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D. Ionascu



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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: 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)

      16:15 - 17:45  |  Author(s): D. Ionascu

      • 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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      MO17.08 - TCP modeling in Stereotactic Body Radiotherapy for early stage non small cell lung cancer: is a dose-volume effect present? (ID 2205)

      16:15 - 17:45  |  Author(s): D. Ionascu

      • Abstract
      • Presentation
      • Slides

      Background
      In early stage non-small cell lung cancer (NSCLC) stereotactic body radiotherapy (SBRT) has become standard of care for inoperable patients. Tumor size >3cm was reported to be a predictor of local recurrence (LR), suggesting a dose-volume effect. Recently, the dose effect relation was questioned[1]. We used a Tumor-Control-Probability (TCP) model on a large pooled multi-center cohort to test this.

      Methods
      850 patients were analyzed from our five institutes. Patients received a 4D CT-scan and plans were inversely optimized using advanced dose calculation algorithms. Treatment was delivered using online cone-beam CT guidance. Immobilization, margins, dose prescription and treatment planning was performed according to institute specific protocols. Median tumor diameter was 2.2 cm (range:0.7-8.0), median prescribed dose was 54 Gy (range:18-64) and median number of fractions were 3 (range:1-10). LRs were either biopsy proven or defined as a FDG-PET positive growing mass on CT-scan. The Web-Nahum TCP-model[2] was fitted to LR-data using maximum-likelihood estimation by optimizing its parameters: α representing the population-average radio-sensitivity, σ~α~ representing the population-variation in α and ρ the clonogen density. Input variables were the patient specific Gross Tumor Volume (estimated from the tumor diameter), for the dosimetric parameter PTV-D~min~, D~max~, D~mean~, D~1~, D~99~ were evaluated after conversion to Biological-Effective-Dose (BED) using the LQ-model with α/β=10Gy. We tested the optimized TCP model against a random model in which TCP was fixed independent of dose and volume. The optimal model was selected based on the Akaike-Information-Criterion (AIC).

      Results
      After a median follow up (FU) of 17 months (range:0-93), 43 LRs (5%) were diagnosed at 14 months FU (range:2-56), of which 25 tumors were biopsy proven and 18 recurrences diagnosed on PET-CT. The PTV-BED~mean~ based TCP model showed the best fit with parameters α=0.43Gy[-1] (CI:0.33–0.75) and σ~α~=0.17 Gy[-1] (CI:0.11–0.37). The model-fit was insensitive to ρ and set to literature values: 10[7]/cm[3]. The AIC of the optimal model was 12 units higher than the random model indicating a clear dose-volume-effect. At high PTV~mean~-BEDs, however, the volume effect is modest. Additionally, the AIC of the BED corrected model was 9.4 units higher than the BED uncorrected model. Figure 1

      Conclusion
      A dose-volume-effect relation in SBRT for early stage NSCLC for local control was derived in a large cohort of patients. This dose-effect relation requires validation in independent datasets and prospective trials. 1.van Baardwijk,Rad.Onc.,2012. 2.Web&Nahum,PMB,1993.

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