiation detectors placed at a consistent location and height beside the patient couch. 4his lack of clarity and consistency surrounding patient and physician radiation dose has likely slowed the adoption of "in-room" CTF (i.e., cCTF or iCTF methods) despite known advantages in terms of procedure speed and patient outcomes.In many centers CT-guided procedures are still performed with physicians walking in-and-out of the room after every needle reposition in a manner virtually indistinguishable from Haaga and Alfidi's initial description 1 over 40 years ago.
The purpose of this study is to quantify physician scatter radiation dose during iCTF.The results are presented across a range of real-world CT parameters and reported "per tap" so that physician exposure can be quickly estimated for individual procedures.We also perform a literature review to contextualize iCTF dose versus interventional procedures performed using c-arm based fluoroscopy.

CT scanner protocols and phantom
Measurements were taken using a multi detector CT scanner (Discovery CT750, GE Healthcare, Waukesha, WI) with a human sized phantom placed at isocenter (Mercury Phantom 4.0, Sun Nuclear Corporation, Middleton, WI).The 31 cm section of the phantom was scanned at 80, 100, 120, and 140 kV using 1.25, 2.5, 5, 10,20,and 40 mm wide beam collimations with and without a 0.5 mm lead apron placed over the dose meter.All scans were acquired with a gantry rotation time of 1 s and the mA was adjusted for each kV to the highest possible value allowed by the scanner.All scatter dose measurements were subsequently normalized to 100 mAs.Scans were repeated six times to calculate mean and standard deviation.Error bars on all plots are standard error unless otherwise noted.

Dose measurement and analysis
Dose was quantified using entrance air kerma (EAK), measured with a 12 cm spherical ionization chamber (800 cc collection volume; Extradin A6, Standard Imaging, Middleton, WI) and an electrometer (MAX-4000, Standard Imaging, Middleton, WI).The chamber was placed to the side of the CT table to mimic the typical position of a physician's torso as shown in Figure A1.A phantom ("LUNGMAN" Kyoto Kagaku Co., Ltd., Fushimiku Kyoto, Japan) was placed behind the chamber to provide backscatter, mimicking a clinical set-up.The chamber was 125 cm from the floor, 54 cm from the center of the CT couch (measured orthogonal from the long axis of the couch), and 85 cm from the scanner iso-center as shown in Figure A1.

Determination of operator scatter dose
Appendix A describes a method for experimental parametrization of operator scatter dose measurements allowing for the calculation of a physician's dose at any beam tube current, rotation time, beam collimation, and beam energy.An easy to follow "worksheet" is provided in Appendix A to facilitate readers performing their own dose calculation.Briefly, our method scales the dose from a reference condition with a dose of D ref and sums doses for each iCTF tap.Scaling accounts for changes in mA, rotation time, collimation, beam energy, short versus full scan geometry (see Appendix A for a description of short versus full scanning), and the presence of a lead apron.The reference condition dose was measured using no lead apron at 120 kV with a collimation of 10 mm, a full scan geometry, 100 mA and a rotation time of 1 s.nerve root block," and "spine sacroiliac injection."We calculated the averages and 25th/50th/75th percentiles for: number of taps, beam energy, rotation time, and tube current.We calculated this usage data using fields obtained from our commercial dose monitoring system (DoseWatch, GE Healthcare, Chicago, IL).

Literature based comparison of scatter dose
We performed a literature survey on papers which quantified operator scatter dose in c-arm based fluoroscopy and CTF.We searched using key words related to cardiology-based catheterization lab procedures, interventional radiology procedures, and biopsy/ablation/drainage procedures in CTF.From each study, we extracted operator dose information and the values for how long the operator was exposed to x-ray radiation.To compare dose measurements between studies using different dose metrics, we normalized all measurements to air kerma.

