Measurement of Three-Dimensional Radiation Dose Distributions Using MRI

Abstract

Recent investigations have shown that nuclear magnetic resonance (NMR) can be used in conjunction with a suitable chemical dosimeter to estimate the dose from ionizing radiation (Gore et al., Phys Med. Biol. 29, 1189-1197, 1984). Based on this fact it was proposed that spatial dose distributions can be measured in gels infused with the chemical dosimeter using NMR imaging. There have been few such attempts and they provided only qualitative results. In this paper, we report results demonstrating the feasibility of obtaining quantitative dose distribution measurements by this technique. It is shown that quantitative dose distribution measurements necessitate the calculation of relaxation rate maps. We have determined that the spin-spin relaxation rate is a more sensitive parameter than the spin-lattice relaxation rate. It is also demonstrated that the addition of chemical sensitizers could improve the dose sensitivity of the measured NMR parameters. The two features characterizing a photon beam, depth-dose relationship, and beam profile as measured by this technique are in good agreement with the measurements using conventional methods, ionization chambers, and film dosimetry.

An investigation into the applications of polymer gel dosimetry in radiotherapy

“…No significant diffusion of the ferric ions in the gel was found for up to 10 hours after irradiation by Prasad et al (1991). In contrast, investigations carried out by Schulz et al (1990) showed a diffusion coefficient of 1.58 ± 0.11 mm2 h-' for a concentration of 25 mM, and 1.83 ± 0.14 mm2 h-' for a concentration of 12.5 mM Sulphuric acid.…”

“…Their results showed an enhancement of about 4.5 in the measurement of the transverse relaxation rate and about 2.5 in the measurement of the longitudinal relaxation rate. In contrast to Prasad et al (1991), Gambarini et al (1994) found no significant enhancement by adding 1.5 mM and 3.5 mM benzoic acid with and without NaCl.…”

“…Appleby et al (1988) indicated that both agarose and gelatin systems increase the ferric ion yield (G value) in the gel. The sensitivity of the Fricke gel system to radiation is higher than the corresponding aqueous Fricke solution by a factor of 4 when agarose gel is used (Olsson et al 1989) and by a factor of 2.2 when gelatin is used (Olsson et al (1989) and Prasad et al (1991). Therefore adding gelling agent to the dosimeter solution does not only have the advantage of the fixing dose distribution within the system but also provides a gain in sensitivity.…”

“…In an attempt to improve the sensitivity of the system (i. e. increase the G value), Prasad et al (1991) added 1.32 mM benzoic acid instead of 1 mM sodium chloride to the system. Their results showed an enhancement of about 4.5 in the measurement of the transverse relaxation rate and about 2.5 in the measurement of the longitudinal relaxation rate.…”

Dosimeter Gel and MR Imaging for Verification of Calculated Dose Distributions in Clinical Radiation Therapy

“…The use of a dosimeter gel, based on ferrous sulphate and agarose, and evaluated in a magnetic resonance (MR) scanner may eliminate some of these problems (4)(5)(6)(7)(8)(9). Other gel systems, based on a monomer solution, have been proposed (10).…”