For many years, radiation therapy has been an indispensable part of cancer therapy. Especially, X-rays and Gamma rays, consisting of small particles called photons, have been used for attacking the tumor. They remove electrons out of tumor cell atoms and destroy larger molecules within the cells by destroying smaller chemical compounds before. Radiation beams also damage the genetic code, the DNA of the cells and thereby the construction plans for essential proteins. Furthermore, cells cannot replicate any more and consequently, they die. However, the energy is only partly transferred to the tumor. This problem has been partly solved by modern techniques in which photon beams hit the tumor from multiple directions and meet at a defined target where they discharge a maximum of energy. At the same time mobile apertures screen the sensitive healthy tissue from radiation. The so called Intensity Modified Radiation Therapy (IMRT) improves the treatment results of conventional radiotherapy considerably.
Ion radiation does not use photons, but positively charged ions, atomic nuclei which have lost at least one electron from the atomic shell. The particles mainly used are hydrogen atomic nuclei (protons) and carbon atomic nuclei, which are very heavy. This particular type of ions is therefore called heavy ion. Atomic nuclei are accelerated in large devices to about three quarters of the speed of light and shot into the tumor. The depth of penetration can be enhanced by speeding up the ions. Ion beams have always been interesting candidates for radiation therapy, since they have special physical characteristics: When they hit the body they travel very fast through the outer layers and lose hardly any energy before they decelerate in the depth and eventually get stuck and transfer their entire deleterious energy to the surrounding tissue. Scientists call this moment the Bragg peak after its discoverer, the English physicist William Henry Bragg. Therefore, ion beams are well-suited for treating tumors located deeply inside the body. Also, tumors with irregular edges can be scanned accurately to the millimeter with the Intensity-Controlled Raster Scan Method.
Radiation therapy with protons and carbon ion beams has been shown to be an effective treatment for tumors. In addition, such therapy has been shown to result in less damage to surrounding healthy tissue than conventional gamma radiation therapy.
Radiation planning for determining the magnitude and position of a radiation dose to be administered is typically based on previous MRI imaging or CT imaging, which may have taken place at a considerable time period before the therapy takes place. In the intervening period, the tissue to be irradiated may have moved, or changed shape. This may result in the irradiation of healthy tissue and/or missing diseased tissue, which may prevent the disease from moving to a remission.
In the past several years, techniques have been developed for more precisely targeting incident radiation upon tumors in a human body. Such techniques have been achieved by using advances in X-ray sources and collimation systems. Also, imaging of the body has been improved by optimizing the related targeting algorithms by mapping the body with CT systems and inputting the data into the algorithm(s). Recently, MRI systems and X-ray systems have been presented that combine attributes of both types of imaging.
Unfortunately, for the treatment of tumors such as those from malignant cancers, X-ray therapy does not possess the precision of dose administration or stopping power that particle-based therapy has. It is difficult or impossible to irradiate targeted tissue and transfer the energy of the radiation to the desired tissue in a precise manner, as X-rays by their nature as highly energetic photons, pass through most soft tissue unimpeded.
While radiations systems and methods do exist to irradiate tumors and other tissue with particles, e.g., protons, carbon nuclei, etc., such charged particles by definition will naturally deflect from a straight line trajectory in the presence of a high-strength magnetic field such as produced by common MRI systems. Such deflection can render ion beam targeting inaccurate, and can potentially cause the irradiation of healthy tissue while at the same time diseased tissue can escape radiation exposure.