Intrafraction Imaging Can Replace the Midtreatment Cone Beam Tomography for Lung Stereotactic Ablative Radiation...

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.

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 (T_X, T_Y, T_Z) and the rotational (R_X, R_Y, R_Z) 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.

The inter-class correlation (ICC) coefficient for T_x was 0.89 (95% CI, 0.80-0.94), T_y was 0.69 (95% CI, 0.49-0.82), T_z was 0.89 (95% CI, 0.82-0.95) in the translational planes, and R_x was 0.79 (95% CI, 0.65-0.88), R_y was 0.79 (95% CI, 0.65-0.88), and R_z was 0.91 (95% CI, 0.84-0.95) in rotational planes.The Bland-Altman (BA) statistics for T_x 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 T_y the bias was 0.01 (UOA: 0.18; LOA: -0.16), T_z bias was 2.6 × 10^-3(UOA: 0.10; LOA: -0.09), R_x bias was 0.09 (UOA: 0.82; LOA: -0.64), R_y bias was -0.04 (UOA: 1.08; LOA: -1.16) and R_z was -0.03 (UOA: 0.44; LOA: -0.51).

The ICC was excellent for T_x, T_z, R_{x, y, z}, and good for T_y. 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.