ESTRO 36 Abstract Book

S904 ESTRO 36 2017 _______________________________________________________________________________________________

5 Fundación Instituto Valenciano de Oncología, Servicio de Radioterapia, Valencia, Spain Purpose or Objective To assess if dual energy computed tomography (DECT) quantitative imaging can distinguish necrotic tumours in lung cancer. Material and Methods From July 2013 to June 2016, 83 patients who underwent a DECT study were reviewed for their lung tumour necrosis status (33 positive; 50 negative). Lesion size varied considerably: the mean lesion volume was 15 cm 3 (range 0.05-138 cm 3 ). Malignant lesions were predominantly adenocarcinoma (77.1%), squamous cell carcinoma (13.2%) and metastases (7.2%). DECT examination was performed on a Discovery CT 750 HD scanner (GE Healthcare, WI, USA). Patients were injected with 1.35 ml/kg of body weight of non-ionic iodinated contrast material at 4 ml/s (Iopamidol, 300 mg/ml; Bracco, Italy). A Gemstone Spectral Imaging (GSI) DECT exam of the entire chest was performed at arterial phase. Lesion volume was semi-automatically segmented using Dexus lung nodule function (ADW4.6; GE Healthcare, USA) by two radiologists. Images for quantitative iodine content ρ I (mg/cm 3 ) and effective atomic number (Z eff ) were reconstructed. Maximum, mean and standard deviation values were recorded for both parameters and for conventional HU image. Lesion volume and diameter were also registered. Inter- and intra-observer intraclass correlation coefficient (ICC) was studied. Bilateral statistical analysis was performed using the Mann-Whitney U test. Due to multiple comparisons, Bonferroni adjustment was made and significance was set at p < 0.007. Receiver operating characteristic (ROC) curves were generated and diagnostic capability was determined by calculating the area under the ROC curve (AUC). The licensed statistical software package SPSS 20 (IBM, Somers, NY, USA) was used. Results Reproducibility of intraobserver lung lesion the ICC was 0.95 (CI 95% 0.80–0.98) and interobserver ICC was 0.92 (CI 95% 0.70–0.98). The bivariate analysis for distinguishing necrotic from non- necrotic lesions revealed statistically significant differences. Larger lesions presented more necrosis than smaller ones, as previously known in the literature. Values for p, AUC and its 95% confidence level interval are shown in Table 1.

Conclusion DECT imaging gives information on tumour necrosis. Quantitative parameters (ρ I and Z eff ) showed better sensibility and specificity compared to standard HU imaging. Mean Z eff showed better correlation with necrosis status, due to necrotic core absorbs less iodine contrast. Our approach has some advantages. Whole tumour semi- automatic contouring had excellent reproducibility. No cases were excluded due to geometry or mediastinal contact. This method could be a solid approach to assess necrosis condition. However, we have not studied relationship with the actual location of necrosis, so it would not be useful for dose-painting protocols at necrotic core. EP-1681 [C11]Choline PET/MRI for Prostate Cancer: Identify Imaging Characteristics Predicting Metastasis J.R. Tseng 1 , L.Y. Yang 2 , H.Y. Chang 2 , T.C. Yen 1 1 Chang Gung Memorial Hospital at Linkou, Nuclear Medicine and Molecular Imaging Center, Kwei-Shan- Taoyuan City, Taiwan 2 Chang Gung Memorial Hospital at Linkou, Biostatistics Unit- Clinical Trial Center of Chang Gung Memorial Hospital, Kwei-Shan- Taoyuan City, Taiwan Purpose or Objective Intergraded PET/MRI is a powerful imaging modality for prostate cancer (Pca) in several aspects, from cancer detection, primary staging, to staging of recurrent Pca. The goal of primary staging is to detect metastatic spread from the main tumor. In high risk Pca patients (PSA >20 ng/ml, or Gleason score of 8–10, or clinical stage T3a), intergraded PET/MRI imaging may have great potential to change clinical management. In the current study, we aimed to identify imaging characteristics of main tumor which can significantly predict distant metastasis. Material and Methods This prospective clinical study was approved by the Ethics Committee (approval 102-3271A and 103-4561C). Since January 2015 to June 2016, total 30 Pca patients committed high risk criteria were enrolled to conduct whole body integrated [C11]Choline PET/MRI (biograph mMR, Simens). The PET and MRI imaging was interpreted independently by one clinically-experienced nuclear medicine physician and radiologist. In the PET imaging analysis, main tumors were segmented using PMOD 3.3 software package. The borders of volumes of interest were set by manual adjustment to avoid physiological [C11]Choline uptake in the urine or intestine. The tumor boundaries were automatically contoured based on the thresholds of SUV 2.65. The gray-level run length encoding matrix (GLRLM) was used for assessing the regional texture features. In the MRI imaging analysis, anatomic (T2- weighted MRI) and functional (diffusion-weighted MRI) imaging features were documented. Multivariate classification and regression tree analysis was used to determine the best combination of variables and the related cutoffs to predict risk for distant metastasis. Results The mean age is 70.1±6.2 years, and the mean PSA level is 91.6 ± 139.4 ng/ml. In these 30 patients, 26 (87%) are categorized as clinical stage IV, 4 (13%) as stage III. Fifteen (50%) patients have distant metastasis, including 7 (23%) non-regional lymph nodes metastasis, 11 (36%) bone metastasis, 1 (3%) visceral organ metastasis. The

Box-whisker and ROC plots are displayed in Fig. 1 for mean Z eff variable, which presented highest AUC (0.890). Mean Z eff presented a 84.0% sensitivity and 81.8% specificity for a threshold of 8.96 in ROC curves.