Online Kilovoltage Cone-beam CT Guided Lung Cancer Radiation: Initial Clinical Experiences from Shanghai

Abstract

To introduce the initial clinical experiences of online Kilovoltage Cone-beam CT (KVCBCT) guided lung cancer radiation in our department. From March 2007 to January 2008, 30 patients with pathologically confirmed lung cancer were included in this study. After patients were positioned using their skin marks, KVCBCT scans were performed before treatment and aligned to planning CT scans using the self-developed semi-automatic alignment method. Treatment table were repositioned according to the alignment results. A second KVCBCT scan was acquired immediately after the table correction. A total of 308 KVCBCT images from 154 fractions were analyzed. The reproducibility of the semi-automatic image alignment method, workflow of the online correction, translational and rotational setup error in three dimensional conditions and residual setup error after online correction were evaluated. The reproducibility of the semi-automatic alignment method was evaluated. The alignment difference was smaller in intraobserver evaluation than in interobserver. The reproducibility of different physicians was better than the physician and radiation therapist in anterior-posterior (AP) and left-right (LR) directions. In superior-inferior (SI) direction, the percentage of alignment difference larger than 3 mm between different physicians, the physician and radiation therapist were both near 15%. The online correction protocol adds 7.6 min to the total treatment time and the workflow proved to be feasible in clinical practice. The total systematic error (∑) before online correction was 3.5 mm, 3.5 mm and 3.0 mm, the overall random error (σ) was 2.7 mm, 2.9 mm and 3.0 mm in the LR, SI, and AP direction, respectively. After online correction, the total systematic error (∑) was 0.7 mm, 0.7 mm and 0.6 mm, the overall random error (σ) was 1.2 mm, 1.5 mm and 1.3 mm in three directions. The average rotational setup error (± 1 SD) was -0.3 ± 1.5°, 0.2 ± 0.9 ° and 0.3 ± 0.8 ° in pitch, roll and yaw, respectively. According to the formalisms suggested by van Herk et al, 3mm can apply to the margin of clinical target volume (CTV) to PTV, when using the online correction. The KVCBCT guided radiation system can be applied successfully in lung cancer patients with reproducible image alignment method. With the help of the system, we have an opportunity of new realization for patient setup error, including both translational and rotational. We can improve patient setup accuracy and reduce the CTV to PTV margin from 11 mm to 3 mm with limited workload.