Physica Medica: European Journal of Medical Physics - Volume 32 - Supplement 1 - February 2016

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Results: Keeping in mind the obstinacy with which some still insist on use
of E having regard to its adaptability to provide dosimetric information for
all diagnostic modalities, it would be convenient to use it only as a quan-
tity to compare different radiological exams of the same anatomic region
or the same exam in different diagnostic centers. We could call it with a
changed name like Effective Dose Index (EDI). Basically, EDI is precisely the
effective dose that a standard patient would receive in the same exposure
conditions of a real patient. For this reason, EDI is not defined for the in-
dividual patient, and so it cannot in any way be related to the individual
risk.
Conclusions: The dose indexes as PKA, CTDIvol, PKL, CT should be in-
cluded in the dosimetric report to be communicated to patient. If the choice
falls on E, it is appropriate to use it as an index to avoid wrong risk esti-
mates of the patient. Here we propose the introduction of Effective Dose
Index (EDI) closely related to a standard patient.
D.407
A WORK PROCESS-ORIENTED ANALYTICAL MODEL FOR THE
CALCULATION OF DOSE AND RISK TO THE OPERATORS INVOLVED IN
FLUOROSCOPIC PROCEDURES
A. Valentini G. Miori A. Martignano a Department of Medical Physics,
Azienda Provinciale per i Servizi Sanitari – APSS, Trento, Italy; b School of Medical
Physics, University of Rome Tor Vergata, Roma, Italy
Introduction: An analytical model for the calculation of dose and risk to
the operators during fluoroscopic examinations was created and imple-
mented in a homemade software.
Materials and Methods: The model starts from the work processes of the
single operator or homogenous group (set of comparable activity opera-
tors) to define the input data needed to calculate dose and risk. The software
is divided into 3 parts: the 1st part consists of general data, number of op-
erators in the group and technical setup parameters (output, kV, mAs, etc.).
In the 2nd part complete radiological exams records are sampled over a
certain period of time; the program estimates the 1-year projection of re-
corded data. In the 3rd part the cumulative charge, the entrance surface
dose to the patient and the scatter dose to the operator are evaluated. The
calculation is based on the annual cumulative exposure time, output of the
fluoroscopic device at the correct duty cycle, mean patient thickness, source
to surface distance, average tension and current.
Results: The program estimates cumulative whole-body effective dose, hands
dose and lens dose to the homogenous group. A 1.5 safety factor is intro-
duced to account for incidents and malfunctions. The program takes into
account the percentage of presence as 2nd operator, the percentage of use
at three specific tube orientations, the transmission factors of X-ray pro-
tective equipment and the percentage of operator presence at four defined
distance ranges. The X-ray tube orientation is of particular importance for
hands and lens dose; for lens dose calculations the lens-torso distance is
also considered. The classification of the operator is conservatively per-
formed by comparing individual dose to half the legal limit levels.
Conclusions: The implemented analytical model considers the radiologi-
cal load and the work processes to give an adequately unbiased method
to calculate operators doses that are consistent with personal dosimeters
readings.
D.408
ATTENUATION OF PROTECTIVE EYEWEAR IN DIFFERENT GEOMETRIES:
EXPERIMENTAL RESULTS
R. De Vincolis *, V. La Monaca, D. Leanza, S. Mele, F. Platania,
N. Romeo. Azienda Sanitaria Provinciale di Messina – UOC Radioterapia,
Taormina, Italy
Introduction: In April 2011, ICRP recommended lowering the equivalent
dose limit for the lens of the eye to 20 mSv/year. The substantial limit re-
duction from the actual 150 mSv/y poses particular concern for certain
workers especially interventional fluoroscopists.
The aim of this work is to evaluate the attenuation properties, in different
exposure geometries, of two protective eyewear manufactured by
EUROPROTEX, mod. 9941 Ultralite and mod. Fitover.
Material and Methods: The patient was simulated by 15 cm thick water
equivalent RW3 slab; two different interventional fluoroscopy proce-
dures were considered (femoral access and gastro-intestinal), positioning
the operator phantom like looking at the image display, during x-ray ex-
posure, and not at the scattered radiation source (patient).
For the femoral access procedure the operator’s eye is around 60 cm far
from the scattered radiation source and the eye-display line form an angle
of 45° with the eye-source line; similarly for the gastro-intestinal proce-
dure there is around 75 cm distance and 90° angle.
For each protective device 4 dosimeters were used: 1 in front and 1 behind
the eyewear lens both for left and right eye. For measurements TLD do-
simeters, calibrated in Hp(0.07), were adopted.
Results: The eyewear protection factor is strongly influenced by the radi-
ation source location. When the described angle is small (source in front
of the fluoroscopist) the device effectiveness is important; however, when
the source was to fluoroscopist’s side, the reduced cross section of the side
shield show significant reduction in protection.
In our experiment transmission factors were evaluated in the range 50–75%.
Conclusions: The use of protective eyewear may provide a false sense of
safety when radiation does not strike from the front direction since a lot
of radiation can slip through the gap created between cheek and eyewear.
This effect could be reduced by raising the bed and positioning the image
display in front of operator’s eye.
D.409
STUDY OF A LINAC TARGET ACTIVATION
A. Mitillo *, S. Anglesio. AOU San Luigi Gonzaga, SS. Radioterapia, Orbassano,
Italy
Introduction: The head components of a linear accelerator, operating with
potential greater than 8–10 MV, exhibit an induced radioactivity, as ex-
pected. Our Elekta Synergy Platform target was replaced on 14/7/2015,
because of a technical intervention on the target mechanical support. The
linac had been in use since January 2010; 50% of the Monitor Units (MU)
were delivered with 10 and 18 MV photon beams. A study of the target ra-
diation emission was carried out in order to identify the activation products.
The study was also performed to approximately estimate the target activ-
ity in view of its disposal.
Materials and Methods: The study started just one day after the target re-
placement, in order to identify radionuclides with very short half-lives.
The target emission has been studied, during the elapsed 6 months, with
a NaI scintillation detector equipped with a digiBase (Ortec) base. The bad
geometrical conditions, due to our sample shape and size, were partially
overcome keeping constant the sample-detector distance and position.
The dose-rate at different measured distances from the target was also evalu-
ated in terms of μSv/h using a Victoreen 451 Ionization Chamber (600 cm3).
The evaluation of target activity, performed immediately after the replace-
ment, was obtained starting from the dose-rate, using the Gamma constant,
and from the spectra counts.
Results: The main identified radioactive components are Ta-183 (T1/
2 = 5.1 d), Re-184 (T1/2 = 38 d), Au-196 (T1/2 = 6.2 d), Au-198 (T1/2 = 2.7 d).
From these components, it has been possible to recognize the originating
nuclides, mainly W-183 and Au-197.
Both the methods, used to estimate the target activity, provide approxi-
mately the same result of about 300 kBq.
Conclusions: The identified components are those expected from litera-
ture. The main identified radionuclides half-lives are lower than 75 days;
however, the study will continue to verify the absence of long-lives radio-
nuclides and to more accurately assess the target activity.
e120 Abstracts/Physica Medica 32 (2016) e116–e123