Dose Tracking System Research Articles

Towards benchmarking paediatric cranial ct protocols using a dose tracking software system: A multicentre study

Objectives To benchmark and standardize regional practice for paediatric cranial CT procedures, in terms of radiation dose and acquisition parameters. Methods Paediatric cranial CT data were retrospectively collected during 1-year, in 3 hospitals of the same country. A dose tracking system was used to automatically gather information. Radiation dose (CTDI and DLP) were stratified by age and clinical indication. Scan length, amount of retakes and demographic data were acquired; appropriate use of child specific protocols was assessed. Results In total, 296 paediatric cranial CT procedures were collected. Although the median dose of each hospital was below the national and international diagnostic reference level (DRL) for all age categories, statistically significant ( p -value Conclusion Even though all hospitals complied with national and international DRLs, dose tracking and benchmarking showed that further dose optimization and standardization is possible by using age-stratified protocols for paediatric cranial CT. Moreover, having a dose tracking system revealed that adult protocols are still applied for paediatric CT, a practice that must be avoided.

An overview of EFOMP experience, with a focus on EuroSafe imaging

The European Society of Radiology has launched the EuroSafe Imaging Campaign to support and strengthen medical radiation protection across Europe following a holistic, inclusive approach. The European Federation of Organisations for Medical Physics (EFOMP) has supported this campaign since its launch. Medical Physics Experts (MPEs) are involved in medical imaging departments to estimate patient and staff radiation doses, monitor doses using dose tracking methods, establish and review diagnostic reference levels, maintain patient doses within diagnostic reference levels, reduce patient doses while maintaining the image quality needed for diagnosis, develop appropriate examination protocols and train staff in medical radiation protection. These activities are of great importance for CT and interventional radiology, where radiation doses are high. Undoubtedly, MPEs can play a major role in radiation protection in the context of EuroSafe Imaging campaign. Activities where MPEs could be provided valuable expertise include the introduction of decision support tools for the implementation of referral guidelines, the use of dose tracking systems, the development and application of tools for patient exposure records, the development of tools for patient dose reduction, the development of methods for accurate organ dose estimation and risk assessment, the development of methods for accurate conceptus dose estimation, the introduction of innovative education and training platforms and the development and application of tools for accurate and prompt measurement of occupational exposure.

A tracking system to calculate patient skin dose in real-time during neurointerventional procedures using a biplane x-ray imaging system.

Neurovascular interventional procedures using biplane fluoroscopic imaging systems can lead to increased risk of radiation-induced skin injuries. The authors developed a biplane dose tracking system (Biplane-DTS) to calculate the cumulative skin dose distribution from the frontal and lateral x-ray tubes and display it in real-time as a color-coded map on a 3D graphic of the patient for immediate feedback to the physician. The agreement of the calculated values with the dose measured on phantoms was evaluated. The Biplane-DTS consists of multiple components including 3D graphic models of the imaging system and patient, an interactive graphical user interface, a data acquisition module to collect geometry and exposure parameters, the computer graphics processing unit, and functions for determining which parts of the patient graphic skin surface are within the beam and for calculating dose. The dose is calculated to individual points on the patient graphic using premeasured calibration files of entrance skin dose per mAs including backscatter; corrections are applied for field area, distance from the focal spot and patient table and pad attenuation when appropriate. The agreement of the calculated patient skin dose and its spatial distribution with measured values was evaluated in 2D and 3D for simulated procedure conditions using a PMMA block phantom and an SK-150 head phantom, respectively. Dose values calculated by the Biplane-DTS were compared to the measurements made on the phantom surface with radiochromic film and a calibrated ionization chamber, which was also used to calibrate the DTS. The agreement with measurements was specifically evaluated with variation in kVp, gantry angle, and field size. The dose tracking system that was developed is able to acquire data from the two x-ray gantries on a biplane imaging system and calculate the skin dose for each exposure pulse to those vertices of a patient graphic that are determined to be in the beam. The calculations are done in real-time with a typical graphic update time of 30 ms and an average vertex separation of 3 mm. With appropriate corrections applied, the Biplane-DTS was able to determine the entrance dose within 6% and the spatial distribution of the dose within 4% compared to the measurements with the ionization chamber and film for the SK150 head phantom. The cumulative dose for overlapping fields from both gantries showed similar agreement. The Biplane-DTS can provide a good estimate of the peak skin dose and cumulative skin dose distribution during biplane neurointerventional procedures. Real-time display of this information should help the physician manage patient dose to reduce the risk of radiation-induced skin injuries.

