ABSTRACT
Three-dimensional conformal radiotherapy (3D-CRT) is one of the targeted therapy techniques which geometrically conforms the three-dimensional radiation dose distributions to the target volume while minimizing the radiationdose to nearby normal organs (1,2). With recent interests in using the advanced form of 3D-CRT, the intensity-modulated radiation therapy (IMRT) (3), for lung cancer radiotherapy (4-7), it is concerned that respiratory induced organ motion may have an impact on the final dose distribution. It is well established that variations in organ shape and position can occur due to inter-and intrafractional motion. Typical interfractional anatomy variations include tumor shrinkage, weight loss, bowel/bladder filling, etc. Typical sources of intrafractional motion include respiration, cardiac motion, peristalsis, etc. Better dose conformality and steeper dose gradients make IMRT plans potentially more sensitive to setup errors and motion of the internal organs (8-12). In a simulation study by Flampouri et al. (13), it was demonstrated that the difference in the equivalent uniform dose of clinical target volume (CTV) between the planed and the delivered doses could be as high as 33Gy if a plan is designed inappropriately for a patient with large motion effect. Therefore, it is important to understand the impact of organ motion on final dose distribution. The current treatment planning and delivery techniques, which do not correct for such daily and the moment-to-moment volumetric variations adequately, may lead to suboptimal treatments.
