Background and purpose: MRI ferrous sulphate gel dosimetry has proven to be a valuable method for assessment of dose delivered in teletherapy. The intention of this study was to investigate ferrous sulphate gel as a possible dosimeter for intracavitary brachytherapy applications.
Materials and methods: A plastic duplicate of a cervix ring applicator set was submerged in Fe2(+)-infused gelatin gel. The gel was subsequently irradiated by a stepwise moving 192Ir source, using automatic afterloading equipment (Microselectron, Nucletron-Oldelft International BV, Veenendaal, The Netherlands). A 3D dose distribution was reconstructed from MR images of the gel.
Results: The gel dose measurements were found to be of the same accuracy as TLD measurements. Isodose curves based on gel dosimetry and isodose curves computed by a dose planning system were generally less than 2 mm apart. MR images showing the position of the applicator set in a patient during treatment were used to obtain images describing patient anatomy in the sagittal and ring planes of the applicator set. Isodose curves computed from the gel measurements were then superimposed on these images, illustrating one possible way of linking dosimetrical and anatomical data.
Conclusions: Our study shows that MRI ferrous sulphate gel dosimetry is a useful tool for studies of dose distributions in brachytherapy and their relation to critical organs. Possible improvements of the gel dosimeter lie in reducing the diffusion of ferric ions and increasing the radiation sensitivity of the gel.