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

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Materials and methods: The Lynx PT is a 2-D high-resolution dosimetry
system consisting of a scintillating screen coupled with a CCD camera, in
a compact light-tight box. A dedicated software is used for image acqui-
sition, raw data correction (background subtraction, calibration) and fast
data analysis. A recently acquired Lynx detector is currently under inves-
tigation for basic characterization in terms of image geometrical distortion
and homogeneity assessment, signal proportionality with delivered dose
and dependence on iris setting, dose rate, particle energy and type. The
scintillator will be systematically tested against EBT3 films. In-air irradia-
tions at the isocenter will be first performed for single beam spot
measurements to determine spot size in terms of FWHM and spot posi-
tion accuracy. Then, field dose homogeneity for protons and carbon ion
scanned beams at different energies will be investigated. The detector re-
sponse dependence on radiation LET will be also analyzed, by measuring
Bragg peak curves using solid slabs in front of the scintillator.
Results: Preliminary results of basic characterization have shown a pro-
portional behavior with delivered number of particles, at selected iris
aperture settings. Strong dependence of the acquired signal on beam energy
and particle type has been found.
Conclusion: The Lynx PT system appears as a promising tool for 2-D rel-
ative dosimetry of scanning particle beams, including carbon ions, enabling
fast QA and beam optics optimization checks.
A.199
ASSESSMENT OF DOSIMETRIC IMPACT OF CARBON FIBER STABILIZATION
DEVICES FOR POSTOPERATIVE PARTICLE THERAPY
S. Russo E. Mastella S. Molinelli A. Mirandola D. Panizza
A. Mairani G. Magro P. Fossati M.R. Fiore C. Grifoni S. Boriani
S. Bandier F. Valvo M. Ciocca a Fondazione CNAO, Pavia, Italy; b Istituto
Ortopedico Rizzoli, Bologna, Italy
Introduction: Carbon fiber reinforced (CFR)-PEEK metal free devices
(CarboFix Orthopedics) have been recently introduced for surgical implant
fixation in case of spinal tumors, which are generally good candidates for
particle therapy (PT). The purpose of this study was to investigate and
compare uncertainties related to the use of titanium and CFR-PEEK screws
in terms of image quality and artifacts, contouring and dose calculation ac-
curacy for both protons and carbon ion beams.
Materials and methods: CT artifacts in the presence of titanium and CFR-
PEEK screws and resultant contouring inaccuracy were evaluated. Water
equivalent path lengths (WEPL) of both implants were measured and imple-
mented in our treatment planning system (TPS) for material density
assignment. Plans were optimized with and without density correction for
both proton and carbon ions. The impact of CT artifacts and contouring un-
certainties on dosimetric calculation accuracy was evaluated in comparison
with Monte Carlo (MC) calculation. The effect of wrong material assign-
ment was analyzed for two clinical cases evaluating the dose deviation to
the target and organs at risks (OARs).
Results: HU artifacts on CT images in case of CFR-PEEK implants are neg-
ligible, while titanium screwmade it difficult to correctly contour both target
and OARs. A good agreement in dose distribution between TPS and MC sim-
ulation was found for CFR-PEEK screws, while in case of titanium significant
differences in high-Z region were observed. Inaccurate material assign-
ment did not significantly vary the clinical case 3D dose distribution for
CFR-PEEK implants (<1%), while in the presence of titanium screws local
dose deviations up to 20% can be found when HU uncertainties are not cor-
rectly managed.
Conclusions: CFR-PEEK devices have clinical advantages for PT of pa-
tients with orthopedic implants leading to less image alteration, less
contouring uncertainties and significantly higher dosimetric accuracy than
commonly-used titanium devices.
A.200
SMALL FIELD OUTPUT FACTOR EVALUATION WITH A MICRODIAMOND
DETECTOR OVER 30 ITALIAN CENTERS
S. Russo M. Casale R. Consorti G. Donofri M. Esposito C. Fiandra
E. Infusin A. Mameli C. Orland L. Paladin I. Redaelli V. Tremolad
P. Mancos a Azienda Sanitaria firenze, Firenze, Italy; b AO Santa Maria, Terni,
Italy; c AO San Filippo Neri, Roma, Italy; d AUSL Pescara, Pescara, Italy; e A.O.U.
