CT Radiation Exposure in Obese Patients Needs Further Evaluation

A group of US researchers has quantified the amount of radiation obese patients receive when undergoing routine medical scans. Their findings revealed that, when undergoing a computed tomography (CT) scan, a forced change of operation parameters for obese patients results in an increase of up to 62% in organ radiation exposure compared to lower weight patients.

Findings published April 5, 2012, in the journal Physics in Medicine & Biology. The researchers, from Rensselaer Polytechnic Institute (Rochester, NY, USA), hope this new study will help optimize CT scanning procedures to generate safe but effective medical images. Lead author of the study, Dr. Aiping Ding, said, “When a morbidly obese patient undergoes a CT scan, something known as the tube potential needs to be increased to make sure there are enough X-ray photons passing through the body to form a good image. So far, such optimization has been done by trial and error without the use of patient-specific quantitative analysis.”

When the researchers simulate the increase, the calculated doses of radiation reaching an obese patient’s organs increase by 62% in males and 59% in females. Their preliminary findings confirmed why the tube potential is frequently increased: a scan of the chest, abdomen, and pelvic area of obese patients, without adjusting the tube potential, revealed that organs deep within the abdomen received 59% less radiation compared to normal weight patients, due to the excess fat tissues.

Such a reduced dose could negatively affect the image quality unless the tube potential and tube current are adjusted accordingly. Results were obtained by creating 10 (5 male, 5 female) computerized phantoms with a body mass index (BMI) ranging from 23.5 kg/m2 (normal weight) to 46.4 kg/m2 (morbidly obese)--such a detailed model of obese patients has not been used before.

Phantoms are specifically designed physical or simulated objects that can be experimented with in the field of medical imaging for evaluating, analyzing, and refining the performance of various devices. This study used computer-simulated deformable phantoms that were put through a CT scanning computer model to calculate the dose of radiation exposed to each one.

The phantoms were unique in that they not only accounted for a large number of organs, but also modeled two types of fat: the subcutaneous adipose tissue (SAT) under the skin and the visceral adipose tissue (VAT) that lies deeper in the body and sits around the organs. This provided the researchers with a more precise determination about the amounts of radiation reaching different organs.

The prevalence of overweight and obese individuals has increased markedly over the past 20 years; a recent survey suggests that nearly 60% of the adult American population can be diagnosed as being clinically overweight or obese.

Given this disturbing trend and the health risks associated with obesity, it is no surprise that an increasing number of overweight or obese individuals are entering radiology clinics. “We hope that this very timely set of data will be integrated with previous work for normal size adult and child patients to form a comprehensive database to support a software package called VirtualDose that will enter clinical testing this summer. Such a tool could be used to analyze radiation exposure trends in a clinic and to study how to optimize the image quality for a large population of patients,” said Prof. X George Xu, the senior corresponding author of the study.

These new phantoms for overweight and obese patients will be part of a forthcoming software package, VirtualDose, developed by Prof. Xu and his team. VirtualDose’s objective is to enable the creation of a personalized, extremely realistic phantom of any patient undergoing a CT scan. The program takes into consideration a patient’s individual characteristics, including age, sex, height, weight, and even if a woman is pregnant. By entering these data into the software, VirtualDose quickly creates a phantom that accurately models the patient’s internal organs. These phantoms will allow physicians and researchers to compare the radiation doses a patient will get from different CT scanner settings, and then choose the most appropriate configuration.

VirtualDose will also enable physicians to keep a highly accurate record of how much radiation patients are exposed to over their lifetime. California recently became the first state in the United States to require radiation dose records for patients undergoing CT examinations.

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Rensselaer Polytechnic Institute