ESTRO 2025 - Abstract Book

S4046

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

ESTRO 2025

In the translation direction,the control group and experimental group were within the range of clinical registration requirements.In the rotation direction,the 95% of the confidence in the experimental group were about 2°.In the control group,the systematic errors of cervical spine in the AP/SI/LR direction were 0.07/0.15/0.1cm,while the random errors were 0.14/0.17/0.12cm;the systematic errors of thoracic spine in the AP/SI/LR direction were 0.16/0.25/0.26cm,while the random errors were 0.17/0.30/0.25cm;the systematic errors of lumbar spine in the AP/SI/LR direction were 0.17/0.25/0.17cm,while the random errors were 0.22/0.32/0.19cm.In the experimental group,the systematic errors of cervical spine in the AP/SI/LR direction were 0.11/0.15/0.14cm,while the random errors were 0.15/0.13/0.16cm;the systematic errors of thoracic spine in the AP/SI/LR direction were 0.16/0.17/0.23cm,while the random errors were 0.13/0.25/0.20cm;the systematic errors of lumbar spine in the AP/SI/LR direction were 0.23/0.22/0.18cm,while the random errors were 0.17/0.25/0.16cm. Conclusion: It’s recommended that patients with thoracic spine and lumbar spine metastasis use six-degree couch positioning and verification.

Keywords: spinal metastasis,six-degree couch

336

Digital Poster Intrafraction motion analyses in pancreatic cancer SBRT

Paulo Ferreira 1 , Filipa Sousa 1 , Sara Poeta 2 , Philippe Martinive 1 , Younes Jourani 2 , Christelle Bouchart 1 1 Department of Radiation Oncology, Institut Jules Bordet, Brussels, Belgium. 2 Department of Medical Physics, Institut Jules Bordet, Brussels, Belgium Purpose/Objective: Stereotactic body radiation therapy (SBRT) offers promising local control for pancreatic cancer. 1 However, challenges include respiratory motion and the lack of consensus on dose, fractionation, and delineation. 2,3 Intrafraction motion after fiducial registration is also not well documented. 4 This study aimed to quantify intrafraction motion in pancreatic cancer patients treated with SBRT and abdominal compression, assessing motion variability pre- and post-treatment to evaluate the effectiveness of current PTV margins and the potential impact of tumor location on deviations. Material/Methods: The study included 102 patients treated between 2018 and 2023. Two CBCTs were acquired per session, pre- and post-treatment, based on the STEREOPAC trial protocol (NCT05083247). 5 PTV and PRV margins were 3-5 mm. Data from Mosaiq (v3.10) were analyzed in MIM Maestro (v7.3.4) to measure intrafraction motion on the x (lateral), y (vertical), and z (longitudinal) axes. Statistical analyses, including F-tests and ANOVA, were used to assess motion variability. Motion results were categorized into groups: under 3 mm (for MRI-LINAC margin adaptation), under 4 mm (fiducial-based risk volume), and under 5 mm (PTV margins). Results: A total of 463 pre- and post-CBCT matchings were analyzed, with 78.4% of tumors located in the pancreas head. Over 95% of motion measurements were under 3 mm (figure 1). Among the 69 instances exceeding 3 mm, 32.8% occurred in the y axis, 27.9% in the z axis, and 21.3% in the x axis. Simultaneous motion across axes occurred in 6.6% of cases. Only 4.97% of measurements exceeded 3 mm, 2.52% surpassed the 4 mm FEV threshold, and 1.73% exceeded the 5 mm PTV margin, suggesting low risk of undercoverage.