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S. Senthi



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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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      MO17.10 - 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): S. Senthi

      • 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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    O10 - Stereotactic Ablative Body Radiotherapy (ID 104)

    • Event: WCLC 2013
    • Type: Oral Abstract Session
    • Track: Radiation Oncology + Radiotherapy
    • Presentations: 1
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      O10.05 - Blinded assessment of radiological changes after stereotactic ablative radiotherapy for early-stage lung cancer: local recurrences versus fibrosis. (ID 1416)

      17:00 - 17:10  |  Author(s): S. Senthi

      • Abstract
      • Presentation
      • Slides

      Background
      Stereotactic ablative radiotherapy (SABR) is now a guideline-recommended treatment for early-stage lung cancer (ES-NSCLC), achieving 5-year local control rates of approximately 10%. The timely detection of local recurrence (LR) and early salvage following SABR is impaired by fibrotic changes, which occur commonly. Seven high-risk CT features (HRFs) that suggest LR include; enlarging opacity, cranio-caudal growth, sequential enlarging opacity, enlarging opacity after 12 months, bulging margin, loss of linear margin and loss of air bronchograms. We validated these, performing blinded clinician assessment in patients with and without LR.

      Methods
      ES-NSCLC patients treated with SABR, who developed pathology-proven LR (n=12), were matched 1:2 to patients without clinical LR (n=24), based on tumor location, SABR fractionation, PTV size and follow-up duration. Three radiation oncologists assessed serial follow-up CT images for HRFs, while blinded to outcomes. The sensitivity and specificity of HRFs and combinations of these were determined.

      Results
      The median follow-up was 24 months (range 6-67) and both cohorts were well matched. All HRFs were significantly associated with LR (p≤0.002), Table 1. The best individual predictor of LR was opacity enlargement after 12 months (100% sensitivity, 83% specificity), however this was detected slowest, at a median 22 months. The earliest HRF detected was cranio-caudal growth detected at a median 13 months. The HRFs enlarging opacity and cranio-caudal growth were each detected at least 3 months prior to the actual diagnosis of LR 42% of the time. The odds of LR increased 4-fold for each additional HRF detected (p<0.001). The sensitivity and specificity of detecting multiple HRFs is shown in Table 2, with ≥3 HRFs being the best predictor of LR (sensitivity 92%, specificity 92%). Figure 1 Figure 2

      Conclusion
      LR following SABR can be accurately predicted by the presence of HRFs on surveillance CT scans. This approach may reduce unnecessary confirmatory procedures, and facilitate earlier salvage treatment.

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