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A. Modh

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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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      MO17.09 - Dosimetric Predictors of Esophageal Toxicity after Stereotactic Body Radiotherapy for Central Lung Tumors (ID 1674)

      16:15 - 17:45  |  Author(s): A. Modh

      • Abstract
      • Presentation
      • Slides

      Stereotactic body radiotherapy (SBRT) is an effective treatment for early-stage non-small cell lung cancer (NSCLC) and lung metastases. However, increased toxicity has been observed for SBRT to lesions near the proximal airways or mediastinal structures. Reported toxicities have primarily pertained to pulmonary complications, but little is known about the risk for esophageal toxicity. Therefore, we sought to evaluate dosimetric predictors of esophageal toxicity in this patient cohort at our institution.

      We identified 125 patients who received SBRT for single lung tumors within 2 cm of the proximal bronchial tree (n=81) or whose planning target volume (PTV) intersected mediastinal structures (n=44). Ninety-one patients had primary NSCLC, 12 had recurrent NSCLC, and 22 had metastatic tumors involving the lung. Patients with prior thoracic radiotherapy were excluded. Toxicity was scored using the Common Terminology Criteria for Adverse Events v.4.0. Biological equivalent doses (BED) were calculated using the linear quadratic formula with either α/β=3 or 10 Gy. Dose-volume histogram variables for the esophagus (D~v~, minimum dose to the hottest volume v and V~d~, volume receiving doses greater than d) were then examined for all patients and correlation with toxicity was assessed using logistic regression. Log rank tests were performed using median splits for variables that were significant in logistic regression.

      With a median follow-up of 14.3 months, the overall rate of grade ≥2 esophageal toxicity was 12.8% (n=16), including two grade 3 events. The median prescription dose was 45Gy. The most common fractionation schemes were 45Gy in 5 fractions (n=56), 48Gy in 4 fractions (n=21), or 50Gy in 5 fractions (n=14). Highly significant logistic models were generated on the basis of D~3.5cc~, D~5cc~, and D~max ~(p<0.001). For a complication rate < 20%, D~3.5cc~ ≤ 29.4 Gy~10~, D~5cc~ ≤ 25.4 Gy~10~, and D~max~ ≤ 50.1 Gy~10~ was observed based on these models (BED~10~). Log rank tests showed that at 2 years, the probability of complication of those with a BED~10~ D~3.5cc~ > 16.6 Gy was 25% (p<0.001), D~5cc~ > 15.1 Gy was 26% (p<0.001), and a D~max~ > 29.6 Gy was 21% (p=0.032). The probability of complication for those with a D~3.5cc~, D~5cc~, and D~max~ (BED~10~) less than or equal to the above limits were 2%, 2% and 7%, respectively. The analysis was insensitive to α/β, and the same D~v~ variables were found to be significant using α/β =3.

      This is a novel quantitative analysis providing dose guidelines for significant esophagitis in the setting of SBRT. Dose to the hottest 3.5cc, 5cc and D~max~ were the best parameters for prediction of esophageal toxicity. Converting the BED~10~ limits to physical doses, D~3.5cc ~to the esophagus should be kept less than 18.3, 19.7 and 20.8 Gy for 3, 4, and 5 fractions, respectively, to keep the esophagitis rate < 20%. However, these guidelines must be weighed against clinical considerations and potential compromise of target coverage. This information will be valuable for treatment planning and identifying patients at risk for esophageal complications from SBRT.

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