ESTRO 2020 Abstract book

S938 ESTRO 2020

3D errors based on 15 CBCT’s per immobilization type are shown in Fig. 2a, while 1D group mean (M) & group systematic (S) errors in the sagittal plane are shown in Fig. 2b. The setup accuracy achieved with 3DPrIm was at least comparable with TM for the occiput & mandible. 3DPrIm setup accuracy was reduced for the more caudal sub-ROI’s (C6 & larynx), due to the current absence of lower neck immobilization. All patients and RTTs evaluated the 3DPrIm as usable and patient-friendly.

however, cannot be created in the physical presence of the patient and thus requires a new RT workflow. In addition, tolerability and comfort cannot be assumed, given the novelty of the proposed 3DPrIm device. In this pilot study, the feasibility of 3DPrIm was evaluated on patients with HNC in terms of workflow, patient comfort and setup accuracy. Being the first application on actual patients, the study focused on 3DPrIm of the head. Material and Methods 3D PrIm was achieved for three HNC patients and was compared with the clinically used TM (5-points, closed face, generic headrest) using repeated CBCT on a linac. For the creation of the 3DPrIm, an additional planning CT was acquired of the patients immobilized without a TM (Fig. 1a). The segmented pristine body contour was used to design a closed posterior shell with cranial back-stop and an anterior shell with open face (Fig. 1b) in the software 3-matic (Materialise, BE). Weekly study CBCT’s (3DPrIm) and clinical CBCT’s (TM) of the same day were rigidly registered with the respective planning CT, based on a global, composite ROI consisting of the occiput and mandible. Residual setup errors were determined for five sub-ROI’s (occiput, mandible, C2, C6 and larynx) by subsequent rigid registration based on each individual sub- ROI and quantification of the difference relative to the global registration. At the end of the RT course, the patients and RTT’s completed a questionnaire polling their experience in terms of comfort and immobilization usability.

Conclusion 3DPrIm is feasible in terms of workflow, is tolerable by HNC patients and can achieve clinically acceptable setup accuracy for the head region. 3DPrIm therefore is a valid option to pursue enhancements in RT of HNC, such as spot- size reducing bolus in IMPT. Further optimization of the initial design, however, with added lower neck immobilization, is required towards clinical use of 3DPrIm in RT of HNC. PO-1624 Fast contour propagation for MR-guided prostate radiotherapy using convolutional networks K.A. Eppenhof 1,2 , M. Maspero 2 , M.H. Savenije 2 , H.C. De Boer 2 , J.R. Van der Voort van Zyp 2 , B.B. Raaymakers 2 , A.J. Raaijmakers 1,2 , M. Veta 1 , J.P. Pluim 1 , C.A. Van den Berg 2 1 Eindhoven University of Technology, Biomedical Engineering, Eindhoven, The Netherlands ; 2 UMC Utrecht, Radiation Oncology, Utrecht, The Netherlands

Purpose or Objective

Results