Interstitial hyperthermia with PdNi thermoseeds

The objective of this study was to improve the temperature control of ferromagnetic seed implants aiming at a more homogeneous temperature distribution in the target volume. A metallurgical procedure was developed for the production of PdNi seeds with a sharp ferromagnetic transition at the Curie temperature. The heat production was improved by the development of seeds composed of a number of filaments with a smaller diameter. The catheters used for implantation of the seeds and possible air layers inside the catheters impair the thermal interaction between the seeds and the tissue. This interaction can be enhanced by inserting the seeds into metallic needles and by filling them with water. As an alternative, one can place tubular seeds on the outside of a catheter or brachytherapy needle. This would also enable a simultaneous application of interstitial hyperthermia and interstitial radiotherapy. A 3‐D thermal treatment planning system developed at the University Hospital Utrecht was used to model the application of different types of seeds and implantation techniques in tissue with discrete vessel structures. The simulations confirmed the importance of a sharp ferromagnetic transition and good heat transfer from the seed to the tissue. They also indicated that the use of seeds with the appropriate Curie temperature could compensate for local hot or cold spots.