Author's Accepted Manuscript
Pediatric interventional radiology and dose reduction techniques Craig Johnson DO, Deborah Rabinowitz MD
www.elsevier.com/locate/enganabound
PII: DOI: Reference:
S0887-2171(14)00043-2 http://dx.doi.org/10.1053/j.sult.2014.05.007 YSULT586
To appear in: Semin Ultrasound CT MRI
Cite this article as: Craig Johnson DO, Deborah Rabinowitz MD, Pediatric interventional radiology and dose reduction techniques, Semin Ultrasound CT MRI , http://dx.doi.org/10.1053/j.sult.2014.05.007 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Pediatric Interventional Radiology and Dose Reduction Techniques Craig Johnson, DO1 Deborah Rabinowitz, MD2
Corresponding Author: Craig Johnson, DO Assistant Professor of Radiology, Department of Radiology, University of Central Florida- College of Medicine Medical Director, Interventional Radiology, Department of Medical Imaging, Nemours Children’s Hospital– Orlando, FL
Deborah Rabinowitz, MD Section Head, Interventional Radiology Alfred I.duPont Children’s Hospital- Wilmington, DE
Address reprint requests to Craig Johnson, DO, Department of Medical Imaging, Nemours Children’s Hospital, 13535 Nemours Parkway, Orlando, FL 32827 phone (407) 650-7654 E-mail: [email protected]
1
Abstract The pediatric interventional radiology community has worked diligently in recent years through education and the use of technology to incorporate numerous dose reduction strategies. This article seeks to describe different strategies in which we can significantly lower dose to the pediatric patient undergoing a diagnostic or therapeutic image-guided procedure and, subsequently, many times lower the dose to ourselves and the staff in the process. These strategies start with patient selection, dose awareness and monitoring, shielding, fluoroscopic techniques and collimation. Advanced features such as cone beam technology, dose reduction image processing algorithms, overlay roadmapping, and volumetric cross sectional hybrid imaging are also discussed.
2
Introduction Pediatric interventional radiology has undergone a transformation in dose reduction strategies over the course of the last decade. There has been a combination of efforts including increased awareness of dose exposure and shielding techniques, advanced technology that allows better spatial resolution with less dose through both physics and software upgrades, increased skill in the use of alternative guidance modalities such as ultrasound, and the ability to merge preprocedure cross sectional imaging with overlay or roadmap to decrease the need for intraprocedural radiation. Increasing media and medical community attention on radiation dose has led to increased public awareness and spurred the world of interventional radiology to make great advances to create the safest possible environment for children. The “Image Gently” campaign subsequently unified the medical community and established pediatric protocols as well as provided resources and education for both practitioner and families alike.1 This education and awareness in interventional radiology has become increasingly important as a field that was rooted in diagnostic studies becomes involved in lengthy image-guided therapies such as embolization procedures that magnify the importance of dose reduction strategies all the more. This effort has become even more important as we have learned that our pediatric patients are more sensitive to radiation than adults, especially the younger patients.2 The imaging community needs to educate itself on all methods and
technologies that can reduce dose as well as be able to answer the family’s questions and guide them in the right direction even if certain technologies are not available at our institutions. Dose awareness, Dose monitoring and shielding The issues of dose awareness, dose monitoring and shielding are the first places to utilize current knowledge on dose reduction strategies. These are the logical places to start since these thought processes come into play even before the patient reaches the angiography suite.
3
Dose awareness starts at knowing what information is being desired by the requested exam or what therapy is requested at the end of the procedure. Understanding what medical, surgical and imaging alternatives there are to achieve the same goal is also part of the responsibility in this category. Understanding when the requested exam is extremely unlikely to achieve the desired information or therapeutic result is important and investing the time to educate the referring physicians and families is important. Although the use of ionizing radiation cannot be excluded, it should be used sparingly and efficiently. Sometimes the best the best recommendation is “do no harm” and wait. An example would be a request for a diagnostic coronary angiogram for which the information could be obtained from a cardiac magnetic resonance image (MRI) or a low dose computed tomography angiogram (CTA). Both would alleviate the small morbidity and mortality risk and MRI would eliminate the need for ionizing radiation altogether. Another example may be late in the day when asked to do a fluoroscopic guided lumbar puncture (LP) on a patient with no significant anatomic abnormality. While the procedure can be performed, there may be a highly effective and successful means to do the procedure without ionizing radiation being involved at all. Even if the overall dose is rather small, there is an important difference between little and none . Less is more is this arena. In the past, the only dose monitoring that was performed was the recording of the fluoroscopy time. Today, that is not enough given that there is a wide variation of patient sizes in pediatrics and that total dose not only involves fluoroscopy time, but also involves the number of runs and frame rates as well as imaging technique (kVp and mAs). Actually, digital angiography (DA) and digital subtraction angiography (DSA) accounts for the largest radiation dose during many interventional procedures even though DA and DSA may represent only a small fraction of the fluoroscopic time.3 Dose monitoring in interventional radiology, usually recorded in DAP or air kerma as well as milligray (mGy) or millisievert (mSv), is important to encourage because while onetime events may have little effect on overall long term risk according to our current knowledge, some procedures on a small child with very difficult anatomy may be requested day after day. Soon the cumulative dose requires a multidisciplinary “time out” to discuss the progress of the case and alternative treatment strategies and alternative treatment strategies. Patient report cards for dose
4
administered are becoming more common. Some of these are given to the patient while others are recorded in the permanent medical record. Patient report cards will also allow the new generation to carry knowledge of their overall risk and to better understand the impact of new radiation encounters that may arise in years to come. Additionally, live dose monitoring devices like Philips Dose aware allow for staff to have instant realization of which staff members are getting high dose and to allow more appropriate staff positioning within the room in real time.4 The system includes small badges which clip onto everybody’s lead aprons and link to a separate feedback monitor. The feedback monitor usually hangs adjacent to the fluoroscopy display and has a list of badges in the room. When fluoroscopy is activated, all badges give real time display on the monitor of the absorption rate and increase radiation awareness. These technologies in real time can show the importance of being on the side of the table with the image intensifier (II) and remind staff of the inverse square law of dose reduction and stepping back if possible.5 Shielding should apply to both patients and staff. It should be prepared before the case starts and constantly adjusted during the case. Unfortunately, it may often be neglected on a busy day in the heat of battle. Clearly there is no reason that children should not have their gonadal regions covered both under and over as long as it is not in the field of view. Other regions such as thyroid and breast are more controversial in the interventional literature but at the very least if imaging near these areas is required, the angle of the entrance beam should be adjusted to limit dose to these radiosensitive areas. There has been little innovation in overall dose reduction designs to the interventional suites in the last forty years which has not followed the innovations within the software or the equipment used.6 Table mounted lead shielding as well as clear ceiling mounted protections should always be used when feasible. All too often the clear upper body shield is pushed as far away as possible in the place of being used. The reduction of this scatter radiation is essential and is the single most effective means, besides lead aprons, that can be used to reduce dose to staff. The overhead ceiling mounted shields have been shown to reduce cervical dose by up to 15-fold.7 Lead table skirts have been shown to reduce scatter to legs and ankles by almost 20-fold.8 Lead aprons and thyroid shields as well as leaded glasses are the essentials of personal protection. There is sometimes the false sense of security that the technologic advances have led to reduced
