Interfraction liver shape variability and impact on GTV position during liver stereotactic radiotherapy using...

Area of Science:

• Radiation Oncology
• Medical Imaging
• Computational Anatomy

Background:

• Liver stereotactic body radiotherapy (SBRT) utilizes abdominal compression to minimize organ motion and daily image guidance for setup accuracy.
• The consistency of liver shape under compression is crucial for precise treatment delivery.

Purpose of the Study:

• To quantify interfractional liver shape variability during SBRT with abdominal compression.
• To assess the impact of this variability on gross tumor volume (GTV) position after rigid registration.

Main Methods:

• Analysis of 83 kilovoltage cone beam CT (CBCT) scans from 16 patients undergoing SBRT with abdominal compression.
• Respiratory sorted CBCT scans were rigidly registered to exhale planning CT scans.
• Deformable registration (MORFEUS) was used to measure liver shape differences.

Main Results:

• Mean liver deformation exceeding 3 mm was 21.7%, with a maximum of 36.3% in one patient (excluding outliers).
• Maximum interfractional deformations were 10.5 mm (left-right), 12.9 mm (anterior-posterior), and 5.6 mm (superior-inferior).
• The mean impact of liver displacement on GTV position was minimal (<0.13 mm in all directions).

Conclusions:

• Interfraction liver deformations under abdominal compression during SBRT are generally small (<5 mm) after rigid registration.
• These findings suggest that liver shape variability does not significantly compromise GTV targeting accuracy in most patients.