Dose Tracking System Research Articles

Real-time Detection of Patient Head Position and Cephalometric Landmarks from Neuro-Interventional Procedure Images Using Machine Learning for Patient Eye-Lens Dose Prediction.

A deep learning (DL) model has been developed to estimate patient-lens dose in real-time for given exposure and geometric conditions during fluoroscopically-guided neuro-interventional procedures. Parameters input into the DL model for dose prediction include the patient head shift from isocenter and cephalometric landmark locations as a surrogate for head size. Machine learning (ML) models were investigated to automatically detect these parameters from the in-procedure fluoroscopic image. Fluoroscopic images of a Kyoto Kagaku anthropomorphic head phantom were taken at various known X (transverse) and Y (longitudinal) shifts, as well as different magnification modes, to create an image database. For each image, anatomical landmark coordinate locations were obtained manually using ImageJ and are used as ground-truth labels for training. This database was then used to train the two separate ML models. One ML model predicts the patient head shift in both the X and Y directions and the other model predicts the coordinates of the anatomical landmarks. From the coordinates, the distance between these anatomical landmarks is calculated, and input into the DL dose-prediction model. Model performance was evaluated using mean absolute error (MAE) and mean absolute percentage error (MAPE) for the head-shift and landmark-coordinate models, respectively. The goal is to implement these two separate models into the Dose Tracking System (DTS) developed by our group. This would allow the DTS to automatically detect the patient head size and position for eye-lens dose prediction and eliminate the need for manual input by the clinical staff.

Cumulative radiation doses from recurrent PET-CT examinations.

Positron emission tomography (PET–CT) is an essential imaging modality for the management of various diseases. Increasing numbers of PET–CT examinations are carried out across the world and deliver benefits to patients; however, there are concerns about the cumulative radiation doses from these examinations in patients. Compared to the radiation exposure delivered by CT, there have been few reports on the frequency of patients with a cumulative effective radiation dose of ≥100 mSv from repeated PET–CT examinations. The emerging dose tracking system facilitates surveys on patient cumulative doses by PET–CT because it can easily wrap up exposure doses of PET radiopharmaceuticals and CT. Regardless of the use of a dose tracking system, implementation of justification for PET–CT examinations and utilisation of dose reduction measures are key issues in coping with the cumulative dose in patients. Despite all the advantages of PET/MRI such as eliminating radiation exposure from CT and providing good tissue contrast in MRI, it is expensive and cannot be introduced at every facility; thus, it is still necessary to utilise PET–CT with radiation reduction measures in most clinical situations.

Comparison of skin dose calculated by the dose tracking system (DTS) with a beam angular correction factor and that calculated by Monte-Carlo.

Skin dose is dependent on the incident beam angle and corrections are needed for accurate estimation of the risk of deterministic effects of the skin. Angular-correction factors (ACF) were calculated and incorporated into our skin-dose-tracking system (DTS) and the results compared to Monte-Carlo simulations for a neuro-interventional procedure. To obtain the ACF's, EGSnrc Monte-Carlo (MC) software was used to calculate the dose averaged over 0.5, 1, 2, 3, 4 and 5 mm depth into the entrance surface of a water phantom at the center of the field as a function of incident beam to skin angle from 90-10 degrees for beam field sizes from 5-15 cm and for beam energies from 60-120 kVp. These values were normalized to the incident primary dose to obtain the ACF. The angle of incidence at each mesh vertex in the beam on the surface of the DTS patient graphic was calculated as the complement of the angle between the normal vector and the vector of the intersecting ray from the tube focal spot; skin dose at that vertex was calculated using the corresponding ACF. The skin-dose values with angular correction were compared to those calculated using MC with a matching voxelized phantom. The results show the ACF decreases with decreasing incident angle and skin thickness, and increases with increasing field size and kVp. Good agreement was obtained between the skin dose calculated by the angular-corrected DTS and MC, while use of the ACF allows the real-time performance of the DTS to be maintained.

