A prospective observational study evaluating two patient immobilisation methods in lung stereotactic radiotherapy

Area of Science:

• Radiation Oncology
• Medical Physics
• Imaging Technology

Background:

• Lung stereotactic body radiation therapy (SBRT) requires precise patient immobilization.
• Assessing immobilization devices is crucial for treatment accuracy and patient safety.

Purpose of the Study:

• To compare inter- and intrafraction errors between a vacuum cushion and a simple arm support for lung SBRT.
• To evaluate the accuracy of patient positioning with these two immobilization devices.

Main Methods:

• Twenty patients undergoing lung SBRT were enrolled, with ten using a vacuum cushion and ten using a simple arm support.
• Four-dimensional cone-beam computed tomography (4D CBCT) and three-dimensional cone-beam computed tomography (3D CBCT) were used to assess positioning accuracy.
• Translational and rotational errors were analyzed based on rigid registration to the planning CT.

Main Results:

• Interfraction errors were similar for both devices, with deviations generally under 1.3mm and 1.2°.
• Longitudinal interfraction errors showed a significant difference: 0.7mm for vacuum cushion vs. -3.9mm for arm support.
• While mean intrafraction errors were comparable, the standard deviation was significantly larger with the arm support, indicating greater variability.

Conclusions:

• Both immobilization devices demonstrated similar mean inter- and intrafraction deviations.
• The vacuum cushion offers more accurate immobilization due to significantly lower intrafraction variability compared to the arm support.