ESTRO 36 Abstract Book

S82 ESTRO 36 _______________________________________________________________________________________________

methods for CT and CBCT radiomics features in rectal cancer, and to provide a harmonization evaluation method. Material and Methods Three harmonization strategies were tested in this study, including no correction, simple correction and phantom based correction. 50 rectal cancer patients with both planning CT images and positioning CBCT images before the first fraction of treatment were collected for harmonization performance evaluation. 203 features were extracted from CT and CBCT images. For the phantom based correction, a texture phantom comprised of 30 different materials was designed for features selection and nonlinear functions generation for normalizing CT and CBCT features.The Main workflow was shown in Figure 1. Mixed datasets consisting of CT and CBCT features were generated for harmonization performance evaluation using cluster analysis. The harmonization performance was evaluated by Chi-square testing between clustering results and scanner machines, and the clustering consistency with original CT feature. These tests were repeated for 50 times with randomized sample generation. Figure 1. Main Workflow. Four steps of this study:(I) Feature selection by features range comparison. (II)Feature selection by spearman correlation test. (III) Nonlinear mapping function generation using texture phantom. (IV)Correction methods performance evaluation on patients. Results 41 of the 203 radiomics features were selected by range comparison and spearman correlation test. Among 50 randomized sampling processes, all clustering (100%) results without any correction showed high correlation with imaging machine (p>0.05, χ^ 2 test), while this probability reduced to 0 % and 42% respectively when simple correction or phantom based correction were applied. Average accuracy and Kappa index increased significantly (p<0.05, t-test), respectively to 0.71±0.07 and 0.42±0.12 for simple correction method and 0.68±0.06 and 0.36±0.14 for phantom based correction method, from 0.61±0.06 and 0.23±0.13 without any correction.

Proffered Papers: Novelties in image guidance

OC-0161 patient tolerance of stereotactic MR-guided adaptive radiation therapy: an assessment using PRO’s R. Bakker 1 , M. Jeulink 1 , S. Tetar 1 , S. Senan 1 , B. Slotman 1 , F. Lagerwaard 1 , A. Bruynzeel 1 1 VU University Medical Center, Radiotherapy, Amsterdam, The Netherlands Purpose or Objective Recently, SMART has been introduced in our center using the MRIdian (Viewray). One key feature of SMART is delivery of radiation while patients are positioned for a prolonged period within the MRI bore, and therefore may experience procedure-related problems such as anxiety, noise and other MR-related undesired signals. Briefly, patients are positioned on the MRIdian with body coils and headphones, after which 0.35T MR-scans are performed prior to each fraction. After alignment of the target volume and re-contouring, re-optimization of the original treatment plan and patient-specific QA is performed while patient remains in treatment position. Treatment is delivered under real-time MR-guidance, with or without breath-hold, depending on location. On average, the duration of a single fraction ranges from 45 minutes (prostate SBRT) up to 75 minutes (breath-hold pancreas SBRT). To gain insight into patient tolerance and experiences of SMART delivery, we prospectively collected patient-reported outcome questionnaires (PRO-Q) in treated patients since May 2016. Material and Methods The intake visit of SMART patients includes providing procedural information by the radiation oncologist, and in case of video-feedback for breath-hold, also by dosimetrists. During the same visit, a MRI-safety questionnaire is completed. Immediately after the intake, a simulation MR-scan is performed on the MRIdian. PRO-Q were collected in 55 patients after the last SMART fraction. The PRO-Q includes questions on anxiety, temperature, noise, and other potential MR-related undesired signals. It also includes a question on the tolerance of the duration of the SMART procedure. Items could be scored as: 1) 'not at all”, 2) 'a bit” 3) 'moderate” and 4) 'considerable”. Results Two of 57 patients withdrew from SMART because of severe claustrophobia during the simulation MRI. Furthermore, anxiety during treatment was reported by 12/55 patients (22%), with half of these reporting anxiety to be considerable. A majority of patients (52%) reported sensations of feeling cold related to the cooling air flow of the MRIdian. Although the MRIdian combines noise of the gradient coils of the MR and retraction of the radiation sources, this sound was experienced to be really disturbing by two patients only. Troublesome paresthesia was reported by two patients, mainly related to prolonged positioning of the arms above the head. Other relevant MR-related undesired signals such as dizziness, local heat sensations or metallic taste sensations were only occasionally reported. Although the total fraction duration was judged to be long by some extent in 22% of patients, only a single patient scored this as being unacceptably long (Fig.1).

Table1. Performance evaluation result for different harmonization strategies. Conclusion This is the first study focused on feature harmonization for CT images. Two proposed correction methods, simple correction and phantom based correction, were verified to be feasible for CT and CBCT harmonization, which could significantly improve the modeling consistency.