ESTRO 2023 - Abstract Book

S254

Saturday 13 May

ESTRO 2023

1 Heidelberg University Hospital, Department of Radiation Oncology, Heidelberg, Germany; 2 Pforzheim University of Applied Sciences, Technical Faculty, Pforzheim, Germany; 3 Heidelberg Institute of Radiation Oncology, Radiation Oncology, Heidelberg, Germany

Purpose or Objective Introduction:

Non-isocentrical Total Body Irradiations (TBI) are commonly only visually monitored by RTTs through video cameras in the bunker, and the available IGRT techniques are limited. The aim of this work is to assess the feasibility of surface guided RT (SGRT) for intrafractional motion-monitoring in a non-isocentrical scenario. Objectives: • Evaluate the feasibility of a mobile system • Assess if the spatial and temporal accuracy are within the clinical requirements • Suggest a clinical workflow Materials and Methods A one-camera system, adapted from a commercial AlignRT (VisionRT) system, AlignRT2TBI, was assembled in a moving tripod and calibrated to an isocenter at the treatment-room floor, with the best achievable resolution, FOV and framerate. Static and dynamic accuracy, reproducibility and other performance tests were designed to measure the performance of the system under TBI-setup conditions (see Figure 1).

Figure 1: A. Clinical Feasibility tests: subject under a spoiler in a ß-angle = 40° towards the camera. A topography-increased lung-block is on the left side of the subject's breast. B. Little Anne Phantom (Laerdal Medical AS) under a spoiler and a gantry in a ß-angle = 40° towards AlignRT2TBI during the Camera Obstruction tests. Results AlignRT2TBI was able to detect motions with an accuracy of 5 mm and 0,125 s, respectively. The practical requirements for applying this technique are: i) minimum ceiling-height of the bunker of 220 cm and a camera-patient-distance of approximately 348 cm; ii) additional 20 minutes required to setup the system in room; iii) need to adapt current workflows, define action levels, and train workers; iv) define regular calibration and QA procedures; v) define necessary ROIs: left/right lung-block and bony structures of the thorax.

Figure 2: A. ROI covering bony structures of the patient’s thorax for interfractional setup purposes (based on B). B. Proposed ROI by Sorgato et al. (doi: 10.1016/j.tipsro.2021.12.002) . C. ROI covering the left lung-block for intrafractional monitoring purposes. Conclusion The use of AlignRT2TBI for motion-monitoring during TBIs showed to be feasible, with reduced additional workload. In order to use the system clinically, a commercial product must be made available, and users need to ensure an adequate commissioning, adapted to the defined workflow. PD-0320 Using CBCT-based adaptive radiotherapy to implement a no-simulation treatment pathway for palliation X. Ray 1 , A. Bruggeman 1 , K. Moore 1 1 UC San Diego, Radiation Medicine and Applied Sciences, San Diego, USA Purpose or Objective Patients receiving palliative single fraction radiation typically require multiple visits to the clinic for consult, simulation, and treatment. In most cases, treatment will not occur until several days following consultation. They are in pain and the plans are simple, thus these extended wait times are suboptimal and waste clinical resources, particularly CT sim time. The purpose of this project was to leverage the daily adaptive radiotherapy platform of the Varian Ethos™ to implement an expedited, no-simulation, same day consult and treatment workflow for single-fraction palliation. Materials and Methods The patient’s most recent diagnostic CT scan is used to create an initial plan in the Ethos treatment planning system (TPS) by the covering Ethos physicist. The physician contours the GTV on this image after the patient consultation. A PTV is auto- generated using a specified symmetric margin (e.g. 5mm). The initial plan is optimized using only two constraints: PTV D95%>100% and PTV D0.03cc<107%. By default, the Ethos TPS will optimize four plans using different beam arrangements: 9-field IMRT, 12-field IMRT, 2 arc VMAT, and 3 arc VMAT. When needed, a custom beam arrangement can be imported for