S2693
RTT - Patient preparation, immobilisation, and verification protocols
ESTRO 2026
Digital Poster 17 Accuracy of Head & Neck Radiotherapy using DSPS Prominent Shells with SGRT Robyn C Stirton, Helen Convery, Hannah M Dyer Radiotherapy, Raigmore, NHS Highland, Inverness, United Kingdom Purpose/Objective: Precision in Head and Neck Radiotherapy is vital due to the close proximity of OARs with treatment volumes. Current standard of care implies immobilising the patient in a full H&N shell[1], “to minimise movement” therefore ensuring accuracy of set-up and treatment delivery. However, technology has advanced and with person-centred care at the forefront, new findings suggest full H&N shells are no longer fit for purpose with better alternatives available[2,3,4]. This study aims to determine if DSPS prominent shells improve set-up accuracy and dose delivery of H&N radiotherapy patients using SGRT. Material/Methods: Twenty oropharynx patients receiving 30# of radiotherapy were analysed retrospectively. 10 were immobilised using the DSPS head only shell and 10 were immobilised using the DSPS prominent shell. All were set-up using SGRT and verified daily by online CBCT. Imaging shifts were recorded from weekly fractions (1,6,11,16,21,26) in 6DoF and CBCT dose calculations were performed to evaluate dose delivery through analysis of the dose difference between CT plan and CBCT clinical goals for PTV65, PTV54 and Cord PRV. Results: In set-up, the prominent shell reduced the range of movement (0.8cm,0.9cm,0.5cm,3.3°,3°,4°) compared to the head only shell (1.4cm,1.5cm,0.9cm,4.6°,3.6°,4.6°) in all 6DoFs. The root mean square (RMSQ) showed that the prominent shell (±0.2cm, ±0.2cm, ±0.1cm, ±1.4°, ±0.7°, ±0.8°) provided similar or improved accuracy in 5 of the 6DoFs compared to the DSPS Head only shell (±0.2cm, ±0.3cm, ±0.2cm, ±0.9°, ±0.9°, ±0.9°)
Three clinical goals were observed throughout this evaluation: 95% of Px to 95% volume for planPTV65 and planPTV54 and 50Gy to 0.1cm3 to cord PRV. The RMSQ of dose difference observed between the CT plan and the CBCT were smaller for the DSPS prominent shells PTV65=±0.55Gy PTV54= ±1.03Gy compared to PTV65= ±0.59Gy PTV54= ±1.28Gy for the DSPS Head only shells. The RMSQ for the Cord PRV clinical goal was larger in the prominent shell ±2.71 compared to ±1.78 within the DSPS Head only.
The Mann-Whitney U test was used to determine statistical significance in imaging shifts and clinical goals. A value of p=<0.01 is considered statistically significant. This found statistical significance in the pitch (p=0.00001). No other statistical significance was found. Conclusion: DSPS prominent shells have improved accuracy in set- up reducing the dose differences within the PTV clinical goals. Further work should be considered to investigate the significance of pitch and any relevance of differences seen in Cord PRV dose. References: 1. The Royal College of Radiologists. On target 2: Updated guidance for image-guided radiotherapy. London: The Royal College of Radiologists; 2021 [cited 2024 Oct 23].2. Essers M, et al. Setup and intra- fractional motion measurements using surface
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