ESTRO 36 Abstract Book

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S186 ESTRO 36
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fields. Treatment was delivered with a Novalis-
TrueBeam™ STx Linac (Palo Alto, CA, USA). IGRT was
achieved with ExacTrac® (version 6.0). ExacTrac®
documented the eye position before and after each
irradiation field.
Results
No local failure and no case of enucleation have been seen
at a median follow-up time of 329 days (range 98 –
678). Complications observed so far were impairment of
visual acuity in half of the cases, intraocular haemorrhage
(1 pts.), xerophthalmia (2 pts.), or keratritis (2 pts). The
minimal, mean, and maximal doses within the target
volumes were 86.3 (± 5.2)%, corresponding to V95% = 98.3
(± 1.4)%, 100.0 (± 0.4)%, and 103.4 (± 1.1)%, respectively.
The conformity index was 1.23 ± 0.16 and the homogeneity
index was 0.04 ± 0.01. Mean dose applied to the ipsilateral
eye lens, cornea, normal tissue of the involved eye, and
the lacrimal gland were 12.1 (± 17.7) Gy, 6.8 (± 11.5) Gy,
18.1 (± 9.2) Gy, and 10.7 (± 7.6) Gy, respectively. Maximal
dose of the ipsilateral optic nerve was 31.7 (± 15.9) Gy.
Doses delivered to the contralateral eye, lens, optic
nerve, and lacrimal gland were less than 0.6 (± 0.7) Gy,
0.2 (± 0.1) Gy, 1.3 (± 1.6) Gy, and 0.2 (± 0.1) Gy,
respectively. The doses given to the chiasma did not
exceed 1.3 (± 1.5) Gy; the pituitary gland 0.9 (± 1.4) Gy,
and the maximal dose to the brain did not exceed 11.1 (±
4.9) Gy. The ITV did not exceed 2mm.
Conclusion
HybridArc® in combination with peritumoral tissue
markers for image-guidance provides highly conformal and
homogenous doses distributions for the treatment of small
and moving target volumes.
Proffered Papers: Adaptive strategies
OC-0351 Analysis of concordance in multicentre
adaptive bladder trials quality assurance
E. Parsons 1, D. Megias1 , A. Baker1, S. Hafeez2, E. Hall2, H.
McNair 3, Y. Tsang1 , R. Huddart3
1 Mount Vernon Hospital, National Radiotherapy Trials
Quality Assurance Group, Northwood- Middlesex, United
Kingdom
2 The Institute of Cancer Research, Clinical Trials Unit,
Sutton- Surrey, United Kingdom
3 Royal Marsden Hospital, Radiotherapy, Sutton- Surrey,
United Kingdom
Purpose or Objective
HYBRID (CRUK/12/055) and RAIDER (CRUK/14/016) are
two randomised phase II multi-centre clinical trials
investigating the use of adaptive 'Plan of the day” (POD)
bladder radiotherapy. In order to promote accurate POD
selection across multiple recruiting centres, a pre-accrual
assessment for adaptive plan selection was developed as
part of an IGRT QA credentialing programme (3rd ESTRO
Forum 2015-OC0564). The purpose of this study was to
establish whether the pre-accrual POD assessment is a
feasible QA process and investigate whether the POD can
be consistently selected by individuals across all recruiting
centres.
Material and Methods
Twelve bladder CT/CBCT image pairs were made available
to individuals to register according to protocol. Individuals
recorded the most appropriate POD selection from a
library of three possible plans and submitted to a central
QA group for review. In order to receive QA approval to
select the POD for HYBRID/RAIDER, individuals were
required to achieve an assessment score of ≥83% (10/12)
agreement with the expert consensus answers.
It was a pre-requisite of HYBRID and RAIDER that centres
already have an appropriate IGRT competency framework
for bladder CBCT in place prior to trial recruitment. The
assessment was first piloted for 10 centres recruiting to
the HYBRID trial in November 2013 and then utilised for a
further 14 RAIDER centres in June 2015. The Mann-Whitney
U test and Kruskal-Wallis test were used to investigate if
there were any significant difference in assessment scores
between the two trials and individual staff grading
respectively.
Results
The POD assessment was completed by 244 individuals
(HYBRID=73, RAIDER=171) from 24 recruiting centres. The
median assessment score was 92% (range: 25-100%) and
86% of individuals achieved the score required for QA
approval on their first attempt. The distribution of
assessment scores in RAIDER was found to be significantly
different to HYBRID (p=0.034). Individuals would be more
likely to achieve a score ≥83% for RAIDER (90%) than
HYBRID (77%). Each centre had an average of 10.2 (Range
3-23) individuals complete the POD assessment. There was
no statistically significant difference in assessment scores
between different staff grades (p=0.713). The median
assessment scores varied between recruiting centres, with
a range between 83% and 100%.
Conclusion
A high median score was achieved by the individuals that
completed the assessment indicating consistent POD
selection with the expert consensus answers across
individuals and centres. The POD assessment proved to be
a feasible way of credentialing multiple individuals across
all recruiting centres. Differences in assessment scores
between HYBRID and RAIDER trials likely reflect the
increased experience with pelvis CBCT in UK centres
between 2013 and 2015. Individuals of all grades were able
to successfully complete the assessment indicating the
importance of appropriate local IGRT training rather than
staff seniority when choosing the POD.
OC-0352 CBCT-guided evolutive library for cervix
adaptive IMRT
B. Rigaud1,2, A. Simon1,2, M. Gobeli3, C. Lafond1,3, D.
Williaume3, J. Leseur3, J. Castelli1,2,3, P. Haigron1,2, R. De
Crevoisier1,2,3
1INSERM, U1099, Rennes, France
2Université de Rennes 1, LTSI, Rennes, France
3Centre Eugene Marquis, Radiotherapy Department,
Rennes, France
Purpose or Objective
In the context of locally advanced cervix carcinoma
adaptive radiation therapy (ART), this study aimed to
simulate five treatment strategies, including an original
CBCT-guided evolutive library. We compared
geometrically the strategies by considering the coverage
by the simulated PTVs for both CTV and OARs.
Material and Methods
Sixteen patients having received a total dose of 45 Gy by
IMRT for locally advanced cervix carcinoma were included.
Each patient had: three planning CTs corresponding to
three bladder volumes (empty (EB), intermediate (IB) and
full (FB)), a CT scan at 20 Gy and bi-weekly CBCTs for 5
weeks. The CTV and the OARs were manually delineated
on each CT and CBCT. Five radiotherapy (RT) strategies
were investigated (Figure 1): (1) “Standard RT” based on
one planning CT with IB and considered as reference, (2)
“ITV-based RT” with an ITV built from the three planning
CT scans, (3) “RT with one midtreatment replanning”
corresponding to the standard RT with replanning at 20
Gy, (4) “Pretreatment library ART” using the three
planning CTs (EB, IB, FB) to define the plan of the day by
a CTV overlapping criteria, and (5) “Evolutive library RT”
corresponding to the 4th strategy enriched by including
CBCTs anatomy in the pretreatment library if the daily
CTV shape was highly different (overlap scores between
the library and the daily CTV). For each strategy, two PTV
margins were used (7 and 10 mm). All the strategies were
geometrically compared by considering, on the CBCTs, the
percentage of coverage of the CTV or the OAR by the