Abstract
Radiation therapy, demand of which is recently increasing, requires irradiation of a tumor with reducing dose onto normal tissues surrounding the tumor in order to reduce risk of side effect of the irradiation such as secondary carcinogenesis. Such requirement led to development of advanced methods such as IMRT and ion-beam therapy, which enable us to plan complicated dose distributions. However, most typically used dosimeters such as ionization chambers and film dosimeters allows us only to measure dose at a certain point or two-dimensional dose distribution on the film plane.
Polymer gel dosimeters are proposed as a promising tool to check three-dimensional dose distributions, however, widespread polymer gel dosimeters contain toxic components such as acrylamide and methacrylic acid, leading to difficulties in handling. It was tried to solve this problem by employing naturally-derived polymer hydroxypropylcellulose (HPC) as a base matrix. Solutes dissolved into hydrogel matrix of HPC were also selected from the viewpoint of low toxicity, and hydroxyethyl 2-methacrylic acid and poly-ethylene glycol ester were selected.
Such environment-friendly polymer gel dosimeter was irradiated with 60Co γ-rays in a practically important dose range of 1-10 Gy, and an increase of white turbidity was observed. This turbidity would be attributed to macromolecule products in radiation-induced polymerization reactions. UV-vis absorption analysis was also done for more brief but quantitative estimation of the turbidity increase. It was found that absorbance dependences on dose are different for different wavelengths and that absorbance at shorter wavelength (300-500 nm) tends to saturate at relatively low dose of about 4 Gy while that at longer wavelength (500-800 nm) is not so much wavelength dependent. In addition, effects of solutes composition on these behaviors will also be discussed.
