Keywords:
Breast, Mammography, Dosimetry, Physics
Authors:
F. Cavagnetto1, R. Bampi2, M. Calabrese1, F. Chiesa1, G. Taccini1; 1Genova/IT, 2Torino/IT
DOI:
10.1594/ecr2011/C-1963
Results
Fig.
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 (2a) and DBT (2b) modality; R2 linear correlations coefficient are higher then 0,98 for each tube potential and modality tested.
PMMA BESAK MOSFET measurements were performed to test and simulate in vivo dosimetry with FFDM,
DBT and COMBO modality: PMMA phantom is placed a the chest wall-to-nipple distance max of 8 cm,
MOSFET at a distance of 12.5 cm as in clinical routine.
FFDM,
DBT and COMBO (FFDM+DBT) modality are tested at different thickness ranging between 20 and 70 mm,
data are shown in Figure 3.
MOSFET results are compared with BESAK calculated from ionization chamber measurement and acquisition parameter data,
Table 1 shows difference as a function of PMMA thickness.
These results agreed with S.L.Dong [4] which concluded that MOSFET provide accurate monitoring of BESAK for compressed breast thicker than 30 mm,
for thickness less than 30 mm the dose level is lower and MOSFET work at the sensibility range limit.
MOSFET in vivo dosimetry has been performed for a sample of 50 patients in a single DBT projection in depth examination or in COMBO modality,
to test the method: percentage differences between calculated and measured values are shown in Figure 4 as histogram distribution for COMBO modality and FFDM or DBT contributions separately.