[formerly_proven]

Proton therapy is another relatively recent development (recent as in "becoming more widely available"). Unlike photons (gamma/x-ray), protons are charged particles, so they follow a Bragg curve - releasing most of their energy in a narrow range before being fully stopped by the material. This can give very accurate control over where dose is delivered, and also leads to the somewhat paradoxical-seeming situation that the tissue "in front" of the cancer actually receives less dose than the cancer covered by it.