R. Dagan

SU-E-T-686: SBRT 4-Dimensional Treatment Planning for Vero Dynamic Tumor Tracking Lung Patients

Purpose: To investigate 4-dimensional (4D) treatment planning for Vero dynamic tumor tracking (DTT) SBRT lung patients and to compare its dosimetry to one single-phase (50%) CT based treatment plan as well as to 4D average-intensity CT based plan. Methods: 7 lung patients with total of 10 tumors were retrospectively selected. Tumor and organ-at-risks (OARs), which include lung, heart, esophagus, spinal cord and proximal airways, were contoured on each phase of the 4DCTs and 4D average-intensity CTs. GTV averages and standard deviations (SD) among phases were obtained for target deformation evaluation. For each tumor, treatment plans of 50Gy in 5 fractions with same beam arrangements were generated for the 3 planning approaches. MimVista was used to deform phase dose matrices to the 50% phase. Doses to the OARs were compared between 4D deformed plans and single-phase plans (clinical DTT plans). Single-phase CT plans were also compared to 4D average-intensity CT plans. Results: The relative SD of phase GTV volume is mostly in an inverse relationship with GTV volume. Compared to 4D average-intensity plan, single-phase DTT plan shows up to 253.9cc reduction of lung volume at 12.5Gy, and reduction of 28.1Gy, 4.8Gy, 5.3Gy of maximum dose to proximal airways, to heart and to spinal cord, respectively; Compared to single-phase DTT plan, 4D deformed plan shows up to 70.3cc reduction of lung volume at 12.5Gy, and reduction of 1.6Gy, 3.4Gy, 1.3Gy of maximum dose to proximal airways, to heart and to spinal cord, respectively. Conclusion: This study showed that small tumors are potentially prone to phase deformation. This study also demonstrated that DTT can significantly reduce doses to OARs for lung SBRT patients. Furthermore, 4D treatment planning with phase dose deformation to 50% phase is more representative of actual dose to OARs than single-phase CT based planning for lung patients treated with DTT. This study is partially supported by Brainlab Inc.

SU-E-J-70: Feasibility Study of Dynamic Arc and IMRT Treatment Plans Utilizing Vero Treatment Unit and IPlan Planning Computer for SRS/FSRT Brain Cancer Patients

PURPOSEnTo investigate the feasibility of utilizing Dynamic Arc (DA) and IMRT with 5mm MLC leaf of VERO treatment unit for SRS/FSRT brain cancer patients with non-invasive stereotactic treatments. The DA and IMRT plans using the VERO unit (BrainLab Inc, USA) are compared with cone-based planning and proton plans to evaluate their dosimetric advantages.nnnMETHODSnThe Vero treatment has unique features like no rotational or translational movements of the table during treatments, Dynamic Arc/IMRT, tracking of IR markers, limitation of Ring rotation. Accuracies of the image fusions using CBCT, orthogonal x-rays, and CT are evaluated less than ∼ 0.7mm with a custom-made target phantom with 18 hidden targets. 1mm margin is given to GTV to determine PTV for planning constraints considering all the uncertainties of planning computer and mechanical uncertainties of the treatment unit. Also, double-scattering proton plans with 6F to 9F beams and typical clinical parameters, multiple isocenter plans with 6 to 21 isocenters, and DA/IMRT plans are evaluated to investigate the dosimetric advantages of the DA/IMRT for complex shape of targets.nnnRESULTSn3 Groups of the patients are divided: (1) Group A (complex target shape), CIs are same for IMRT, and DGI of the proton plan are better by 9.5% than that of the IMRT, (2) Group B, CI of the DA plans (1.91+/-0.4) are better than cone-based plan, while DGI of the DA plan is 4.60+/-1.1 is better than cone-based plan (5.32+/-1.4), (3) Group C (small spherical targets), CI of the DA and cone-based plans are almost the same.nnnCONCLUSIONnFor small spherical targets, cone-based plans are superior to other 2 plans: DS proton and DA plans. For complex or irregular plans, dynamic and IMRT plans are comparable to cone-based and proton plans for complex targets.