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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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    MO17.05 - Recurrence, Survival, and Toxicity after Stereotactic Lung Radiotherapy (SBRT) for Central versus Peripheral Stage I Non-Small Cell Lung Cancer (NSCLC): Results from an International Collaborative Research Group (ID 3436)

    16:35 - 16:40  |  Author(s): J. Belderbos
    • Abstract
    • Presentation
    • Slides

    Background
    SBRT is an accepted safe and effective treatment modality for peripheral (P) stage I NSCLC tumors. Concern of excessive toxicity, however, limits its use for central (C) tumors. This study evaluates outcomes and toxicities after cone-beam CT (CBCT) image-guided SBRT for central vs. peripheral NSCLC.

    Methods
    959 lung tumors were treated with lung SBRT from 1998-2012 at five international centers participating in the Elekta Collaborative Lung Research Group; 98% underwent online CBCT IGRT. 100 cases were classified as Central (C) and 869 Peripheral (P), defined as ≤2cm vs. >2cm from the proximal bronchial tree, respectively. Staging included chest CT and routine chemistry for all; 93% had PET staging (mean time PET to SBRT 6.4 weeks); 6% had mediastinal sampling (mediastinoscopy or endobronchial ultrasound). 61% had tumor biopsy (84% C vs. 59% P, p<0.001). 89% were medically inoperable with mean baseline FEV1 of 1.6L (63% of predicted) and mean baseline DLCO of 12.1 ml/min/mmHg (56% of predicted). Mean age was 74y (42-93) with a large range in ECOG performance status (27%; 47%; 23%; 26% for 0-3, respectively). Clinical stage was T1aN0 44%, T1bN0 30%, T2aN0 23%, T2bN0 32%. Mean tumor maximum dimension was 2.5cm (range 0.5-8.5cm); C tumors were larger (mean 3.lcm vs. 2.4 cm, p<0.001). Mean SBRT prescription dose was 51.5±6.4 Gy, with mean dose per fraction of 14.5±4.0 Gy in 3.9±1.5 fractions. Mean biological equivalent dose (BED) was 126.6±26.6 Gy, higher for P vs. C tumors (129.2 vs. 104.0 Gy, p<0.001. Chemotherapy was administered more for C (9%) than P tumors (2%), p<0.001. Groups were compared with t-test & chi-square. Competing risks analyses were used, accounting for the competing risk of death.

    Results
    Mean follow-up for all cases was 1.8y (0.1-7.7y; mean potential follow-up 3.4y), similar for C&P. C tumors had higher Local Failure (LF) (3y-LF 16.2%C vs. 5.9%P; 5y-LF 20.4%C vs. 8.3%P, p<0.001), similar regional nodal recurrences (RR) (3y-RR 12%C vs.12%P, p=0.69) and distant metastases (DM) (3y-DM 19%C vs 20%P, p=0.75), lower cause-specific survival (CSS) (3yr-CSS 75%C vs. 88%P, p<0.001), but similar overall survival (OS) (3y-OS 50%C vs. 51%P, p=0.70). Grade > 2 pneumonitis was higher for C tumors (8%C vs. 1%P, p<0.001). Incidence of grade 3 pneumonitis, chest wall pain/myositis, rib fracture, and skin dermatitis were rare (0.8%, 0.5%, 0.4%, 0.6% respectively for all) with no differences between C&P. No grade 4 toxicities were noted, though 2 cases (1C & 1P) of fatal pneumonitis were potentially attributable to SBRT. On multivariate analysis, BED (HR:0.975, p<0.001) predicted CSS, and both BED (HR:0.978, p=0.002) and baseline SUVmax (HR:1.04, p=0.001) predicted LF. Weeks from PET-staging until SBRT (HR:1.25, p=0.004) and the percent of lungs receiving >20 Gy (HR:1.063, p=0.001) were the strongest independent predictors of OS.

    Conclusion
    In this large data set, pneumonitis was higher for central tumors, but both central & peripheral SBRT were safe with similar overall and cause-specific survival. LF was higher for central tumors, which were larger, had higher baseline SUVmax, and received lower dose. Results of the ongoing RTOG 0813 dose-finding study for central tumors are awaited.

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