Verification of the 3D dose distribution in spinal radiosurgery by using a BANG3® polymer gel dosimeter

In intensity-modulated radiosurgery (IMRS) treatment, radiation delivery techniques require the ability to accurately verify complex three-dimensional (3D) dose distributions. This study was designed to evaluate and verify dosimetry generated from gels, films, and treatment planning systems. In this study, commercially available BANG3® polymer gel was used to confirm the accuracy of the treatment plan and to assess the dosimetric uncertainty of the radiosurgery procedure. BANG3® gels that are read with R2 magnetic resonance (MR) imaging mapping are useful options. The gel is a tissue equivalent, and the relaxation ratio measured using MR imaging is proportional to the dose absorbed in the gel. A cylindrical container (5″ deep, 7″ high) filled with BANG3® gel was mounted in a cubic phantom (The EASY CUBEr, Euromechanics, Schwarzenbruck, Germany). We then carried out the same process using the gel and gafchromic film as would be used for a patient with metastatic T-spine cancer by using a Novalis Radiosurgery system (Brain LAB Inc., Germany). Our experimental results provided the dose distribution and the radiation delivery precision. Comparisons of the measured and the calculated relative dose distributions showed good agreement in the high-dose region with differences of 2 mm. BANG3® polymer gel dosimetry can be useful for the verification of clinical treatment radiosurgery plans.