S2742
RTT - Patient preparation, immobilisation, and verification protocols
ESTRO 2026
Reducing Treatment Time through Optimisations of Motion Management Kendell Shields-Dowton 1 , Joel Poder 1,2 , Johnson Yuen 1,3 , Laurel Schmidt 1 , Yaw Chin 1,4 1 Department of Radiation Oncology, St George Cancer Care Centre, Kogarah, Australia. 2 Centre for Medical Radiation Physics, University of Wollongong, Wollongong, Australia. 3 Medical Physics, Ingham Institute for Applied Medical Research, Sydney, Australia. 4 St George and Sutherland Clinical School, UNSW Medicine, Sydney, Australia Purpose/Objective: We previously presented on the development and clinical translatability of a Mid-Ventilation (MidV) workflow for lung stereotactic ablative radiotherapy (SABR) using a single radiation treatment planning system1. Changes in the average tumour position during delivery of lung SABR are usually assessed by 3- dimensional (3D) or 4-dimensional (4D) cone beam computed tomography (CBCT) before and during the delivery. Although 4D-CBCT is the recommended image verification for the MidV technique, it can potentially prolong time taken for treatment delivery due to time taken for image reconstruction. For linac- based SABR delivery, longer treatment times have been shown to increase intra-fractional stability with increased positional drift and patient motion2-3. This study therefore aims to assess the potential of reducing lung SABR treatment time by quantifying the degree of adjustment required during the mid- treatment 4D-CBCT with the hypothesis of omitting this and substituting it with triggered intrafraction kilovoltage (kV) imaging. Material/Methods: 30 patients were treated with lung SABR using the MidV workflow. Time for treatment delivery and each 4D-CBCT were recorded. Inter and intra-fraction motion were evaluated using pre- and mid-treatment 4D-CBCTs. The range and median of the corrective shifts made in 6 degrees of freedom after the mid- treatment 4D-CBCT were analysed. It is postulated that shifts of ≤ 3mm (translation) and ≤ 2degrees (rotation), would allow for omission of the mid-treatment 4D- CBCT. A corresponding reduction in treatment delivery time by 5 minutes is considered to be clinically significant. Results: Corrective isocentre shifts following the mid-treatment 4D-CBCT demonstrated small intra-fraction variations. For 4D-CBCT 1, median translational corrections were 0.36cm (vertical), 0.40cm (longitudinal), and 0.21cm (lateral) (Figure 1), and median rotational corrections were 0.8° (pitch), 0.7° (roll), and 0.9° (rotation)(Figure 2). For 4D-CBCT 2, median translational corrections were reduced to ≤ 0.07 cm across all axes, with
Figure 1: Structure of the Gynecological applicator, radiopaque markers are inside the end-effector.
Figure 2: CT and MRI with radiopaque markers (circled in red). Results: The CT analysis revealed that the PLA component
exhibited a mean value of +22 HU, indicating radiological equivalence to soft tissues. The
experimental WEPL measurement evidenced a value of 1.19, which is comparable to that of PMMA. The dosimetric evaluation showed that the presence of the applicator introduced negligible perturbations in the dose distribution on both proton and carbon-ion beams. The embedded radiopaque markers were clearly visible on both CT and DRR images, confirming their suitability for image-guided alignment. Finally, the device was found to be fully compatible with 3T MRI, showing no significant image artifacts or thermal effects during acquisition. Conclusion: The proposed device demonstrated full compatibility with standard imaging modalities, including CT and MRI. The plastic components had tissue-equivalent properties, allowing accurate characterization within the treatment planning system. Radiopaque surrogates and markers were discernible across all evaluated imaging modalities [3]. Further in-vivo investigations are planned to validate the device’s effectiveness under clinical conditions. References: [1] Kubota Y., et al., "Development of a Vaginal Immobilization Device: A Treatment-planning Study of Carbon-ion Radiotherapy and Intensity-modulated Radiation Therapy for Uterine Cervical Cancer", Anticancer Res 2019;39:1915-21.[2] Ramot Y., et al., "Biocompatibility and safety of PLA and its copolymers", Advanced Drug Delivery Reviews, 107, 153–162.[3] Qin X., et al., "Efficacy and safety of a 3D- printed applicator for vaginal brachytherapy in patients with central pelvic-recurrent cervical cancer after primary hysterectomy", Brachytherapy. 2022;21:193-201. Keywords: gynecological/particle therapy/3D printing
Poster Discussion 3827 Streamlining Lung SABR with Mid-Ventilation:
Made with FlippingBook - Share PDF online