Dosimetría Polimérica para Radioterapia

D. CHACON; M. STRUMIA; F. MALANO; F. MATTEA; J. VEDELAGO; M. VALENTE

Carlos Paz

Congreso; 7mo Congreso ALFIM & 13avo Congreso SAFIM; 2016

ALFIM & SAFIM

p { margin-bottom: 0.1in; direction: ltr; color: rgb(0, 0, 10); line-height: 120%; text-align: left; widows: 2; orphans: 2; }p.western { font-family: "Calibri",serif; font-size: 11pt; }p.cjk { font-family: "Calibri"; font-size: 11pt; }p.ctl { font-size: 11pt; }Introduction: Dosimetry represents an essential tool forradiology applicationsand among the different alternatives, gel dosimeters are theonly ones capable of recording 3D dose distributions in a tissueequivalent material acting as a dosimeter and phantom at the sametime (Baldock et al. 2010). During the last decades two types of geldosimeters have been widely studied, first Fricke gel dosimeters,which rely on the oxidation of ferrous ions by the water radicalsformed during irradiation. This material has been improved greatlyfrom its presentation (Schreiner 2004) but still has some limitationsregarding to the loss of information within time after beingirradiated because of ion diffusion. Because of that, polymer gelswere introduced, minimizing post irradiation limitations. Originally,the first polymer gel dosimeters required complex and specificlaboratory setups to ensure reproducibility and adequate sensitivityto radiation. However, the addition of an antioxidant agentsimplified the manufacture of these materials and gave place tonormoxic dosimetry (De Deene et al. 2002).Materials and methods: In this study, two different polymericmaterials based on N-isopropylacrylamide (NIPAM)and acrylamide (PAGAT) have been used in a low energy X-ray tubeavailable at LiifamirXwith energies of 44 kVp and dose rates of 65.5 cGy /min. Also, NIPAMdosimeters were irradiated in a linear accelerator (CLINAC 600C) withenergies of 6 MV and dose rates around 320 cGy/min and together with(benzoic acid-added) Fricke gel dosimeters (BFGD), Treatment planningsystem (TPS) and Monte Carlo simulations (MC) have been consideredfor comparison using of a gamma index analysis with distance toagreement (DTA) and dose difference (DD) parameters of 1 mm and 2%respectively. The irradiated materials were evaluated by simpletechniques like optical absorbance or light transmission using theadequate configuration for each material. Results:Both PAGAT and NIPAM dosimeters were able to record doses between 0and 20 Gy with a linear response and sensitivity values depending onthe light wavelength used for their analysis. The results obtained inthe low energy X-ray tube were 0.085absorbance/Gy forNIPAM and 0.067 absorbance/Gy forPAGAT. These results are comparable with the ones obtained by otherauthors (Mesbahi and Zakariaee2014) and useful for the dose distribution quantification byoptical methods. The dose distributions obtained by MC, TPS and BFGDwere also comparable to the one obtained for NIPAM dosimeters in theLinear accelerator. Gamma indices shows that 99.29% of the points inthe dosimeters meet thepassing criterion demonstrating that this polymeric dosimeter couldprovide the same reliability that MC and the other methods tested inthis study. Conclusions: Two different polymeric dosimeters were testedfor X-ray sources presenting excellent performance as dosimetricmaterials. Also, one of these materials was compared to typicaldosimetric methods like MC simulations, TPS and Fricke gel withexcellent agreements when compared with the aid of a gamma indexmethod. References:Baldock C, De Deene Y, Doran S, et al (2010). PhysMed Biol 55:R1?63. De Deene Y, Hurley C, Venning A, et al (2002).Phys Med Biol 47:3441?3463.Schreiner LJ (2004). J Phys Conf Ser 3:9?21.Mesbahi, A. and Zakariaee, S.-S. (2014). Iranian Journal of MedicalPhysics, 11(1):188?194.