**4. Simulation and advantages**

In according to the latest recommendations of international institutes of radioprotection, an increasing attention must be paid to the patient protection during cancer radiotherapy. Therefore one of the primary attempts should be protection of the patient from hazardous radiation and minimizing un-useful doses. Designing a Body Chemical Composition Analyzer (BCCA) in order to use for cancer therapy while having the lowest gamma and neutron dose equivalent rate in the soft tissue is desirable. The Design of the BCCA need to be modeled by Monte Carlo N-particle general code (MCNP) (Briesmeister, 2000) before the construction. By this way we can assess all the geometry and material's effects and other parameters affect the dose received by the patient and the personnel. Also if we have an improving idea we can investigate its subsequent role in simulation design before the real structure.
