Is There A Link Between CT Scans And Higher Cancer Rates?

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     Physicians reportedly obtain over 60 million computed tomography (CT) scans each year in the United States. However, a recent study in the New England Journal of Medicine (NEJM) suggests that CT scans may be linked to an increased risk of radiation exposure and cancer.

     Citing evidence from epidemiologic studies, the authors of the NEJM article indicate that organ doses from a common CT study, consisting of two or three scans, may result in an increased risk of cancer.

      “As compared with plain film radiography, CT involves much higher doses of radiation, resulting in a marked increase in radiation exposure in the population,” note the authors of the NEJM review article.

     They concede that there are no currently published epidemiologic studies that look at cancer risks associated with CT scans. [3]However, the authors of the NEJM article note that “applying organ-specific cancer incidence or mortality data” from long-term follow-up studies of atomic bomb survivors allows estimates of the link between radiation exposure from CT scans and cancer risk.

     Citing reports from the literature, the authors of the NEJM review suggest that CT scans are overutilized and may be part of a defensive medicine approach. Robert Baron, DPM, echoes the study’s concern about defensive medicine.

      “Unfortunately, this has developed largely due to our litigious society,” says Dr. Baron, a Professor and Chairman of the Department of Radiology at William M. Scholl College of Podiatric Medicine at Rosalind Franklin University. “These exams are also ordered without much regard to the radiation exposure received by patients. Exposure can be minimized with proper workup and scanning limited to a very specific area.”

     Daniel Evans, DPM, says there is “no question” that ionizing radiation can lead to cell changes, which may precipitate the development of cancer. However, no longitudinal study has demonstrated a direct connection between CT exposure and the development of cancer, and he notes that the NEJM review extrapolated gamma radiation from Hiroshima and Nagasaki to other types of radiation such as X-ray. “The level and extent of the biological effects may vary,” says Dr. Evans.

     Dr. Evans, the Assistant Chairman of the Department of Radiology at the William M. Scholl College of Podiatric Medicine, also points out that the NEJM review looked at CT scans done on the abdomen and chest, which would give more ionizing radiation to internal organs, lymphatic tissue and gonadal tissue. There is no data specific to the lower extremity.

     Podiatrists most commonly use CT scans for conditions such as Lisfranc fractures, calcaneal fractures, coalitions, suspected osteomyelitis, Charcot neuroarthropathy and ankle fractures, according to Drs. Evans and Baron. Dr. Evans notes that podiatric scans are performed in areas that have a low incidence for the development of cancer. He says podiatric studies are rarely done repeatedly on the same patient, which minimizes the cumulative dosing to patients.

Reducing Radiation Risk And Addressing Patient Concerns

     How can physicians reduce the risks associated with radiation? Dr. Evans suggests DPMs not be cavalier when ordering CT scans and should exercise caution when scanning kids. Dr. Baron says advances in magnetic resonance imaging (MRI) are making that modality the gold standard for imaging various pathological conditions that were once the province of CT. He says the drawback to MRI remains the cost. Another option is ultrasound although the application is somewhat more limited, according to Dr. Baron.

     How can one address patient concerns about CT scans? Dr. Baron says he would explain the benefit/risk ratio but says he would not force the issue. Dr. Evans says one should take patient concerns seriously, informing patients there is a potential risk with any type of ionizing radiation.

      “It would be foolish to say there is not any danger,” says Dr. Evans.

How Does Obesity Alter Antimicrobial Dosage?

By Brian McCurdy, Senior Editor

     Obesity can lead to a range of health complications in patients. Can obesity also complicate the dosing of antimicrobials? A recent review in Pharmacotherapy explores the impact of obesity on appropriate dosing of antimicrobial therapies.

     As the review notes, the physiologic changes of obesity can change both the volume of distribution and clearance of various commonly used antimicrobials. According to the authors of the Pharmacotherapy article, such physiologic changes can pose challenges such as the estimation of creatinine clearance to predict drug clearance. [4]

     The review suggests that physicians dose vancomycin and aminoglycosides on total body weight and adjusted body weight respectively. Fluoroquinolones are variably altered by obesity, according to the article authors. They add that drugs such as quinupristin-dalfopristin, linezolid (Zyvox, Pfizer) and daptomycin (Cubicin, Cubist), which have activity against gram-positive organisms, may also be altered in obese patients. However, the authors of the review say more research is needed to determine dosing recommendations.

