Patient orientation may reduce x-ray radiation for the obese
Effective doses from radiographic exams in the extremely obese can exceed 100 mSv from only a small number of abdominal exams and should be minimized to the extent possible and monitored, according to study published online April 29 in Radiology.
Jacquelyn C. Yanch, PhD, from the department of nuclear science and engineering at the Massachusetts Institute of Technology in Cambridge, Mass., and colleagues sought to estimate the increase in effective radiation dose from diagnostic x-rays for overweight and obese adult patients, as compared with the effective dose for lean reference phantoms.
The researchers calculated the relative effective radiation doses (E/E0) for the acquisition of chest and abdominal radiographs by using Monte Carlo computer simulations of effective doses delivered to adult phantoms with (E) and without (E0) subcutaneous adipose tissue added to the torso for five fat distributions. Total (anterior plus posterior) fat thicknesses ranged from 0 to 38 cm.
The investigators found that for 30 cm of additional fat, E/E0 values for 120-kVp chest and 80-kVp abdomen radiographs ranged from approximately two to 31 and two to 83 for male patients, respectively, and from two to 45 and two to 76 for female patients, respectively, depending on the type of fat distribution and patient orientation in the x-ray beam.
However, Yanch and colleagues reported that orienting the patient such that the thinnest fat layer was facing away from the x-ray tube minimized E/E0. They also found that reductions in E/E0 reached 14 percent and 20 percent for the thickest phantoms when x-ray tube voltages were increased by 10 and 20 kVp, respectively, for abdominal radiography in the male phantom.
The authors concluded that exponential dose increases for increased subcutaneous fat thicknesses can be reduced substantially by positioning the patient so that the thinnest fat layer (anterior or posterior) is closest to the image receptor. "Increasing the tube voltage also reduces the dose--but to a much smaller extent," they added.
To limit increases in radiation dose to patients with excess body fat, Yanch and colleagues recommended that the effect of patient orientation "be carefully considered."
Jacquelyn C. Yanch, PhD, from the department of nuclear science and engineering at the Massachusetts Institute of Technology in Cambridge, Mass., and colleagues sought to estimate the increase in effective radiation dose from diagnostic x-rays for overweight and obese adult patients, as compared with the effective dose for lean reference phantoms.
The researchers calculated the relative effective radiation doses (E/E0) for the acquisition of chest and abdominal radiographs by using Monte Carlo computer simulations of effective doses delivered to adult phantoms with (E) and without (E0) subcutaneous adipose tissue added to the torso for five fat distributions. Total (anterior plus posterior) fat thicknesses ranged from 0 to 38 cm.
The investigators found that for 30 cm of additional fat, E/E0 values for 120-kVp chest and 80-kVp abdomen radiographs ranged from approximately two to 31 and two to 83 for male patients, respectively, and from two to 45 and two to 76 for female patients, respectively, depending on the type of fat distribution and patient orientation in the x-ray beam.
However, Yanch and colleagues reported that orienting the patient such that the thinnest fat layer was facing away from the x-ray tube minimized E/E0. They also found that reductions in E/E0 reached 14 percent and 20 percent for the thickest phantoms when x-ray tube voltages were increased by 10 and 20 kVp, respectively, for abdominal radiography in the male phantom.
The authors concluded that exponential dose increases for increased subcutaneous fat thicknesses can be reduced substantially by positioning the patient so that the thinnest fat layer (anterior or posterior) is closest to the image receptor. "Increasing the tube voltage also reduces the dose--but to a much smaller extent," they added.
To limit increases in radiation dose to patients with excess body fat, Yanch and colleagues recommended that the effect of patient orientation "be carefully considered."