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A.96
LUNG SABR: A LARGE-SCALE MULTI-INSTITUTIONAL DOSIMETRIC AND
RADIOBIOLOGICAL PLANNING COMPARISON
F. Giglioli
* , a ,L. Strigari
b ,C. Marino
c ,R. El Gawhary
d ,M. Zani
e ,D. Fedele
f ,V. Landoni
b ,M. Quattrocchi
g ,M.D. Falco
h ,E. Cagni
i ,P. Mancos
u j .a
A.O.U.
Città della Salute e della Scienza di Torino, Torino, Italy;
b
Regina Elena Cancer
Center IFO, Roma, Italy;
c
Humanitas C.C.O., Catania, Italy;
d
O. San Pietro
Fatebenefratelli, Roma, Italy;
e
AOU Careggi, Firenze, Italy;
f
Casa di Cura Privata
San Rossore, Pisa, Italy;
g
USL 2 di Lucca, Lucca, Italy;
h
Fondazione Policlinico
Tor Vergataa, Rom, Italy;
i
Arcispedale Santa Maria Nuova (RE), Reggio Emilia,
Italy;
j
IRCCS Istituto Clinico Humanitas, Milano, Italy
Introduction:
The Italian Association of Medical Physics (AIFM) insti-
tuted in 2012 a working group dedicated to the Stereotactic ablative body
radiotherapy (SABR). Large-scale multi-institutional planning compari-
son on lung cancer SABR is presented with the aim of investigating possible
criticism in carrying out retrospective multicentre data analysis from a do-
simetric and radiobiological prospective.
Materials and Methods:
Five CT series were sent to the participants. The
dose prescription to PTV was 54 Gy in 3 fractions of 18 Gy; each partici-
pant was asked to prescribe dose in conformity to its experience (i.e. 100%,
80%, mean dose) to stress the individuality of every center. The plans were
compared in terms of PTV-gEUD2 (generalized equivalent uniform dose
equivalent to 2Gy), mean dose to PTV, Homogeneity Index (PTV-HI), Con-
formity Index (PTV-CI), and Gradient Index (PTV-GI). We calculated the
maximum dose for each OAR (organ at risk) considered as well as the MLD2
(mean lung dose equivalent to 2Gy) for the ipsilateral lung. The data were
stratified according to expertise and technology.
Results:
Twenty-six centers equipped with Linacs (3DCRT (8%-2 centers)
IMRT (4%-1 center), VMAT (76%-20 centers)), CyberKnife (4%-1 center), and
Tomotherapy (8%-2 centers) collaborated. Almost every region of Italy was
represented. Significant PTV-gEUD2 differences were observed (range: 105–
161 Gy); mean-PTV dose, PTV-HI, PTV-CI, and PTV-GI were, respectively,
56.8
±
3.4 Gy, 14.2
±
10.1%, 0.70
±
0.15, and 4.9
±
1.9. Significant correla-
tions for PTV-gEUD2 vs. PTV-HI, and MLD2 vs. PTV-GI, were observed.
Conclusions:
A notable inter-institutional difference in terms of gEUD2 and
general planning strategies was found. For a multi-institutional study per-
spective, detailed dose specification and planning strategies based on
collaboration and discussion are mandatory and the differences in terms
of PTV-gEUD2 may suggest the inclusion of PTV-gEUD2 calculation for ret-
rospective data inter-comparison.
http://dx.doi.org/10.1016/j.ejmp.2016.01.100A.97
IGRT CONE BEAM CT: A METHOD TO EVALUATE PATIENT DOSE
F. Giglioli
* , a ,O. Rampado
a ,V. Rossetti
a ,M. Lai
a ,C. Fiandra
b ,R. Ropol
o a ,R. Ragon
a b .a
Physics Department, A.O.U. Città della salute e della Scienza di
Torino, Torino, Italy;
b
Radiation Oncology Department, University of Torino,
Torino, Italy
Introduction:
The objective of the study was to calculate organ doses for
several protocols of a radiotherapy cone beam equipment using the PCXMC
software, validated comparing doses with TLDs. Furthermore a set of co-
efficients to provide an estimation of organ doses was assessed for patients
of different genders and sizes.
Materials and Methods:
Dose evaluations were performed on an Elekta
CBCT (XVI) for different protocols and acquisition parameters. The first part
of the study investigated the opportunity to use PCXMC, a software based
on Montecarlo simulation generally employed for projective radiology, for
calculating organ doses. The software was adapted to better simulate the
modulated filtration of this particular CBCT considering different filtered
beam contributions.
A set of 50 TLDs (Harshaw – TLD 100) was selected, irradiated and analysed,
for each protocol, to compare measurements with PCXMC results. The in-
fluence of patient size on organ dose was evaluated varying heights, weights
and genders. The organ doses were normalized to the PCXMC standard adult
phantom doses and the calculated ratios were plotted versus the equiva-
lent diameter of each patient size.
