Surgery for Obesity and Related Diseases 11 (2015) 308–312
Original article
Roux-en-Y gastric bypass is associated with an increased exposure to ionizing radiation Peter Nau, M.D., M.S.a,*, George Molina, M.D.b, Aran Shima, M.D.b, Abujudeh Hani, M.D.b, Ozanan Meireles, M.D.b a
The University of Iowa Hospitals and Clinics, Iowa City, Iowa b Massachusetts General Hospital, Boston, Massachusetts Received June 4, 2014; accepted July 16, 2014
Abstract
Background: Bariatric surgery provides for a reliable and sustainable solution to the obesity epidemic. The gold standard bariatric surgical procedure is the Roux-en-Y gastric bypass (RYGB). Assessment of this population preoperatively and work-up of postoperative complications often includes radiographic evaluation. Repeated exposure to radiation is not without complication. Objective: Assess the association between the RYGB and exposure to ionizing radiation. Setting: Academic medical center. Methods: Patients were identified by their ICD-9 code as having had a RYGB at the Massachusetts General Hospital (MGH) from 2002 to 2012. The number of abdominal and pelvis (A/P) computed tomography (CT) scans performed was determined and converted into an effective dose (ED) and expressed as milliSeiverts (mSv) to illustrate the biologic effects of radiation. Results: From 2002 to 2012, 1789 primary laparoscopic RYGBs were completed. Fifty-five revisional operations were completed on 51 patients. Of these, 38 had both their index and second operation at the MGH. A total of 1065 A/P CTs were completed in the laparoscopic RYGB population (mean ¼ .6), and 106 A/P CTs were done in the revisional surgery cohort (mean ¼ 2.8). The mean ED of radiation was 56.1 mSv and 19.5 mSv for the index and revisional populations, respectively. Conclusions: This study demonstrated the significant cumulative radiation exposure attributable to A/P CTs. This exposes the patient to a potential increased risk of malignancy as well as imposing a financial burden on the healthcare system. The findings of this study raise the awareness of an increased risk of radiation exposure for this population and the necessity of creation of a dedicated algorithm for the mindful utilization of CT imaging. (Surg Obes Relat Dis 2015;11:308–312.) r 2015 American Society for Metabolic and Bariatric Surgery. All rights reserved.
Keywords:
Roux-en-Y gastric bypass; Ionizing radiation; Weight loss surgery; Radiation exposure
According to the National Center for Health Services, more than 78 million Americans above the age of 20 are obese [1]. Obesity and the attendant metabolic syndrome are associated with an increased prevalence of medical comorbidities and mortality rates [2,3]. Nonsurgical attempts *
Correspondence: Peter Nau, M.D., 200 Hawkins Drive, Iowa City, Iowa 52242-1086. E-mail:
[email protected] at weight loss are limited by a lack of durability and clinically significant outcomes [4,5]. Conversely, bariatric surgery provides for a reliable and sustainable solution to this important public health problem [4–7]. The current gold standard bariatric surgical procedure is the laparoscopic Roux-en-Y gastric bypass (RYGB). On average, this operation produces 470% excess weight loss at 3 years with an associated decrease in medical comorbidities [4–11]. Preoperative evaluation of this
http://dx.doi.org/10.1016/j.soard.2014.07.022 1550-7289/r 2015 American Society for Metabolic and Bariatric Surgery. All rights reserved.