Estimation of Patient Eye-Lens Dose During Neuro-Interventional Procedures using a Dense Neural Network (DNN).

The patient's eye-lens dose changes for each projection view during fluoroscopically-guided neuro-interventional procedures. Monte-Carlo (MC) simulation can be done to estimate lens dose but MC cannot be done in real-time to give feedback to the interventionalist. Deep learning (DL) models were investigated to estimate patient-lens dose for given exposure conditions to give real-time updates. MC simulations were done using a Zubal computational phantom to create a dataset of eye-lens dose values for training the DL models. Six geometric parameters (entrance-field size, LAO gantry angulation, patient x, y, z head position relative to the beam isocenter, and whether patient's right or left eye) were varied for the simulations. The dose for each combination of parameters was expressed as lens dose per entrance air kerma (mGy/Gy). Geometric parameter combinations associated with high-dose values were sampled more finely to generate more high-dose values for training purposes. Additionally, dose at intermediate parameter values was calculated by MC in order to validate the interpolation capabilities of DL. Data was split into training, validation and testing sets. Stacked models and median algorithms were implemented to create more robust models. Model performance was evaluated using mean absolute percentage error (MAPE). The goal for this DL model is that it be implemented into the Dose Tracking System (DTS) developed by our group. This would allow the DTS to infer the patient's eye-lens dose for real-time feedback and eliminate the need for a large database of pre-calculated values with interpolation capabilities.

Vendor-independent skin dose mapping application for interventional radiology and cardiology.

PurposeThe purpose of this paper is to present and validate an originally developed application SkinCare used for skin dose mapping in interventional procedures, which are associated with relatively high radiation doses to the patient’s skin and possible skin reactions.MethodsSkinCare is an application tool for generating skin dose maps following interventional radiology and cardiology procedures using the realistic 3D patient models. Skin dose is calculated using data from Digital Imaging and Communications in Medicine (DICOM) Radiation Dose Structured Reports (RDSRs). SkinCare validation was performed by using the data from the Siemens Artis Zee Biplane fluoroscopy system and conducting “Acceptance and quality control protocols for skin dose calculating software solutions in interventional cardiology” developed and tested in the frame of the VERIDIC project. XR‐RV3 Gafchromic films were used as dosimeters to compare peak skin doses (PSDs) and dose maps obtained through measurements and calculations. DICOM RDSRs from four fluoroscopy systems of different vendors (Canon, GE, Philips, and Siemens) were used for the development of the SkinCare and for the comparison of skin dose maps generated using SkinCare to skin dose maps generated by different commercial software tools (Dose Tracking System (DTS) from Canon, RadimetricsTM from Bayer and RDM from MEDSQUARE). The same RDSRs generated during a cardiology clinical procedure (percutaneous coronary intervention—PCI) were used for comparison.ResultsValidation performed using VERIDIC's protocols for skin dose calculation software showed that PSD calculated by SkinCare is within 17% and 16% accuracy compared to measurements using XR‐RV3 Gafchromic films for fundamental irradiation setups and simplified clinical procedures, respectively. Good visual agreement between dose maps generated by SkinCare and DTS, RadimetricsTM and RDM was obtained.ConclusionsSkinCare is proved to be very convenient solution that can be used for monitoring delivered dose following interventional procedures.

Improved field-portable system to measure Cs-137 in wildlife

We have developed an improved system to measure Cs-137 in wildlife at the Savannah River Site. This field-portable system consists of a shielded 5 cm by 10 cm by 40 cm NaI detector controlled by an Ametek Ortec Digibase. Measurement of an animal’s radioactivity is made by placing the animal at a predefined location on the detector system for a one minute count-time. The counts, animal type, and animal weight are then used as inputs to an algorithm which calculates the amount of Cs-137 within the whole animal and within the edible meat portion of the animal. The results from these calculations are used to estimate the received dose from eating this animal and is included in the Savannah River Site’s Hunter Dose Tracking System. This system has a detection limit of 0.60 pCi/g (22.20 Bq/kg) with a typical measurement uncertainty of less than 0.32 pCi/g (11.84 Bq/kg).