Benchmarking pediatric cranial CT protocols using a dose tracking software system: a multicenter study

To benchmark regional standard practice for paediatric cranial CT-procedures in terms of radiation dose and acquisition parameters. Paediatric cranial CT-data were retrospectively collected during a 1-year period, in 3 different hospitals of the same country. A dose tracking system was used to automatically gather information. Dose (CTDI and DLP), scan length, amount of retakes and demographic data were stratified by age and clinical indication; appropriate use of child-specific protocols was assessed. In total, 296 paediatric cranial CT-procedures were collected. Although the median dose of each hospital was below national and international diagnostic reference level (DRL) for all age categories, statistically significant (p-value < 0.001) dose differences among hospitals were observed. The hospital with lowest dose levels showed smallest dose variability and used age-stratified protocols for standardizing paediatric head exams. Erroneous selection of adult protocols for children still occurred, mostly in the oldest age-group. Even though all hospitals complied with national and international DRLs, dose tracking and benchmarking showed that further dose optimization and standardization is possible by using age-stratified protocols for paediatric cranial CT. Moreover, having a dose tracking system revealed that adult protocols are still applied for paediatric CT, a practice that must be avoided. • Significant differences were observed in the delivered dose between age-groups and hospitals. • Using age-adapted scanning protocols gives a nearly linear dose increase. • Sharing dose-data can be a trigger for hospitals to reduce dose levels.

MO-FG-CAMPUS-IeP1-04: Kerma Area Product Calculation for Non-Uniform X-Ray Fields Using a Skin Dose Tracking System

Purpose: The functionality of the Dose-Tracking System (DTS) has been expanded to include the calculation of the Kerma-Area Product (KAP) for non-uniform x-ray fields such as result from the use of compensation filters during fluoroscopic procedures Methods: The DTS calculates skin dose during fluoroscopic interventions and provides a color-coded dose map on a patient-graphic model. The KAP is the integral of air kerma over the x-ray field and is usually measured with a transmission-ionization chamber that intercepts the entire x-ray beam. The DTS has been modified to determine KAP when there are beam non-uniformities that can be modeled. For example, the DTS includes models of the three compensation filters with tapered edges located in the collimator assembly of the Toshiba Infinix fluoroscopic C-Arm and can track their movement. To determine the air kerma after the filters, DTS includes transmission factors for the compensation filters as a function of kVp and beam filtration. A virtual KAP dosimeter is simulated in the DTS by an array of graphic vertices; the air kerma at each vertex is corrected by the field non-uniformity, which in this case is the attenuation factor for those rays which pass through the filter. The products of individual vertex air-kerma values for all vertices within the beam times the effective-area-per-vertex are summed for each x-ray pulse to yield the KAP per pulse and the cumulative KAP for the procedure is then calculated. Results: The KAP values estimated by DTS with the compensation filter inserted into the x-ray field agree within ± 6% with the values displayed on the fluoroscopy unit monitor, which are measured with a transmission chamber. Conclusion: The DTS can account for field non-uniformities such as result from the use of compensation filters in calculating KAP and can obviate the need for a KAP transmission ionization chamber. Partial support from NIH Grant R01-EB002873 and Toshiba Medical Systems Corp

TU‐D‐209‐02: A Backscatter Point Spread Function for Entrance Skin Dose Determination

