title: Magnetic Resonance-Guided High-Intensity Focused Ultrasound Hyperthermia for Recurrent Rectal Cancer: MR Thermometry Evaluation and Preclinical Validation.
abstract: To evaluate the feasibility of magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) mild hyperthermia in deep tissue targets for enhancing radiation therapy and chemotherapy in the context of recurrent rectal cancer. A preclinical study was performed to evaluate the safety and performance of MR-HIFU mild hyperthermia. A prospective imaging study was performed in volunteers with rectal cancer to evaluate MR thermometry quality near the rectum and accessibility of rectal tumors using MR-HIFU.
  
  
  
  Mild hyperthermia was performed in pig thigh (9 sonications, 6 pigs) using a clinical MR-HIFU system. Targets near the rectal wall and deep thigh were evaluated. Thermal maps obtained in 6 planes every 3.2 seconds were used to control sonications in 18-mm diameter treatment regions at temperatures of 42°C to 42.5°C for 10 to 60 minutes. Volunteer imaging-only studies to assess the quality of MR thermometry (without heating) were approved by the institutional research ethics board. Anatomic and MR thermometry images were acquired in consenting volunteers with rectal cancer. In 3 of 6 study participants, rectal filling with saline was used to reduce motion-related MR thermometry artifacts near the tumor.
  
  
  
  In pigs, mean target temperature matched the desired hyperthermia temperature within 0.2°C; temporal standard deviation ≤0.5°C. With optimized control thresholds, no undesired tissue damage was observed. In human volunteers, MR temperature measurements had adequate precision and stability, especially when rectal filling was used to reduce bowel motion.
  
  
  
  In pigs, MR-HIFU can safely deliver mild hyperthermia (41°C-43°C) to a targeted volume for 30 minutes. In humans, careful patient selection and preparation will enable adequate targeting for recurrent rectal cancers and sufficient MR temperature mapping stability to control mild hyperthermia. These results enable human trials of MR-HIFU hyperthermia.
authors.affiliation: Department of Radiation Oncology, Sunnybrook Health Sciences Centre and the University of Toronto, Toronto, Ontario, Canada; Physical Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada. Electronic address: William.Chu@sunnybrook.ca.
authors.forename: William
authors.initials: W
authors.lastname: Chu
authors.affiliation: Clinical Sites Research Program, Philips Research, Cambridge, Massachusetts.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Staruch
authors.affiliation: Thunder Bay Regional Research Institute, Thunder Bay, Ontario, Canada; Physics and Electrical Engineering, Lakehead University, Thunder Bay, Ontario, Canada.
authors.forename: Samuel
authors.initials: S
authors.lastname: Pichardo
authors.affiliation: MR Therapy, Philips Healthcare, Vantaa, Finland.
authors.forename: Matti
authors.initials: M
authors.lastname: Tillander
authors.affiliation: MR Therapy, Philips Healthcare, Vantaa, Finland.
authors.forename: Max O
authors.initials: MO
authors.lastname: Köhler
authors.affiliation: Physical Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada.
authors.forename: Yuexi
authors.initials: Y
authors.lastname: Huang
authors.affiliation: MR Therapy, Philips Healthcare, Vantaa, Finland.
authors.forename: Mika
authors.initials: M
authors.lastname: Ylihautala
authors.affiliation: Department of Radiation Oncology, Sunnybrook Health Sciences Centre and the University of Toronto, Toronto, Ontario, Canada.
authors.forename: Merrylee
authors.initials: M
authors.lastname: McGuffin
authors.affiliation: Department of Radiation Oncology, Sunnybrook Health Sciences Centre and the University of Toronto, Toronto, Ontario, Canada; Physical Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada.
authors.forename: Gregory
authors.initials: G
authors.lastname: Czarnota
authors.affiliation: Physical Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada.
authors.forename: Kullervo
authors.initials: K
authors.lastname: Hynynen
mesh_terms: D000818:Animals; D057086:High-Intensity Focused Ultrasound Ablation / Q000379:methods*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009364:Neoplasm Recurrence, Local / Q000000981:diagnostic imaging / Q000628:therapy*; D012004:Rectal Neoplasms / Q000000981:diagnostic imaging / Q000628:therapy*; D013552:Swine; D062125:Thermometry