Preliminary Evidence of Natural-Respiration Breath Hold (NRBH) Superior to Deep-Inspiration Breath Hold (DIBH) for Radiotherapy of Abdominal Cancer
Abstract
Purpose
To determine whether natural-respiration breath hold (NRBH) should be used to freeze organ motion rather than deep-inspiration breath hold (DIBH) in abdominal cancer treatments, as NRBH should be more reproducible, retaining organ normal size, shape, and position without forced organ compression/expansion.
Methods
The clinical free-breathing (FB) and DIBH (x2) CT images of 42 liver cancer patients were analyzed, focusing on liver changes in volume, shape, and position. A deep-learning automatic segmentation tool was applied to contour major organs, and a deformable image registration (DIR) was applied to calculate the Jacobian determinants (J) of the FB-to-DIBH deformable vector field, estimating tissue compression (J1.0). Fiducials were identified in 15 patients to assess DIBH reproducibility. Statistical analysis was conducted to show the diversity of these measured parameters. Additionally, MRI images of 6 volunteers at DIBH and NRBH were acquired and analyzed under a prospective time-resolved 4DMRI protocol, and the reproducibility of diaphragmatic position was assessed.
Results
Diverse liver volume, shape, and position changes are observed among the 42 patients. Based on mean J values, 22 liver compressions and 20 liver expansions are found in 42 patients, while the body (100%) and lung (95%) within the CT-scan ranges are expanded. Liver volume is unchanged (∆V=-1.0%±1.8%) in 19, increased (∆V=19.2%±15.1%) in 8, and decreased (∆V=-6.4%±2.1%) in 12 patients. The liver fiducial reproducibility between DIBHs is 4.4mm±3.2mm among the 15 patients. In contrast, the NRBH diaphragm reproducibility in 6 subjects is 1.7mm ±1.5mm at full exhalation and 1.3mm±1.6mm at full inhalation within free breathing range.
Conclusion
The preliminary results demonstrate that NRBH is more reproducible and easier to achieve than DIBH, without extra-force causing diverse tissue compression/expansion that may introduce unpredictable impacts on treatment uncertainties. The NRBH appears to be a favorable solution to freeze abdominal organ motion during radiotherapy treatments.