Dynamic tomotherapy delivery.

Purpose: Several dynamic techniques are introduced to speed up TomoTherapy® delivery and improve longitudinal conformity. These techniques include dynamic jaws, dynamic couch, and their combinations.Methods: In general, dynamic jaws techniques allow jaws to move during a treatment. On the one hand, the jaws open wide to increase efficiency and thus reduce beam-on time. On the other hand, the jaws can close and follow the target border when sharp penumbra is required near the superior and inferior borders of tumor sites, which results in improved longitudinal dose conformity. The main purpose of the dynamic couch technique is to move the couch as fast as possible at variable speed to reduce beam-on time. Delivering most conformal dose as fast as possible requires a combination of dynamic jaws and dynamic couch techniques (DJDC). Motions of the jaws and couch are determined from the longitudinal fluence profile, which is calculated from an optimized leaf sinogram of small jaw width regular delivery or running start and stop delivery (RSS). We focused on RSS and DJDC in this study and also discussed other delivery techniques.Results: Several conceptual cases are simulated to compare different delivery techniques. The results show that beam-on time can be reduced by about 60% compared to regular delivery with a 2.5 cm jaw width (REG 2.5 cm) for these cases and arbitrary longitudinal fluence profiles can be delivered. Two clinical cases, a prostate and a head-and-neck case, with different delivery techniques are calculated. The results show that plan quality yielded by DJDC with a maximum 5.0 cm jaw width is overall comparable to or better than that of the existing REG 2.5 cm.Conclusions: The DVH comparisons show better critical structure avoidance with the dynamic techniques. At the same time, beam-on time is reduced by about one half compared to REG 2.5 cm. Dynamic delivery techniques provide users more tools to speed up delivery and/or improve plan quality. [ABSTRACT FROM AUTHOR]