Verification of MRI MAGAT polymer gel dosimetry in clinical radiotherapy applications

Introduction: The objective of this work is to study the ability of MRI normoxic polymer gel dosimetry system to be used to verify the calculated dose distribution, in a simple geometry, in clinical radiotherapy. Materials and Methods:  Initially, 2 liters of the normoxic MAGAT polymer gel was prepared and then poured into two cylindrical Perspex phantom (simulating a patient) and four calibration test tubes. The phantoms were then CT scanned and a dose plan was generated using the obtained CT data. The gel phantoms and the calibration test tubes were irradiated using a cobalt-60 teletherapy unit. Prior to the irradiation MRI scans of the phantom was taken to measure the background value of R2. Immediately after the irradiation, new images of the phantom and the calibration test tubes were obtained using the MRI scanner. Finally, using the MRI images in MATLAB environment R2 maps and dose maps were calculated. Results: In radiation treatment of prostate cancer according to the three and two field techniques a homogenous absorbed dose distribution was obtained for the planning target volume (PTV) within the phantom using gel dosimeter and treatment planning systems (TPS). In the region of interest at the point center, the difference in the dose obtained from the gel dosimeter and TPS was 1.2 %. Dose sensitivity, R Square (R2) and dose resolution of MAGAT gel dosimeter also were determined and became 5.033 S-1Gy-1, .9953, .97 Gy respectively Conclusion: In this study, two clinical treatment procedures were investigated using MRI normoxic polymer gel dosimetry and TPS. The data obtained from TPS calculations was    compared to the polymer gel dosimeter measurements and a good agreement was found.