Purpose:To determine the distribution of backscattered radiation to the skin resulting from a non‐uniform distribution of primary radiation through convolution with a backscatter point spread function (PSF).Methods:A backscatter PSF is determined using Monte Carlo simulation of a 1 mm primary beam incident on a 30 × 30 cm × 20 cm thick PMMA phantom using EGSnrc software. A primary profile is similarly obtained without the phantom and the difference from the total provides the backscatter profile. This scatter PSF characterizes the backscatter spread for a “point” primary interaction and can be convolved with the entrance primary dose distribution to obtain the total entrance skin dose. The backscatter PSF was integrated into the skin dose tracking system (DTS), a graphical utility for displaying the color‐coded skin dose distribution on a 3D graphic of the patient during interventional fluoroscopic procedures. The backscatter convolution method was validated for the non‐uniform beam resulting from the use of an ROI attenuator. The ROI attenuator is a copper sheet with about 20% primary transmission (0.7 mm thick) containing a circular aperture; this attenuator is placed in the beam to reduce dose in the periphery while maintaining full dose in the region of interest. The DTS calculated primary plus backscatter distribution is compared to that measured with GafChromic film and that calculated using EGSnrc Monte‐Carlo software.Results:The PSF convolution method used in the DTS software was able to account for the spread of backscatter from the ROI region to the region under the attenuator. The skin dose distribution determined using DTS with the ROI attenuator was in good agreement with the distributions measured with Gafchromic film and determined by Monte Carlo simulationConclusion:The PSF convolution technique provides an accurate alternative for entrance skin dose determination with non‐uniform primary x‐ray beams.Partial support from NIH Grant R01‐EB002873 and Toshiba Medical Systems Corp.

TU‐D‐209‐05: Automatic Calculation of Organ and Effective Dose for CBCT and Interventional Fluoroscopic Procedures

Purpose:To compare PCXMC and EGSnrc calculated organ and effective radiation doses from cone‐beam computed tomography (CBCT) and interventional fluoroscopically‐guided procedures using automatic exposure‐event grouping.Methods:For CBCT, we used PCXMC20Rotation.exe to automatically calculate the doses and compared the results to those calculated using EGSnrc with the Zubal patient phantom. For interventional procedures, we use the dose tracking system (DTS) which we previously developed to produce a log file of all geometry and exposure parameters for every x‐ray pulse during a procedure, and the data in the log file is input into PCXMC and EGSnrc for dose calculation. A MATLAB program reads data from the log files and groups similar exposures to reduce calculation time. The definition files are then automatically generated in the format used by PCXMC and EGSnrc. Processing is done at the end of the procedure after all exposures are completed.Results:For the Toshiba Infinix CBCT LCI‐Middle‐Abdominal protocol, most organ doses calculated with PCXMC20Rotation closely matched those calculated with EGSnrc. The effective doses were 33.77 mSv with PCXMC20Rotation and 32.46 mSv with EGSnrc. For a simulated interventional cardiac procedure, similar close agreement in organ dose was obtained between the two codes; the effective doses were 12.02 mSv with PCXMC and 11.35 mSv with EGSnrc. The calculations can be completed on a PC without manual intervention in less than 15 minutes with PCXMC and in about 10 hours with EGSnrc, depending on the level of data grouping and accuracy desired.Conclusion:Effective dose and most organ doses in CBCT and interventional radiology calculated by PCXMC closely match those calculated by EGSnrc. Data grouping, which can be done automatically, makes the calculation time with PCXMC on a standard PC acceptable. This capability expands the dose information that can be provided by the DTS.Partial support from NIH Grant R01‐EB002873 and Toshiba Medical Systems Corp.

TU‐D‐209‐03: Alignment of the Patient Graphic Model Using Fluoroscopic Images for Skin Dose Mapping

