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R. McGurk

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    MINI 18 - Radiation Topics in Localized NSCLC (ID 139)

    • Event: WCLC 2015
    • Type: Mini Oral
    • Track: Treatment of Localized Disease - NSCLC
    • Presentations: 1
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      MINI18.12 - Assessment of Dose Response via Regional Lung Perfusion following Stereotactic Radiotherapy for Lung Cancer (ID 910)

      16:45 - 18:15  |  Author(s): R. McGurk

      • Abstract
      • Presentation
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      Radiation therapy (RT)-induced lung injury is one of the major causes of morbidity in patients with thoracic cancer. Extensive work has been done to understand the predictors of lung injury in patients receiving conventionally fractionated RT. However, less work has been done in the setting of hypo-fractionation. Further, conventional methods to consider lung injury typically assess global lung function (e.g. symptoms, pulmonary function tests), are affected by many other (non-radiation) factors, and are thus non-specific. Single photon emission computed tomography (SPECT) perfusion imaging affords an objective quantitative manner to assess the effects of RT on regional lung function. We herein report the preliminary results of a prospective study to assess the magnitude of RT-induced reductions in regional lung perfusion following hypo-fractionated stereotactic RT.

      Four patients undergoing hypo-fractionated stereotactic lung RT (SBRT: 12 Gy x 4 fractions or 10 Gy x 5 fractions) had a pre-treatment SPECT (single-photon emission computed tomography) perfusion scan providing a 3D map of regional lung perfusion. Scans were repeated 3-6 months post-treatment. Pre- and post SPECT scans were registered to the planning CT scan (and hence the 3D dose data). Changes in regional perfusion (counts per cc on the pre-post scans) were computed in regions of the lung exposed to different doses of radiation (in 5 Gy intervals), thus defining a dose-response function. SPECT scans were internally normalized such that total counts in the regions receiving <5 Gy were equal between pre- and post-treatment scans.

      3 months post-RT, changes in perfusion are highly variable. At 6 months, there is a consistent dose-dependent reduction in regional perfusion. Average percent decline in regional perfusion was 10% at 15-20 Gy, 20% and 20-25 Gy, and 30% at 25-30 Gy representing a relatively linear dose response with an approximate 2% reduction per Gray for doses in excess of 10 Gy. Subtle increases in perfusion were seen in lung receiving <10 Gy. Figure 1

      Hypo-fractionated stereotactic RT appears to cause a dose-dependent reduction in regional lung perfusion. There appears to be a threshold effect with no apparent perfusion loss at doses <10 Gy, in both normalized and unnormalized dose-response curves. Additional data is needed from a larger number of patients to better assess this issue. This sort of data can be used to assist optimizing RT treatment plans that minimize the risk of lung injury.

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