ESTRO 36 Abstract Book

S351 ESTRO 36 _______________________________________________________________________________________________

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.