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

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A.161
NEUTRON ACTIVATION DETECTORS FOR CLINICAL DOSIMETRY IN
EXTERNAL BEAM RADIATION TREATMENTS
A. Ostinelli M. Duchin V. Cont M. Frigeri S. Gelosa C. Berlusconi
P. Lattuada F. Guallin E. Vallazz M. Prest a A.O. Sant’Anna, Como, Italy;
b s.r.l., Trezzano s/N, Italy; c INFN, Trieste, Italy; d Università dell’Insubria,
Como, Italy
Introduction: Radiation therapy with high energy (>10 MV) photon beams
produces secondary neutrons. The practical problems related to neutron
dosimetry (mixed fields, integrated electronics and energy spectra simu-
lations) are investigated in the development of a dosimeter based on
dysprosium activation. In this work the dosimeter was used to obtain an
estimation of the effective dose En of the neutron out-of-field radiation.
Materials and Methods: The detector is a dysprosium disk (12 mm diam-
eter, 0.1 mm thickness and 0.104 g weight). The discs were exposed to the
18 MV photon beams of the Varian Clinac-iX linacs of the Radiotherapy
Department-Sant’Anna Hospital (Como). The neutron flux was estimated
by measuring the induced activity with an HPGe detector (AMETEK) and
simulating the neutron spectra (GEANT4). En was calculated by a dosi-
metric model based on neutron energy transfer to biological matter. The
model was validated by phantom tests and “in vivo” measurements during
prostate/pelvis IMRT treatments.
Results: The neutron energy deposition in the biological tissues is due to
the H1(n,gamma)H2 and N14(n,p)C14 reactions. Summing the contribu-
tions due to the five fields of a prostate/pelvis treatment session (750 MU),
a 0.417 mGy + 0.048 mGy = 0.456 mGy dose is obtained, with an effective
dose of 1.16 mSv. It follows that for a complete treatment (78 Gy/39 frac-
tions) the effective dose amounts to 35 mSv.
Conclusions: Both phantom and clinical trials have shown that the Dy do-
simeter is a useful tool in the out-of-field radiation study. The dosimetric
model allowed an estimation of the clinical effective dose, showing that
the neutron contamination may not be negligible in such treatments.
A.162
MOVING TARGET IN TOMOTHERAPY TREATMENT: A PHANTOM STUDY
S. Pallotta C. Talamonti L. Marrazzo S. Scocciant P. Bonomo
P. Dionisio a Department of Clinical and Experimental Biomedical Sciences
-Mario Serio, University of Florence, Firenze, Italy; b Medical Physics Unit AOU
Careggi, Firenze, Italy; c Radiotherapy Unit AOU Careggi, Firenze, Italy
Introduction: Dose delivered to moving lung lesions with TomoTherapy
(TT) may differ from planned dose, due to the simultaneous gantry rota-
tion, patient couch translation and lesion movement. Moreover the planning
CT can be acquired following different approaches: Free-Breathing (FB),
Breath-Hold (BH) or Average Intensity Projection (AIP) from 4DCT. In this
study the outcome of how these factors interplay and their effects on mea-
sured dose distributions are explored using a moving phantom and
Gafchromic EBT3 films.
Materials and Methods: Two pieces of tissue equivalent material, embed-
ded and held together in two adjacent polystyrene slabs, were used to
simulate a lung lesion. A motor-driven motion platform was used to slit
the phantom (3 cm extension, 16 cycle/min) along the cranio-caudal di-
rection. FB and AIP images of the moving phantom as well as BH images
of the static phantom were acquired and sent to the TT planning station
where three plans for delivering 2 Gy to the central tissue equivalent ma-
terial were prepared. Planning and delivered dose distributions were
compared using Gafchromic films, sandwiched between the two phantom
parts considering both a moving and a static film configuration.
Results: A significant difference between planned and delivered dose dis-
tributions was observed in the moving phantom. Gamma index passing rates
(3%, 3 mm, 10% threshold, local criterion) changed from 89.48% for the static
phantom (BH-CT) to 63.89% and 61.38% for the moving phantom using AIP
and FB CT respectively. Dose delivered by treatments planned on FB and
AIP CT data sets shows under dosages and over dosages in the target and
surrounding regions, respectively, compared to that delivered to the static
target.
