ESTRO 36 Abstract Book

S933 ESTRO 36 2017 _______________________________________________________________________________________________

was still valid.

lower using T1 series (P<0.05) and larger using T2 series (P<0.01). Significantly larger SNR of Body6x1 was also noted comparing to Body6x2 using T1 series (P<0.01). For image uniformity assessment, UI of Body6x1 (T1:92.8±0.6%, T2:89.0±0.3%) was significantly smaller than Body18x1 (T1:96.4±0.6%, T2:82.5±0.2%) and Body6x2 (T1:96.0±0.2%, T2:82.6±0.2%) using T1 series (P<0.01), and significantly larger than Body18x1 and Body6x2 using T2 series (P<0.01). In terms of SNR and UI, Body6x1 outperformed other two settings for T2-weighted abdominal MR-simulation. However, shorter coverage along SI direction and smaller maximum acceleration factor of Body6x1 might be a limitation for some applications due to its smaller coil size and fewer array elements.

Conclusion The performed optimisation process allowed us to manage the image quality which met expected quality criteria with significant reduction in dose. EP-1724 Phantom image quality evaluation under 3 coil settings for abdominal MR-simulation at 1.5T O.L. Wong 1 , J. Yuan 1 , S. Yu 1 , K. Cheung 1 1 Hong Kong Sanatoirum & Hospital, Medical Physics and Research Department, Hong Kong, Hong Kong SAR China Purpose or Objective MR-simulation for abdominal radiotherapy often involves the use of customized immobilization vacuum bags and radiofrequency (RF) coil holders. Although several types of RF coils are available for abdominal MR scans, the influence of different RF coils and settings on image quality has rarely been studied. In this study, we aimed to quantitatively compare the quality of image acquired by three different coil settings for abdominal MR-simulation scan on a 1.5T MR-simulator. Material and Methods A homogeneous cylindrical water phantom (diameter~21cm, length~35cm, volume~15L) was positioned on a flat couch top with a vacuum-bag. In combination with a spine coil, three sets of scans, with 4 repeats each, were performed under the coil settings (Fig1) with either a 18-channel body array (Body18x1), two 6-channel body arrays (Body6x2) or a single 6-channel body array (Body6x1) on a dedicated 1.5T MR-simulator (Aera, Siemens Healthineers, Erlangen, Germany). All images were acquired using a 2D spin-echo T1-weighted (TR/TE=500/20ms) and T2-weighted (TR/TE1/TE2=2000/20/80ms) sequences (FOV=448mm, matrix=448x448, slice thickness=5mm, geometric distortion correction and prescan normalization=ON, 11 slices). For all scans, the coil-to-phantom distance remained constant by fixing the coil holder height. SNR was calculated based on AAPM Report 100 using the central slice from each image set. For image uniformity assessment, the percent of pixels with intensity within 10% of the mean signal was calculated as uniformity index (UI). A rank-sum test was performed to compare SNR and UI differences between three coil settings.

Conclusion Our results suggested that Body6x1 might provide better SNR and image uniformity for T2-weighted abdominal MR- simulation scan than other two settings. EP-1725 Predicting radiation-induced pneumonitis in NSCLC: a radiobiological and texture analysis study W. Nailon 1 , W. Lu 2 , D. Montgomery 1 , L. Carruthers 1 , J. Murchiston 3 , A.W. Yong 3 , G. Ritchie 3 , T. Evans 4 , F. Little 4 , S.C. Erridge 4 , A. Price 4 , D.B. McLaren 4 , S. Campbell 4 1 Edinburgh Cancer Centre Western General Hospital, Department of Oncology Physics, Edinburgh, United Kingdom 2 School of Engineering University of Edinburgh, Institute of Digital Communications, Edinburgh, United Kingdom 3 Royal Infirmary of Edinburgh, Department of Radiology, Edinburgh, United Kingdom 4 Edinburgh Cancer Centre Western General Hospital, Department of Clinical Oncology, Edinburgh, United Kingdom Purpose or Objective In patients with inoperable non-small cell lung cancer (NSCLC) reliably estimating susceptibility to radiation- induced pneumonitis is challenging. Typically dose-volume histogram (DVH) parameters, normal tissue complication probability (NTCP) and changes in lung density are used, however, there is still considerable uncertainty in predicting individual patient susceptibility. The aim of this work was to investigate the presence of patient-specific density patterns that predict the likelihood of pneumonitis based on image analysis of radiotherapy planning CT images. The predictive image analysis measures were

Results As illustrated in Fig2, the SNR of Body6x1 (T1:51.2±1.3, T2:103.8±26.3) was significantly larger than that of Body18x1 (T1:47.7±1.1, T2:81.9±6.7) for both T1 (P<0.01) and T2 series (P<0.05). Compared to Body18x1, the SNR of Body6x2 (T1:46.1±0.9, T2:96.7±10.5) was significantly