Marguerite T. Parisi

Pediatric Radiopharmaceutical Administered Doses: 2010 North American Consensus Guidelines

Dose reduction has been a work in progress in pediatric imaging for nearly a decade. A 1996 report indicated that the long-term risk of carcinogenesis due to ionizing radiation in atomic bomb survivors was higher than had been previously estimated. For solid tumors, representing about 75% of excess cancer mortality, the likelihood of a radiation-induced malignancy after exposure to ionizing radiation was about 1.0–1.8 times higher in a 10-y-old child than in a young adult. For leukemia, representing the remaining 25% of excess cancer mortality, the likelihood of a radiation-induced malignancy after exposure to ionizing radiation was about twice as high for a 10-y-old child as for a young adult (1). The new risk estimates led to dose-reduction efforts in pediatric imaging that initially focused on CT. Because of the increased use of CT and the relatively high effective radiation dose per study, CT had emerged as a major source of medical radiation received by children in the United States. A careful look at CT image quality and CT exposure parameters indicated that significant reductions in absorbed radiation dose per study were possible without compromising the diagnostic information or image quality of pediatric CT scans (2–6). The ALARA concept, As Low As Reasonably Achievable, was extended to pediatric diagnostic imaging and may be restated as imaging at the lowest absorbed radiation dose that is consistent with quality imaging. The need for reduced CT exposure was then publicized— in the public domain, in the pediatric radiology community, and throughout general radiology. The introduction of reduced-exposure parameters was assessed in a follow-up survey (7–9). Equipment manufacturers made improvements in CT technology that facilitated the reduction of radiation exposures in children. In addition, at this time new dose-reduction efforts are under way in pediatric interventional radiology and fluoroscopy (10). A survey conducted in 2008 revealed a wide variation of pediatric radiopharmaceutical administered doses among 13 leading pediatric hospitals in North America (11). Among the institutions surveyed, the administered activity per kilogram and the maximum administered activity in children older than 1 y varied on average by a factor of 3 and, in 1 case, by a factor of 10. Minimum administered activity varied, on the average, by a factor of 10 and as much as a factor of 20 for 1 procedure. The greatest variability in administered dose occurred in the smallest, youngest, and most at-risk patients. Because the survey included only leading pediatric institutions in North America, concern was raised that the variability among other institutions would be even greater. The survey highlighted the need for a consensus on pediatric radiopharmaceutical administered doses for nuclear medicine imaging in children. The ALARA concept may be extended to pediatric nuclear medicine and restated as the use of the lowest administered activities in children that are consistent with high-quality imaging. The response to this need for dose reduction and uniformity was the formation of a Pediatric Nuclear Medicine Dose Reduction Workgroup, consisting of pediatric nuclear medicine physicians, technologists, and physicists in North America, representing the Society of Nuclear Medicine through the Pediatric Imaging Council, the Society for Pediatric Radiology, and the American College of Radiology (Appendix). The workgroup conducted consensus workshops at annual meetings of the Society of Nuclear Medicine and the Society for Pediatric Radiology. Dose reduction was also featured in categoric courses presented at the 2009 and 2010 Society of Nuclear Medicine annual meetings. Likewise, dose reduction and image optimization in conventional and hybrid imaging were prominently featured in the Pediatric Nuclear Medicine Special Focus Session entitled “New Challenges” at the 52nd Annual Meeting of the Society for Pediatric Radiology in 2009. A symposium on pediatric radiopharmaceutical dosimetry was also held at the Society of Nuclear Medicine 2009 annual meeting. As a result of these consensus workshops, the Workgroup has achieved consensus on pediatric administered radiopharmaceutical doses for 9 commonly used radiopharmaceuticals, in terms of administered activity per kilogram Received Oct. 15, 2010; revision accepted Oct. 26, 2010. For correspondence or reprints contact: S. Ted Treves, Division of Nuclear Medicine and Molecular Imaging, Department of Radiology, Children’s Hospital Boston, Harvard Medical School, 300 Longwood Ave., PV2C12, Boston, MA 02115. E-mail: Ted.Treves@childrens.harvard.edu COPYRIGHT a 2011 by the Society of Nuclear Medicine, Inc. DOI: 10.2967/jnumed.110.084327

Weight-based, low-dose pediatric whole-body PET/CT protocols.

