New Technologies in 3D Conformal Radiation Therapy: Introduction and Overview

Abstract

Radiotherapy is, after surgery, the most successfully and most frequently used treatment modality for cancer. It is applied in more than 50% of all cancer patients. Radiotherapy aims to deliver a radiation dose to the tumor which is high enough to kill all tumor cells. That is from the physical and technical point of view a diffi cult task, because malignant tumors often are located close to radiosensitive organs such as the eyes, optic nerves and brain stem, spinal cord, bowels, or lung tissue. These so-called organs at risk must not be damaged during radiotherapy. The situation is even more complicated when the tumor itself is radioresistant and very high doses are needed to reach a therapeutic effect. At the time of being diagnosed, about 60% of all tumor patients are suffering from a malignant localized tumor which has not yet disseminated, i.e., no metastatic disease has yet occurred; thus, these patients can be considered to be potentially curable. Nevertheless, about one-third of these patients (18% of all cancer patients) cannot be cured, because therapy fails to stop tumor growth. This is the point where new technologies in radiation oncology, especially in 3D conformal radiotherapy, come into play: it is expected that they will enhance local tumor control. In conformal radiotherapy, the dose distribution in tissue is shaped in such a way that the high-dose region is located in the target volume, with a maximal therapeutic effect throughout the whole volume. In the neighboring healthy tissue, the radiation dose has to be kept under the limit for radiation damage. This means a steep dose falloff has to be reached between the target volume and the surroundings; thus, in radiotherapy there is a rule stating that with a decrease of dose to healthy tissue, the dose delivered to the target volume can be increased; moreover, an increase in dose will also result in better tumor control (tumor control probability, TCP), whereas a decrease in dose to healthy tissue will be connected with a decrease in side effects (normal tissue complication probability, NTCP). Increase in tumor control and a simultaneous decrease in side effects means a higher probability of patient cure. In the past two decades, new technologies in radiation oncology have initiated a signifi cant increase in the quality of conformal treatment techniques. The development of new technologies for conformal radiation therapy is the answer to the wishes and guidelines of the radiation oncologists. The question of whether clinical improvements are driven by new technical developments, or vice versa, should be answered in the following way: the development of new technologies should be motivated by clinical constraints. In this regard the physicists, engineers, computer scientists, and technicians are service providers to the radiologists and radiotherapists, and in this conCONTENTS