Room: AAPM ePoster Library
Purpose: This work aims to investigate stability and reproducibility of spirometry assisted deep inspiration breath hold (DIBH) for liver stereotactic body radiotherapy (SBRT). Additionally, we explore the feasibility of using surface guided radiotherapy (SGRT) as a motion surrogate by correlating diaphragm and surface positions.
Methods: Stability and reproducibility of spirometry assisted DIBH was quantified by investigating the diaphragm position of a cohort of seven patients undergoing liver SBRT. The variation in diaphragm position was extracted from CBCT projection data by comparing projections to the corresponding digitally reconstructed radiographs (DRRs) from the planning CT. On each projection image, the diaphragm/lung edge was enhanced by vertical pixel shifting, subtraction and filtering. Each row of the edge-enhanced image was then integrated and the required shift to align the projection to the DRR was recorded as the diaphragm position variation. Mean diaphragm position variation between (inter-) DIBH was denoted as reproducibility and standard deviation of diaphragm position during (intra-) DIBH as stability. Finally, for a subset of the patients, the recorded abdomen surface amplitude was captured with AlignRT system to assess for correlation between diaphragm motion and surface variation.
Results: The maximum intra- and inter-breath hold diaphragm position variation were approximately 10.0 mm and 15.9 mm, respectively. The mean stability and reproducibility with DIBH were 3.2±1.9 mm and 7.8±4.4 mm, respectively. A negative correlation (maximum of -0.94) between diaphragm motion and surface variation was observed in this cohort.
Conclusion: Diaphragm position and lung volume varies greatly during and between DIBH. The observation of a negative correlation between diaphragm motion and surface variation indicates a potential of using SGRT for liver SBRT.