ESTRO 2022 - Abstract Book

S907

Abstract book

ESTRO 2022

Conclusion Target volume delineation and radiotherapy plans particularly in brain, head & neck as well as other complex subsites require mandatory prospective review as highlighted above. We have shown this to be practically achievable and successful despite challenging times.

PO-1072 Mechanical re-inflation to maintain chest inflation during prolonged breath-holds for radiotherapy

M. Parkes 1 , I. Van Dijk 1 , J. Veldman 1 , Z. Van Kesteren 1 , M. Stevens 2 , G. Van Tienhoven 1 , J. Van Den Aardweg 3 , S. Green 4 , T. Clutton-Brock 5 , A. Bel 1 1 Academic Medical Centre (AMC), Department of Radiation Oncology, Amsterdam, The Netherlands; 2 Academic Medical Centre (AMC), Anaesthesiology, Amsterdam, The Netherlands; 3 Academic Medical Centre (AMC), Lung diseases, Amsterdam, The Netherlands; 4 University Hospitals Birmingham, Medical Physics, Birmingham, United Kingdom; 5 University Hospitals Birmingham, Critical Care Medicine, Birmingham, United Kingdom Purpose or Objective During all breath-holds, the chest slowly deflates by ~250 ml/min. During single prolonged breath-holds of > 5 min., this causes the left breast to move linearly at 2 mm/min. (± 0 standard error) dorsally (Parkes et al. , 2016) and the diaphragm to move linearly at 3 mm/min. (range 1-5mm) cranially (van Dijk et al., 2021). When using such prolonged breath-holds for radiotherapy, this would alter tumour position. Here we studied whether the mechanical ventilator can be used to re-inflate the chest during the breath-hold. Simply applying continuous inflation during breath-holding is ineffective because the larynx may close. Instead, we tested here whether subjects could be instructed at intervals to attempt a minimal inhalation using their diaphragm. This could trigger the ventilator to superimpose a constant inflation of short duration. The net effect of these short inflations should be to maintain the chest inflated until the breakpoint ( i.e., to have abolished the slow deflation). Materials and Methods Single prolonged breath-holds of > 5 min. were induced by mechanical hyperventilation and preoxygenation (Parkes et al. , 2016) with Hamilton MR1 or T1 non-invasive ventilators in 8 healthy volunteers. In 5, chest circumference was measured continuously with a wrap-around band connected to a spring-loaded resistor. In 3 others, diaphragm position was measured in the MRI using a 1D navigator acquisition at 2 Hz frequency. Results During single prolonged breath-holds in 5 subjects ( mean duration 7 min. (±1 se min)), they were instructed to attempt a minimal inhalation each time deflation had reached an arbitrary threshold level. This enabled the chest to remain at the inflation circumference at breakpoint (figure 1). During prolonged breath-holds in 3 subjects (mean duration 6 min. (± 1), they were instructed to attempt a minimal inhalation once or twice every minute (figure 2a). Here, while the diaphragm briefly descended and re-ascended by ~5 mm during each inhalation, for ~90% of time the diaphragm position remained stable within 4 mm of its mean position (figure 2b). At breakpoint the diaphragm was within 3 ± 1 se mm of its starting position. Conclusion We demonstrate how instructing healthy volunteers to perform this manoeuvre can overcome the deflation that normally occurs during all breath-holds. Training patients with thoracic or abdominal tumours to perform this manoeuvre during prolonged breath-holds could prevent the chest deflating. This could reduce tumour movement during, and increase the usable breath-hold duration available for radiotherapy treatment. Parkes MJ, et al., (2016) B J Radiol 89, 20160194. van Dijk IW et al., (2021) ESTRO OC-0339.