Experimental physician dose measurement results
Table 1 lists physician scatter doses as a function of beam energy, collimation thickness, and inclusion of lead apron.In general, for all beam energies physician scatter dose increases with beam collimation thickness.In general,for all collimation thicknesses,physician scatter dose increases with beam energy.Appendix A includes a regression analysis of the data shown in Figure A2.Quantitative changes in physician scatter dose measured in our data with rotation time, beam energy, mA, and beam collimation thickness are shown in Table 2.
A total of 2005 interventional CT cases were identified from which 1720 had iCTF taps series (i.e., some are done using ultrasound).The average number of iCTF taps per case was 30.1; the 25th/50th/75th percentiles in tap number were 10/24/40, respectively.The mean iCTF beam energy was 121 kV; the 25th/50th/75th percentiles in beam energy was 120/120/120 kV respectively.The average beam collimation was 6 mm; the 25th/50th/75th percentiles in beam collimation was 5/5/10 mm respectively.The average tube current was 58 mA; the 25th/50th/75th percentiles in tube current was 40/60/60 mA, respectively.The average rotation time was 0.5 s; the 25th/50th/75th percentiles in rotation time was 0.5/0.5/0.5 s.All of our iCTF taps are performed using a short scan mode in which the beam is on for 326 ms out of the 500 ms rotation time, therefore F SS = 326 ms 500 ms = 0.652 (discussed in Appendix A).Using "typical" acquisition techniques (all procedures) at UW-Madison of 120 kV, 60 mA, 5 mm beam collimation, 0.5 s rotation time, lead shielded operators, short scan geometry, and iCTF tap counts of 10, 24, 30.1, and 40 (corresponding to our 25th, median, average, and 75th percentiles representing our variety in case complexity) physician dose calculated using Appendix B for 10, 24, 30.1, and 40 iCTF taps is 0.20, 0.48, 0.60, and 0.80 µGy.Unshielded statistics for UW-Madison doses are presented in Table 1.

3.2
Literature survey and analysis TA B L E 3 iCTF usage descriptive statistics reported as "mean, 25th/50th/75th percentile."Physician radiation dose was obtained using the procedure described in Appendix A with the acquisition parameters of the typical acquisition techniques (i.e., 50th percentile) for each procedure type and the mean number of taps.We report on a total of 2005 procedures, where only 1720 had a tap series.