Bariatric Surgery and Radiation Exposure / Surgery for Obesity and Related Diseases 11 (2015) 308–312
population is often insensitive to identify pathology due to the patient’s body habitus. What’s more, postoperatively the RYGB generates potential sites for internal hernia formation, occurring in .8%—9% of cases [12–18]. The herniation of small bowel through these mesenteric defects may lead to disastrous outcomes including long segments of strangulated intestine, short bowel syndrome necessitating a reliance on total parenteral nutrition, and even multiorgan failure and death [19,20]. Early diagnosis of this potentially devastating condition is key to achievement of positive patient outcomes. A confounding factor in the diagnosis of this complication for this population is the patient’s body habitus, vague symptomatology, and the inability to reproduce a specific and reliable physical exam. It is for this reason that, in the event that a patient who is status post-RYGB presents to the emergency department with abdominal pain, CT scans are ordered as the diagnostic test of choice to elucidate the etiology of the pain [20,21]. Furthermore, evaluation for other concerning symptoms also often will include radiographic assessment. The repeated exposure to diagnostic radiation is not without its complications, including the potential for the development of malignancy [22–26]. Herein is a discussion of patients presenting to a tertiary referral center with a past surgical history of RYGB investigating their cumulative exposure to radiation attributed to the number of A/P CT scans performed. Methods Patients enrolled in this study were identified by their ICD-9 code as having had a RYGB at the Massachusetts General Hospital (MGH) from the period of 2002 to 2012. Next, a search of the Render database was performed. Render is an online radiographic study repository that allows for investigation of tests performed at the MGH. For this study, the number of A/P CT scans performed for any reason in those patients who had undergone a laparoscopic RYGB or re-operative procedure at the MGH was assessed. Keywords used for this search included “Roux-enY gastric bypass” and the years 2002–2012. In the case of a surgical revision for which the patient did not have his or her index operation at the MGH, the patient was excluded from the data analysis. This was done in an effort to limit the uncertainty about the number of scans performed before their referral. Further, the patient record was excluded from analysis in the event that the gastric bypass did not occur in the setting of a weight loss operation. In addition to the number of scans completed, the dose-length product (DLP) was recorded. The availability of this data point was not uniform due to changes in reporting and imported CT scans over the study period. To calculate the amount of radiation to which each patient was exposed, a generic method for estimation of the ED as defined by the European Commission in 2000 was used [27].
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The most accurate technique for estimation of radiation exposure is based on the Monte Carlo simulations. In this methodology, the simulations account for scan variables, including scanner geometry, tube potential, and CT dose index. When combined with information provided by the IMPACT Group, the ED can be determined based on the different model of CT scanner being used. Using this formula, the ED is derived in relation to different organs. Because of the limitation that many of the scans were performed at outside facilities and scanner information was not consistently available, this technique was not workable. Conversely, the protocol provided with the European Commission provides a radiation dosage based on anatomic regions (i.e., head, neck, abdomen, and/or pelvis). This is necessarily an estimate that represents the biological risk to which the patient is exposed; therefore, it is not dependent on the individual scanner used. To do this, the volume CT dose index (CTDIvol) was calculated. The CTDIvol, which is measured in milligray, quantifies the relative intensity of the radiation that is exacted on the patient. The total amount of radiation delivered to the patient at a given examination is dependent on this CTDIvol and the CT scan length. It is the standard that these 2 values are given in each CT report. It should be noted that this may underestimate the overall radiation exposure due to the irradiated length commonly including more than the prescribed radiation window [28]. The product of these 2 numbers is the DLP. Different tissues and organs have varying degrees of sensitivity to radiation. To ascertain how this radiation exposure affects tissue health, the DLP is multiplied by a factor related to the risk for a particular tissue or organ (Table 1). This multiplication provides the effective dose (ED) absorbed by the body. The unit for the ED is the milliSievert (mSv) and can be used to assess the potential for long-term effects of repeated radiation exposure. Data analysis was completed using SPSS 16.0 (IBM, Armonk, New York). Student’s t tests were used and statistical significance was set with a P value of .05. Permission from the MGH Institutional Review Board was obtained before beginning the study. Results In the 11-year period from 2002 to 2012, there were 2188 metabolic procedures performed on 2150 patients. A total of Table 1 Conversion factors to characterize the effect of radiation on different areas of the body—the effective dose (milliSeivert) Region of the body
Dose-length product conversion factor
Head Neck Chest Abdomen Pelvis
.0023 .0054 .017 .015 .019
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P. Nau et al. / Surgery for Obesity and Related Diseases 11 (2015) 308–312
