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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
  • Moderators:M. Zwitter, S.K. Vinod
  • Coordinates: 10/29/2013, 16:15 - 17:45, Bayside 204 A+B, Level 2

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    MO17.10 - Late radiologic change after stereotactic ablative radiotherapy for early stage lung cancer: A comparison between fixed-beam versus arc delivery techniques (ID 1405)

    17:10 - 17:15  |  Author(s): P.M. Van De Ven
    • Abstract
    • Presentation
    • Slides

    Background
    Treatment-related radiologic change occurs commonly following stereotactic ablative radiotherapy (SABR) and often confound the interpretation of follow-up CT scans. SABR is frequently delivered using both fixed-beams and rotational-arcs, resulting in different dose distributions and it is unclear how this influences radiological change. We studied the morphology, timing and severity of radiologic change after both delivery techniques.

    Methods
    Twenty-nine patients with early stage non-small cell lung cancer receiving SABR by arc delivery, without clinical evidence of local recurrence, and a follow-up of more than two years, were assessed using a published scoring system [Dahele M, JTO 2011]. Here, the morphology of acute (within six months) radiologic change was characterized between ‘patchy (less than 5 cm) ground glass opacity’, ‘patchy consolidation’, ‘diffuse (more than 5 cm) ground glass opacity’, or ‘diffuse consolidation’. The late (after 6 months) morphology was characterized between ‘scar-like’, ‘mass-like’ and ‘modified conventional’. Additionally the severity of radiologic change was scored as ‘pronounced’ (more than expected), ‘expected’, ‘mild’ (less than expected) and none. These outcomes were compared to 54 patients treated with SABR by fixed-beam delivery, who we previously assessed using the same scoring system.

    Results
    Baseline characteristics of the arc and fixed-beam cohorts were well matched and respective median follow-ups were no different, 31.7 vs. 28.4 months (p=0.20). Patients treated by arc delivery trended towards being more likely to have any radiologic change (p=0.06). This was strongly time-dependent (p<0.001) and more pronounced early, as by two years radiologic changes were almost universally present irrespective of delivery technique. Figure 1 shows the morphology of these changes with time. Acute changes were not technique dependent (p=0.23). After six months, arc delivery resulted in a modified-conventional morphology throughout follow-up, while fixed-beam delivery resulted in an increasing probability of scar-like or mass-like morphologies. The predicted probabilities of a modified-conventional pattern following SABR by arc and fixed-beam delivery were 96.3% vs. 68.9% (p<0.001) respectively. Following arc delivery, radiologic changes were more likely to be scored as pronounced or expected (p=0.009) than mild or none, a finding that became more evident with longer follow-up (p=0.014). The predicted probability of pronounced or expected changes two years following arc or fixed-beam delivery was 83.1% and 26.2%, respectively. Figure 1

    Conclusion
    Patterns of radiologic change more than six months post-SABR are influenced by delivery technique. Diagnostic algorithms used to differentiate suspected local recurrence and benign change should therefore consider the delivery technique used.

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