Comparative Analysis of an Image-Guided Versus a Non–Image-Guided Setup Approach in Terms of Delivered Dose to the Parotid Glands in Head-and-Neck Cancer IMRT

Purpose To assess the impact of interfractional variations of shape and setup uncertainties on the dose to the parotid glands (PGs) in head-and-neck cancer intensity-modulated radiotherapy and image-guided radiotherapy (IGRT ). Methods and Materials Two scenarios were analyzed retrospectively for 10 head-and-neck cancer patients, treated with helical TomoTherapy (TomoTherapy Inc., Madison, WI): the IGRT scenario and the non-IGRT scenario. The initial dose–volume histograms derived from the planning computed tomography (PCT) scan and 120 recalculated dose–volume histograms of the PGs of each scenario and of corresponding fractions were compared. Setup errors, cumulative median doses (CMDs) for 6 fractions, overall volumes of the PGs, and volumes that received less than 1 Gy or more than 1.6 Gy per fraction were analyzed. Results The mean decrease in the PG volume was 0.13 cm3 /d. There was a significantly higher CMD than initially predicted (mean increase for 6 fractions, 1.13 Gy for IGRT and 0.96 Gy for non-IGRT). The volume that received less than 1 Gy per fraction decreased (mean difference to PCT, 1.36 cm3 for IGRT [ p = 0.003] and 1.35 cm3 for non-IGRT [ p = 0.003]) and the volume that received more than 1.6 Gy per fraction increased with increasing fraction number (mean difference to PCT, 1.14 cm3 for IGRT [ p = 0.01] and 1.16 cm3 for non-IGRT [ p = 0.006]). There was no statistically significant difference between the two scenarios (CMD, p = 0.095; volume that received 1.6 Gy per fraction, p = 0.855). Conclusions In the analyzed group the actual delivered dose to the PGs does not differ significantly between an IGRT and a non-IGRT approach. However, IGRT in head-and-neck cancer intensity-modulated radiotherapy is strongly recommended to improve patient setup.