DISCUSSION
Our literature review will hopefully serve to mitigate some of the apparent fear within the radiology com-munity of CTF in-room procedures.We anecdotally find many physicians who think c-arm based procedures are "safer" than CTF procedures.Table 4 demonstrates the average operator dose per procedure is 9 times higher for c-arm relative to CTF.Therefore, to obtain an average equal dose, a physician would have to perform 9 times as many CTF procedures as c-arm procedures.These comparisons are an average, and as is visible In particular, the 9-fold difference we found for C-Arm and CTF procedures is based on both mean fluoroscopy times and mean dose rates.The large ratio of fluoroscopy times (31.57C-Arm-to-CTF) can be attributed to many factors including: (1) procedure complexity, (2) physician experience, (3) variations in site-to-site practices.Bias may be imparted if a single physician or group of physicians is selected for procedure dose comparisons.Stated differently, experience of the physician can vary at a given site where residents/fellows or physicians with decades worth of experience may perform a procedure.This can play a role given that less experienced physicians may require more time on the pedal for navigation purposes.Additionally, physician experience may also contribute to optimization of radiation reduction techniques, primarily in C-Arm procedures where gantry orientation can vary greatly and play a large role in automatic exposure control response.However, to strictly control for this source of bias would require a well-defined multi-institutional evaluation of doses.Our literature review pulled manuscripts from many institutions representing many procedures and physicians.Therefore, our opinion is that this should not contribute largely to the difference in fluoroscopy time and, hence, physician dose that we report.
Each modality lends itself to different clinical indications and, hence, procedure complexity.That is, C-Arms are well suited for device navigation through vasculature due to temporal constraints and patient motion.These procedures tend to be more complex in nature than CTF-guided biopsies and drainages due to poorer image quality in addition to the task of device navigation through tortuous blood vessels.CTF, on the other hand, typically requires short-distance navigation of a needle and less adjustment of device trajectory comparatively.While the dose per image frame at the detector may likely be lower for C-Arm procedures than for CTF procedure, the complexity of navigational and therapeutic needs may contribute to longer fluoroscopy times.
Differences in fluoroscopy time between C-Arm and CTF procedures may also be attributed to site-to-site variations in practice.That is, each site may have differing methods and levels of comprehensiveness for radiation safety training.The quality of training for fluoroscopy system operators can play a large role in physician dose, particularly for C-Arm procedures, given considerations for AEC response of the imaging system.To thoroughly evaluate any systematic discrepancies in the dose comparisons pulled from literature would require a detailed comparison of technique and geometric parameters reported and stored by the system through either radiation dose structure reports (RDSRs) or controller area network (CANs). 20Unfortunately, this level of detail was not available in the literature we found and does pose an additional limitation of this study.Although, as state previously, the literature we pulled represents many institutions, procedures, and physicians.Therefore, we don't expect this is a significant source of error in our dose comparisons.
The methods we describe in this paper for dose calculation could be retrospectively applied to operator acquisition data to compare badge doses with our dose estimates.This is a future work for our group.Additionally, a dose monitoring vendor or scanner vendor could implement our approach to produce a real time or daily feedback of cumulative operator scatter dose.Such a display could help physicians optimize their use of CTF by allowing the physician to understand how changes to kV, beam collimation, mA, and tap number affect their dose.Based on our measurements, these important acquisition parameters have varying (and sometimes non-linear) impacts on operator dose.With real time feedback, the operator could better find a set of acquisition parameters that provided them with interventional image utility with the smallest scatter dose.Data needed for real time or retrospective calculation is readily available in image DICOM metadata, making this approach amenable to widespread implementation if all DICOM images from an interventional CTF procedure are archived.
Inaba et al. 16 reported an eye lens personal dose equivalent of 39.1 (±36.3)µSv which is equal to an air kerma value of 23.0 ± 21 μGy.Inaba et al. 16 reported average scan parameters of 120 kV, 8 mm collimation, 20 mA, 0.5 s rotation time, and 26.6 s of CTF time.We can apply these parameters to Appendix A's worksheet.The tap number for this calculation we assume equal to the fluoroscopy time divided by the rotation time, 26.6/0.5 = 53.2taps.This assumes a single tap duration is equal to single rotation time.Inputting the Inaba et al. 16 parameters of 20 mA, 0.5 s rotation time, 8 mm beam collimation, and 120 kV beam energy for 53.2 taps, results in a physician dose of 27.57μGy using Appendix A. Our result calculated dose at chest height, while the Inaba et al. 16 measurement was at the height of the eyes.Assuming an average height for a human is approximately 170 cm, an inverse square law correction to this height from the geometry assumed in our experimental set up yields an eye level dose of 21.61 µGy.This value is well within the uncertainty obtained by the author of 23.0 ± 21 μGy.
Our paper allows a physician to calculate an estimate for their own scatter dose.The dose calculation is based on our experimental data, parametrization and worksheet method described in Appendix A.In Appendix A, we also discuss how applicable our method is to other makes and models.The limits for our method's accuracy on other makes and models are within the federal regulation 21 CFR 1020.33 (c)(2)(v) guide.This federal specification on dose output accuracy states manufacturers must specify the maximum deviations.Typically, the maximum deviation is within 30% and 40%.Readers desiring to use the dose calculation worksheet presented in Appendix A should perform a comparison of their vendor's reported scatter measurements, which are provided for planning radiation protection, to the scatter measurements for the GE Discovery 750CT, which are available on GE HealthCare's Customer Documentation Portal [citation].Example comparisons are provided in Appendix A.
A limitation of this study is our fixed location for ion chamber placement.We placed the chamber at the location an experienced interventional CTF physician at UW-Madison usually works from.This location was modelled at chest height.For different chest heights, different body regions (e.g., the eye lens), and different distances from iso-center the scatter dose will change.We did not quantify this change.Additionally, we only reported dose values from a single phantom size.Future works will investigate operator scatter dose from different locations and patient sizes.
Our prior work in this area measured operator scatter dose as a function of gantry position.We found that operator scatter doses increased the closer the tube was to the operator, 23 similar to C-arm fluoroscopy. 24e are aware that some CT vendors use partial angle scanning (i.e., the x-ray beam is on for less than 360 degrees of rotation) when the operator is in a iCTF mode.The total exposure time, if reported by the vendor, can be used to scale the mAs in place of the number of taps on scanners using partial angle scanning.While the method we describe in Appendix A accounts for partial scanning, it does not account for optimal beam angles for iCTF as described in Knott et al. 23

CONCLUSION
To our knowledge, this paper represents the first methodology for a physician using a CTF scan mode to calculate their scatter dose.The calculation uses readily available DICOM metadata and is therefore amenable to a third part dose calculation or calculation by the scanner OEM.Our literature review normalized dose rates from c-arm based fluoroscopy and CTF demonstrated that while CTF has a roughly 3.5 times higher dose rate, an average c-arm procedure lasts roughly 31 times longer.On average, this results in a need to perform nine CTF procedures to equal a single c-arm based procedure operator dose.

