ESTRO 36 Abstract Book

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S936 ESTRO 36 2017
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The use of different coils at greater distance from the
organ of interest and the use of a flat carbon fibre
tabletop produced a reduction of the SNR. Even safe under
the protocol we used, we believe that the use of more
appropriated materials for MRI should be recommended.
Nevertheless, this setup could be a low-cost first step for
departments who want to start to integrate MRI images
into their RT workflow.
EP-1728 Inter-observer contouring similarity metrics,
correlation with treatment outcome for prostate cancer
D. Roach1,2, M. Jameson1,2 , J. Dowling3, M. Ebert4,5,6, P.
Greer7,8, S. Watt 2, L. Holloway1,2,5,9
1 University of New South Wales, South Western Clinical
School, Sydney, Australia
2 Sydney South West Area Health Service, Ingham
Institute and Liverpool and Macarthur Cancer Therapy
Centres, Sydney, Australia
3 CSIRO, Australian e-Health Research Centre, Brisbane,
Australia
4 Sir Charles Gairdner Hospital, Radiation Oncology,
Perth, Australia
5 University of Wollongong, Centre for Medical Radiation
Physics, Wollongong, Australia
6 University of Western Australia, School of Physics,
Perth, Australia
7 Calvary Mater Hospital Newcastle, Radiation Oncology,
Newcastle, Australia
8 University of Newcastle, School of Mathematical and
Physical Sciences, Newcastle, Australia
9 University of Sydney, Institute of Medical Physics,
Sydney, Australia
Purpose or Objective
To determine the geometric and statistical metrics
quantifying inter-observer contouring variation displaying
the strongest correlation with simulated treatment
outcome for prostate cancer.
Material and Methods
Data was available for 39 patients with localised prostate
cancer, each having undergone CT and MRI scanning prior
to radiotherapy. Three observers independently
contoured CTV, bladder, and rectum on T2 MRI. A 7mm
margin was applied to each observer’s CTV to create
observer PTVs. An estimate of the true volume of each
structure was generated using the STAPLE
algorithm. Geometric and statistical metrics spanning the
literature for inter-observer contouring variation studies
were calculated for each observer’s contours with respect
to the STAPLE volume. VMAT treatment plans (78 Gy to
PTV) were simulated for each observer’s contoured
structures, as well as for the STAPLE volumes, for all
patients. Radiobiological metrics assessing treatment
outcome (TCP, EUD, NTCP, etc.) were calculated for
STAPLE CTV, PTV, bladder, and rectum for all treatment
plans. Correlations between contouring variation metrics
and radiobiological metrics were assessed using
Spearman’s rank correlation coefficient ρ
Results
In total 117 observer treatment plans were simulated,
resulting in a study with power to detect statistically
significant (p < 0.05) correlations of ρ ≥ 0.3. No
statistically significant correlations were found between
contouring variation and radiobiological metrics for CTV
and bladder. Figures 1 and 2 observed correlations for PTV
and rectum respectively. For both structures volume
similarity, sensitivity, and specificity showed moderate
levels of correlation with a range of radiobiological
metrics, although no correlations were observed between
contouring variation and maximum dose within the
rectum. Dice Similarity Coefficient (DSC) and Jaccard
Index were found to have no significant correlation with
simulated outcome for either structure, despite their
prevalence within the literature. Centre-of-mass
variations in the coronal and sagittal planes for PTV and
rectum respectively were the only distance metrics
displaying significant correlations to simulated treatment
outcome. Euclidean centre-of-mass variations, Hausdorff
Distance, and Mean Absolute Surface Distance showed no
correlation with any radiobiological metric.
Conclusion
Results indicate that volume similarity, sensitivity,
specificity, and centre-of-mass significantly correlate with
simulated treatment outcome within the rectum and PTV
for prostate cancer radiotherapy. This information could
inform future automated registration and atlas methods,
allowing them to be guided on metrics based on clinical
significance.
Electronic Poster: Physics track: Implementation of new
technology, techniques, clinical protocols or trials
(including QA &amp; audit)
EP-1729 Air pockets in the urinary bladder during
hyperthermia treatment reduce thermal dose
G. Schooneveldt1, H.P. Kok1, E.D. Geijsen1, A. Bakker1,
J.J.M.C.H. De la Rosette2, M.C.C.M. Hulshof1, T.M. De
Reijke2, J. Crezee1
1Academic Medical Center, Radiotherapy, Amsterdam,
The Netherlands
2Academic Medical Center, Urology, Amsterdam, The
Netherlands
Purpose or Objective
Hyperthermia is a (neo)adjuvant treatment modality that
increases the effectiveness of radiotherapy or
chemotherapy by heating the tumour area to 41–43 °C.
This has been shown to improve treatment outcome for a
number of tumour sites, including the urinary bladder.
Hyperthermia may be given both for muscle-invasive
bladder cancer, where it is combined with radiotherapy,
and for non-muscle invasive disease (NMIBC), where it is
combined with chemotherapy. However, some air may be
present in the bladder during treatment, which effectively
blocks the microwave radiation used to warm the bladder.
This may lead to a lower thermal dose to the bladder wall,
which is associated with a lower treatment response. This
study investigates the size of that effect.
Material and Methods
We analysed thirteen NMIBC patients treated at our
institute with mitomycin C (40 mg in 50 ml) plus
hyperthermia (60 min). Hyperthermia was delivered using
our hyperthermia device with four 70 MHz antennas
around the pelvis. A CT scan was made after treatment
and a physician delineated the bladder on the CT scan. On
the same scan, the amount of air present in the bladder
was delineated. Using our in-house developed
hyperthermia treatment planning system, we simulated
the treatment using the clinically applied device settings.
We did this with the air pocket delineated on the CT scan,
and alternatively with the same volume filled with fluid
(urine).
Results
The patients had on average 4.2 ml (range 0.8 – 10.1 ml)
air in the bladder. The bladder volume delineated by the
physician (including air pocket and bladder wall), was on
average 253 ml (range 93 – 452 ml). The average bladder
volume in which changes exceeded 0.25 °C was 22 ml
(range 0 – 108 ml), with the bladder being up to 2 °C cooler
when an air pocket was present. There was no evident
relation between the quantity of air and the difference in
temperature. Although in particular the part of the
bladder close to the air pocket absorbs less energy, the
temperature in the entire bladder is typically lower
because of convective mixing in the bladder contents.