968 / 1096
S952
ESTRO 36
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proton beams. H&N/brain audit is more complex than
prostate one, and chamber cavity volume is taken into
account more carefully which enables to keep tight
tolerances.
Results
Centres which participated in the previous run did not
perform better than centres which participated for the
first time in prostate audit. However, results were
sufficient in all cases. There was not significant
improvement in results with installations of new linac and
TPS. Better MLC performance was observed but CT
number to RED was still the problematic
point. Differences in planning approaches can be seen.
Weakest point for the head audit was the phantom
positioning on the couch (despite using IGRT). Tolerances
for film evaluation depend on the dose gradient in the
direction perpendicular to the film plane. We use 95% or
90% (4%/3mm) for gamma index for prostate/ H&N or brain
plans respectively. In future, pseudo-3D gamma analysis
will be implemented.
Conclusion
It is not straighforward to identify the causes of
deviations, especially when they lie within tolerance
limits. Nevertheless, it is possible to identify systematic
errors which might be vendor dependent, user dependent,
or TPS dependent. These can help to optimise the national
quality standard in radiotherapy. We recommend not to
use rigid marks on phantom but let the centre apply their
own fixation and positioning procedure. We recommend to
include CT scanning process and identical „patient“ set-
up procedure employing RTTs. When designing audit
methodology, it is necessary to analyze pilot run results
first and then optimise procedure dependent tolerances.
This work has been supported by the project No.
TB04SUJB001 and by the Ministry of Interior of the Czech
Republic, project No. MV-25972-53/OBVV-2010.
EP-1732 Treatment planning of dose escalation for anal
cancer in the PLATO trial
N.L. Abbott
1
, D. Christophides
2
, M. Robinson
3
, J.
Copeland
4
, R. Adams
5
, M. Harrison
6
, M. Hawkins
3
, R.
Muirhead
3
, D. Sebag-Montefiore
2
1
Velindre Cancer Centre, National Radiotherapy Trials
QA group, Cardiff, United Kingdom
2
University of Leeds, Leeds Cancer Centre- St James
University Hospital & Leeds CRUK Centre, Leeds, United
Kingdom
3
University of Oxford, CRUK/MRC Oxford Institute for
Radiation Oncology, Oxford, United Kingdom
4
University of Leeds, Clinical Trials Research Unit,
Leeds, United Kingdom
5
Velindre Cancer Centre, Cardiff, United Kingdom
6
The Hillingdon Hospital NHS Foundation Trust,
Uxbridge, United Kingdom
Purpose or Objective
P
ersona
L
ising
A
nal cancer radiotherapy
d
O
se
(PLATO)
is
a complex integrated protocol, including ACT5 for high
risk patients.
ACT5 compares standard and dose escalated radiotherapy.
As part of trial development a planning study was carried
out by lead centres to determine the impact of dose
escalation on OAR sparing. Following this study a
benchmark planning case was selected and sent to fifteen
UK centres as part of the radiotherapy quality assurance
programme (RT QA), co-ordinated by the national QA
group. These centres will randomsie the first 60 patients
in a pilot phase of the trial.
We report the results of the planning study and benchmark
planning case with respect to achievable OAR sparing with
ACT5
dose
escalation.
Figure 1: Planning Study target doses
Material and Methods
Eight clinical cases were identified as part of the initial
planning study and independently re-planned per the RT
trial protocol with and without dose escalation by two
experienced IMRT planners. A single (female) case was
then selected representative of a typical yet challenging
case and used as the planning benchmark.
Ten of the fifteen centres participating in the pilot phase
of the trial completed the benchmark planning case,
planning with dose escalation only. All pilot centre data
was processed with CERR
[1]
software enabling dose
distribution and dose volume histograms to be assessed.
Results
Dose escalated plans for the initial eight cases showed no
statistically significant increase in dose to the OAR with
dose escalation (p-value>0.1) whilst maintaining PTV
coverage (D95%>95%).
Ten centres participating in the pilot phase completed the
pre-trial exercise. A range of plan beam configurations
were used: 1x 2arc 6 flattening filter free (FFF) MV, 2x
3arc 6MV, 2x 7-field IMRT 6MV, 2x2arc 6MV, 2x
Tomotherapy and 1x 4arc 6MV.
All centres met all trial mandatory dose objectives for the
benchmark planning case and the vast majority of optimal
constraints, see table 1
.