Radiation Effective Dose Above 100 mSv From Fluoroscopically Guided Intervention: Frequency and Patient Medical Condition.

OBJECTIVE. The purpose of this article was to investigate the medical condition of patients who received substantial cumulative effective dose (CED) in fluoroscopically guided interventional (FGI) procedures. MATERIALS AND METHODS. We examined 25,253 patients (mean age, 58.2 years; 50.6% male) who underwent 46,491 FGI procedures at a tertiary care center in the United States from January 2010 to January 2019. Radiation dosage data were retrieved from an in-house semiautomated dose-tracking system. A cohort was identified as those who received a CED of 100 mSv or greater and was categorized by medical disorder from longitudinal medical records. Statistical software was used to determine mean value, five percentiles (10th, 25th, 50th, 75th, 95th), and interquartile range for age and dose. RESULTS. Among 1011 (4.0%) patients (30.4% female) with a CED of 100 mSv or more, the median number of procedures was 2.0, the median age at first procedure was 60.0 years old, and the median value of CED was 177.2 mSv. The patients' medical disorders included cancer (36.7%), chronic disease of the torso (30.0%), internal bleeding (24.8%), trauma (4.6%), organ transplant (3.2%) and cerebrovascular disease (0.7%). Eight-hundred (79.1%) patients underwent all of their procedures within 365 days. CONCLUSION. This is the first cohort study of the medical condition of patients receiving substantial cumulative doses from FGI procedures over a long period. In the critical care of patients with serious medical disorders, 4.0% of patients may be exposed to substantial radiation dose (CED ≥ 100 mSv). The risks associated with such a high level of radiation warrant continued attention.

Optimizing Staff Dose in Fluoroscopy-Guided Interventions by Comparing Clinical Data with Phantom Experiments

PurposeTo evaluate conditions for minimizing staff dose in interventional radiology, and to provide an achievable level for radiation exposure reduction. Materials and MethodsComprehensive phantom experiments were performed in an angiography suite to evaluate the effects of several parameters on operator dose, such as patient body part, radiation shielding, x-ray tube angulation, and acquisition type. Phantom data were compared with operator dose data from clinical procedures (n = 281), which were prospectively acquired with the use of electronic real-time personal dosimeters (PDMs) combined with an automatic dose-tracking system (DoseWise Portal; Philips, Best, The Netherlands). A reference PDM was installed on the C-arm to measure scattered radiation. Operator exposure was calculated relative to this scatter dose. ResultsIn phantom experiments and clinical procedures, median operator dose relative to the dose-area product (DAP) was reduced by 81% and 79% in cerebral procedures and abdominal procedures, respectively. The use of radiation shielding decreased operator exposure up to 97% in phantom experiments; however, operator dose data show that this reduction was not fully achieved in clinical practice. Both phantom experiments and clinical procedures showed that the largest contribution to relative operator dose originated from left-anterior-oblique C-arm angulations (59%–75% of clinical operator exposure). Of the various x-ray acquisition types used, fluoroscopy was the main contributor to procedural DAP (49%) and operator dose in clinical procedures (82%). ConclusionsAchievable levels for radiation exposure reduction were determined and compared with real-life clinical practice. This generated evidence-based advice on the conditions required for optimal radiation safety.

