ESTRO 2021 Abstract Book

S1464

ESTRO 2021

All plans showed better target coverage respect reference. CA plays a small rule in PTV coverage (0,5% for D98, 3°GS_100°10° vs reference). 2°GS better performs in PTV coverage respect 3°GS (see figure 1 for D98 and D95). SV technique improve of 2%. The spine was better protected with 2°GSSW with a significant reduction in Dmax, D1 and mean (-6%, -7.5% and -7.8% respectively for 2°GSSW100°10°). Dose sparing evaluation of other organs at risk was warranted with 2°GSSW100°10°.

Figure 1: 2°GSSW100°10°plan was characterized by dose reduction in posterior area, significant reduction in DVH spine and better PTVs coverage (dotted line). Asterisks show on histogram plots statistically significant differences Conclusion 2°GSSW100°10° resulted the best feasible strategy in HNC to improve PTV coverage and organ at risk dose reduction. CA 100°10° vs 350°10° warranted better wash out dose in posterior area improving reduction in maximum spine dose (figure 1 dose distribution comparison) with a reduction in Dmax, D1 and mean. PTV increases D98 and D95 significantly. The combination of SW, CA 100°10° and 2°GS, resulted the best VMAT treatment planning techniques in HNC. Reference: (1) Jung-In Kim et al. Radiation Oncology (2018);13(1):88. DOI:10.1186/s13014-018-1039-5 PO-1742 Early clinical experience with Ethos Therapy system for delivery of urgent palliative IMRT plans D. Withers 1 , A. Ward 2 , S. Graham 3 , G. Kidane 1 , E. Almond 1 1 Queen's Hospital, Radiotherapy Physics, Romford, United Kingdom; 2 Queen's Hospital, Clinical Oncology, Romford, United Kingdom; 3 Queen's Hospital, Radiotherapy, Romford, United Kingdom Purpose or Objective Our clinic upgraded an existing Varian Halcyon linear accelerator to Ethos Therapy. Whilst the primary purpose of Ethos is for daily on-line adaptive radiotherapy, we have also recognised that its efficient automated plan generation is likely to confer other benefits. There is often a need to treat with palliative RT for urgent symptom control. Typically there is short notice involved and limited additional capacity for both clinicians and treatment planners. As such virtual simulation conformal radiotherapy techniques are often used despite the desire for the better dose distributions that could be achieved with IMRT. This work describes our early clinical experience of using the ETHOS system to provide IMRT plans in a timely manner along with a streamlined administrative and checking workflow. Materials and Methods To date, eight treatments have been delivered to seven patients (see Table 1). Planning directives were created with goals for PTV coverage. Priority was given to uniform target coverage, with limited hotspots. Typically the only OAR considered was spinal canal which was delineated automatically by Ethos. Contours were delineated directly in ETHOS or on Eclipse and imported. Plan previews were reviewed and the priority of goals changed on a case-by-case basis. IMRT plans with seven equidistant fields were generated automatically by the ETHOS Intelligent Optimisation Engine (IOE). This was reviewed and clinically approved by the oncologist.

Results