Helical tomotherapy is an image-guided, intensity-modulated radiation therapy delivery system, a hybrid between a linear accelerator and a helical CT scanner. With its unique design features, tomotherapy has improved dose conformity and homogeneity of the target volumes, and conformal avoidance of the adjacent normal tissues. The daily pretreatment megavoltage computed tomography (MVCT) is a powerful tool used in image guided treatment delivery and patient setup verification. If anatomic changes occur during the course of treatment, MVCT images are utilized in correcting target volumes and constructing appropriate adaptive plans. Helical tomotherapy can be applied to more complicated cases, where conventional techniques find their limits: complex tumors with critical organ sparing, simultaneous irradiation of multiple targets, large volume and large superficial tumor irradiation, and recurrent tumor re-irradiation are a few examples. Tomothearpy may change the current paradigm in radiation oncology in the near future. Further studies regarding clinical implementation and treatment outcome of helical tomotherapy will be needed.