Kevin Wunderle

Comparison of indirect radiation dose estimates with directly measured radiation dose for patients and operators during complex endovascular procedures

BACKGROUND A great deal of attention has been directed at the necessity and potential for deleterious outcomes as a result of radiation exposure during diagnostic evaluations and interventional procedures. We embarked on this study in an attempt to accurately determine the amount of radiation exposure given to patients undergoing complex endovascular aortic repair. These measured doses were then correlated with radiation dose estimates provided by the imaging equipment manufacturers that are typically used for documentation and analysis of radiation-induced risk. METHODS Consecutive patients undergoing endovascular thoracoabdominal aneurysm (eTAAA) repair were prospectively studied with respect to radiation dose. Indirect parameters as cumulative air kerma (CAK), kerma area product (KAP), and fluoroscopy time (FT) were recorded concurrently with direct measurements of dose (peak skin dose [PSD]) and radiation exposure patterns using radiochromatic film placed in the back of the patient during the procedure. Simultaneously, operator exposure was determined using high-sensitivity electronic dosimeters. Correlation between the indirect and direct parameters was calculated. The observed radiation exposure pattern was reproduced in phantoms with over 200 dosimeters located in mock organs, and effective dose has been calculated in an in vitro study. Scatter plots were used to evaluate the relationship between continuous variables and Pearson coefficients. RESULTS eTAAA repair was performed in 54 patients over 5 months, of which 47 had the repair limited to the thoracoabdominal segment. Clinical follow-up was complete in 98% of the patients. No patients had evidence of radiation-induced skin injury. CAK exceeded 15 Gy in 3 patients (the Joint Commission on Accreditation of Healthcare Organizations [JCAHO] threshold for sentinel events); however, the direct measurements were well below 15 Gy in all patients. PSD was measured by quantifying the exposure of the radiochromatic film. PSD correlated weakly with FT but better with CAK and KAP (r = 0.55, 0.80, and 0.76, respectively). The following formula provides the best estimate of actual PSD = 0.677 + 0.257 CAK. The average effective dose was 119.68 mSv (for type II or III eTAAA) and 76.46 mSv (type IV eTAAA). The operator effective dose averaged 0.17 mSv/case and correlated best with the KAP (r = 0.82, P < .0001). CONCLUSION FT cannot be used to estimate PSD, and CAK and KAP represent poor surrogate markers for JCAHO-defined sentinel events. Even when directly measured PSDs were used, there was a poor correlation with clinical event (no skin injuries with an average PSD >2 Gy). The effective radiation dose of an eTAAA is equivalent to two preoperative computed tomography scans. The maximal operator exposure is 50 mSv/year, thus, a single operator could perform up to 294 eTAAA procedures annually before reaching the recommended maximum operator dose.

Reduction of Radiation During Fluoroscopic Urodynamics: Analysis of Quality Assurance Protocol Limiting Fluoroscopic Images During Fluoroscopic Urodynamic Studies

OBJECTIVE To evaluate whether the decrease in fluoroscopic images after initiation of a quality assurance (QA) protocol to decrease the amount of fluoroscopy during fluoro urodynamics (FUDS) translates into a significant reduction in radiation. METHODS The number of spot films, fluoroscopy time, air kerma, and dose area product from FUDS performed by our division during the 3 months before the conceptualization of the QA protocol were compared with the parameters of FUDS performed by our division 3 months after the initiation of the protocol. To ensure the protocol did not adversely affect the analysis of FUDS, 10 FUDS studies were evaluated by 4 fellowship-trained female urologists who compared the interpretation when only the images per QA protocol were reviewed with that when the additional images were reviewed. RESULTS A total of 54 FUDS studies performed in the 3 months before the conceptualization of the protocol were compared with 43 FUDS studies performed after initiation of the protocol. The mean number of spot films recorded before and after the QA protocol was 11.2 and 5.6, respectively (P<.001). The mean fluoroscopy time decreased from 40.9 to 11.7 seconds per procedure (P<.001). The mean air kerma decreased from 15.48 to 4.25 mGy, and the mean dose area product decreased from 518.90 to 150.28 mGy·cm2 (P<.001 and P<.001, respectively). No difference was found in the treatment or diagnosis in 100% of the 40 FUDS evaluations. CONCLUSION Our QA protocol significantly decreased the amount of fluoroscopy time, dose area product, and air kerma during each FUDS without changing the diagnosis or treatment recommendations.

