Dose uniformity of ferromagnetic seed implants in tissue with discrete vasculature: a numerical study on the impact of seed characteristics and implantation techniques

Abstract

The results from simulations with a new three-dimensional treatment planning system for interstitial hyperthermia with ferromagnetic seeds are presented in this study. The thermal model incorporates discrete vessel structures as well as a heat sink and enhanced thermal conductivity. Both the discrete vessels and the ferroseeds are described parametrically in separate calculation spaces. This parametric description has the advantage of an arbitrary orientation of the structures within the tissue grid, easy manipulation of the structures and independence from the resolution of the tissue voxels (tissue calculation space). The power absorption of the self-regulating seeds is according to empirical data. The thermal effects of an unlimited number of thin layers surrounding the seed (coatings, catheters) can be modelled. The initial calculations have been performed for an array of 12 identical ferromagnetic seeds in a tissue volume with a computer generated artificial vessel network spanning four vessel generations in both the arterial and venous tree. The heterogeneously distributed large isolated vessels impair the temperature distribution significantly, indicating the limited accuracy of continuum models. Simulations with different types of ferromagnetic seeds have confirmed that the efforts of previous studies to optimize the self-regulating temperature control and the implantation techniques of the ferroseeds will improve the homogeneity of the temperature distribution in the target volume. Multifilament seeds implanted in brachytherapy needles and tubular seeds appear to be the most favourable configurations. The division of long seeds into shorter segments with the appropriate Curie temperature will further improve the homogeneity of the temperature distribution without increasing the average temperature in the volume of interest. Given the proper thermal tissue data, the model presented in this study will prove to be a useful tool in making choices for the implant geometry, seed spacing and Curie temperature.

Magnetic Heating by Tunable Arrays of Nanoparticles in Cancer Therapy

“…• C. It is important to note that the profiles are convex ones and there are no relatively low temperatures further away from the magnetic needles similarly, as it was found in the hyperthermia treatments using macroscopic ferromagnetic seeds in [28].…”

“…• C was found in the vicinity the large vessels during interstitial hyperthermia using ferromagnetic seeds (inter-seeds spacing 13 mm) in [28]. Tumor blood perfusion could be adjusted with the goal to obtain the needed uniformity and rate of temperature increase in hyperthermia treatments.…”

Feasibility study of high-temperature thermoseed inductive hyperthermia in melanoma treatment

“…Basic research mainly focused on heat generation by different materials (19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33), thermoseed processing methods (34,35), heating coil designs (36,37), improving uniform temperature distribution (38)(39)(40)(41)(42)(43)(44)(45)(46)(47), and the in vivo effects on animals (12,21,25,28,30,32,33,36,38,41,(48)(49)(50)(51). Clinical research mainly focused on intracranial tumors (52,53), prostate cancer (54)(55)(56)57), and some other tumors …”

Magnetic Nanoparticles in Cancer Diagnosis and Hyperthermic Treatment

“…Techniques such as nanoparticle-mediated laser energy absorption [48,49], microwave absorption [50,51], enhanced radiation absorption [52], and magnetic-field energy absorption [53] are a few examples of studies demonstrating nanoparticle-mediated energy transfer. Magnetic field energy absorption approaches use a wide variety of mediator materials from macroscopic "needles" to nanoparticles [54][55][56]. This review will focus on energy transfer mediated by magnetic nanoparticles.…”

“…A comprehensive historical review was presented by Seegenschmiedt and Vernon [59]. Methods varied widely from laser-induced hyperthermia [60][61][62] to microwave-induced [63][64][65][66] and hysteretic (magnetic) heating using both large implanted "needles" or "rods" [54][55][56], or nanoparticles [53,67,68].…”