Room: AAPM ePoster Library
Purpose: It is known that using jaw tracking technique for VMAT treatment planning reduces dose to normal tissue while keeping good target coverage. In this study, we aim to evaluate the dosimetric effect of jaw tracking technique for off-axis multiple targets.
Methods: Five patients with two planning target volumes (PTVs) separated from each other were chosen for the comparison. The treatment plan for each patient was optimized with and without jaw tracking technique under exactly the same steps and optimization parameters with AcurosXB (v13.6) in Varian Eclipse. Three metrics were calculated for the evaluations of PTV dose coverage; (1) Dose difference (DD) in PTV volume ((Dmax-Dmin)/DRx), (2) Conformity Index (CI) = VRx/VPTV and (3) Homogeneity Index (HI) = (D2-D98)/DRx. Also, DVHs and dose distributions around the target were analyzed for each case.
Results: While both techniques provided satisfactory target dose coverage, DDs were reduced by 6% on average (up to 10%) by jaw tracking technique except one case. This fact indicates that jaw tracking technique provides more uniform dose distribution. CIs showed no difference between both techniques. HIs were smaller (up to 9%) when jaw tracking was used, while two out of five cases showed no difference or 3% higher values. DVHs showed normal tissue doses were reduced by jaw tracking technique while PTV uniformities were increased.
Conclusion: For VMAT plan optimization of two separated PTVs, using jaw tracking improves target dose uniformity as well while reduces normal tissue dose. The result provides a suggestion of selection whether jaw tracking technique is necessary based on patient-specific dosimetric objects.