Percent Depth Doses and X-ray Beam Characterizations of a Fluoroscopic System Incorporating Copper Filtration

Purpose In this investigation, we sought to characterize X‐ray beam qualities and quantitate percent depth dose (PDD) curves for fluoroscopic X‐ray beams incorporating added copper (Cu) filtration, such as those commonly used in fluoroscopically guided interventions (FGI). The intended application of this research is for dosimetry in soft tissue from FGI procedures using these data. Methods All measurements in this study were acquired on a Siemens (Erlangen, Germany) Artis zeego fluoroscope. X‐ray beam characteristics of first half‐value layer (HVL), second HVL, homogeneity coefficients (HCs), backscatter factors (BSFs) and kVp accuracy and precision were determined to characterize the X‐ray beams used for the PDD measurements. A scanning water tank was used to measure PDD curves for 60, 80, 100, and 120 kVp X‐ray beams with Cu filtration thicknesses of 0.0, 0.1, 0.3, 0.6, and 0.9 mm at 11 cm, 22 cm, and 42 cm nominal fields of view, in water depths of 0 to 150 mm. Results X‐ray beam characteristics of first HVLs and HCs differed from previous published research of fluoroscopic X‐ray beam qualities without Cu filtration. PDDs for 60, 80, 100, and 120 kVp with 0 mm of Cu filtration were comparable to previous published research, accounting for differences in fluoroscopes, geometric orientation, type of ionization chamber, X‐ray beam quality, and the water tank used for data collection. PDDs and X‐ray beam characteristics for beam qualities with Cu filtration are presented, which have not been previously reported. Conclusions The data sets of X‐ray beam characteristics and PDDs presented in this study can be used to estimate organ or soft tissue doses at depth involving similar beam qualities or to compare with mathematical models.

SU-D-209-02: Percent Depth Dose Curves for Fluoroscopic X-Ray Beam Qualities Incorporating Copper Filtration

PURPOSE The purpose of this investigation was to quantify percent depth dose (PDD) curves for fluoroscopic x-ray beam qualities incorporating added copper filtration. METHODS A PTW (Freiburg, Germany) MP3 water tank was used with a Standard Imaging (Middleton, WI) Exradin Model 11 Spokas Chamber to measure PDD curves for 60, 80, 100 and 120 kVp x-ray beams with copper filtration ranging from 0.0-0.9 mm at 22cm and 42cm fields of view from 0 to 150 mm of water. A free-in-air monitor chamber was used to normalize the water tank data to fluctuations in output from the fluoroscope. The measurements were acquired on a Siemens (Erlangen, Germany) Artis ZeeGo fluoroscope. The fluoroscope was inverted from the typical orientation providing an x-ray beam originating from above the water tank. The water tank was positioned so that the water level was located at 60cm from the focal spot; which also represents the focal spot to interventional reference plane distance for that fluoroscope. RESULTS PDDs for 60, 80, 100, and 120 kVp with 0 mm of copper filtration compared well to previously published data by Fetterly et al. [Med Phys, 28, 205 (2001)] for those beam qualities given differences in fluoroscopes, geometric orientation, type of ionization chamber, and the water tank used for data collection. PDDs for 60, 80, 100, and 120 kVp with copper filtration were obtained and are presented, which have not been previously investigated and published. CONCLUSION The equipment and processes used to acquire the reported data were sound and compared well with previously published data for PDDs without copper filtration. PDD data for the fluoroscopic x-ray beams incorporating copper filtration can be used as reference data for estimating organ or soft tissue dose at depth involving similar beam qualities or for comparison with mathematical models.

SU-F-I-75: Half-Value Layer Thicknesses and Homogeneity Coefficients for Fluoroscopic X-Ray Beam Spectra Incorporating Spectral Filtration

PURPOSE The purpose of this investigation is to quantify various first half-value-layers (HVLs), second HVLs and homogeneity coefficients (HCs) for a state-of-the-art fluoroscope utilizing spectral (copper) filtration. METHODS A Radcal (Monrovia, Ca) AccuPro dosimeter with a 10×6-6 calibrated ionization chamber was used to measure air kerma for radiographic x-ray exposures made on a Siemens (Erlangen, Germany) Artis ZeeGo fluoroscope operated in the service mode. The ionization chamber was centered in the x-ray beam at 72 cm from the focal spot with a source-to-image-distance of 120 cm. The collimators were introduced to limit the x-ray field to approximately 5 cm × 5 cm at the ionization chamber plane. Type-1100 aluminum filters, in 0.5 mm increments, were used to determine the HVL. Two HVL calculation methods were used, log-linear interpolation and Lambert-W interpolation as described by Mathieu [Med Phys, 38(8), 4546 (2011)]. Multiple measurements were made at 60, 80, 100, 120 kVp at spectral filtration thicknesses of 0, 0.1, 0.3, 0.6 and 0.9 mm. RESULTS First HVL, second HVL, and HCs are presented for the fluoroscopic x-ray beam spectra indicated above, with nearly identical results from the two interpolation methods. Accuracy of the set kVp was also determined and deviated less than 2%. First HVLs for fluoroscopic x-ray beam spectra without spectral filtration determined in our study were 7%-16% greater than previously published data by Fetterly et al. [Med Phys, 28, 205 (2001)]. However, the FDA minimum HVL requirements changed since that publication, requiring larger HVLs as of 2006. Additionally, x-ray tube and generator architecture have substantially changed over the last 15 years providing different beam spectra. CONCLUSION X-ray beam quality characteristics for state-of-the-art fluoroscopes with spectral filtration have not been published. This study provides reference data which will be useful for defining beam qualities encountered on fluoroscopes using spectral filtration.

