Program Information
CT Breast Dose Dependence On Breast Volume, Tissue Composition and Body Circumference: A Monte Carlo Simulation Study
J Holmes*, D Carver , R Price , D Pickens , M Stabin , Vanderbilt University Medical Center, Nashville, TN
Presentations
MO-B-BRD-9 (Monday, March 9, 2015) 10:00 AM - 12:00 PM Room: Ballroom D
Purpose: To determine the dependency of CT breast dose with respect to patient size, patient tissue composition, breast composition, and total breast volume.
Methods: Computerized human phantoms were generated to simulate female patients of varying size and tissue composition. A Monte Carlo simulation of a 64 slice CT scanner was created using a radiation particle transport software toolkit with CT technique variables kept constant at 120kVp, 100mAs, body bow-tie filter, helical scan pitch of 1.0, and beam collimation of 64x0.625. Anatomical landmarks for start and stop of a routine chest CT protocol scan kept constant for all phantoms. To simulate varying body size, each phantom was scaled in circumference in the axial dimension only. Breast tissue was simulated as homogeneous mixtures of adipose and glandular tissues. Patient body composition was simulated with varying degrees of excess adipose and soft tissue.
Results: A linear dependence of breast dose on the percent of glandular tissues was found in simulations ranging from 0% glandular (100% adipose) to 100% glandular. An inverse relationship was found between breast dose and body circumference. As the breast tissue gets closer to the edge of the gantry and farther away from isocenter, the dose to the breast tissue decreases. Breast dose was found to be relatively higher in phantoms comprised of higher fractions of body adipose tissue.
Conclusion: These simulations demonstrate decreasing breast dose with increasing body circumference. Breast dose increased with increasing percentages of glandular breast tissues and in large patients with excess adipose tissue. The latter result is partially explained by the diminished attenuation of the excess adipose tissues throughout a patient’s scan. This information could be used to optimize CT scan protocols of the chest region to allow dose savings in young and adolescent women, where breast radiosensitivity is higher.
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