How important is breathing in radiation therapy of the thorax?

Abstract

Repeated computed tomographic (CT) scanning has been used to assess the effect of quiet breathing on the dosimetry in radiation therapy of the thorax. Density variations as great as 80 CT numbers (8 % of the density of water) have been observed between the inspiration and expiration limits of quiet breathing, and movement of anatomical points of greater than 1 cm have been measured. However, dose variations around the breathing cycle are generally less than 5% and the true time-averaged dose is well approximated by a static plan at any point within the cycle. Treatment plans based on “blurred” slow CT scans give a comparable accuracy to those performed at the mid-point of quiet respiration.