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  5. Clinical Evaluation of a Prior Knowledge-Based 4D-CBCT Estimation Technique for Lung Radiotherapy

Clinical Evaluation of a Prior Knowledge-Based 4D-CBCT Estimation Technique for Lung Radiotherapy

X Liu1*, Y Zhang2 , W Harris3 , Y Zhang4 , F Yin5 , L Ren6 , (1) Duke University, Durham, NC, (2) Duke University Medical Center, Durham, NC, (3) Duke University Medical Center, Durham, NC, (4) UT Southwestern Medical Ctr at Dallas, Dallas, TX, (5) Duke University Medical Center, Durham, NC, (6) Duke University Medical Center, Durham, NC

Presentations

(Wednesday, 8/1/2018) 1:45 PM - 3:45 PM

Room: Karl Dean Ballroom B1

Purpose: To clinically evaluate the accuracy and efficiency of a prior knowledge-based 4D-CBCT reconstruction technique for lung radiotherapy through patient studies.

Methods: Patient data with two sets of 4D-CT scans were used for evaluation: The first 4D-CT scan was considered as planning CT images acquired during simulation, and the second 4D-CT was considered as on-board ground truth images and was acquired several weeks after the first 4D-CT scan. Each pair 4D-CT scans were registered for alignment and standardized to the same resolution and dimension. Digital reconstructed radiographs (DRRs) were generated from the second 4D-CT scan to simulate onboard 4D-CBCT projections in limited angle. Each phase of the 4D-CBCT was generated by deforming the prior CT volume based on Deformation Field Maps solved by motion modeling and free-form deformation in the data fidelity constraint. Patients with tumors at different locations were selected for evaluation. The estimated images (EIs) were quantitatively evaluated against ground truth images by calculating the Dice Coefficient and Center-of-Mass-Shift (COMS) of the tumor volume. The minimal total scan angle/time was also determined for all patients.

Results: Results of 6 patient cases showed that the technique was able to accurately estimate 4D-CBCT using as fewer as 320 projections for 10 phases acquired in 32 seconds over scan angle of 169.8°. The estimation accuracy was consistent with different patient scenarios. The results also showed the possibility of further reducing projection number and scanning angle/time for estimation of tumors with less respiratory motion.

Conclusion: The technique can be potentially applied for fast and low-dose target verification for lung radiotherapy. It estimates patient onboard 4D-CBCT with higher efficiency and reduced imaging dose compared to conventional reconstruction techniques. Clinical implementation of this technique can potentially improve the inter/intrafractional 4D-localization efficiency and pave the way for on-line adaptive radiotherapy for lung cancer.

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