In the radiation therapy, ionization chambers and/or film dosimeters are usually used to measure dose distribution, and three-dimensional absorbed dose distribution of the human body is calculated by computer simulation. However, at the treatment site, measurements of actual three-dimensional absorbed dose distribution become more important, because the commission of radiation therapy apparatus of high-precision, SRT, IMRT, IGMRT and so on, are important. Gel dosimeter can be directly used as water equivalent phantom, and using 3D gel printer, radiation sensitive artificial organs are expected to see the absorbed dose distribution directly. In this research, we developed a gel dosimeter by polymer chain cleavage mechanism using 3D printable gels and a device measuring the internal structure of gels., and development of 3D printable gel dosimeter using polymeric polymerization .We could not find any differences of internal structure of gels by our original DLS apparatus, but we have confirmed that tested gels are stable in usual dose level of radiation therapy. In addition, by developing of 3D printable gel dosimeter using polymeric polymerization, we succeeded to make dose distributions by using UV light.