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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
- 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): D. Ionascu
- Abstract
- Presentation
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.Only Members that have purchased this event or have registered via an access code will be able to view this content. To view this presentation, please login, select "Add to Cart" and proceed to checkout. If you would like to become a member of IASLC, please click here.
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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)
17:00 - 17:05 | Author(s): D. Ionascu
- Abstract
- Presentation
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 1Conclusion
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.Only Members that have purchased this event or have registered via an access code will be able to view this content. To view this presentation, please login, select "Add to Cart" and proceed to checkout. If you would like to become a member of IASLC, please click here.
