R Dickinson

Radiation-induced complications in endovascular neurosurgery: Incidence of skin effects and the feasibility of estimating risk of future tumor formation

BACKGROUND The incidence of radiation-induced complications is increasingly part of the informed consent process for patients undergoing neuroendovascular procedures. Data guiding these discussions in the era of modern radiation-minimizing equipment is lacking. OBJECTIVE To quantify the rates of skin and hair effects at a modern high-volume neurovascular center, and to assess the feasibility of accurately quantifying the risk of future central nervous system (CNS) tumor formation. METHODS We reviewed a prospectively collected database of endovascular procedures performed at our institution in 2008. The entrance skin dose and brain dose were calculated. Patients receiving skin doses >2 Gy were contacted to inquire about skin and hair changes. We reviewed several recent publications from leading radiation physics bodies to evaluate the feasibility of accurately predicting future cancer risk from neurointerventional procedures. RESULTS Seven hundred two procedures were included in the study. Of the patients receiving >2 Gy, 39.6% reported subacute skin or hair changes following their procedure, of which 30% were permanent. Increasing skin dose was significantly associated with permanent hair loss. We found substantial methodological difficulties in attempting to model the risk of future CNS tumor formation given the gaps in our current understanding of the brains susceptibility to low-dose ionizing radiation. CONCLUSION Radiation exposures exceeding 2 Gy are common in interventional neuroradiology despite modern radiation-minimizing technology. The incidence of side effects approaches 40%, although the majority is self-limiting. Gaps in current models of brain tumor formation after exposure to radiation preclude accurately quantifying the risk of future CNS tumor formation.

Hybrid Modality Fusion of Planar Scintigrams and CT Topograms to Localize Sentinel Lymph Nodes in Breast Lymphoscintigraphy: Technical Description and Phantom Studies

Lymphoscintigraphy is a nuclear medicine procedure that is used to detect sentinel lymph nodes (SLNs). This project sought to investigate fusion of planar scintigrams with CT topograms as a means of improving the anatomic reference for the SLN localization. Heretofore, the most common lymphoscintigraphy localization method has been backlighting with a 57Co sheet source. Currently, the most precise method of localization through hybrid SPECT/CT increases the patient absorbed dose by a factor of 34 to 585 (depending on the specific CT technique factors) over the conventional 57Co backlighting. The new approach described herein also uses a SPECT/CT scanner, which provides mechanically aligned planar scintigram and CT topogram data sets, but only increases the dose by a factor of two over that from 57Co backlighting. Planar nuclear medicine image fusion with CT topograms has been proven feasible and offers a clinically suitable compromise between improved anatomic details and minimally increased radiation dose.

AAPM medical physics practice guideline 6.a.: Performance characteristics of radiation dose index monitoring systems

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education and professional practice of medical physics. The AAPM has more than 8,000 members and is the principal organization of medical physicists in the United States. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized. The following terms are used in the AAPM practice guidelines: •Must and Must Not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline. •Should and Should Not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances.

Estimated Skin Dose Look-Up Tables and Their Effect on Dose Awareness in the Fluoroscopy-Guided Imaging Suite

OBJECTIVE The displayed air kerma during a fluoroscopy-guided procedure often does not represent the entrance skin dose. The purpose of this work is to develop a system-specific air kerma-to-entrance skin dose look-up table (LUT) for immediate reference and to evaluate its clinical utility. MATERIALS AND METHODS Physicists are often involved in retrospective dosimetry and risk estimates. Conservative dosimetry conversion factors, represented by the total conversion factor, prospectively estimate the maximum potential skin dose from the displayed air kerma. Air kerma-to-skin dose LUTs with corresponding tissue reactions and approximate time-of-onset can be posted for reference. By developing skin dose LUTs, physicians can actively evaluate during the procedure the potential for deterministic skin reactions. System user surveys evaluated the impact of LUTs on dose awareness. RESULTS The range of the total conversion factor to the displayed air kerma for the nine systems evaluated was 0.8-1.6 for frontal x-ray tubes. Skin dose LUTs were posted in all imaging suites, and two surveys reported user feedback. Radiology technologists indicated that LUTs improved user dose awareness. Twelve of 14 physician respondents indicated an understanding that entrance skin dose is not equal to the displayed air kerma. CONCLUSION Our efforts focused on educating fluoroscopy users about differences between displayed air kerma and the entrance skin dose while increasing dose awareness using an accessible and easy-to-understand tool. Skin dose LUTs provide physicians and staff an immediate reference for the maximum estimated entrance skin dose and the associated deterministic skin effects, allowing appropriate patient management.

