Development of a dosimetric tool employing new chemical formulation of nPAG-Type polymer gel for the head region

A dose distribution that optimizes target volume of radiotherapy treatment is of great interest. For this purpose, treatment plans must be verified experimentally before being transferred to patient. Accuracy of delivered dose and spatial resolution can be analyzed in gel dosimeter that has tissue equivalence, in addition to enabling dose distribution in three dimensions. Same time, this form of dosimetry can complement dosimetric information obtained by ionization chamber. Thus, nPAG dosimeter must be analyzed through the relaxation time T₂, which varies with absorbed dose value. In this work, a new chemical formulation for production of dosimetric solution was developed; flasks containing nPAG gel dosimeter and ionization chamber (reference standard) were irradiated following TRS 398 protocol in high energy photon beams used for oncological treatment. Through MR images of dosimetric samples, response curve was generated and evaluation of uncertainties was determined in relation to main input quantities of system. Phantom filled with agar gels and dosimetric were irradiated and MRI images were also obtained and post-processed. Results of analysis demonstrated that relative uncertainty of system is within an expected limit according to protocols adopted for quality control. It was observed that new chemical formulation of polymeric dosimeter has (i) sensitivity for the energy and dose range used for stereotaxic radiosurgery, (ii) constant sensitivity independent of beam energy and dose rate delivered by equipment and (iii) insensitivity to macroscopic diffusion. (author)