IMRT

Changes in anatomy over the course of treatment

• 10 H&N – oropharingeal ca pts, IMRT

• Three radiation oncologists delineating OARs, three contouring sessions one week apart

• Mean difference in total volume for each OAR was 1 cm3 for each OAR. • Considerable spatial differences in contours, ipsilateral parotis and pharingeal constrictors showing most variability. • Despite substantial differences in OAR contours, optimization was barely affected with less than a 1 Gy difference in dose (Feng et al , 2012)