放射線治療では、がん細胞が大きなダメージを受けますが、その周辺の正常細胞にも何らかのダメージが生じます。臓器ごとのある決められた量以上の放射線を当てると、正常細胞も弱って放射線による害が出てしまいます。正常細胞が受けた放射線の影響は何年経っても多少残りますので、同じ場所に再度、放射線治療をする事は出来ないことが多いのです。ただし、がんのタイプによっては、初回の治療で照射した放射線の量が少なく、もう一度安全に治療できる場合もあります。
Radiation therapy does cause great damage to cancer cells, but it also has some effect on surrounding normal cells. If radiation is above the decided levels for that organ damage can be delivered to normal cells making them weak. The radiated normal cells will still remain slightly effected even after several years, and therefore repeat radiation treatment in the same area is not performed. However, depending on the type of cancer, there are cases where it can be performed safely again in the same area, where the first time irradiation quantity was small and it was a first time therapy.
放射線治療は手術と同じく体の一部分への局所的な治療ですので、放射線がかかっていない部分への影響はありません。従って、照射する場所が違えば、臓器の機能が許容される限り何度目であろうと問題なく安全に治療することができます。
Radiation therapy is a local trearment that aimed to one part of the body as surgeries are. It doesn't have effects on the part which haven't been exposed to radiation. Therefore, just being careful of changing the parts to which you deliver radiation, as long as the function of organs allows, you can give treatments safely as many times as needed.
