ESTRO 2025 - Abstract Book

S3341

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2025

Material/Methods: 43 patients treated with SRS technique were enrolled in this Study: 33 using closed masks and 10 using open masks CBCT scans were conducted before and after the treatment. Intrafraction variability was evaluated. For the open mask group, the AlignRT system and the head adjuster device were used to assist with patient positioning and real-time monitoring. The agreement between the positioning errors from Align RT and the CBCT scan results was assessed. For 33 patients in the closed mask group, the dosimetric impact of the accepted rotational adjustments post-CBCT on PTV coverage and the brain stem was evaluated. Dosimetric planning on the CBCT was carried out on Monaco 6.3 based on the CBCT calibration curve. Results: The mean bias values between the AlignRT guided positioning errors and CBCT were as follows: 0.4 mm, -0.5 mm, 0.5 mm, -0.20°, -0.1°, and 0.02°. We noticed that Intrafraction variability was comparable between the two mask types. In the closed mask group, the average accepted rotational errors were 1°, -0.7°, and 0.9°. PTV coverage in the CBCT plan gave a significant difference compared to the CT plan We recorded an under-dosage of the PTV which reached 93.7% compared to 99.6% found in initial CT Maximum dose in brain stem exceeded the tolerated dose (30Gy) in 4 cases and the difference between this value in the CBCT and the CT reached 3.5Gy. Conclusion: Using surface-guided radiotherapy with an open-face mask and a head adjuster or 6D table enhances both patient comfort and positioning accuracy. Additionally, the AlignRT system demonstrated excellent concordance with the CBCT. In this study we did not find an intrafrational variation with open and closed masks but if this is the case, it is important to follow any movements in real time during the treatment. Digital Poster Initial Experience and Short-Term Clinical Outcomes of Lung cancer Patients Treated with SBRT Using the Radixact Synchrony Tumor Tracking System Evren Ozan Goksel 1,2 , Zeynep Ozen 2 , Seckin Gunduz 2 , Artunc Osman Ture 2 , Halil Kucucuk 2 , Alptekin Arifoglu 2 , Evrim Kadriye Tezcanli 1,2 , Ufuk Mehmet Abacioglu 1,2 , Meric Kazım Sengoz 2 1 Radiotherapy, Acibadem MAA University, Istanbul, Turkey. 2 Radiation Oncology, Acibadem Altunizade Hospital, Istanbul, Turkey Purpose/Objective: Stereotactic body radiotherapy (SBRT) is a proven approach for achieving excellent local control in primary and metastatic lung lesions. Effective motion management techniques are critical for accurately delivering high fractional doses to mobile targets. This study presents our initial clinical experience using the "lung with respiratory" feature of the Synchrony ® real-time tumor tracking system integrated into the Radixact ® platform and reports the short-term clinical outcomes of lung cancer and lung metastasis patients treated with this advanced motion management technique. Material/Methods: This retrospective study analyzed the treatment processes of 13 patients who underwent radiotherapy for lung metastases using the Synchrony "lung with respiratory" technique. Tumor locations were categorized as central in 7 Keywords: SGRT, Dosimetric constraints, open face mask 4034