MO-F-16A-06: Implementation of a Radiation Exposure Monitoring System for Surveillance of Multi-Modality Radiation Dose Data

PURPOSE We have implemented a commercially available Radiation Exposure Monitoring System (REMS) to enhance the processes of radiation dose data collection, analysis and alerting developed over the past decade at our sites of practice. REMS allows for consolidation of multiple radiation dose information sources and quicker alerting than previously developed processes. METHODS Thirty-nine x-ray producing imaging modalities were interfaced with the REMS: thirteen computed tomography scanners, sixteen angiography/interventional systems, nine digital radiography systems and one mammography system. A number of methodologies were used to provide dose data to the REMS: Modality Performed Procedure Step (MPPS) messages, DICOM Radiation Dose Structured Reports (RDSR), and DICOM header information. Once interfaced, the dosimetry information from each device underwent validation (first 15-20 exams) before release for viewing by end-users: physicians, medical physicists, technologists and administrators. RESULTS Before REMS, our diagnostic physics group pulled dosimetry data from seven disparate databases throughout the radiology, radiation oncology, cardiology, electrophysiology, anesthesiology/pain management and vascular surgery departments at two major medical centers and four associated outpatient clinics. With the REMS implementation, we now have one authoritative source of dose information for alerting, longitudinal analysis, dashboard/graphics generation and benchmarking. REMS provides immediate automatic dose alerts utilizing thresholds calculated through daily statistical analysis. This has streamlined our Closing the Loop process for estimated skin exposures in excess of our institutional specific substantial radiation dose level which relied on technologist notification of the diagnostic physics group and daily report from the radiology information system (RIS). REMS also automatically calculates the CT size-specific dose estimate (SSDE) as well as provides two-dimensional angulation dose maps for angiography/interventional procedures. CONCLUSION REMS implementation has streamlined and consolidated the dosimetry data collection and analysis process at our institutions while eliminating manual entry error and providing immediate alerting and access to dosimetry data to both physicists and physicians. Brent Stewart has funded research through GE Healthcare.

SU‐E‐E‐01: ABR Diagnostic Radiology Core Exam: Was Our Redesigned Physics Course Successful in Teaching Physics to Radiology Residents?

PURPOSE Our purpose is to evaluate the effectiveness of our two year physics course in preparing radiology residents for the American Board of Radiology (ABR) diagnostic radiology exam. METHODS We designed a new two-year physics course that integrates radiology clinical content and practice and is primarily based on the AAPM curriculum and RSNA/AAPM physics modules. Biweekly classes focus on relevant concepts from assigned reading and use audience response systems to encourage participation. Teaching efficiency is optimized through lecturer rotations of physicists, radiologists, and guest speakers. An emphasis is placed on clinical relevance by requiring lab work and providing equipment demonstrations. Periodic quiz were given during the course. The course website was also redesigned for usability, and physics review lectures were conducted two weeks before the board exam to refresh key concepts. At the completion of our first two-year course, we conducted a confidential evaluation of the faculty and course. The evaluation assessed metrics such as overall organization, clinical relevance of content, and level of difficulty, with a rating scale from poor to excellent. RESULTS Our evaluation indicated that the redesigned course provided effective board exam preparation, with most responses between good and excellent. There was some criticism on the course length and on chronological discontinuity, but the review lectures were appreciated by the residents. All of our residents passed the physics component of the ABR exam with scores exceeding the minimum passing score by a significant margin. CONCLUSION The course evaluation and board exam results indicate that our new two-year course format provides valuable board exam preparation. This is possible thanks to the time and effort taken by the physics faculty on ensuring the residents get quality physics education.

MO‐F‐213CD‐07: Implementation of Dose Monitoring in a Cardiology Department with Independent Medical Reporting Systems

Purpose: Not all clinical service sections within a large hospital system are incorporated into the main radiology information system (RIS) and picture archiving and communication system (PACS); attaining and analyzingdose data for a cardiology department at our institution is challenging. The aim is to implement a dose monitoring program in a cardiology department whose medical recording systems are independent of the institutional systems. Methods: During a cardiac case the technologist documents the activities (catheterization, biometrics, biopsy, valve replacement, etc.) performed by the medical staff. Physics worked with the cardiology staff to identify what standard notations would indicate the procedure type, and where to reliably enter cumulative air kerma (AK). This information was compiled into a report, and the data was manually classified into seven pertinent procedure types. For a particular procedure and quarter, cases exceeding a z_score of 5 (indicating >5 SD above mean) were excluded and catalogued. Basic statistics (mean/SD/median/percentiles/min/max) were calculated for the purpose of observing longitudinal trends. A list of flagged studies ‐ cases exceeding the 95 th percentile for a given data subset ‐ was generated for the purpose of clinical review. Result: Preliminary analysis shows that common low dosecardiac procedures such as heart biopsies, intra‐arterial balloon pump insertions, and right heart catheterizations (RHC) exhibit stable median AK of approximately 200 mGy over the last two quarters. Higher dose procedures include left heart catheterizations (LHC), combination LHC/RHCs (both with median AK approximately 900 mGy), and the more complex interventional LHC (median AK approximately 3000 mGy). Cases exceeding the 95th percentile for a given procedure are currently being used to develop a follow‐up process for potential deterministic effects. Conclusions: A robust system of analyzingdose data from an RIS/PACS‐independent cardiology system has been developed. The results are being used to improve physician training and fluoroscopic practice.

