Monte Carlo and Phantom Study of the Radiation Dose to the Body from Dedicated CT of the Breast

Abstract

Purpose-To prospectively determine the radiation dose absorbed by the organs and tissues of the body during a dedicated computed tomography of the breast (DBCT) study using Monte Carlo methods and a phantom. Materials and Methods-Using the Geant4Monte Carlo toolkit, the Cristy anthropomorphic phantom and the geometry of a prototype DBCT was simulated. The simulation was used to track x-rays emitted from the source until their complete absorption or exit from the simulation limits. The interactions of the x-rays with the 65 different volumes representing organs, bones and other tissues of the anthropomorphic phantom that resulted in energy deposition were recorded. These data were used to compute the radiation dose to the organs and tissues during a complete DBCT acquisition relative to the average glandular dose to the imaged breast (ROD, relative organ dose), using the xray spectra proposed for DBCT imaging. The effectiveness of a lead shield for reducing the dose to the organs was investigated.Results-The maximum ROD among the organs was for the ipsilateral lung with a maximum of 3.25%, followed by the heart and the thymus. Of the skeletal tissues, the sternum received the highest dose with a maximum ROD to the bone marrow of 2.24%, and to the bone surface of 7.74%. The maximum ROD to the uterus, representative of that of an early-stage fetus, was 0.026%. These maxima occurred for the highest energy x-ray spectrum (80 kVp) analyzed. A lead shield does not protect substantially the organs that receive the highest dose from DBCT.Discussion-Although the dose to the organs from DBCT is substantially higher than that from planar mammography, they are comparable or considerably lower than those reached by other radiographic procedures and much lower than other CT examinations. Advances in Knowledge1. Our study, based on Monte Carlo methods and an anthropomorphic phantom, found that although the radiation dose received by the organs and tissues of the body outside the primary x-ray field from DBCT is considerably higher than that from planar mammography, it is still low (less than 8% of the average glandular dose to the imaged breast), and comparable to other radiographic applications.2. The inclusion of a 1 mm lead sheet inside the table top between the patient and the x-ray source does not substantially lower the dose to the higher-exposed organs, but it does decrease the dose to the uterus (by up to a factor of twenty). 3.The dose deposited in the uterus, representative of that deposited in an early-stage fetus, is low (less than 0.03% of the average glandular dose to the imaged breast). Implications for Patient Care 1.Our study results provide information on the radiation dose to the organs of the body from dedicated breast computed tomography. 2.In regards to using this procedure for women in early stages of pregnancy, we found low dose levels absorbed by the uterus during DBCT imaging.

Dosimetric characterization of a dedicated breast computed tomography clinical prototype

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] BCT involves the adaptation of standard whole body computed tomography ͑CT͒ to breast cancer imaging. This involves not only changing the acquisition geometry to limit the primary x-ray beam to include only the breast but also optimizing the acquisition parameters to the needs of breast cancer imaging, namely, higher contrast and spatial resolution.…”

Personalized estimates of radiation dose from dedicated breast CT in a diagnostic population and comparison with diagnostic mammography

“…Initial reports without administration of iodinated contrast media indicate an improvement in visualization of soft tissue abnormalities with dedicated breast CT compared to mammography (Lindfors et al, 2008, O’Connell et al, 2010). However for microcalcifications, conspicuity (Lindfors et al, 2008) and visualization of its details (O’Connell et al, 2010) were better with mammography than dedicated breast CT. Several research groups are investigating breast CT (Pani et al, 2004, Glick et al, 2007, Altunbas et al, 2007, Sechopoulos et al, 2008, Madhav et al, 2009, Mettivier and Russo, 2011, Shikhaliev and Fritz, 2011, Kalender et al, 2012, Vedantham et al, 2012a, Mettivier et al, 2012, Vedantham et al, 2012b, Chen et al, 2013) and its extension to multi-modality breast SPECT/CT (Mettivier et al, 2011, Cutler et al, 2010) and breast PET/CT (Wu et al, 2009) systems.…”

The effect of breast compression on mass conspicuity in digital mammography

“…Monte Carlo has been used to study how beam quality, antiscatter grids, slot-scan techniques, breast thickness, and breast composition affect the scatter magnitude, contrast, and dose in breast imaging, general radiography, and fluoroscopy. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] Due to recent advances in computing power, Monte Carlo methods can now model, with greater statistical power, more complex geometries, including breast CT 24,25 and tomosynthesis. [26][27][28] .…”