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B. Sawyer

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    MO17 - Radiotherapy I: Stereotactic Ablative Body Radiotherapy (ID 106)

    • Event: WCLC 2013
    • Type: Mini Oral Abstract Session
    • Track: Radiation Oncology + Radiotherapy
    • Presentations: 1
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      MO17.01 - Response assessment of Stereotactic Ablative Body Radiotherapy (SABR) for pulmonary metastases: utility of 4D-FDG-PET and CT perfusion (ID 2225)

      16:15 - 17:45  |  Author(s): B. Sawyer

      • Abstract
      • Presentation
      • Slides

      Response assessment using conventional RECIST criteria after SABR of lung targets can be confounded by fibrotic response. The purpose of this study was to evaluate the utility of 4D-FDG-PET/CT and CT perfusion scans in the response assessment of single fraction SABR for inoperable pulmonary oligometastases.

      This is a prospective ethics approved clinical study of patients undergoing single fraction SABR with 26Gy for pulmonary metastases. Eligible patients had 1-2 metastases with no extrathoracic disease on staging FDG-PET. Serial 3D / 4D-FDG-PET and CT perfusion studies were performed at baseline, 14 days and 70 days after therapy. Two radiologists independently reported CT perfusion scans.

      At a median follow-up of 16 months (range 3-27), 10 patients with 13 metastases received SABR. A further 7 patients (41%) were screened from the study due to interval progression of disease between the time of the original FDG-PET and trial 4D-FDG-PET / perfusion CT. The mean time between the original FDG-PET and trial scans was 62 days. No patient progressed locally, 7/10 patients progressed distantly of which 2/7 received subsequent SABR. At the end of study period, 5/10 patients are alive without disease. The median progression free survival was 14 months. The change in SUVmax from baseline was higher on 3D than 4D-PET by a mean of 20.6% (range 0.2%-47.2%) at 14 days and 14.8% (range 0-37.8%) at 70 days. Overall, the SUVmax increased at 14 days (mean 104.9%, p<0.01) and decreased at 70 days (mean=55.5%, p<0.01), despite persistent morphological lesions on the concurrent late timepoint CT. There was strong level of inter-observer agreement of CT perfusion interpretation with a median intraclass correlation coefficient of 89% (range 57%-98%). Perfusion parameters of Time to Peak Blood Flow and Blood Volume showed a median increase of 18.8% and 23.0% at 2 weeks post-therapy and decreased below baseline by a median 7.0% and 14.0% at 70 days (non-significant).

      High rates of interval progression between staging scans indicates a need to expedite management of oligometastases in a timely fashion. Increased tumour perfusion and FDG-PET intensity at 2 weeks post-RT is likely due to an inflammatory response to large single dose SABR. Late PET response was associated with tumour control despite CT apparent morphological lesions. Conventional 3D PET may overestimate change in PET intensity post SABR as compared to 4D PET. These findings, in particular CT perfusion findings, require a larger patient cohort for validation.

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