Intensity-modulated radiotherapy--what is it?

Abstract

Intensity-modulated radiotherapy (IMRT) is one of the most important recent developments in oncology. It enables precise conformation of the radiation dose to the target volume. It has the potential to significantly reduce long-term morbidity and improve local control. This article explains the basic principles of IMRT in comparison to other planning techniques. The current clinical data are presented and future lines of research are discussed.

Figure 1

Conventional field (yellow) defined by bony landmarks.

Figure 2

Conformal field. The volume is outlined on each CT slice and a three-dimensional volume is created (white). Fields are shaped with MLC leaves (blue).

Figure 3

Conformal dose colour-wash. The target volume is contoured in white. The high dose region (red) is brick-shaped and includes part of the bladder.

Figure 4

IMRT fluence represented with colour. The field is divided into multiple beamlets with variable intensities.

Figure 5

IMRT dose colour-wash. The high dose region (red) conforms to the target volume (white) in a concave shape reducing the bladder and bowel dose.

Figure 6

Comparative dose-volume histogram for the three techniques.

Figure 7

Dose-painting for an oropharyngeal tumour. The target doses for the spinal cord (sc), parotid, lymph nodes and tumour are marked. The IMRT plan delivers a high dose (red) to the tumour and low dose (blue) to the contralateral parotid gland.