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

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is statistically significant (p < 0.001). Difference in target dose is not sig-
nificantly affected by using different bevelled applicators. Backscatter
contribution was about 18% for all energies at the depth of 90% and about
5% at the depth of 100% isodose, as confirmed in literature. Absorbed dose
from Plexiglass was 5%. In all cases exit dose under the steel shield was
negligible.
Conclusions: The results show that there is a better agreement between
prescribed and measured dose when using steel and Plexiglass shields
together.
A.124
A PROACTIVE STUDY OF RISK APPLIED TO THE PLANNING PROCESS FOR
IMRT/VMAT TREATMENTS
F. Lucio *, E. Calamia, A. Boriano, C. Fillini, A. Melano, A. Gerbino, A. Dutto,
S. Chauvie. ASO S. Croce e Carle, Cuneo, Italy
Purpose: The directives 2013/59 requires that in radiotherapy are carried
out studies of risk of accidental or unintended exposures (art 63, comma
b). The aim of this work was applying a proactive approach (FMEA) to the
process of planning in IMRT/VMAT treatment. As indicated in the litera-
ture it is the most critical step in this type of treatment.
Materials and Methods: FMEA was applied to identify all the sub-
processes involved in the stage planning of IMRT/VMAT treatment. The work
was done by a multidisciplinary team (2 physicists, 2 physicians and 2 tech-
nologists) at the Radiotherapy Department of S. Croce Hospital of Cuneo.
The procedure includes sub-processes determination. For each step, all po-
tential failure modes were identified, together with their causes and effects,
using the risk probability number (RPN) and scoring it basing on the product
of three parameters as proposed by Ford. Finally, improvement actions were
planned defining a time schedule for their implementation.
Results: Twenty-five sub-processes were identified by the working group.
Thirty-seven potential failure modes were identified. These were divided
into three groups depending on the RPN value: 13.5% have RPN lower than
75, 54.1% have a value between 75 and 125 and, finally, in 12 failure modes
the evaluation has led to obtain a RPN greater than 125. Four corrective
actions have been identified to reduce the risk: adoption of reading system
with barcode, second independent dose calculation system, introduction
of checklist completed by the radiation oncologist, technologist and medical
physics and carrying out control of the treatment planning process by a
second physicist. These actions could be carried out over a period of 10
months.
Conclusions: Since the new European directive shall ensure that for ra-
diotherapeutic practices the quality assurance programme includes a study
of the risk of accidental or unintended exposures, this study can serve as
a guide for other users.
A.125
FEASIBILITY OF INTRAOPERATIVE RADIOTHERAPY WITH ELECTRONS IN
BREAST CANCER PATIENTS WITH CARDIAC DEVICES
R. Luraschi R. Lazzari V. Galimberti A. Bazani E. Rondi
M.C. Leonard G. Corso N. Colombo B.A. Jereczek-Foss F. Cattan
a Physics Department, European Institute of Oncology, Milan, Italy; b Radiation
Oncology Division, European Institute of Oncology, Milan, Italy; c Molecular
Senology Unit, European Institute of Oncology, Milan, Italy; d Cardiology Division,
European Institute of Oncology, Milan, Italy; e University of Milan, Milan, Italy
Introduction: Pacemakers or defibrillators can malfunction if exposed to
ionizing radiation. Dose measurements during intraoperative radiothera-
py (ELIOT) in the subclavicular (SVC) region, where a cardiac implantable
electronic device (CIED) would be positioned, were performed in patients
without heart disease. The study aim is to verify that the dose does not
exceed 2 Gy, that is the recommended maximum dose to the CIEDs.
