ESTRO 36 Abstract Book

S81 ESTRO 36 2017 _______________________________________________________________________________________________

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).

Conclusion Despite standardized information and performing simulation on the treatment machine, anxiety remains an item that needs specific attention. Even with fraction duration times of up to 75 minutes, only a single patient perceived this as being unacceptably long. OC-0162 Optimizing sequences for MRI-guided radiotherapy in cranial and head and neck regions W.W.K. Fung 1 , S.Y. Man 1 , J. Yuan 2 , L.H. FUNG 2 , W.P. LUK 2 , G. Chiu 1 1 Hong Kong Sanatorium & Hospital, Department of Radiotherapy, Happy Valley, Hong Kong SAR China 2 Hong Kong Sanatorium & Hospital, Medical Physics & Research Department, Happy Valley, Hong Kong SAR China Purpose or Objective MR sequences using parallel acquisition technique (PAT) with increasing acceleration factors could reduce the scan time for treatment verification, but with the cost of losing image quality that could affect verification accuracy. This study assessed the effect of different PAT factors on image quality, scan time and fusion accuracy, thus choosing a sequence which is clinically suitable for MRI-guided RT in cranial (C) and HN regions. Material and Methods Ten healthy volunteers were set up in treatment position using headrest and immobilization mask on the flat couch of a 1.5T MRI-simulator (Siemens MAGNETOM Aera). High resolution isotropic (1.05mm) 3D TSE T1W and T2W MR sequences were acquired (MR-ref). Based on MR-ref, 11 low-resolution (isotropic 1.4mm) verification sequences (MR-P xy s) were acquired with GRAPPA where acceleration factors x and y were altered in respectively phase encoding and slice encoding directions. Effective PAT factor (PAT-f) equals x times y. Four therapists (2 seniors & 2 juniors) performed two sets of fusions: MR-ref & MR- P xy s and MR-ref & duplicated MR-ref (control set) for C and HN region. Shift results (6DOF) were recorded. Survey was given to observers for scoring the image quality. Logistic and linear regression were used. Results The scan time for MR-ref were 301s and 330s, and for MR- P xy s it ranged from 249s to 49s and 254s to 59s for T1W and T2W images respectively when PAT-f increased from 3 (MR-P 31 ) to 16 (MR-P 44 ). Subjective analysis showed that the scores of all verification series were lower than the reference and decreased with increasing PAT-f. Image quality decreased when reducing the scan time (Fig.1). Significant reduction of image quality (p<0.05) occurred when PAT-f reached 12 for T1W and 6 for T2W images. Observers favored T1W over T2W images (p<0.0001). Scores from senior observers were significantly better than juniors (p<0.0001).