Time course of radiological lung density changes after postmastectomy radiotherapy

The purpose of this study was to quantify the time course of radiological lung changes in patients after postmastectomy radiotherapy assessed from routine follow-up chest x-rays. Radiological density changes in the apex of the irradiated lung were quantified by a recent lung densitometry assay. Lung changes were expressed as the so-called Relative change in Equivalent Absorber Thickness (REAT). The clinical series comprised 329 patients treated with postmastectomy radiotherapy between 1978 and 1982. Of these patients 100 were treated with chemotherapy (CTX or CMF) and 41 were given tamoxifen as an additional adjuvant treatment; 290 patients (88.2%) had pretreatment x-rays and at least one x-ray after completion of radiotherapy and these were included in the study. A total of 2,209 chest x-rays was taken during follow-up, and among these 1921 x-rays (86.9%) were judged to be assessable. Late changes were defined as changes occurring more than a year after radiotherapy. A total of 280 patients had at least one chest x-ray taken more than one year after radiotherapy and these were evaluable with respect to late changes. There were 1,390 follow-up x-rays in these patients and 207 patients (73.9%) had three or more follow-up x-rays. Linear regression of REAT vs. observation time was used to identify three patterns of time changes: progressive, regressive, and stable. The results were as follows. Two phases of lung changes were observed. The early phase peaks around 6 months and the density changes may subsequently resolve, completely or in part. In most cases (173 patients or 84%), the lung density changes reached a stable level 12 months after irradiation. Yet, in 16 patients (7.7%) the lung changes progressed for five or more years. Regression of the density changes was seen in 18 patients (8.7%), and in some cases there were signs that this apparent regression was caused by contraction of the fibrotic tissue. We conclude that two phases of lung response can be distinguished and can be graded according to severity using this assay. Early lung changes reach a maximum around 6 months after RT. Late reactions reach a plateau in most patients after one year, but progress in some cases for five or more years.