ESTRO 38 Abstract book

S564 ESTRO 38

textural analysis of the whole lung can help differentiate between tumour and RILI after SABR. Material and Methods We compared the 6 month post SABR single phase CT scan of 25 patients (who had not recurred at 2 years), with 4 patients who had PET-CT proven recurrence 6 months after treatment. The ipsilateral lung was segmented on the CT scan. A Grey Level Co-occurrence matrix (GLCM) for each lung containing tumour was created. Each voxel had a density and an entropy score assigned relative to the neighbouring 26 voxels. Previously we showed that a 2D data plot of each voxel (density vs entropy) showed an ‘elephant plot’ with the tumour corresponding to the elephant ‘trunk’ when comparing the lung ipsilateral to tumour with the contra-lateral lung. We performed a sub-region analysis on the elephant trunks, which included those voxels, which had a high density, but low entropy score. We performed 4 sub-analyses using different density and entropy thresholds, to include different parts of the elephant trunk. Results The most statistically significant differences were found using an entropy score of 2 or less and density (HU) of 0- 150. P values for Mann-Whitney test comparing recurrence vs non-recurrence was: number of voxels in sub-ROI (p=0.007) and Entropy Standard Deviation (p=0.048).

extremities). Averaged over all sites, 3D conformal PT is used in 60% and IMPT in 80% of the proton centers. Averaged over all enquired indications, 70% of institutes follow (inter)national clinical treatment protocols, although varying protocols are used depending on indication and institute. Most institutes treat patients in supine position (range, 82% for CSA to 94% for brain). Regarding image guidance during treatment delivery, in- room 3D CBCT (kV) is used most frequently (range, 57% for CSA to 86% for thorax, Table 1). Daily online imaging is used by the majority (range, 85% for extremities to 90% for abdomen and pelvis), and offline imaging protocols (eNAL) are used by 14% (H&N) to 21% (thorax) of institutes.

Conclusion CT texture analysis may be useful as a cost effective means of differentiating between tumour and RILI after SABR. This technique provides a promising model to track changes in lung parenchyma in malignant or benign lung disease. However, further validation in a prospective trial on a larger cohort of patients is required. PO-1020 The Sicily Dosimetric Project: a multi- institutional project on IMRT/VMAT lung treatment C. Marino 1 , E. Bonanno 1 , N. Cavalli 1 , G.R. Borzì 2 , A. Brogna 3 , R. Costa 4 , V. D'Antoni 5 , I. Fazio 6 , G. Iacoviello 7 , S.I. Illari 8 , S. Mele 9 , A. Rabito 10 , N. Romeo 11 , V. Salamone 12 , L. B. Tonghi 13 1 Humanitas - Centro Catanese di Oncologia, Medical Physics, Catania, Italy ; 2 REM Radioterapia, Radiotherapy, Catania, Italy ; 3 AOU Policlinico G.Martino, Medical Physics, Messina, Italy ; 4 ASP 2 Caltanissetta, Radiotherapy, Gela, Italy ; 5 Casa di Cura La Maddalena, Radiotherapy, Palermo, Italy ; 6 Casa di Cura Macchiarella, Radiotherapy, Palermo, Italy ; 7 ARNAS Ospedale Civico, Medical Physics, Palermo, Italy ; 8 Freelance Physicist, Via D. Sanfilippo 1, Catania, Italy ; 9 AOE Cannizzaro, Medical Physics, Catania, Italy ; 10 ASP 7 Ragusa, Medical Physics, Ragusa, Italy ; 11 ASP 5 Messina, Radiotherapy, Taormina, Italy ; 12 AOU Policlinico Vittorio Emanuele, Medical Physics, Catania, Italy ; 13 ARNAS Garibaldi, Medical Physics, Catania, Italy Purpose or Objective Multi-Institutional dosimetric projects allow to share knowledges and to ensure adequate quality of practice

Conclusion Our results show moderate agreement in clinical pediatric IGRT use in European institutes. The findings from this survey can help to define internationally acceptable standard quality criteria for ‘best practice’ guidelines for pediatric IGRT. PO-1019 The elephant plot: Differentiating between early recurrence and Benign Lung Injury after SABR I. Phillips 1 , H. Wang 2 , P. Evans 2 , V. Ezhil 3 , H. Saxby 3 , C. South 3 , M. Hussein 4 , A. Nisbet 3 , S. Alobaidli 5 , E. Chandy 3 1 Edinburgh Cancer Centre, Clinical Oncology, Edinburgh, United Kingdom ; 2 University of Surrey, Centre for Vision- Speech and Signal Processing, Guildford, United Kingdom ; 3 Royal Surrey County Hospital, St Lukes Cancer Centre, Guildford, United Kingdom ; 4 National Physical Laboratory, Medical Radiation Physics, Teddington, United Kingdom ; 5 Kuwait Cancer Control Centre, Radiotherapy Physics, Kuwait City, Kuwait Purpose or Objective SABR (Stereotactic Ablative Body Radiotherapy) is an effective radiotherapy treatment for early stage lung tumours. Differentiating between the morphology of early recurrent/residual tumour and radiation induced lung injury (RILI) after SABR is challenging using both CT and PET-CT imaging. In this study we investigated whether CT