A comparative study of four-dimensional cone beam computed tomography (4DCBCT) and three-dimensional cone beam computed tomography (3DCBCT) guided treatment setup in liver cancer radiotherapy

Abstract Background and purpose To compare the setup errors and the clinical target volume (CTV) to planning target volume (PTV) margins in image-guided radiotherapy (IGRT) for liver cancer using three-dimensional cone beam computed tomography (3DCBCT) and four-dimensional cone beam computed tomography (4DCBCT), and explore the advantages of 4DCBCT for the position verification in liver cancer irradiation. Materials and methods Fifty-five patients with liver cancer were enrolled. All patients’ CT, four-dimensional computed tomography (4DCT) and Magnetic Resonance (MR) simulation images were collected. Image registration, target delineation, and plan design were accomplished in Pinnacle treatment planning system. Pre-treatment’s 3DCBCT and 4DCBCT images were collected at a certain frequency and registered with the simulation CT images. Before beam delivery, the therapy couch was corrected based on the setup errors measured by 4DCBCT. Investigators recorded the setup errors and calculated the CTV to PTV margins using van Herk’s formula. Paired t-test was used to compare the difference of the two groups. Results A total of 452 sets of 3DCBCT and 4DCBCT images were collected. The setup errors in 4DCBCT group in superior-inferior (S-I) direction, anterior-posterior (A-P) direction, transverse plane, and coronal plane were significant smaller than in 3DCBCT group, which were 2.6 ± 4.8 mm and 2.1 ± 4.0 mm, P < 0.001; 1.8 ± 1.9 mm and 1.4 ± 1.7 mm, P < 0.001; 0.80 ± 0.76° and 0.75 ± 0.61°, P < 0.001; 0.90 ± 0.74° and 0.78 ± 0.75°, P < 0.001. And the CTV-PTV margins in three-dimensional directions are (5.7, 9.8, 5.8) mm and (5.1, 8.0, 4.6) mm, respectively. Conclusion 4DCBCT is superior to 3DCBCT in monitoring setup errors and supports smaller PTV margins for liver cancer radiotherapy.