Four dimensional digital tomosynthesis using on-board imager for the verification of respiratory motion

Abstract

Purpose: To evaluate respiratory motion of a patient by generating four-dimensional digital tomosynthesis (4D DTS), extracting respiratory signal from patients' on-board projection data, and ensuring the feasibility of 4D DTS as a localization tool for the targets which have respiratory movement.

Methods and materials: Four patients with lung and liver cancer were included to verify the feasibility of 4D-DTS with an on-board imager. CBCT acquisition (650-670 projections) was used to reconstruct 4D DTS images and the breath signal of the patients was generated by extracting the motion of diaphragm during data acquisition. Based on the extracted signal, the projection data was divided into four phases: peak-exhale phase, mid-inhale phase, peak-inhale phase, and mid-exhale phase. The binned projection data was then used to generate 4D DTS, where the total scan angle was assigned as ±22.5° from rotation center, centered on 0° and 180° for coronal "half-fan" 4D DTS, and 90° and 270° for sagittal "half-fan" 4D DTS. The result was then compared with 4D CBCT which we have also generated with the same phase distribution.

Results: The motion of the diaphragm was evident from the 4D DTS results for peak-exhale, mid-inhale, peak-inhale and mid-exhale phase assignment which was absent in 3D DTS. Compared to the result of 4D CBCT, the view aliasing effect due to arbitrary angle reconstruction was less severe. In addition, the severity of metal artifacts, the image distortion due to presence of metal, was less than that of the 4D CBCT results.

Conclusion: We have implemented on-board 4D DTS on patients data to visualize the movement of anatomy due to respiratory motion. The results indicate that 4D-DTS could be a promising alternative to 4D CBCT for acquiring the respiratory motion of internal organs just prior to radiotherapy treatment.

Figure 1. Scheme of generating the motion of the diaphragm (Amsterdam shroud) through compressing and combining 2D projection data.

Figure 2. Extracted respiratory signals of two patients of lung (a) and liver (b) cases.

Figure 3. Plot of Lung Patient #1 patient's case where projections are sorted to each four phase bins with respect to corresponding projection angle.

Figure 4. Diagram of acquiring projection data to generate coronal “half-fan” DTS.

Figure 5. Coronal 4D CBCT and 4D DTS images of QUASAR phantom with peak-exhale (a), (e), mid-inhale (b), (f), peak-inhale (c), (g) and mid-exhale (d), (h) phases.

Figure 6. Sagittal and coronal DTS images reconstructed for the case of liver cancer patient #1 with 3D (a), peak-exhale (b), mid-inhale (c), peak-inhale (d), and mid-exhale (e) phases, emphasizing the patient's diaphragm and gold marker.

Figure 7. Coronal DTS images of lung cancer patient #1 emphasizing the cancer (white arrow) and diaphragm with 3D (a), peak-exhale (b), mid-inhale (c), peak-inhale (d) and mid-exhale (e) phases.

Figure 8. Comparative result (Coronal view) between 4D CBCT and DTS of liver cancer patient #1 case with peak-exhale (a), (e), mid-inhale (b), (f), peak-inhale (c), (g) and mid-exhale (d), (h) phases.

Figure 9. Results (Coronal view) showing 4D CBCT and DTS of liver cancer patient #2 with peak-exhale (a), (e), mid-inhale (b), (f), peak-inhale (c), (g) and mid-exhale (d), (h) phases.

Figure 10. Coronal view of 4D CBCT and DTS reconstructed using lung cancer patient #1 scans with peak-exhale (a), (e), mid-inhale (b), (f), peak-inhale (c), (g) and mid-exhale (d), (h) phases.

Figure 11. Comparative result (Coronal view) between 4D CBCT and DTS of lung cancer patient #2 case with peak-exhale (a), (e), mid-inhale (b), (f), peak-inhale (c), (g) and mid-exhale (d), (h) phases.

Figure 12. Residual blur of metal from outer plane cause significant amount of distortion of the patient's anatomy.