RESUMEN
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.
RESUMEN
PURPOSE: Multiple survey results have identified a demand for improved motion management for liver cancer IGRT. Until now, real-time IGRT for liver has been the domain of dedicated and expensive cancer radiotherapy systems. The purpose of this study was to clinically implement and characterise the performance of a novel real-time 6 degree-of-freedom (DoF) IGRT system, Kilovoltage Intrafraction Monitoring (KIM) for liver SABR patients. METHODS/MATERIALS: The KIM technology segmented gold fiducial markers in intra-fraction x-ray images as a surrogate for the liver tumour and converted the 2D segmented marker positions into a real-time 6DoF tumour position. Fifteen liver SABR patients were recruited and treated with KIM combined with external surrogate guidance at three radiotherapy centres in the TROG 17.03 LARK multi-institutional prospective clinical trial. Patients were either treated in breath-hold or in free breathing using the gating method. The KIM localisation accuracy and dosimetric accuracy achieved with KIM + external surrogate were measured and the results were compared to those with the estimated external surrogate alone. RESULTS: The KIM localisation accuracy was 0.2±0.9 mm (left-right), 0.3±0.6 mm (superior-inferior) and 1.2±0.8 mm (anterior-posterior) for translations and -0.1⦱0.8⦠(left-right), 0.6⦱1.2⦠(superior-inferior) and 0.1⦱0.9⦠(anterior-posterior) for rotations. The cumulative dose to the GTV with KIM + external surrogate was always within 5% of the plan. In 2 out of 15 patients, >5% dose error would have occurred to the GTV and an organ-at-risk with external surrogate alone. CONCLUSIONS: This work demonstrates that real-time 6DoF IGRT for liver can be implemented on standard radiotherapy systems to improve treatment accuracy and safety. The observations made during the treatments highlight the potential false assurance of using traditional external surrogates to assess tumour motion in patients and the need for ongoing improvement of IGRT technologies.
