Introduction of intensity modulated radiation therapy

Yong Chan Ahn

doi:10.5124/jkma.2011.54.11.1172

J Korean Med Assoc > Volume 54(11); 2011 > Article

Ahn: Introduction of intensity modulated radiation therapy

Continuing Education Column

Journal of the Korean Medical Association

Journal of the Korean Medical Association 2011; 54(11): 1172-1178.

Published online: November 15, 2011

DOI: http://dx.doi.org/10.5124/jkma.2011.54.11.1172

Introduction of intensity modulated radiation therapy

Yong Chan Ahn, MD

Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.

Corresponding author: Yong Chan Ahn, ahnyc@skku.edu

Received September 09, 2011 Accepted September 23, 2011

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The role of radiation therapy (RT) in cancer management has grown remarkably during the past few decades. For successful RT, the most important factor is highly conformal radiation delivery focused to the tumor-bearing region while minimizing the surrounding normal tissue damage. RT has evolved from 2-dimensional and 3-dimensional techniques to intensity modulated RT (IMRT) along with the development of computer science and mechanical engineering. IMRT is a special form of 3-dimensional conformal RT techniques, by which the intensities of radiation coming though the beamlets are modulated so that conformal radiation dose distribution around the tumor-bearing region is achieved. IMRT has been covered by the Korean health insurance system since July 2001. The basic principles and process of IMRT are introduced.

Intensity-modulated radiation therapy; Radiotherapy

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Figure 1

Intensity modulated radiation therapy using the linear accelerator with multi-leaf collimator system. The shape and the intensity of radiation coming through the multi-leaf collimator are modulated to achieve a highly conformal radiation dose distribution around the target region, while limiting the radiation doses to the surrounding normal organs below the acceptable tolerance limits.

Figure 2

The design of tomotherapy. The radiation intensity is modulated while the megavoltage X-ray tube is continuously rotating, and the patient's couch is moving. CT, computed tomography.

Figure 3

An example case of nasopharynx cancer treated by tomotherapy. The radiation doses to the gross tumor volume (GTV), clinical target olume (CTV), and the normal organs (parotid glands, brainstem) are optimized.

Table 1

Definitions of terms used in radiation therapy planning

GTV, gross tumor volume; MRI, magnetic resonance imaging; CT, computed tomography; PET, positron emission tomography; CTV, clinical target volume; ITV, internal target volume; PTV, planning target volume; OAR, organ at risk..