Page 421 - 2014 Printable Abstract Book
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scans. Major organs were contoured from individual patient CT images. CT scan procedures with AEC
techniques were simulated in MCNPX2.7, a computational Monte Carlo radiation transport code, to
calculate the doses to the major organs. Results were compared with the organ doses estimated using the
conventional method ignoring AEC techniques. Results: Results comparing patient organ doses using AEC
parameters verses no-AEC parameters show that actual organ doses under AEC are typically
overestimated in regions of low density (lungs) and underestimated in regions of higher density (shoulders
and pelvis) using the conventional calculation method ignoring AEC. Conclusion: These results indicate
representative modeling of the newer AEC imaging procedure is significant for reconstructing more
accurate patient organ doses, and here we present the first example of that.
(PS7-74) Development of a size-specific dose length product-to-effective dose conversion factor for
computed tomography patients. Anna Romanyukha, NCI, Rockville, MD
Over the last decade, there has been an exponential increase in the number of computed
tomography (CT) scans administered every year, making CT radiation exposure a large component of the
per capita dose and a public health concern. Patient effective dose from CT examinations is usually
estimated in the clinical setting using the scanner-provided dose length product (DLP) and conversion
factors, also known as k-factors. Originating from medical physics guidelines, k-factors correspond to
anatomical protocol regions and differ by age according to five categories: 0, 1, 5, 10 yrs, and adult.
However, real patients often deviate from the standard body size on which the conversion factor is based.
In this study, we present a method for deriving a body size-specific k-factor, which can be determined
from a simple regression curve based on patient diameter in the center of the scan range. Using
anatomically realistic numerical representations of the body (computational phantoms) paired with
Monte Carlo simulation of CT x-ray beams, we derived regression-based k-factors for the following CT
imaging protocols: head, neck, head and neck; chest, abdomen-pelvis (AP), chest-abdomen-pelvis (CAP),
abdomen, and pelvis. The resulting regression curves were applied to 117 adult patients and 81 pediatric
patients randomly sampled from patients who underwent chest, abdomen-pelvis, and chest-abdomen-
pelvis CT scans at the National Institutes of Health (NIH) Clinical Center. We calculated and compared the
effective doses derived from the conventional age-dependent k-factors to the effective doses computed
using our body size-specific k-factor. We found that in using the age-dependent k-factor, underweight
patients tend to have underestimates of effective dose, while obese patients tend to have overestimates
of effective doses when compared with size-specific effective dose. We present these body-size
dependent k-factors as an alternative to previously used age-dependent factors. The size-specific k-factor
will assess effective dose more precisely on an individual level than the currently applied k-factor and,
hence, improve awareness of the true exposures, which is important for the clinical community.
techniques were simulated in MCNPX2.7, a computational Monte Carlo radiation transport code, to
calculate the doses to the major organs. Results were compared with the organ doses estimated using the
conventional method ignoring AEC techniques. Results: Results comparing patient organ doses using AEC
parameters verses no-AEC parameters show that actual organ doses under AEC are typically
overestimated in regions of low density (lungs) and underestimated in regions of higher density (shoulders
and pelvis) using the conventional calculation method ignoring AEC. Conclusion: These results indicate
representative modeling of the newer AEC imaging procedure is significant for reconstructing more
accurate patient organ doses, and here we present the first example of that.
(PS7-74) Development of a size-specific dose length product-to-effective dose conversion factor for
computed tomography patients. Anna Romanyukha, NCI, Rockville, MD
Over the last decade, there has been an exponential increase in the number of computed
tomography (CT) scans administered every year, making CT radiation exposure a large component of the
per capita dose and a public health concern. Patient effective dose from CT examinations is usually
estimated in the clinical setting using the scanner-provided dose length product (DLP) and conversion
factors, also known as k-factors. Originating from medical physics guidelines, k-factors correspond to
anatomical protocol regions and differ by age according to five categories: 0, 1, 5, 10 yrs, and adult.
However, real patients often deviate from the standard body size on which the conversion factor is based.
In this study, we present a method for deriving a body size-specific k-factor, which can be determined
from a simple regression curve based on patient diameter in the center of the scan range. Using
anatomically realistic numerical representations of the body (computational phantoms) paired with
Monte Carlo simulation of CT x-ray beams, we derived regression-based k-factors for the following CT
imaging protocols: head, neck, head and neck; chest, abdomen-pelvis (AP), chest-abdomen-pelvis (CAP),
abdomen, and pelvis. The resulting regression curves were applied to 117 adult patients and 81 pediatric
patients randomly sampled from patients who underwent chest, abdomen-pelvis, and chest-abdomen-
pelvis CT scans at the National Institutes of Health (NIH) Clinical Center. We calculated and compared the
effective doses derived from the conventional age-dependent k-factors to the effective doses computed
using our body size-specific k-factor. We found that in using the age-dependent k-factor, underweight
patients tend to have underestimates of effective dose, while obese patients tend to have overestimates
of effective doses when compared with size-specific effective dose. We present these body-size
dependent k-factors as an alternative to previously used age-dependent factors. The size-specific k-factor
will assess effective dose more precisely on an individual level than the currently applied k-factor and,
hence, improve awareness of the true exposures, which is important for the clinical community.
