ESTRO 2024 - Abstract Book

S5629

RTT - Patient care, preparation, immobilisation and IGRT verification protocols

ESTRO 2024

Three patients with head and neck cancer with nodal involvement were randomly selected for inclusion in the pilot with in house approval from the quality assurance department. For each patient, head immobilization was achieved with a three point double-shell open facemask mask (Orfit Industries). The anterior shell was open to expose the forehead, nose, eyes and cheekbones and mouth. The exposed facial area was used as an initial region-of-interest for surface tracking on each patient by AlignRT (VisionRT Inc, UK). This ROI was refined on a patient-by-patient basis as required. The posterior set up included a firm foam head rest and elevation blocks if required (orfit industries). Shoulder movement was minimised by using Civco Shoulder retractors. Initial patient setup was guided by real-time deltas (RTD) using the reference surface obtained from the skin contour delineated on the planning CT images. Align RT’s Postural video was utilised to guide shoulder position. The tolerance deltas on SGRT were set to 1-2 mm in translational RTD and 2 degree in rotational RTD. The pilot workflow for set up is outlined in Figure 1. Daily Online CBCT imaging guidance was performed and couch shifts for setup correction were applied prior to treatment delivery. ROI design changes, 6DOF was available to two patients. CBCT couch shifts, AlignRT RTD values, repositioning rate and setup time were recorded and analysed.

Results:

Learning from the pilot study were very valuable. We made workflow adjustments, notably eliminating reference capture for subsequent sessions, instead defaulting to the CT simulation reference capture for daily setup. This change addressed diminishing image quality over each treatment session, making set up more difficult. Placement of the ROI required a lot of personalisation to each patient factors such as large breast size, prominence of clavicles and breathing motion all impacted ROI placement. One patient experienced neck swelling as a chemotherapy reaction, which required a longer treatment time, an amended ROI and part of the mask under the mandible to be cut out, however treatment could continue without a rescan or replan.