CONICET | Buscador de Institutos y Recursos Humanos

Purpose: Modern applications of SBRT provide treatments with higher doses per fraction, high dose gradients and great accuracy, thus improving the protection of surrounding tissue. However, dose verification of treatment plans has become complex due to the large number of irradiation fields. In this context, 3D dosimetry, such as polymer gel dosimetry (PGD), represents a suitable alternative for 3D dose verification within tissue-equivalent materials. This study reports on a spine SBRT treatment planning and the 3D dose distribution measurement by using PGD. Methods: Treatment planning was performed by using the Elements Spine SRS v1.5 (Brainlab) with a total dose of 36 Gy with 6XFFF beams Verification was carried out by PAGAT PGD, delivering a maximum of 7 Gy. Two cubic dosimeters with a volume of 1 L were used to calibrate the system and to verify the treatment planning. The positioning of dosimeter was defined by means of CT and the irradiation was carried out in a Novalis TrueBeam STx VARIAN BrainLab. The readout of the dosimeters was performed by magnetic resonance imaging (MRI) and processed by a home-made Matlab script. The obtained 3D dose distribution was compared to the TPS dose distribution by using a 3D gamma index test (3 mm/2%). Results: 3D experimental dose distributions were successfully obtained by PGD and NMR with a 1 mm resolution for a spine SBRT treatment. For that purpose, a calibration dose vs R2 curve was studied and optimized. It is worthwhile noting that a 94% pass rate was obtained in the gamma index test by using a 3D inherent method. Conclusion: The results prove the potential of PGD clinical implementation as verification tools and show the great capacity of PGDs to provide experimental 3D dose distributions in complex irradiation treatments like SBRT.