5
need to wear the primary protective agents. Advances in this arena have led to lighter glasses that still protect and can help prevent radiation-associated cataracts. Studies have shown reductions in radiation exposure to the eyes of the interventional radiologist by up to 90%.9 Additionally, two piece light lead has led to better weight distribution which should help the long term musculoskeletal complaints of many in this field. Finally, while overheating and fluid loss is sometimes sited for using less shielding, there are cooling systems available that allow those who overheat in long cases the ability to remain comfortable and still have appropriate radiation shielding. Through these techniques, scatter radiation can be reduced to the patient and staff.
Fluoroscopic techniques for dose reduction Once the time out has been performed, there are many techniques that can be used to reduce dose in the room using current equipment. These include basic techniques such as collimation and using pulsed fluoroscopy techniques and advanced techniques such as Siemens Care position product that allows to move and collimate on a last image hold instead of requiring to move on a live patient. This radiation free repositioning of a patient under visual control of the last image hold can lead to significant dose reduction. Brackets on the last image hold display show where the new center of the x-ray beam will be as the table is repositioned. There is also the so-called Philips fluoroscopy “flavors” that allow for automated changes in pulse fluoroscopy rate and both kVp and mAs. increasing and decreasing as needed throughout a procedure. This is done with preset pulsed fluoroscopy and dose settings which are automated with three buttons simply saying one, two and three. Commonly we keep the setting at flavor “one” which is the lowest dose but also the lowest quality. If there is need for improved resolution such as determining reflux into parent vessel during particle embolization, you could simply hit “two” for a short period for improved resolution until the procedure is complete and then revert back to base setting with a push of a button. Dose can also be reduced by using high quality alternative imaging methods for portions of the procedures that can be done without radiation such as ultrasound guidance.
6
Pulsed fluoroscopy has been around for many years in the fluoroscopy areas of pediatric imaging centers but not as long in angiography suites and cardiac interventional suites. Many of the older units do not have this option. This allows up to a 50% to 75% dose reduction depending on pulse rate, especially for the portion of the procedure that does not require fine detail. A recent study optimizing the pulse settings and dose level to the detector during pediatric retinoblastoma intra-arterial chemotherapy procedures resulted in a 73% dose reduction to the radiosensitive region of the eye.10 This is a variable that should be constantly adjusted even within the procedure itself several times to allow for the best efficacy using as low as reasonably achievable (ALARA) principles. Magnification and entrance angle are two other important factors that influence dose in pediatric interventional radiology. While the imaging of small children and small anatomic regions necessitates magnification at times, it is important to be aware of the increased dose to the region and to magnify only when essential for the procedure and then return to non-magnified field of view as soon as not essential. When deciding on working angles for particle embolization or nBCA embolization, it is important to realize the effect of magnification and working in the lateral versus AP plane in an abdominal arteriovenous malformation. Studies have shown entrance doses four times as high in the lateral projection as compared to AP.11 Under the category of partial usage of alternative imaging is ultrasound guidance. For example, using ultrasound guidance for the five dilation steps of a chest tube placement and fluoroscopy only for the final pigtail placement, and advancement, would lead to significant dose reduction. This reduction of radiation is significant over the course of many procedures to both the operator as well as to the patient. Also useful in reducing fluoroscopy time and dose is the commitment to closely examine the anatomy and information obtained from previous studies before the procedure. Typically the pre-procedure imaging is displayed on one of the monitors or on a portion of the big monitor as a reminder of the tumor location or anatomic angles of the arterial anatomy.
7
Another time commitment that can lead to significant dose reduction to the patient and staff is collimation. Typically poor collimation involves including the patient’s or operator’s hands in the field of view. Optimal collimation requires a team effort of observation and calling “time outs” to identify the best positioning and taking the time to properly collimate. If the patient is not moving, software packages like the Care position (Siemens Healthcare, Erlangen, Germany) are invaluable in being able to move the image intensifier on a last image hold without having to use live fluoroscopy. Collimation helps limit dose to the patient significantly by reducing scatter radiation that also helpful in improving image quality. Soft cones are also very helpful and do the same to a lesser degree. Advanced Technologies for dose reduction Advanced technologies for dose reduction are currently flourishing with the current focus on radiation dose and dose reduction. Among the most important technologies is the cone beam CT (CBCT) technology that has allowed an 8590% decreased radiation dose while still providing excellent 3D guidance.12-13 The rising awareness in the last decade of relatively high ionizing radiation dose with conventional CT and the potential risks to the pediatric population was in large part responsible for the media attention and subsequent reflection on the available historical data by the medical community.14-16 These techniques have saved significant dose over the course of difficult bone and soft tissue biopsies and ablations with spatial resolution adequate to give the precise guidance needed (Fig. 1).17 The newest software packages such as Phillips Allura Clarity will allow for an even further dose reduction of about 50% with no image degradation using a unique image processing algorithm.18 The lack of image degradation was proven by randomizing lengthy interventional procedures and saw no statistical difference between the two groups with regards to fluoroscopy times, exposure frames or overall procedure duration. This advanced software achieves this dose reduction by noise and artifact reduction as well as edge sharpening and advanced motion correction software which results in equivalent image quality with lower dose. Other companies will likely offer similar advanced software packages.