Adult PET/CT acquisition protocols need to be modified for pediatric imaging to minimize the radiation dose while maintaining diagnostic utility. We developed pediatric PET/CT acquisition protocols customized to patient weight and estimated the dosimetry and cancer risk of these low-dose protocols to communicate basic imaging risks. Methods: Protocols were developed for whole-body 18F-FDG imaging of patients in PET mode with a weight-based injected activity (5.3 MBq/kg) and acquisition times (3–5 min/field of view) and for CT for attenuation correction and localization with a weight-based tube current ranging from 10 to 40 mAs. Patients were categorized on the basis of the Broselow–Luten color-coded weight scale. Dosimetry and radiation-induced cancer risk for the PET and CT acquisition in each category were derived from mean patient sizes and the interpolation of factors from accepted patient models. Results: Whole-body pediatric PET/CT protocols require the customization of PET-acquisition settings and task-specific selection of CT technique. The proposed weight-based protocols result in an approximate effective dose ranging from 8.0 mSv for a 9-kg patient up to 13.5 mSv for a 63-kg patient. The radiation dose from the proposed protocols is 20%−50% (depending on patient weight), the dose from PET/CT protocols that use a fixed CT technique of 120 mAs and 120 kVp. The approximate, conservative estimate of additional lifetime attributable risk (LAR) of cancer incidence for females using the proposed protocols was approximately 3 in 1,000, with a variation of 18% across patient categories. For males, the additional LAR of cancer incidence was approximately 2 in 1,000, with a variation of 16% across categories. Conclusion: Low-dose PET/CT protocols for 11 patient weight categories were developed. The proposed protocols offer an initial set of acquisition parameters for pediatric PET/CT. The use of multiple categories allows for the continued refinement of dose-reduction parameters to minimize dose while maintaining image quality across the range of pediatric patient sizes.

Procedure Guideline for Diuretic Renography in Children 3.0

Hydronephrosis (distension of the pelvicalyceal system) is one of the most common indications for radionuclide evaluation of the kidneys in pediatrie patients. The etiology of the hydronephrosis can be an obstructed renal pelvis, an obstructed ureter, vesicoureteral reflux, the bladder itself or the bladder outlet, infection or congenital in nature. Contrast intravenous urography, ultrasonography and con ventional radionuclide renography cannot reliably differentiate obstructive from nonobstructive causes of hydronephrosis and hydroureteronephrosis (distension of the pelvicalyceal system and ureter). The pressure perfusion study (Whitaker test), which mea sures collecting system pressure under conditions of increased pelvic infusion is relatively invasive. The evaluation of function in the presence of obstruction does not give reliable indication of potential for recovery following surgical correction. High pressure in the collecting system results in reduction of renal blood flow and function. The most common cause of unilateral obstruction is the presence of a ureteropelvic obstruction. Obstructions can also occur more distally at the ureterovesical junction. Bilateral hydronephrosis can be produced by posterior urethral valves, bilateral ureteropelvic obstructions or even a full bladder. The purpose of diuretic renography is to differentiate a true obstruction from a dilated nonobstructed system (stasis) by serial imaging after intravenous administration of furosemide (Lasix).

Phase II Study of Oral Capsular 4-Hydroxyphenylretinamide (4-HPR/Fenretinide) in Pediatric Patients with Refractory or Recurrent Neuroblastoma: A Report from the Children's Oncology Group

Purpose: To determine the response rate to oral capsular fenretinide in children with recurrent or biopsy proven refractory high-risk neuroblastoma. Experimental Design: Patients received 7 days of fenretinide: 2,475 mg/m2/d divided TID (<18 years) or 1,800 mg/m2/d divided BID (≥18 years) every 21 days for a maximum of 30 courses. Patients with stable or responding disease after course 30 could request additional compassionate courses. Best response by course 8 was evaluated in stratum 1 (measurable disease on CT/MRI ± bone marrow and/or MIBG avid sites) and stratum 2 (bone marrow and/or MIBG avid sites only). Results: Sixty-two eligible patients, median age 5 years (range 0.6–19.9), were treated in stratum 1 (n = 38) and stratum 2 (n = 24). One partial response (PR) was seen in stratum 2 (n = 24 evaluable). No responses were seen in stratum 1 (n = 35 evaluable). Prolonged stable disease (SD) was seen in 7 patients in stratum 1 and 6 patients in stratum 2 for 4 to 45+ (median 15) courses. Median time to progression was 40 days (range 17–506) for stratum 1 and 48 days (range 17–892) for stratum 2. Mean 4-HPR steady-state trough plasma concentrations were 7.25 μmol/L (coefficient of variation 40–56%) at day 7 course 1. Toxicities were mild and reversible. Conclusions: Although neither stratum met protocol criteria for efficacy, 1 PR + 13 prolonged SD occurred in 14/59 (24%) of evaluable patients. Low bioavailability may have limited fenretinide activity. Novel fenretinide formulations with improved bioavailability are currently in pediatric phase I studies. Clin Cancer Res; 17(21); 6858–66. ©2011 AACR.

