Proton Beam Therapy

Introduction

Particle beam therapy exploits subatomic particles with mass rather than X-rays or gamma rays to deliver radiation dose. It has gained increasing interest, development, and application due to its physical and radiobiologic properties. The physical property allows for precise dose localization and superior depth dose distribution with heavy charged particles such as protons. The advantageous radiobiologic property of heavier charged particles, such as carbon and helium, is that high linear energy transfer (LET) radiation deposits more dose along its path than conventional X-rays, which are low LET. High-LET radiation is more damaging to hypoxic cells, less cell cycle dependent, and there is less repair of induced damage. Protons are 1800 times heavier than electrons, so accelerating and delivering them to the patient requires higher energies and heavier magnets than photon linear accelerators, which accelerate electrons. Heavy ion particle accelerators are significantly more costly to build and maintain. Currently, only proton therapy facilities exist in the United States. Proton therapy, in addition to heavier particles, such as carbon ion therapy facilities, can be found in Europe and Asia. An experimental heavy ion facility is being planned in the United States.