Dosimetric Validation of a System to Treat Moving Tumors Using Scanned Ion Beams That Are Synchronized With Anatomical Motion

The Lancet Oncology, 16(2), 187-199

Charged particle therapy is generally regarded as cutting-edge technology in oncology. Many proton therapy centres are active in the USA, Europe, and Asia, but only a few centres use heavy ions, even though these ions are much more effective than x-rays owing to the special radiobiological properties of densely ionising radiation. The National Institute of Radiological Sciences (NIRS) Chiba, Japan, has been treating cancer with high-energy carbon ions since 1994. So far, more than 8000 patients have had this treatment at NIRS, and the centre thus has by far the greatest experience in carbon ion treatment worldwide. A panel of radiation oncologists, radiobiologists, and medical physicists from the USA and Europe recently completed peer review of the carbon ion therapy at NIRS. The review panel had access to the latest developments in treatment planning and beam delivery and to all updated clinical data produced at NIRS. A detailed comparison with the most advanced results obtained with x-rays or protons in Europe and the USA was then possible. In addition to those tumours for which carbon ions are known to produce excellent results, such as bone and soft-tissue sarcoma of the skull base, head and neck, and pelvis, promising data were obtained for other tumours, such as locally recurrent rectal cancer and pancreatic cancer. The most serious impediment to the worldwide spread of heavy ion therapy centres is the high initial capital cost. The 20 years of clinical experience at NIRS can help guide strategic decisions on the design and construction of new heavy ion therapy centres. Copyright © 2015 Elsevier Ltd. All rights reserved.

This article presents a method of quantitative assessment of the degree of conformality and its designation by a single numerical value. A conformation number is introduced to evaluate objectively the degree of conformality. A comparison is made between the conformation number as found for external beam treatment plans and ultrasonically guided 125I seed implants for localized prostate cancer. The conformation number in case of a planning target volume irradiated with two opposed open beams, three open beams, and three beams with customized blocks amounted to 0.17, 0.39, and 0.65, respectively. The conformation number as found for ultrasonically guided permanent prostate implants using 125I seeds averaged 0.72. The conformation number is a convenient instrument for indicating the degree of conformality by a single numerical value. Treatments with a conformation number greater than 0.60 might be termed conformal radiotherapy.