97 / 146
Results:
As the PMMA thickness and kVp decreased, data of LCD turned
out to be smaller, proving a better detectability for each detail. Given a thick-
ness, the IQFinv gap between Sectra and Novation was 15–30%. Difference
in LCD between the two systems was 40% for smaller details and 20% for
larger ones, with a better performance of Sectra.
Conclusions:
The statistical method was in accordance with the automat-
ic readout of CDMAM images corrected by the human eye response function;
thus it is currently adopted in image quality assurance, being more rapid
and allowing LCD assessment for several thicknesses representing the an-
atomical region under investigation.
http://dx.doi.org/10.1016/j.ejmp.2016.01.315B.311
EVALUATION OF CT RADIATION PROFILE WIDTH WITH GAFCHROMIC®
XR-QA2 FILMS
S. Spampinato
*
, L. Raffaele, A. Gueli.
Scuola Di Specializzazione In Fisica
Medica, Università Di Catania, Catania, Italy
Introduction:
In recent years, patient exposure to ionizing radiation as a
result of Computed Tomography (CT) has been of paramount concern. With
ever-increasing technological advances, of particular interest is the eval-
uation of Radiation Profile Width (RPW) in Multi-Slice CT (MSCT). Indeed,
accurately identifying the location of the primary radiation beam is of great
importance in patient protection, especially in procedures that require high
values of dose. This work proposes a method for evaluating the RPW through
GafChromic® XR-QA2 films, especially designed for radiology Quality
Assurance.
Materials and Methods:
The XR-QA2 films were calibrated using a con-
ventional x-ray tube, exposing with different radiation beams qualities and
with simultaneous measurements of dose performed by a diagnostic ion-
ization chamber (PTW 233612). The films were digitized with a flatbed
scanner in reflective mode, extracting the red channel for data analysis. CT
RPWs were obtained using a 64 slice Optima CT660 scanner (GE Health-
care), applying several nominal beam widths and positioning the films at
the isocenter (identified by landmarks) on an air-equivalent block. Subse-
quently, films were acquired with the scanner (150 dpi, 48 bit color depth)
and the calibration curve was applied to the red channel. Two indepen-
dent processing softwares were used: FilmAnalyse (PTW Mc2) and a
combination of ImageJ and Origin. To evaluate RPWs, the profile for each
beam width was extracted at the isocenter: normalizing the values to the
maximum, it is defined as the FWHM of the profile.
Results:
The comparison between the two softwares showed comparable
results in terms of RWP and compatible with the nominal beam width. The
error associated with measurements is determined by the resolution of the
film image and the film positioning.
Conclusions:
XR-QA2 films are suitable for RWP measurement and allow
extracting profiles also for very small collimation, important for the new
CT generation, with great precision.
http://dx.doi.org/10.1016/j.ejmp.2016.01.316B.312
EVALUATION OF THE EFFECTIVE RESOLUTION OF AN OPTICAL FLATBED
SCANNER FOR RADIOCHROMIC FILMS ANALYSIS
G. Asero
a ,C. Greco
b , c ,A. Gueli
a , c ,G. Mannino
b , c ,L. Raffaele
b , c ,S. Spampinato
* , a , c .a
PH3DRA Laboratories, Dipartimento di Fisica e Astronomia,
Università di Catania&INFN, Sez. CT, Catania, Italy;
b
Azienda Ospedaliero,
Universitaria Policlinico Vittorio Emanuele, Catania, Italy;
c
Scuola di
Specializzazione in Fisica Medica, Scuola Facoltà di Medicina, Università di
Catania, Catania, Italy
Introduction:
The radiochromic film is a 2D dosimeter which does not
require developing and gives values of absorbed dose with accuracy and
precision. Since this dosimeter colors directly after irradiation, it can be
scanned with commercial optical flatbed scanners to obtain a calibration
curve that links blackening of the film with dose. Although the film has
an intrinsic high spatial resolution, the actual resolution of this dosim-
eter is determined by the scanner, in particular by the “dot per inch” (dpi)
parameter.
