Clinical Evaluation of an Immbolization System for Stereotactic Body Radiotherapy Using Helical Tomotherapy

Abstract

In this study, a clinical evaluation of the Body Pro-Lok™ System combined with the TomoTherapy megavoltage computed tomography (MVCT) was performed for lung and liver stereotactic body radiotherapy (SBRT) to reduce interfractional setup uncertainty. Twenty patients treated with 3–5 fractions of SBRT were analyzed retrospectively. The Body Pro-Lok™ system was used in both CT simulation and during patient treatment setup. Patients were immobilized with a vacuum cushion placed posteriorly over the thoracic region, an abdominal compression plate, and a knee and foot sponge. Pretreatment MVCT scans of the TomoTherapy HI-ART II unit were fused with the planning kVCT before delivery of each fraction to determine the interfractional setup error. A total of 84 shifts were analyzed to assess the interfractional setup accuracy. Results showed that the mean interfractional setup errors and standard deviations were –0.9 ± 3.1 mm, 1.2 ± 5.5 mm, and 6.5 ± 2.6 mm for lateral (IEC-X), longitudinal (IEC-Y), and vertical (IEC-Z) variations, respectively. The maximum motion was 17.1 mm in the longitudinal direction. When all 3 translational coordinates were analyzed, a mean composite displacement vector of 8.2 ± 2.0 mm (range 4.1–11.7 mm) was obtained for all patients. Based on the findings, image-guided SBRT using the Body Pro-Lok™ system in conjunction with the MVCT of TomoTherapy is capable of minimizing interfractional setup error and improving treatment accuracy.