ESTRO 36 Abstract Book

S841 ESTRO 36 _______________________________________________________________________________________________

volumes and the delivered dose to target volumes and organs at risk (OAR). Material and Methods PET/CT and planning CT images for ten patients diagnosed with advanced inoperable non-small cell lung cancer (NSCLC) were retrieved retrospectively. The gross tumour volume (GTV) contour was used to segment the primary tumour from the CT and PET images. A volumetric voxel based map of intratumoural heterogeneity was generated from tumour CT image using a second-order statistical texture analysis method of grey level co-occurrence matrices. The FDG PET image was converted to SUV map. The low CT intratumoural heterogeneity regions within the generated texture map overlapped with high FDG uptake regions within the PET image (overlap of 65±11%). Hence, two boost volumes were identified, the low CT intratumoural heterogeneity region (Boost Heterogeneity ) and the high FDG uptake region of >50% SUVmax (Boost FDG ). A 3mm margin was added to the boost volumes to account for physical uncertainties and these volumes were labelled PTV Heterogeneity and PTV FDG . Two volumetric arc therapy plans (VMAT) were created for each patient, with a prescribed dose of 84Gy in 32 fractions to PTV Heterogeneity or PTV FDG and 64Gy in 32 fractions to the remainder of the clinical PTV. The dose to the boost volumes and OARs (spinal cord, oesophagus, normal lung and heart) was measured and compared between the two plans. Results The dose escalation to the boost volumes in the created plans were shown to be clinically feasible with the dose to OARs within tolerance limits and 95% of the target volume receiving ≥95% of the prescribed dose. When boosting based on PTV Heterogeneity, the dose to 95% of PTV FDG received ≥95% of the prescribed dose for 3 patients while the other seven patients received 80-92% of the prescribed dose. However, 95% of the Boost FDG volume received ≥95% of the prescribed dose for 9 of the 10 patients. Conclusion The results show the feasibility of dose escalation in advanced NSCLC while keeping to normal tissue constraints. Moreover, the preliminary results suggest that boosting based on intratumoural heterogeneity measured from CT images, results in the high 18F-FDG regions receiving a high dose, indicating the potential of using CT intratumoural heterogeneity generated from standard CT images as a surrogate for functional imaging in dose painting. L. Day 1 , L.M. Smyth 2 , M. Holm 3 , P.A.W. Rogers 2 , P.E. Engström 4 , C. Ceberg 4 , C.M. Poole 1 , J.C. Crosbie 1 , S. Senthi 5 , K. Woodford 5 1 RMIT University, School of Science, Melbourne, Australia 2 University of Melbourne, Department of Obstetrics and Gynaecology, Melbourne, Australia 3 Lund University, Department of Medical Radiation Physics, Lund, Sweden 4 Lund University Hospital, Department of Radiation Physics, Lund, Sweden 5 Alfred Hospital, William Buckland Radiotherapy Centre, Melbourne, Australia Purpose or Objective Synchrotron microbeam radiation therapy (MRT) is a novel radiotherapy modality with significant clinical potential. We have produced a simple dose calculation algorithm for MRT using the Eclipse Treatment Planning System (TPS), by Varian Medical Systems. Material and Methods The calculation engine in Eclipse was configured to directly evaluate ‘peak’ doses. Monte Carlo-simulated EP-1563 Treatment planning for synchrotron microbeam radiotherapy

Conclusion The use of IMRT for SIB in right breast has to be limited to those patients for which electron boost or brachytherapy is not adequate as the mean dose to heart is significantly higher. The use of DIBH in left-sided breast considerably reduces mean and V 25 heart doses. IMRT in left-sided breast shows an increase in D mean and a decrease in V 25 , which leads to significant differences in dose distribution over the heart. Heart toxicity could, therefore, have different patterns depending on the technique, being D mean a poor surrogate for heart toxicity. Skin toxicity has to be followed-up carefully in patients with high breast volumes. EP-1562 A Dose Painting Study Based on CT Intratumoural Heterogeneity vs. FDG PET Uptake in NSCLC S. Alobaidli 1 , C. South 2 , S. McQuaid 2 , J. Scuffham 2 , I. Phillips 3 , V. Prakash 4 , V. Ezhil 3 , A. Nisbet 2 , P. Evans 1 1 University of Surrey, CVSSP-Electronic Engineering, Guildford, United Kingdom 2 Royal Surrey County Hospital, Medical Physics, Guildford, United Kingdom 3 Royal Surrey County Hospital, Clinical Oncology, Guildford, United Kingdom 4 Royal Surrey County Hospital, Nuclear Medicine, Guildford, United Kingdom Purpose or Objective Intratumoural heterogeneity has been reported in the literature to correlate to treatment outcome and overall survival. In this study, a volumetric voxel based map of intratumoural heterogeneity measured from CT images was used to guide dose painting. This approach was compared against dose painting based on FDG PET uptake distributions in regards to the overlap between the boost