What You Should Know About Dosing Obese Patients

     Javier LaFontaine, DPM, has not altered antibiotic dosages when treating foot infections in obese patients, saying he initially addresses severe foot infections surgically. However, he says many of the patients with diabetes he sees may be dosed differently since many obese patients have diabetes and their renal problems may be apparent. [5]Vancomycin is the most common antibiotic to be dosed differently, according to Dr. LaFontaine, the Podiatry Residency Director at the University of Texas Health Science Center at San Antonio.

     Chad Friedman, DPM, does change antibiotic dosages for his obese patients. He most often changes dosing for beta lactam antibiotics and cephalosporins such as amoxicillin clavulanate (Augmentin, GlaxoSmithKline), amoxicillin, ampicillin, cephalexin (Keflex, MiddleBrook Pharmaceuticals), cefadroxil (Duricef) and cefdinir (Omnicef, Medicis). He also changes dosages for ciprofloxacin (Cipro, Bayer) and vancomycin.

     When choosing antibiotics, Dr. Friedman says one should consider the patient’s ideal body weight (IBW) and total body weight (TBW). For example, he cites literature that shows the following dosage formula for beta lactams: the adjusted body weight = IBW + 0.3 (TBW-IBW), which would calculate the new dosing weight. In addition, one should take into account the patient’s creatinine clearance although he says this is not always present when prescribing antibiotics. Some obese patients have increased creatinine clearance levels that can lead to inaccurate equations, according to Dr. Friedman, who is in private practice in Ocean and Monmouth Counties, N.J.

     Dr. LaFontaine notes the importance of understanding the drug’s pharmacokinetics. He adjusts dosages when it comes to treating neuropathy in obese patients.

What About Future Research?

     Dr. LaFontaine suggests future research concentrating on the response of any lipophilic drugs. In the case of morbidly obese patients, Dr. Friedman says it can be very difficult to dose them. He advocates having more data on them and studying the levels of absorption and distribution of particular drugs in this patient population.

      “Since it is not an exact science, it seems that a lot of the dosage recommendations will need to be based on equations, and the only way to have significance of these equations is to have more people and studies involved,” says Dr. Friedman.

Study Examines Test For Diabetic Ulcer Risk

By Brian McCurdy, Senior Editor

     While there are a variety of screening methods to help identify those at risk for diabetic complications, a new modality may aid physicians in detecting systemic microcirculatory changes that signal a greater risk of diabetic complications.

     In a recent abstract presentation at the American Heart Association conference, researchers assessed the potential impact of hyperspectral technology cutaneous oxygenation monitoring (HTcOM). Using interim data from an ongoing study by the National Institutes of Health (NIH) and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), the study authors evaluated 162 diabetic patients with HTcOM.
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     In using this technology, researchers found that patients with diabetic foot ulcers had lower oxyhemoglobin (HT-Oxy) in their forearms and palms than those without ulcers, according to the abstract.

      “(Patients) with poorer systemic microcirculation as manifested by lower HTcOM readings on the forearm were significantly more likely to have or develop a foot ulcer than other (patients) considered at high risk by standard clinical assessment,” point out the authors in the abstract.

     Abstract co-author Aristidis Veves, MD, DSc, cites the HTcOM’s simplicity, noting it is not time consuming and there is minimal training necessary to analyze the images.

     HTcOM can potentially identify patients at risk of ulceration and at risk of failing to heal their ulcer, says Dr. Veves, an Associate Professor at Harvard Medical School. He notes that more research regarding the test’s sensitivity and specificity will be required.

Clarification

Two of the photos for the feature, “Do Prefab Orthoses Have A Place In Treating Plantar Fasciitis?,” in the November issue were inadvertently misrepresented during the editing process. The photo on Page 67 is not a representation of a prefabricated orthoses used to reduce sports medicine injuries. The photo on page 72 is not a Root type orthosis nor is it a device that has become a standard in the world of custom orthoses. We regret the errors.

In Brief

     * Ceftobiprole, a broad-spectrum cephalosporin, has demonstrated activity against pathogens including methicillin-resistant Staphylococcus aureus (MRSA), according to a poster recently presented at the 47th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy.

     In assessing 1,271 patients from two phase III multicenter trials, researchers found that ceftobiprole’s potency against Enterobacteriaceae and P. aeruginosa was comparable to cefepime (Maxipime). Furthermore, ceftobiprole reportedly inhibited 100 percent of the staphylococcal isolates, including MRSA isolates, at £ 4 Ìg/ml, according to the poster presentation.

     * John S. Steinberg, DPM, recently received a Distinguished Alumni Award from Barry University. Dr. Steinberg is an Assistant Professor at Georgetown University Medical Center.