ESTRO 2021 Abstract Book

S1678

ESTRO 2021

gating efficiency. Materials and Methods

The visual tracking system is comprised of a mirror mounted above the patient inside the bore and reflects a screen outside the MRI bore where the breath hold tracking and gating window are displayed. 41 patients were evaluated for this study, in order to compare efficiency, some patients were treated with the visual tracking device and some without. For all treatment fractions, CINE images were exported and gating efficiency was evaluated by calculating the ratio of the time the GTV or gating structure was inside the gating window, divided by the total time of the CINE. From the 41 patients, 15 patients who completed their course of treatment with visual tracking system received a survey with four statements, where the patients were asked to give a score between 0 to 10. The survey contained following statements; following the breathing commands I found, seeing my tumor during treatment I found, actively participating in my treatment I found, and the provided information I found. The results of these surveys were collected and evaluated Results Mean gating efficiency with and without visual tracking was 64.7% and 68.0%, respectively (Wilcoxon-test: not significant, p=0.0697). Question (n=number of patients) Rating 10-9 (very difficult) 8-6 5-3 0-2 (not at all difficult) Following the breathing commands I found: 1 3 0 11 Seeing my tumor during treatment I found: (3 patients did not see the tumor) 1 0 0 11 Actively participating in my treatment I found: 1 0 2 12 10-9 (enough) 8-6 5-3 0-2 (not enough) The provided information I found: 12 1 0 2 Table 1: Survey respond of patients treated with the visual tracking device. Conclusion Overall, the patient experience was positive as patients found the visual tracking system easy to use with adequate information and training. Patients appreciated participating in their own treatment and seeing their tumor was not considered disturbing. However, no significant difference in gating efficiency with or without visualization of the target structure was found. 1 Guys and St Thomas NHS Foundation Trust, Radiotherapy, LONDON, United Kingdom; 2 Guys and St Thomas NHS Foundation Trust, Medical physics, LONDON, United Kingdom; 3 University of Oxford, Nuffield Department of Population Health, Oxford, United Kingdom; 4 Guys and St Thomas' NHS Foundation Trust, Clinical oncology, LONDON, United Kingdom; 5 Kings College London, School of Cancer and Pharmaceutical sciences, LONDON, United Kingdom Purpose or Objective The aim of this work was to analyse our experience of treating mediastinal lymphoma in deep inspirational breath hold (DIBH) using surface guided radiotherapy (SGRT), with either butterfly volumetric arc therapy (BVMAT) or full arc VMAT (FVMAT) over 5 years. The purpose was to identify the challenges of implementation, learn from our experience and review our current protocol accordingly. Materials and Methods Patient data (pre-treatment, planning and treatment data) was collected and analysed. Protocol, training packages and staff experience was also collated. The implementation and challenges of these developments for mediastinal lymphoma: DIBH, SGRT, BVMAT and daily cone beam computed tomography (CBCT) were reviewed. Results We reviewed all patients referred for mediastinal lymphoma RT from October 2016 until July 2020. Seventy-six patients were referred for DIBH, with 71 completing treatment. A variety of immobilisation options (N=4) was required for disease locations and decided on a patient by patient basis. Implementation of 3 new techniques has been successful, utilising a MDT approach and cascade training. No patient treatments were delayed, even in the implementation phase when both FVMAT and BVMAT plans were produced. Six patients needed re-scan and three re-plan (Table 1), with two patients requiring a re-scan on treatment after being unable to maintain breath-hold; thus the pre-treatment screening process assessing patients for breath-hold was sufficient, and DIBH was achieved by a majority of mediastinal lymphoma patients irrespective of age. The low rate of rescans (Table 1) indicates that the technique is reproducible, and training pre- treatment Radiotherapy Radiographers (RTT’s) in choosing the correct immobilisation has translated to accurate set-up on treatment, with only five patients showing set-up issues recorded. RTT’s had specialist training in IGRT, including assessing soft tissue anatomy in the thorax and head and neck, and plan coverage daily. The evaluation highlighted the necessity of daily 3D imaging as patients were escalated for further intervention from the CBCT data (n=2). PO-1972 DIBH for mediastinal lymphoma: Implementation and evaluation of a 5-year service K. Jones 1 , A. Webster 1 , G. Ntentas 2,3 , J. Brady 4 , N.G. Mikhaeel 4,5