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Re: Bilateral versus Unilateral Femoral Access for Uterine Artery Embolization—Results of a Randomized Comparative Trial
Letters to the Editor
Re: Bilateral versus Unilateral Femoral Access for Uterine Artery Embolization—Results of a Randomized Comparative Trial From: Donald L. Miller, MD Department of Radiology National Naval Medical Center 8901 Wisconsin Ave. Bethesda, MD 20889-5601; and Department of Radiology and Radiological Sciences F. Edward Hébert School of Medicine Uniformed Services University Bethesda, Maryland Editor: I read with interest the article by Costantino et al (1) regarding bilateral versus unilateral femoral access for uterine artery embolization. The authors are to be congratulated for the careful design and conduct of this randomized controlled trial. Unfortunately, their analysis of patient radiation dose places inappropriate emphasis on fluoroscopy time and inadequate emphasis on kerma–area product (KAP; referred to by the authors as dose–area product). Fluoroscopy time is measured in units of time, not dose, and does not incorporate the effects of fluoroscopy dose rate or dose from angiography images. Fluoroscopy time is not recommended for monitoring patient radiation dose during procedures such as embolization or for documenting radiation dose from these procedures (2,3). KAP is the integral of air kerma across the entire x-ray beam emitted from the x-ray tube. It is a surrogate measurement for the entire amount of energy delivered to the patient by the beam (2). It is commonly used as a proxy for the risk of stochastic effects (4,5). It is a more appropriate measure of patient radiation dose than fluoroscopy time. The authors demonstrated significant differences in fluoroscopy time and number of angiographic images between the unilateral and bilateral access techniques, but no difference in KAP. How is this possible? It is difficult to be certain without observing the operators performing procedures of each type, but I can offer a likely explanation. KAP is the product of the air kerma (without backscatter) at the radiation field and the area of the radiation field. Decreasing the size of the radiation field by 50% will decrease KAP by 50% if all other factors are unchanged. The authors are experienced interventional radiologists, and aware of the importance of collimation. I suspect that, when the bilateral access technique was used, the radiation field was coned to include both uterine arteries, but when the unilateral access technique was used, each radiation field was coned to half that size to limit the field to one uterine artery. Thus, imaging
The views expressed in this article are those of the author and do not necessarily reflect the official policy or position of the Navy, the Department of Defense, the National Cancer Institute, the Department of Health and Human Services or the United States Government. The author has not identified a conflict of interest. DOI: 10.1016/j.jvir.2010.07.015
each uterine artery separately would yield approximately the same KAP as imaging both uterine arteries together. The important point is that KAP is the appropriate metric for estimating the risk of stochastic effects. Fluoroscopy time and the number of angiographic images are not appropriate metrics. Because Costantino et al (1) were not able to demonstrate a difference in KAP between the two methods they investigated, they did not demonstrate a difference in stochastic risk. The data on fluoroscopy time and number of angiographic images are irrelevant in this regard. Regardless of the relative merits of the unilateral and bilateral techniques, Costantino et al (1) are to be commended for their attention to the importance of optimizing patient radiation dose. Their patients received a mean dose of 130 or 162 Gy·cm2, depending on the technique used, approximately half that of the mean KAP of 298 Gy·cm2 for typical procedures earlier this decade (6). (Note that there appears to be a misprint in table 2 of this publication (1)— the Axiom Artis fluoroscope [Siemens, Erlangen, Germany] displays KAP in units of Gy·m2, not Gy/cm2.) References 1. Costantino M, Lee J, McCullough M, Nsouli-Maktabi H, Spies JB. Bilateral versus unilateral femoral access for uterine artery embolization: results of a randomized comparative trial. J Vasc Interv Radiol 2010; 21:829 – 835. 2. Stecker MS, Balter S, Towbin RB, et al. Guidelines for patient radiation dose management. J Vasc Interv Radiol 2009; 20(suppl): S263–S273. 3. Miller DL, Balter S, Wagner LK, et al. Quality improvement guidelines for recording patient radiation dose in the medical record. J Vasc Interv Radiol 2004; 15:423– 429. 4. Tsapaki V, Ahmed NA, AlSuwaidi JS, et al. Radiation exposure to patients during interventional procedures in 20 countries: initial IAEA project results. AJR Am J Roentgenol 2009; 193:559 – 569. 5. Vano E, Sanchez R, Fernandez JM, et al. Patient dose reference levels for interventional radiology: a national approach. Cardiovasc Intervent Radiol 2009; 32:19 –24. 6. Miller DL, Balter S, Cole PE, et al. Radiation doses in interventional radiology procedures: The RAD-IR study: part I. Overall measures of dose. J Vasc Interv Radiol 2003; 14:711–727.