8
Additionally, all major brands now have needle guidance systems that can significantly reduce the number of spins (limited CBCT’s) needed to achieve one’s goal. These systems may use orthogonal 2D data or 3D data from a CBCT or even a fused volumetric MRI or contrast-enhanced CT. Either way the systems allow needle or trocar advance in a 2D plane with 3D guidance provided the patient doesn’t move and there have been no anatomic changes since the volumetric cross sectional imaging was obtained.19 Some of these technologies have screen displays only and some have external laser guidance systems. This greatly reduces the dose for cases that used to be done under regular CT guidance, during which multiple CT images were obtained during needle advancement. Not only was fluoroscopy time and dose decreased, but operator hand dose was also decreased as well.20 Finally, improving roadmapping techniques can be very helpful in limiting time and dose by providing optimal imaging with less degradation. Traditionally roadmap processing algorithms allow for better spatial resolution and wire visualization and advanced mask overlay roadmapping procedures such as Phillips SmartMask or Siemens Fluoro Fade. These guidance techniques simplify roadmapping by fusing traditional fluoroscopy with a selected reference image on a single monitor. Adjustments can then be made by fading in and out between the two images to allow for optimal image guidance to ultimately decrease time of procedure and dose. This technique avoids the necessity of a dedicated “roadmap” injection and therefore a second or higher dose of radiation in the same vessel distribution. Alternative modalities for image guidance Alternative methods for image-guided procedures may, on occasion, be the best dose reduction of all because often a 100% dose reduction can be achieved. As mentioned above it may involve committing large portions of the procedure to purely ultrasound guidance or, rarely, MRI guidance. While MRI shows great promise for image guidance in the future, the long periods of time required for the procedures and the lack of affordable MRI-compatible equipment at present keep this modality from having a significant impact on pediatric interventional practices. In the future MRI may have a place in the development of ultrasound-guided and MRI-guided high intensity focused ultrasound (HIFU)
9
treatments for tumors. Currently, such technologies are being used in the adult population on a limited basis in prostate and uterine tumors.21-22 In general, ultrasound-guided procedures have been largely pioneered in the pediatric setting for a number of reasons. First, pediatric patients are generally much smaller and allow for better visualization of deep structures as compared to adults. However, this is a generalization because patients in the pediatric population range from preemies to obese teenagers. A perfect example of the switch from fluoroscopy to ultrasound guidance is peripherally inserted central venous catheter placement. Initially this procedure was performed by inserting a peripheral IV into the hand and obtaining a venogram with the tourniquet on. This puncture was made under fluoroscopic guidance giving radiation dose to both the physician and patient. Then ultrasound guidance was used for the puncture with the remainder of the procedure one under fluoroscopic guidance. Most recently, many pediatric interventional centers have evolved to purely ultrasound placement on patients in the NICU and on small non ambulatory children using ultrasound guidance from the saphenous approach for puncture then using the liver as an acoustic window to the IVC for proper positioning avoiding any ionizing radiation all together (Fig. 2). Another example is abscess drainage or chest tube placement for empyema that now can be performed under ultrasound guidance alone or with very minimal fluoroscopic guidance. Finally, lengthy angiographic embolizations of arteriovenous malformations can be at least partially done under ultrasound guidance to perform glue embolization (Fig. 3). Finally, many advanced angiographic devices now provide for using previously available volumetric cross sectional imaging. These MRI or CT image overlays that can be very helpful in allowing c-arm, fluoroscopy and cone beam CT technology to focus on portions of the bone, liver or orbit that have specific signal abnormality on MRI not visible on the non-contrast 3D guidance systems currently used.23 This technology also helps assess treatment areas during sclerotherapy procedures of complex irregular-shaped vascular malformations (Fig. 4). Additionally, fusion technology is developing to not only assist with lesion localization but is also being developed to fuse pre-procedural CT angiograms and MR angiograms in order to decrease radiation dose and contrast dose.24-25
10
Conclusion The field of pediatric interventional radiology is among the leaders in dose reduction strategies. This has been achieved through a combination of technologic innovation, education of both ourselves and the families we serve, and our own specialized training. Using different modalities and non-interventional techniques with medical management or hybrid procedures provides the best care for the children we serve. The involvement of pediatric radiologists in clinical care and advanced therapeutic procedures that commonly take longer than there surgical counterparts requires us to master these techniques and as leaders of our teams to educate our staffs also. As we realize the long lives ahead of so many we serve, now is the time to spread the knowledge we have in this arena.
