ESTRO 37 Abstract book

S755

ESTRO 37

(HR = 1.066) were associated with DFS. No level of TLG was found to be associated with OS nor DFS. LC was no statistically related with any metabolic or clinical factor. We further analyzed the site of tumor recurrence i.e. mediastinal/visceral vs. local: MTV 30 (HR = 1.091) MTV 40 (HR = 1.099) MTV 50 (HR = 1.116) and TD (1.099) were associated with distant failure (DF). In multivariate analysis MTV 2 (HR = 1.385, p = 0.104) MTV 30 (HR = 1.167, p = 0.63) and TD (HR = 1.117, p = 0.59) showed a trend for predicting OS, DFS and DF respectively. Conclusion MTV, but no TLG neither SUVmax, was associated with outcome in univariate analysis. Due to small number of patients, multivariate analysis demonstrated no significant association of MTV neither TLG with any end point. TD was the only non-metabolic tumor factor associated with prognosis. The results of this study suggest that MTV and TD could identify patients with high risk of distant tumor recurrence. EP-1382 USE OF CONE BEAM CT (CBCT) TO EVALUATE THE INTRAFRACTION PATIENT MOVEMENTS DURING SBRT M. Soraya 1 , A. Giraldo 1 , A. Seoane 2 , M. Ramos 1 , D. Santamaria 1 , D. Moreno 1 , J. Giralt 1 1 Vall D'Hebron, radiation oncologist, Barcelona, Spain 2 Vall D'Hebron, medical physics, Barcelona, Spain Purpose or Objective Our standard IGRT protocol for SBRT of pulmonary lesions consists of an initial CBCT (BT-CBCT) to determine the couch shift that adjusts the tumour position to the planning CT. With the objective of evaluating the intrafraction movement, we acquired a CBCT post treatment (PT-CBCT) after every fraction Material and Methods 41 patients (pts) with lung lesions (primary tumour or metastasis) were treated either with IMRT or VMAT techniques. All pts were immobilised with a vacuum customised cushion and immobilised with arms raised above the head. We adapted the motion compensation strategy with abdominal compression in all pts. 4D-PET images were used for internal target volume (ITV) generation, and a 5mm isotropic margin was added to create the planning target volume (PTV). The dose and number of fractions were selected according to our institution protocol, ranging from 3-8 fractions and from 50-60 Gy. Prior to and after each fraction, a CBCT was acquired. Firstly, the pt was positioned and aligned with the lasers on the CT marks. CBCT was obtained and registered to the planning CT in order to obtain and apply the setup corrections (rotation was not allowed) helped by automated soft-tissue registration; the BT-CBCT was used to correct the tumour position, and PT-CBCT to evaluate the intrafraction movements. The tumour position variability in Left/Right(LR), Cranial/Caudal(CC) and Anterior/Superior(AP) was calculated in terms of Group Mean(GM), systematic(∑) and random(σ) variations. After every fraction, with the displacements obtained from the PT-CBCT, and in accordance with our PTV margin, the pts were classified into 2 groups: Low risk group: every axis was ≤4mm: no action was required for the next fraction. High risk group: at least 1 axis was >4mm: for the next fraction, a repositioning CBCT in the middle of the fields/arcs of treatment was acquired. Results 164 treatment fractions were administered between February 2015 and August 2017. The mean time from localisation of the tumour to the end-fraction CBCT was 23 minutes (range 9-51 ), other characteristics are available on Table 1. The mean systematic error for all pts was in LR -0.2mm (range-3 to 3), in CC -0.6mm (range -4 to 5) and in AP -

Cavitation

0.806

0.668 0.550 0.463 0.456 0.632 0.586 0.524 0.450 0.524 0.735 0.616 0.620

Pleural Retraction 0.681

Emphysema

0.554 0.598

GGO

Air Bronchogram 0.790

Pleural Thickening

0.477

Necrosis

0.703

Satellite Nodules 0.624 Suspect Nodules 0.616

Fibrosis

0.653

Pleural Effusion 0.784 Pleural Contact 0.749

Conclusion It is possible to describe some common semantic features by a combination of radiomic features. Since our analysis only looked at the primary tumor, model performance of lung specific features can potentially be increased by calculating radiomic features for the whole lung. Patients with lung abnormalities generally have a worse prognosis, models containing semantic features as well as radiomic features have potentially a better prognostic value. EP-1381 Role of Metabolic Tumor Volume and Total Lesion Glycolysis on FDG-PET/CT in NSCLC treated with SBRT J. Cabrera 1 , J. Infante 2 , C. Cruz 1 , M. Moreno 2 , M. Gonzalez 1 , J. Rayo 2 , P. Simon 1 , B. Ortiz 1 , J. Muñoz 1 1 Universitary Hospital Infanta Cristina, Radiation Oncology., Badajoz, Spain 2 Universitary Hospital Infanta Cristina, Nuclear Medicine, Badajoz, Spain Purpose or Objective Maximum Standardized Uptake Value (SUV max) is the most widely applied parameter on FDG-PET/CT for staging and monitoring treatment response in NSCLC. Recent work suggest that volumetric parameters Metabolic Tumor Volume (MTV) and Total Lesion Glycolysis (TLG) can be used as prognostics factors in surgical and non-surgical series of patients with early stage NSCLC. The aim of this study was to determine whether MTV and TLG are associated with outcomes in patients treated with SBRT. Material and Methods Retrospective study of 42 patients treated with SBRT for NSCLC Stage T1 – T2 (AJCC 8 th ed.) between June 2008 to February 2016. Mean age 75.3 ± 9.2 years. Men: 34, women: 8. SBRT dose BED 10 mean was 108.6 Gy ± 16.7. Biopsy proven cancer: 22, non-biopsy: 20. Central tumors: 7, peripheral tumors: 35. The volume within the GTV with SUV greater than or equal to a given SUV threshold x was MTV X TLG was defined as MTV X x SUVmean. MTV and TLG at several levels were registered. Prognostic factors for overall survival (OS) local control (LC) and disease free survival (DFS) were analyzed using Cox’s proportional hazards model and survival curves were calculated using the Kaplan-Meier method. P values < 0.05 were considered statatistically significant. Results Median follow up: 31.13 months (mo) Median OS: 45.7 mo. 3 year OS, LC and DFS rates were 71.9%, 78.3% and 45.2%, respectively. In univariate analysis MTV 2 (HR = 1.030) MTV 2.5 (HR = 1.039) MTV 30 (HR = 1.124) MTV 40 (HR = 1.131) MTV 50 (HR = 1.150) and tumor diameter (TD) (HR = 1.098) were associated with OS. MTV 2 (HR = 1,024) MTV 30 (HR = 1.08) MTV 40 (HR = 1.087) MTV 50 (HR = 1.101) and TD