Radiation dose response of normal lung assessed by Cone Beam CT – A potential tool for biologically adaptive radiation therapy

Abstract

BackgroundDensity changes of healthy lung tissue during radiotherapy as observed by Cone Beam CT (CBCT) might be an early indicator of patient specific lung toxicity. This study investigates the time course of CBCT density changes and tests for a possible correlation with locally delivered dose. MethodsA total of 665 CBCTs in 65 lung cancer patients treated with IMRT/VMAT to 60 or 66Gy in 2Gy fractions were analyzed. For each patient, CBCT lung density changes during the treatment course were related to the locally delivered dose. ResultsA dose response is observed for the patient population at the end of the treatment course. However, the observed dose response is highly variable among patients. Density changes at 10th and 20th fraction are clearly correlated to those observed at the end of the treatment course. ConclusionsCBCT density changes in healthy lung tissue during radiotherapy correlate with the locally delivered dose and can be detected relatively early during the treatment. If these density changes are correlated to subsequent clinical toxicity this assay could form the basis for biological adaptive radiotherapy.