ESTRO 36 Abstract Book

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S185 ESTRO 36 2017
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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. Simon 1,2, M. Gobeli3, C. Lafond1,3, D.
Williaume3, J. Leseur3, J. Castelli 1,2,3, P. Haigron1,2, R. De
Crevoisier1,2,3
1 INSERM, U1099, Rennes, France
2 Université de Rennes 1, LTSI, Rennes, France
3 Centre 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
strategy PTVs. The under-coverage of the CTV by the PTV
was investigated using elastic registration.
Results
The “Evolutive library RT” corresponded to a mean
number of one per-treatment replanning (up to 3). For
50% of the cohort, no per-treatment replanning was
needed. The table shows the CTV and OARs coverage by
the PTV for all strategies. The evolutive library strategy
provided the highest CTV coverage compared to the other
strategies corresponding to a mean CTV coverage (min –
max) of 98.3 % (96.4 – 100%) with 10mm margins and to
96.0 (93.0 – 99.7) with 7mm margins (p<0.05). Moreover,
this strategy significant decreased the bowel-PTV
overlapping.
Conclusion
The “Evolutive library RT” strategy increased the CTV to
PTV coverage, while not increasing the PTV bladder
overlapping and even decreasing the bowel to PTV
overlapping.
OC-0353 Implementation of RTT led ‘plan of the day’
adaptive radiotherapy in cervical cancer