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

Authors


Abstract

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.

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