J Korean Med Assoc 2008; 51 (7) : 638 -642 P roton is quite different from x-ray in terms of energy emission. As it enters a cancer patient's body through skin and tissue, it releases a relatively low dose of energy before it reaches the target. It, however, hits the targeted tumor by depositing the biggest dose of energy on it, then suddenly stopping its activity afterwards. The point where the highest energy is released is called as the Bragg peak. The proton beam has many advantages over the

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... conventional x-ray beam because the proton beam radiates primarily the tumor site, leaving the surrounding healthy tissue and organs totally unharmed or relatively less damaged. Thus, the patients can enjoy much more enhanced quality-of-life during and after the treatment as well as have a high probability to be cured from their diseases.