title: Toward online adaptive hyperthermia treatment planning: correlation between measured and simulated specific absorption rate changes caused by phase steering in patients.
abstract: OBJECTIVE
  Hyperthermia is the clinical application of heat, in which tumor temperatures are raised to 40°C to 45°C. This proven radiation and chemosensitizer significantly improves clinical outcome for several tumor sites. Earlier studies of the use of pre-treatment planning for hyperthermia showed good qualitative but disappointing quantitative reliability. The purpose of this study was to investigate whether hyperthermia treatment planning (HTP) can be used more reliably for online adaptive treatment planning during locoregional hyperthermia treatments.
  
  
  METHODS
  This study included 78 treatment sessions for 15 patients with non-muscle-invasive bladder cancer. At the start of treatments, temperature rise measurements were performed with 3 different antenna settings optimized for each patient, from which the absorbed power (specific absorption rate [SAR]) was derived. HTP was performed based on a computed tomography (CT) scan in treatment position with the bladder catheter in situ. The SAR along the thermocouple tracks was extracted from the simulated SAR distributions. Correlations between measured and simulated (average) SAR values were determined. To evaluate phase steering, correlations between the changes in simulated and measured SAR values averaged over the thermocouple probe were determined for all 3 combinations of antenna settings.
  
  
  RESULTS
  For 42% of the individual treatment sessions, the correlation coefficient between measured and simulated SAR profiles was higher than 0.5, whereas 58% showed a weak correlation (R of <0.5). The overall correlation coefficient between measured and simulated average SAR was weak (R=0.31; P<.001). The measured and simulated changes in average SAR after adapting antenna settings correlated much better (R=0.70; P<.001). The ratio between the measured and simulated quotients of maximum and average SARs was 1.03 ± 0.26 (mean ± SD), indicating that HTP can also correctly predict the relative amplitude of SAR peaks.
  
  
  CONCLUSIONS
  HTP can correctly predict SAR changes after adapting antenna settings during hyperthermia treatments. This allows online adaptive treatment planning, assisting the operator in determining antenna settings resulting in increased tumor temperatures.
authors: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands. Electronic address: H.P.Kok@amc.uva.nl.
authors: H Petra
authors: HP
authors: Kok
authors: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands; Department of Civil Engineering and Computer Science, University of Rome Tor Vergata, Rome, Italy.
authors: Silvia
authors: S
authors: Ciampa
authors: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
authors: Rianne
authors: R
authors: de Kroon-Oldenhof
authors: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
authors: Eva J
authors: EJ
authors: Steggerda-Carvalho
authors: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
authors: Gerard
authors: G
authors: van Stam
authors: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
authors: Paul J
authors: PJ
authors: Zum Vörde Sive Vörding
authors: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
authors: Lukas J A
authors: LJ
authors: Stalpers
authors: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
authors: Elisabeth D
authors: ED
authors: Geijsen
authors: Department of Civil Engineering and Computer Science, University of Rome Tor Vergata, Rome, Italy.
authors: Fernando
authors: F
authors: Bardati
authors: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
authors: Arjan
authors: A
authors: Bel
authors: Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
authors: Johannes
authors: J
authors: Crezee
mesh_terms: D000465:Algorithms; D000903:Antibiotics, Antineoplastic / Q000008:administration & dosage; D006801:Humans; D006979:Hyperthermia, Induced / Q000379:methods*; D008297:Male; D016685:Mitomycin / Q000008:administration & dosage; D011859:Radiography; D012189:Retrospective Studies; D013813:Therapy, Computer-Assisted / Q000379:methods*; D001749:Urinary Bladder Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000628:therapy*
chemical_list: D000903:Antibiotics, Antineoplastic; D016685:Mitomycin