ESTRO 2021 Abstract Book

S783

ESTRO 2021

Results On average, the MR procedure and patient transfer added 9mins to the in-room MVCT plus treatment process of 16.8mins, giving 25.8mins in total. When adopting this workflow in clinical reality, only MR verification would be done and the in-room treatment process would only need 9.6mins. The whole process would be 18.6mins which is actually comparable to a routine in-room setup tomotherapy (19.5 mins). For patient transfer stability in cranial and HN cases, respectively >97% and >86% fraction achieved <±1.5mm/° position deviation between the MR and MVCT except in longitudinal (Y) direction, where the largest Y-shift recorded was 1.9mm and 2.7mm respectively. For cranial cases, using MR significantly improved the verification accuracy in almost all 6 shift directions compared to MVCT ( p <0.05), in which 12.9% and 1.9% data had verification accuracy increased by 1-2mm/° and >2mm/° respectively. The largest improvement was 3.1mm. For HN cases, the verification accuracy increased by 1-2mm/° and >2mm/° in 18.5% and 2.7% data respectively, but no significant difference was seen. The largest improvement was 3.5mm. Using MR for verification, the probability of having improved accuracy was higher in HN than in cranial region. Conclusion Excellent stability was achieved during patient transfer process on cranial cases, improvement on immobilization and patient education would be needed on HN cases. The superb soft tissue contrast of MR over MVCT allowed clearer view of tumor and OARs, led to an increase in verification accuracy and a potential for tumor response tracking throughout the treatment course. This pilot study showed MR-guided tomotherapy using setup room approach deemed feasible and beneficial. PD-0940 CBCT-guided online adaptive radiotherapy: implementation of an RTT-led workflow D. Daal 1 , L. Haverkate 1 , L. ten Asbroek-Zwolsman 1 , L. Zwart 1 , E. van Dieren 1 , E. de Wit 1 1 Medisch Spectrum Twente, Radiotherapy, Enschede, The Netherlands Purpose or Objective In February 2020, the first prostate cancer patients were treated with CBCT-guided online adaptive radiotherapy (oART) in our department. Clinical staffing, especially the availability of physicians, limited the capacity of oART. To facilitate oART for more patients, the implementation of an RTT-led workflow was needed. The aim of this study was to describe the implementation of an RTT-led workflow for CBCT-guided oART. Materials and Methods A training and education program was developed to train five RTTs to advanced adapters. The program consisted of five elements, including an application training, anatomy and contouring lessons given by a physician and treatment planning training by the senior RTT in treatment planning. In addition, the emulator, the simulation environment for oART, was intensively used for training purposes. The final element of the training program was the on-couch performance of twenty adaptive sessions by the advanced adapter in- training supervised by a (technical) physician. Results All five RTTs completed the training to advanced adapter successfully , resulting in the implementation of an RTT-led workflow in July 2020. After implementation, the (technical) physician was still present during the first week of treatment (4/20 fractions), because of the possible occurrence of clinical issues during the first adaptive fractions of each patient. The RTTs were able to treat the patients independently after the first week of treatment of each patient. Between July 2020 and February 2021 the (technical) physician was consulted 5/1000 fractions after the first week of treatment. The RTT-led workflow enabled us to treat a maximum of fifteen prostate cancer patients adaptively per day. Conclusion We have successfully implemented an RTT-led workflow for CBCT-guided oART based on an in-house developed training program. As a result we can treat all our prostate cancer patients adaptively. In the near future, more RTTs are trained to advanced adapter. PD-0941 Feasibility of prostatic calcifications tracking using 4D transperineal ultrasound (TPUS). W.K. leung 1 , E.P.P. Pang 2 , S.K.T. Cheung 3 , W.H. Mui 3 , B.B.W. Wo 4 , H. Liu 3 , J.C.W. Siang 2 , J.K.L. Tuan 2 , T.W.K. Tan 2 , W.L. Nei 2 , M.L.C. Wang 5 , M.A.B. Atan 2 , J.Y.H. Chai 2 , J.M. Loh 2 , A.W.T. Kor 2 , L.H. Lip 2 , G.K. Low 2 , C.H.A. Liu 6 , K.C. Lee 3 1 Auckland Radiation Oncology, Oncology, Auckland, New Zealand; 2 National Cancer Centre Singapore, Division of Radiation Oncology, Singapore, Singapore; 3 Tuen Mun Hospital, Clinical Oncology, Hong Kong, Hong Kong (SAR) China; 4 Tuen Mun Hospital, Clinical Oncology, Hong Kong , Hong Kong (SAR) China; 5 National Cancer Centre Singapore, Division of Radiation Oncology, Singapore , Singapore; 6 Auckland District Health Board, Radiation Therapy, Auckland, New Zealand Purpose or Objective Traditional approach for prostate tracking relies on the visualisation of prostate boundaries which can be subjected to image quality in some cases. Prostate calculi are common features presented in most prostate patients as seen on in four-dimensional (4D) transperineal ultrasound (TPUS). This study investigates the feasibility of using prostatic calcifications as internal surrogate for real-time monitoring of prostate displacements.