We investigated the relationship between the local dose delivered and median pixel-value change following
radiation therapy (RT) by comparing anatomically matched regions of interest (ROIs) in pre- and post-RT computed
tomography (CT) scans. Six patients' clinical pre-treatment baseline CT scans, follow-up CT scans, treatment planning
CT scans, and dose maps were collected. The lungs were extracted using an automated segmentation algorithm, and
demons deformable registration was used to register each patient's follow-up scan and treatment planning scan to their
baseline scan. Median pixel values were calculated in anatomically matched ROIs in the baseline and deformed followup
CT scans, and mean dose delivered to the same ROIs was determined from the deformed dose map. Pearson's
correlation coefficients, rank correlation coefficients, and linear modeling were utilized to quantify the relationship
between median pixel-value change and mean dose delivered. Pearson's correlation coefficients for the six patients
ranged from -0.13-0.67. Rank correlation coefficients ranged from -0.12-0.80. Linear regression analysis on the six
patients' combined data yielded a slope of 2.62 (p < 0.001) and R-squared value of 0.24. General positive trends were
observed between radiation dose and median pixel value change, but no two patients had the same relationship between
these variables, indicating it may not be possible to generalize patients' reactions to varying dose levels of radiation.
Thus, an individualized method for evaluating normal lung tissue damage based on changes in each patient's CT scan
following radiation treatment may be required to assess radiation-induced lung damage.