Purpose
Digital breast tomosynthesis (DBT) is a relatively new and promising techniques in mammography[1,2]: it can be use in addition or as a replacement for traditional viewing,
in both cases an increase in mean glandular dose (MGD) is registered.
The aim of this work is topresent and analyzed a method to perform in vivo dosimetry using MOSFET during mammography.
Methods and Materials
BestMedical TN-1002RDM microMOSFET,
high sensitivity bias power supply,
were calibrated for the digital mammography system Hologic Selenia Dimensions for all clinical parameters [3]: target-filter combinations W/Rh (28-31 kVp) and W/Ag (30kVp) for FFDM and W/Al (30-35 kVp) for DBT.
Linear response with mAs has been tested varying kVp and anode-filter.
To avoid MOSFET perturbation of the image,
the dosimeter is placed at a fix chest wall-to-nipple distance outside compressed breast: to determine breast entrance skin air kerma (BESAK) a correction factor is used.
MOSFET sensitivity...
Results
Fig.
1a-b shows the energy response of the high sensitivity MOFSET TN-1002RDM per unit of kerma (mV/cGy) in FFDM and DBT modality respectively.
An increasing response with increasing tube potential is evident in particular for DBT modality.
Sensitivity range extended from 28,4 +0.7 mV/cGy to 29,5 +0.7 mV/cGy for FFDM modality and from 24,7 +0.9 mV/cGy to 28,6 +0.9 mV/cGy for DBT modality,
data are a mean of five measurements.
Fig.
2a-b shows the MOSFET signal response at different tube output without backscatter for FFDM...
Conclusion
Our results indicate that in vivo dosimetry with MOSFET can be use in DBT and also in Hologic unit COMBO modality,
even if accurate monitoring is provided for compressed breasts thicker than 30 mm (Tube current time < than 50 mAs); MOSFET sensitivity is stable and the response is almost linear also in DBT modality in the routine mammographic dose ranges,
in spite of the 15° rotation of the x-ray tube.
References
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D.E.Hintenlang “Characterization of metal oxide semiconductor field effect transistor dosimeter for application in clinical mammography” Med.
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[4] S.L.Dong,
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J.J.Hwang “Estimantion of mean-glandular dose from monitorino breast entranceskin...
