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First, lung volumes and respiration-induced tumour
motion amplitudes were compared between CPAP and
noCPAP images at both time-points.
Next, rigid registration based on the bony anatomy was
performed between T0 and T1 images (2 registrations per
patient: noCPAP
T0
/noCPAP
T1
and CPAP
T0
/CPAP
T1
). Changes
in the time-averaged tumour position relative to the
anatomy (baseline shifts) were computed in order to
assess whether CPAP impacted or not the tumour baseline
shift.
Results
Patient recruitment is ongoing. Preliminary results based
on the first 10 patients (12 tumours) are presented. Mean
CPAP was 7 cm H
2
O (range: 6-8). CPAP was well tolerated
by all patients.
As expected, CPAP induced a significant increase of lung
volumes from 4.62±1.12L to 4.86±1.22L (t(9)=3.41,
p<0.01), and from 4.63±0.91L to 4.95±1.03L (t(9)=3.79,
p<0.01), at T0 and T1 time-points, respectively.
On the other hand, CPAP had significant impact neither on
the tumour motion amplitude (noCPAP
T0
: 11.6±11.0mm vs.
CPAP
T0
: 10.8±11.2mm; noCPAP
T1
: 11.5±13.7mm vs.
CPAP
T1
: 10.7±11.2mm), nor the tumour baseline shift
(noCPAP: 4.1±2.6mm vs. CPAP
:
3.6±3.0mm).
Conclusion
CPAP is a simple and well-tolerated approach to safely
increase the lung volume, without modification of tumour
motion amplitude or baseline shift. As a result, CPAP
might allow for better sparing of the lungs during RT.
Further analysis is warranted to evaluate the actual
dosimetric impact of such strategy.
PO-0671 Influence of “radioresistant” histologies on
SBRT outcome for lung metastases
D. Franceschini
1
, L. Cozzi
1
, F. De Rose
1
, P. Navarria
1
,
G.R. D'Agostino
1
, S. Tomatis
1
, C. Franzese
1
, T. Comito
1
,
F. Lobefalo
1
, P. Mancosu
1
, M. Scorsetti
1
1
Istituto Clinico Humanitas, Radiotherapy and
Radiosurgery, Rozzano Milan, Italy
Purpose or Objective
Literature data suggest a relevant role of histologies on
the outcome of Stereotactic Body Radiation Therapy
(SBRT) for oligometastatic disease. We reviewed our
experience in the treatment of lung oligometastases from
the historically considered “radioresistant” histologies
(colorectal, renal, melanoma, sarcoma, hepatocellular
and adenoid cystic carcinoma).
Material and Methods
Data on oligometastatic patients (less than 5 metastatic
sites) treated with SBRT for lung metastases from the
above described histologies were analyzed. Primary end
point of this study was local control (LC), secondary end
points were overall survival (OS) and progression free
survival (PFS). Kaplan Meyer analysis was performed.
Univariate analysis was done, including many different
parameters that could have influenced the outcomes.
Toxicity was scored according to CTCAE v. 4.03
Results
200 patients treated in our Institution between 2006 and
2015 were included in this analysis. Mean age at SBRT was
66.87 years, (range 22-90). Main characteristics of
patients and treatments are showed in table 1.
With a mean follow up of 24.2 months (range 2.2-115.5),
126 (63%) patients were still alive (24 with no evidence of
residual disease). In 27 cases (13.5%) patients
experienced a local progression of the irradiated lesion
during follow up. Local control at 1, 2 and 3 years was 91%,
84.9% and 82%, respectively. Primary histology and the
presence of extrapulmonary disease had a significant
impact on LC. OS at 1,2 and 3 years was 88.7%, 65.4% and
55%. Primary histology, disease free interval, presence of
extrapulmonary disease, number of irradiated lung lesions
and age at SBRT all showed a correlation with prognosis at
univariate analysis. PFS at 1, 2 and 3 years was 84%, 57.7%
and 47%. Again the presence of extrapulmonary disease
and the number of irradiated lung lesions correlated with
prognosis. Treatment was well tolerated with no G3-4
acute or late toxicity recorded.
Conclusion
In our experience, SBRT remains a valid treatment for lung
oligometastases also in the setting of radioresistant
histologies. Colorectal metastases showed a higher rate of
local relapse. However, the factors mostly influencing
prognosis in our experience were the presence of
extrapulmonary disease and the number of lung
lesions. This means that the selection of “real”
oligometastatic patients for local ablative treatments is
crucial, in order to have a positive impact on prognosis.
PO-0672 Delineation and eye-tracking: How to analyze
treatment decisions according physician experience?
F. Legouté
1
, A. Paumier
1
, A. Marquis
1
, J. Blanchecotte
1
,
P.J. Mention
2
, P. Gustin
1
, P. Trémolières
1
, D. Caron
1
, C.
Cavaro-Ménard
3
1
ICO - Paul Papin, Service de Radiothérapie, Angers,
France
2
Centre Hospitalier Universitaire, Médecine nucléaire,
Angers, France
3
Centre Hospitalier Universitaire, Laboratoire Angevin
de Recherche en Ingénierie des Systèmes, Angers, France
Purpose or Objective
Inter-observer variability (IOV) in target volume
delineation is a source of potential dosimetric error in
radiation therapy treatment. The main objective of this
study was to identify IOV in volume delineation among
radiation oncologists in a specialist care center (ICO, Paul
Papin, Angers, France) for patients treated for advanced-
stage non small-cell lung carcinoma (NSCLC). Then, the
potential of automatic segmentation in order to
harmonize segmentations was investigated.
Material and Methods
Seven observers (six radiation oncologists and one nuclear
medicine physician) were recruited. For each of five
patients included (twenty-eight preselected cases), GTV
(Gross Tumor Volume) were manually and automatically
delineated separately with PET registration. To assess the
geometric difference between the physicians and
automatic segmentations, DICE similarity coefficient
(DSC), which measured the geometrical similarity
between the two GTVs, was computed. As exploratory
aim, eye gaze registrations during an observation task
were recorded for ten physicians (residents and
specialists).
Results
Two PET segmentation methods were used, applying an
isocontour at a standardized uptake value (SUV) of 2.5
(GTV2.5) or using fixed thresholds of 41 % (GTV41%) of the
maximum intra-tumoural 18FDG activity. The overall
mean volume of GTV2.5 was greater than GTV41%, the
mean DSC was: 0,70 (± 0,06) versus 0,44 (± 0,18) and the
common delineated volume (CDV) was: CDV=0,79 (± 0,13)
versus CDV=0,33 (± 0,16). GTV41% led to significant under-
contouring errors (-66%), whereas GTV2.5 volume
achieved the best predictive value for physicians GTV. The
similarity among physicians GTV was suitable in most cases
(80%): DSC=0,67 (± 0,08), CDV=0,71 (± 0,13). The
feasibility of eye-tracking for cognitive processes analysis
in radiotherapy should be taken into account. Rapid and
robust data of the eye movement metrics during test tasks
helped to define image parameters (colors, contrasts, PET
registration, number of slides...) that could influence
medical decisions.