Conclusions: Treatments performed with TT on moving targets showed a
significant difference between planned and delivered dose distributions.
The use of AIP CT images, adequate for dose calculation in most circum-
stances, does not seem to provide better results.
A.163
SLICED MARY: A DEFORMABLE PHANTOM FOR THE VALIDATION OF
SET-UP BASED ON SURFACE IMAGING IN RADIOTHERAPY TREATMENTS
S. Pallotta S. Russo M. Esposito L. Marrazzo C. Talamonti
P. Bonom L. Livi C. Svensso M. Giust a Department of Clinical and
Experimental Biomedical Sciences-Mario Serio, University of Florence, Firenze,
Italy; b Medical Physics Unit AOU Careggi, Firenze, Italy; c Azienda Sanitaria
di Firenze, Firenze, Italy; d Radiotherapy Unit AOU Careggi, Firenze, Italy;
e 4C-RAD Positioning AB, Uppsala, Sweden
Introduction: In radiotherapy treatments, patient setup verification is gen-
erally performed using ionizing radiation but data concerning patient
position can also be derived using optical systems (OS) capable of recon-
structing body surface. The absence of additional radiation exposure makes
this approach particularly interesting, but the deformation of body sur-
faces may question its accuracy. Deformable image registration algorithms
could potentially solve this problem, and for this reasons some OS vendors
included deformable image registration (DIR) tools in their software. In this
work a deformable phantom, suitable for OS acquisitions, and with inter-
nal tissue contrast visible in both kilovoltage and megavoltage images has
been developed to evaluate DIR algorithms.
Materials and Methods: Sliced Mary is a deformable phantom consisting
of 33 slices of expanded polystyrene slabs shaped thus to simulate a female
body and containing anatomical details that simulate ribs, spinal cord and
internal targets. Two mammalian prosthesis and two objects, simulating
arms, were fixed to the phantom, which was finally covered with a white
Lycra tissue. Realistic head rotation, arms flexion and body torsions can be
achieved. The deformable phantomusabilitywas preliminary assessed testing
the DIR algorithm implemented in an advanced tool of the C-RAD Sentinel
optical system. Different body bending and torsion were applied to the
phantom and CBCT and OS registration results were compared.
Results: CT, CBCT, portal images and optical acquisitions demonstrate that
the phantom features necessary to perform the registrations are visible.
Mean differences between CBCT and Sentinel DIR registration parameters
are less than 2 mm and 2,3°.
Conclusions: A deformable phantom capable of independent and realis-
tic movement has been developed. Promising performances of the DIR
algorithm have been observed on realistic deformations.
A.164
ADAM: A 3D PRINTED BREATHING PHANTOM FOR END TO END TESTS
ON RT TREATMENTS
S. Pallotta L. Fogg S. Calus L. Marrazzo C. Talamont M. Casati
L. Livi G. Simontacchi P. Dionisio a Department of Clinical and
Experimental Biomedical Sciences -Mario Serio, University of Florence, Firenze,
Italy; b Medical Physics Unit AOU Careggi, Firenze, Italy; c Radiotherapy Unit
AOU Careggi, Firenze, Italy
Introduction:In radiotherapy the accuracy of dose delivered tomoving targets
is a problem still under investigation. Different approaches have been pro-
posed for the management of respiratory motion, such as respiration-
synchronized techniques or motion encompassing methods. Due to the
complexity and plurality of the factors at play, there is the need for devel-
oping solutions for thorough QA, both for dose verification and for imaging
and synchronization devices. Here we present ADAM (Anthropomorphic
Dynamic breAthing Model), a new phantom capable of simulating realistic
patient movements, and the results of preliminary tests on its performances.
Material and Methods: ADAM is a male torso containing motor-driven
moving parts reproducing real lung lesions movements. The phantom shell
is printed with a 3D printer using a model reconstructed from a real patient
CT, while the internal parts are realized considering simplified internal organs
shapes. The anterior part of the phantom moves up and down in sync with
lungs movements both driven by an Arduino programmable board. This
allows using real patients’ respiratory signal as an input, and to change the
e48 Abstracts/Physica Medica 32 (2016) e1–e70