Nelie,

There's a fairly useful dictionary on the National Cancer Institute site (www.cancer.gov) that covers many of the standard terms related to cancer diagnosis and treatment. I've copied its language about differentiation here:

"In cancer, refers to how mature (developed) the cancer cells are in a tumor. Differentiated tumor cells resemble normal cells and tend to grow and spread at a slower rate than undifferentiated or poorly differentiated tumor cells, which lack the structure and function of normal cells and grow uncontrollably."

IMRT is designed to target the most powerful radiation on specific locations and is particularly suitable for tumors that are well-differentiated. By targeting in this way, it can spare the surrounding areas better than field radiation and in many cases lessen the long-term dry mouth effects. My understanding is that, because of the more unpredictable nature (and potential aggressiveness) of tumors that are poorly differentiated, IMRT can be less effective with them, as there is a greater likelihood that it will miss some cancerous cells.

Cathy