319. Effective Dose Assessment on an Hybrid Equipment: Results and challenges to integrate with MDCT

Purpose The aim of this study was to measure, monitor and report effective dose in nuclear medicine and to assess current challenges in integrating these measures with CT. Methods In 2014 we connected a CT-PET to a dose tracking software and started to collect dose data from CT modality; in late 2015 the software was upgraded to a version which includes a nuclear medicine module for dose tracking. Data from the PET part of the scanner, in terms of administered activity and effective dose, were also collected. Results Data from 12000 CT doses and 3700 PET doses were collected, mostly from: Whole Body (WB) 18F-FDG (63.2%), WB 11C-Choline (12.8%), WB 68Ga-DOTATOC (5.5%), Head 11C-Methionine for a total of 18.4% of the whole activity of the scanner. CT mean DLP (mGy∗cm) data values were (range between brackets): WB 18F-FDG 1486.3 (76.1-7700.9), WB 11C-Choline 2451.9 (290.9-5023.1), WB 68Ga-DOTATOC 1183.8 (41.0-3728.4) and Head 11C-Methionine 766.7 (52.3-2326.9). Mean effective doses (mSv) were: WB 18F-FDG 15.3 ± 4.7, WB 11C-Choline 26.5 ± 5.6, WB 68Ga 13.4 ± 3.7 and Head 11C-Methionine 1.2 ± 0.7. Mean administered activities (MBq) and effective doses (mSv) for radiopharmaceuticals used in PET were: WB 18F-FDG 335.9-6.4, Head 11C-Methionine 294.6-2.5, WB 68Ga-DOTATOC 168.3-3.5 and WB 11C-Choline 322.2–1.5. The mean total effective doses (mSv) due to both modality were: WB 18F-FDG 21.7 ± 4.9, Head 11C-Methionine 3.7 ± 0.8, WB 11 C-Choline 27.9 ± 5.6 and WB 68Ga-DOTATOC 16.9 ± 2.8. Conclusions The implementation of a dose tracking system to nuclear medicine is of great value for accurate and regular recording, reporting and analysis of patient’s effective doses. It can help to improve the evaluation of radiation exposures in the clinical practice.

P080] Assessment of effective dose in hybrid imaging

Purpose The aim of this study is to assess the typical doses associated with PET/CT examination in a large population and to evaluate the difference of effective dose estimation in fixed vs patient-adapted activity utilizing the same imaging protocols. Doses differences in the urinary bladder are also estimated for PET examination. Methods and materials DoseWatch™ tracking system was utilized to collect patient information and to measure effective dose (for WB 18 F-FDG PET/CT) and organ dose data (for PET only) associated with a fixed activity by retrospectively analyzing existing data. For CT examination DLP values and effective dose data was collected; for PET examination DoseWatch™ provides the administered activity, the effective and the organ doses, based on ICRP 106. Effective and organ dose (for PET only) in a PET/CT examination where the administered activity is adapted to the patient’s weight will be estimated from the same database using a theoretical calculation. The dose in the urinary bladder is also assessed on theoretical calculations. Results Dose data from 6900 CT and 1700 WB 18F-FDG PET were collected. CT mean DLP (mGy*cm) data values were: 1481.3 (76.1–7700.9) and mean effective doses (mSv): 15.2 ± 4.9. Mean administered activities (MBq) and effective doses (mSv) for 18F-FDG PET are: 333.9–6.4. The mean total effective doses (mSv) due to both modality are: 21.5 ± 5.2. equivalent doses (mSv) to urinary bladder are: 43.7 ± 5.8. Conclusions The implementation of a dose tracking system in nuclear medicine is of great value for accurate and regular recording, reporting and analysis of patient’s effective doses.

OA144] Measuring, monitoring and reporting effective dose on hybrid equipment: Results and challanges to integrate with MDCT in a large population study