Purpose:The Dose Tracking System (DTS) was developed to provide realtime feedback of skin dose and dose rate during interventional fluoroscopic procedures. A color map on a 3D graphic of the patient represents the cumulative dose distribution on the skin. Automated image correlation algorithms are described which use the fluoroscopic procedure images to align and scale the patient graphic for more accurate dose mapping.Methods:Currently, the DTS employs manual patient graphic selection and alignment. To improve the accuracy of dose mapping and automate the software, various methods are explored to extract information about the beam location and patient morphology from the procedure images. To match patient anatomy with a reference projection image, preprocessing is first used, including edge enhancement, edge detection, and contour detection. Template matching algorithms from OpenCV are then employed to find the location of the beam. Once a match is found, the reference graphic is scaled and rotated to fit the patient, using image registration correlation functions in Matlab. The algorithm runs correlation functions for all points and maps all correlation confidences to a surface map. The highest point of correlation is used for alignment and scaling. The transformation data is saved for later model scaling.Results:Anatomic recognition is used to find matching features between model and image and image registration correlation provides for alignment and scaling at any rotation angle with less than onesecond runtime, and at noise levels in excess of 150% of those found in normal procedures.Conclusion:The algorithm provides the necessary scaling and alignment tools to improve the accuracy of dose distribution mapping on the patient graphic with the DTS.Partial support from NIH Grant R01‐EB002873 and Toshiba Medical Systems Corp.

SU‐G‐IeP3‐12: Preliminary Report On the Experience of Patient Radiation Dose Monitoring and Tracking Systems; PEMNET, Radimetrics and DoseWatch

Purpose:Three patient radiation dose monitoring and tracking (PRDMT) systems have been in operation at this institution for the past 6 months. There are useful information that should be disseminated to those who are considering installation of PRDMT programs. In addition, there are “problems” uncovered in the process of estimating fluoroscopic “peak” skin dose (PSD), especially, for those patients who received interventional angiographic studies and in conjunction with surgical procedures.Methods:Upon exporting the PRDMT data to Microsoft Excel program, the peak skin dose can be estimated by applying various correction factors including; attenuation due to the tabletop and examination mattress, table height, tabletop translation, backscatter, etc. A procedure was established to screen and divide the PRDMT reported radiation dose and estimated PSD to three different levels of threshold to assess the potential skin injuries, to assist patient follow‐up, risk management and provide radiation dosimetry information in case of “Sentinel Event”.Results:The Radiation Dose Structured Report (RDSR) was found to be the prerequisite for the PRDMT systems to work seamlessly. And, the geometrical parameters (gantry and table orientation) displayed by the equipment are not necessarily implemented in the “patient centric” manner which could result in a large error in the PSD estimation. Since, the PRDMT systems obtain their pertinent data from the DICOM tags including the polarity (+ and − signs), the geometrical parameters need to be verified.Conclusion:PRDMT systems provide a more accurate PSD estimation than previously possible as the air‐kerma‐area dose meter become widely implemented. However, care should be exercised to correctly apply the geometrical parameters in estimating the patient dose. In addition, further refinement is necessary for these software programs to account for all geometrical parameters such as the tabletop translation in the z‐direction in particular.

Integration of kerma-area product and cumulative air kerma determination into a skin dose tracking system for fluoroscopic imaging procedures.

The skin dose tracking system (DTS) that we developed provides a color-coded mapping of the cumulative skin dose distribution on a 3D graphic of the patient during fluoroscopic procedures in real time. The DTS has now been modified to also calculate the kerma area product (KAP) and cumulative air kerma (CAK) for fluoroscopic interventions using data obtained in real-time from the digital bus on a Toshiba Infinix system. KAP is the integral of air kerma over the beam area and is typically measured with a large-area transmission ionization chamber incorporated into the collimator assembly. In this software, KAP is automatically determined for each x-ray pulse as the product of the air kerma/ mAs from a calibration file for the given kVp and beam filtration times the mAs per pulse times the length and width of the beam times a field nonuniformity correction factor. Field nonuniformity is primarily the result of the heel effect and the correction factor was determined from the beam profile measured using radio-chromic film. Dividing the KAP by the beam area at the interventional reference point provides the area-averaged CAK. The KAP and CAK per x-ray pulse are summed after each pulse to obtain the total procedure values in real-time. The calculated KAP and CAK were compared to the values displayed by the fluoroscopy machine with excellent agreement. The DTS now is able to automatically calculate both KAP and CAK without the need for measurement by an add-on transmission ionization chamber.

Can Digital Tools Be Used for Improving Immunization Programs?