11
References 1. Goske MJ, Applegate KE, Boylan J, et al: The ‘Image Gently’ campaign: increasing CT radiation dose awareness through a national education and awareness program. Pediatr Radiol 38: 265-269, 2008
2. Hall E. Introduction to session I: helical CT and cancer risk. Pediatr Radiol 32:225-227, 2002 3. Swobada NA, Armstrong DG, Smith J, et al: Pediatric patient surface doses in neuroangiography. Pediatr Radiol 35:859-866, 2005
4. Racadio J, Nachabe R, Carelsen B, et al: Effect of real-time radiation dose feedback on pediatric interventional radiology staff radiation exposure. J Vasc Interv Radiol 25(1):119-26, 2014
5. Huda W, Slone R (eds). Review of Radiological Physics. Philadelphia, PA, Lippincott Williams and Wilkins, 2nd Edition 2003
6. Lloyd W. Klein, MD; Justin Maroney, MD. Optimizing Operator Protection by Proper Radiation Shield Positioning in the Interventional Cardiology Suite. J Am Coll Cardiol Intv 4(10): 1140-1141, 2011
7. Tsapaki V, Kottous S, Vano E, et al: Occupational dose constraints in interventional cardiology procedures: the DIMOND approach. Phys Med Biol 49:997-1005, 2004
8. Wyart P, Dumant D, Gourdier M, et al: Contribution of self-surveillance of the personnel by electronic radiation dosimeters in invasive cardiology. Arch Mal Coeur Vaiss 90:233-238, 1997
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9. Pages J. Effective dose and dose to the crystalline lens during angiographic procedures. JBR-BTR 83:108-110, 2000
10. Cooke DL, Stout CE, Kim WT, et al: Radiation dose reduction in intra-arterial chemotherapy infusion for intraocular retinoblastoma. J Neurointerv Surg doi: 10.1136/neurintsurg-2013-010905, 2014 (in press).
11. Connolly C, Racadio J, Towbin R. Practice of ALARA in the pediatric interventional suite. Pediatr Radiol 36 Suppl 2; 163-7, 2006
12. Schapiro A1, Racadio J, Kinnett D, et al: Combined C-arm fluoroscopy and C-arm cone beam computed tomography for the evaluation of patients with possible intrathecal baclofen delivery system malfunctions. Neurosurgery 69 (1 Suppl Operative): 27-33, 2011 13. Racadio JM, Babic D, Homan R, et al: Live 3D guidance in the interventional radiology suite. AJR Am J Roentgenol 189(6):W357-64, 2007
14. Brody AS, Frush DP, Huda W, et al: Radiation risk to children from computed tomography. Pediatrics 120: 677682, 2007
15. Brenner DJ, Hall EJ. Current concepts - Computed tomography- An increasing source of radiation exposure. N Engl J Med 357: 2277-2284, 2007
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16. Amis ES, Jr., Butler PF, Applegate KE, et al: American College of Radiology white paper on radiation dose in medicine. J Am Coll Radiol 4: 272-284, 2007
17. Johnson ND, Racadio JM. IR challenges in the MSK system. Pediatr Radiol 40(4): 474-7, 2010
18. Dekker LR, van der Voort PH, Simmers TA, et al: New image processing and noise reduction technology allows reduction of radiation exposure in complex electrophysiologic interventions while maintaining optimal image quality: a randomized clinical trial. Heart Rhythm 10(11):1678-82, 2013
19. Carrafiello G, Fontana F, Mangini M, et al: Initial experience with percutaneous biopsies of bone lesions using XperGuide cone-beam CT (CBCT): technical note. Radiol Med.117(8):1386-97, 2012
20. Kroes MW, Busser WM, Fütterer JJ, et al: Assessment of needle guidance devices for their potential to reduce fluoroscopy time and operator hand dose during C-arm cone-beam computed tomography-guided needle interventions. J Vasc Interv Radiol 24(6):901-6, 2013
21. Marien A, Gill I, Ukimura O, et al: Target ablation-Image-guided therapy in prostate cancer. Urol Oncol pii: S1078-1439(13)00456-0 2014 (in press).
22. Park MJ, Kim YS, Rhim H, et al: Safety and therapeutic efficacy of complete or near-complete ablation of symptomatic uterine fibroid tumors by MR imaging-guided high-intensity focused US therapy. J Vasc Interv Radiol 25(2):231-9, 2014
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23. Cooke DL, Levitt M, Kim LJ, et al: Intraorbital access using fluoroscopic flat panel detector CT navigation and three-dimensional MRI overlay. J Neurointerv Surg 2(3):249-51, 2010
24. Gupta A, Grünhagen T. Live MR angiographic roadmapping for uterine artery embolization: a feasibility study. J Vasc Interv Radiol 24(11):1690-7, 2013
25. Sadek M, Berland TL, Maldonado TS, et al: Use of preoperative magnetic resonance angiography and the Artis zeego fusion program to minimize contrast during endovascular repair of an iliac artery aneurysm. Ann Vasc Surg 28(1):261.e1-5, 2014
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Illustration Legends Fig. 1. Radiofrequency ablation. A: A sagittal cone beam CT scan demonstrates the radiofrequency trocar (arrow) in the center of the small painful tibial epiphyseal lesion. B: A sagittal reconstructed conventional CT image demonstrates improved spatial resolution of the same bony structures and of the subtle sclerotic epiphyseal bone lesion (arrow). C: Sagittal fat-saturated T1-weighted post contrast image better demonstrates the enhancing epiphyseal bone lesion (arrow) and was used as a roadmap during the ablation procedure. Fig. 2. Neonatal ultrasound-guided PICC placement. A: Patent common femoral vein (arrow) near the saphenous vein anastamosis which is accessed after tunneling from the medial thigh to reduce infection rate. B: Longitudinal ultrasound image through the liver demonstrates catheter tip (arrow) in the desired location of the intrahepatic IVC at the end of the procedure. Fig. 3. Ultrasound-guided AVM glue embolization. A: Left external carotid angiogram in the venous phase demonstrates a large draining vein superiorly (arrow) and several smaller draining veins. B: Transverse ultrasound image of the left face demonstrates a hyperechoic shadowing focus representing nBCA glue (arrow). C: Fluoroscopic image after the glue embolization demonstrates glue filling of the large draining vein (arrow) and reflux back into the AVM nidus. Fig. 4. Vascular malformation treatment of the left femur. Volumetric 3D fusion image of fat-saturated T2-weighted preprocedure MRI demonstrating malformation in white (arrow) overlaid on 3D CBCT image with treated lesion in red (blue arrowhead) with two separate access needles entering at near orthogonal angles. This fusion image changed management and lead to third access site which successfully treated the remainder of the lesion and saved an additional treatment for residual disease.