1789 primary laparoscopic and 344 open RYGB were completed. Most open operations were completed between 2002 and 2005 (304). Fifty-five revisional operations were completed on 51 patients. An average of 161.8 laparoscopic RYGB were performed each year. This number peaked in 2009 at 246 procedures and has declined since that time. This decreasing trend correlates with a growth in the number of vertical sleeve gastrectomies performed at the MGH. A total of 1065 A/P CT scans were performed on the 1789 people who had their operation completed laparoscopically. The number of people who had CT scans was 398 or 22% of patients undergoing RYGB. The mean number of scans performed for the entire group was .6. The mean number of scans for those who underwent radiographic evaluation was 2.7. The DLP data were available on 575 of the scans performed (54%). The average DLP per completed A/P CT was 3298.4. This was equivalent to an ED of 56.1 milliSeiverts. The mean milliSeiverts for the entire cohort and for only those who had a scanned performed was 33.7 and 151.5, respectively. Of these 55 revisions performed over this time period, 38 patients underwent both the initial and follow-up operations at the MGH. Seventeen patients in this group underwent A/ P CT scans (45%). The mean number of scans performed for the entire cohort was 2.8. When considering only those who had a scan, the average was 6.23. The DLP data was available in 57 of the cases (54%). The mean DLP and ED were 1147 and 19.5 milliSeiverts, respectively. The mean ED to which the patients were exposed as a group was 54.6 milliSeiverts. When considering only those who had imaging studies, the mean ED was 121.5. Discussion Obesity has become a problem of epidemic proportions, not just in the United States, but globally. As recently as 2008, an estimated 1.5 billion people were considered to be either overweight or obese. This number is conservatively predicted to balloon to 3.38 billion by the year 2030 [29]. What’s more, this problem is not limited to just the adult population. The rate of obesity is documented to be increasing in populations as young as preschool age children [30–32]. It is also clear that medical attempts to manage this pandemic are often unsuccessful due to recidivism or failure to lose clinically significant amounts of weight. A recent study published in the New England Journal of Medicine reported that surgical attempts at weight loss were more successful than medical attempts (29.4 ⫾ 9.0 kg versus 5.4 ⫾ 8.0 kg, P o .001) [5]. Furthermore, this population was significantly more likely to decrease the use of medications to lower blood pressure, glucose, and lipid levels. Perhaps most importantly, a Swedish study noted that the weight loss after bariatric surgery provided for
long-lasting weight loss with an associated decrease in overall mortality [9]. A critical evaluation of the available evidence supports the use of weight loss surgery as a first line treatment for the morbidly obese. Notwithstanding the success of this therapeutic modality, there are potential negative sequelae related to the altered anatomy. This includes, but is not limited to, marginal ulcer formation, dumping syndrome, and intussusception of the small intestine at the jejunojejunostomy. Perhaps the most feared complication, however, is the internal hernia and associated potential for strangulation of the involved small intestine. There are 3 sites for internal hernia formation with the RYGB including the mesenteric, mesocolic, and Peterson’s defects [33]. The routine closure of these sites with a running, nonabsorbable stich decreases the risk of hernia occurrence [13,17]. However, as the patient loses weight and visceral fat decreases, the sites may re-open. Risk factors for this complication include the laparoscopic approach, a retrocolic roux limb, the orientation of the roux limb, and extreme weight loss [16,34]. This condition is complicated by the difficulty in diagnosing the finding. Pain may be severe and unrelenting with an impending intraabdominal catastrophe, or chronic and intermittent due to transient incarceration. The time frame for presentation may be as early as postoperative day 1 or 43 years after the initial operation, further complicating the diagnosis. Given the vague and inconsistent presentation of this complication, radiographic evaluation of this population is used more liberally. The foundation of this workup is the CT scan of the abdomen and pelvis, but also may include the upper GI series. CT evidence of an internal hernia includes loops of small bowel in the left upper quadrant, evidence of small bowel mesentery traversing colonic mesentery, and a swirl of the mesentery seen when the herniated segment of small intestine twists along its axis [18]. Unfortunately, radiographic assessment for evidence of internal hernias is not reliably sensitive, with false negatives in up to 20% of cases [12]. Notwithstanding this deficiency, radiographic assessment remains an important tool in the workup of this population due to the importance of early identification of this complication. The number of CT scans performed in the United States increased from approximately 3 million in 1980 to almost 70 million by 2007. This is a significant financial burden for the economy and healthcare system. Further, this has important health implications for the patient. The risk of cancer related to ionizing radiation is associated with the organ in question and the cumulative dose of radiation. Colon and lung cancers account for most radiation-induced malignancies [35]. It is estimated that as many as 2% of cancers and 1% of cancer mortalities may be attributed to the radiation from CT imaging [36]. In a multi-institutional study, it was determined that the median effective dose attributed to a A/P CT scan was associated with a median adjusted lifetime attributable risk (LAR) of 4 cancers per
Bariatric Surgery and Radiation Exposure / Surgery for Obesity and Related Diseases 11 (2015) 308–312