In order to successfully control and eliminate vaccine-preventable infectious diseases, an appropriate vaccine coverage has to be achieved and maintained. This task requires a high level of effort as it may be compromised by a number of barriers. Public health agencies have issued specific recommendations to address these barriers and therefore improve immunization programs. In the present review, we characterize issues and challenges of immunization programs for which digital tools are a potential solution. In particular, we explore previously published research on the use of digital tools in the following vaccine-related areas: immunization registries, dose tracking, and decision support systems; vaccine-preventable diseases surveillance; surveillance of adverse events following immunizations; vaccine confidence monitoring; and delivery of information on vaccines to the public. Subsequently, we analyze the limits of the use of digital tools in such contexts and envision future possibilities and challenges.

TH-AB-201-01: A Real-Time Skin-Dose Mapping System for Region-Of-Interest (ROI) Fluoroscopy

Purpose: The real-time dose-tracking system (DTS) which we developed for fluoroscopically–guided procedures has been upgraded so that it can track the patient skin dose when using a region-of-interest (ROI) beam attenuator. Methods: ROI fluoroscopy is a method for greatly reducing patient dose by inserting an attenuator with an aperture into the x-ray beam. The aperture defines an ROI with normal dose and image quality, while under the attenuator the dose and quality are reduced. A moveable copper ROI attenuator has been installed in the collimator assembly of a Toshiba Infinix system. The DTS provides a 3D-dose mapping on a patient graphic and, to track dose for ROI fluoroscopy, the software now models the attenuator shape and position. A calibration file provides values for the transmission of the attenuator as a function of kVp and beam filtration and dose corrections are performed if a ray to a given point on the patient graphic is determined to intersect the attenuator. Backscatter is included in the skin-dose determination and is dependent on the ROI beam size projected onto the patient. In the current version, a spatially invariant factor corrects for backscatter within the ROI and from the ROI region into the attenuated region. The agreement of the dose distribution calculated by the DTS with the actual distribution was verified by measurement with calibrated radiochromic film and a 20-cm PMMA phantom. Results: The DTS is able to accurately model the size and position of the ROI attenuator as projected onto the patient graphic. Measurements with radiochromic film show the skin-dose estimation agreement to be within +/−12%, with most error arising from the spatial variation of backscatter. Conclusion: The dose distribution on the patient can now be tracked in real-time with acceptable accuracy when the new dose-saving feature of ROI fluoroscopy is used. This research was supported in part by Toshiba Medical Systems Corporation and NIH Grant R01EB002873.

MO‐F‐CAMPUS‐I‐01: A System for Automatically Calculating Organ and Effective Dose for Fluoroscopically‐Guided Procedures

Purpose:A system was developed that automatically calculates the organ and effective dose for individual fluoroscopically‐guided procedures using a log of the clinical exposure parameters.Methods:We have previously developed a dose tracking system (DTS) to provide a real‐time color‐coded 3D‐ mapping of skin dose. This software produces a log file of all geometry and exposure parameters for every x‐ray pulse during a procedure. The data in the log files is input into PCXMC, a Monte Carlo program that calculates organ and effective dose for projections and exposure parameters set by the user. We developed a MATLAB program to read data from the log files produced by the DTS and to automatically generate the definition files in the format used by PCXMC. The processing is done at the end of a procedure after all exposures are completed. Since there are thousands of exposure pulses with various parameters for fluoroscopy, DA and DSA and at various projections, the data for exposures with similar parameters is grouped prior to entry into PCXMC to reduce the number of Monte Carlo calculations that need to be performed.Results:The software developed automatically transfers data from the DTS log file to PCXMC and runs the program for each grouping of exposure pulses. When the dose from all exposure events are calculated, the doses for each organ and all effective doses are summed to obtain procedure totals. For a complicated interventional procedure, the calculations can be completed on a PC without manual intervention in less than 30 minutes depending on the level of data grouping.Conclusion:This system allows organ dose to be calculated for individual procedures for every patient without tedious calculations or data entry so that estimates of stochastic risk can be obtained in addition to the deterministic risk estimate provided by the DTS.Partial support from NIH grant R01EB002873 and Toshiba Medical Systems Corp.

