ESTRO 38 Abstract book

S1147 ESTRO 38

defined as the bilateral retro-ocular soft tissues including the ocular muscles and the retro-bulbar fat and excluding the lacrimal glands with a 3mm margin. CTV was expanded to PTV with a 2mm margin. Lenses, optic chiasm, brain, lacrimal ducts, brainstem, hippocampus, pituitary, nasal cavity and lacrimal glands were defined as OARs. HA, 2F- V and 2F-PO plans were generated with Eclipse TPS v15.5 (Varian Medical Systems, Palo Alto, CA, USA). HA used up to 4 arc fields, 3 of which were non-coplanar, optimised collimator angles and a SRS normal tissue objective (NTO) feature for plan optimisation. 2F-V plans consisted of two full rotational arcs. HA and 2F-V plans were generated using high definition 2.5 mm leaf width MLCs along with a 1.25 mm optimisation resolution and grid size. 2F-PO plans were constructed with both anterior field edges placed posterior to the lenses and the posterior field edges covering the orbital apex. All plans were generated using a photon beam energy of 6MV, a dose rate of 600 MU/min, and a dose prescription of 2004 cGy in 12 fractions to the PTV. Dosimetric parameters for PTV and organs at risk (OARs) were evaluated. Results Ten patients were included in the study. HA plans offered superior PTV coverage (p<0.05) at particular dose metrics compared to 2F-V (D99%, D98%) and 2F-PO (D99%, D98%, D95%, D50%). For the HA plans, Dmean to the brain, brainstem, hippocampus, pituitary and nasal cavity were reduced (p<0.05) compared to the 2F-V plans. For the 2F- PO plans, Dmax to optic chiasm, Dmean to lacrimal ducts, nasal cavity and lacrimal glands was higher (p<0.05), while Dmax to lenses, Dmean to brain, brainstem, hippocampus and pituitary was lower (p<0.05) compared to the HA and 2F-V plans. HA gave an increased Dmean to brain, brainstem, hippocampus and pituitary in the range of 0.8- 2.4Gy compared to 2F-PO. The dosimetric results are reported in Table 1.

BOWTIE method is event based, which enables to focus on the distinctions. It is suitable to identify single hazards, root causes and measures that are MR-linac specific. The BOWTIE method has been used in the process of setup and planning. The HFMEA method is process-based and more appropriate to identify potential failures and risks in the treatment phase. The steps of this process (MR acquisition, online plan adaptation and treatment) don’t have an equivalent within the process of the conventional linac. The final integral assessment is executed with the Fishbone method. By analyzing the ‘process defects’ based on 4 potential causes (treatment, technology, management/organization and environment) potential interface risks are included in the risk assessment. Results The program resulted in 25 initiated outcome measures. (table 1a). The measures from the BOWTIES where more related with technology, materials, QA and SOP’s, were the HFMEA and Fishbone resulted measures associated with task, responsibilities and authorizations. The comprehensive risk assessment program was executed in five sessions with an average duration of 1h 40’ with 19 different healthcare professionals (table 1b) over a period of 8 months (Oct‘17 – Jun’18).

Conclusion By tailoring the risk assessment methods for each sub process we able to thoroughly and efficiently identify root causes and potential risks relevant for the patient safety with respect to a complex chain process like MR-linac based radiotherapy. This avoids the need of multiple HFMEA assessments. The integral risk assessment, with the Fishbone method, ensured that overall logistics, interface and process based (potential) risks were identified. [1] Chatman I.J. (The Joint Commission, 2010) [2] Gould J, et al. (Health & Safety Laboratory, 2010) EP-2079 HyperArcTM RT for thyroid eye disease: a plan comparison with VMAT and parallel opposed techniques R. Valentine 1 , S. Schipani 2,3 , P. Cauchi 4 , V. Chadha 4 , J. Connolly 4 , T. Mitchell 2 , D. Ritchie 2 , S. Currie 1 1 Beatson West of Scotland Cancer Centre, Radiotherapy Physics Department, Glasgow, United Kingdom ; 2 Beatson West of Scotland Cancer Centre, Radiation Oncology Department, Glasgow, United Kingdom ; 3 University of Glasgow, Institute of Cancer Sciences, Glasgow, United Kingdom ; 4 Gartnavel General Hospital, Tennent Institute of Ophthalmology, Glasgow, United Kingdom Purpose or Objective To compare HyperArc TM (HA) radiotherapy with 2-Field VMAT (2F-V) and 2-Field Parallel Opposed (2F-PO) technique for the treatment of Thyroid Eye Disease (TED). Material and Methods Patients with high dose steroid refractory TED were selected. The patients were immobilized with a stereotactic radiosurgery (SRS) encompass shell. A non- contrast enhanced CT was acquired with 1mm slices for planning purposes. CT was fused with a baseline diagnostic MRI to better define the Organs at Risk (OARs). CTV was

Conclusion HA offers better compromise between PTV coverage and OARs sparing especially for lacrimal glands with possible advantage in TED symptom control and long term complications (ocular dryness). A prospective study will be carried out in our institution. EP-2080 MC simulations on the dose enhancement effect of antibody conjugated AuNPs in targeted radiotherapy A. Klapproth 1 , W. Li 2 , S. Stangl 1 , C. Diederichs 1 , M. Shevtsov 1 , V. Ntziachristos 3 , G. Multhoff 1 1 Klinikum Rechts der Isar, Department of Radiation Oncology, Munich, Germany ; 2 Helmholtz Zentrum