Material and Methods: This analysis was performed on 20 patients, which
underwent breast conserving surgery. After tumor removal and before de-
livering ELIOT, two catheters, each of them containing 8 thermoluminescent
dosimeters (TLDs), were positioned. The first catheter, the internal one, was
attached to the thoracic shielding and became an integral part of it. The
shielding was located beneath the reconstructed breast parenchyma of the
tumor bed, to minimize the underlying dose, and the catheter tip was po-
sitioned in the SVC region. The second catheter, the external one, was placed
on the skin, parallel to the first one, next to the applicator. The TLD reading
showed the absorbed dose due to the scattered dose correlated to the dis-
tance from the applicator.
Results: For a prescribed dose of 21 Gy at 90% isodose, the doses mea-
sured by the external catheter TLDs were homogenous and below the CIED
threshold (mean dose: 0.38 Gy, range: 0.10–0.80 Gy). The doses mea-
sured by the internal catheter TLDs varied according to the distance from
the applicator. At 2.5 cm distance from the applicator, the internal TLD doses
were lower than those detected by their external counterparts.
Conclusions: ELIOT seems to be safe for patients using CIEDs as long as
the minimum distance of 2.5 cm is kept between the CIED edge and the
applicator wall. No correlation with tumor site and electron energy was
observed. ELIOT might be a valid alternative to external irradiation, which
is conditioned by the low threshold dose for CIEDs, as recommended by
current guidelines.
A.126
AN EPID BASED QUALITY ASSURANCE METHOD OF FFF BEAMS ON
CONVENTIONAL LINAC
I. Løvik * A. Anoja S. Canino A. Cristofaro M. Licandro
C. Scalzo a Medical Physics, AO Pugliese-Ciaccio, Catanzaro, Italy;
b Radiotherapy Dept., AO Pugliese-Ciaccio, Catanzaro, Italy
Introduction: The purpose of this work was to investigate the use of EPID
images for quality assurance of flattening filter free (FFF) beams on con-
ventional linac. Due to the distinct characteristics of FFF beams compared
to conventional photon beams, specific QA to ensure the consistency of the
shape of the beam profile is required.
Material and Method: EPID (iViewGT) measurements were performed on
an Elekta VersaHD linac equipped with high energy photon beams (6, 10
MVRX) in standard and FFF mode.
An in-house developed software (Matlab) was used to analyse the images
in terms of dosimetric field sizes of FFF fields compared to FF fields,
unflatness, slope, peak position and symmetry. At the beginning of each
measurement session an image was taken with a Port Film Graticule (PFG)
in order to detect the centre of the radiation field on the detector in terms
of pixel position. The PFG was removed and exposures were made in stan-
dard and FFF mode for field sizes from 5 × 5 to 20 × 20cm2. The collimator
settings for a given field were left unchanged for all energies.
Results: The dosimetric field edges were determined as the position of the
50% value of a sigmoidal fit starting from the inflection point. The dosi-
metric field sizes of the FFF fields measured with our method of analysis
were 0.3–0.5 mm smaller than the corresponding FF field sizes. The
unflatness values, due to the EPIDs energy dependency, were in accor-
dance with nominal values only for the largest field. The slope was
determined for the 10 × 10 and 20 × 20 fields and used to determine the
peak position as the off-axis position. The peak position was within 1.5 mm
from the radiation centre determined with the PFG. The symmetry of the
beam profile was within acceptance (<3%). The reproducibility of the method
was within detection limit.
Conclusion: EPID images have been used to measure the properties of the
beam profile of FFF beams. All parameters but the unflatness were found
within acceptance and this will be object of further studies.
A.127
VERIFICATION OF A PORT FILM GRATICULE FOR DAILY QUALITY
ASSURANCE
I. Løvik A. Anoja S. Canino A. Cristofaro M. Licandro C. Scalz
a Medical Physics, AO Pugliese-Ciaccio, Catanzaro, Italy; b Radiotherapy Dept.,
AO Pugliese-Ciaccio, Catanzaro, Italy
Introduction: We investigated the use of a Port Film Graticule (PFG) to see
whether it proves effective and accurate for daily quality assurance of FF
and FFF beams on conventional linac.
e37 Abstracts/Physica Medica 32 (2016) e1–e70