Patient Radiation Exposure: Imaging During Radiation Oncology Procedures: Executive Summary of NCRP Report No. 184

The National Council on Radiation Protection and Measurements (NCRP) recently assessed patient radiation exposure in the United States, which was summarized in its 2019 NCRP Report No. 184. This work involved an estimation of the number of medical procedures using ionizing radiation, as well as the associated effective doses from these procedures. The NCRP Report No. 184 committee elected to not incorporate radiation dose from radiotherapy into its calculated population dose exposures, as the assessment of effective dose for the population undergoing radiotherapy is more complex than that for other medical radiation exposures. However, the aim of NCRP Report No. 184 was to raise awareness of ancillary radiation exposures to patients undergoing radiotherapy. Overall, it was estimated that annually, in 2016, approximately 800,000 patients received approximately 1 million courses of radiation therapy. Each of these treatments includes various types of imaging that may not be familiar to radiologists or others. Exposures from radiotherapy planning and delivery are reviewed in the report and summarized in this executive summary. The imaging techniques, use of this imaging, and associated tissue doses are described. Imaging can contribute a few percent to the planned treatment doses (which are prescribed to specified target volumes) as well as exposing patients to radiation outside of the target volume (in the imaging field of view).     

Minimizing Radiation Exposure in Evaluation of Pediatric Head Trauma: Use of Rapid MR Imaging

BACKGROUND AND PURPOSE:With >473,000 annual emergency department visits for children with traumatic brain injuries in the United States, the risk of ionizing radiation exposure during CT examinations is a real concern. The purpose of this study was to assess the validity of rapid MR imaging to replace CT in the follow-up imaging of patients with head trauma.MATERIALS AND METHODS:A retrospective review of 103 pediatric patients who underwent initial head CT and subsequent follow-up rapid MR imaging between January 2010 and July 2013 was performed. Patients had minor head injuries (Glasgow Coma Scale, >13) that required imaging. Initial head CT was performed, with follow-up rapid MR imaging completed within 48 hours. A board-certified neuroradiologist, blinded to patient information and scan parameters, then independently interpreted the randomized cases.RESULTS:There was almost perfect agreement in the ability to detect extra-axial hemorrhage on rapid MR imaging and CT (κ = 0.84, P < .001). Evaluation of hemorrhagic contusion/intraparenchymal hemorrhage demonstrated a moderate level of agreement between MR imaging and CT (κ = 0.61, P < .001). The ability of MR imaging to detect a skull fracture also showed a substantial level of agreement with CT (κ = 0.71, P < .001). Detection of diffuse axonal injury demonstrated a slight level of agreement between MR imaging and CT (κ = 0.154, P = .04). However, the overall predictive agreement for the detection of an axonal injury was 91%.CONCLUSIONS:Rapid MR imaging is a valid technique for detecting traumatic cranial injuries and an adequate examination for follow-up imaging in lieu of repeat CT.

