S2720
RTT - Patient preparation, immobilisation, and verification protocols
ESTRO 2026
used for the Head/Image Gently protocol, while the CTDI Φ 16 cm (pediatric body/adult head) and CTDI Φ 32 cm (adult body) phantoms were used for the remaining protocols. Measurements were obtained from one central and four peripheral positions and were combined to calculate the weighted Cone Beam Dose Index (CBDIw), using CBDIw = 1/3 Dc + 2/3 Dp, where Dc is the central dose and Dp the mean peripheral dose. Results: CBDIw values were determined for all protocols and grouped according to phantom size to allow comparison between pediatric and adult dose levels.Pediatric phantoms: 5.198 mGy (Head), 12.366 mGy (Thorax), 44.370 mGy (Pelvis), 1.65 mGy (Image Gently – Head), and 1.23 mGy (Image Gently – Body).Adult phantoms: 3.822 mGy (Head), 5.558 mGy (Thorax), 20.796 mGy (Pelvis), 1.230 mGy (Image Gently – Head), and 0.501 mGy (Image Gently – Body).An average difference of approximately 103% was observed between pediatric and adult measurements, demonstrating the influence of phantom diameter on dose distribution and on the calculation of CBDIw. Conclusion: The CBDIw values were consistent with data reported in the literature and by manufacturers. Dose reduction in CBCT can be achieved through optimization of acquisition parameters such as mAs and kV. The Image Gently protocols showed reduced dose values and may serve as a clinical reference for both adult and pediatric head protocols. Optimization of the remaining CBCT protocols is recommended to achieve comparable dose levels. References: 1. Østergaard DE, Scandurra D, McCowan C, Rwigema JCM, Teoh M, Greig L, et al. Paediatric CBCT protocols for image-guided radiotherapy: a scoping review and survey. Radiother Oncol. 2024;190:109037.2. Wilson LJ, Mendes R, Hansen VN, McCowan C, Thomas RAS, Teoh M, et al. Cone beam CT dose optimisation: a review and expert recommendations. Radiother Oncol. 2025; Epub ahead of print. doi:10.1016/j.radonc.2025.109500.3. Amer A, Marchant T, Sykes J, Czajka J, Moore C, Henry A. Cone beam computed tomography doses to the brain and body in pediatric radiotherapy patients. Br J Radiol. 2020;93(1107):20190643. Keywords: Cone-Beam CT, Radiotherapy, Pediatrics
enhanced by surface-guided radiotherapy and fiducial marker tracking. References: Guckenberger M, Andratschke N, Dieckmann K, Hoogeman MS, Hoyer M, Hurkmans C, et al. ESTRO ACROP consensus guideline on implementation and practice of stereotactic body radiotherapy for peripherally located early stage non-small cell lung cancer. Radiother Oncol. 1 juill 2017;124(1):11 - 7.Fu W, Zhang Y, Mehta K, Chen A, Pucci P, et al. Evaluating intra - fractional tumor motion in lung stereotactic radiotherapy with deep inspiration breath - hold. J Appl Clin Med Phys. 27 mai 2024;25(8):e14414.Meng YJ, Mankuzhy NP, Chawla M, Lee RP, Yorke ED, Zhang Z, et al. A Prospective Study on Deep Inspiration Breath Hold Thoracic Radiation Therapy Guided by Bronchoscopically Implanted Electromagnetic Transponders. Cancers. 17 avr 2024;16(8):1534. Keywords: Lung SBRT, DIBH, Reproducibility. Digital Poster 1922 Are We Giving Too Much? Rethinking CBCT Dose in Pediatric Radiotherapy Daniela Saraiva 1,2 , Ana Cravo Sá 3,4 , Fernando M. Costa 1,3 , Gabriel Farinha 1 , Ana Rita Figueira 1 , Armanda Monteiro 1,3 , Lígia Osório 1 1 Radiotherapy, ULS São João, Porto, Portugal. 2 University of Vigo, University of Vigo, Vigo, Spain. 3 Radiotherapy, E2S - Escola Superior de Saúde do Politécnico do Porto, Porto, Portugal. 4 Center for Translational Health and Medical Biotechnology Research, School of Health, Porto, Portugal Purpose/Objective: Cone Beam Computed Tomography (CBCT) is used in radiotherapy as the preferred imaging method, supporting treatment accuracy and patient positioning. In pediatrics, its importance is greater due to increased radiosensitivity and longer life expectancy, making the evaluation of dose in each imaging protocol essential, particularly when CBCT is performed on a daily basis. The objective of this study is to evaluate and compare CBCT doses used in adult and pediatric patients, when standard/manufacturer protocols are used without optimization. Material/Methods: Fifteen CBCT scans were performed for each imaging protocol (Head, Pelvis, Thorax, and Image Gently), totaling 150 scans. A TrueBeam Linear Accelerator CBCT system (Varian Medical Systems, Palo Alto, California) was used, together with a 100 mm pencil ionization chamber (X2 Raysafe, Sweden) and a Gammex CTDI phantom (Sun Nuclear, Melbourne, Florida). The Φ 10 cm phantom (pediatric head) was
Digital Poster 2004
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