Radiation Therapy for Cancer: Current Status and Future Direction

Abstract

  Radiotherapy has been one of the main options of the cancer treatment, and divided into three types of therapy; external beam radiotherapy, brachytherapy using sealed radiation source, and systemic radioisotope therapy using unsealed radiation source. Recent advances in the treatment planning system and radiotherapy equipment, three-dimensional conformal radiotherapy (3D-CRT) is becoming the standard treatment for a number of tumors. Stereotactic radiotherapy (SRT) is a special type of 3D-CRT targeting the well-defined tumors using narrow radiation beam. It is used for the treatment of small-sized tumors in the brain, spine and body trunk. Intensity-Modulated Radiation Therapy (IMRT) is an advanced type of 3D-CRT using intensity-modulation of external beams in order to optimize the isodose distribution. These high-precision radiation therapies allows better tumor targeting, and decrease the risk of side effects, and in the result, improved treatment outcomes.

  Recently, particle-beam radiotherapy using ionizing particles (protons and heavy-ions) has been focused in the areas of cancer therapy. While ionizing particles penetrate the tissue, the radiation dose increases up to a maximum near the end of the particle's range (the Bragg peak), and thereafter drops to the almost zero. This feature in the energy deposition profile is very useful to concentrate the dose to the tumor and to decrease the dose to the important normal tissues adjacent to the tumors. Especially, heavy-ions represented by carbon ions have high biological effect to the tumor cells; the relative biological effectiveness (RBE) is considered 2.0-3.0 comparing to the photon (X-ray, γ-ray) and protons. Therefore, heavy-ions therapy is clinically very effective also in the treatment of radio-resistant tumor such as sarcomas, melanoma and adenocarcinoma, and large tumors including large number of hypoxic cells.