Head trauma continues to be a leading cause of death and disability in children in the United States.¹ Every year, >473,000 visits to the emergency department are related to brain injury,² most resulting from minor injuries or falls. Although most head injuries are classified as mild, approximately 10%–15% of children sustain a severe one. The incidence of intracranial injury following minor head trauma is unknown; however, with increasing public awareness of traumatic brain injury and concussion, there has been a rise in research of minor head injuries. Methods of diagnosis,^3,4 hospital admission criteria,^5,6 and return-to-play criteria^7,8 are a few of the active areas of research.Children with head trauma, at risk for intracranial injury, should be initially imaged with CT⁹ because it remains the criterion standard technique for the evaluation of head trauma.¹⁰ Although the incidence of injuries requiring neurosurgical intervention in children with minor head injuries is low, the use of CT for evaluation has been increasing. The use of CT increased from 13% to 22% from 1995 to 2003, with a peak of 29% in 2000.¹¹ The decision to obtain neuroimaging for children with minor head trauma must balance the importance of identifying head injuries with the risks of CT. There is growing awareness in the medical community and public of increased cancer risk caused by ionizing radiation.¹² Brenner et al¹³ estimated that 170 additional fatal cancers will develop due to head CT examinations performed in children younger than 15 years of age in the United States in a single year. In addition, some children may require sedation to obtain an adequate CT examination, which can be associated with as high as a 20.1% chance of an adverse event.¹⁴MR imaging is an alternative technique that avoids ionizing radiation exposure altogether and produces high-quality images. A study with conventional sequences requires long acquisition times and is susceptible to motion artifacts. The need for sedation increases the risk to the patient, lengthens the time needed to acquire patient images, and further increases the cost of standard MR imaging.^14,15Modified MR imaging protocols with reduced acquisition times have been used successfully in non-neurosurgical patients,^16,17 and rapid MR imaging (rMRI) or “quick-brain” MR imaging protocols have become an accepted technique to evaluate and follow patients with hydrocephalus.^18–20 Missios et al²¹ investigated the use of rMRI in patients without hydrocephalus and concluded that it was an adequate neuroimaging tool for evaluation and follow-up. The use of rMRI protocols in evaluating pediatric patients with minor head injuries remains to be validated.As far as we are aware, a systematic search of current literature did not yield a previous study examining the validity of rMRI in the imaging of pediatric patients with head trauma. The purpose of our study was to demonstrate the efficacy of replacing ionizing CT imaging with nonionizing rMRI for follow-up of patients with minor head trauma.     

Reduced Patient Radiation Exposure during Neurodiagnostic and Interventional X-Ray Angiography with a New Imaging Platform

BACKGROUND AND PURPOSE:Advancements in medical device and imaging technology as well as accruing clinical evidence have accelerated the growth of the endovascular treatment of cerebrovascular diseases. However, the augmented role of these procedures raises concerns about the radiation dose to patients and operators. We evaluated patient doses from an x-ray imaging platform with radiation dose–reduction technology, which combined image noise reduction, motion correction, and contrast-dependent temporal averaging with optimized x-ray exposure settings.MATERIALS AND METHODS:In this single-center, retrospective study, cumulative dose-area product inclusive of fluoroscopy, angiography, and 3D acquisitions for all neurovascular procedures performed during a 2-year period on the dose-reduction platform were compared with a reference platform. Key study features were the following: The neurointerventional radiologist could select the targeted dose reduction for each patient with the dose-reduction platform, and the statistical analyses included patient characteristics and the neurointerventional radiologist as covariates. The analyzed outcome measures were cumulative dose (kerma)-area product, fluoroscopy duration, and administered contrast volume.RESULTS:A total of 1238 neurointerventional cases were included, of which 914 and 324 were performed on the reference and dose-reduction platforms, respectively. Over all diagnostic and neurointerventional procedures, the cumulative dose-area product was significantly reduced by 53.2% (mean reduction, 160.3 Gy × cm²; P < .0001), fluoroscopy duration was marginally significantly increased (mean increase, 5.2 minutes; P = .0491), and contrast volume was nonsignificantly increased (mean increase, 15.3 mL; P = .1616) with the dose-reduction platform.CONCLUSIONS:A significant reduction in patient radiation dose is achievable during neurovascular procedures by using dose-reduction technology with a minimal impact on workflow.