MO‐PIS‐Exhibit Hall‐4: Toshiba Dose Tracking System: A Paradigm Shift in Patient Dose Monitoring in Fluoroscopically Guided Interventions

No Abstract provided

Incorporating Corrections for the Head-Holder and Compensation Filter when Calculating Skin Dose during Fluoroscopically-Guided Interventions.

The skin dose tracking system (DTS) that we developed provides a color-coded illustration of the cumulative skin dose distribution on a 3D graphic of the patient during fluoroscopic procedures for immediate feedback to the interventionist. To improve the accuracy of dose calculation, we now have incorporated two additional important corrections (1) for the holder used to immobilize the head in neuro-interventions and (2) for the built-in compensation filters used for beam equalization. Both devices have been modeled in the DTS software so that beam intensity corrections can be made. The head-holder is modeled as two concentric hemi-cylindrical surfaces such that the path length between those surfaces can be determined for rays to individual points on the skin surface. The head-holder on the imaging system we used was measured to attenuate the primary x-rays by 10 to 20% for normal incidence, and up to 40% at non-normal incidence. In addition, three compensation filters of different shape are built into the collimator apparatus and were measured to have attenuation factors ranging from 58% to 99%, depending on kVp and beam filtration. These filters can translate and rotate in the beam and their motion is tracked by the DTS using the digital signal from the imaging system. When it is determined that a ray to a given point on the skin passes through the compensation filter, the appropriate attenuation correction is applied. These corrections have been successfully incorporated in the DTS software to provide a more accurate determination of skin dose.

A Real-Time Skin Dose Tracking System for Biplane Neuro-Interventional Procedures.

A biplane dose-tracking system (Biplane-DTS) that provides a real-time display of the skin-dose distribution on a 3D-patient graphic during neuro-interventional fluoroscopic procedures was developed. Biplane-DTS calculates patient skin dose using geometry and exposure information for the two gantries of the imaging system acquired from the digital system bus. The dose is calculated for individual points on the patient graphic surface for each exposure pulse and cumulative dose for both x-ray tubes is displayed as color maps on a split screen showing frontal and lateral projections of a 3D-humanoid graphic. Overall peak skin dose (PSD), FOV-PSD and current dose rates for the two gantries are also displayed. Biplane-DTS uses calibration files of mR/mAs for the frontal and lateral tubes measured with and without the table in the beam at the entrance surface of a 20 cm thick PMMA phantom placed 15 cm tube-side of the isocenter. For neuro-imaging, conversion factors are applied as a function of entrance field area to scale the calculated dose to that measured with a Phantom Laboratory head phantom which contains a human skull to account for differences in backscatter between PMMA and the human head. The software incorporates inverse-square correction to each point on the skin and corrects for angulation of the beam through the table. Dose calculated by Biplane DTS and values measured by a 6-cc ionization chamber placed on the head phantom at multiple points agree within a range of -3% to +7% with a standard deviation for all points of less than 3%.

A National System for Incident Reporting in Radiation Therapy: Development of a Taxonomy and Severity Classification

