The big advantage of proton therapy is the remarkably better sparing of the healthy tissue which unavoidably will be irradiated as well.
The following figure shows a comparison of tissue exposure using conventional therapy and proton therapy.
The areas marked in yellow show the increased dose of radiation to the surrounding healthy tissue using X-rays and subsequently causing side effects. This illustration clearly shows the dose saving capability outside the marked target volume, which is e.g. in a depth of 15-25 cm, when using protons. This shows impressively that the normal tissue lying outside the target area is significantly better protected with the use of protons.
As a consequence, in the frame of clinical studies the dose in the target volume can be increased successively. The treatment will be more radical at the tumour and a better chance to cure can be achieved.