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P1.03 - Poster Session/ Treatment of Locoregional Disease – NSCLC (ID 212)
- Event: WCLC 2015
- Type: Poster
- Track: Treatment of Locoregional Disease – NSCLC
- Presentations: 1
- Coordinates: 9/07/2015, 09:30 - 17:00, Exhibit Hall (Hall B+C)
P1.03-022 - The Effect of Adaptive Planning on Target and Critical Structures During Radiation Treatment for Locally Advanced Lung Cancer (ID 1057)
09:30 - 17:00 | Author(s): E. Kucukmorkoc
Many patients with lung cancer have tumor changes like shrinkage, improvement in atelectasis or mediastinal replacement during radiotherapy. The aim of this study is to determine the dosimetric effects of repeated CT scanning and adaptive planning during intensity modulated radiotherapy (IMRT) on both target volumes and critical structures.
Patients treated with concurrent chemoradiation were included within the study. The initial IMRT planning (IMRT~initial~) was done on the primary CT and 4DCT scan using the ITV technique. The dose was prescribed to 66 Gy in 33 fractions. After the initiation of the study weekly cone beam CT (CBCT) images were obtained before treatment. The volumes were evaluated by the treating physician in terms of target volume changes or mediastinal replacement. When adequate change was distinguished on the CBCT images an adaptive CT (CT~adapt~) was obtained and the volumes were recontoured by the same physician and replanned by the same physicist (IMRT~adapt~). The calculated multileaf collimator (MLC) motion on IMRT~initial~ was transferred on CT~adapt ~and a recalculation was performed. The plan obtained was renamed as IMRT~transfer. ~The changes occurred in critical organs such as lung, spinal cord, heart, esophagus and the target volumes were obtained and compared with IMRT~initial ~using paired samples t-test.
A total of 15 patients were included in the analysis. The mean PTV volumes on initial and adaptive planning CT scans were significantly different (791 vs 498 cc; p<0.001). Significant changes were observed in lung doses between IMRT~initial~ vs IMRT~transfer~ and IMRT~adapt~ vs IMRT~transfer~ (mean V5, 50% vs 54%, p=0.001 and 40% vs 54%, p=0.003; mean V20, 24% vs 28% p<0.001 and 20% vs 28%, p<0.001). Spinal cord dosed also significantly changed on these 3 plans (mean Dmax on IMRT~initial~ vs IMRT~transfer~ and IMRT~adapt~ vs IMRT~transfer~ 41.4Gy vs 45.5Gy, p=0.042 and 37.8Gy vs 45.5Gy, p=0.005). The PTV coverage significantly changed in 3 patients because of replacement. Figure 1
Repeat CT imaging and replanning during the course of IMRT for selected patients with lung cancer may help to identify dosimetric changes and to ensure safe doses to critical structures such as lung and spinal cord. With the implementation of adaptive treatments dose escalation may be possible in the future for improvements in clinical outcome without significant increase in toxicity. The anatomic changes seen throughout the treatment may increase the lung doses when replanning is not performed.
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