Purpose The aim of this study was to measure, monitor and report the effective dose in nuclear medicine on s large population and to integrate these measurements with CT dose data. Methods and materials A dose tracking software (GE Dosewatch™) with a NM module was connected to a CT-PET and collected DLP and effective dose from CT modality and administered activity and effective from PET modality. The mean DLP and the mean effective doses with the ranges was assessed for CT. The mean administered activities and mean effective doses for the different radiopharmaceuticals used in PET were evaluated. Examinations were performed with a GE Discovery 690 which has a 64-detector CT scanner; PET scan is performed in stop and go imaging mode. Results Doses data from 11000 CT and 2700 PET were collected, mostly from: Whole Body (WB) 18F-FDG (63.2%), WB 11C-Choline (12.8%), Head 11C-Methionine (18.4%), WB 68Ga-DOTATOC (5.5%). CT mean DLP (mGy*cm) data values were (range between brackets): WB 18F-FDG 1486.3 (76.1-7700.9), WB 11C-Choline 2451.9 (290.9-5023.1), WB 68Ga-DOTATOC 1184.2 (41.0-3728.4) and Head 11C-Methionine 766.7 (52.3-2326.9). Mean effective doses due to CT modality (mSv) were: WB 18F-FDG 15.3 ± 4.7, WB 11C-Choline 26.5 ± 5.6, WB 68Ga-DOTATOC 13.4 ± 2.7 and Head 11C-Methionine 1.7 ± 2.9. Mean administered activity (MBq) and effective doses (mSv) for radiopharmaceuticals used in PET were: WB 18F-FDG 335.9-6.4, Head 11C-Methionine 294.4.6-2.5, WB 68Ga-DOTATOC 168.3-3.5 and WB 11C-Choline 322.2-1.5. The mean total effective doses (mSv) due to both modality were: WB 18F-FDG 21.7 ± 4.9, Head 11C-Methionine 4.3 ± 2.9, WB 11C-Choline 27.9 ± 5.6 and WB 68Ga-DOTATOC 16.9 ± 2.8. Conclusions The implementation of a dose tracking system in nuclear medicine is of great value for accurate and regular recording, reporting and analysis of patient’s effective doses. It can help to improve and optimize the evaluation of radiation exposures in the clinical practice.

Calculation of Forward Scatter Dose Distribution at the skin entrance from the patient table for fluoroscopically guided interventions using a pencil beam convolution kernel.

The forward-scatter dose distribution generated by the patient table during fluoroscopic interventions and its contribution to the skin dose is studied. The forward-scatter dose distribution to skin generated by a water table-equivalent phantom and the patient table are calculated using EGSnrc Monte-Carlo and Gafchromic film as a function of x-ray field size and beam penetrability. Forward scatter point spread function's (PSFn) were generated with EGSnrc from a 1×1 mm simulated primary pencil beam incident on the water model and patient table. The forward-scatter point spread function normalized to the primary is convolved over the primary-dose distribution to generate scatter-dose distributions. The utility of PSFn to calculate the entrance skin dose distribution using DTS (dose tracking system) software is investigated. The forward-scatter distribution calculations were performed for 2.32 mm, 3.10 mm, 3.84 mm and 4.24 mm Al HVL x-ray beams for 5×5 cm, 9×9 cm, 13.5×13.5 cm sized x-ray fields for water and 3.1 mm Al HVL x-ray beam for 16.5×16.5 cm field for the patient table. The skin dose is determined with DTS by convolution of the scatter dose PSFn's and with Gafchromic film under PMMA "patient-simulating" blocks for uniform and for shaped x-ray fields. The normalized forward-scatter distribution determined using the convolution method for water table-equivalent phantom agreed with that calculated for the full field using EGSnrc within ±6%. The normalized forward-scatter dose distribution calculated for the patient table for a 16.5×16.5 cm FOV, agreed with that determined using film within ±2.4%. For the homogenous PMMA phantom, the skin dose using DTS was calculated within ±2 % of that measured with the film for both uniform and non-uniform x-ray fields. The convolution method provides improved accuracy over using a single forward-scatter value over the entire field and is a faster alternative to performing full-field Monte-Carlo calculations.

Investigation of organ dose variation with adult head size and pediatric age for neuro-interventional projections.

