**3. Intensity modulated radiotherapy (IMRT)**

Intensity-modulated radiotherapy (IMRT) is an advanced form of 3-D conformal radiation therapy that allows modifying the intensity of the beam by considering each radiation beam as multiple rays or beamlets, and assigning different beam strengths to the individual rays [4]. The radiation intensity is adjusted according to the shape, size, and location of the tumor with the use of computer-controlled, moveable "leaves" called Multi-Leaf Collimator (MLC) systems. It consists of pairs of highly absorbing tungsten leaves that can either block or allow the passage of radiation from the many beams as shown in **Figure 1** to deliver a high dose to the target volume and acceptably low dose to the surrounding normal structures [5].

*Intensity Modulated Radiation Therapy Plan (IMRT) Verification Using Indigenous… DOI: http://dx.doi.org/10.5772/intechopen.102710*

**Figure 1.** *Multileaf collimators (MLCs).*

It uses advanced imaging procedures such as Ultrasound (US), Computed Tomography (CT), Magnetic Resonance Imaging (MRI), Positron Emission Tomography (PET), and PET/CT, to achieve precise treatment modality for cancer patients [6]. A computer-controlled multileaf collimator has been programmed in three different ways to deliver IMRT [7].

