S2724
RTT - Patient preparation, immobilisation, and verification protocols
ESTRO 2026
Interclass correlation coefficients were additionally calculated to compare the reliability of each pre-set. Results: Clinically significant inter-observer error was defined as exceeding departmental tolerances for a confirmation image (0.2 cm translationally and 1.0° rotationally). Although statistically significant differences were observed in the vertical and rotational parameters (p = 0.0283, p = 0.0099), all mean errors remained below clinical thresholds for a confirmation image ( ≤ 0.025 cm, ≤ 0.159°) and were therefore clinically insignificant. No pre-set consistently resulted in lower inter-observer error across all parameters. Intraclass correlation coefficient (ICC) analysis showed poor reliability for the ‘Head – Normal’ pre-set in vertical and lateral parameters (ICC = 4.5 × 10 ⁻ ¹⁵ , 0.172), while all other results demonstrated moderate to excellent reliability, with the ‘Extremity – Normal’ pre-set showing excellent reliability laterally. Conclusion: The differences between the pre-sets, even where statistically significant, did not demonstrate clinical significance. Neither pre-set provided consistently lower inter-observer reliability across all parameters. ICC results suggested that the ‘Extremity – Normal’ pre-set provided greater reliability overall. The recommendation would be that the use of the ‘Extremity – Normal’ pre-set is continued, as ability of observers to match effectively is unaffected and concomitant dose to patient will be lowered. Keywords: 2DkV Imaging PBT Digital Poster 2227 Assessment of translational set-up errors in frameless cranial radiotherapy using a customised stereotactic immobilisation system Poonam D Negi 1 , Divya Patil 2 , Abhishek Wagh 3 , Pooja Jadhav 1 , Kamlesh Bagul 1 , Pratyusha Mukherjee 1 , Archya Dasgupta 1 , Abhishek Chatterjee 1 , Tejpal Gupta 1 1 Department of Radiation Oncology, Clinical Research Centre, Advanced Centre for Treatment, Research & Education in Cancer (ACTREC), Tata Memorial Centre, Navi Mumbai, India. 2 Department of Medical Physics, Clinical Research Centre, Advanced Centre for Treatment, Research & Education in Cancer (ACTREC), Tata Memorial Centre, Navi Mumbai, India. 3 Department of Medical Physics, Sant Tukaram Hospital & Medical Research Center, Akola, India Purpose/Objective: To evaluate the patient set-up accuracy quantify translational setup errors and residual error in frameless cranial Stereotactic radio-surgery (SRS) with
support SGRT as aprecise, efficient, and patient- friendly alternative for breast cancer RT management. Further multicentervalidation is warranted. References: 1.doi: 10.1016/S0140-6736(11)61629-2.2.doi: 10.1007/s00066-013-0437-8.3.doi: 10.1093/jnci/djh297.4.doi: 10.1016/S1470- 2045(05)70251-5.5.doi: 10.1056/NEJMoa1209825.6.doi:
10.1007/s00066-017-1257-z.7.doi: 10.1016/j.radonc.2022.10.0178.doi: 10.1002/acm2.12557.9.doi: 10.1016/j.prro.2016.02.001.10.doi: 10.1120/jacmp.v15i5.4921. Keywords: SGRT, tattoo, breast cancer
Digital Poster 2180 Using a lower dose ‘Extremity – Normal’ 2DkV preset to image intracranial or head and neck sites in paediatric patients in proton beam therapy. Ellen Gibson 1,2 , Mike Kirby 2 1 Proton Beam Therapy, The Christie NHS Foundation Trust, Manchester, United Kingdom. 2 School of Allied Health Professions and Nursing, University of Liverpool, Liverpool, United Kingdom
Purpose/Objective: Proton Beam Therapy often demands more
comprehensive imaging regimens to ensure the high level of accuracy that the modality offers. Healthy tissues are spared when a ‘Spread out Bragg peak’ delivers highly conformal dose with a steep drop off where the disease ends. The sparing of healthy tissues makes the modality useful in the management of paediatric cancer where due to increased radiosensitivity it is even more pertinent to ensure concomitant dose is minimised. A study centre assessed whether the use of a lower dose pre-set, (‘Extremity – Normal, previously measured at 80 microGy per 2DkV pair) could replace the current protocol ‘Head – Normal’ pre-set (192 microGy), in the imaging of patients receiving intracranial or head and neck treatment. Material/Methods: Five qualified Radiographers acted as observers, retrospectively matching patient images, half acquired with the ‘Head – Normal’ pre-set and half with the ‘Extremity – Normal’ pre-set. The images selected were from patients aged 2 – 15 years old, receiving intracranial treatment or treatment to the head and neck. Observers drew new clip-boxes to ‘auto-match’ to bone; differences between online and offline images were recorded. The spread of matches was compared using Bland-Altman plots and using mean standard deviation to give overall inter-observer error.
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