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S983
ESTRO 36 2017
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EP-1819 EORTC RTT Delineation Project: improving
volume definition of OAR within the EORTC Lungtech
trial
M. Van Os
1
, M. Rossi
2
, C. Hurkmans
3
1
Erasmus MC Cancer Institute, Department of Radiation
Oncology, Rotterdam, The Netherlands
2
Netherlands Cancer Institute, Radiation Oncology
Department, Amsterdam, The Netherlands
3
Catharina Ziekenhuis EIndhoven, Radiation Oncology,
Eindhoven, The Netherlands
Purpose or Objective
To accurately evaluate toxicity within a trial, it is
important that the delineation of the Organs at risk (OAR)
is performed
consistently.
The aim of the EORTC ROG/RTT delineation project is to
reduce variability in OAR delineation to allow better
comparison of toxicity in EORTC trials between institutes.
Within the EORTC LungTech trial we evaluated whether
provided delineation guidelines are explicit enough to
avoid misinterpretation in volume definition of OAR and
whether a hands-on delineation workshop adds to this.
Material and Methods
A questionnaire was developed and distributed amongst
participating institutes requesting feedback after they had
completed their benchmark delineation for the EORTC
LungTech trial. Difficult areas could be identified.
Subsequently two groups were defined: Group A to
perform delineation of OAR according to protocol
guidelines and with additional visual guidelines. Group B
was invited to a delineation workshop where an expert
teacher addressed the difficult areas provided from the
benchmark cases. The consequent delineations were then
evaluated per organ at risk between group A and B and
also compared to the benchmark cases. The volume of
agreement
was
calculated.
Our hypothesis is that a delineation workshop prior to
launching a trial improves consistent volume definition.
Results
Introducing visual guidelines as an extra aid to the written
guidelines significantly reduced misinterpretation and
greatly improves the consensus of delineation. Although
not specifically tested between the groups the RTT’s
performance in delineating the OARs was deemed as
consistent as the clinicians. We aim to demonstrate the
additional value of teaching by means of a delineation
workshop, but this analysis is still ongoing.
Conclusion
The EORTC ROG advised to involve RTTs in future EORTC
trials for volume definition of
OAR.
In future EORTC trials, a kick-off including a delineation
workshop for participating institutes is planned to achieve
more consistent delineation of OAR.
Electronic Poster: RTT track: Treatment planning and
dose calculation / QC and QA
EP-1820 RapidArc vs IMRT in adjuvant gastric cancer
irradiation: any dosimetric advantage?
K. Mashhour
1
, W. Hashem
1
, R. Fawzy
1
, H. Abdelghany
2
1
Kasr el ainy school of medicine-Cairo university, clinical
oncology, cairo, Egypt
2
Kasr el ainy school of medicine-Cairo university,
radiation physics, cairo, Egypt
Purpose or Objective
The outcome of intensity modulated radiation therapy
(IMRT) plans depends on the choice of number of fields,
beam orientations, optimization algorithms & planner
experience. The RapidArc has the characteristics of both
good plan quality as well as high delivery efficiency. The
purpose of this work was to compare dosimetric endpoints
between IMRT & RapidArc techniques for gastric
carcinoma patients in the adjuvant setting.
Material and Methods
Twenty gastric cancer patients who had a radical
gastrectomy with D2 dissection were eligible. The clinical
target volume (CTV) included the gastric bed, anastomosis
with 2-cm proximal/distal margins & regional LN areas.
The planning target volume (PTV) consisted of CTV plus a
10 mm margin.All plans were created in the Eclipse
treatment planning system (v8.6 Varian Medical System).
For IMRT, a coplanar seven-field plan was performed.
Regarding the RapidArc, plans were done using a double
arc plan consisting of 2 co-planar arcs of 360° in clockwise
& counter clockwise direction. Dose prescribed was 45 Gy
to the PTV in 25 fractions using 6MV photons. The PTV dose
coverage criteria were as follows: at least 95% of PTV
received 45Gy; The conformity index (CI) & homogeneity
index (HI) were calculated. The organs at risk (OAR) were
the spinal cord, both kidneys and liver.
Results
Target coverage was similar for both techniques. The
mean V95 was found to be 94.7% & 94.8% for the IMRT and
RapidArc respectively (p = 0.32). The CI for IMRT and
RapidArc were 0.93 ± 0.01 & 0.94 ± 0.01, respectively;
while the HI was 1.15 ± 0.01 for IMRT & 1.14 ± 0.02 for
RapidArc (both p > 0.04).All the plans met the required
dose limitations. The maximum spinal cord dose for IMRT
and RapidArc was 37.87 Gy vs 36.42 Gy (p = 0.34). For the
right kidney, IMRT had significantly lower mean V20
(volume that receives 20 Gy) compared to RapidArc (23.2
vs. 30.3, p = 0.01). The mean V20 to the left kidney were
28.4 and 27.4 in the IMRT and RapidArc respectively (p =
0.01). The IMRT produced a similar liver mean V30 (volume
that receives 30 Gy) (24.3 vs. 23.1, p = 0.52) to RapidArc.
The treatment delivery time was 193.5 ± 25.0 s (range 157–
230 s) to IMRT and 66.0 ± 8.7 s (range 55–77 s) to RapidArc
(p = 0.00). The total monitor units (MU) for IMRT and
RapidArc were
343.0 ± 94.0 & 363.0 ± 44.0 (p = 0.07),
respectively.
Conclusion
RapidArc obtained similar dosimetric outcomes to IMRT
plans regarding target coverage & OAR sparing with an
advantage of shorter delivery time & lower number of MU.
EP-1821 Air gap between patient surface and
immobili
zation devices: dosimetric impact on H&N IMRT
plans
S. Moragues-Femenia
1
, M. Pozo-Massó
2
, J.F. Calvo-
Ortega
2
, J. Casals-Farran
2
1
Moragues Femenia Sandra, HOSPITAL QUIRON
BARCELONA- Radiotherapy, Barcelona, Spain
2
HOSPITAL QUIRON BARCELONA- Radiotherapy, HOSPITAL
QUIRON BARCELONA- Radiotherapy, Barcelona, Spain
Purpose or Objective
In head and neck (H&N) treatments, there is an avoidable
air gap between the typical mask-based immobilization
device used and the patient surface ("air gap" from now
on). Our aim is to evaluate the dosimetric effect of
considering the "air gap" on the patient dose distribution
on H&N IMRT plans.
Material and Methods
A
total of 5 H&N patients were selected. The
"immobilization" device consisted of a thermoplastic mask
covering the head, neck and shoulders, and attached to a
board on the linac couch. Targets (PTVs) and organs-at-