Rozlytrek-

HI Simone,

While this article was published in 2002 it's still or maybe more relevant when considering lung tissue (central and peripheral lung parenchyma) because ct resolution has increased quite a bit. 

"Results: Although overall image quality was better with standard-dose CT, the quality of reduced-dose CT was acceptable. The differences in mean scores were statistically significant. There was a correlation of 0.59 between observers. The mean scores of standard-dose CT were always greater than or equivalent to those of low-dose CT for both observers. The assessment of great vessels and soft tissue of the chest wall contributed mainly to the differences in image quality. Both the central and peripheral lung parenchyma and the airway were adequately visualized on low-dose CT. Radiation doses (based on weighted-CT-dose index) from standard-dose CT and 50%-reduced-dose CT were 15.6-21.4 mSv and 7.8-10.7 mSv, respectively (from the manufacturer's data).

Conclusion: Chest CT image quality appears to be acceptable for evaluating normal anatomic structures even with a 50% reduction in radiation dose."

Since progression probably means changing treatment or adding a focal radiation treatment to Rozlytrek a discussion about your concerns with her oncologist is appropriate.  Before changing treatments especially when there's no obvious next choice a 2nd opinion is also appropriate (2 heads are better than 1).  This is one of my favorite posts.

Best of luck and stay safe,

Janine