S2743
RTT - Patient preparation, immobilisation, and verification protocols
ESTRO 2026
Tumor Motion. Int J Radiat Oncol Biol Phys 2012; 84: S559–S560. Keywords: Lung SABR, Mid-Ventilation, Treatment delivery
rotational corrections of 0°. Overall, 87% of mid- treatment corrections were within ≤ 3mm and ≤ 2°, the predefined tolerance threshold for considering omission of the mid-treatment 4D-CBCT. Average 4D- CBCT 1 and 4D-CBCT 2 times were 9.19 and 7.31 minutes respectively.
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DSPS mask moulding with a head support: Does it enhance inter-fraction setup reproducibility? Leonie van Daal, Robert Smits, Marjolein Wever, Anna Dinkla, Johan Cuijpers, Sjoerd Hoek Department of Radiation Oncology, Amsterdam UMC, Amsterdam, Netherlands
Purpose/Objective: In intracranial radiotherapy, DSPS masks
(Macromedics, Moordrecht, The Netherlands) are moulded following the manufacturer’s instructions, where the back of the head settles by gravity without support. However, this may cause limited occipital contact potentially compromising mask setup reproducibility. Since small PTV margins require strict tolerances and thus optimal immobilization, this study evaluated whether using a head support during DSPS mask moulding enhances occipital fit and thereby improves setup reproducibility (Fig. 1).
Conclusion: We demonstrated that majority of positional
corrections made after the mid-treatment 4D-CBCT were small and within the normal accepted tolerances of lung SABR delivery. This potentially allows for the omission of the mid-treatment 4D-CBCT with a corresponding reduction of an average of 7.31 minutes in the treatment delivery time. However, there is still 13% of patients outside this threshold and ongoing work is being defined to identify this cohort that do require a mid-treatment 4D-CBCT. References: 1.Shields-Dowton K, Poder J, Yuen J et al. Implementation of Mid-Ventilation Stereotactic Ablative Body Radiotherapy (SABR) for Stage I Non- Small Cell Lung Carcinoma (NSCLC). Radiother & Oncol 2025; 206 (S1): 4348-4349).2.Purdie TG, Bissonnette P, Franks K, et al. Cone beam computed tomography for
Material/Methods: A retrospective analysis was performed using data from online image-guided setup procedures. Setup data were retrospectively collected from thirty patients with intracranial tumors, whose DSPS masks were moulded either with (n=15) or without (n=15) head support. Patients were treated with standard CTV-to- PTV margins of 1–2 mm using VMAT on a TrueBeam linear accelerator (Varian Medical Systems, Palo Alto, USA) equipped with a 6DoF couch. For patient setup KV-kV imaging and CBCT were used, and all translational and rotational corrections were applied using the 6DoF couch. The range and standard deviation of the setup correction data were calculated. Statistical differences in rotational setup variability were assessed using Levene’s test for variance comparison and an independent two-sample t-test for
on-line image guidance of lung stereotactic radiotherapy: Localization, verification and
intrafraction tumour position. Int J Radiat Oncol Biol Phys 2007; 68: 243-252.3.H. Boggs, S. Feigenberg, R. Walter, et al., Stereotactic Body Radiation Therapy (SBRT) Using Tomotherapy for Early Stage NSCLC: The Utility of Mid-Fraction CT Scans to Assess Intrafraction
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