An investigation on LDR Ir-192 wires dose distribution inAn investigation on LDR Ir-192 wires dose distribution in triangle implant of Paris system using polymer gel dosimetry

Polymer gels providing 3D radiation dose distributions can be used in brachytherapy in which the target volume is relatively small and there are high dose gradient regions. In this study, the potential application of MAGICA normoxic polymer gel for the assessment of dose values and dose distribution resulted from low dose rate (LDR) Ir-192 wires, was investigated. This was carried out for the triangle implant in interstitial brachytherapy . Material and methods: Perspex phantom was made for the triangle shape implant. Thin glass applicators were used as the holder of Ir-192 wires. MAGICA polymer gel was prepared. The calibration vials were irradiated with a Co-60 machine. The phantom filled with the gel was then irradiated using the low dose rate (LDR) Ir-192 wires. The insertion of the wires in the applicators was performed. MRI technique was used to obtain images from the phantom and corresponding calibration vials. R2 images of the phantom and the calibration vials were derived. By using data obtained from calibration vials, absolute dose values were experimentally calculated. The results were then compared with those calculated based on Paris system. In addition, isodose curves, obtained from gel medium, were compared with those calculated by a brachytherapy treatment planning system . Results: The MAGICA dose resolution was found to be within 0.78 - 1.26 Gy for a range of 0 – 9 Gy dose values. Absolute dose values at basal dose points, measured by the gel, were 62.75%, higher than calculated values based on Paris system for the triangle double plane implant. The maximum distance to agreement (DTAmax) between the measured and calculated isodose curves were less than 3 mm at different isodose levels . Conclusion: Although MAGICA polymer gel demonstrates an overestimation for absolute dose values measured in the triangle implant, it can be utilized as a powerful tool to evaluate relative dose values. It can also be used for treatment planning quality assurance tests .

کلیدواژه ها:

Polymer gel dosimetry ، Interstitial brachytherapy ، Normoxic polymer gels ، MAGICA ، Paris system