Abstract
Purpose:The dose‐dependent nature of radiation therapy (RT)‐induced lung injury following hypo‐fractionated stereotactic RT is unclear. We herein report preliminary results of a prospective study assessing the magnitude of RT‐induced reductions in regional lung perfusion following hypo‐fractionated stereotactic RT.Methods:Four patients undergoing hypo‐fractionated stereotactic lung RT (SBRT: 12 Gy × 4 fractions or 10 Gy × 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 to the regions receiving <5 Gy.Results:At 3 months post‐RT, the changes in perfusion are highly variable. At 6 months, there is a consistent dose‐dependent reduction in regional perfusion. The average percent decline in regional perfusion was 10% at 15–20 Gy, 20% at 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. There was a subtle increase in perfusion in the lung receiving <10 Gy.Conclusion: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, though this might be in part due to the normalization technique used. 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.Partly supported by the NIH (CA69579) and the Lance Armstrong Foundation
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