Results:
The differences between PCXMC and TLDs doses are generally below
10%; the respiratory airways and the prostate show a difference over 15%,
probably as a consequence of their position at the boundaries of the beam,
with a critical match of exposure geometry for actual and virtual anthro-
pomorphic phantoms. Regarding simulations with patients of different
heights, weights and genders, a variability in a range
±
40% for pelvic region
and
±
30% for chest was observed; specifically, for the same acquisition pro-
tocol, organ doses for a slim patient could be much higher than the organ
dose of an overweight patient.
Conclusion:
Our results confirm the validity of PCXMC with rotational
module also for particular geometrical conditions; dose difference due to
patient size can be evaluated considering patient equivalent diameter.
http://dx.doi.org/10.1016/j.ejmp.2016.01.101A.98
PREDICTIVE MODELS FOR RADIO-INDUCED EFFECTS AFTER SRS FOR
UVEAL MELANOMA: A MONO-INSTITUTIONAL ANALYSIS
C. Gigliotti
*
, A. Del Vecchio, L. Perna, C. Fiorino, M. Di Nicola, G. Modorati,
P. Mortini, P. Picozzi, A. Franzin, A. Bolognesi, R. Calandrino.
IRCCS San Raffaele
Scientific Institute, Milano, Italy
Introduction:
Uveal melanoma(UM) is a life threatening intraocular ma-
lignant tumor. Gamma Knife Stereotactic Radiosurgery (GKSRS) is a well
assessed strategy for conservative treatment of UM providing good results
for survival, local control and eye preservation. Despite severe side effects
following GKSRS having been reported, literature studies designed to in-
vestigate dose–effect relationship of critical structures are rather poor. Our
aim is to develop predictive models for radio-induced effects in UM pa-
tients (pts) treated with GKSRS.
Materials and Methods:
In our institute, 149 pts were treated with ex-
clusive GKSRS for UM between 1994 and 2014. Prospectively collected
clinical data are available. For 66/149 pts, 3D dosimetry data of involved
critical structures could be recovered and a median follow-up of 2 years
is available. Cox’s analyses were used to identify selected variables as in-
dependent risk factor of main side effects: cataract, radiation
vasculopathy(RV), radiation papillopathy (RP) and neovascular glaucoma
(NVG), visual acuity (VA) reduction
>
20% (VA20%) and complete loss of basal
VA (VA100%). ROC curve analysis allowed predicting cutoff value of sig-
nificant variables.
Results:
The 2 year incidences were: cataract 39%, RV 10%, RP 12%, NVG
14%, VA 20% 59% and VA 100% 27%. Concerning cataract V30 of whole bulb
and tumor thickness resulted highly predictive. A clear relationship with
Dmax to optic nerve (ON) was found for RP and RV. Also, for RV, tumor in
the anterior position to equator was predictive. The V20 of posterior bulb
and tumor thickness were predictive for NVG. Multivariate analyses re-
sulted in 2 variables predictive model both for VA20% and VA100%, including
tumor longest basal diameter and Dmax to ON.
Conclusions:
We found clinical and dosimetric variables to predict the risk
of main side effects after GKSRS for UM. These results may provide new
dose constraints to critical structures that, when implemented in treat-
ment planning, could reduce radiation toxicities.
http://dx.doi.org/10.1016/j.ejmp.2016.01.102A.99
QUALITATIVE AND QUANTITATIVE DIFFERENCES IN MULTIPLE HDR
BRACHYTHERAPY APPLICATION TO LOCALLY ADVANCED CERVICAL
CANCER
R. Gimenez De Lorenzo
*
, M. Enfasi, G. Cocco, G. Spagnoletti, G. Bove.
Azienda
Ospedaliero-Universitaria Ospedali Riuniti, Foggia, Italy
Introduction:
This study focused variability in multiple HDR intracavi-
tary brachytherapy (ICBT) application regarding applicator geometry and
reconstruction, tumor and organs at risk (OARs) contouring. In planning,
DVH variability between BRT-HDR fractions with or without CT simula-
tion (CTS) was analyzed as well.
Materials and Methods:
Treated with radiation therapy, nine patients with
carcinoma cervix (FIGO STAGES, IB2-IVA) underwent first concurrent CHT
and EBRT (DTF:45-50,4 Gy) and then HDR-ICBT fractions of 5–6 Gy at weekly
intervals. Surface Matching fusion was used not only to observe varia-
tions of intrauterine tandem (IT) geometry, but also the distance between
the tip end of the IT and the distance between the ovoids both in cranio-
e29
Abstracts/Physica Medica 32 (2016) e1–e70