title: Quantitative ultrasound characterization of responses to radiotherapy in cancer mouse models.
abstract: OBJECTIVE
  Currently, no imaging modality is used routinely to assess tumor responses to radiotherapy within hours to days after the delivery of treatment. In this study, we show the application of quantitative ultrasound methods to characterize tumor responses to cancer radiotherapy in vivo, as early as 24 hours after treatment administration.
  
  
  METHODS
  Three mouse models of head and neck cancer were exposed to radiation doses of 0, 2, 4, and 8 Gray. Data were collected with an ultrasound scanner using frequencies of 10 to 30 MHz. Ultrasound estimates calculated from normalized power spectra and parametric images (spatial maps of local estimates of ultrasound parameters) were used as indicators of response.
  
  
  RESULTS
  Two of the mouse models (FaDu and C666-1) exhibited large hyperechoic regions at 24 hours after radiotherapy. The ultrasound integrated backscatter increased by 6.5 to 8.2 dB (P < 0.001) and the spectral slopes increased from 0.77 to 0.90 dB/MHz for the C666-1 tumors and from 0.54 to 0.78 dB/MHz for the FaDu tumors (P < 0.05), in these regions compared with preirradiated tumors. The hyperechoic regions in the ultrasound images corresponded in histology to areas of cell death. Parametric images could discern the tumor regions that responded to treatment. The other cancer mouse model (Hep-2) was resistant to radiotherapy.
  
  
  CONCLUSIONS
  The results indicate that cell structural changes after radiotherapy have a significant influence on ultrasound spectral parameters. This provides a foundation for future investigations regarding the use of ultrasound in cancer patients to individualize treatments noninvasively based on their responses to specific interventions.
authors.affiliation: Department of Medical Biophysics, University of Toronto, Sunnybrook Health Sciences Centre, and Department of Physics, Ryerson University, Toronto, Ontario, Canada. Roxana.Vlad@sunnybrook.ca
authors.forename: Roxana M
authors.initials: RM
authors.lastname: Vlad
authors.forename: Sebastian
authors.initials: S
authors.lastname: Brand
authors.forename: Anoja
authors.initials: A
authors.lastname: Giles
authors.forename: Michael C
authors.initials: MC
authors.lastname: Kolios
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Czarnota
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D006801:Humans; D020287:In Situ Nick-End Labeling; D008297:Male; D051379:Mice; D009368:Neoplasm Transplantation; D009374:Neoplasms, Experimental / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D014183:Transplantation, Heterologous; D014463:Ultrasonography