Abstract Book

S1225

ESTRO 37

rotational) were collected. Random (σ) and systemic errors (Σ) were computed. To evaluate the overall shift from isocenter, total vector error (TVE) was also calculated. To assess absolute mean differences between the immobilization systems, independent samples t-test was performed. Results Median age of patients was 43.8 years (range: 18-74). Predominant STS site was lower extremity (57.1%). Preoperative RT was given to 5 patients (35.7%) and postoperative RT was given to 9 patients (64.3%). Mean displacements for the Vac-Lok™ and thermoplastic cast, respectively, were as follows: vertical, -0.01±0.06 cm vs. 0.02±0.16 cm (P = 0.63); longitudinal, 0.03±0.04 cm vs. 0.04±0.07cm (P = 0.60); lateral, 0.04±0.17cm vs. 0.00±0.11cm (P = 0.55) and TVE, 0.15±0.10 vs. 0.19±0.07 (P = 0.44). No statistical differences were seen in σ or Σ between Vac-Lok™ and thermoplastic cast. Similarly, no statistical differences were seen in the margins calculated for each axis using the two immobilization systems by using van Herk’s formula. Conclusion Based on the findings of our study, we concluded that both the Vac-Lok™ immobilizer and thermoplastic cast had comparable results, as both systems offered better reproducibility during RT in STS of extremities without significant daily set-up displacement. A prospective study needs to be undertaken on a larger scale to better explore the outcomes of patient immobilization systems. EP-2342 A Survey on SBRT for Lung Cancer:Current Practice and the Perceived Role of the Radiation Therapist E. Sexton 1 , S. Barrett 1 , G. Menezes 1 1 Trinity College Dublin, Radiation Therapy, Dublin, Ireland Purpose or Objective Stereotactic body radiation therapy (SBRT) is the standard of care for the treatment of inoperable early stage lung cancer. There is a paucity of evidence to support one pre-treatment simulation procedure or piece of equipment over the other across centres. The role of the radiation therapist (RT) has been poorly documented in published guidelines for the implementation of SBRT, despite overlapping roles between professions in the SBRT patient pathway. The overall goal of this research project was to investigate the current status of SBRT across centres and determine the role of the RT during the implementation, pre-treatment and planning of SBRT as a new treatment technique. Material and Methods Radiation therapy centres across Europe, Asia, Australia and Canada were surveyed. Descriptive data about SBRT practice and the role of the RT was acquired and analysed. Results 68/76 respondents were eligible for inclusion. Section 1: The main treatment sites were lung (n=70), and liver (n=32) cancers. Motion control methods included gating (n=30) and breath-hold (n=11). Motion management was carried out using Varian Systems Real- time Position ManagementTM System (n=21), abdominal compression (n=11), Elekta’s Active Breathing CoordinatorTM (n=2) and VisionRT (n=2). Technology available and tumour location were the main driving factors (both n=16) to choose motion control technology. Centres reported the use of 12 separate dose volume constraint guidelines, with the most frequent being RTOG

(n=4) and Timmerman (n=3). Limited variation was found between centres regarding the pre-treatment procedures and equipment used for SBRT. Section 2: Evidence-based practice was ranked the highest weighted average (3.88) as main driver towards the implementation of SBRT in all centres. A difference between public and private centres was observed in the second highest driver. Public centres ranked departmental resources and private centres ranked patient factors as number 2 (Figure 1). There was agreement that the RT should have an increased role in the implementation of new treatment techniques and the treatment planning. 100% of ROs and RTs reported that they themselves are responsible for protocol production. RTs should have a greater role in the implementation of new treatment techniques and SBRT planning. 1: Main driver towards the implementation of SBRT as treatment technique between public and private centres in weighted averages. Figure

Conclusion A consensus exists among centres in selected areas of pre-treatment procedures and equipment, while variation is evident in other areas. The role of the RT is expanding in the SBRT process. EP-2343 A new method for monitoring voluntary breath hold using laser-based surface guided radiotherapy E.M. Franken 1 , E. Lefeber 1 , F. Hofwegen- van 1 , M. Dhont 1 , B.G. Hollmann 1 , G.G.M. Speijer 1 , C.L. Ong 1 , I. Russel 1 1 Haga Ziekenhuis Locatie Leyenburg, Radiotherapy, Den Haag, The Netherlands Purpose or Objective For patients with a left-sided breast tumor, radiotherapy treatment is preferably in deep-inspiration breath hold (DIBH) condition to limit the dose to the heart. The patients’ DIBH can be monitored using several (commercially available) methods. These are however either uncomfortable for the patient (e.g. ABC (Elekta)), expensive (e.g. AlignRT (VisionRT)), non-reproducible (DIBH without any real-time check), or not IMRT/VMAT- compliant (e.g. Bartlett et al. , R&O 2013). The newly devised method, using laser based surface guided radiotherapy (SGRT), has none of these drawbacks and is adaptable to any radiotherapy institute. Material and Methods The DIBH is monitored by the position of a laser-line projected on the patient’s sternum. At each treatment fraction, first the standard positioning procedure is followed to align the patient’s caudal sternum tattoo in expiration condition to the in-room lasers. Then the distance of the line position of the lateral in-room lasers between in- and expiration is verified to be at least 90 %