S2735
RTT - Patient preparation, immobilisation, and verification protocols
ESTRO 2026
3051 Optimizing the Gating Window in DIBH for Left- Sided Breast Radiotherapy Using Chest Wall Reproducibility Analysis Prakash Umbarkar, Sudesh Deshpande, Vivek Anand, Suresh Naidu, Vinay Babu, Ritika Hinduja, Omkar Jadhav, Sandeep Shinde, Ashwini Jejurkar, Neeta Parmar, Prashant Kamble, V Kannan Department of Radiation Oncology, P. D. Hinduja National Hospital, Mumbai, India Purpose/Objective: To evaluate chest wall setup reproducibility during deep inspiration breath-hold (DIBH) in patients with left-sided breast cancer (LBC), and to determine whether the gating window width can be optimized to improve treatment accuracy. Material/Methods: Eighty-two patients with LBC were included. Patients were treated with DIBH if they were able to maintain a breath-hold of ≥ 20 seconds. CT simulation was performed in free breathing and DIBH using a breast board. Daily patient positioning was reproduced using laser alignment with three reference tattoos on the sternum.A marker block was placed on the xiphisternum, and audio coaching was used to achieve a reproducible breathing pattern. Treatment planning was done on the DIBH CT dataset. Setup verification was performed using pre-treatment portal images for the first three fractions and weekly thereafter. Images were matched with digitally reconstructed radiographs (DRR) using bony anatomical landmarks, and couch shifts were applied when required.All portal images were acquired using the Varian aS1200 EPID in CINE mode during tangential field delivery. The left medial (LMT) and left lateral (LLT) tangential fields were evaluated. The RPM respiratory trace was recorded for offline analysis.Data analysis and statistics:A total of 820 portal CINE images were analyzed offline to determine chest wall deviation. Differences between the chest wall position on DRR and CINE images were quantified as mean error (M), systematic error ( Σ ), and random error ( σ ). Results: The mean patient age was 50 years (25–74). Motion analysis used algebraic sign, where a positive mean error indicates the treated lung volume was smaller than planned. The upper and lower gating thresholds were 2.2 ± 0.4 cm and 1.1 ± 0.2 cm, giving an effective gating window of 1.1 ± 0.3 cm.The mean setup error for LMT was 0.276 cm (range − 0.95 to +1.26 cm; Σ = 0.230 cm; σ = 0.479 cm), and for LLT was 0.187 cm (range − 0.99 to +1.22 cm; Σ = 0.228 cm; σ = 0.477 cm). LMT error was slightly higher than LLT, and the difference was statistically significant (p = 0.003). Conclusion:
measured).
References: 1
Vikström J, Hjelstuen MH, Mjaaland I et al. Cardiac and pulmonary dose reduction for tangentially irradiated breast cancer, utilizing deep inspiration breath-hold with audio-visual guidance, without compromising target coverage. Acta Oncol 2011; 50 (1): 42-50.2 Berg M, Lorenzen EL, Jensen I et al. The potential benefits from respiratory gating for breast cancer patients regarding target coverage and dose to organs at risk when applying strict dose limits to the heart: results from the DBCG HYPO trial. Acta Oncol 2018; 57 (1): 113-119. Keywords: Respiratory gating, Instructional video
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