Practical usefulness of partial-range 4-dimensional computed tomography in the simulation process of lung stereotactic body radiation therapy

Four-dimensional computed tomography (4DCT) scans to cover the entire lungs often fail due to changes in the patient's respiratory cycle, highlighting the need for an improved method that can facilitate successful 4DCT for lung stereotactic body radiation therapy (SBRT). This study aimed to present partial-range 4DCT (PR-4DCT) as a new simulation method to increase the success rate of 4DCT and to verify the practical usefulness of PR-4DCT. We retrospectively analyzed 230 consecutive patients (270 tumors) who underwent SBRT for primary lung cancer or pulmonary metastasis between January 2014 and December 2021. We developed a new CT simulation method (PR-4DCT) in 2019 that scans only a partial-range around the tumor. To verify the usability of PR-4DCT, CT simulation methods were compared by period. Until 2018, before the PR-4DCT method was introduced, the rate of 4DCT implementation was less than 40%. However, the proportion has continued to increase since then, and rate of implementation of 4DCT improved to approximately 94% in 2021. Moreover, 4DCT could be performed on almost all lower-lobe tumors after the introduction of PR-4DCT. In particular, the success rate increased dramatically after using the PR-4DCT method in patients who had decided to try 4DCT, and in 2021, PR-4DCT was successful in all of these patients. PR-4DCT is a very simple method that can be used immediately in any institution currently performing 4DCT, and it is an effective solution to increase the success rate of 4DCT in patients with an irregular respiratory cycle.