ESTRO 2024 - Abstract Book

S5539

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

ESTRO 2024

To compare the use of a separate thermoplastic shoulder and head immobilisation device to a 5 point thermoplastic mask in patients receiving radical Intensity Modulated Radiotherapy (IMRT) for head and neck squamous cell cancer (HNSCC). The aim of the study is to improve patient immobilisation for better image matching in highly conformal IMRT under proposed new UK Royal College of Radiologists (RCR) guidelines 1 .

Material/Methods:

This study comprised of 15 consecutive patients immobilised with a 3 point thermoplastic mask, shoulder shell and a standard perspex head rest.

The verification of cone-beam computed tomography CBCT images of patients receiving radical IMRT for HNSCC were retrospectively reviewed by a single, experienced observer. Standard verification imaging was daily CBCT with a zero millimetre tolerance applied on treatment. All images were performed initially on bone to a specific match point provided by the Clinician at the planning stage of treatment. These match points were in the high dose volume region of the plan which was typically situated superiorly to the shoulder region. Displacements were recorded in all 3 planes with the addition of the Pitch, Roll and Rotation (PRR). PRRs were evaluated in the matching but could not be corrected as we do not have a 6 degrees of freedom treatment couch in our department. PRR values <3 degrees were accepted, if greater than this the patient was re-setup. All online shifts were applied. Population random and systematic errors were calculated using the method as outlined in ‘On Target’ 2 and compared to previous studies from 2017 and 2019 undertaken by our institution, where corresponding data points were recorded for a similar number of CBCTs.

Results:

Population random and systematic errors for CBCT (120 images) are shown below (Figure 1).