ESTRO 2025 - Abstract Book

S4137

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

ESTRO 2025

The SGRT group exhibited larger roll and yaw deviations (roll 0.8°, yaw 0.8°) compared to the tattoo group (roll 0.7°, yaw 0.6°). Although statistically significant, these differences were small and not considered clinically relevant. The necessity to reposition to correct for large rotations was less in the SGRT group (23 fractions, 4.5%) compared to tattoo group (29 fractions, 5.7%). Conclusion: Setting up the patients with SGRT instead of skin marks is feasible without a clinically relevant decrease in treatment accuracy or increase in number of fractions in which patients needed to be repositioned. This new setup strategy is more patient-friendly due to the elimination of tattoos.

Keywords: SGRT, Tattooless, Pelvis

3814

Digital Poster Cranial Radiosurgery with a Linear Accelerator and Real-Time Monitoring: A Retrospective Study on the Impact of Bite Block Use on Patient Positioning Rosa Patricio, Patricia Varzim, Fátima Aires, Daniela Saraiva, Fernando Costa, Alice Alves, Anabela Gonçalves, Pedro Soares, João Casalta Lopes, Gabriel Farinha, Ana Rita Figueira, Armanda Monteiro, Lígia Osório Radiotherapy, ULS São João, Porto, Portugal Purpose/Objective: Stereotactic Cranial Radiosurgery (SRS) is an advanced, non-invasive therapeutic approach used for the treatment of brain tumors. The success of this treatment modality critically depends on sub-millimeter precision in the delivery of high-dose radiation, so that it minimizes the exposure of surrounding healthy tissues to the radiation. The aim of this study is assessing the impact of bite block on the treatment deviations from planning computed tomography (CT) in patient undergoing SRS. Material/Methods: We included patients with brain lesions treated with SRS in our Department between January/2023 and September/2024, with 1 to 5 fractions. Patients were grouped according to the use (group A) or absence (group B) of bite-block. Deviations from planning CT were assessed in 3 translational (longitudinal, lateral, vertical) and 3 rotational (pitch, roll and yaw) dimensions. Deviations were reported through median (interquartile range [IQR]); absolute values for deviation were also analyzed. Comparison between fractions was performed using Friedman’s ANOVA, and Mann-Whitney test was used for comparing groups. A significance threshold of .05 was considered. Results: A total of 83 patients were included, with 49 (59.0%) using bite-block. The number of SRS fractions was as follows: 1 fraction in 7.2%, 2 fractions in 16.9%, 3 fractions in 36.1%, 4 fractions in 2.4% and 5 fractions in 37.3%. Since there were no significant differences in deviations between fractions (for all treatments including ≥2 fractions), comparison between groups was done for the first fraction. Significantly lower absolute values of deviations were observed for group A, namely for longitudinal (.11 [.19] vs. .19 [.17], Z=-2.04, p=.042), lateral (.05 [.06] vs. .085 [.12], Z=-3.06 , p=.002), roll (.40 [.50] vs. .70 [.90], Z=-2.69, p=.007) and yaw (.20 [.50] vs. .70 [1.00], Z=-3.85, p<.001). Deviation quartiles 1 and 3 for both groups A and B were the following: longitudinal(A)={-.22;.02}, longitudinal(B)={- .29;-.04}, lateral(A)={-.05;.06}; lateral(B)={-.08;.09}; vertical(A)={-.11;.04}, vertical(B)={-.08;.11}, pitch(A)={.15;1.00}; pitch(B)={-.83;.40}; roll(A)={-.40;.30}, roll(B)={-.73;.78}, yaw(A)={-.40;.20}; yaw(B)={-.70;1.20}.