C O N F L I C T O F I N T E R E S T S TAT E M E N T
The authors declare no conflicts of interest.

A P P E N D I X A EXPERIMENTAL DETERMINATION OF THE SCAT-TER CORRECTION FACTORS Method for operator dose calculation
We parameterized our experimental scatter results in Table 1 to allow an arbitrary CTF acquisition's operator scatter dose calculation.EAK (i.e., entrance air kerma with a backscattering medium) versus beam collimation was plotted for each kV with and without the lead apron.Plots were fit using a linear regression model.Our method scales operator scatter either higher or lower from the "reference case" of 100 mA, 1 s rotation time, 10 mm beam collimation, a full scan geometry, and 120 kV.Our parameterization accounts for changes to the number of taps, mA, rotation time, beam collimation, use of lead shielding, full versus short scan geometry, and kV.The parameterization uses the following methodology: (1) calculate the scatter correction factors (F) for each CT tap relative to the reference case, (2) multiply the scatter correction factors by the scatter dose at the reference case (D ref ), and (3) sum all the contributions from each tap.
Operator Scatter Dose for n taps D ref Is the reference operator unshielded scatter dose of 6.26 µGy, F i mA is the mA adjustment factor relative to the reference condition, F i T is the rotation time adjustment factor relative to the reference condition, F i C is the collimation unshielded factor relative to the reference condition, and F i kV is the kV adjustment factor relative to the reference condition.In non-technical terms, Equation A1 simply scales the operator unshielded scatter dose per tap by increasing it or decreasing it relative to the "reference case" using the scatter correction factors and then adds all the contributions from each tap.The reference unshielded scatter dose condition uses 100 mA and 1 s rotation, therefore F mA and F T are defined as, F T accounts for changes in beam collimation width and cannot be assumed to be linear with collimation width.This is because the effects of the penumbra of the beam should have a larger influence on increasing operator scatter dose at small collimations relative to larger collimations. 3,25Therefore, we will determine F C from our experimental measurements.
F kV accounts for changes in beam energy and cannot be assumed to be linear with beam energy.The effect of changing kV changes the total number of photons produced in a non-linear way 26 and when kV changes the energy distribution of photons scattering from the patient will change altering the operator scatter dose in non-linear ways. 27Therefore, we will determine F kV from our experimental measurements.
accounts for changes in the total time the x-ray beam is turned on due to the use of a short scan geometry 21 versus a full scan geometry.Some vendors, in an effort to create higher frame rates for CTF, allow less than 360 degrees of data to be collected for use in CTF.This means the x-ray beam is on for less than the gantry rotation time for a single iCTF tap.This factor reduces the physician exposure to account for this effect.We expect this may vary vendor to vendor and suggest interrogating DICOM headers to understand how one's specific scanner operates in CTF modes.For our GE HD 750 in "smartview" mode, the scanner uses a short scan geometry resulting in an actual exposure time of 326 ms (e.g., for this scanner model this was reported using DICOM tag "0018 1150") for a 500 ms rotation time (e.g., for this scanner model this was reported using DICOM tag "0018 9305").Addi-tionally, for CTF modes that allow more than a single tap to be acquired at a time, F SS can take on values greater than unity.For cCTF, the exposure time is longer than the tube rotation time making multiple rotation time's worth of scan data add to physician dose but would otherwise appear as a single CTF tap.Statements in this paragraph may be vendor/model/scan mode dependent.F S accounts for the reduction in physician scatter dose due to lead shielding.F S was calculated as the mean value of the ratios between the EAK with and without lead apron for each size of collimation.This produced 6 values of F S for each beam collimation at each kV, we averaged over beam collimation and then fit the resulting curve using linear regression.For those using lead aprons of a different thickness or composition than our 0.5 mm Pb aprons, the transmission factor from your apron is usually supplied by the apron manufacturer or typical transmission can be used. 22o experimentally determine F C ,we divided the operator scatter doses at 100 mAs for each kV by the result at 10 mm beam collimation.This produced four values of F C for each kV at each beam collimation, we averaged over kV and then fit the resulting curve using a second order polynomial regression.Likewise, to experimentally determine F kV we divided the operator scatter doses at 100 mAs for each beam collimation by the result at 120 kV.This produced 6 values of F kV for each beam collimation at each kV, we averaged over beam collimation and then fit the resulting curve using a second order polynomial regression.F I G U R E A 2 F C accounts for changes in operator scatter dose (i.e., entrance air kerma) with changes in beam collimation from the reference condition of 10 mm collimation.For example, the operator scatter dose at 20 mm collimation is roughly 1.5 times the dose at 10 mm collimation based on the data in Table 1.For a given measurement, the standard error is plotted but is roughly as large as the data points (i.e., the uncertainty in each measurement was smaller than the graph's symbols).

