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Intensity-modulated radiotherapy (IMRT)


IMRT is a 3D conformal radiotherapy technique, which applies multiple beams with optimized intensity-modulated fluence distributions. The optimal modulated intensity for each beam is determined through the dose optimization process, referred to as inverse planning, incorporating dose criteria not only for the target volume but also for the neighboring organs at risk. IMRT is generally delivered with MLC-equipped linacs using either a static or a dynamic approach with moving leaves. In the latter approach the beams can be delivered without, or concurrently with gantry rotation (intensity-modulated arc therapy, IMAT). A set of commissioning and QA tests specific to the IMRT planning and delivery equipment, as well as treatment techniques applied in a particular institute, must be implemented before its clinical routine use.

Important Principles

The routine clinical application of IMRT requires detailed knowledge of the software used for inverse treatment planning, the equipment used for dose delivery, quality assurance issues related to the dose distribution optimization process and the dose delivery process. It is recommended to carry out a verification of all IMRT plans; at least until the entire IMRT team is comfortable with the planning and treatment delivery process. Such a QA programme must include verification of linac radiation output as well as tests of the MLC positioning and movement.

Introduction to References

A large number of publications on IMRT are available dealing with the various aspects of IMRT. An introduction to and overview of the topic can be found in the AAPM document , the IAEA Handbook, J. Van Dyk's Compendium, and the Handbook of Radiotherapy Physics. A comprehensive discussion of both physical and clinical aspects of IMRT is provided in the books edited by Bortfeld et al. and Meyer, and in the IPEM Report. QA of IMRT is discussed extensively in the ESTRO booklet and the recent AAPM Report.