Figure 5 represents an updated attempt to represent the dose distribution and high LET advantages of the various heavy particles, summarizing the conclusions discussed above. Neutrons are the cheapest form of high LET radiation. Their biological properties are excelled only by argon ions, but of course, they yield quite ordinary dose distributions. Protons give the best physical dose distribution and are by far the cheapest charged particles. Their biological properties, however, are similar to gamma-rays. Pions are comparable to carbon and neon ions in dose effect distribution, but are not as good because of dose/rate limitations and a less sharp edge to the beam. Two principal questions remain: 1. Are super dose distributions worth the substantial cost? 2. Do hypoxic cells limit radiocurability? These questions can only be answered in clinical trials and cannot even be addressed in the radiobiology laboratory.