Figure 11.

Central axis depth dose profiles from several particle beams. Note that these distributions are from solitary beams in order to clearly compare the differences in the physical properties of various radiations. The important features are that proton beams offer relatively low entrance dose and virtually no exit dose. However, many clinical treatment techniques exploit multiple field directions to enhance the uniformity of tumor coverage and to spare sensitive healthy tissues. In fact, in some cases proton treatments provide inferior skin sparing to photons and/or inferior target coverage, e.g., because of proton beams’ sensitivity to range errors. Nonetheless, beam for beam, proton beams provide excellent tissue sparing, especially beyond the end of range. (Larsson, 1993)