Polymer gel dosimetry using a three‐dimensional MRI acquisition technique

Abstract

In this work, three-dimensional (3-D) MRI techniques are employed in N-Vinylpyrrolidone-Argon-(VIPAR-) based polymer gel dosimetry. VIPAR gels were irradiated using a Nucletron microSelection 192Ir HDR brachytherapy remote afterloading system with single source dwell position and intravascular brachytherapy irradiation protocols. A single VIPAR gel and a single irradiation are adequate to obtain the full calibration curve needed. The 3-D dose distributions obtained with the 3-D MRI method were found to be in good agreement with the corresponding Monte Carlo calculations, for brachytherapy and intravascular irradiations. The method allows the reconstruction of isodose contours over any plane, with increased spatial resolution and accuracy following a single MR acquisition. VIPAR gel measurements using a 3-D MRI readout technique can be of particular use in the experimental dosimetry of brachytherapy sources, as well as for dose verification purposes when complex irradiation regimes and three-dimensional dose gradients are investigated.

Mechanical and dose delivery accuracy evaluation in radiosurgery using polymer gels

“…A volume‐selective 32‐echo Carr‐Purcell‐Meiboom‐Gill pulse sequence was used ($\text{TE}1,\hspace{0.17em}\text{TE}2,\dots ,\hspace{0.17em}\text{TE}32=40\hspace{0.17em}\text{ms},\hspace{0.17em}80\hspace{0.17em}\text{ms},\dots ,\hspace{0.17em}1280\hspace{0.17em}\text{ms}$, TR of 2.3 s, reconstructed voxel size of $1\times 1\times 1\hspace{0.17em}{\text{mm}}^3$), with phase encoding being applied in two orthogonal directions and Fourier interpolation taking place in the slice reconstruction direction (15) . After discarding the first echo of the 32‐echo train, a single T2 map (an image on which pixel signal intensity represents the nuclear magnetic resonance spin‐spin relaxation time T2 of the corresponding gel voxel) was automatically derived for each reconstructed slice.…”

Physics-aspects of dose accuracy in high dose rate (HDR) brachytherapy: source dosimetry, treatment planning, equipment performance and in vivo verification techniques

“…These include thermoluminescent dosimeters [17–20], ionisation chambers [21], semiconductor diodes [18], MOSFETS [22, 23], radiochromic film [24–28] and Polymer or Fricke gel dosimetry [29]. Theoretical Monte Carlo (MC) calculations have also been extensively utilised [17, 18, 30–35].…”

High-resolution NMR imaging of objects with dipolar-broadened spectra

“…Among line-narrowing multi-pulse sequences the ones based on the magic echo [9] are especially convenient for imaging applications [10][11][12]. The systems with broadened spectra, studied with MRI techniques, include polymers [13][14][15][16], porous materials [17,18], and multi-phase systems [19]. A review of imaging techniques for solid materials can be found in [20].…”