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

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tomotherapy HD unit. Superficial dose was measured for each of the treat-
ment deliveries using calibrated Gafchromic EBT3 films cut on a dimension
of 5 5 cm2 positioned on the phantom surface. An Epson flatbed scanner
was used to scan the films and FilmQAPro software was used to convert
the optical film density in dose.
Results: The superficial dose measured for the four plans previously cal-
culated decrease as the separation between the phantom surface and the
PTV increases: the superficial dose measured for the contraction of PTV
of 1 mm is 70 percent of the prescribed dose and it is 60, 55 and 50 percent
of the prescribed dose for the contraction of PTV of 3, 5 and 7 mm
respectively.
Conclusions: This work is a preliminary study to evaluate the variation of
superficial dose as a function of used PTV eval. This is important, for example,
in case of breast and chest wall treatments where sparing the skin reac-
tion or delivering sufficient doses to the target surface is a fundamental
issue.
A.69
THE NEUTRON CONTAMINATION IN RADIOTHERAPY TREATMENTS WITH
PHOTON AND ELECTRON BEAMS: DY ACTIVATION MEASUREMENTS
M. Duchini M. Frigeri C. Berluscon S. Gelosa P. Lattuad M. Pres
E. Vallazza F. Guallini A. Ostinelli a A.O. Sant’Anna, Como, Italy;
b Università Insubria, Como, Italy; c INFN, Trieste, Italy; d srl, Trezzano S/N,
Italy
Introduction: External beam radiotherapy is a standard choice in cancer
care, but both electron and photon treatments expose patients to an un-
wanted dose due to neutron contamination. Neutron production occurs in
high Z material by electrons or photons interaction with matter, over a
threshold energy. Their detection represents a challenge in physical re-
search and this work regards the neutron field characterization with an
innovative dysprosium (Dy) dosimeter.
Materials and methods: The dosimeter is based on the Dy neutron acti-
vation and the associated gamma-rays were measured with a HPGe detector
(E&G-ORTEC). Dy disks of different sizes (diameter: 20 mm and 12 mm;
thickness: 0.25 and 0.1 mm) were exposed to 18 MV photon and to 12.16
and 20 MeV electron beams to analyze the detection efficiency. Various ir-
radiation condition and setups (RW3-phantom) were studied. Neutron
activation was studied as a function of treatment beam, dose, field size,
isocenter distance, off-axis, and RW3 thickness. GEANT4 simulations of the
energy spectra were also performed.
Results: The RW3 phantom measurements allowed a thorough character-
ization of neutron field properties. In all cases, the activation efficiency was
10 times greater for larger disks. The dose linearity test was verified for
photon (R2 = 0.994) and electron (R2 = 0.986 at 20 MeV) beams. A statisti-
cal linear correlation was found between field size (side dimensions) and
activation (R2 = 0.859) for the 18 MV photon beam. For the neutrons gen-
erated by electrons, the effects of the beam energy, of the applicator and
of the collimating insert were investigated.
Conclusions: Detection efficiency results confirm that Dy dosimeter is an
extremely suitable tool in neutron contamination measurements. RW3-
phantom tests and Monte Carlo simulations allowed to characterize neutron
fields and to establish the physical background to perform “in vivo” neutron
dose measurements.
A.70
LOCAL IMPLEMENTATION OF TSEI: PHYSICAL ASPECTS
F. Dusi A. Fium F. Saiani A. Cavalli G.P. Prandell M. Maddalo
C. Pinard R. Morett a Medical Physics Unit, Hospital Spedali Civili, Brescia,
Italy; b School of Medical Physics, University of Milan, Milano, Italy
Introduction: Total skin electron irradiation (TSEI) is used for the treat-
ment of mycosis fungoides. The aim of this study was to optimize the
treatment setup, using the Stanford technique, in order to treat the entire
skin surface with homogeneous dose distribution. The effect of two PMMA
spoilers of different thicknesses was evaluated; in vivo dose verification
was performed by Gafchromic® films (EBT3).
