title: Feasibility evaluation of diffusion-weighted imaging using an integrated MRI-radiotherapy system for response assessment to neoadjuvant therapy in rectal cancer.
abstract: OBJECTIVE
  To evaluate the feasibility of on-board diffusion-weighted imaging (DWI) with an integrated low-field MRI radiotherapy system to assess responses to neoadjuvant chemoradiation (NAC) in rectal cancer.
  
  
  METHODS
  A spin echo-based planar imaging diffusion sequence on a 0.35-T MRI radiotherapy system was acquired over the course of NAC. The apparent diffusion coefficients (ADCs) from the tumour regions of interest (ROIs) were calculated. A functional diffusion map (fDM) was created showing a pixelwise ADC analysis of the ROI over the course of treatment. Surgical pathology was correlated with ADC data.
  
  
  RESULTS
  Consecutive patients treated on a 0.35-T MRI radiotherapy system were evaluated. Patient A had the worst pathological response to NAC with a tumour regression score of 1 and was the only patient with a negative slope in the change of ADC values over the entire course of NAC, and during both the first and second half of NAC. The fDM from the first half of NAC for Patient A showed discrete dark areas in the tumour ROI, reflecting subregions with decreasing ADC values during NAC. Patient C had the most favourable pathological response to NAC with a Grade 3 response and was the only patient who had an increase in the slope in the change of ADC values from the first to the second half of NAC.
  
  
  CONCLUSIONS
  DWI using a low-field MRI radiotherapy system for evaluating the responses to NAC is feasible. Advances in knowledge: ADC values obtained using a 0.35-T MRI radiotherapy system over the course of NAC for rectal cancer correlate with pathological responses.
authors.affiliation: 1 Department of Radiation Oncology, University of California, Los Angeles, CA, USA.
authors.forename: Narek
authors.initials: N
authors.lastname: Shaverdian
authors.affiliation: 1 Department of Radiation Oncology, University of California, Los Angeles, CA, USA.
authors.forename: Yingli
authors.initials: Y
authors.lastname: Yang
authors.affiliation: 2 Department of Radiological Sciences, University of California, Los Angeles, CA, USA.
authors.forename: Peng
authors.initials: P
authors.lastname: Hu
authors.affiliation: 3 Department of Pathology and Laboratory Medicine, University of California, Los Angeles, CA, USA.
authors.forename: Steven
authors.initials: S
authors.lastname: Hart
authors.affiliation: 1 Department of Radiation Oncology, University of California, Los Angeles, CA, USA.
authors.forename: Ke
authors.initials: K
authors.lastname: Sheng
authors.affiliation: 1 Department of Radiation Oncology, University of California, Los Angeles, CA, USA.
authors.forename: James
authors.initials: J
authors.lastname: Lamb
authors.affiliation: 1 Department of Radiation Oncology, University of California, Los Angeles, CA, USA.
authors.forename: Minsong
authors.initials: M
authors.lastname: Cao
authors.affiliation: 1 Department of Radiation Oncology, University of California, Los Angeles, CA, USA.
authors.forename: Nzhde
authors.initials: N
authors.lastname: Agazaryan
authors.affiliation: 1 Department of Radiation Oncology, University of California, Los Angeles, CA, USA.
authors.forename: David
authors.initials: D
authors.lastname: Thomas
authors.affiliation: 1 Department of Radiation Oncology, University of California, Los Angeles, CA, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Steinberg
authors.affiliation: 1 Department of Radiation Oncology, University of California, Los Angeles, CA, USA.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Low
authors.affiliation: 1 Department of Radiation Oncology, University of California, Los Angeles, CA, USA.
authors.forename: Percy
authors.initials: P
authors.lastname: Lee
mesh_terms: D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D017352:Echo-Planar Imaging / Q000379:methods; D005240:Feasibility Studies; D006801:Humans; D053783:Magnetic Resonance Imaging, Interventional / Q000379:methods*; D020360:Neoadjuvant Therapy / Q000379:methods*; D012004:Rectal Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D012007:Rectum / Q000000981:diagnostic imaging / Q000528:radiation effects; D016896:Treatment Outcome