Researchers in the Institute of Modern Physics, CAS(IMP), have made major progress in testing an active spot-scanning beam delivery technique last month, which plays an important role in intensity-modulated radiation therapy with heavy ions, in the heavy-ion therapy terminal for deep-seated tumor treatment at Heavy Ion Research Facility in Lanzhou (HIRFL)

Depth-dose distributions of carbon ion beams with various energies in the range of 80~430MeV/u provided by Cooling Storage Ring (CSR) at HIRFL (HIRFL-CSR) were measured in water tank, which proves that HIRFL-CSR has the capability of supplying carbon-ion beams with energy ranges suitable for tumor therapy. The relationship between current variation of the scanning magnets and lateral displacement of beam spots at the iso-center of the therapy facility were determined for carbon ion beams with energies varying from 172 to 207MeV/u in a spacing of 7MeV/u provided by HIRFL-CSR. Then the position and dose accuracy at single scan point achieved by the spot scanning technique was measured. The results show that the position deviation of beam spots was less than 1mm and the dose deviation at single scan points was within 5%. Arbitrary irradiation fields such as the shape of China map and the Chinese characters of Lanzhou city were generated successfully by the spot-scanning beam delivery technique. Having calibrated the dose monitors with the method recommended by the International Atomic Energy Agency (IAEA), different target volumes were irradiated in a way of the active spot-scanning technique. Finally compliance of planned and measured doses with an error of 10% was found.

The test proves that the deep-seated tumor therapy terminal with heavy ions at IMP has already achieved the condition of performing active spot-scanning beam delivery for heavy ion intensity modulated radiotherapy and is of great importance to further develop precise spot scanning technique for the Heavy Ion tumor Therapy Facility in Lanzhou (HITFiL).

　　Active energy variation with a wide range from 80 to 430MeV/u by HIRFL-CSR (Image/IMP)

　　Arbitrary irradiation fields shaped by the spot scanning technique (Image/IMP)

　　Dose verification in a target irradiated with the spot scanning technique (Image/IMP)