An investigation into the use of polymer gel dosimetry in low dose rate brachytherapy.

An investigation has been carried out into the properties of the BANG polymer gel and its use in the dosimetry of low dose rate brachytherapy. It was discovered that the response of the gel was reproducible and linear to 10 Gy. The gel was found to be tissue equivalent with a response independent of energy to within experimental accuracy (standard error of measurement +/- 5%). The slope of the calibration curve was found to increase from 0.28 +/- 0.01 s-1 Gy-1 to 0.50 +/- 0.02 s-1 Gy-1 for an increase in monomer concentration from 6 to 9%. Absorbed dose distributions for a straight applicator containing 36 137Cs sources were measured using the gel and the results compared with measurements made with thermoluminescent dosemeters (TLDs) and calculated values. Good agreement was found for the relative measurements. The root mean square residual percentage errors were 3%, 1% and 4% for the gel and the two groups of TLDs, respectively. There were some significant differences in absolute values of absorbed dose in the gel, possibly owing to the effects of oxygen. Measurements of a complex gynaecological insert were also made and compared with isodose curves from a planning system (Helax TMS), and in areas unaffected by oxygen diffusion the isodose levels from 100 to 50% agreed to within less than 0.5 mm.

[1]  J C Gore,et al.  Dose-response curves for Fricke-infused agarose gels as obtained by nuclear magnetic resonance. , 1990, Physics in medicine and biology.

[2]  M D Evans,et al.  Imaging of HDR brachytherapy dose distributions using NMR Fricke-gelatin dosimetry. , 1994, Magnetic resonance imaging.

[3]  T. Holmes,et al.  Acceptance testing computerized radiation therapy treatment planning systems: direct utilization of CT scan data. , 1985, Medical physics.

[4]  T. J. Godden,et al.  Physical Aspects of Brachytherapy , 1988 .

[5]  J. Gore,et al.  NMR relaxation enhancement in gels polymerized and cross-linked by ionizing radiation: a new approach to 3D dosimetry by MRI. , 1993, Magnetic resonance imaging.

[6]  L E Olsson,et al.  Ferrous sulphate gels for determination of absorbed dose distributions using MRI technique: basic studies. , 1989, Physics in medicine and biology.

[7]  J C Gore,et al.  Radiation therapy dosimetry using magnetic resonance imaging of polymer gels. , 1996, Medical physics.

[8]  J J Battista,et al.  Computed tomography for radiotherapy planning. , 1980, International journal of radiation oncology, biology, physics.

[9]  S. Webb,et al.  An investigation into the dosimetry of a nine-field tomotherapy irradiation using BANG-gel dosimetry. , 1998, Physics in medicine and biology.

[10]  Bo Nordell,et al.  Diffusion of ferric ions in agarose dosimeter gels , 1992 .

[11]  I.R.H. De Vrome.  Recommendations for Brachytherapy Dosimetry , 1994 .

[12]  C Baldock,et al.  Experimental procedure for the manufacture and calibration of polyacrylamide gel (PAG) for magnetic resonance imaging (MRI) radiation dosimetry. , 1998, Physics in medicine and biology.

[13]  A. Nahum,et al.  The quality dependence of LiF TLD in megavoltage photon beams: Monte Carlo simulation and experiments. , 1996, Physics in medicine and biology.

[14]  R. P. Parker,et al.  The direct use of CT numbers in radiotherapy dosage calculations for inhomogeneous media. , 1979 .

[15]  J C Gore,et al.  Effects of crosslinking and temperature on the dose response of a BANG polymer gel dosimeter. , 1997, Physics in medicine and biology.

[16]  J C Gore,et al.  Magnetic resonance imaging of radiation dose distributions using a polymer-gel dosimeter , 1994, Physics in medicine and biology.

[17]  J. Gore,et al.  Measurement of radiation dose distributions by nuclear magnetic resonance (NMR) imaging. , 1984, Physics in medicine and biology.

[18]  D. Olsen,et al.  Absorbed dose distribution measurements in brachytherapy using ferrous sulphate gel and magnetic resonance imaging. , 1994, The British journal of radiology.