The purpose of this study was to evaluate the effect of patient head size on radiation dose to radiosensitive organs, such as the eye lens, brain and spinal cord in fluoroscopically guided neuro-interventional procedures and CBCT scans of the head. The Toshiba Infinix C-Arm System was modeled in BEAMnrc/EGSnrc Monte-Carlo code and patient organ and effective doses were calculated in DOSxynrc/EGSnrc for CBCT and interventional procedures. X-ray projections from different angles, CBCT scans, and neuro-interventional procedures were simulated on a computational head phantom for the range of head sizes in the adult population and for different pediatric ages. The difference of left-eye lens dose between the mean head size and the mean ± 1 standard deviation (SD) ranges from 20% to 300% for projection angles of 0° to 90° RAO. The differences for other organs do not vary as much and is only about 10% for the brain. For a LCI-High CBCT protocol, the difference between mean and mean ± 1 SD head size is about 100% for lens dose and only 10% for mean and peak brain dose; the difference between 20 and 3 year-old mean head size is an increase of about 200% for the eye lens dose and only 30% for mean and peak brain dose. Dose for all organs increases with decreasing head size for the same reference point air kerma. These results will allow size-specific dose estimates to be made using software such as our dose tracking system (DTS).

An automated dose tracking system for adaptive radiation therapy

Background and objectiveThe implementation of adaptive radiation therapy (ART) into routine clinical practice is technically challenging and requires significant resources to perform and validate each process step. The objective of this report is to identify the key components of ART, to illustrate how a specific automated procedure improves efficiency, and to facilitate the routine clinical application of ART. MethodsData was used from patient images, exported from a clinical database and converted to an intermediate format for point-wise dose tracking and accumulation. The process was automated using in-house developed software containing three modularized components: an ART engine, user interactive tools, and integration tools. The ART engine conducts computing tasks using the following modules: data importing, image pre-processing, dose mapping, dose accumulation, and reporting. In addition, custom graphical user interfaces (GUIs) were developed to allow user interaction with select processes such as deformable image registration (DIR). A commercial scripting application programming interface was used to incorporate automated dose calculation for application in routine treatment planning. Each module was considered an independent program, written in C++or C#, running in a distributed Windows environment, scheduled and monitored by integration tools. ResultsThe automated tracking system was retrospectively evaluated for 20 patients with prostate cancer and 96 patients with head and neck cancer, under institutional review board (IRB) approval. In addition, the system was evaluated prospectively using 4 patients with head and neck cancer. Altogether 780 prostate dose fractions and 2586 head and neck cancer dose fractions went processed, including DIR and dose mapping. On average, daily cumulative dose was computed in 3 h and the manual work was limited to 13 min per case with approximately 10% of cases requiring an additional 10 min for image registration refinement. ConclusionsAn efficient and convenient dose tracking system for ART in the clinical setting is presented. The software and automated processes were rigorously evaluated and validated using patient image datasets. Automation of the various procedures has improved efficiency significantly, allowing for the routine clinical application of ART for improving radiation therapy effectiveness.

Benchmarking adult CT-dose levels to regional and national references using a dose-tracking software: a multicentre experience

ObjectivesTo benchmark CT-dose data for standard adult CT studies to regional and national reference levels using a dose-tracking system.MethodsData from five CT systems from three hospitals were collected over a 1- to 2.5-year period (2012–2014), using the same type of dose management system. Inclusion criteria were adult patients and standard CT-head, CT-abdomen-pelvis, CT-thorax, CT-lumbar spine, CT-pulmonary embolism, CT-cervical spine and CT-thorax-abdomen studies, with one helical scan. Volumetric CT-dose index (CTDIvol), dose length product (DLP) and scan length from 31,709 scans were analysed statistically.ResultsAfter dose optimisation CTDIvol and DLP values were below the national diagnostic reference levels (DRLs) for all CT studies and for all systems investigated. Mostly no significant differences were found between CTDIvol and DLP levels (p values ≥ 0.01) of CT studies performed on different scanners within the same hospital. Significant dose differences (p values < 0.01) were instead observed among hospitals for comparable CT studies. Dose level range and scan length differences for similar CT studies were revealed.ConclusionsDose-tracking systems help to reduce CT-dose levels below national DRLs. However, dose and protocol data comparison between and within hospitals has the potential to further reduce variability in dose data of standard adult CT studies.Key Points• Retrospective three-centre study on dose levels of standard adult CT procedures.• Dose-tracking systems help hospitals to stay below national dose reference levels.• Dose-tracking systems help to align CT dose levels between scanners within hospitals.• Benchmarking shows CT dose level variability for similar examinations in different hospitals.• Differences in dose level range/scan length for similar CT studies are revealed.

