¹H NMR AND OPTICAL SPECTROSCOPY STUDY OF THE RADIODOSIMETRIC PROPERTIES OF THE PIRA GEL

Abstract

The radiation-response of the Fricke-doped protein-polymer gel (PIRA) was studied by ¹H NMR, as well as with spectrophotometric and fluorescence methods. In this gel, the ionizing radiation induces an increase in the NMR longitudinal relaxation rate, R1, of protons. It was observed that: I) the main mechanism responsible for the increase in R1 was the oxidation of ferrous to ferric ions; ii) the total amount of acrylamide with the same weight fraction (50%C) of the crosslinker N,N′-methylene-bis-acrylamide in the range 6%–12% by weight had no effect upon the R1 dose sensitivity; iii) the increase in the bovine serum albumin (BSA) concentration caused a drop in the R1 dose response sensitivity; iv) the R1 dose sensitivity was pH dependent. The four-site fast exchange model for R1 dose response was applied to calculate the ferric ions chemical yield G(Fe³⁺). The G(Fe³⁺) value obtained from the NMR data agreed with that determined independently from spectrophotometric measurements.

Keywords:

• MRI dosimetry
• Proton relaxation times
• Fluorescence
• Protein-polymer gel (PIRA)
• Phantom material
• Fricke-doped gels

ACKNOWLEDGMENTS

The authors would like to thank the Department of Radiotherapy in the Centre Eugene Marquis in Rennes and the Department of Oncology and Radiotherapy of the Medical University of Gdansk for allowing the use of their irradiation units. The help of Dr. François Husson, Mrs Renata Nowak and Mr Piotr Szewczyk in sample irradiation is appreciated. The authors are particularly grateful to Dr. Grzegorz Piszczek, Department of Biochemistry, University of Maryland for many useful tips and discussions regarding optical spectroscopy experiments. This work was supported by KBN (Committee on Scientific Research) grant No. 2PO3B 148 12 (Poland). G.Z. was supported by 93/2155 grant from CNOUS, Paris.