New technique reduces the effect of tumor motion during proton therapy

April 27, 2015
by Lauren Dubinsky, Senior Reporter
Proton therapy is able to accurately deliver treatment to a tumor while limiting the dose to surrounding tissue, but precise targeting is challenging in mobile organs, especially the lungs. But researchers at the Paul Scherrer Institute in Switzerland developed a technique to solve that.

A proton beam only penetrates tissue up to a certain depth based on its energy, which delivers maximum dose to the tumor and limits dose elsewhere. But mobile tumors in the liver and lung can deteriorate the dose distribution during proton therapy if there is a gap between the radiation delivery timeline and the tumor motion timeline.

The technique to solve that is called rescanning and it works by reducing the effect of motion during therapy. The researchers conducted experiments using a breathing model of the patient and integrated measurement tools to measure the dose distribution.

The breathing model consists of a sphere, to represent the tumor moving around an inflating lung, encompassed by a rib cage complete with surrounding muscles and skin layers. The model can be programmed to the individual breathing patterns of each patient.

While the tumor was moving, the radiation dose was measured and the researchers found that the rescanning technique “allowed the application of clinically acceptable dose distribution to the [tumor], and only minimal dose to surrounding tissue.” It was effective for tumor motions of up to 1 centimeter.

The next step for the researchers is to bring the technique into clinical practice but challenges relating to cost are standing in the way of that. They believe that if randomized clinical studies are conducted proving that proton therapy is better for certain cancer types, then politicians and insurance providers may be encouraged to “make appropriate decisions.”