Analysis of the amplitude changes and baseline shifts of respiratory motion using intra-fractional CBCT in liver stereotactic body radiation therapy

Abstract

Using intra-fractional cone-beam CT (CBCT) to evaluate the amplitude changes and baseline shifts of respiratory motion in liver stereotactic body radiation therapy (SBRT). Methods: The amplitude changes and baseline shifts of respiratory motion for 24 liver patients were evaluated by the four-dimensional (4D) CT, inter-and intra-fractional CBCT. The difference of the average liver position errors among all treatment fractions and the 4D CT representthe baseline shifts. According to the baseline shifts, the ITV to PTV margin was recalculated and the plan was re-designed to compare the dosimetric variation. Results: The systematic and random errors of the baseline shifts for intra-fractional CBCT in the left-right (LR), superior-inferior (SI), and anterior-posterior (AP) directions were 0.99/1.60 mm, 2.03/2.46 mm, and 1.02/2.07 mm, respectively. The new ITV to PTV margins should be 4.0 mm, 7.0 mm, and 4.0 mm, respectively. The amplitude change of motion between the 4D CT and the intra-fractional CBCT was 1.03 ± 4.35 mm, with 31% of fractions exceeding 5 mm. To achieve the same dose coverage of the new PTV, the D mean , V50, V40, V30, V25 of normal liver and maximum dose of the duodenum were significantly different. Conclusions: Significant amplitude changes and baseline shifts of motion occurred during dose delivery compared with those in 4D CT. Using the ITV to PTV margin of 4.0 mm (LR), 7.0 mm (SI), and 4.0 mm (AP) can ensure the target dose coverage and keep the dose constrain of normal tissues at an acceptable level.

Real‐time image‐guided treatment of mobile tumors in proton therapy by a library of treatment plans: a simulation study

“…The tumor's motion observed in the planning 4DCT might be different than the one observed during the day of the treatment. There might be a difference in breathing amplitude, or there could be a baseline shift 20 . To account for the true breathing pattern of the day, we implemented an initialization phase during which we observe the tumor motion 30 s before starting the beam.…”

“…Treatment delivery process of our library of treatment plans approach breathing amplitude, or there could be a baseline shift. 20 To account for the true breathing pattern of the day, we implemented an initialization phase during which we observe the tumor motion 30 s before starting the beam. During this period, images are acquired in the same way they are acquired during treatment, that is, a few images per second.…”

A novel external/internal tumor tracking approach to compensate for respiratory motion baseline drifts

“…Several groups have reported baseline drifts in respiratory tumor motion for different tumor locations (Rietzel et al 2005, Suh et al 2008, Case et al 2009, Quirk et al 2013, Dhont et al 2018, Liang et al 2018, Hoekstra et al 2021, Zeng et al 2022. The physiological nature of baseline drifts is not yet fully understood, shifts between abdominal and chest breathing, relaxation/contraction of skeletal muscles and patient relaxation are mentioned as potential reasons (Rietzel et al 2005).…”