Ultrasound screening of the lambdoid suture in the child with posterior plagiocephaly

BackgroundThe child with posterior plagiocephaly may have positional molding or unilateral lambdoid synostosis. Molding responds to conservative treatment, lambdoid synostosis requires surgical reconstruction. CT is diagnostic, but uses ionizing radiation, may need sedation, and the incidence of lambdoid fusion is only 2–3%.ObjectiveThe purpose of this prospective study was to evaluate ultrasound as a screening test of lambdoid sutural patency using CT as the reference standard.Materials and methodsIn total, 41 children having head CT examinations were enrolled over 6xa0months. Of those, 29 were referred for abnormal head shape and suspected synostosis, of whom two had lambdoid fusion; 12 were referred for indications not related to head shape and found to have a normal study. Ultrasound scanning and interpretation of the lambdoid sutures was performed blinded to the CT reference standard. The lambdoid suture was read as patent or fused if a hypoechoic gap could or could not be seen between the hyperechoic calvarial bones, respectively.ResultsThe mean sensitivity and specificity of ultrasound in distinguishing a patent from fused lambdoid suture by three blinded pediatric radiologists was 100% and 89%, respectively.ConclusionsSonography of the lambdoid sutures shows excellent preliminary promise as a screening test of lambdoid sutural patency.

Pediatric Radiopharmaceutical Doses: New Guidelines

New consensus guidelines for pediatric administered radiopharmaceutical doses have been recently established and, in late 2010, were approved by the Society of Nuclear Medicine, the Society for Pediatric Radiology, and the American College of Radiology.

Evaluation of Optimal Acquisition Duration or Injected Activity for Pediatric 18F-FDG PET/CT

Pediatric 18F-FDG dosing and acquisition durations are generally based on coarse extrapolation from adult guidelines. This study sought to determine whether shorter acquisition durations or a lower 18F-FDG injected activity could be used for pediatric 18F-FDG PET/CT examinations while maintaining diagnostic utility. Reduction of overall scan time potentially reduces motion artifacts, improves patient comfort, and decreases length of sedation. Alternatively, decreased 18F-FDG dose minimizes radiation risk. Methods: Fourteen whole-body 18F-FDG PET/CT examinations were performed on 13 patients (weight, 13–109 kg; age range, 1–23 y) with a weight-based injected activity (5.3 MBq/kg [0.144 mCi/kg]), fixed acquisition durations (3 min/field of view [FOV] if < 22 kg, 5 min/FOV if > 22 kg), and list-mode acquisition. For each examination, the list-mode data were truncated to form multiple datasets with shorter acquisition durations down to a minimum of 1 min/FOV (i.e., 1, 2, 3, 4, and 5 min/FOV data were formed from single 5 min/FOV acquisition). Fifty-six image volumes were generated, randomized, and reviewed in a masked manner with corresponding CT image volumes by 5 radiologists. Overall, subjective adequacy and objective lesion detection accuracy by body region were evaluated. Results: All examinations with maximum acquisition duration were graded as adequate and were used as the reference standard for detection accuracy. For patients less than 22 kg, 1 of the 3 PET/CT examinations was graded as inadequate for clinical tasks when acquisition duration was reduced to 2 min/FOV, and all examinations were graded as inadequate when reduced to 1 min/FOV. For patients more than 22 kg, all 3–5 min/FOV studies were graded as adequate, and 2 of the 9 studies were graded as inadequate for 2 min/FOV studies. Lesion detection accuracy was perfect for acquisition times between 3 min/FOV and 5 min/FOV for all regions of the body. However, lesion detection became less accurate when imaging acquisition time was reduced more than 40%. Conclusion: Evaluation of image volumes generated from simulated shorter acquisition durations suggests that imaging times for larger patients (>22 kg) can be reduced from 5 min/FOV to 3 min/FOV without a loss of diagnostic utility. Using decreased acquisition times as a surrogate for 18F-FDG dose, 18F-FDG dose can be reduced by approximately 40% when all patients were scanned for 5 min/FOV.

