BANG-3® polymer gel dosimetry in Cyberknife

In this study, we performed BANG-3® polymer gel dosimetry to propose an experimental technique for relative output factor and 3D dose distribution measurements of small radiosurgical fields.We were irradiated 2 collimators (5 and 30 mm diameter) with 6 MV radiosurgery beam. And, MR scanned with the same slice thickness and three different in plane resolutions. In these experiments, output factor measurements with the Pin Point ion chamber and diode, EBT films are compared with BANG-3® polymer gel. We used a spherical phantom filled with BANG-3® polymer gel to measure 3D dose distributions. The irradiated phantom was scanned with an MRI scanner. Dose distributions were obtained by calibrating the polymer gel for a relationship between the absorbed dose and the spin-spin relaxation rate of the magnetic resistance signal. As results, the output factors founded agreement within ±1% as a reference the collimators 30 mm. Therefore, results suggest that polymer gel dosimetry coupled with the proposed experimental procedure helps overcome not only tissue-equivalence and beam perturbation implications but also volume averaging and positioning uncertainties in small radiosurgical beam dosimetry. In 3D dose distribution, the MRI artifacts cause a geometrical distortion of less than 2 mm and less than 10% change in the dose distribution. In conclusion, the gel dosimetry has the potential to qualitatively characterize the relative output factor and the dose distributions.