Purpose. Fricke gel dosimeters (FGDs) based on poly-vinyl alcohol (PVA) as gelling agent and glutaraldehyde (GTA) as cross-linker, were developed with the aim to overcome the drawbacks affecting the FGDs prepared with traditional natural gel matrices like gelatin or agarose [1]. Here, we investigate the dosimetric robustness of PVA-GTA FGDs against parameters influencing their preparation, like pH and temperature of gelling. Materials and Methods. PVA-GTA matrices undergo gelling by heating instead of cooling. Gelling temperatures from 6 C to 40 C were considered. FGDs with PVA and GTA concentrations of 10% w/w and 1% w/w respectively, were arranged preparing Fricke solutions with different amounts of sulfuric acid in the interval 18–100 mM. FGDs in spectrophotometry cuvettes (10 mm optical path) were uniformly irradiated with a 137Cs source. The optical absorbance (OA) properties and dose-response in the interval 0–35 Gy were investigated. Furthermore, FGDs in form of thin layers (3 mm optical path, area 10 5 cm2 ) were irradiated with 80 kV X-rays producing a steep dose gradient. Light transmittance images were acquired before irradiation and at consecutive times up to 6 h post-irradiation to derive the Fe3+ diffusion coefficient. Results. OA spectra and dose-response curves of FGDs were independent of the gelling temperature. A sensitivity of approximately 0.073 Gy-1 was obtained. By contrast, as in traditional FGDs, sulfuric acid concentration significantly affected the OA spectra as well as the sensitivity and linearity of the PVA-GTA FGDs. Both gelling temperature gradient and pH did not influence the Fe3+ diffusion coefficient, assessed equal to approximately 0.22 mm2 /h, i.e. more than two times lower than in traditional FGDs. Conclusions. The robustness of PVA-GTA-FGDs against preparation parameters represent a significant advantage over traditional FGDs. In particular, the response independence of the gelling temperature may enable the manufacture of large FGD phantoms without any gradient in sensitivity

Study of the dosimetric robustness of PVA-GTA based Fricke gels against manufacture parameters / S. Gallo, G. Gambarini, L. Ianni, I. Veronese. - In: PHYSICA MEDICA. - ISSN 1120-1797. - 56:Supplement 2(2018 Dec 20), pp. 132.146-132.147. ((Intervento presentato al 10. convegno National Congress of the Associazione Italiana di Fisica Medica tenutosi a Bari nel 2018 [10.1016/j.ejmp.2018.04.143].

Study of the dosimetric robustness of PVA-GTA based Fricke gels against manufacture parameters

S. Gallo
Primo
;
G. Gambarini
Secondo
Writing – Original Draft Preparation
;
I. Veronese
Ultimo
Supervision
2018-12-20

Abstract

Purpose. Fricke gel dosimeters (FGDs) based on poly-vinyl alcohol (PVA) as gelling agent and glutaraldehyde (GTA) as cross-linker, were developed with the aim to overcome the drawbacks affecting the FGDs prepared with traditional natural gel matrices like gelatin or agarose [1]. Here, we investigate the dosimetric robustness of PVA-GTA FGDs against parameters influencing their preparation, like pH and temperature of gelling. Materials and Methods. PVA-GTA matrices undergo gelling by heating instead of cooling. Gelling temperatures from 6 C to 40 C were considered. FGDs with PVA and GTA concentrations of 10% w/w and 1% w/w respectively, were arranged preparing Fricke solutions with different amounts of sulfuric acid in the interval 18–100 mM. FGDs in spectrophotometry cuvettes (10 mm optical path) were uniformly irradiated with a 137Cs source. The optical absorbance (OA) properties and dose-response in the interval 0–35 Gy were investigated. Furthermore, FGDs in form of thin layers (3 mm optical path, area 10 5 cm2 ) were irradiated with 80 kV X-rays producing a steep dose gradient. Light transmittance images were acquired before irradiation and at consecutive times up to 6 h post-irradiation to derive the Fe3+ diffusion coefficient. Results. OA spectra and dose-response curves of FGDs were independent of the gelling temperature. A sensitivity of approximately 0.073 Gy-1 was obtained. By contrast, as in traditional FGDs, sulfuric acid concentration significantly affected the OA spectra as well as the sensitivity and linearity of the PVA-GTA FGDs. Both gelling temperature gradient and pH did not influence the Fe3+ diffusion coefficient, assessed equal to approximately 0.22 mm2 /h, i.e. more than two times lower than in traditional FGDs. Conclusions. The robustness of PVA-GTA-FGDs against preparation parameters represent a significant advantage over traditional FGDs. In particular, the response independence of the gelling temperature may enable the manufacture of large FGD phantoms without any gradient in sensitivity
Fricke gel, dosimetry, Dose, PVA, GTA
Settore FIS/07 - Fisica Applicata(Beni Culturali, Ambientali, Biol.e Medicin)
Settore FIS/01 - Fisica Sperimentale
Associazione Italiana di Fisica Medica (AIFM)
Article (author)
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2434/616661
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