Physician Documentation of Fluoroscopy Time in Voiding Cystourethrography Reports Correlates With Lower Fluoroscopy Times: A Surrogate Marker of Patient Radiation Exposure

OBJECTIVEnRadiation awareness has been advocated as a method of decreasing radiation exposure. For fluoroscopy, one indicator of radiation use is fluoroscopy time. We retrospectively reviewed fluoroscopy times on voiding cystourethrography (VCUG) studies performed at a major pediatric center, comparing the average fluoroscopy time of examinations with the fluoroscopy time documented in the report to the average time of those without documentation.nnnMATERIALS AND METHODSnA database search of records for the period between June 1, 2002, and March 31, 2009, identified all VCUG examinations and their recorded fluoroscopy time in the radiology information system. Those examinations in which the fluoroscopy time was documented in the radiologists report were also identified. Average fluoroscopy times were calculated for three groups: all VCUG examinations, examinations without the fluoroscopy time documented in the dictated report, and examinations including the fluoroscopy time in the dictated report.nnnRESULTSnOver the 7-year study period, 10,594 VCUG examinations were performed. The average fluoroscopy time was 47 seconds for all examinations, 50 seconds for examinations without fluoroscopy time reported (n = 8484), and 32 seconds for examinations with fluoroscopy time reported (n = 1979). There was a statistically significant difference between examinations with and without fluoroscopy time reported by the radiologist (p < 0.0001). A decreasing trend in average fluoroscopy time for all VCUG examinations was identified over time (average fluoroscopy time: 65 seconds for 2002-2003 vs 29 seconds for 2008-2009). Radiologists also increasingly reported fluoroscopy time over time (fluoroscopy time reported in 1% of reports in 2002-2003 vs 82% in 2008-2009).nnnCONCLUSIONnRadiologist reporting of fluoroscopy time correlates with a decrease in fluoroscopy time, a surrogate indicator of radiation dose. Our findings suggest that the radiologists documentation of fluoroscopy time in the report is part of a radiation awareness strategy leading to decreased fluoroscopy times.

Gastric pneumatosis and portal venous gas: benign findings in hypertrophic pyloric stenosis

A 6-week-old boy with progressively increasing non-bilious emesis was referred for evaluation of suspected pyloric stenosis. US revealed thickening and elongation of the pylorus, classic for pyloric stenosis, with reverberation artefact from the gastric wall. Echogenic foci compatible with portal venous gas were noted in appropriate distribution within the imaged liver (Fig. 1). Abdominal plain films confirmed gastric pneumatosis as the cause of portal venous gas (Fig. 2). Gas in the bowel wall in infants is an alarming finding, raising concerns for gut ischemia and necrotizing enterocolitis. Gastric pneumatosis in the absence of ischemia has been reported in gastric outlet obstruction, including that from

Imaging of Pediatric Renal Transplants and Their Complications: A Pictorial Review

Renal transplantation is the treatment of choice for end-stage renal disease in children. As a technically demanding surgery with complex medical management, it is associated with a number of complications. Anatomic imaging including ultrasonography with color and spectral Doppler and functional assessment with renal perfusion scintigraphy are complementary for the detection and characterization of posttransplant complications. Complications can be characterized by the time of appearance after transplantation (immediate, early, or late) or the anatomic site of origin (perinephric, vascular, urologic, or renal parenchymal). Perinephric fluid collections include hematomas and seromas, abscesses, lymphoceles, and urinomas. Noninfected collections frequently resolve spontaneously but should be monitored to exclude progression. Vascular complications are more prevalent in pediatric patients because of the small vessel caliber and include vascular thrombosis and stenosis. Arteriovenous fistulas and pseudoaneurysms can complicate biopsy and are typically transient. Common urologic complications include urine leak and urinary tract obstruction. Renal perfusion scintigraphy can be invaluable in elucidating the nature of such complications. Renal parenchymal abnormalities include acute tubular necrosis, rejection, and toxic effects of medication. Imaging features of renal parenchymal abnormalities can overlap, and the primary role of imaging is to exclude alternative causes of renal dysfunction. Renal and nonrenal mass lesions are more common in immunosuppressed patients after transplantation. Familiarity with the normal imaging appearance of the renal allograft and the appearances of common complications facilitates accurate diagnosis and timely treatment, with the ultimate goal of increasing graft survival. This goal is particularly crucial in children, given their greater number of projected life years.