The Relationship with Radiation Pneumonitis Followed By Stereotactic Body Radiotherapy and Emphysema Evaluated By CT

Abstract

was equal to the GTV. The internal target volume (ITV) was derived from the GTV delineations on a maximum intensity projection. The SBRT was delivery to respiratory movement using image-guided radiotherapy (IGRT). Dose volume histogram in the exhalation phase CT was analyzed using a treatment planning system with an anisotropic analytical algorithm. Tumors were divided into two groups by location: in lung field (lowdensity) and on chest wall (high-density) groups. The volumetric dose differences between the GTV and PTV were assessed in both groups. Local control rates of the doses to the GTV and PTV were compared. Results: Seventy-nine patients' dose-volume histograms were analyzed. The median patient age was 77 (range: 29e95) years (51 male, 28 female patients). Sixty-two and 17 patients received SBRT doses of 50 and 60 Gy respectively, in 5 fractions. The actuarial 3-year local control rate was 80.1% (95% confidence interval: 65.9e88.8), during the median observation period was 25.9 (range: 6.2e106.7) months. All volumetric doses that indicated a difference between the GTV and the PTV were significantly higher in the lung field than on the chest wall (p < 0.01). The homogeneity index (HI) of the PTV in lung field was significantly higher than that on chest wall (p Z 0.03), but the HI differences in the GTV were not significant. Local control was only significantly higher when 50% of the GTV (D50 %) was prescribed 100 Gy 10 (biological equivalent dose, ab Z 10 Gy) and more (p Z 0.008). The local control rates were not significant for the GTV D98 % (p Z 0.06), PTV D98 % (p Z 0.11), or PTV D50 % (p Z 0.06). The GTV D50 % [Hazard ratio (HR) Z 0.25, p Z 0.04] and GTV volume (HR Z 4.26, p Z 0.04) were significant prognostic factors for local control, but the results for PTV D50 % were not significant by multivariate analysis. Conclusion: The dose differences between the GTV and the PTV were significant according to tumor location. The prescribed dose to the GTV had more impact on local control than that to the PTV. A detailed volumetric description of the GTV is needed to achieve optimal local control of stage I NSCLC.