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Pediatric interventional radiology and dose reduction techniques Craig Johnson DO, Deborah Rabinowitz MD
www.elsevier.com/locate/enganabound
PII: DOI: Reference:
S0887-2171(14)00043-2 http://dx.doi.org/10.1053/j.sult.2014.05.007 YSULT586
To appear in: Semin Ultrasound CT MRI
Cite this article as: Craig Johnson DO, Deborah Rabinowitz MD, Pediatric interventional radiology and dose reduction techniques, Semin Ultrasound CT MRI , http://dx.doi.org/10.1053/j.sult.2014.05.007 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Pediatric Interventional Radiology and Dose Reduction Techniques Craig Johnson, DO1 Deborah Rabinowitz, MD2
Corresponding Author: Craig Johnson, DO Assistant Professor of Radiology, Department of Radiology, University of Central Florida- College of Medicine Medical Director, Interventional Radiology, Department of Medical Imaging, Nemours Children’s Hospital– Orlando, FL
Deborah Rabinowitz, MD Section Head, Interventional Radiology Alfred I.duPont Children’s Hospital- Wilmington, DE
Address reprint requests to Craig Johnson, DO, Department of Medical Imaging, Nemours Children’s Hospital, 13535 Nemours Parkway, Orlando, FL 32827 phone (407) 650-7654 E-mail: [email protected]
1
Abstract The pediatric interventional radiology community has worked diligently in recent years through education and the use of technology to incorporate numerous dose reduction strategies. This article seeks to describe different strategies in which we can significantly lower dose to the pediatric patient undergoing a diagnostic or therapeutic image-guided procedure and, subsequently, many times lower the dose to ourselves and the staff in the process. These strategies start with patient selection, dose awareness and monitoring, shielding, fluoroscopic techniques and collimation. Advanced features such as cone beam technology, dose reduction image processing algorithms, overlay roadmapping, and volumetric cross sectional hybrid imaging are also discussed.
2
Introduction Pediatric interventional radiology has undergone a transformation in dose reduction strategies over the course of the last decade. There has been a combination of efforts including increased awareness of dose exposure and shielding techniques, advanced technology that allows better spatial resolution with less dose through both physics and software upgrades, increased skill in the use of alternative guidance modalities such as ultrasound, and the ability to merge preprocedure cross sectional imaging with overlay or roadmap to decrease the need for intraprocedural radiation. Increasing media and medical community attention on radiation dose has led to increased public awareness and spurred the world of interventional radiology to make great advances to create the safest possible environment for children. The “Image Gently” campaign subsequently unified the medical community and established pediatric protocols as well as provided resources and education for both practitioner and families alike.1 This education and awareness in interventional radiology has become increasingly important as a field that was rooted in diagnostic studies becomes involved in lengthy image-guided therapies such as embolization procedures that magnify the importance of dose reduction strategies all the more. This effort has become even more important as we have learned that our pediatric patients are more sensitive to radiation than adults, especially the younger patients.2 The imaging community needs to educate itself on all methods and
technologies that can reduce dose as well as be able to answer the family’s questions and guide them in the right direction even if certain technologies are not available at our institutions. Dose awareness, Dose monitoring and shielding The issues of dose awareness, dose monitoring and shielding are the first places to utilize current knowledge on dose reduction strategies. These are the logical places to start since these thought processes come into play even before the patient reaches the angiography suite.
3
Dose awareness starts at knowing what information is being desired by the requested exam or what therapy is requested at the end of the procedure. Understanding what medical, surgical and imaging alternatives there are to achieve the same goal is also part of the responsibility in this category. Understanding when the requested exam is extremely unlikely to achieve the desired information or therapeutic result is important and investing the time to educate the referring physicians and families is important. Although the use of ionizing radiation cannot be excluded, it should be used sparingly and efficiently. Sometimes the best the best recommendation is “do no harm” and wait. An example would be a request for a diagnostic coronary angiogram for which the information could be obtained from a cardiac magnetic resonance image (MRI) or a low dose computed tomography angiogram (CTA). Both would alleviate the small morbidity and mortality risk and MRI would eliminate the need for ionizing radiation altogether. Another example may be late in the day when asked to do a fluoroscopic guided lumbar puncture (LP) on a patient with no significant anatomic abnormality. While the procedure can be performed, there may be a highly effective and successful means to do the procedure without ionizing radiation being involved at all. Even if the overall dose is rather small, there is an important difference between little and none . Less is more is this arena. In the past, the only dose monitoring that was performed was the recording of the fluoroscopy time. Today, that is not enough given that there is a wide variation of patient sizes in pediatrics and that total dose not only involves fluoroscopy time, but also involves the number of runs and frame rates as well as imaging technique (kVp and mAs). Actually, digital angiography (DA) and digital subtraction angiography (DSA) accounts for the largest radiation dose during many interventional procedures even though DA and DSA may represent only a small fraction of the fluoroscopic time.3 Dose monitoring in interventional radiology, usually recorded in DAP or air kerma as well as milligray (mGy) or millisievert (mSv), is important to encourage because while onetime events may have little effect on overall long term risk according to our current knowledge, some procedures on a small child with very difficult anatomy may be requested day after day. Soon the cumulative dose requires a multidisciplinary “time out” to discuss the progress of the case and alternative treatment strategies and alternative treatment strategies. Patient report cards for dose
4
administered are becoming more common. Some of these are given to the patient while others are recorded in the permanent medical record. Patient report cards will also allow the new generation to carry knowledge of their overall risk and to better understand the impact of new radiation encounters that may arise in years to come. Additionally, live dose monitoring devices like Philips Dose aware allow for staff to have instant realization of which staff members are getting high dose and to allow more appropriate staff positioning within the room in real time.4 The system includes small badges which clip onto everybody’s lead aprons and link to a separate feedback monitor. The feedback monitor usually hangs adjacent to the fluoroscopy display and has a list of badges in the room. When fluoroscopy is activated, all badges give real time display on the monitor of the absorption rate and increase radiation awareness. These technologies in real time can show the importance of being on the side of the table with the image intensifier (II) and remind staff of the inverse square law of dose reduction and stepping back if possible.5 Shielding should apply to both patients and staff. It should be prepared before the case starts and constantly adjusted during the case. Unfortunately, it may often be neglected on a busy day in the heat of battle. Clearly there is no reason that children should not have their gonadal regions covered both under and over as long as it is not in the field of view. Other regions such as thyroid and breast are more controversial in the interventional literature but at the very least if imaging near these areas is required, the angle of the entrance beam should be adjusted to limit dose to these radiosensitive areas. There has been little innovation in overall dose reduction designs to the interventional suites in the last forty years which has not followed the innovations within the software or the equipment used.6 Table mounted lead shielding as well as clear ceiling mounted protections should always be used when feasible. All too often the clear upper body shield is pushed as far away as possible in the place of being used. The reduction of this scatter radiation is essential and is the single most effective means, besides lead aprons, that can be used to reduce dose to staff. The overhead ceiling mounted shields have been shown to reduce cervical dose by up to 15-fold.7 Lead table skirts have been shown to reduce scatter to legs and ankles by almost 20-fold.8 Lead aprons and thyroid shields as well as leaded glasses are the essentials of personal protection. There is sometimes the false sense of security that the technologic advances have led to reduced
