ESTRO 2025 - Abstract Book

S4100

RTT - Patient care, preparation, immobilisation and IGRT verification protocols

ESTRO 2025

Pulmonary function tests (PFTs) were conducted using the SDX spirometer (DYN’R) and Asma-1 respiratory monitor (Vitalograph), with nose clips. Surface motion tests were performed using a structured light grid projected onto participants’ chests, centred on the xiphoid process, using the Thora-3Di (PneumaCare). Tests involved measurements of: two minutes tidal breathing, three vital capacity (VC), one maximum-duration DIBH at 80% of inspiratory capacity (IC) ± 0.2 L, four peak expiratory flow (PEF), and four forced expiratory volume in one second (FEV1). Results: All participants achieved the minimum 25-second DIBH clinical target for both positions. Expiratory reserve volume (p < 0.001), VC (p = 0.003), FEV1 (p < 0.001) and FEV1/VC (p < 0.001) were all significantly larger in upright (two-tailed t-tests). IC (p < 0.001) and maximum DIBH length (p = 0.003) were greater for supine. No difference (p = 0.63) was shown in breath-hold stability between positions. Conclusion: This study demonstrated that spirometry-guided and surface-guided radiotherapy can be undertaken in the upright position. FEV1/VC being larger for upright, consistent with other publications, implies that upright should reduce respiratory obstruction, enabling certain patients to breathe easier during treatments, Figure 2. When breathing normally, lung volume is greater upright than supine (Figure 1), which could result in a lower mean lung dose for patients. However, the maximum length DIBH is greater in supine.

Figure 1: Example breath volumes showing typical differences between upright (blue) and supine (red).

Figure 2: Difference between FEV1/VC upright and supine. All participants had a greater FEV1/VC upright, implying less obstructive lung function.