title: Tumor volume changes on serial imaging with megavoltage CT for non-small-cell lung cancer during intensity-modulated radiotherapy: how reliable, consistent, and meaningful is the effect?
abstract: OBJECTIVE
  Adaptive radiotherapy allows treatment plan modification based on data obtained during treatment. Assessing volume changes during treatment is now possible with intratreatment imaging capabilities on radiotherapy devices. This study assesses non-small-cell lung cancer (NSCLC) volume changes during treatment with conformal intensity-modulated radiotherapy by evaluating serial megavoltage computed tomography (MVCT) scans, with a specific emphasis on the frequency, reliability, and meaningfulness of these changes.
  
  
  METHODS
  Megavoltage CTs were retrospectively reviewed for 25 patients treated with the TomoTherapy Hi-Art system at the University of Wisconsin. Twenty-one patients received definitive radiotherapy, 4 with extracranial stereotactic radioablation (60 Gy in five fractions) and 17 on a dose-per-fraction escalation protocol (57-80.5 Gy in 25 fractions). Four patients were treated palliatively (22-30 Gy in 8 to 10 fractions). Gross tumor volumes were contoured on serial MVCTs at weekly intervals. Each patient had 4 to 25 scans, including at least one at the beginning, midway, and one at the end of treatment.
  
  
  RESULTS
  At completion of treatment, no patient demonstrated a complete response. Partial response occurred in 3 (12%) and marginal response was noted in 5 (20%). The remaining 17 patients (68%) showed stable disease. The minimum "scorable threshold" for volume discrepancy between scans to account for interscan assessment variability was set at >25% volume change; 10 patients (40%) had >25% tumor regression. None of the patients treated ablatively or palliatively showed tumor regression during treatment.
  
  
  CONCLUSIONS
  Although gross tumor regression during treatment may be objectively measured using MVCTs, substantial volumetric decrease occurs only in a minority. The clinical significance of this regression is questionable, because there is no way to document histologic tumor clearance, and therefore field reductions during radiotherapy cannot be recommended.
authors.affiliation: Department of Human Oncology, University of Wisconsin School of Medicine and Public Health, Madison, WI 53792, USA.
authors.forename: Malika L
authors.initials: ML
authors.lastname: Siker
authors.forename: Wolfgang A
authors.initials: WA
authors.lastname: Tomé
authors.forename: Minesh P
authors.initials: MP
authors.lastname: Mehta
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D011879:Radiotherapy Dosage; D011881:Radiotherapy, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated; D012074:Remission Induction; D012189:Retrospective Studies; D013238:Stereotaxic Techniques; D014057:Tomography, X-Ray Computed / Q000379:methods; D047368:Tumor Burden