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Image-guided radiotherapy (IGRT)


Introduction

IGRT is the process of using images after the initial plan has been established, and making decisions based on these images with respect to the remainder of the treatment process. IGRT is generally applied within the treatment room during a course of radiotherapy, and can be 2D, 3D or 4D. IGRT reduces the chance of geographical miss of the target and allows reduced treatment margins in the planning target volume (PTV), which may result in fewer treatment complications, and permits dose escalation.


Important Principles

IGRT solutions can be categorized by beam quality, i.e., whether they are based on MV or kV beams, and by beam collimation, i.e., whether they are cone-beam or fan-beam solutions. 2D IGRT systems are available based on integration of a linac with paired orthogonal planar imagers. 3D kV-imaging of the patient in treatment position directly prior to treatment is one of the most common 3D IGRT procedures currently performed in clinical practice. As the actual treatment beam is used for imaging, 3D MV-based solutions provide the most direct geometric information concerning the alignment of treatment beam and the target volume. On the other hand, MV-based solutions will inherently be inferior to kV-based solutions as the latter provides better soft-tissue contrast. Other approaches include 2D or 3D ultrasound systems.


Introduction to References

IGRT has been discussed in detail in the Report of the Consultant’s meeting and in the ESTRO-EIR Report. More information on IGRT techniques can be found in J. Van Dyk's Compendium, in the IAEA Handbook, and in the books edited by Bortfeld et al. and Meyer. The IPEM Report describes a number of evidence-based practices for geometric verification, and provides guidelines how individual centres may implement geometric verification processes locally. In 2009, the American College of Radiology published practice guidelines and technical standard for IGRT.