Advantages of protons over Gamma rays.
The peculiarity of protons is that it is possible to stop them at the necessary point and get higher irradiation dose precisely inside the tumor with minimal harm to healthy organs.
With changing the energy and thin beam direction of protons we can scan the whole tumor destructing it gradually.
In spite of having low workability of protons during their succession when irradiating from one side (one irradiation field) it is impossible to increase the tumor dose endlessly since the influence on healthy organs would become considerable.
Comparative pictures of hitting ability of Gamma rays on electron accelerators and protons with different energy.