Abstract
For intravascular brachytherapy with catheter-based systems, AAPM Task Group 60 has recommended measurements that should be made to characterize the sources. Beta emitters, including (90)Sr/(90)Y are ideal for intravascular brachytherapy, but problems arise in measuring dose distributions in the high dose gradient region at short distances from the source. In this paper, measurements of radial and orthogonal dose distributions and dose profiles for a (90)Sr/(90)Y source train using polyacrylamide gel (PAG) dosimetry and a high-field 4.7 Tesla MRI scanner are presented and compared with measurements made with two types of radiochromic film, MD-55 and HD-810. For the PAG system, the dose distributions were determined with in-plane resolutions of 0.4 mm and 0.2 mm. The measurements of absorbed dose distributions both orthogonal and parallel to the source axis show good agreement between the PAG and radiochromic film. The absolute dose at a radial distance of 2 mm in the central 32 mm of a line parallel to the axis was measured. For the PAG the measured absorbed dose was 1.25% lower, for MD-55 4% higher and for the HD-810 1.6% higher when compared with the value given by the source calibration. These results confirm that both absorbed dose and dose distributions for high gradient vascular brachytherapy sources can be measured using PAG but the disadvantages of gel manufacture and the need for access to a high resolution scanner suggests that the use of radiochromic film is the method of choice.
Highlights
Radiochromic film is one method that has been used for the dosimetry of vascular brachytherapy sources [3], but it is restricted to measurements in two dimensions, as are measurements with scintillator devices [4]
Polyacylamide gel (PAG) dosimetry has been used for measurements of several brachytherapy sources [5,6,7,8,9,10], and relies on radiation-induced cross-linking of the polymer, which alters both the optical density of the gel and the nuclear
A calibration curve for the PAG is shown in Figure 4; the number of calibration points was limited by the available scanner time
Summary
Radiochromic film is one method that has been used for the dosimetry of vascular brachytherapy sources [3], but it is restricted to measurements in two dimensions, as are measurements with scintillator devices [4]. Polyacylamide gel (PAG) dosimetry has been used for measurements of several brachytherapy sources [5,6,7,8,9,10], and relies on radiation-induced cross-linking of the polymer, which alters both the optical density of the gel and the nuclear. In MRI dosimetry, the changes in the nuclear transverse relaxation rate (R2) (the inverse of the relaxation time (T2)) with dose are exploited. Using a high-field MRI system, the resolution achievable may be sufficient for the needs of vascular brachytherapy dosimetry. The purpose of this paper is to compare radiochromic film dosimetry with PAG in meeting the requirements of AAPM Task Group 60 [2]
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