Why is PET/CT considered superior to CT for evaluating post-treatment response in lymphoma?

PET/CT is regarded as superior to CT for evaluating post-treatment response in lymphoma primarily due to its ability to differentiate viable tumor tissue from fibrosis. After treatment for lymphoma, imaging can reveal changes in the affected tissues. While CT scans can provide information about changes in size or shape of lymph nodes and other structures, they do not distinguish between viable lymphoma cells and benign post-treatment changes such as fibrosis or necrosis.

In contrast, PET imaging detects metabolic activity through the uptake of radiotracers, like FDG (fluorodeoxyglucose), which is preferentially taken up by metabolically active cells, including cancer cells. A viable tumor will typically show increased radiotracer uptake, whereas inactive or fibrotic tissue will show lower levels of uptake. Therefore, PET can provide critical information regarding whether the lymphoma has responded to treatment by confirming whether active disease persists.

While higher resolution imaging capability, better visualization of organ structures, and reduced radiation exposure can be important in many clinical contexts, these factors do not directly address the specific need for assessing the viability of lymphoma post-treatment, which is why the ability to differentiate viable tumor from fibrosis is paramount in this scenario.