Abstract
Cancer is the second leading cause of death behind heart disease in the United States (National Center for Health Statistics, 2006). Various caner treatments are available now, but the three most common types are surgery, chemotherapy, and radiotherapy. Radiotherapy uses radiation—in the form of a special kind of x-rays, ?-rays, electrons, or protons to kill cancer cells. The advance of modern radiotherapy is closely linked to the evolution of computer and information technology. Intensity-modulated radiation therapy (IMRT) is an advanced form of three-dimensional conformal radiotherapy (3DCRT). It has become today’s standard for state-of-the-art radiation treatment. IMRT is based on the concept of inverse treatment planning. By optimizing a constrained objective function, IMRT can modulate the shape and intensity of radiation beams to create a dose distribution highly conformal to the target volume. In this article, we report the results of our investigation on the feasibility and potential benefits of combining electrons with intensity-modulated photons, called IMRT+e, for selected types of caner, particularly for superficial tumors with critical organs underneath. The aim is to deliver high radiation dose to the tumor while sparing all the surrounding normal tissues, thereby minimizing radiation induced side-effects.
Key Terms in this Chapter
PTV: Planning target volume is a composite margin of subclinical margin of gross tumor volume, internal margin accounting for variations due to organ movement and respiration, and set-up margin accounting for all the uncertainties in patient/beam positioning.
DMLC: IMRT plans can be delivered with a conventional multileaf collimator (MLC) in the dynamic mode. The MLC leaves continuously move while the beam is on. DMLC delivers intensity-modulated beam profiles previously determined by plan optimization algorithms.
Three-Dimensional Conformal Radiotherapy (3DCRT): A complex process that begins with the creation of 3D digital data sets of patient tumors, and normal anatomy. These data are then used to generate 3D computer images and to develop complex treatment plans to deliver a highly “conformed” 3D radiation dose while sparing normal adjacent tissues.
Linear Accelerator: The most commonly used device for external beam radiation treatment for cancer patients. It delivers radiation dose of high-energy photons and/or electrons to the region of the patient’s tumor.
IMRT: Intensity-modulated radiation therapy is an advanced form of 3DCRT. It uses sophisticated software and hardware to modulate the shape and intensity of radiation beams targeted on different parts of the treatment area.