Calculation of the entrance skin dose distribution for fluoroscopically guided interventions using a pencil beam backscatter model.

Radiation backscattered from the patient can contribute substantially to skin dose in fluoroscopically guided interventions (FGIs). The distribution of backscatter is not spatially uniform, and use of a single backscatter factor cannot provide an accurate determination of skin dose. This study evaluates a method to determine the backscatter spatial distribution through convolution of a backscatter-to-primary (BP) point spread function (PSFn). The PSFn is derived for a pencil beam using EGSnrc Monte Carlo software and is convolved with primary distributions using a dose-tracking system. The backscatter distribution calculated using the convolution method is validated with Monte Carlo-derived distributions for three different size "uniform" fields and with XR-QA2 Gafchromic film for nonuniform x-ray fields obtained using region-of-interest (ROI) attenuators and compensation filters, both with homogenous poly-methyl methacrylate and nonhomogenous head phantoms. The BP ratios inside uniform fields were calculated within [Formula: see text] of that determined using EGSnrc. For shaped fields, the BP ratio in the unattenuated ROI was calculated within [Formula: see text] of that measured with film; in the beam-attenuated periphery, agreement was within [Formula: see text], due to the larger uncertainty of the dose-response curve of the film in the low-dose region. This backscatter PSFn convolution method is much faster than performing full-field Monte Carlo calculations and provides improved accuracy in skin dose distribution determination for FGI procedures.

Efficacy of radiation dose reduction due to real-time monitoring and visualization of peak skin dose during coronary angiography and percutaneous coronary intervention.

This study assessed that the use of real-time monitoring and visualization of peak skin dose could reduce radiation dose during coronary angiography (CAG) and percutaneous coronary intervention (PCI). Exposure to ionizing radiation has dose related effects including skin damage. Reducing the radiation exposure is important during CAG and PCI. The skin dose-tracking system (DTS) has a real-time monitor of radiation peak skin dose. A total of 323 consecutive patients who underwent CAG and PCI between September 2014 and June 2015 were enrolled. Patients were classified into with DTS group (CAG alone in 104 and PCI in 57 patients) or without DTS group (CAG alone in 106 and PCI in 56 patients). There was no significant difference in reference air kerma between CAG alone with and without DTS groups. Reference air kerma with DTS group during PCI was lower than without DTS group (204.6 ± 141.1 mGy vs. 294.2 ± 237.4 mGy, P = 0.016). Moreover, kerma area product (17.8 ± 13.0 Gycm2 vs. 25.2 ± 19.3 Gycm2 , P = 0.019) and number of cine runs (12.8 ± 5.0 vs. 15.5 ± 6.5, P = 0.013) with DTS group were lower than without DTS group. Multiple regression analysis showed increased reference air kerma was associated with male gender, body mass index and type B2/C lesion. Conversely, DTS correlated with decreased reference air kerma. The use of DTS could reduce radiation dose during PCI. Real-time radiation monitoring and visualization of peak skin dose was effective for the patients with PCI.

Monte Carlo investigation of backscatter point spread function for X-ray imaging examinations.

