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is indexed on the patient couch. The cube can be moved
to a predefined translational and rotational offset position
on the couch. Two planar images were acquired and
registered to the CT.The calculated correction vector was
applied by the patient positioning system. This workflow
was repeated at three index positions (equal distributed
along the treatment volume), payloads (0kg, 100kg,
150kg), cube offsets (long.: 10mm, lat.: 15mm, vert.: -
3mm with/without rot 3°) and couch positions. After the
alignment into the isocenter the absolute position was
measured with a lasertracker (u: 0.1mm)(see figure
1b). To determine the total accuracy including the
treatment beam and patient alignment system, an EBT3
film was inserted into the cube. Two fiducials in a row are
used to shift the Bragg peak into the layer of the film (see
figure 1c). For the combined workflow with an EBT3 film,
a rotation error of 1° results in a fading of the fiducials.
Results
The mean 3D accuracy for all workflows was 0,34mm
(n=24). Most of the residual rotational errors were below
0.15°. The mean deviation in x and y changes significantly
in relation to the couch rotation (xmean for 0°: -0.74mm;
xmean for 180°: +0.27mm)(see table 1). In figure 1d) an
EBT3 film after image guided alignment and radiation with
a proton beam is shown. For the combined workflow with
treatment beam the translation in y and z axes was below
1mm and the rotation for rot Y and rot Z is lower than 1°.
Conclusion
The dependencies for couch rotations might arise from a
lateral offset of the imaging ring. A flexmap calibration
with exactly known phantom position may reduce the
lateral offset. The largest deviation (mean 3D vector =
0.78mm) was found for couch rotation 0°.The inserted
EBT3 film allows determining the overall accuracy of the
whole treatment workflow.The IGRT Phantom is an
appropriate equipment for daily QA and for more detailed
workflow tests.
Symposium: Focus on prostate cancer: what is the best
of radiotherapy we need to treat our patients with
SP-0492 What are the best ingredients to deliver the
optimal radiotherapy for prostate cancer
V. Khoo
1
1
Royal Marsden Hospital Trust & Institute of Cancer
Research, Department of Clinical Oncology, London,
United Kingdom
Optimisation for prostate radiotherapy involves
understanding the natural history of prostate cancer, its
prognosticators, the underlying radiobiology and
strategies for radiotherapy treatment as well as how best
to deliver the therapy regimes devised. Prostate cancer
presents with a large spectrum of risk factors that drives
its natural history as such the presenting prostate specific
antigen (PSA) levels, the summed Gleason score and the
local tumour nodal and metastasis (TNM) staging. Taken
together this combination of prognostic factors still
provides the most reliable disease stratification compared
to new tests or potential biomarkers that still require
validation. It is well recognised that more reliable and
sensitive predictive and prognostic factors are needed to
distinguish risk groups within each risk stratification due
to the large heterogeneity that exists within them. Using
this approximately set of factors, prostate cancer can be
divided into low, intermediate and high to very high risk
groups for localised to regional disease that may receive
radiotherapy curatively. This further guides the treatment
volumes needed to achieve the best curative rate as well
as the treatment strategies ie external beam photon
therapy alone or in combination with high dose rate (HDR)
brachytherapy or HDR monotherapy or proton therapy In
addition, over the past one to two decades, the
understanding of prostate radiobiology has changed from
accepting the standard alpha-beta ratio of 10 assigned for
the majority of cancer diseases to a much lower alpha-
beta ratio much more akin to that of late reacting tissues.
This lower alpha-beta ratio of around 1.2 to 2.5 has driven
the radiotherapy rationale for using larger dose per
fraction or hypofractionation. Earlier trials have suggested
that this may provide a therapeutic benefit. Recently in
the past year, 2 very large randomised trials have provided
outcome equivalence for the use of moderate
hypofractionation
compared
to
conventional
fractionation. The first randomised trial of over 800 cases
from USA in early stage disease compared 2.75Gy to 1.8Gy
dose fractions in a non-inferiority study can reported
equivalence for the schedules. The second non-inferiority
UK/International trial recruited nearly 3300 cases and
reported equivalence of 3Gy to 2Gy dose fractions for
early to intermediate stage prostate cancer. These
outcomes have now established a new standard for the
radiotherapeutic management of early to intermediate
stage localised prostate cancer. These results should not
be confused with the Dutch study looking for superiority
of 3.3Gy over 2Gy dose fractions where the primary
endpoint was not achieved. It remains to be determined if
larger dose fractions (≥ 5Gy) delivered over 1 week such
as that used in stereotactic radiotherapy may provide
further benefit. Trials are currently on going and their
results are eagerly awaited. As important as the dose
fractionation are the therapy regimes and the potentially
combinations listed above. It is recognised that local
failure often occurs at the site of dominant clonagenic
numbers thus the utilisation of simultaneous integrated
boosts with hypofractionation has potential. This is being
assessed in several studies such as the FLAME study where
toxicity was demonstrated to be similar to standard and
conventional regimes. Important questions that need to be
addressed include identification of appropriate treatment
volumes and potential regions of dose escalation or even
dose de-escalation. Just as important will be methods of
ensure that these shorter treatment regimes are delivered
both accurately and reliably. These aspects will be
reviewed by the co-lecturers within this symposium.
SP-0493 The role of spacers in the era of highly
conformal, hypo-fractionated, image guided, adaptive
radiotherapy of the prostate
P. Scherer
1
, F. Wolf
1
, C. Gaisberger
1
, F. Sedlmayer
1
1
Gemeinn. Sbg. Landeskliniken Betriebs. GmbH,
University Clinic for Radiotherapy and RadioOncology,
Salzburg, Austria