title: Magnetic nanoparticles for interstitial thermotherapy--feasibility, tolerance and achieved temperatures.
abstract: BACKGROUND
  The concept of magnetic fluid hyperthermia is clinically evaluated after development of the whole body magnetic field applicator MFH 300F and the magnetofluid MFL 082AS. This new system for localized thermotherapy is suitable either for hyperthermia or thermoablation. The magnetic fluid, composed of iron oxide nanoparticles dispersed in water, must be distributed in the tumour and is subsequently heated by exposing to an alternating magnetic field in the applicator. We performed a feasibility study with 22 patients suffering from heavily pretreated recurrences of different tumour entities, where hyperthermia in conjunction with irradiation and/or chemotherapy was an option. The potential to estimate (by post-implantation analyses) and to achieve (by improving the technique) a satisfactory temperature distribution was evaluated in dependency on the implantation technique.
  
  
  METHODS
  Three implantation methods were established: Infiltration under CT fluoroscopy (group A), TRUS (transrectal ultrasound)--guided implantation with X-fluoroscopy (group B) and intra-operative infiltration under visual control (group C). In group A and B the distribution of the nanoparticles can be planned prior to implantation on the basis of three-dimensional image datasets. The specific absorption rates (SAR in W/kg) can be derived from the particle distribution imaged via CT together with the actual H-field strength (in kA/m). The temperature distribution in the tumour region is calculated using the bioheat-transfer equation assessing a mean perfusion value, which is determined by matching calculated temperatures to direct (invasive or endoluminal) temperature measurements in reference points in or near the target region.
  
  
  RESULTS
  Instillation of the magnetic fluid and the thermotherapy treatments were tolerated without or with only moderate side effects, respectively. Using tolerable H-field-strengths of 3.0-6.0 kA/m in the pelvis, up to 7.5 kA/m in the thoracic and neck region and >10.0 kA/m for the head, we achieved SAR of 60-380 W/kg in the target leading to a 40 degrees C heat-coverage of 86%. However, the coverage with > or =42 degrees C is unsatisfactory at present (30% of the target volume in group A and only 0.2% in group B).
  
  
  CONCLUSIONS
  Further improvement of the temperature distribution is required by refining the implantation techniques or simply by increasing the amount of nanofluid or elevation of the magnetic field strength. From the actual nanoparticle distribution and derived temperatures we can extrapolate, that already a moderate increase of the H-field by only 2 kA/m would significantly improve the 42 degrees C coverage towards 100% (98%). This illustrates the great potential of the nanofluid-based heating technology.
authors: Clinic for Radiotherapy, Charité - Universitätsmedizin Berlin, Berlin, Germany. peter.wust@charite.de
authors: Peter
authors: P
authors: Wust
authors: Uwe
authors: U
authors: Gneveckow
authors: Manfred
authors: M
authors: Johannsen
authors: Dirk
authors: D
authors: Böhmer
authors: Thomas
authors: T
authors: Henkel
authors: Frank
authors: F
authors: Kahmann
authors: Jalid
authors: J
authors: Sehouli
authors: Roland
authors: R
authors: Felix
authors: Jens
authors: J
authors: Ricke
authors: Andreas
authors: A
authors: Jordan
mesh_terms: D000328:Adult; D004574:Electromagnetic Fields; D005240:Feasibility Studies; D006801:Humans; D006979:Hyperthermia, Induced / Q000295:instrumentation / Q000379:methods*; D053768:Metal Nanoparticles / Q000627:therapeutic use*; D016879:Salvage Therapy / Q000295:instrumentation / Q000379:methods*