Determination of F C , F kV , and F S Figures A2-A4
depend on the amount of scanner-to-scanner variation in geometry, filtration, and beam quality.Future work will specifically address the magnitude of this variation.We are confident, however, that a single parametrization should be applicable across a wide range of CT scanners.All vendors provide room scatter diagrams that are used by medical physicists to calculate room shielding requirements.We obtained three vendor-provided scatter diagrams from CT OEM supplied technical reference manuals.These diagrams include the scatter dose in air normalized to 100 mAs at various locations.The scatter doses in air at a point 140 cm out from isocenter at a 45-degree angle from the CT couch were then compared for the three CT scanner models considered.From a Siemens Somatom Go.Sim at 140 kV and a 19.2 mm F I G U R E A 3 F kV accounts for changes in operator scatter dose (i.e., entrance air kerma) with changes in beam energy from the reference condition of 120 kV.Data is listed in Table 1.For a given measurement, the standard error is plotted but is roughly as large as the data points (i.e., the uncertainty in each measurement was smaller than the graph's symbols).
collimation the scatter dose in air was 5.6 µGy/100 mAs.For a GE Discovery HD 750 at 140 kV at a 40 mm collimation, the scatter dose in air was 10.4 µGy/100 mAs.For a GE LightSpeed LS 16 at 140 kV at a collimation of 20 mm, the scatter dose in air was 5.3 µGy/100 mAs.If we scale the Siemens and GE LightSpeed LS 16 by a factor of 2 to get all the results reported at roughly a 40 mm beam collimation, we see the three different models would provide 11.2, 10.4, and 10.6 µGy/100 mAs.This range of scanner model-dependent air dose varies by less than 10%.This is well within the variations one will see in the clinic on a single scanner, as we demonstrate in the next section.Therefore, we currently believe our parametrization should be applicable across a wide range of CT scanners, albeit we would advise performing a similar check using a vendor's room scat- Shielding factor accounting for changes in dose (i.e., entrance air kerma) for different kV when the operator wears a lead apron with a thickness of 0.5 mm Pb.F S was obtained for each collimation size and represents the fraction of the radiation that reaches the operator penetrating through the lead apron.For example, the transmission factor of a 140 kV beam is approximately 4%, while for 80 kV the factor is 0.8%.Datapoints are shown with whiskers denoting the standard error in each measurement.The linear fit was made using the average of the six collimation sizes ratios with/without lead apron for each kV.
ter diagrams as we just performed here before using our parametrization to calculate operator scatter dose.Additionally, some error is imparted through our single parameterization given that there is a co-dependence for collimation and tube voltage.The heel effect and variation of scatter intensity with patient thickness implies that a multivariate function for collimation and tube voltage would lead to more accurate dose prediction.However, we evaluated the validity of the single-parameterization method in this paper using a multivariate function derived from multiple regression analysis.With parameters reported in the study by Inaba et al., 16 mentioned in the Discussion section, we computed physician dose with our worksheet as well as the multivariate dose function.Further, we used the reported physician dose in the Inaba et al. 16 study as a reference for dose values computed with our singleparameterization method used in this study as well as the multivariate function.We found percent differences of 2.98% and 1.89% for the single-parameterization and multivariate methods, respectively.Therefore, we do not expect a significant source of uncertainty from our single parameterization, and we believe our method provides a simpler and more intuitive insight into how these parameters may affect occupational dose.
