A heavy-ion treatment system generates a high-energy carbon-ion beam using an accelerator complex and irradiates it only to the tumor in the patient's body through the irradiation devices. The accelerator complex consists of three parts:

• ECR Ion Source: A beam source that produces highly charged carbon ions from a methane gas hit by RF-accelerated electrons.
  
• RFQ + IH-DTL Linear Accelerator: A series of electrodes that accelerate the carbon-ion beam up to 10% of the speed of light by applying RF voltages.
  
• Synchrotron: A circular accelerator that revolves the ion beam, accelerating the ions numerous times toward the specified energy.
  

Each device is composed of acceleration cavities, magnets, power sources, and vacuum devices.

Heavy-ion therapy has the advantage of dose distribution, which produces less damage to the normal organs as compared with the conventional radiotherapy. Moreover, we are faced with the challenge to find a more precise irradiation method. It requires extremely high precision and stability of the beam control. Improvements of the accelerator and optimized operation parameters are necessary for such high-precision irradiation.

Our targets of the machine developments are:

• Stable beam extraction from the synchrotron using the RF knock out method.
  
• Combination of respiratory gating and layer-stacking irradiations to minimize the damage to normal organs adjacent to the tumor in the case of moving organs (lung, liver, etc.)
  
• Spot-scanning irradiation of small-size targets with a strongly focused beam.

Quality assurance is used to keep and improve the availability of the system, and is also carried out for the stable operation of the treatment irradiations.

The biological effect of heavy-ion beams is higher than that of X-rays and proton beams, and it intricately varies in the body. In order to evaluate more detailed biological effects quantitatively, we are developing a radiation detector to measure the “radiation quality” in addition to the physical dose. We are also working on establishing an online beam monitoring system for the verification of the irradiation field. Moreover, projects based on three-dimensional dose measurement are in progress, which will improve the efficiency of clinical practice. New knowledge obtained through research and development of these measurement techniques will contribute to the sophistication of the heavy-ion radiotherapy.

To realize a safer and more accurate treatment at Gunma University, we are studying new methods of treatment planning, patient positioning, and irradiation techniques.
In radiotherapy, patient positioning is performed just before the treatment. It is necessary to detect and correct a three-dimensional deviation using two X-ray images for the patient positioning. The conditions of a patient at the time of treatment, such as joint position and gas, may have changed from the condition at the time of the treatment planning CT; therefore, patient positioning is difficult and needs high technology and experience. Moreover, the work is time intensive because it takes 10 to 20 min for one patient. Thus, the aim of our study is to improve the treatment throughput and realize a highly accurate treatment by automatizing and sophisticating patient positioning.

Although treatment with focused irradiation field is realized using the gating irradiation method for mobile organs with respiratory motion, such as the lung and liver, there are some problems. For example, the current irradiation method cannot fully adapt to a patient’s inter-fractional changes (e.g., tumor position or increase/decrease in body weight). In photon therapy, it is common to match the irradiation position to the tumor position using a cone-beam CT. However, we have to confirm not only the reproduction of the tumor position but also the reproduction of the water-equivalent path length of the carbon-ion radiotherapy. At our facility, we installed an in-room CT to confirm the reproductions. We are studying robust planning and adaptive irradiation methods using the information from the in-room CT to ensure the prescription dose, which is derived by decreasing the dose owing to inter-fractional changes.

We are working on three major areas of radiation biology research that contribute to effective heavy-ion radiotherapy.

1. To show the advantages of heavy-ion radiotherapy on various types of cancer cells:

By collecting the evidence of the effects of heavy-ions on cells that are resistant to X-rays (such as, hypoxic cells and cancer stem-like cells).

2. To improve efficiency of heavy-ion radiotherapy:

1. Local tumor control: confirmation of the heavy-ion combined effects such as with anticancer drugs, sensitizers, and hyperthermia.
2. Metastasis tumor control: collecting the evidence of the combined effects such as using immunotherapy.

3. To clarify optimization of heavy-ion radiotherapy;

1. Effect on normal tissue.
2. Effect of fractionated radiotherapy.
3. Effect of micro-beam and scanning radiotherapy.