(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: Stereotactic ablative radiotherapy for centrally located non-small cell lung cancer (NSCLC) can be associated with high risks of toxicity. The aim of this work was to assess the effect of treatment planning volume (PTV) margin reduction on dose sparing of critical organs and on dose coverage of the tumor throughout the treatment.
Methods: patients with central or ultra-central tumors were selected. The internal gross tumor volume (IGTV) was defined using 4DCT images. The planning target volume margins were 5 mm for the clinical plans (PTV5mm) and 2 mm for the test plans (PTV2mm). The dose prescription was 60 Gy in 8 fractions to 99% of PTV2mm. We used cone beam computed tomography (CBCT) verification images to assess the IGTV dose coverage for each treatment fraction.
Results: test plans had similar or superior IGTV dose coverage compared to the clinical plans. The mean dose to the proximal normal tissue (within 2 cm of PTV5mm) was on average 8 Gy lower for Plan2mm. The median D3cc value for the proximal bronchial tree was reduced from 23.3 Gy to 10.7 Gy. The median D1cc value for the great vessels was reduced from 48.7 Gy to 34.6 Gy. For the Esophagus, the median D1cc value was reduced from 14.8 Gy to 8.6 Gy respectively. The maximum dose for the spinal cord, heart, and chest wall was reduced by up to 9 Gy and 22.4 Gy, and 17.4 Gy respectively. 99.6% of the IGTV volume was covered by the prescription dose for each treatment fraction.
Conclusion: the PTV margin from the standard 5 mm to 2 mm significantly reduced the dose to most critical organs at risk without compromising tumor coverage. This improvement of the therapeutic ratio can potentially reduce toxicity and allow dose escalation to the tumor.
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