This work provides full dosimetric data for a new high-strength 192Ir source currently launched by Varian Oncology Systems for use in their high dose rate remote afterloading systems. The active core length of the new source is reduced to 5 mm compared to a value of 10 mm for the existing VariSource source design, with all other geometric source and encapsulation details being similar. Dose-rate constant, radial dose functions, geometry factors, and anisotropy functions, utilized in the AAPM Task Group 43 dose calculation formalism, were calculated using Monte Carlo simulation. Results are compared with corresponding data published for the existing VariSource and microSelectron high dose rate sources. The dose-rate constant for the new Varian source was found to be equal to 1.101 +/- 0.006cGyh(-1) U(-1), compared to values of 1.043 +/- 0.005 and 1.116 +/- 0.006 cGyh(-1) U(-1) calculated for the existing VariSource and microSelectron sources, respectively. The radial dose functions between the three sources are similar with the exception of their values at radial distances very close to the source (r approximately 2 mm) where differences of approximately 3% are observed. The new Varian source demonstrates a smaller anisotropy relative to the existing VariSource source design for polar angles close to the source longitudinal axis, due to its smaller active core length.

An analytical Monte Carlo simulation code has been used to perform dosimetry calculations around an 192Ir high dose-rate brachytherapy source utilized in the widely used microSelectron afterloaded system. Radial dose functions, dose rate constant and anisotropy functions, utilized in the AAPM Task Group 43 dose estimation formalism, have been calculated. In addition, measurements of anisotropy functions using LiF TLD-100 rods have been performed in a polystyrene phantom to support our Monte Carlo calculations. The energy dependence of LiF TLD response was investigated over the whole range of measurement distances and angles. TLD measurements and Monte Carlo calculations are in agreement to each other and agree with published data. The influence of phantom dimensions on calculations was also investigated. Radial dose functions were found to depend significantly on phantom dimensions at radial distances near phantom edges. Deviations of up to 25% are observed at these distances due to the lack of full scattering conditions, indicating that body dimensions should be taken into account in treatment planning when the absorbed dose is calculated near body edges. On the other hand, anisotropy functions do not demonstrate a strong dependence on phantom dimensions. However, these functions depend on radial distance at angles close to the longitudinal axis of the source, where deviations of up to 20% are observed.

New composition polymer gels, the N-vinylpyrrolidone argon (VIPAR) gels, were developed and investigated as MRI dosimeters. VIPAR gels were irradiated in the dose range of 0-12 Gy by a 6 MV x-ray linear accelerator and MR-scanned in a 1.5 T magnetic resonance imager. A linear relationship was found between absorbed dose and spin spin relaxation rate R2. The dose sensitivity was found to be approximately 0.1 s(-1) Gy(-1) for a gel composition of 4% w/w in N-vinylpyrrolidone, 4% w/w in N,N'-methylene-bisacrylamide, 5% w/w in gelatine type A and 87% w/w in water. This dose sensitivity was stable with time and did not deteriorate even when a boost radiation dose of 2.5 Gy was applied 15 days after the first irradiation. Good reproducibility of these results was observed when a new batch of gels was produced and used for corresponding measurements and analysis.