Purpose/Objective(s): Computerized Record and Verify System (RVS) has been used to detect and prevent mistakes in the delivery of external beam radiation therapy for more than 20 years. Conventional dose tracking mechanism in RVS is monitor unit (MU) based, assuming patients are treated exactly as planned. Without incorporating parameters such as machine behavior, patient setup, and patient anatomy, the cumulative doses do not accurately represent the actual doses delivered to patients, which is the goal of a RVS. We developed an automatic system to compute and accumulate daily doses through re-computation using daily imaging, and verify dose volume information in the context of RVS. Materials/Methods: Our system consists of several components, including a DICOM data retriever, dosimetric computation engine, and review platform. The workflow begins after each treatment; the DICOM daemon automatically retrieves daily volumetric images from patient records. The delivered dose is computed using a convolution-superposition based dose calculator implemented in-house on graphic cards. The deformation field between the daily and planning CT is computed using Morphons algorithm to warp the planning structures and delivered doses. The dose volume histograms of the daily and cumulative doses are generated for dose tracking and reporting. These data are queryable and a triggering system using a configurable tolerance table can be set up to prompt a clinical review. Possible root causes are analyzed such as machine output drifting, patient set up error. A user-friendly 4D image viewer is integrated for efficient review of images and doses. Results: Various aspects of the system were validated. Our dose calculator passed 97% gamma test evaluated in 3D with 2% dose difference and 2mm distance-to-agreement compared with tomotherapy calculated dose. With proper calibration of the imaging systems on tomotherapy machines, recomputed daily doses agreed with measurements in phantom within 2% for all jaw sizes. Visual inspection shows acceptable and consistent deformable registration results, except for cases with large or unrealistic deformations. This system is used clinically and more than 35,000 fractions were computed. More than 50 incidences, which would otherwise not be caught with conventional MU-based dose tracking system, were detected. The automatic triggering system is able to detect significant patient setup errors and anatomical changes. Conclusions: We developed a system to automatically accumulate and verify the actual distribution of delivered dose over the course of radiation therapy. This system helps detect and prevent further deviations in treatments, quantifies the dosimetric impact of the deviations, provides necessary information for adaptive radiation therapy, and hence is invaluable in improving the quality of patient care. Author Disclosure: X. Mo: None. Y. Chen: None. M. Chen: None. D. Parnell: None. S. Key: None. W. Lu: None. G. Olivera: None. D. Galmarini: None.

A Delivered Dose–Based Record and Verify System in the Era of IGRT

Purpose/Objective(s): Computerized Record and Verify System (RVS) has been used to detect and prevent mistakes in the delivery of external beam radiation therapy for more than 20 years. Conventional dose tracking mechanism in RVS is monitor unit (MU) based, assuming patients are treated exactly as planned. Without incorporating parameters such as machine behavior, patient setup, and patient anatomy, the cumulative doses do not accurately represent the actual doses delivered to patients, which is the goal of a RVS. We developed an automatic system to compute and accumulate daily doses through re-computation using daily imaging, and verify dose volume information in the context of RVS. Materials/Methods: Our system consists of several components, including a DICOM data retriever, dosimetric computation engine, and review platform. The workflow begins after each treatment; the DICOM daemon automatically retrieves daily volumetric images from patient records. The delivered dose is computed using a convolution-superposition based dose calculator implemented in-house on graphic cards. The deformation field between the daily and planning CT is computed using Morphons algorithm to warp the planning structures and delivered doses. The dose volume histograms of the daily and cumulative doses are generated for dose tracking and reporting. These data are queryable and a triggering system using a configurable tolerance table can be set up to prompt a clinical review. Possible root causes are analyzed such as machine output drifting, patient set up error. A user-friendly 4D image viewer is integrated for efficient review of images and doses. Results: Various aspects of the system were validated. Our dose calculator passed 97% gamma test evaluated in 3D with 2% dose difference and 2mm distance-to-agreement compared with tomotherapy calculated dose. With proper calibration of the imaging systems on tomotherapy machines, recomputed daily doses agreed with measurements in phantom within 2% for all jaw sizes. Visual inspection shows acceptable and consistent deformable registration results, except for cases with large or unrealistic deformations. This system is used clinically and more than 35,000 fractions were computed. More than 50 incidences, which would otherwise not be caught with conventional MU-based dose tracking system, were detected. The automatic triggering system is able to detect significant patient setup errors and anatomical changes. Conclusions: We developed a system to automatically accumulate and verify the actual distribution of delivered dose over the course of radiation therapy. This system helps detect and prevent further deviations in treatments, quantifies the dosimetric impact of the deviations, provides necessary information for adaptive radiation therapy, and hence is invaluable in improving the quality of patient care. Author Disclosure: X. Mo: None. Y. Chen: None. M. Chen: None. D. Parnell: None. S. Key: None. W. Lu: None. G. Olivera: None. D. Galmarini: None.