SU-F-I-76: Fluoroscopic X-Ray Beam Profiles for Spectra Incorporating Copper Filtration

PURPOSE The purpose of this investigation is to characterize and quantify X-ray beam profiles for fluoroscopic x-ray beam spectra incorporating spectral (copper) filtration. METHODS A PTW (Freiburg, Germany) type 60016 silicon diode detector and PTW MP3 water tank were used to measure X-ray beam profiles for 60, 80, 100 and 120 kVp x-ray beams at five different copper filtration thicknesses ranging from 0-0.9 mm at 22 and 42 cm fields of view and depths of 1, 5, and 10 cm in both the anode-cathode axis (inplane) and cross-plane directions. All measurements were acquired on a Siemens (Erlangen, Germany) Artis ZeeGo fluoroscope inverted from the typical orientation providing an x-ray beam originating from above the water surface with the water level set at 60 cm from the focal spot. RESULTS X-ray beam profiles for beam spectra without copper filtration compared well to previously published data by Fetterly et al. [Med Phys, 28, 205 (2001)]. Our data collection benefited from the geometric orientation of the fluoroscope, providing a beam perpendicular to the tank water surface, rather than through a thin side wall as did the previously mentioned study. Profiles for beams with copper filtration were obtained which have not been previously investigated and published. Beam profiles in the anode-cathode axis near the surface and at lower x-ray energy exhibited substantial heel effect, which became less pronounced at greater depth. At higher energy with copper filtration in the beam, the dose falloff out-of-field became less pronounced, as would be anticipated given higher scatter photon energy. CONCLUSION The x-ray beam profile data for the fluoroscopic x-ray beams incorporating copper filtration are intended for use as reference data for estimating doses to organs or soft tissue, including fetal dose, involving similar beam qualities or for comparison with mathematical models.

TH‐AB‐201‐09: Effect of X‐Ray Beam Quality On Fluoroscope Reported Reference Plane Air Kerma When Measured by DAP Meters: TG190 Protocol Implications for Interventional Fluoroscopes

Purpose: To investigate the accuracy of the correction factor (CF) determined using the AAPM-TG190 protocol and applied to measurements made across a full spectrum of x-ray beam qualities on interventional c-arm fluoroscopes. Methods: The x-ray beam area was measured to allow for the calculation of the air-kerma-area-product (Pk,a). Air kerma was measured using a calibrated ionization chamber centered in the x-ray beam free-in-air. Manual technique factors were set with vendor service support. Data were collected on 10 fluoroscopic systems at 55 kVp to 125 kVp in 10-kVp increments and also at 100 kVp. At each available combination of kVp and spectral filter (copper) thickness, three measurements were taken. A CF for each beam quality was determined by dividing the measured Pk,a by the Pk,a reported by the fluoroscope. Two normalized correction factors (NCFs) were defined to determine the potential error in using a single CF across a spectrum of beam qualities. The first normalized the CF at a given beam quality to the CF at 100 kVp without filtration (NCF[100,0]) and another normalized to the CF at 100 kVp with 0.1 mm copper (NCF[100,0.1]). Results: The accuracy of the CF varied depending on whether it was determined using spectral filtration, which was apparent in comparisons of NCF(100,0) with NCF(100,0.1). In general, the CF was dependent on beam quality, an effect that was most pronounced at low kVps with spectral filtration. Conclusion: For interventional fluoroscopes employing spectral filtration, better accuracy is achieved when copper is used to establish the CF. Additionally, a CF determined at 100 ± 10 kVp may not be optimal for pediatric applications, in which the beam quality typically consists of low kVps and large amounts of copper filtration. The accuracy of the CF can be improved for pediatric applications by using a more clinically relevant beam quality.

Radiation recall after a transarterial hepatic chemoembolization.

Radiation recall is a rare side effect observed in patients treated with certain medications after radiation therapy. This effect mimics a radiation-induced tissue reaction in expression; however, it occurs outside of the traditional time course and only in the presence of a catalyzing agent. The authors report a case of radiation recall resulting from an interaction between radiation delivered during a fluoroscopically guided hepatic chemoembolization for treatment of metastatic carcinoid tumor and the oral chemotherapeutic agents capecitabine and temozolomide administered 7 weeks later.