5
need to wear the primary protective agents. Advances in this arena have led to lighter glasses that still protect and can help prevent radiation-associated cataracts. Studies have shown reductions in radiation exposure to the eyes of the interventional radiologist by up to 90%.9 Additionally, two piece light lead has led to better weight distribution which should help the long term musculoskeletal complaints of many in this field. Finally, while overheating and fluid loss is sometimes sited for using less shielding, there are cooling systems available that allow those who overheat in long cases the ability to remain comfortable and still have appropriate radiation shielding. Through these techniques, scatter radiation can be reduced to the patient and staff.
Fluoroscopic techniques for dose reduction Once the time out has been performed, there are many techniques that can be used to reduce dose in the room using current equipment. These include basic techniques such as collimation and using pulsed fluoroscopy techniques and advanced techniques such as Siemens Care position product that allows to move and collimate on a last image hold instead of requiring to move on a live patient. This radiation free repositioning of a patient under visual control of the last image hold can lead to significant dose reduction. Brackets on the last image hold display show where the new center of the x-ray beam will be as the table is repositioned. There is also the so-called Philips fluoroscopy “flavors” that allow for automated changes in pulse fluoroscopy rate and both kVp and mAs. increasing and decreasing as needed throughout a procedure. This is done with preset pulsed fluoroscopy and dose settings which are automated with three buttons simply saying one, two and three. Commonly we keep the setting at flavor “one” which is the lowest dose but also the lowest quality. If there is need for improved resolution such as determining reflux into parent vessel during particle embolization, you could simply hit “two” for a short period for improved resolution until the procedure is complete and then revert back to base setting with a push of a button. Dose can also be reduced by using high quality alternative imaging methods for portions of the procedures that can be done without radiation such as ultrasound guidance.
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Pulsed fluoroscopy has been around for many years in the fluoroscopy areas of pediatric imaging centers but not as long in angiography suites and cardiac interventional suites. Many of the older units do not have this option. This allows up to a 50% to 75% dose reduction depending on pulse rate, especially for the portion of the procedure that does not require fine detail. A recent study optimizing the pulse settings and dose level to the detector during pediatric retinoblastoma intra-arterial chemotherapy procedures resulted in a 73% dose reduction to the radiosensitive region of the eye.10 This is a variable that should be constantly adjusted even within the procedure itself several times to allow for the best efficacy using as low as reasonably achievable (ALARA) principles. Magnification and entrance angle are two other important factors that influence dose in pediatric interventional radiology. While the imaging of small children and small anatomic regions necessitates magnification at times, it is important to be aware of the increased dose to the region and to magnify only when essential for the procedure and then return to non-magnified field of view as soon as not essential. When deciding on working angles for particle embolization or nBCA embolization, it is important to realize the effect of magnification and working in the lateral versus AP plane in an abdominal arteriovenous malformation. Studies have shown entrance doses four times as high in the lateral projection as compared to AP.11 Under the category of partial usage of alternative imaging is ultrasound guidance. For example, using ultrasound guidance for the five dilation steps of a chest tube placement and fluoroscopy only for the final pigtail placement, and advancement, would lead to significant dose reduction. This reduction of radiation is significant over the course of many procedures to both the operator as well as to the patient. Also useful in reducing fluoroscopy time and dose is the commitment to closely examine the anatomy and information obtained from previous studies before the procedure. Typically the pre-procedure imaging is displayed on one of the monitors or on a portion of the big monitor as a reminder of the tumor location or anatomic angles of the arterial anatomy.
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Another time commitment that can lead to significant dose reduction to the patient and staff is collimation. Typically poor collimation involves including the patient’s or operator’s hands in the field of view. Optimal collimation requires a team effort of observation and calling “time outs” to identify the best positioning and taking the time to properly collimate. If the patient is not moving, software packages like the Care position (Siemens Healthcare, Erlangen, Germany) are invaluable in being able to move the image intensifier on a last image hold without having to use live fluoroscopy. Collimation helps limit dose to the patient significantly by reducing scatter radiation that also helpful in improving image quality. Soft cones are also very helpful and do the same to a lesser degree. Advanced Technologies for dose reduction Advanced technologies for dose reduction are currently flourishing with the current focus on radiation dose and dose reduction. Among the most important technologies is the cone beam CT (CBCT) technology that has allowed an 8590% decreased radiation dose while still providing excellent 3D guidance.12-13 The rising awareness in the last decade of relatively high ionizing radiation dose with conventional CT and the potential risks to the pediatric population was in large part responsible for the media attention and subsequent reflection on the available historical data by the medical community.14-16 These techniques have saved significant dose over the course of difficult bone and soft tissue biopsies and ablations with spatial resolution adequate to give the precise guidance needed (Fig. 1).17 The newest software packages such as Phillips Allura Clarity will allow for an even further dose reduction of about 50% with no image degradation using a unique image processing algorithm.18 The lack of image degradation was proven by randomizing lengthy interventional procedures and saw no statistical difference between the two groups with regards to fluoroscopy times, exposure frames or overall procedure duration. This advanced software achieves this dose reduction by noise and artifact reduction as well as edge sharpening and advanced motion correction software which results in equivalent image quality with lower dose. Other companies will likely offer similar advanced software packages.
