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

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biomarker. This formed the basis for the definition of a phase I study to
be undertaken on 12 GBM relapse patients, simulated with multi-parametric
MRI and re-treated with a dose-painted hypo-fractionated regime. To realise
in a consistent way the MRI data extraction and the DPBN planning pro-
cedure with RapidArc or 4pi-IMRT techniques, Eclipse scripting API (Varian)
and MATLAB software were realised.
Results: Considering the literature (cellularity vs. ADC) and our results that
correlate patient outcome to histogram change in the ADC post STUPP values,
specific transfer functions (dose vs. ADC) with appropriate thresholds were
reached. Dose levels (30–50 Gy/5 fr with a cumulative BED10 > 120 Gy) were
estimated in an attempt to see some changes in the pattern of recurrence
without causing excessive radiation necrosis (<12 Gy/fr) inside the irradi-
ated area and respecting the previously irradiated healthy tissue
(EQD2 < 100 Gy).
Conclusions: The phase I/II protocol was recently approved by Ethical Com-
mittee. Preliminary data will be presented.
A.114
PARAMETER INCIDENCE ON GAMMA INDEX FOR IMRT-VMAT PROSTATE
TREATMENT PLANS: THE INFLUENCE OF MU AND PTV SHAPE
M. Italiani M. Casale M. Muti S. Fabiani E. Maranzano a Azienda
Ospedaliera S.Maria – S.C. Radioterapia – S.S.Fisica Sanitaria, Terni, Italy;
b Universita’ degli Studi dell’Aquila – Scuola di Specializzazione in Fisica Medica,
L’Aquila, Italy; c Azienda Ospedaliera S.Maria -S.C. Radioterapia, Terni, Italy
Introduction: The purpose has been to evaluate if some parameters in-
fluence the IMRT and VMAT prostate plan calculation quality.
Methods and Materials: We analyzed 60 VMAT and IMRT treatment plans
for different PTV shapes (prostate and seminal vesicles with or without pelvic
lymph nodes).
The isodoses have been calculated using the Treatment Planning System
Oncentra (Enhanced Collapsed Cone calculation algorithm). The 3D dose
verification for IMRT/VMAT plan pre-treatment quality assurance has
been measured on 3D cylindrical phantom Delta4 using a 6MV linear
accelerator. These data have been evaluated by gamma index method. All
plans were accepted with 90% of the points with a gamma index > 1 for
3% and 3 mm criteria (optimal number of points > 95%). We have evalu-
ated if some parameters have had a significant incidence on this number
of points.
Results: The prescribed fractional dose to PTV was 2 Gy daily. In all plans
the mean value of monitor units (MU) was 528 ± 168. When PTV did not
include pelvic lymph nodes, the mean values of MU and number of points
in gamma index analysis were equal to 509 ± 112 and 97.7% ± 1.4% for IMRT
(7/9 gantry angles) and 536 ± 159 and 96.5% ± 3.5% for VMAT (1/2arcs) re-
spectively. When PTV included pelvic lymph nodes the mean values of MU
and number of points were equal to 635 ± 230 and 95.8% ± 4.7% for IMRT
and 550 ± 150 and 96.4% ± 2.5% for VMAT. When MU ≤ 600 the number of
points was superior than 95% in 94.9% of cases. When MU > 600, the number
of points was superior than 95% in 57% of cases.
Conclusions: There is a significant difference about gamma index value from
IMRT/VMAT plans with respect to MU ≤ 600 than MU > 600 (Fisher test
P < 0.001). We conclude that the number of MU is a good parameter to fore-
cast an optimal plan calculation quality. No significant difference in gamma
index analysis there was from IMRT and VMAT technique and from differ-
ent PTV shapes. The MU range has been superior in VMAT plans than IMRT
plans.
