In this work, the properties of the new BANG gel, specifically made for high-ionization density dosimetry, were investigated. The measurements were performed at NIST using a small calibrated 60Co gamma field of 1 cm x 1 cm, and a 1 cm active diameter ophthalmic applicator 90Sr/90Y beta particle source. A commercial high-resolution laser computer tomography (CT) scanner was used to quantify the response. The results show that the response of the gel is linear up to 15 Gy for both radiation type and is reproducible up to 1 month post-irradiation. For higher doses, the response decreases as the time increases and the higher the dose, the earlier is the onset. Based on this feature, we have evaluated the effect of accumulated doses on the radiation-induced polymerization process and have found that the response of the gel is statistically the same using individual exposures or accumulated doses. On the other hand, the temperature of the gel during irradiation does not appear to affect the dose response. Also, unlike magnetic resonance imaging, the temperature of the gel during the reading process doesn t affect its response when the optical CT scanner is used. In addition, we do not observe any trend related to a dose rate dependence of the response of the gel for dose rates lower than or equal to 15 mGy/s. Within the measurement uncertainty, the gel responds almost the same to beta particles and to high energy photons. This feature suggests that this gel can be a good candidate for high-ionization density dosimetry. Finally, we can conclude that this gel together with this reading system can be used where very high dose gradient is present if the linear region of the dose-response curve is considered.
Citation: Medical Physics
Pub Type: Journals
BANG gel dosimetry, beta particles, Co60 gamma rays, CT scanner, ionization density, small radiation field