We fit the scatter correction factors for collimation and beam energy using second order polynomial fits.This is an empirical decision based on our data.The realities of scatter variations present in the clinic due to operator location relative to the patient create higher uncertain-ties in operator dose than errors associated with making assumptions in the parameterization of our scatter correction factors.For example, our measurement probe was 85 cm from isocenter.Assuming the operator may move plus or minus 15 cm toward or away from the bore and the operator scatter dose falls off with a one over distance squared behavior, we should expect a factor of 1.47 times increase (i.e., ( Step 1 Fill in the blanks labeled Rows B1-B5 Tube current (units of milli amps (mA)) Row B1 Tube Rotation time (units of seconds) Row B2 Beam Collimation (units of mm, i.e., width of the beam at iso-center) Row B3 plot EAK values normalized to the reference condition for collimation, beam energy, and beam energy respectively to obtain F C , F kV , and F S .The fits from these figures define the F correction factors, withF C = −7.4* 10 −5 mm −2 * Collimation 2 + 8.04 * 10 −2 mm −1 * Collimation + 1.860 * 10 −1 , (A4) F kV = 8.8 * 10 −5 kV −2 * beam energy 2 − 2 * 10 −4 kV −1 * beam energy − 2.505 * 10 −1 , (A5) F S = 5 * 10 −4 kV −1 * beam energy − 3.193 * 10 −2 .(A6) Considerations for the methods of physician dose calculation CT scanners do use slightly different geometries and beam filtrations, which should change the operator scatter dose.Therefore, the accuracy of our method will F I G U R E A 1 Experimental set up showing the dose chamber unshielded (left) and shielded (right) using a lead apron.
72) when the operator moves 15 cm toward or away from the scanner isocenter respectively.This is a clinically realistic amount of operator position uncertainty causing a change in operator scatter by more than our previously mentioned scanner model to model changes.In layman terms, the error that might be present in applying our GE HD 750 derived scatter data to a specific scanner model, is likely less than the error present in the location one physician stands relative to their colleague.Dose worksheet for calculating operator scatter dose.This worksheet assumes you have iCTF tap acquisitions that use identical values of tube current, rotation time, beam collimation, beam energy, scan geometry, and physician shielding.If your procedure used different combinations of the beforementioned parameters, use this worksheet for each unique set of parameters and add the resulting doses (i.e., air kerma) values.
Entrance air kerma mean in µGy at 100 mAs without and with a 0.5 mm lead apron.
TA B L E 1Note: N/A*-signal was too low to produce a measurement.Standard deviation is shown in parenthesis (±SD).

Table 1 . iCTF acquisition parameter Parameter change Percent change in physician dose Comments
The impact of changing common iCTF acquisition parameters on physician dose is shown in this table.The percent changes in physician dose were calculated using Equation (A1) and the methodology explained in Appendix A which is based on the data presented in

Table 4 ,
Literature review of operator dose values during fluoroscopy procedures using C-arm and MDCT based imaging.A full version of this table with the originally reported dose values and our air kerma normalization procedure is presented in Appendix B. all procedure types have widely varying amounts of dose and irradiation time.Physicians should always understand the dose they are receiving for the techniques and duration specific to the procedures and case complexities they perform.
TA B L E 4 Assumes a lead apron thickness of 0.5 mm Pb equivalent.If your apron uses another Pb thickness or material, insert your apron's transmission factor.Footnote 2 The actual beam on time for a single tap divided by the rotation time.This accounts for short scan iCTF acquisitions where the beam on time is less than the rotation time or "lead foot" physicians using cCTF modes where the beam is on for multiple tube rotations.Literature review of operator dose values during fluoroscopy procedures using C-arm and MDCT based imaging.Dose units are as follows: a Data was initially reported as a cumulative dose of several months, we divided the reported cumulative dose by the number of cases.
TA B L E B 1 Ɨ