On the Development of the VIPAR Polymer Gel Dosimeter for Three‐Dimensional Dose Measurements

Abstract

Summary:The new polymer gel dosimeter, based on the modification of the VIPAR gel composition, is described for the purpose of radiation dose distribution measurement in radiotherapy. It features increased concentration of the two VIPAR substrates: N-vinylpyrrolidone (8%) and gelatine (7.5%) (N,N 0 -methylenebisacrylamide was maintained at 4%), and the addition of copper sulphate (0.0008%) and ascorbic acid (0.007%) in order to facilitate the preparation through elimination of the need for deoxygenation of the gel. Following the exposure to ionizing radiation, polymerisation and cross-linking of the new gel monomers occurs retaining the spatial distribution of absorbed dose and causing opacity of the gel. Quantitative parameters of the new gel dose response were studied using magnetic resonance imaging to relate polymerisation induced physicochemical changes of the gel to dose. The dose threshold is found significantly lower than that of the original VIPAR gel. The linear part of measured spin-spin relaxation rate R 2 (D) ( ¼ 1/T 2 (D)) reaches up to 35 Gy. Its slope and an intercept are slightly higher relative to the original VIPAR. The efficiency of the new polymer gel-magnetic resonance imaging dosimeter was also tested for dose verification of a 3D dose distribution planned by a commercially available treatment planning software (Eclipse External Beam v.6.5) and delivered by a 6 MV medical linear accelerator. The new polymer gel is proposed to be called, VIPAR nd (after VIPAR-normoxic-double).

Dosimetric accuracy of a deterministic radiation transport based brachytherapy treatment planning system. Part II: Monte Carlo and experimental verification of a multiple source dwell position plan employing a shielded applicator

“…This normoxic formulation introduced by our group presents dose-response characteristics suitable for experimental brachytherapy dosimetry, 19,[22][23][24] and alike other polymer gel formulations it comprises a water equivalent material for the 192 Ir energies. 25 About 2 l of gel substance were prepared using 4% ͑w / v͒ N , NЈ-methylenebisacrylamide, 8% ͑w / v͒ N-vinylpyrrolidone, 7.5% ͑w / v͒ gelatin, 0.0008% ͑w / v͒ copper sulfate, 0.007% ͑w / v͒, and hyperpure water ͑resistivity Ͼ18 M⍀ cm͒ following a procedure described in detail in previous works.…”

Characterization of a new polymer gel for radiosurgery dosimetry using Magnetic Resonance Imaging

“…Given the augmented concentration of NVP, the concentration of gelatin had to be increased in order to ensure mechanical stiffness of the solidified solution. Along the lines of Fong et al [1], Copper Sulfate Pentahydrate and Ascorbic Acid were added as oxygen scavengers [3] allowing the gel preparation procedure to be carried out in normal atmospheric conditions.…”

“…The concentration of N, N -methylenebisacrylamide (MBA) was maintained at its solubility value at 21 o C (4%) and, hence, the new gel formulation (hereafter to be referred to as VIP 1 for simplicity) was: 8% N-Vinylpyrrolidone, 7.5% gelatin, 4% N, N -methylenebisacrylamide, 0.0008% Copper Sulfate and 0.007% Ascorbic Acid [3].…”

Radiological characteristics of MRI-based VIP polymer gel under carbon beam irradiation

“…VIP gel, one of representative polymer gel dosimeters, was originally introduced by a Greek group in 1999 (Pappas et al, 1999). Its characterization and improvement have been reported in numerous investigations, especially for low LET radiation (Karaiskos et al, 2005;Kipouros et al, 2001;Kozicki et al, 2007;Pantelis et al, 2008;Papagiannis et al, 2001;Papoutsaki et al, 2013aPapoutsaki et al, , 2013bPappas et al, 2003Pappas et al, , 2006Pappas et al, , 2008Pappas et al, , 2005Pappas et al, , 2001. With its wide range of linear dose response up to ca.…”

“…With its wide range of linear dose response up to ca. 40 Gy Kozicki et al, 2007) and small dose rate dependence , VIP polymer gel is expected to be advantageous also for the case of high LET radiation. The distribution of the transverse relaxation rate R 2 in irradiated samples was measured by MRI.…”