1000 patients. Put another way, as few as 470 patients would need to undergo a routine CT A/P with intravenous contrast to produce one radiation-induced cancer [24]. There is very little data in the literature describing the degree of radiation to which the bariatric population is exposed. The only study published to date is a retrospective assessment of the cumulative radiation doses to which a group of 100 patients who underwent RYGB and 100 patients who had adjustable bands placed were exposed. In this manuscript, the authors noted that the levels of radiation to which this group was exposed resulted in an increased lifetime risk of developing a radiation-related malignancy [23]. Although the amount of radiation a patient is exposed to and the risk of a secondary malignancy varies based on the patient, organ system, and type of imaging study, there is no question that the radiation to which individuals are exposed to with A/P CTs places them at a very real risk of developing cancer. In this current study, the cumulative radiation exposure attributable to the A/P CT scans was assessed. The query was limited to this test because this imaging study is uniquely indicated in this population. Further, the nature of the disease and patient characteristics often result in the transfer and treatment of the patients at the MGH before an extensive workup. Because of the retrospective nature of this study, it is impossible to accurately collect data on radiographic studies that were ordered outside of the facilities affiliated with the MGH. Therefore, to expand the search to CT scans protocoled for other areas of the body or other radiographic tests would necessarily lack sensitivity and miss an unacceptable number of evaluations. In this group of patients, 1065 A/P CT scans were ordered on the 1789 individuals who underwent RYGB at the MGH. These studies were completed in only 22% of that group. In other words, whereas the number of scans performed per patient was .6, the actual number to which the patient would be exposed to after having the first scan was almost 3 CTs. Extrapolating the radiation data, the mean level of ionizing radiation to which a RYGB patient is exposed is 33.7 Sieverts. When considering only those who had scans, the dose of radiation to which they were exposed was 151.5 Sieverts. In the event that a patient needed a revisional procedure, the mean number of A/P CTs to which the group was exposed was 2.8. If taking into account only those who had scans, that number increases to 6.23. The mean ED for these 2 populations is 54.6 and 121.5 milliSeiverts. This is significant when considering the fact that a risk of cancer was seen with survivors of nuclear events when exposed to as little as 35 Sieverts [31]. Moreover, these data do not include other tests that many RYGB patients undergo such as upper gastrointestinal series, which expose the stomach to as much as 9.3 Sieverts per exam. There are several limitations to this study. The immediately obvious deficiency is the fact that the study only
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accounts for the radiation associated with an A/P CT. Given that this is a tertiary referral hospital in an urban center, many patients do not seek out the MGH as their initial care provider; therefore, attempts to collect and evaluate data related to other scans would appreciably underestimate the true incidence. Another weakness of this work is that the number of scans for which the radiation data was available was low at only 54%. This is certainly a multifactorial issue, but likely is related to the fact that many of the scans were uploaded to the system from outside facilities, limiting the technical data related to the completion of the scan. Lastly, because this is a retrospective chart review, there is no question that this represents an incomplete data sample. However, this does not minimize the importance of the findings that almost a quarter of the individuals who have a RYGB are exposed to levels of radiation that place them at a significant increased risk for the development of secondary malignancies over the course of their life. Conclusions Obesity is an important public health issue in which attendant co-morbidities permeate much of the healthcare that is delivered worldwide. The preponderance of data agrees that addressing this disease surgically provides for the most durable and clinically meaningful outcomes. The RYGB is still the gold standard surgery for obesity. It is associated with its own set of complications, including the potential for internal hernias. This study has shown that the cumulative exposure to ionizing radiation attributable to A/ P CTs performed for the workup of intra-abdominal pathology is significant. This places this population at a very real increased risk for malignancy, and imposes a financial burden on the healthcare system. This highlights the need for further study into the risk of malignancy development, as well as the creation of a dedicated algorithm for managing these patients, including the responsible use of CT imaging. Disclosures The authors have no commercial associations that might be a conflict of interest in relation to this article. References [1] Ogden CL, Carroll MD, Kit BK, Flegal KM. Prevalence of Obesity in the United States, 2009–2010. NCHS Data Brief. No 82. January 2012. [2] Adams KF, Leitzmann MF, Ballard-Barbash R, et al. Body mass and weight change in adults in relation to mortality risk. Am J Epidemiol 2014;179:135–44. [3] Jeffreys M, McCarron P, Gunnell D, et al. Body mass index in early and mid-adulthood, and subsequent mortality: a historical cohort study. Int J Obes Relat Metab Disord 2003;27:1391–7. [4] Picot J, Jones J, Colquitt JL, et al. The clinical effectiveness and costeffectiveness of bariatric (weight loss) surgery for obesity: a
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