Fifty-seventh annual meeting of the American association of physicists in medicine
SU-E-T-497: Initial Characterization of a Novel 2D Computed Radiography (CR) Dosimeter for SBRT
For 2D, sub-mm resolution dose measurements Gafchromic™ film is currently a standard in radiotherapy; mainly because of its energy independence and water equivalence. However, EBT film is disposable. Therefore, the dosimetric and uniformity characteristics needs to be estimated from a second, possibly different, (calibration) film. Moreover, EBT has a post-irradiation coloration and a non-linear dose dependence with saturation, which limits the applicable time interval and dose range. CR technology forms an interesting alternative for EBT. Dose dependent CRplates have a sub-mm resolution, and additionally a linear dose dependence over decades of dose. But, CR has an inherent signal fading and energy dependence. Here, for the first time, a radiotherapy 2D CR prototype was characterized for an extended dose range (up to 35Gy), signal fading, and basic energy dependence.
The prototype was irradiated with a standard 10×10cm 6MV photon beam, and scanned with a commercial CR 15-X(R) scanner. The time between the start of irradiation and scanning (T_Scan) was monitored. The linearity of the dose response was evaluated between 0 and 35Gy using a fixed T_Scan of 4min, if possible (i.e. ≤10Gy). Next, the signal fading was characterized for a T_Scan-range of 4 to 20min. The energy dependence was assessed by a comparison of out-of-field measurements of CR, EBT, and TLD.
The radiotherapy CR prototype has a linear response over the complete SBRT dose range (0– 35Gy). The prototype had a small (5%), but linear signal fading over the time interval of interest (4–20min). Out-of-field, the prototype has a 8% over response due to an increased amount of low energy photons. The impact of the over response on intensity modulated radiotherapy remains to be evaluated.
CR technology is promising for SBRT dose measurements up to 35Gy. It is a reusable linear alternative for film dosimetry.