- Clinical Studies Regarding Radiotherapy
- Medical Physics
- Radiation Biology
Less Invasive and More Effective 〜 Next Generation of Radiotherapy 〜
Radiobiological Gamma Index, a novel dose index for radiobiological effects
Dose verification of patient-specific quality assurance (QA) is generally performed before actual radiation therapy, particularly intensity-modulated radiotherapy and stereotactic radiotherapy. The 3D Gamma index is commonly used to evaluate dose distributions between planned and measured doses from the physical aspect. The initiation of an actual treatment depends on the passing rate of the 3D gamma index, which is predefined at each institution. In the case of the gamma passing rate being lower than the tolerated criteria, the medical physicist asks the radiation oncologist to judge whether the QA results are acceptable from the clinical aspect. However, the judgment is subjective and physician dependent. In order to solve this matter, we have proposed a novel dose evaluation index, the radiobiological gamma index (RGI), which modifies the physical gamma index (Sumida I, et al. Int J Radiat Oncol Biol Phys, 2015; Sumida I et al. J Radiat Res. 2015; Kurosu K, et al. J Radiat Res, 2015). Tumor control probability (TCP) and normal tissue complication probability (NTCP) were used to incorporate radiobiological effects in each organ. RGI could support evaluation of the dose distribution, not only from the physical point of view but also the clinical point of view.
Combination of radiation with antitumor immunotherapy
Radiation therapy has been long utilized as a localized cancer therapy or as a conditioning regimen to suppress systemic immune responses before hematopoietic transplant. There is a well-known but anecdotal phenomenon, called the abscopal effect, in which tumor regression is observed outside the radiation field due to an enhancement of the immune response. We have investigated whether radiation combined with immunomodulatory drugs increase the probability of the abscopal effect in various tumors (Takahashi Y, et al. Submitted). Furthermore, we are trying to elucidate the mechanism to predict and intentionally induce the abscopal effect with an optimal radiation delivery regimen. These studies will lead to future clinical trials.
Cancer stem cells and radioresistance
Cancer recurrence and metastatic potential can be due to a subpopulation of cells with stem-like characteristics, cancer stem cells, which maintain the capacity to regenerate entire tumors. We stably infected cancer cell lines with an expression vector that included a fusion protein of a green fluorescent protein, ZsGreen, and the C-terminal degron of murine ornithine decarboxylase to visualize cancer stem cells (Tamari K, et al. Int J Oncol. 2014; Hayashi K, et al. Int J Oncol. 2014). We are now working on omics analysis in cancer stem cells to elucidate the radioresistance mechanism and develop new treatment strategies.