EGS Application - The Medical Problem
The physician wants to maximize radiation dose to the tumor and, at the same time, minimize radiation damage to the patient's healthy tissue.
Consider these facts:
- radiation has been used quite successfully for many years to treat cancer. . . this is called radiotherapy.
- barring a miracle cure, roughly one in eight of us in our lifetime will find ourselves being treated for cancer using radiotherapy.
- almost all radiation treatments involve electrons or photons (also called x-rays).
- maximizing dose to the tumor while minimizing dose to healthy tissue is the goal of efficient radiotherapy.
Patient dosimetry is the accurate determination of the radiation dose given during radiotherapy. The equipment used today to perform radiotherapy, such as the electron electron accelerator, is complex. The actual radiation dose to the patient and to the tumor is dependent upon the radiation scattering from components inside the machine as well as structures within the human body.
Consider a cross section of the human body as shown in the diagram on the right. The organs in the body can be viewed as discrete units, each with boundaries and densities. Most tissue in the body has a density close to water. However, the lungs are filled with air and, as such, are 1,000 times less dense than surrounding tissue. The bones, on the other hand, are almost twice as dense as the surrounding tissue. These differences in densities are what we call "discontinuities" and they make the dosimetry problem very complex, as you might expect, particularly near the "interface."
Why does radiation affect cancer cells more than it does normal tissue cells?
