Room: Davidson Ballroom A
Purpose: Although efficacy of jaw tracking (JT) with flattening filter beam has been proposed, dosimetric impact of JT with flattening filter-free (FFF) beam has not been reported yet. Additionally, even as the movement of JT is an important parameter to decide the efficacy of JT, relationship between complexity of JT and that of multi-leaf collimators (MLCs) movements has not been investigated. The goals of this study were to clarify a potential of JT technique in FFF beam for lung stereotactic body radiation therapy (SBRT), and to investigate correlations between complexity of JT and that of MLCs movements.
Methods: The SBRT plans of 15 patients were created in volumetric modulated arc therapy (VMAT) using FFF beam with JT (JT-VMAT) and without JT (FJ-VMAT). Dosimetric parameters for lung (V20, V5, Dmean), spinal cord (D1%), body (D90, D80, Dmean), skin (Dmax), and PTV (D98) were compared between JT-VMAT and FJ-VMAT plans. For the evaluation of relationship between complexity of JT and MLCs movements, jaw tracking complexity score (JTCS) was defined and compared with conventional MLCs modulation complexity score (MCS).
Results: By using the JT technique, OAR doses were significantly decreased (p < 0.05), e.g., the V20 of lung was reduced to 2.42% from 2.45% and the reduction rate was 1.22%. The D98 of PTV showed insignificant difference between JT-VMAT and FJ-VMAT plans. The median values of JTCS and MCS were 0.84 cm and 0.35, and the correlations between them showed insignificant.
Conclusion: JT-VMAT with FFF beam has a potential to decrease OAR doses compared with FJ-VMAT plans. Moreover, complexity of JT did not correlate with that of MLCs movements. The JTCS could be used as a quantitative parameter for JT technique.