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Additionally, all major brands now have needle guidance systems that can significantly reduce the number of spins (limited CBCT’s) needed to achieve one’s goal. These systems may use orthogonal 2D data or 3D data from a CBCT or even a fused volumetric MRI or contrast-enhanced CT. Either way the systems allow needle or trocar advance in a 2D plane with 3D guidance provided the patient doesn’t move and there have been no anatomic changes since the volumetric cross sectional imaging was obtained.19 Some of these technologies have screen displays only and some have external laser guidance systems. This greatly reduces the dose for cases that used to be done under regular CT guidance, during which multiple CT images were obtained during needle advancement. Not only was fluoroscopy time and dose decreased, but operator hand dose was also decreased as well.20 Finally, improving roadmapping techniques can be very helpful in limiting time and dose by providing optimal imaging with less degradation. Traditionally roadmap processing algorithms allow for better spatial resolution and wire visualization and advanced mask overlay roadmapping procedures such as Phillips SmartMask or Siemens Fluoro Fade. These guidance techniques simplify roadmapping by fusing traditional fluoroscopy with a selected reference image on a single monitor. Adjustments can then be made by fading in and out between the two images to allow for optimal image guidance to ultimately decrease time of procedure and dose. This technique avoids the necessity of a dedicated “roadmap” injection and therefore a second or higher dose of radiation in the same vessel distribution. Alternative modalities for image guidance Alternative methods for image-guided procedures may, on occasion, be the best dose reduction of all because often a 100% dose reduction can be achieved. As mentioned above it may involve committing large portions of the procedure to purely ultrasound guidance or, rarely, MRI guidance. While MRI shows great promise for image guidance in the future, the long periods of time required for the procedures and the lack of affordable MRI-compatible equipment at present keep this modality from having a significant impact on pediatric interventional practices. In the future MRI may have a place in the development of ultrasound-guided and MRI-guided high intensity focused ultrasound (HIFU)
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treatments for tumors. Currently, such technologies are being used in the adult population on a limited basis in prostate and uterine tumors.21-22 In general, ultrasound-guided procedures have been largely pioneered in the pediatric setting for a number of reasons. First, pediatric patients are generally much smaller and allow for better visualization of deep structures as compared to adults. However, this is a generalization because patients in the pediatric population range from preemies to obese teenagers. A perfect example of the switch from fluoroscopy to ultrasound guidance is peripherally inserted central venous catheter placement. Initially this procedure was performed by inserting a peripheral IV into the hand and obtaining a venogram with the tourniquet on. This puncture was made under fluoroscopic guidance giving radiation dose to both the physician and patient. Then ultrasound guidance was used for the puncture with the remainder of the procedure one under fluoroscopic guidance. Most recently, many pediatric interventional centers have evolved to purely ultrasound placement on patients in the NICU and on small non ambulatory children using ultrasound guidance from the saphenous approach for puncture then using the liver as an acoustic window to the IVC for proper positioning avoiding any ionizing radiation all together (Fig. 2). Another example is abscess drainage or chest tube placement for empyema that now can be performed under ultrasound guidance alone or with very minimal fluoroscopic guidance. Finally, lengthy angiographic embolizations of arteriovenous malformations can be at least partially done under ultrasound guidance to perform glue embolization (Fig. 3). Finally, many advanced angiographic devices now provide for using previously available volumetric cross sectional imaging. These MRI or CT image overlays that can be very helpful in allowing c-arm, fluoroscopy and cone beam CT technology to focus on portions of the bone, liver or orbit that have specific signal abnormality on MRI not visible on the non-contrast 3D guidance systems currently used.23 This technology also helps assess treatment areas during sclerotherapy procedures of complex irregular-shaped vascular malformations (Fig. 4). Additionally, fusion technology is developing to not only assist with lesion localization but is also being developed to fuse pre-procedural CT angiograms and MR angiograms in order to decrease radiation dose and contrast dose.24-25
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Conclusion The field of pediatric interventional radiology is among the leaders in dose reduction strategies. This has been achieved through a combination of technologic innovation, education of both ourselves and the families we serve, and our own specialized training. Using different modalities and non-interventional techniques with medical management or hybrid procedures provides the best care for the children we serve. The involvement of pediatric radiologists in clinical care and advanced therapeutic procedures that commonly take longer than there surgical counterparts requires us to master these techniques and as leaders of our teams to educate our staffs also. As we realize the long lives ahead of so many we serve, now is the time to spread the knowledge we have in this arena.
