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4-Dimensional radiotherapy planning

2003; Elsevier BV; Volume: 57; Issue: 2 Linguagem: Inglês

10.1016/s0360-3016(03)01056-3

1879-355X

Paul Keall, Sarang Joshi, Gregg Tracton, V. R. Kini, S. S. Vedam, R Mohan,

Radiomics and Machine Learning in Medical Imaging

Purpose/Objective: Four-dimensional radiotherapy is the explicit inclusion of the temporal changes in anatomy during the imaging, planning and delivery of radiotherapy. Temporal anatomic changes can occur for many reasons, though the focus of the current investigation was respiration motion for lung tumors. 4D radiotherapy treatment planning requires new tools and paradigms not yet available on commercial treatment planning systems. The aims of this study were to (a) develop 4D radiotherapy treatment planning methodology and (b) apply this methodology to determine the potential clinical impact of 4D vs. 3D planning. Materials/Methods: A 4D CT scan consisting of a series of 3D CT image sets acquired at different respiratory phases was used for treatment planning. On the end-inhale CT image the GTV, lungs, heart and the spinal cord were defined. Deformable image registration was performed to map each CT set from the end-inhale respiration phase to the CT images sets corresponding to subsequent respiration phases. This deformable registration allowed the contours drawn on the end-inhale CT to be automatically drawn on the other respiratory phase CT image sets. Treatment planning was simultaneously performed on each of the 3D image sets. The dose distribution from each respiratory phase CT image set was mapped back to the end-inhale CT image set for analysis. Results: Substantial deformation with respiration was observed for the lung tumor as shown in the accompanying figure. The image on the left shows the PA beam portal surrounding the PTV at peak inhale; on the right is the corresponding peak exhale image. This deformation was verified by examining the high contrast objects, such as the lungs, cord and external contour mapping between image sets. Dosimetric reductions for the cord, heart and lungs (corresponding to approximately a 5% reduction in pneumonitis risk) were found for 4D planning compared to 3D planning. Conclusions: 4D radiotherapy planning has been shown be feasible and offers tumor dose escalation and/or a reduction in treatment-related complications. In principle, 4D planning requires no more human interaction time than a 3D plan, however new planning tools such as deformable registration and simultaneous dose calculations on multiple CT image sets are required.