Quantification of Motion Reduction using Pre-simulation Assessment Sessions (PASS) for Stereotactic Ablative Body Radiotherapy (SABR)

Background:Pre-simulation Assessment Sessions (PASS) can be utilised to assess respiratory motion in patients receiving stereotactic ablative body radiotherapy (SABR). PASS is an assessment process that uses cine x-ray images to determine whether expiration breath-hold (EBH) or abdominal compression (AC) can be effectively utilised to manage diaphragm motion, prior to computed tomography (CT) simulation. This study aimed to determine the effectiveness of PASS for eligible patients based on diaphragm motion in free breathing (FB) compared to using MMSs. Material and Methods: Retrospective data on diaphragm motion in FB and elected MMS was collected for 73 patients. Eligible patients were treated between 2018-2022 using SABR for abdominal and lower lobe lung tumours. In the PASS process, the diaphragm motion seen on cine x-ray images was measured through three cycles of FB versus the elected MMS. Differences in FB and MMS diaphragm motion was found for each patient using Wilcoxon Matched Pairs Test. Results: Of the 73 patients, 28 were treated with EBH, 34 with AC, 2 with alternate strategies and 11 were treated using FB as they were not suitable for a MMS. There was a statistically significant difference between the mean of the amplitude of the diaphragm motion when comparing FB and EBH and FB and AC (p= 0.05). There were no associations found between the PASS success rate for any MMS and BMI or age. Conclusion: PASS is a useful tool which can be used to shape the future of radiotherapy by selecting the patient specific MMS for the reduction of tumour motion during SABR treatments. This study will be used to further investigate the dosimetric effects of MMS on internal margin reductions and normal tissue sparing.