PET/CT is essential in determining staging and re-staging of disease, detecting recurrent or residual disease, evaluating response to therapy, and providing prognostic information. PET/CT is also critically important in radiation therapy planning by determining the extent of active disease, including an assessment of functional tumor volume. The current approach in tumor imaging is a significant advance over conventional imaging (Greenspan et al).
NCCN, on the other hand, does not recommend PET to monitor response to therapy.
Greenspan BS. Role of PET/CT for precision medicine in lung cancer: perspective of the Society of Nuclear Medicine and Molecular Imaging. Transl Lung Cancer Res. 2017;6(6):617-620. doi:10.21037/tlcr.2017.09.01
American Journal of Roentgenology. 2017;208: 420-433. 10.2214/AJR.16.16532
https://www.ajronline.org/doi/10.2214/AJR.16.16532