SU‐E‐CAMPUS‐I‐04: Automatic Skin‐Dose Mapping for An Angiographic System with a Region‐Of‐Interest, High‐Resolution Detector

Purpose:Our real‐time skin dose tracking system (DTS) has been upgraded to monitor dose for the micro‐angiographic fluoroscope (MAF), a high‐resolution, small field‐of‐view x‐ray detector.Methods:The MAF has been mounted on a changer on a clinical C‐Arm gantry so it can be used interchangeably with the standard flat‐panel detector (FPD) during neuro‐interventional procedures when high resolution is needed in a region‐of‐interest. To monitor patient skin dose when using the MAF, our DTS has been modified to automatically account for the change in scatter for the very small MAF FOV and to provide separated dose distributions for each detector. The DTS is able to provide a color‐coded mapping of the cumulative skin dose on a 3D graphic model of the patient. To determine the correct entrance skin exposure to be applied by the DTS, a correction factor was determined by measuring the exposure at the entrance surface of a skull phantom with an ionization chamber as a function of entrance beam size for various beam filters and kVps. Entrance exposure measurements included primary radiation, patient backscatter and table forward scatter. To allow separation of the dose from each detector, a parameter log is kept that allows a replay of the procedure exposure events and recalculation of the dose components. The graphic display can then be constructed showing the dose distribution from the MAF and FPD separately or together.Results:The DTS is able to provide separate displays of dose for the MAF and FPD with field‐size specific scatter corrections. These measured corrections change from about 49% down to 10% when changing from the FPD to the MAF.Conclusion:The upgraded DTS allows identification of the patient skin dose delivered when using each detector in order to achieve improved dose management as well as to facilitate peak skin‐dose reduction through dose spreading.Research supported in part by Toshiba Medical Systems Corporation and NIH Grants R43FD0158401, R44FD0158402 and R01EB002873

SU‐E‐I‐22: Dependence On Calibration Phantom and Field Area of the Conversion Factor Used to Calculate Skin Dose During Neuro‐Interventional Fluoroscopic Procedures

Purpose:To determine the appropriate calibration factor to use when calculating skin dose with our real‐time dose‐tracking system (DTS) during neuro‐interventional fluoroscopic procedures by evaluating the difference in backscatter from different phantoms and as a function of entrance‐skin field area.Methods:We developed a dose‐tracking system to calculate and graphically display the cumulative skin‐dose distribution in real time. To calibrate the DTS for neuro‐interventional procedures, a phantom is needed that closely approximates the scattering properties of the head. We compared the x‐ray backscatter from eight phantoms: 20‐cm‐thick solid water, 16‐cm diameter water‐filled container, 16‐cm CTDI phantom, modified‐ANSI head phantom, 20‐cm‐thick PMMA, Kyoto‐Kagaku PBU‐ 50 head, Phantom‐Labs SK‐150 head, and RSD RS‐240T head. The phantoms were placed on the patient table with the entrance surface at 15 cm tube‐side from the isocenter of a Toshiba Infinix C‐arm, and the entrance‐skin exposure was measured with a calibrated 6‐cc PTW ionization chamber. The measurement included primary radiation, backscatter from the phantom and forward scatter from the table and pad. The variation in entrance‐skin exposure was also measured as a function of the skin‐entrance area for a 30×30 cm by 20‐cm‐thick PMMA phantom and the SK‐150 head phantom using four different added beam filters.Results:The entranceskin exposure values measured for eight different phantoms differed by up to 12%, while the ratio of entrance exposure of all phantoms relative to solid water showed less than 3% variation with kVp. The change in entrance‐skin exposure with entrance‐skin area was found to differ for the SK‐150 head compared to the 20‐cm PMMA phantom and the variation with field area was dependent on the added beam filtration.Conclusion:To accurately calculate skin dose for neuro‐interventional procedures with the DTS, the phantom for calibration should be carefully chosen since different phantoms can contribute different backscatter for identical exposure parameters.Research supported in part by Toshiba Medical Systems and NIH Grants R43FD0158401, R44FD0158402 and R01EB002873