Effects of respiratory motion on accurate four-dimensional computed tomography acquisition and plan delivery for lung stereotactic body radiation therapy

This study evaluated the impact of respiratory movement on four-dimensional computed tomography (4D-CT) acquisition and radiotherapy delivery. QUASAR^™ Respiratory Motion Phantom with nine sinusoidal waveforms that combined three amplitudes (10, 20, and 30 mm) and three breaths per minute (BPMs) (10, 15, and 20) was used. We acquired 4D-CT for nine respective waveforms and measured and compared geometrical factors (volume, shape, and motion) to reference static CT. We optimized and delivered radiotherapy plans on a Vital Beam and evaluated gamma for dose distribution analysis with three acceptance criteria: 3%/3 mm, 3%/3 mm, and 5%/5 mm. Geometrical analysis revealed that an increase in amplitude decreased 4D-CT acquisition accuracy. Geometrical factors for an amplitude of ≤ 20 mm were within tolerance limits, however, amplitude 30 mm resulted in significant deviations over tolerance limits. BPM had a minimal effect on geometrical accuracy when accurate pitch values for respective BPMs were selected for scanning. Dose distribution analysis also indicated that an increase in amplitude decreased the gamma passing rates. Amplitude 30 mm failed to achieve a 95% passing rate for all three gamma evaluation criteria adopted in the present study. Overall, our results demonstrate that respiratory motion has significant effects on the accuracy of both 4D-CT acquisition and planned radiotherapy delivery. Small amplitude of ≤ 20 mm is required to ensure accuracy.