  The IMPRESSIONS section of a radiology report about an imaging study is a
summary of the radiologist's reasoning and conclusions, and it also aids the
referring physician in confirming or excluding certain diagnoses. A cascade of
tasks are required to automatically generate an abstractive summary of the
typical information-rich radiology report. These tasks include acquisition of
salient content from the report and generation of a concise, easily consumable
IMPRESSIONS section. Prior research on radiology report summarization has
focused on single-step end-to-end models -- which subsume the task of salient
content acquisition. To fully explore the cascade structure and explainability
of radiology report summarization, we introduce two innovations. First, we
design a two-step approach: extractive summarization followed by abstractive
summarization. Second, we additionally break down the extractive part into two
independent tasks: extraction of salient (1) sentences and (2) keywords.
Experiments on English radiology reports from two clinical sites show our novel
approach leads to a more precise summary compared to single-step and to
two-step-with-single-extractive-process baselines with an overall improvement
in F1 score Of 3-4%.
