Cancer treatment outcome should be evaluated not only with conventional parameters of survival, local control, and response rate, but with quality-of-life (QOL) based parameters. As radiation therapy is a treatment to eradicate cancer without resection of tissues or organs, a better functional or cosmetic result could be obtained compared with surgical treatment. If basically functional or cosmetic results are better, QOL of the patient could be expected to be even more superior. Patient QOL should be assessed from the physical, psychological, and social standpoints. So, adequate instruments or scoring systems are essential to obtain data. In this paper, we introduce an outline of QOL-related research activities in cancer treatment, especially in radiation therapy. We also attempt to assess the functional outcome and late complications, which would affect patient QOL. Finally, the concept of quality adjusted survival time or utility analysis is also mentioned.