Author of

• 20163

  +

  P1.14 - Radiotherapy (ID 700)

  • Event: WCLC 2017
  • Type: Poster Session with Presenters Present
  • Track: Radiotherapy
  • Presentations: 1
  • Moderators:
  • Coordinates: 10/16/2017, 09:30 - 16:00, Exhibit Hall (Hall B + C)

  • 24648

    +

    P1.14-018a - Stereotactic Ablative Radiotherapy for Ultra-Central Lung Tumors: Optimize Tumor Control or Minimize Toxicity? (ID 9509)

    09:30 - 09:30  |  Author(s): A. Erickson
    • Abstract

    Background:
    Lung stereotactic ablative radiotherapy (SABR) is associated with low morbidity, however there is an increased risk of treatment-related toxicity in tumors directly abutting or invading the proximal bronchial tree, termed ‘ultra-central’ tumors. For such tumors, there is no consensus regarding the most appropriate dose-fractionation scheme. The purpose of this planning study was to evaluate the therapeutic ratio of SABR treatment plans for ultra-central tumours using commonly utilized dose fractionation regimens.
    
    Method:
    In this research ethics board approved study, 10 patients with ultra-central lung tumors were identified from our institutional database. New plans were generated for each of the 10 cases using 3 different hypofractionated schedules: 50 Gy in 5 fractions, 60 Gy in 8 fractions and 60 Gy in 15 fractions. For each of the three dose regimens, 2 plans were generated, one prioritizing tumor coverage and the other plan compromising PTV coverage in order to respect the dose constraints for the esophagus, lung and proximal bronchial tree. Using published normal tissue complication probability models, plans were evaluated for likelihood of toxicity to these organs at risk.
    
    Result:
    In the scenario where PTV coverage was prioritized, the probabilities of acute esophageal or pulmonary toxicity were low, ranging from 0.9-1.2% and 3.7-4.3%, respectively. In contrast, the estimated risk of grade 4 or 5 toxicity to the proximal bronchial tree varied significantly: 68% for 50 Gy in 5 fractions, 44% for 60 Gy in 8 fractions and 2% for 60 Gy in 15 fractions. When dose to the organs at risk was prioritized, risk of toxicity to the proximal bronchial tree was reduced to <1% for all 3 dose fractionation schemes. This compromise resulted in a reduction in the calculated tumor control probabilities, from 92.9% to 60.3% for 50 Gy in 5 fractions, 92.4% to 65.7% for 60 Gy in 8 fractions and 52% to 47.8% for 60 Gy in 15 fractions.
    
    Conclusion:
    With the use of SABR or hypofractionated radiotherapy for ultra-central lung tumors, the competing risks of tumor local control and treatment toxicities need to be considered. Predicted rates of local control are inversely related to the risk of severe pulmonary toxicity due to trade-offs in the radiation planning process. Further prospective research is needed to better assess the optimal dose fractionation schedule for ultra-central lung tumors.