Intrafraction Imaging Can Replace the Midtreatment Cone Beam Tomography for Lung Stereotactic Ablative Radiation Therapy Patients for Increased Treatment Efficiency

Purpose: To determine the feasibility of replacing the mid treatment cone beam computed tomography (MT CBCT) image with Intrafraction Imaging (IFI) acquired concurrently during dose delivery in lung Stereotactic Ablative Body Radiation therapy (SABR) patients, and thus improve treatment efficiency. Methods and Materials: A review of departmental imaging data was performed on ten lung SABR patients treated with dual arc volumetric modulated arc therapy (VMAT) on an Elekta Versa HD linear accelerator with XVI imaging software.IFI data was extracted and a database of the translational (TX, TY, TZ) and the rotational (RX, RY, RZ) position errors was created for retrospective comparison, with the values of the MT CBCT for the same patients, treated between March 2021 and March 2022 at our center. The data was evaluated for correlation between the values in all 6° of freedom. Results: The inter-class correlation (ICC) coefficient for Tx was 0.89 (95% CI, 0.80-0.94), Ty was 0.69 (95% CI, 0.49-0.82), Tz was 0.89 (95% CI, 0.82-0.95) in the translational planes, and Rx was 0.79 (95% CI, 0.65-0.88), Ry was 0.79 (95% CI, 0.65-0.88), and Rz was 0.91 (95% CI, 0.84-0.95) in rotational planes.The Bland-Altman (BA) statistics for Tx had a bias of –1.22 × 10−3, with an upper limit of agreement (UOA) of 0.07, and a lower limit of agreement (LOA) of –0.07, for Ty the bias was 0.01 (UOA: 0.18; LOA: –0.16), Tz bias was 2.6 × 10−3(UOA: 0.10; LOA: –0.09), Rx bias was 0.09 (UOA: 0.82; LOA: –0.64), Ry bias was –0.04 (UOA: 1.08; LOA: –1.16) and Rz was –0.03 (UOA: 0.44; LOA: –0.51). Conclusions: The ICC was excellent for Tx, Tz, Rx, y, z, and good for Ty. The data demonstrated promising correlation between IFI and MT CBCT values, and therefore supports the use of IFI for clinical decision making and improving treatment efficiency