ESTRO 2020 Abstract book

S1074 ESTRO 2020

international guidelines. The recommendations from this study provide learning for international departments. PO‐1832 Assessment of set up accuracy using an evacuated cushion for Proton Beam Therapy D. Roberts 1 , P. Foden 2 , L. Elliff 1 , K. Allen 3 , M. Lowe 4 , C. Eccles 3 1 The Christie NHS Foundation Trust, Proton Therapy, Manchester, United Kingdom ; 2 The Christie NHS Foundation Trust, Proton Clinical Outcomes Unit, Manchester, United Kingdom ; 3 The Christie NHS Foundation Trust, Radiotherapy Department, Manchester, United Kingdom ; 4 The Christie NHS FoundationTrust, Medical Physics and Engineering, Manchester, United Kingdom Purpose or Objective Effective, reproducible patient positioning is paramount for radiotherapy. With the introduction of a new proton beam therapy (PBT) service in January 2019, evacuated cushions (vacbags) have been implemented for patients receiving treatment to the limbs, abdomen, thorax and pelvis. This work reports on an audit reviewing set up times, image review times and positional reproducibility to confirm the suitability of the vacbag as an immobilisation tool in PBT. Material and Methods The first ten patients treated on vacbags were included in this study. Patients were initially imaged with kilovoltage (kV) 2-dimensional (2D) image pairs as a gross error check (GEC), followed by a conebeam CT (CBCT) from which positional errors were corrected and verified with a final 2DkV image before proceeding to treatment. Images were compared to the planning CT to determine translational and rotational displacements. Treatment and image review times were also reported to audit the new service. Results Compared to the planning CT, translational displacements were satisfactory with 95% <5mm and 100% <10mm. Greater variation was seen in rotational displacements, however, on average only 3% of all exceeded the 2⁰ tolerance. Agreement between 2D and 3D imaging were within the institutions defined GEC tolerance of <1cm and <2⁰. This agreement was reached in 99% of translational and 91% of rotational displacements. A Bland-Altman analysis demonstrated that there was no statistical significance for the bias between the 2D and 3D measurements. In total 181 CBCT images were assessed against confirmation 2D images. Agreement was achieved in 89.1% of translational (2mm tolerance) and 94.3% of rotational (1⁰ tolerance) orientations. Treatment delivery times in minutes (mins) were reduced from a mean of 55 mins for the first patient to 47 mins for the most recent patient. Average Image review time for the GEC 2D orthogonal images also reduced from 6 mins to 3 mins, however the trend for review time of CBCT remained an average of <10 mins (range 7 mins – 12mins). Conclusion Initial results show that vacbags are suitable for accurate patient positioning and minimising translational displacements. Rotational displacements appeared more random, especially pitch. As such it has been determined, the use of a 6⁰ of freedom bed, combined with daily imaging, is paramount for accurate set up. Future investigations will include a comparison of this data to external institutional data and further review of the effects of contour change on patient position and set up accuracy.

use during CT planning can enhance soft tissue contrast of the scan facilitating Target Volume (TV) and Organ At Risk (OAR) delineation. Despite this known benefit, there are no current guidelines for what sites should receive IVC during the Planning CT scan and because of this variation may occur. There are international diagnostic imaging recommendations on how IVC should be administered. The primary aim of the study is to examine the patterns of practice in relation to the use of IVC in RT Planning scans in Ireland and to determine the level of compliance with recommendations. Radiation Therapists (RTT) IVC training An evidence-based anonymised online survey was distributed to all RT department in Ireland. The IVC questions in the survey were taken or adapted from published literature and based on the UK Royal College Radiologists ‘Imaging for Oncology’ publication (2004). The questions relating to patient safety were informed by the European Society of Urogenital Radiology (ESUR) and the Royal Australian and New Zealand College of Radiologists (RANZCR) IVC guidelines. The survey contained open, closed and Likert scale questions that investigated IVC protocols in each department. Results 75% of departments responded (n=9/12) and all responding departments used IVC to varying degrees (Figure 1). RTTs cannulated patients in 67% of departments and administration contrast in all departments. Variations from guidelines were reported in the disease sites where IVC was used (Figure 2) and in the assessment of renal functioning prior to contrast use. Training varied in duration and number of supervised procedures. Figure 1: The frequency of intravenous contrast (IVC) usage per department in one month was also investigated. Material and Methods

Figure 2: Usage of intravenous contrast (IVC) for radiation therapy planning scans by the UK Royal College Radiologists (RCR) Imaging for Oncology report guidelines for the disease sites where IVC should (‘recommended’) and could be used (‘suggested’)

Conclusion IVC is used extensively in Irish RT departments with some practices inconsistent between departments and with