Citta della Salute e della Scienza, Torino, Italy; f Università Campus Bio-Medico,
Roma, Italy; g Policlinico Umberto I, Roma, Italy; h USL 2, Lucca, Italy; i AO San
Gerardo, Monza, Italy; j IRCCS Humanitas, Milano, Italy
Introduction: The current study is conducted in the framework of AIFM
SBRT working group and presents measured MLC-defined small field output
factors (OF) for the three major linear accelerator manufacturers and for
different X-ray energies.
Materials and methods: A pre-questionnaire was sent to each center in
order to evaluate specific differences in terms of the used methodology and
detectors. Each center performed OF measurements by the new PTW 60019
microDiamond detector and by routine used detectors for nominal field
sizes ranging from 10 × 10 cm2 to 0.5 × 0.5 cm 2, defined by both second-
ary jaws and MLC. Two set-up conditions were indicated: 10 cm depth in
water phantom at SSD 90 cm and SSD 100 cm. To speed up the measure-
ments, two identical diamond detectors were adopted. The National Institute
of Ionizing Radiation Metrology ENEA-INMRI carried out a complete char-
acterization of the response of the two diamond dosimeters to ensure the
equivalence of the detectors.
Results: The project enrolled 30 Italian centers; micro-ion chambers were
used for OF measurements in most of the centers (80%); in the remaining
cases diode was used. For very small fields OF have been measured with
Gafchromic films in 10% of the cases and in one center with TLD detectors.
OF average values for 6 MV major linear accelerator manufacturers mea-
sured by user detectors and microDiamond resulted in agreement within
2% for field sizes larger than 2 × 2 cm2 and within 4% for 1 × 1 cm2 field size.
Comparison between the two microDiamond detectors showed the equiv-
alence of the devices.
Conclusions: The results show that there is a relatively high degree of con-
sistency regarding OF for Linac with the same model of the head. Differences
between centers decrease with PTW-60019, in particular for very small
fields. The agreement between microDiamond and user detector measure-
ments confirms PTW-60019 detector as a candidate for small field clinical
radiation dosimetry in advanced radiation therapy techniques.
A.201
DOSIMETRIC BENEFITS AND REPRODUCIBILITY OF DIBH TECNIQUE
GUIDED BY AN OPTICAL SYSTEM
S. Russo A. Ghirelli F. Rossi R. Barca M. Esposito S. Fondelli
L. Paoletti S. Pin G. Zatell P. Bastiani a S.C. Fisica Sanitaria – Azienda
Sanitaria Firenze, Firenze, Italy; b S.C. Radioterapia- Azienda Sanitaria Firenze,
Firenze, Italy
Introduction: Surface imaging systems without using ionizing radiation
have been recently introduced in radiotherapy to check patient setup and
to manage gated treatment procedure. The aim of this work is the evalu-
ation of a deep inspiration breath-hold (DIBH) technique guided by an optical
system for left breast radiotherapy.
Material and Methods: The C-RAD Catalyst™ system is a valid solution for
respiratory gated treatments offering visualization of the respiratory pattern
and direct beam control.
20 patients that underwent left side adjuvant radiotherapy during 2015
were included in this study. Treatments were performed in DIBH with 3D
conformal tangential beams. Prescription dose to the whole breast was
50 Gy in 25 fractions. For each patient a free breathing (FB) and DIBH
treatment plans were calculated and dose volume histograms were
compared.
The reproducibility of the DIBH during treatment was monitored by cap-
turing 3D surfaces with CatalystTM system before and after the treatment
fraction. Interfraction and intra-fraction variability were quantified in mean
and SD displacements in translation (Lat., Long., Vert.) and rotations (Rot,
Roll, Pitch) over all the treatment fractions of the enrolled patients.
e59 Abstracts/Physica Medica 32 (2016) e1–e70