690 / 1082
S674
ESTRO 36 2017
_______________________________________________________________________________________________
Conclusion
Image-guided IMRT with a SIB approach concomitant to 5-
FU/MMC based chemotherapy is a safe and well tolerated
treatment strategy in an unselected anal cancer patient
population.
EP-1266 In silico evaluation of subcutaneous skin dose
associated to use of MRIdian MRI- 60Co System
G.C. Mattiucci
1
, L. Boldrini
2
, D. Cusumano
3
, L. Azario
4
, M.
Ferro
2
, S. Chiesa
2
, G. Chiloiro
2
, N. Dinapoli
2
, M.A.
Gambacorta
1
, C. Masciocchi
5
, E. Placidi
6
, D. Piccari
7
,
M.V. Antonelli
7
, M. Rapisarda
7
, S. Teodoli
6
, M. Balducci
1
,
A. Piermattei
4
, F. Cellini
2
, V. Valentini
1
1
Università Cattolica del Sacro Cuore, Gemelli ART -
Radiation Oncology, Rome, Italy
2
Fondazione Policlinico A. Gemelli, Gemelli ART -
Radiation Oncology, Rome, Italy
3
Fondazione Policlinico A. Gemelli, UOC di Fisica
Sanitaria - Gemelli ART - Radiation Oncology, Rome,
Italy
4
Università Cattolica del Sacro Cuore, Rome, Italy
5
Fondazione Policlinico A. Gemelli, KBO Labs - Gemelli
ART - Radiation Oncology, Rome, Italy
6
Fondazione Policlinico A. Gemelli, UOC Fisica Sanitaria -
Gemelli ART - Radiation Oncology, Rome, Italy
7
Fondazione Policlinico A. Gemelli, TSRM - Gemelli ART -
Radiation Oncology, Rome, Italy
Purpose or Objective
The MRIdian MRI-
60
Co radiotherapy system (ViewRay,
Oakwood, Ohio) combines an open split-solenoid MRI
scanner equipped for parallel imaging and three
60
Co
gamma-ray sources.
The dose delivered to the subcutaneous tissues of skin by
such system should be evaluated: the lower mean beam
energy of the Cobalt source compared to those of clinical
X-ray beam lead to increase of the surface dose.
A previous study (SIMBAD 01) investigated the feasibility
of comparative planning among different radiotherapy
technologies (i.e: IMRT vs VMAT vs MRI-
60
Co) optimizing for
target coverage and organs at risk sparing. Hardware and
software implementation on MRIdian will be completed at
our institution within February 2017. Experimental
measurements are planned when the system will become
clinically operative. Aim of the present analysis is to
quantify the dose delivered to subcutaneous tissues in the
SIMBAD 01 planning conditions (without specific
optimization for subcutaneous tissues).
Material and Methods
Ten patients affected by locally advanced rectal cancer
(LARC) were included in this study. For each patient a
VMAT RapidArc, a 5-beams sliding window IMRT and one
MRIdian treatment plan were performed.
All treatment plans were calculated according to the
Quality Assurance protocols adopted in our Institution: the
PTV1 was represented by tumor and corresponding
mesorectum; the PTV2 by mesorectum in toto and pelvic
nodes. Isotropic 0.7 cm margins were added to PTVs. The
total prescribed dose for PTV1 was 55 Gy and 45 Gy for
PTV2 through Simultaneous Integrated Boost.
All plans were optimized for PTV coverage and sparing of
bowel bag and bladder.PTV coverage was evaluated by
calculating the V95 and V105 values. For bowel bag V45
and for bladder the mean dose was considered.
The presence of magnetic field has been taken into
account during MRIdian MRI-
60
Co planning procedures..
The evaluation of subcutaneous skin dose was obtained
calculating the median dose in a 5 mm wide ring dummy
structure contoured 3 to 8 mm far from body surface.
The first 3 mm from body surface were not taken into
account to avoid inconsistencies related to uncertainties
in dose calculation at air-body interface due to different
dose calculation algorithms (AAA Collapse Cone for VMAT
and IMRT treatments, Montecarlo for MRIdian TPS).
Results
All plans optimized for this study satisfied the constraints
on PTV coverage and organs at risk sparing. Dosimetric
values obtained in this planning comparison are listed in
table 1.
The median skin dose resulted higher using the MRIdian
system (1.97 Gy against 1 Gy for IMRT and 0.98 Gy for
VMAT)
Conclusion
A subcutaneous skin dose increase is observed with the
employment of MRI-
60
Co RT when compared to LINAC
treatment planning, even if still in clinically acceptable
constraints. Considering and contouring such a structure
seems useful. Specific study will be performed to define
how reducing dose to subcutaneous tissues by optimizing
for
such
structures.
EP-1267 In silico Evaluation of the impact of Magnetic
Field on dose distribution using of MRIdian MRI- 60Co
D. Cusumano
1
, L. Boldrini
2
, L. Azario
3
, S. Teodoli
1
, M.
Balducci
4
, G.C. Mattiucci
4
, S. Chiesa
2
, G. Chiloiro
2
, N.
Dinapoli
2
, M.A. Gambacorta
4
, C. Masciocchi
5
, D. Piccari
6
,
M. Rapisarda
6
, M.V. Antonelli
6
, M. Ferro
2
, E. Placidi
1
, A.
Piermattei
3
, F. Cellini
2
, V. Valentini
4
1
Fondazione Policlinico A. Gemelli, UOC Fisica Sanitaria -
Gemelli ART - Radiation Oncology, Rome, Italy
2
Fondazione Policlinico A. Gemelli, Gemelli ART -
Radiation Oncology, Rome, Italy
3
Università Cattolica del Sacro Cuore, Rome, Italy
4
Università Cattolica del Sacro Cuore, Gemelli ART -
Radiation Oncology, Rome, Italy
5
Fondazione Policlinico A. Gemelli, KBO Labs - Gemelli
ART - Radiation Oncology, Rome, Italy
6
Fondazione Policlinico A. Gemelli, TSRM - Gemelli ART -
Radiation Oncology, Rome, Italy
Purpose or Objective