919 / 1096
S903
ESTRO 36
_______________________________________________________________________________________________
Results
Thirteen patients had their RT plan adapted at least once
during treatment. In the first adaptation (13 pts), the
median decrease in the CTV receiving 95% of prescribed
dose (V95%) and the planning target volume (PTV) was
0.2% [0-6.4%] and 5.2% [0-11.7%], respectively, see Fig2.
The largest underdosage was related to interfractional
baseline shifts in the diaphragm position (6 pts), with a
median decrease in CTV V95% of 0.6% [0-6.4%] and PTV
V95% of 8.6% [1.7-11.7%]. Target deviations registered as
changes in SS (8 pts), were typically caused by swelling of
the target area (7 pts), shrinkage or swelling of the
mediastinum (4 pts) and/or compression or stretching of
the target due to changed diaphragm position (1 pt).
Changes in SS were pooled and showed a median decrease
in CTV V95% of 0.2% [0-0.6%] and PTV V95% of 5.0% [0.5-
6.9%].
Four pts had a second adaptation during RT. For these pts,
changes above tolerance were solely observed for SS. The
median decrease in CTV V95% was 0.2% [0-2.1%] and PTV
V95% was 4.5% [0.6-7.2%]. None of the twice adapted
patients showed changes in anatomy which justified
reverting to the original treatment plan – either the
changes were further in the same direction or in a
different region.
Conclusion
Target coverage during the chemoRT in EC patients was
compromised in some cases due to interfractional
anatomical changes. Changes observed during RT
persisted and in some cases they increased, making
adaptation of the RT plan necessary.
EP-1662 Interfractional trend analysis of sinograms: a
decision-making for adaptive radiotherapy
S. Bresciani
1
, A. Garello
1
, A. Miranti
1
, A. Maggio
1
, A. Di
Dia
1
, P. Gabriele
2
, M. Stasi
1
1
Candiolo Cancer Institute - FPO- IRCCS, Medical Physics,
Candiolo TO, Italy
2
Candiolo Cancer Institute - FPO- IRCCS, Radiotherapy,
Candiolo TO, Italy
Purpose or Objective
The aim of this study is to investigate how geometric and
anatomical changes can be detected in daily sinogram
informations and how this information can be used to
examine interfractional trends, building toward a
methodology to optimize treatment and support adaptive
replanning.
Material and Methods
Sensitivity of detectors and sinograms complex to detect
shift errors and anatomical variations was previously
tested on thoracic phantom. In particular systematic
variations in shifts (1-5 mm in lateral direction),
anatomical variations (adding 1.25-2.5 cm bolus over
phantom) were applied.
Subsequently, a total amount of 106 patients treated with
Tomotherapy and their related 1573 sinograms were
analyzed. The sinograms, measured using Xenon
detectors integrated in Tomotherapy unit, were compared
with a reference one (usually the first fraction) using both