The radiobiological and physical basis for radiotherapy with protons and heavier ions.

Heavy charged particles exhibit a superior dose distribution compared to all conventionally used beams. The small lateral and range straggling, combined with an increase of the dose deposition with increasing penetration depth enables the production of dose profiles shaped precisely to the contours of the treatment volume. In addition, heavy ion beams exhibit an elevated biological efficiency close to the end of the particle range. Therefore, beams of heavy ions deliver a high physical dose combined with a high biological efficiency to a tumor volume while the surrounding healthy tissue is maximally spared.