Materials and methods: The TSEI was performed according to the six dual-
field Stanford technique, delivering a total dose of 30 Gy in five weeks, 6 Gy/
week, 2 Gy/2 days. 6 MeV high dose rate electron beam (HDRE6) was used.
The patient was positioned on a rotating platform at a source to surface
distance of 325 cm. Different gantry angles were investigated to obtain uni-
formity of at least ±10% on a treatment area of (200 × 80) cm 2. The two
spoilers of different thicknesses (8 mm and 10 mm) were placed 45 cm from
the patient and their effect on dose distribution and uniformity was in-
vestigated. Beam profiles and depth dose curves were measured using a
water phantom and a semiconductor diode. Water solid phantom with a
parallel plate ionization chamber was used to measure absolute dose, to
evaluate dose uniformity and to calibrate Gafchromic® EBT3, used to verify
daily patient dosimetry during the treatment.
Results: The best dose uniformity to the entire skin surface was achieved
using ±20° beam angle. 8 mm spoiler R100 was 6.2 mm and R50 was
15.6 mm, 10 mm spoiler R100 was 3 mm and R50 was 11.7 mm. The mean
eye dose was measured and eye shielding was created. From film dosim-
etry results the clinician decided to add boost fields.
Conclusion: 10 mm spoiler was used for treated patients, as the disease
was superficial and the patients showed superficial plaques. In vivo do-
simetry confirmed phantom dosimetry.
A.71
CHARACTERIZATION OF OSLD DETECTORS FOR DOSIMETRIC CHECKS ON
CLINICAL PHOTON BEAM
R. Emmanuele E. Bonanno N. Cavalli A. Girlando A.M. Gueli
C. Marino S.O. Troja a PH3DRA Labs, Dipartimento di Fisica e Astronomia,
Università di Catania, Catania, Italy; b Humanitas Centro Catanese di Oncologia,
Catania, Italy
Introduction: Thermoluminescence dosimetry (TLD) represented, both for
in vivo measurements for quality assurance, the passive technique of choice.
To overcome the disadvantages, first of all the destructiveness of the reading
process, particular attention was paid to the dosimetry based on optically
stimulated luminescence (OSLD) which, instead, retains the information.
The main objective of this work concerns the characterization of a meth-
odology for dose measurements with a fast and reliable OSLD system.
Materials and methods: The study focused on the characterization of crystal
nanoDot OSLD and reader microSTARii (Landauer Inc.) at Humanitas Ca-
tania’s Cancer Center (Humanitas CCO) and the validation of the results based
on the comparison with the data obtained with the instrumentation Risø
TL/OSL at PH3DRA Laboratories (Department of Physics and Astronomy, Uni-
versity of Catania). This instrumentation requires long time for dosimetry
but allows you to control each parameter of the sensing process.
The work done at the PH3DRA Laboratories through reading mode CW-
OSL (continuous wave-OSL) involved a methodological study that allowed
the characterization of signals and a more applicative study to character-
ize the commercial reader, at Humanitas CCO.
Results: The methodological study highlighted the bright performance of
nanoDots in terms of the linearity of response and repeatability.
The application study highlighted the limitations and potentials of the closed
system for the routine use of OSLD dosimetry.
Conclusions: Given the achieved results, it is appropriate to further char-
acterize the crystals in exam using also the reading mode LM-OSL (linear
modulation-OSL) and POSL (pulsed-OSL) with the aim to separate the various
components constituting the OSL signal and obtain the relationship with
the dose.
A.72
CHARACTERIZATION OF A COMMERCIAL EPID 3D SOFTWARE FOR VMAT
VERIFICATIONS
M. Esposito *, A. Ghirelli, S. Mazzocchi, S. Pini, G. Zatelli, S. Russo. Fisica
Sanitaria Azienda Sanitaria di Firenze, Firenze, Italy
Introduction: Dosimetry check (DC) is a commercial software that allows
reconstruction of 3D dose distributions using transit and through-air EPID
images. DC is composed of two parts: a deconvolution kernel that con-
e21 Abstracts/Physica Medica 32 (2016) e1–e70