S2239
Physics - Intra-fraction motion management and real-time adaptive radiotherapy
ESTRO 2026
Muto 1,3 , Ida Rosalia Scognamiglio 1,2 , Lorella Lo Conte 1,2 , Paolo Muto 4,2 1 Radiationtherapy, Emicenter, Naples, Italy. 2 Radiationtherapy, Fondazione Muto ETC, Naples, Italy. 3 Radiationtherapy, Fodazione Muto ETC, Naples, Italy. 4 Radiationtherapy, Istituto tumori ICCRS Fondazione Pascale, Naples, Italy Purpose/Objective: Respiratory-induced tumor motion can compromise the precision of lung SBRT [1]. The Synchrony® motion tracking system on the Radixact® platform enables real-time beam adaptation to this motion [2]. The following study compared the Synchrony® performance with conventional non-adaptive ITV- based planning and validated results through deformable dose accumulation (DAA) across respiratory phases. Material/Methods: A retrospective study was conducted on 11 patients with primary NSCLC (1.5–8.0 cm lesions, ≤ 2 cm respiratory motion) treated with Radixact® Synchrony® between 2019 and 2024. Two plans were compared: Synchrony-based adaptive (TVSYNC) and conventional non-adaptive ITV-based. Dose–volume metrics (DMIN, DMEAN, D99%, V100%) and lung dose (V20Gy < 10%) were analysed. DAA across 10 respiratory phases (MIM® Software) provided phase- resolved dosimetry on manually contoured GTVACC volumes [3]. Results: Figure 1. Comparison of V100% and Vmean using ITV, TVSYNC, and GTVACC DAA planning approaches.Synchrony-based adaptive delivery improved dose conformity and target coverage compared with non-adaptive ITV-based plans. Among 11 patients, average Synchrony beam on time (BOT) ranged from 382s to 624s, and modulation factor 1.2 to 2.3. Maximum tumor displacement (vmax) was between 0.86 cm and 1.76 cm. TVSYNC volumes had consistent densities (0.86–1.07 g/cm ³ ), while PTV densities were lower (0.28–0.55 g/cm ³ ) due to ITV expansion. The ITV-based approach met dose thresholds (DMIN ≥ 98%, V100% ≥ 98%, D99% ≥ 98%) in only 3, 1, and 1 of cases (n=11), whereas TVSYNC achieved these in 7, 6, and 7 cases (n=11), and GTVACC in 5, 6, and 7 (n = 9). DAA planning yielded the best D99% coverage, while TVSYNC provided superior target coverage (V100% ≥ 98%) (Figure 1). On average,
without significant differences in OAR doses (Box plot in Figure 1). Median total treatment time was 28 minutes, with an average 5-minute ASRT workflow. No grade ≥ 3 toxicities were reported; grade 2 events occurred in 10.3% of patients. Figure 2 reports Kaplan- Meier curve: at a median follow-up of 19.8 months, 1- year local control, disease-free survival, and overall survival for the whole cohort were 94%, 80%, and 84%, respectively.
Conclusion: Daily changes in the body contour and ED
heterogeneity can result in major effects on plan dosimetry which can be quickly corrected with ASRT procedure. ASRT is a safe, effective, and time-efficient alternative for online MRIgRT adaptation in thoracic tumours, with promising clinical outcomes and toxicity profiles. Keywords: New adaptive approach, Lung, MRIgRT Digital Poster Highlight 2833 Dosimetric evaluation of real-time adaptive radiotherapy with Radixact® Synchrony® for lung carcinoma IVONA ZLATKOVA 1,2 , Ferdinando Francomacaro 1,2 , Vincenzo Iorio 1,2 , Gaetano Gagliardo 1,2 , Caterina
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