In a small experimental patient study, researchers have increased the effectiveness of using protons to treat lung tumors. In traditional radiation therapy, one must use multiple beams of x-rays to deliver a uniform dose to a lung tumor; often at least one of the x-ray beams will exit from the healthy (non-tumor-containing) lung and potentially damage it. On the other hand, positively charged, subatomic protons only travel a limited distance through the body; they never make it to the other lung, and they also are more likely to spare nearby organs such as the esophagus and heart.
In any radiation treatment of the lung, it is a challenge to keep the radiation on target while the tumor moves as a result of patient breathing. In the 4D approach, one takes into account how the patient's breathing moves the lung back and forth over time (the fourth dimension) so that the radiation hits the tumor precisely over all phases of a patient's breathing cycle.
Now, researchers at Massachusetts General Hospital have applied the 4D approach to proton therapy. In a study of four patients, they have found that planning and carrying out 4D proton therapy delivers excellent dose levels to lung tumors in all cases.
The only thing preventing this technique from wider use is the need to develop an algorithm that cuts down the currently lengthy time it takes to calculate and plan the proton beam's direction and intensity for each breathing phase. The 4D approach is also applicable to radiation therapy using carbon ions, which is currently being used to help defeat lung cancer in a couple of centers in Japan.