X-ray imaging examinations, especially complex interventions, may result in relatively high doses to the patient's skin inducing skin injuries. A method was developed to determine the skin-dose distribution for non-uniform x-ray beams by convolving the backscatter point-spread-function (PSF) with the primary-dose distribution to generate the backscatter distribution that, when added to the primary dose, gives the total-dose distribution. This technique was incorporated in the dose-tracking system (DTS), which provides a real-time color-coded 3D-mapping of skin dose during fluoroscopic procedures. The aim of this work is to investigate the variation of the backscatter PSF with different parameters. A backscatter PSF of a 1-mm x-ray beam was generated by EGSnrc Monte-Carlo code for different x-ray beam energies, different soft-tissue thickness above bone, different bone thickness and different entrance-beam angles, as well as for different locations on the SK-150 anthropomorphic head phantom. The results show a reduction of the peak scatter to primary dose ratio of 48% when X-ray beam voltage is increased from 40 keV to 120 keV. The backscatter dose was reduced when bone was beneath the soft tissue layer and this reduction increased with thinner soft tissue and thicker bone layers. The backscatter factor increased about 21% as the angle of incidence of the beam with the entrance surface decreased from 90° (perpendicular) to 30°. The backscatter PSF differed for different locations on the SK-150 phantom by up to 15%. The results of this study can be used to improve the accuracy of dose calculation when using PSF convolution in the DTS.

Skin dose mapping for non-uniform x-ray fields using a backscatter point spread function.

Beam shaping devices like ROI attenuators and compensation filters modulate the intensity distribution of the x-ray beam incident on the patient. This results in a spatial variation of skin dose due to the variation of primary radiation and also a variation in backscattered radiation from the patient. To determine the backscatter component, backscatter point spread functions (PSF) are generated using EGS Monte-Carlo software. For this study, PSF's were determined by simulating a 1 mm beam incident on the lateral surface of an anthropomorphic head phantom and a 20 cm thick PMMA block phantom. The backscatter PSF's for the head phantom and PMMA phantom are curve fit with a Lorentzian function after being normalized to the primary dose intensity (PSFn). PSFn is convolved with the primary dose distribution to generate the scatter dose distribution, which is added to the primary to obtain the total dose distribution. The backscatter convolution technique is incorporated in the dose tracking system (DTS), which tracks skin dose during fluoroscopic procedures and provides a color map of the dose distribution on a 3D patient graphic model. A convolution technique is developed for the backscatter dose determination for the non-uniformly spaced graphic-model surface vertices. A Gafchromic film validation was performed for shaped x-ray beams generated with an ROI attenuator and with two compensation filters inserted into the field. The total dose distribution calculated by the backscatter convolution technique closely agreed with that measured with the film.

Evaluation of Methods to Produce an Image Library for Automatic Patient Model Localization for Dose Mapping During Fluoroscopically-Guided Procedures.

The purpose of this work is to evaluate methods for producing a library of 2D-radiographic images to be correlated to clinical images obtained during a fluoroscopically-guided procedure for automated patient-model localization. The localization algorithm will be used to improve the accuracy of the skin-dose map superimposed on the 3D patient-model of the real-time Dose-Tracking-System (DTS). For the library, 2D images were generated from CT datasets of the SK-150 anthropomorphic phantom using two methods: Schmid's 3D-visualization tool and Plastimatch's digitally-reconstructed-radiograph (DRR) code. Those images, as well as a standard 2D-radiographic image, were correlated to a 2D-fluoroscopic image of a phantom, which represented the clinical-fluoroscopic image, using the Corr2 function in Matlab. The Corr2 function takes two images and outputs the relative correlation between them, which is fed into the localization algorithm. Higher correlation means better alignment of the 3D patient-model with the patient image. In this instance, it was determined that the localization algorithm will succeed when Corr2 returns a correlation of at least 50%. The 3D-visualization tool images returned 55-80% correlation relative to the fluoroscopic-image, which was comparable to the correlation for the radiograph. The DRR images returned 61-90% correlation, again comparable to the radiograph. Both methods prove to be sufficient for the localization algorithm and can be produced quickly; however, the DRR method produces more accurate grey-levels. Using the DRR code, a library at varying angles can be produced for the localization algorithm.