MO‐F‐213CD‐05: Establishing a Follow‐Up Process for Angiographic Patients Receiving an Estimated Entrance Skin Dose in Excess of 5 Gy

Purpose: To establish a follow‐up process for angiography patients estimated to receive an entrance skindose (ESD) in excess of 5 Gy. Methods: A look‐up table showing the estimated ESD corresponding to incremental displayed air kerma (AK) values was posted within each angio suite. Patients receiving a cumulative AK value corresponding to an ESD exceeding 5 Gy are identified by the technologist. The technologist notifies the diagnostic physics section (DPS) which calculates a more accurate estimation of the ESD by taking into account system and exam‐specific estimated table height and attenuation, backscatter, and mean energy absorption coefficient. The DPS then generates and sends a standard notification alert to the attending physician including case information, estimated ESD, and potential tissue effects. Hospital staff follows‐up with the patient via phone to discuss possible skin effects and the location of where those effects may be observed. The patient is asked to call the clinic if any skin redness or epilation in the area of exposure is observed. Results: In the past 4 months, 15 cases greater than 5 Gy ESD were identified across the different services using the angio suite. Of the 15 cases, the neuro radiology interventional group had the maximum number of cases at 10 (median: 5.2 Gy, max: 7.3 Gy) while the vascular surgery group had 2 cases (median: 7.1 Gy, max: 7.6 Gy) and the vascular interventional group had 3 cases (median: 5.7 Gy, max: 6.8 Gy). All cases received follow‐up. No deterministic effects were observed in these cases as of yet. Conclusions: Establishing a follow‐up procedure for angiography patients receiving an ESD > 5 Gy is essential to anticipate possible skin injury. This is good patient safety practice which falls in line with our institutions patient first initiative.

MO-F-213CD-06: Implementation of Fluoroscopy Dose Mining and Analysis Process for Continuous Quality Assurance

Purpose: The varied dose reporting capabilities of fluoroscopic equipment combined with the difficultly in compiling and correlating data to specific procedures represents a challenge. The aim is to establish a method of collecting and analyzing cumulative dose from a collection of fluoroscopic equipment in a radiology department. Methods: Preliminary work was performed on each fluoroscopic system, including verification of dose display availability (software modification/upgrade) and accuracy and documentation of current dose metric capabilities and units. For a given procedure, the technologist manually entered the cumulative air kerma (AK) into the radiology information system (RIS). A quarterly report was generated containing AK values and procedure information for every fluoroscopy case performed. Data was separated by equipment classification (customized based on clinical application) and procedure type. For each data subset, cases exceeding a z_score of 5 (indicating >5 SD above mean) were excluded and catalogued. Basic statistics (mean/SD/median/percentiles/min/max) were calculated for the purpose of observing longitudinal trends. Finally, a list of flagged studies ‐ cases exceeding the 95 th percentile for a given data subset ‐ was generated for the purpose of clinical review. Results: Presentation of longitudinal data as a box‐and‐whisker plot highlights shifts in median AK and in the population distributions. For gastrointestinal (GI) studies using a remote digital unit, we observed median AK ranging from 25 mGy for a video esophagram up to 165 mGy for an upper GI with KUB. For mobile c‐arms, median AK values ranged from 0.1 mGy to 402 mGy, depending on procedure. Conclusions: We have developed a robust method of collecting and analyzingdose data from fluoroscopic equipment. By reviewing identified high dose cases, we hope to improve training and clinical practice. To better discern explicit procedure types, modification of the RIS procedure codes is necessary for certain equipment classifications.

TU‐G‐217BCD‐09: Integration of Recent NEMA (MITA) XR‐25 CT Dose‐Check Standard into Clinical Practice

Purpose: The aim of this work is to implement vendor mandated alert value (AV) and notification value (NV) Dose‐Check metrics into neuro radiology CT exams without adversely affecting clinical workflow and to evaluate these tools as a method of active dose monitoring. Methods: The NV represents an expected ‘reasonable’ CTDIvol (or DLP) value, and is assigned at the group level of the protocol prescription; projected surpassing of the NV displays a simple warning message. Preliminary NV implementation included neurological exams, which normally utilize manual (rather than modulated) tube current. Appropriate NV levels were established using internal population DLP metrics, ACR Dose Index Registry results, AAPM recommendations, and projected CTDIvol values. When an NV alert is issued, the technologist attains and documents radiologist approval and then proceeds with the exam. The AV is as a threshold that is compared to the maximum cumulative CTDIvol at any scan location for a given examination. If the forthcoming scan is projected to surpass the AV, login credentials are required to proceed with the scan. Our institution collectively established an AV of 1000 mGy to allow for expected high doses commonly observed for cerebral perfusion exams. Results: Effective implementation requires a balance of appropriate alerting and reasonable clinical interruption. After three months, we have received 6 NV alerts (2 T‐spine, 2 C‐spine, 2 Neck). Alerts came about from manual modification of the standard protocol by the technologist. On average, the projected CTDIvol exceeded the NV by 8.4% for spine and 18.5% for neck. No adverse effects on clinical workflow have been experienced. Conclusions: Active monitoring using AV and NV is a useful, non‐invasive tool in minimizing the likelihood of gross overdose (AV) and of abnormal incremental overdose (NV). Future work will involve implementing the NV values for the abdomen exams that use tube current modulation.