Dose response characterization of novel presage sheets for radiotherapy dose verification / 中华放射医学与防护杂志

ABSTRACT

Objective:To characterize the key dose response properties of the novel presage sheet dosimeters for radiotherapy dose verification, including absorption spectra, linearity, dose range and stability.Methods:The same batch of presage sheet dosimeters were irradiated by a radiotherapy linac. The absorption spectra within 400-700 nm were read out with a spectrophotometer, and the R-G-B3 absorption changes read out with a film flatbed scanner was compared before and after irradiation.Results:An absorption peak was clearly identified at 628 nm, where absorptions change in high linearity with delivered doses ( R2=0.9999). A flat valley region is identified around 490 nm, where dose induced absorption changes were negligible. The readout sensitivity of the R-channel of the flatbed scanner was higher than both in green and blue channels. In the dose range below 10 Gy, the R-channel absorptions are in significant linearity with doses ( R2=0.9999), with absorptions change in an obvious quadratic trend in the range beyond 10 Gy ( R2=0.9999). The dose range of presage sheets was more than 94.6 Gy. The absorptions were well preserved within 1 h post-irradation, and then are shown to increase gradually, where the increase speeds are dose-related. The post-irradiation integrity of dose falloff gradients are shown with negligible gradient blurring. Conclusions:The novel presage sheets shown to have reasonable dose response linearity, large dose range, desirable post-irradiation dose gradient integrity and negligible fractionation effect, which indicates its great potentials in integral dose verification of high-dose and multiple target radiotherapy deliveries.