Drs. Constantino et al respond: We appreciate Dr. Miller’s interest in our research and his very insightful comments. We would agree with many of the points made by Dr. Miller and provide the following additional thoughts. We agree that the kerma-area product is a better measure of patient radiation dose than fluoroscopy time. However, the kerma-area product is heavily influenced by patient body habitus and the anatomy of any individual’s uterus and pelvis, and it varies tremendously based on these factors alone. The impact of this variability on radiation dose is difficult to estimate in individual patients and makes its use in a power analysis difficult. Therefore, we chose to use
None of the authors have identified a conflict of interest. DOI: 10.1016/j.jvir.2010.07.014
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Re: Bilateral versus Unilateral Femoral Access for Uterine Artery Embolization—Results of a Randomized Comparative Trial From: Donald L. Miller, MD Department of Radiology National Naval Medical Center 8901 Wisconsin Ave. Bethesda, MD 20889-5601; and Department of Radiology and Radiological Sciences F. Edward Hébert School of Medicine Uniformed Services University Bethesda, Maryland Editor: I read with interest the article by Costantino et al (1) regarding bilateral versus unilateral femoral access for uterine artery embolization. The authors are to be congratulated for the careful design and conduct of this randomized controlled trial. Unfortunately, their analysis of patient radiation dose places inappropriate emphasis on fluoroscopy time and inadequate emphasis on kerma–area product (KAP; referred to by the authors as dose–area product). Fluoroscopy time is measured in units of time, not dose, and does not incorporate the effects of fluoroscopy dose rate or dose from angiography images. Fluoroscopy time is not recommended for monitoring patient radiation dose during procedures such as embolization or for documenting radiation dose from these procedures (2,3). KAP is the integral of air kerma across the entire x-ray beam emitted from the x-ray tube. It is a surrogate measurement for the entire amount of energy delivered to the patient by the beam (2). It is commonly used as a proxy for the risk of stochastic effects (4,5). It is a more appropriate measure of patient radiation dose than fluoroscopy time. The authors demonstrated significant differences in fluoroscopy time and number of angiographic images between the unilateral and bilateral access techniques, but no difference in KAP. How is this possible? It is difficult to be certain without observing the operators performing procedures of each type, but I can offer a likely explanation. KAP is the product of the air kerma (without backscatter) at the radiation field and the area of the radiation field. Decreasing the size of the radiation field by 50% will decrease KAP by 50% if all other factors are unchanged. The authors are experienced interventional radiologists, and aware of the importance of collimation. I suspect that, when the bilateral access technique was used, the radiation field was coned to include both uterine arteries, but when the unilateral access technique was used, each radiation field was coned to half that size to limit the field to one uterine artery. Thus, imaging
The views expressed in this article are those of the author and do not necessarily reflect the official policy or position of the Navy, the Department of Defense, the National Cancer Institute, the Department of Health and Human Services or the United States Government. The author has not identified a conflict of interest. DOI: 10.1016/j.jvir.2010.07.015
each uterine artery separately would yield approximately the same KAP as imaging both uterine arteries together. The important point is that KAP is the appropriate metric for estimating the risk of stochastic effects. Fluoroscopy time and the number of angiographic images are not appropriate metrics. Because Costantino et al (1) were not able to demonstrate a difference in KAP between the two methods they investigated, they did not demonstrate a difference in stochastic risk. The data on fluoroscopy time and number of angiographic images are irrelevant in this regard. Regardless of the relative merits of the unilateral and bilateral techniques, Costantino et al (1) are to be commended for their attention to the importance of optimizing patient radiation dose. Their patients received a mean dose of 130 or 162 Gy·cm2, depending on the technique used, approximately half that of the mean KAP of 298 Gy·cm2 for typical procedures earlier this decade (6). (Note that there appears to be a misprint in table 2 of this publication (1)— the Axiom Artis fluoroscope [Siemens, Erlangen, Germany] displays KAP in units of Gy·m2, not Gy/cm2.) References 1. Costantino M, Lee J, McCullough M, Nsouli-Maktabi H, Spies JB. Bilateral versus unilateral femoral access for uterine artery embolization: results of a randomized comparative trial. J Vasc Interv Radiol 2010; 21:829 – 835. 2. Stecker MS, Balter S, Towbin RB, et al. Guidelines for patient radiation dose management. J Vasc Interv Radiol 2009; 20(suppl): S263–S273. 3. Miller DL, Balter S, Wagner LK, et al. Quality improvement guidelines for recording patient radiation dose in the medical record. J Vasc Interv Radiol 2004; 15:423– 429. 4. Tsapaki V, Ahmed NA, AlSuwaidi JS, et al. Radiation exposure to patients during interventional procedures in 20 countries: initial IAEA project results. AJR Am J Roentgenol 2009; 193:559 – 569. 5. Vano E, Sanchez R, Fernandez JM, et al. Patient dose reference levels for interventional radiology: a national approach. Cardiovasc Intervent Radiol 2009; 32:19 –24. 6. Miller DL, Balter S, Cole PE, et al. Radiation doses in interventional radiology procedures: The RAD-IR study: part I. Overall measures of dose. J Vasc Interv Radiol 2003; 14:711–727.
Drs. Constantino et al respond: We appreciate Dr. Miller’s interest in our research and his very insightful comments. We would agree with many of the points made by Dr. Miller and provide the following additional thoughts. We agree that the kerma-area product is a better measure of patient radiation dose than fluoroscopy time. However, the kerma-area product is heavily influenced by patient body habitus and the anatomy of any individual’s uterus and pelvis, and it varies tremendously based on these factors alone. The impact of this variability on radiation dose is difficult to estimate in individual patients and makes its use in a power analysis difficult. Therefore, we chose to use
None of the authors have identified a conflict of interest. DOI: 10.1016/j.jvir.2010.07.014
1773