Unit:
Faculty of MedicineLibrary of the School of Health Sciences
Dissertation committee:
Ε. Γιακουμάκης, Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Ε. Γεωργίου, Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Π. Καραϊσκος, Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Ι. Σεϊμένης, Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Σ. Κόττου, Καθηγήτρια, Ιατρική Σχολή, ΕΚΠΑ
Ι. Μαλλαμίτση, Αναπληρώτρια Καθηγήτρια, ΕΚΠΑ
Κ. Λουκάς, Επίκουρος Καθηγητής,ΕΚΠΑ
Original Title:
Δοσιμετρία με Monte Carlo προσομοίωση σε εξετάσεις μαστογραφίας με ψηφιακές και τομογραφικές τεχνικές
Translated title:
Dosimetry with Monte Carlo simulation in mammography examinations with digital and tomographic techniques
Summary:
Breast cancer has a significant impact on the well-being of the female population both nationwide and worldwide. Although the incidence of breast cancer has increased over the past two decades, mortality has steadily decreased. An important factor contributing to successful treatment is early detection of the disease. X-ray mammography is considered the current gold standard technique for breast cancer detection.
Breast imaging has changed dramatically over the past decade and mammography with film system has been replaced by digital mammography. However, this suffers from performance limitations due to tissue superposition which can either mimic or obscure malignant pathology. Therefore, alternative X-ray modalities, such as digital breast tomosynthesis (DBT) and Contrast Enhanced Digital Mammography (CEDM) are being explored in order to improve breast cancer detection rates.
Although the radiation doses submitted to mammograms are low, the International Commission on Radiation Protection (ICRP) accepts that there is a potential risk of breast cancer caused by irradiation. The European Union, by means of relevant regulations and directives incorporated into Greek legislation, requires the estimation of doses from the various mammography techniques with a view either to establishing, developing diagnostic reference levels, optimizing the practice and the equipment used.
The estimation of the absorbed dose in the breast during X-ray imaging is a long established part of the quality control procedures for breast imaging systems and is also necessary for risk assessment. The main purpose of this work was the estimation of the mean glandular dose (MGD) for mammography, digital breast tomosynthesis (DBT) and Contrast Enhanced Digital Mammography (CEDM).
While previous studies have investigated digital mammography dosimetry by providing coefficients for converting the input dose to the breast surface into a mean glandular dose, detailed characterization of dosimetry in absolute terms was performed at this work, including the exposure parameters automatically chosen by the AEC system for different sizes and different breast composition.
For these purpose 950 Monte Carlo simulations, of which 450 were for CEDM mammography, 250 for the DBT and 250 for conventional digital mammography have been made for a wide range of x-ray spectra, breast sizes and glandularities using a realistic voxel phantom.
Under auto-exposure conditions (AEC) the MGD was found to range from 0,306mGy to 2,738mGy for CC view and from 0,352mGy to 3,113mGy for MLO view in CEDM mode.
The dose contribution analysis of each projection for all voxel phantom thicknesses indicates that low dose part mammography is the main contributor of the total glandular breast dose. The dose of high energy part in CEDM is low because of the higher penetration of the former spectra through the breast. The differences between the mean glandular dose for CC and MLO view were less than 9% and are due to the different distribution of glandular tissue that is causing various attenuations of the X-ray beam through the breast.
Acquisition of a single CC view resulted in an MGD ranging from 0.718 - 2.778mGy in FFDM mode and 0.840 - 4.4 559mGy in DBT mode.
For the MLO view, MGD ranges from 0.716 - 3.068mGy in FFDM and 0.818 - 4.596mGy in DBT. For a 50 mm thick breast thickness and 50% glandularity, MGD for the acquisition of FFDM and DBT was 1,248 and 2,235mGy, respectively.
MGD in DBT is almost always greater than MGD in FFDM, differences ranging from 1% to 59% and the MGD from DBT is higher than MGD in CEDM. The difference between the two techniques was found to be 28% (1,545mGy in CEDM and 2,133mGy in DBT) for a breast 50 mm thick and 50% glandularity. It should be noted here that all three mammography techniques for a typical breast (50mm thickness and 50% glandularity) the MGD not exceed the recommended limit (2.5mGy) from the European Breast Dosimetry Protocol.
Significant differences were found between the values of MGD presented in the literature and those derived from this work. For the cases considered, the differences may be up to 42% and are due to differences in the distribution of glandular tissue in the breast. The comparison with studies based on breast models with non-uniform distribution of glandular tissue (A. Sarno, 2018) is considered satisfactory as a perfect reconciliation between MGD values is not expected due to methodological differences between the two approaches. These results clearly demonstrate the limitations of the data currently used for breast dosimetry and that realistic breast voxel phantom provide a powerful tool for the study of breast dosimetry.
Main subject category:
Health Sciences
Keywords:
Mammography, Digital breast tomosynthesis, Monte Carlo, Voxel phantom, Mean glandular dose
Number of references:
152
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Tzamicha Elsa PhD.pdf
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