Tomotherapeutic stereotactic body radiation therapy: Techniques and comparison between modalities

Abstract

Presentation and comparison of tomotherapeutic intensity-modulated techniques for planning and delivery of stereotactic body radiation therapy. Serial tomotherapeutic SBRT has been planned and delivered at our institution since 8/2001. Since 12/2005, 12 patients have been treated using a helical tomotherapy unit. For these 12 patients both helical and serial tomotherapy plans were computed and clinically approved. Techniques and considerations of tomotherapy SBRT planning, associated image-guidance, and delivery are presented. The respective treatment plans were compared based on dosimetric parameters as well as time to develop a treatment plan and delivery times. Also the associated quality of megavoltage CT (MVCT) image-guidance inherent to the helical tomotherapy unit was assessed. Tumor volumes averaged 9.3, 9.8, and 58.7 cm³ for liver, lung, and spinal targets. Helical and serial tomotherapy plans showed comparable plan quality with respect to maximum and average doses to the gross tumor and planning target volumes. Time to develop helical tomotherapy plans averaged 3.5 h while serial tomotherapy planning consistently required less than one hour. Treatment delivery was also slower using helical tomotherapy, with differences of less than 10 min between modalities. MVCT image-guidance proved satisfactory for bony and lung targets, but failed to depict liver lesions, owing to poor soft-tissue contrast. SBRT planning and delivery is clinically feasible using either tomotherapeutic modality. While treatment planning time was consistently shorter and more readily accomplished in a standardized approach using the serial tomotherapy modality, actual plan quality and treatment delivery times are grossly comparable between the modalities. MVCT volumetric image-guidance, was observed to be valuable for thoracic and spinal target volumes, whereas it proved challenging for liver targets.