The advancement of neurointerventional practice offers increasingly safe and minimally invasive treatment for a variety of neurovascular diseases. In most cases, the benefits of neurointerventional treatment afforded by fluoroscopic image guidance clearly outweigh the associated radiation risks to patients, especially in comparison with invasive surgical alternatives.¹ However, the growing use of diagnostic procedures and complex fluoroscopy-guided interventions² has led to heightened concerns over ionizing radiation exposure to patients and staff.^3,4To address these concerns, a new commercially available angiographic imaging platform has been developed.⁵ Its dose-reduction strategy applies to digital fluoroscopy and digital subtraction angiography, which accounts for approximately 70%–80% of the total patient radiation dose in vascular angiographic procedures.^6,7 At the core of the system is an image postprocessing chain intended to yield diagnostic-quality DSA images at a lower radiation dose to the patient.⁷ Key features of this image-processing chain are multiscale implementations of real-time motion correction, image contrast-dependent temporal averaging, and image noise reduction.⁷ Lower dose acquisitions further allow the use of a smaller focal spot size, reducing magnification-dependent focal spot blur.⁷ Additional hardware optimization includes the use of Cu beam filtration, depending on x-ray tube loading and a narrower x-ray pulse width.⁸ Herein, these noise reduction algorithms and optimized exposure settings⁷ will be collectively referred to as “dose-reduction technology,” which is implemented on the dose-reduction x-ray imaging platform (IP_DRT).Procedural dose reductions and the noninferiority of image quality by using IP_DRT have been described for iliac^9,10 and coronary angiography in adults^8,11–13 and in children.¹³ For neuroangiographic procedures, a randomized, blinded review of consecutive DSA runs with dose-reduction technology targeting one-fourth of the standard radiation dose showed the ability to maintain diagnostic image quality.⁷ A larger European study in 614 patients provided further evidence of significant reductions in total dose-area products of 62% and 65% for diagnostic and interventional procedures, respectively, while not significantly affecting fluoroscopy time, procedure duration, and the number of acquired images.⁵A unique aspect of this study was that the neurointerventional radiologist with the dose-reduction platform had the flexibility to select, per case and per acquisition, a targeted dose reduction of 0%, 50%, or 75% as preferred, rather than using a protocol with a prespecified dose-reduction target.⁵ This paradigm was investigated so that any equivocal image finding may be better visualized at different settings. Our study investigated the dose-reduction achieved in cumulative dose (kerma)-area product (CP_KA) by using such a flexible protocol for common interventional treatments and diagnostic examinations based on a retrospective review of all such procedures during a 2-year period in a North American academic practice. In addition, a key feature of this study that distinguishes it from prior studies was the inclusion of the neurointerventional radiologist (operator) and patient-specific factors as covariates in the statistical analyses.     

Radiation Dose Concerns for the Pregnant or Lactating Patient

This article discusses issues regarding administration of radiopharmaceuticals to pregnant women or nursing mothers. Uncertainties in calculated dose estimates and possible biological effects on the unborn child are presented. Models and dose estimates for pregnant women at several stages of gestation are given; the radionuclide of highest concern is ¹³¹I-NaI due to its affinity for the fetal thyroid and the potentially high fetal thyroid doses. The article also reviews the extant literature regarding the expression of radiopharmaceuticals in breast milk, and suggested time periods for interruption of breast feeding after a nursing mother receives a radiopharmaceutical, if needed. Again, ¹³¹I-NaI is often the radiopharmaceutical of most concern, for the same reasons in the nursing infant as were shown for the unborn child. Strategies for preventing unwanted administrations of radiopharmaceuticals to these patients are reviewed, with strategies for minimizing radiation doses where possible.     

Radiation Exposure in Vascular Angiographic Procedures

PurposeTo evaluate dose reduction in vascular angiographic procedures by using fluoroscopy capture instead of digital subtraction angiography frames for documentation.Materials and MethodsA total of 764 consecutive vascular interventional procedures performed over a period of 1 year were retrospectively analyzed with respect to the fluoroscopy time and the resulting dose–area product (DAP), the DAP of the radiographic frames, and the overall DAP.ResultsA total of 70% of the total DAP was a result of the acquisition of radiographic frames, leaving only 30% being applied by fluoroscopy.ConclusionsFluoroscopy capture should be used for documentation whenever possible. A registry of radiation exposure should not only comprise a sufficiently large number of interventions but also different intervention types to allow the development of interventional reference levels.     

