S2155
Physics - Inter-fraction motion management and daily adaptive radiotherapy
ESTRO 2026
for automatic segmentation of MRI scans in the male pelvis for adaptive radiotherapy. Front Oncol. 2023;13:1285725. Keywords: prostate, hypofractionation, online adaptive
Digital Poster 3325
Enhancing inter-fraction Setup Accuracy and Margin Minimization (E-SAMM) : A maskless surface guided radiotherapy study in pelvic cancers Pramod K Gupta 1 , Sumanta Manna 2 , Sharad Singh 1 , Rumita Singh 1 , Ragul T 2 1 Department of Radiation Oncology, Kalyan Singh Super Speciality Cancer Institute, Lucknow, India. 2 Medical Physics(Department of Radiation Oncology), Kalyan Singh Super Speciality Cancer Institute, Lucknow, India Purpose/Objective: Surface Guided Radiotherapy (SGRT) is a non-invasive technique that uses real-time optical surface monitoring for accurate patient setup and motion management during radiotherapy (RT). The E-SAMM study compared setup accuracy, planning target volume (PTV) margins, and setup duration between maskless SGRT and conventional mask-based laser setups in pelvic cancer RT. Material/Methods: From June 2023 to July 2025, 100 consecutive patients with pelvic cancers (cervical, endometrial, rectal, and prostate) receiving radical or neoadjuvant RT (45–68 Gy in 25–28 fractions) were prospectively enrolled. A total of 2376 RT fractions were analysed. Patients were randomized into two groups.Group A (n = 50): Maskless SGRT setup using AlignRT with knee rest and intrafraction monitoring. Group B (n = 50): Six-clamp thermoplastic mask-based laser setup with image guidance (IGRT).All radiotherapy treatments were delivered on a TrueBeam SVC linear accelerator with a 6-degree-of-freedom (6DOF) couch. All patients underwent CBCT for online verification. Setup accuracy was evaluated using translational (mediolateral [ML], craniocaudal [CC], anteroposterior [AP]) and rotational (pitch, roll, yaw) shifts obtained from CBCT. The corresponding PTV margins were calculated using the Van Herk formula. Setup time was recorded for each session. Statistical analysis employed Analysis of variance (ANOVA) and Mann– Whitney U tests to evaluate the impact of multiple factors on the setup accuracy. Results: SGRT (Group A) demonstrated superior inter-fraction translational accuracy compared with mask-based laser alignment (Group B), except in the vertical (AP)
During treatment, Group-B showed significantly smaller and less variable rectal volumes and wall areas within the high-dose region. Bladder volumes were also smaller, as expected, but bladder wall areas were similar. Comparing simulation and treatment for both groups, all metrics demonstrated significant correlations, indicating that anatomy at simulation is somewhat reproducible despite procedural differences, particularly regarding the overlap of the organ wall with the high-dose region (R>0.79). For the rectal volume, Group-B showed high reproducibility, whereas Group-A exhibited only a modest correlation. Regardless of the bladder filling procedure, the reproducibility of bladder volume was low (R<0.5). Conclusion: Use of enema and reduced bladder filling improved prostate stability, supporting accurate ultra- hypofractionated online adaptive radiotherapy. The overlap between the high-dose region and rectal wall was reduced, while the bladder wall within the high- dose region remained unchanged. The more reproducible anatomy and lower inter-patient variability also facilitates template-based planning commonly used in online adaptive radiotherapy. References: [1]: Preziosi F, et al. AI-driven online adaptive radiotherapy in prostate cancer treatment: considerations on activity time and dosimetric benefits. Radiation Oncology 2025; 20, 116.[2]: Lorenzen EL, et al. An open-source nnU-net algorithm
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