抄録
This study retrospectively examined the effects of head and neck volume reduction （external volume loss, EVL） on prescribed doses in 31 patients with oropharyngeal and hypopharyngeal cancer receiving curative intensity-modulated radiation therapy （IMRT） using the Tomotherapy system. This study focused on the relationship between treatment duration and EVL, differences in EVL between cases, and dose variation rates associated with EVL and other dosimetric indicators. To evaluate computed tomography （CT） volume data used in treatment planning （IMGplan） and mega-voltage CT images taken during treatment （IMGMV）, deformable image registration （DIR） was employed. This study noted a statistically significant moderate correlation between treatment duration and EVL, with head and neck volume decreasing at a rate of 0.09％ per day （r＝0.4515, p＜0.0001）. EVL varied by case, ranging from an average of 10.6％ to cases with little variation. Regarding EVL-related dose variation rates, the median EVL of 6.5％ led to a 1.3％ increase in dose at D0.03cc for planning target volume_highrisk but only a 0.3％ change in Dmax for Spinal cord_PRV （r＝0.5101, 0.0251; p＜0.0001, 0.4038）. This study emphasizes the significance of replanning treatments on the basis of volume changes during radiation therapy and suggests that using DIR technology for longitudinal dose assessments could be a critical practical tool for improving treatment precision. In future works, evaluating the impact of volume changes for each patient and determining the optimal timing for treatment replanning will be crucial for further improving patient outcomes.
