846 / 1082
S830
ESTRO 36 2017
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Conclusion
The use of IMRT for SIB in right breast has to be limited to
those patients for which electron boost or brachytherapy
is not adequate as the mean dose to heart is significantly
higher. The use of DIBH in left-sided breast considerably
reduces mean and V
25
heart doses. IMRT in left-sided
breast shows an increase in D
mean
and a decrease in V
25
,
which leads to significant differences in dose distribution
over the heart. Heart toxicity could, therefore, have
different patterns depending on the technique, being D
mean
a poor surrogate for heart toxicity.
Skin toxicity has to be followed-up carefully in patients
with high breast volumes.
EP-1562 A Dose Painting Study Based on CT
Intratumoural Heterogeneity vs. FDG PET Uptake in
NSCLC
S. Alobaidli
1
, C. South
2
, S. McQuaid
2
, J. Scuffham
2
, I.
Phillips
3
, V. Prakash
4
, V. Ezhil
3
, A. Nisbet
2
, P. Evans
1
1
University of Surrey, CVSSP-Electronic Engineering,
Guildford, United Kingdom
2
Royal Surrey County Hospital, Medical Physics,
Guildford, United Kingdom
3
Royal Surrey County Hospital, Clinical Oncology,
Guildford, United Kingdom
4
Royal Surrey County Hospital, Nuclear Medicine,
Guildford, United Kingdom
Purpose or Objective
Intratumoural heterogeneity has been reported in the
literature to correlate to treatment outcome and overall
survival. In this study, a volumetric voxel based map of
intratumoural heterogeneity measured from CT images
was used to guide dose painting. This approach was
compared against dose painting based on FDG PET uptake
distributions in regards to the overlap between the boost
volumes and the delivered dose to target volumes and
organs at risk (OAR).
Material and Methods
PET/CT and planning CT images for ten patients diagnosed
with advanced inoperable non-small cell lung cancer
(NSCLC) were retrieved retrospectively. The gross tumour
volume (GTV) contour was used to segment the primary
tumour from the CT and PET images. A volumetric voxel
based map of intratumoural heterogeneity was generated
from tumour CT image using a second-order statistical
texture analysis method of grey level co-occurrence
matrices. The FDG PET image was converted to SUV map.
The low CT intratumoural heterogeneity regions within the
generated texture map overlapped with high FDG uptake
regions within the PET image (overlap of 65±11%). Hence,
two boost volumes were identified, the low CT
intratumoural heterogeneity region (Boost
Heterogeneity
) and
the high FDG uptake region of >50% SUVmax (Boost
FDG
). A
3mm margin was added to the boost volumes to account
for physical uncertainties and these volumes were labelled
PTV
Heterogeneity
and PTV
FDG
. Two volumetric arc therapy plans
(VMAT) were created for each patient, with a prescribed
dose of 84Gy in 32 fractions to PTV
Heterogeneity
or PTV
FDG
and
64Gy in 32 fractions to the remainder of the clinical PTV.
The dose to the boost volumes and OARs (spinal cord,
oesophagus, normal lung and heart) was measured and
compared between the two plans.
Results
The dose escalation to the boost volumes in the created
plans were shown to be clinically feasible with the dose to
OARs within tolerance limits and 95% of the target volume
receiving ≥95% of the prescribed dose. When boosting
based on PTV
Heterogeneity,
the dose to 95% of PTV
FDG
received
≥95% of the prescribed dose
for 3 patients while the other
seven patients received 80-92% of the prescribed dose.
However, 95% of the Boost
FDG
volume received ≥95% of the
prescribed dose
for 9 of the 10 patients.
Conclusion
The results show the feasibility of dose escalation in
advanced NSCLC while keeping to normal tissue
constraints. Moreover, the preliminary results suggest that
boosting based on intratumoural heterogeneity measured
from CT images, results in the high 18F-FDG regions
receiving a high dose, indicating the potential of using CT
intratumoural heterogeneity generated from standard CT
images as a surrogate for functional imaging in dose
painting.
EP-1563 Treatment planning for synchrotron
microbeam radiotherapy
L. Day
1
, L.M. Smyth
2
, M. Holm
3
, P.A.W. Rogers
2
, P.E.
Engström
4
, C. Ceberg
4
, C.M. Poole
1
, J.C. Crosbie
1
, S.
Senthi
5
, K. Woodford
5
1
RMIT University, School of Science, Melbourne,
Australia
2
University of Melbourne, Department of Obstetrics and
Gynaecology, Melbourne, Australia
3
Lund University, Department of Medical Radiation
Physics, Lund, Sweden
4
Lund University Hospital, Department of Radiation
Physics, Lund, Sweden
5
Alfred Hospital, William Buckland Radiotherapy Centre,
Melbourne, Australia
Purpose or Objective
Synchrotron microbeam radiation therapy (MRT) is a novel
radiotherapy modality with significant clinical potential.
We have produced a simple dose calculation algorithm for
MRT using the Eclipse Treatment Planning System (TPS),
by Varian Medical Systems.
Material and Methods
The calculation engine in Eclipse was configured to
directly evaluate ‘peak’ doses. Monte Carlo-simulated
Peak-to-Valley Dose Ratios were used to obtain the
‘valley’ dose displayed in Eclipse. We compared dose
profiles generated by Eclipse with Geant4 Monte Carlo
simulations and measurements from the Imaging & Medical