The present study investigates the effective spatial resolution of a scanner
used for XR-QA2 film (designed for radiology Quality Assurance) analysis.
Material and Methods:
The quantitative evaluation of the resolution was
performed with the Modulation Transfer Function (MTF) method, com-
paring the nominal resolution with the experimental one.
The analysis was performed with two procedures. First, the 1951 USAF res-
olution test chart, a tool that tests the performance of optical devices, was
used. Secondly, a combined system of mammography, XR-QA2 film and a
bar pattern object was used. In both cases the MTF method has been applied
and the results were compared.
Results:
The USAF and the film images have been acquired with increas-
ing dpi and a standard protocol for radiochromic analysis, to evaluate
horizontal, vertical and diagonal resolution. The effective resolution cor-
responds to the value of the MTF at 50%. In all three cases and for both
procedures, it was verified that, starting from a certain dpi, the effective
resolution saturates.
These results were confirmed by a comparison with the Flat Panel Detec-
tor of mammography, in which the effective resolution is the size of each
pixel detector.
Conclusion:
The study found that, for dosimetric applications, the dpi of
the scanner have to be adjusted to a reasonable value because, if too high,
it requires high scanning and computational time without providing ad-
ditional information.
http://dx.doi.org/10.1016/j.ejmp.2016.01.317B.313
IMPLEMENTATION OF EUREF QUALITY CONTROL PROTOCOL IN DIGITAL
BREAST TOMOSYNTHESIS (DBT)
C. Stancampiano
* , a ,L. Boschiroli
a ,M. Campoleoni
b ,L.O. Vismara
a .a
ASST
Nord, Milano, Italy;
b
Fondazione IRCCS Ca’ Granda Ospedale Maggiore
Policlinico, Milano, Italy
Introduction:
The aim of this work was the implementation of EUREF quality
control protocol in digital breast tomosynthesis with the aid of different
phantoms and the comparison of results obtained on two Hologic Selenia
Dimensions mammography systems.
Material and Method:
We based our work on EUREF tomo protocol version
1.0 published in March 2015. We analyzed several aspects such as x ray
generation, image receptor, image quality of the reconstructed images and
dosimetry. We evaluated focal spot motion measuring projection the ex-
posure time and the time for a complete scan. We verified the stability of
the exposure distribution over the projections. We also measured image
receptor response, uncorrected defective detector elements and detector
homogeneity on reconstructed images using a homemade code and freeware
softwares (plugin COQ for ImageJ and Flatfield test from EUREF). We as-
sessed in-plane projection and system MTF at different positions above the
bucky with edge phantoms made of different materials and thicknesses.
We also measured in-plane projection MTF using a 0.22 mm diameter tung-
sten wire (Agatha phantom).We evaluated Z-resolution with a 0.5 mm
diameter aluminum sphere and a 0.22 mm diameter tungsten wire (Agatha
phantom). We assessed NNPS for the standard breast thickness at clini-
cally selected parameters. We investigated in-plane image quality in different
noise conditions with CDMAM phantom using the software CDCOM. Finally,
we assessed AGD for different breast thicknesses to be compared with AGD
in FFDM for the same thicknesses.
Results and Conclusions:
EUREF protocol doesn’t indicate tolerances for
many parameters in evaluation; as a consequence we had to fix our base-
line relying on the comparison between the two devices in study and the
values found in literature. The performance of the two equipments tested
resulted is comparable and close to the values found in literature.
http://dx.doi.org/10.1016/j.ejmp.2016.01.318B.314
SIZE-SPECIFIC, SCANNER-INDEPENDENT ORGAN DOSE ESTIMATES IN
MULTI-SLICE ABDOMINAL CT EXAMINATIONS OF OVERWEIGHT AND
OBESE PATIENTS
M. Sutto
* , a ,A. Malder
a a ,M. Maddalo
b ,P.E. Colomb
o a ,A. Torresi
n a .a
Ospedale
Niguarda Ca’ Granda, Milano, Italy;
b
Spedali Civili di Brescia, Brescia, Italy
e92
Abstracts/Physica Medica 32 (2016) e71–e96