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References 1. Goske MJ, Applegate KE, Boylan J, et al: The ‘Image Gently’ campaign: increasing CT radiation dose awareness through a national education and awareness program. Pediatr Radiol 38: 265-269, 2008
2. Hall E. Introduction to session I: helical CT and cancer risk. Pediatr Radiol 32:225-227, 2002 3. Swobada NA, Armstrong DG, Smith J, et al: Pediatric patient surface doses in neuroangiography. Pediatr Radiol 35:859-866, 2005
4. Racadio J, Nachabe R, Carelsen B, et al: Effect of real-time radiation dose feedback on pediatric interventional radiology staff radiation exposure. J Vasc Interv Radiol 25(1):119-26, 2014
5. Huda W, Slone R (eds). Review of Radiological Physics. Philadelphia, PA, Lippincott Williams and Wilkins, 2nd Edition 2003
6. Lloyd W. Klein, MD; Justin Maroney, MD. Optimizing Operator Protection by Proper Radiation Shield Positioning in the Interventional Cardiology Suite. J Am Coll Cardiol Intv 4(10): 1140-1141, 2011
7. Tsapaki V, Kottous S, Vano E, et al: Occupational dose constraints in interventional cardiology procedures: the DIMOND approach. Phys Med Biol 49:997-1005, 2004
8. Wyart P, Dumant D, Gourdier M, et al: Contribution of self-surveillance of the personnel by electronic radiation dosimeters in invasive cardiology. Arch Mal Coeur Vaiss 90:233-238, 1997
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9. Pages J. Effective dose and dose to the crystalline lens during angiographic procedures. JBR-BTR 83:108-110, 2000
10. Cooke DL, Stout CE, Kim WT, et al: Radiation dose reduction in intra-arterial chemotherapy infusion for intraocular retinoblastoma. J Neurointerv Surg doi: 10.1136/neurintsurg-2013-010905, 2014 (in press).
11. Connolly C, Racadio J, Towbin R. Practice of ALARA in the pediatric interventional suite. Pediatr Radiol 36 Suppl 2; 163-7, 2006
12. Schapiro A1, Racadio J, Kinnett D, et al: Combined C-arm fluoroscopy and C-arm cone beam computed tomography for the evaluation of patients with possible intrathecal baclofen delivery system malfunctions. Neurosurgery 69 (1 Suppl Operative): 27-33, 2011 13. Racadio JM, Babic D, Homan R, et al: Live 3D guidance in the interventional radiology suite. AJR Am J Roentgenol 189(6):W357-64, 2007
14. Brody AS, Frush DP, Huda W, et al: Radiation risk to children from computed tomography. Pediatrics 120: 677682, 2007
15. Brenner DJ, Hall EJ. Current concepts - Computed tomography- An increasing source of radiation exposure. N Engl J Med 357: 2277-2284, 2007
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16. Amis ES, Jr., Butler PF, Applegate KE, et al: American College of Radiology white paper on radiation dose in medicine. J Am Coll Radiol 4: 272-284, 2007
17. Johnson ND, Racadio JM. IR challenges in the MSK system. Pediatr Radiol 40(4): 474-7, 2010
18. Dekker LR, van der Voort PH, Simmers TA, et al: New image processing and noise reduction technology allows reduction of radiation exposure in complex electrophysiologic interventions while maintaining optimal image quality: a randomized clinical trial. Heart Rhythm 10(11):1678-82, 2013
19. Carrafiello G, Fontana F, Mangini M, et al: Initial experience with percutaneous biopsies of bone lesions using XperGuide cone-beam CT (CBCT): technical note. Radiol Med.117(8):1386-97, 2012
20. Kroes MW, Busser WM, Fütterer JJ, et al: Assessment of needle guidance devices for their potential to reduce fluoroscopy time and operator hand dose during C-arm cone-beam computed tomography-guided needle interventions. J Vasc Interv Radiol 24(6):901-6, 2013
21. Marien A, Gill I, Ukimura O, et al: Target ablation-Image-guided therapy in prostate cancer. Urol Oncol pii: S1078-1439(13)00456-0 2014 (in press).
22. Park MJ, Kim YS, Rhim H, et al: Safety and therapeutic efficacy of complete or near-complete ablation of symptomatic uterine fibroid tumors by MR imaging-guided high-intensity focused US therapy. J Vasc Interv Radiol 25(2):231-9, 2014
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23. Cooke DL, Levitt M, Kim LJ, et al: Intraorbital access using fluoroscopic flat panel detector CT navigation and three-dimensional MRI overlay. J Neurointerv Surg 2(3):249-51, 2010
24. Gupta A, Grünhagen T. Live MR angiographic roadmapping for uterine artery embolization: a feasibility study. J Vasc Interv Radiol 24(11):1690-7, 2013
25. Sadek M, Berland TL, Maldonado TS, et al: Use of preoperative magnetic resonance angiography and the Artis zeego fusion program to minimize contrast during endovascular repair of an iliac artery aneurysm. Ann Vasc Surg 28(1):261.e1-5, 2014
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Illustration Legends Fig. 1. Radiofrequency ablation. A: A sagittal cone beam CT scan demonstrates the radiofrequency trocar (arrow) in the center of the small painful tibial epiphyseal lesion. B: A sagittal reconstructed conventional CT image demonstrates improved spatial resolution of the same bony structures and of the subtle sclerotic epiphyseal bone lesion (arrow). C: Sagittal fat-saturated T1-weighted post contrast image better demonstrates the enhancing epiphyseal bone lesion (arrow) and was used as a roadmap during the ablation procedure. Fig. 2. Neonatal ultrasound-guided PICC placement. A: Patent common femoral vein (arrow) near the saphenous vein anastamosis which is accessed after tunneling from the medial thigh to reduce infection rate. B: Longitudinal ultrasound image through the liver demonstrates catheter tip (arrow) in the desired location of the intrahepatic IVC at the end of the procedure. Fig. 3. Ultrasound-guided AVM glue embolization. A: Left external carotid angiogram in the venous phase demonstrates a large draining vein superiorly (arrow) and several smaller draining veins. B: Transverse ultrasound image of the left face demonstrates a hyperechoic shadowing focus representing nBCA glue (arrow). C: Fluoroscopic image after the glue embolization demonstrates glue filling of the large draining vein (arrow) and reflux back into the AVM nidus. Fig. 4. Vascular malformation treatment of the left femur. Volumetric 3D fusion image of fat-saturated T2-weighted preprocedure MRI demonstrating malformation in white (arrow) overlaid on 3D CBCT image with treated lesion in red (blue arrowhead) with two separate access needles entering at near orthogonal angles. This fusion image changed management and lead to third access site which successfully treated the remainder of the lesion and saved an additional treatment for residual disease.
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