S2699
RTT - Patient preparation, immobilisation, and verification protocols
ESTRO 2026
Purpose/Objective: This study aimed to evaluate the accuracy and precision of the surface-guided deep inspiration breath-hold(DIBH) technique. A statistical comparison of lung and liver patient cohorts treated with surface- guided DIBH was conducted to determine whether there is a significant difference in intrafractional displacement between the cohorts. Material/Methods: Data for this study were collected retrospectively by reviewing all offline review records of all patients who underwent lung and liver SBRT in DIBH from 2021 to 2024. Only patients who could maintain consistent, reproducible DIBH, as determined by the surface- guidance tool, were included.Intrafractional displacements were measured by examining the gross tumor volume (GTV) or anatomical surrogate corrections made at the fraction's midpoint in the three translational directions (VRT, LNG, LAT). Analysis included 86 lung and 124 liver patients, with 182 and 159 fractions, respectively.The mean, standard deviation (SD), median, 95% confidence interval (CI), and 3D spatial vector were calculated for the results.The difference in displacements between these two patient groups was assessed using the Mann- Whitney U test, as the data did not follow a normal distribution, confirmed by the Shapiro-Wilk test. Results: In the liver patient cohort, the greatest intrafractional displacement was in the mean VRT direction (0.087 cm), with lower mean shifts of -0.031 cm and -0.042 cm in the LAT and LNG directions, respectively. The highest SD was in LNG (±0.275 cm), and the 95% CI excluded zero in all directions, indicating systematic displacements rather than random. The 3D mean displacement was 0.351 ± 0.181 cm.In the lung patient cohort, the highest mean intrafractional displacement was noted in the LNG direction (-0.092 cm), with lower means of -0.025 cm and 0.036 cm in LAT and VRT directions, respectively. The highest SD was also in LNG (±0.251 cm), with a 95% CI excluding zero across all directions, suggesting a systematic trend. The 3D spatial displacement is 0.298 ± 0.186 cm.Significant differences in VRT, LNG, and 3D spatial intrafractional displacement between liver and lung cohorts (p-values = 0.0140, 0.0331, and 0.0032, respectively) were noted. Conclusion: Surface-guided DIBH SBRT showed high accuracy and precision in maintaining target positional stability. Significant differences between lung and liver patients in most directions suggest a region-specific approach may be needed when treating with this technique. Keywords: DIBH, SBRT
Digital Poster 572 Real-time intra-fraction motion monitoring in prostate cancer patients undergoing radiotherapy: a scoping review Harley Stephens 1 , Pauline Humphrey 1 , Mary Cramp 2 , Mwidimi Ndosi 2 1 Radiotherapy, UHBW, Bristol, United Kingdom. 2 School of Health and Social Wellbeing, UWE, Bristol, United Kingdom Purpose/Objective: There is increasing evidence for the efficacy and favourable toxicity profile of hypofractionated stereotactic ablative radiotherapy (SABR) for treatment of localised prostate cancer. The high dose per fraction and reduced number of treatments in SABR require smaller margins and result in steeper dose gradients compared with conventional fractionation, emphasising the need for precise image-guided radiotherapy (IGRT).While IGRT improves daily setup accuracy and may enhance biochemical control and reduce acute toxicity, limited evidence exists on real- time intra-fractional motion monitoring. Earlier studies relied on pre- and post-treatment imaging, failing to capture real-time prostate motion. Given the random and unpredictable nature of intra-fraction motion, continuous tracking is recommended over intermittent imaging. With the growing use of prostate SABR, maintaining treatment accuracy within 3 mm has become increasingly important. This scoping review aimed to identify, map, and summarise existing evidence on the clinical use of intra-fractional IGRT in prostate cancer radiotherapy and to describe how such interventions are reported in the literature. Material/Methods: This study followed the JBI methodology for scoping reviews and adhered to the PRISMA-ScR reporting guidelines. A systematic search was conducted in Embase, Ovid Emcare, Ovid MEDLINE, CINAHL, and AMED for studies addressing intra-fraction prostate imaging. Records were imported into EndNote X9.3.3 for deduplication and subsequently screened in Rayyan by independent reviewers. Data regarding study design, imaging modality, and methodological characteristics were extracted and summarised. Results: The database search identified 1,650 records, of which 1,093 remained after duplicate removal. Following title and abstract screening, 90 full-text articles were assessed for eligibility by 3 reviewers and 44 met the inclusion criteria. Studies were published between 2006 and 2025, with sample sizes ranging from 5 to 189 participants. Most were cohort studies (29 prospective, 15 retrospective), with two methodological and one interventional study. The
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