@misc{oai:repo.qst.go.jp:00073338,
 author = {Inaniwa, Taku and 稲庭 拓},
 month = {Nov},
 note = {Abstract: The goal of charged-particle therapy is to control the tumors while maintaining the normal tissues. This goal is generally accomplished by the design of the dose distribution to deliver a large enough dose to the tumor while sparing the organs at risk (OARs). A highly-localized dose distribution by charged-particle beams is useful for this purpose. However, the planning target volume (PTV) occasionally overlaps the OARs.
For such clinical cases, the treatment planners have to choose a compromised dose level in the overlapped region. In addition, the cancer cells can coexist with the normal cells within the PTV, for instance in brain cancer. Also for such clinical cases, the treatment planners have to choose a compromised dose level for cancer cells and normal cells.
Since the radiation response of tissues (cells) depends differently on radiation quality most commonly represented by the linear energy transfer (LET) in radiation biology studies, there must be an optimum value of radiation quality which effectively kills the cancer cells while maintaining the normal cells. It is thus desirable to control the radiation quality within the patient independently, in addition to the dose distribution.
Carbon-ion beam is known as a high-LET radiation, and thus has ideal characteristics for cancer treatments, e.g., a high relative biological effectiveness (RBE) and a low oxygen enhancement ratio (OER) especially at the Bragg-peak region. The carbon-ion beam is therefore very effective to control the radio-resistant tumors. This is definitely true as the clinical experiences of carbon-ion therapy have proven. However, when we look at the dose-averaged LET distributions of typical carbon-ion therapy treatment fields, high LET of > 80 keV/μm is delivered only at the peripheral region of the target, and the moderate LET is delivered at the middle of the target. Therefore, we can conclude that the current charged-particle therapy, even carbon-ion therapy, does not make the best use of its potential. In other words, there is ａ room to drastically improve the clinical results of charged-particle therapy by taking advantages of its characteristics. We investigated ａ new therapeutic technique using two or more ion species in one treatment session, which we call an Intensity Modulated composite PArtiCle Therapy (IMPACT), for optimizing the dose and LET distributions in ａ patient. Protons and helium, carbon, and oxygen ions were considered as ion species for IMPACT. We made IMPACT plans for a prostate case.
In accordance with the prescriptions, LETs in prostate, planning target volume (PTV), and rectum could be adjusted at 80 keV/μm, at 50 keV/μm and below 30 keV/μｍ，respectively, while keeping the dose to the PTV at 2 Gy uniformly. IMPACT enables the optimization of the dose and the LET distributions in a patient, which will maximize the potential of charged particle therapy by expanding the therapeutic window., International Symposium on Ion Therapy 2018 (ISIT2018)},
 title = {Advanced optimization technique for ion-beam RT},
 year = {2018}
}