Can photodynamic therapy treat deep tumors?

Not well. Photodynamic therapy is less helpful for large, deep tumors.

The reason is the light. The light used in photodynamic therapy cannot pass through more than about a third of an inch, or 1 centimeter, of tissue. Because of this, PDT can only be used to treat tumors that are on or just under the skin, or on the lining of internal organs or cavities.

Since the light cannot reach very far into large tumors, photodynamic therapy is less useful for treating them.

For tumors in places like the throat, airways, or lungs, a doctor can use an endoscope — a thin, lighted tube — to bring the light closer to the tumor. But the same depth limit still applies once the light reaches the tissue. Your care team can tell you whether PDT is a good fit for your specific tumor.