Effects of Radiation Exposure on the Cost-Effectiveness of CT Angiography and Perfusion Imaging in Aneurysmal Subarachnoid Hemorrhage

BACKGROUND AND PURPOSE:CT angiography and perfusion imaging is an important prognostic tool in the management of patients with aneurysmal subarachnoid hemorrhage. The purpose of this study was to perform a cost-effectiveness analysis of advanced imaging in patients with SAH, incorporating the risks of radiation exposure from CT angiography and CT perfusion imaging.MATERIALS AND METHODS:The risks of radiation-induced brain cancer and cataracts were incorporated into our established decision model comparing the cost-effectiveness of CT angiography and CT perfusion imaging and transcranial Doppler sonography in SAH. Cancer risk was calculated by using National Cancer Institute methodology. The remaining input probabilities were based on literature data and a cohort at our institution. Outcomes were expected quality-adjusted life years gained, costs, and incremental cost-effectiveness ratios. One-way, 2-way, and probabilistic sensitivity analyses were performed.RESULTS:CT angiography and CT perfusion imaging were the dominant strategies, resulting in both better health outcomes and lower costs, even when incorporating brain cancer and cataract risks. Our results remained robust in 2-way sensitivity analyses varying the prolonged latency period up to 30 years, with either brain cancer risk up to 50 times higher than the upper 95% CI limit or the probability of cataracts from 0 to 1. Results were consistent for scenarios that considered either symptomatic or asymptomatic patients with SAH. Probabilistic sensitivity analysis confirmed our findings over a broad range of selected input parameters.CONCLUSIONS:While risks of radiation exposure represent an important consideration, CT angiography and CT perfusion imaging remained the preferred imaging compared with transcranial Doppler sonography in both asymptomatic and symptomatic patients with SAH, with improved health outcomes and lower health care costs, even when modeling a significantly higher risk and shorter latency period for both cataract and brain cancer than that currently known.

Aneurysmal subarachnoid hemorrhage is a devastating illness with the reported incidence estimated as 14.5 per 100,000 person years in the United States.¹ SAH is associated with a mortality of 15%, and approximately 58% of survivors experience functional disability, with global cognitive impairment being a major contributor to poor functional status.² SAH is also associated with a considerable economic burden, with average inpatient costs of $150,101 for patients with symptomatic vasospasm in the United States and $110,310 for patients without symptomatic vasospasm.³ A study conducted in the United Kingdom in 2010 found the total annual economic burden of SAH to be approximately £510 million ($873.5 million),⁴ accounting for outpatient care, cerebrovascular rehabilitation, and social services. The same study found an estimated annual total of 74,807 quality-adjusted life years (QALYs) lost due to SAH. Therefore, SAH is associated with a substantial burden on health care resources, most of which are related to the long-term effects of functional and cognitive disability.The marked increase in CT use during the past several decades has revolutionized the practice of medicine and is associated with a marked rise in administered radiation doses.⁵ This increase in radiation dose is attributable, in part, to the increased speed of image acquisition, allowing multiphase examinations to evaluate greater coverage of the body and provide functional information. This has resulted in a significant increase in the population''s cumulative exposure to ionizing radiation and concern for the potential increase in cancer risk.⁶ In 2009, the US Food and Drug Administration issued a notification regarding the safety of CT perfusion in administering high radiation doses.⁷ Consequently, there has been a focus on reducing radiation exposure from medical imaging and evaluating the appropriate use of CT.⁸The purpose of our study was to incorporate the short- and long-term risks of ionizing radiation exposure from CT angiography and CT perfusion (CTAP) imaging into our established cost-effectiveness decision model of patients with aneurysmal subarachnoid hemorrhage⁹ to determine whether the risks of radiation-induced brain cancer and cataracts would potentially alter the model results. In our previous work, which did not include the downstream effects of radiation exposure from CTAP on health outcomes and health care costs, our model results indicated that CTAP is the preferred imaging strategy compared with transcranial Doppler sonography (TCD), leading to improved clinical outcomes and lower health care costs in patients with SAH.⁹ Our hypothesis is that CTAP will remain the preferred imaging strategy in patients with SAH due to its relatively low risk from radiation exposure coupled with the high morbidity and mortality rates in this patient population.