A.115
MEDICAL PHYSICIST AND HEALTH TECHNOLOGY ASSESSMENT: ADDED
VALUE IN A CASE OF IORT EVALUATION
R. De Vincolis, V. La Monaca *, D. Leanza, S. Mele, F. Platania,
N. Romeo. Azienda Sanitaria Provinciale di Messina – UOC Radioterapia,
Taormina, Italy
Introduction: IORT is a single fraction of radiotherapy during surgery. In
our clinic, electron beams from a dedicated linear accelerator have been
used since 2004. After operating rooms renovation, IORT has not been used
anymore due to new arisen difficulties. As last treatment has been deliv-
ered in 2011, the Oncology Department asked for a health technology
assessment (HTA) in order to evaluate if it is worth to reactivate IORT or it
is better to put it out of service. The aimof this work is to show one example
of medical physicist effort needed to correctly write a mini HTA report.
Material and Methods: Policy question: On the base of available evidence,
is it possible to support the cost aimed to reactivate IORT technology?
Research question: In case of an intraoperative radiotherapy indication, IORT
is more effective, equal effective or less effective than external radiotherapy?
A mini HTA Report has been structured adopting the well established P.I.C.O.
methodology (P = cancer; I= IORT; C = external radiotherapy; O = surviv-
al). Of course many issues have been discussed during the multidisciplinary
work.
Results:
The medical physicist was the professional which put in evidence some crit-
ical issues otherwise neglected:
a) Time and personnel needed for a new linear accelerator commissioning;
b) Radiation protection in a not shielded operating room;
c) Radiation protection in the environment around the operating room
(which deeply changed after four year of inactivity);
d) Possible workload limitations;
e) In vivo dosimetry which is necessary according to Italian legislation.
We believe that the expertise and the usual medical physicist rigorous train-
ing contributed to correctly address the mini HTA report.
Conclusions: Each aspect of a health technology assessment should be ex-
amined by the appropriate professional in order to avoid misleading
conclusions.
A.116
DOSIMETRIC CHARACTERIZATION OF A LASER-DRIVEN ACCELERATION
SYSTEM
D. Lamia G. Russo L. Labate F. Baffigi L. Fulgentini A. Giulietti
P. Koester D. Palla c, P. Pisciotta a,e, L.A. Gizzi c,d, M.C. Gilardi f ,g. a Institute of
Molecular Bioimaging and Physiology IBFM CNR LATO, Cefalù, Italy; b Nation-
al Institute for Nuclear Physics INFN LNS, Catania, Italy; cIntense Laser Irradiation
Laboratory (ILIL) National Institute of Optics INO CNR, Pisa, Italy ; d National
Institute for Nuclear Physics INFN, Pisa Section and LNF, Pisa and Frascati, Italy ;
e University of Catania, Catania, Italy; f University of Milano Bicocca, Milano,
Italy; g Institute of Molecular Bioimaging and Physiology IBFM CNR, Segrate,
Italy
Introduction:The Laser-Driven Accelerator (LDA) based on the Laser Wake-
Field Acceleration mechanism in plasma is able to produce electron bunches
with energies up to ten MeV in a very small area, thus representing a new
option, in perspective, for medical applications.
The LDA is different by a clinical accelerator for the energy distribution, the
broad energy spectrum, the beam angular distribution and the very high
dose-per-pulse (~0.07 Gy).
For these reasons, it is not possible to carry out a dosimetric characteriza-
tion with the indications of international dosimetric protocols. The aim of
our study is to characterize dosimetrically the electrons accelerated by LDA.
Materials and Methods: We developed a GEANT4 Monte Carlo applica-
tion that simulates the system to obtain the 3D dose distribution. For the
absolute and relative dosimetry measurements, we used EBT3 Gafchromic
films because they are independent from beam energy and dose-rate. The
films were calibrated with a Novac7 clinical accelerator.
Results: The dosimetric characterization of the electron beam was vali-
dated by comparing numerical simulations with measurements carried out
with a LDA. From the simulation analysis, the energy distribution and angular
spread of the beam were evaluated. Moreover, we developed a metric test
to compare simulated and experimental PDD curves; it has shown a
maximum percentage error of 2%. The 3D dose profiles were analysed with
the γ index test that it was exceeded by the 80% of the points.
Conclusions: The validation of the dosimetric characterization has shown
that the results obtained by experimental and simulated data were com-
parable, so a complete dosimetric characterization was obtained.
The developed Geant4 application is suitable to study the dose distribu-
tions to be delivered for experimental measurements. For a first dosimetric
e34 Abstracts/Physica Medica 32 (2016) e1–e70