Room: ePoster Forums
Purpose: To evaluate the variation of dose-volume parameters on tumor target volumes and organs at risk (OARs) during intensity-modulated radiotherapy (IMRT) on nasopharyngeal carcinoma (NPC) based on deformation registration.
Methods: Eighteen NPC patients who accepted simultaneous integrated boost intensity-modulated radiotherapy were enrolled. All patients underwent simulation CT (CT1) and replanning CT (CT2) scan after 20-25 fractions of radiation therapy. The treatment plans were designed on CT1 and CT2 were called Plan1 and Plan2, respectively. The Planreg and Plandef were obtained after registering from CT2 to CT1 using rigidity and deformation technology by Velocity. And then compared the dose-volume parameters differences on GTV and OARs among Plan1, Plan2, Planrig and Plandef.
Results: The volume of GTV in CT2 was decreased by 20.8%ï¼ˆPï¼œ0.001ï¼‰and the volume of left and right parotid glands in CT2 were decreased by 36.8%ï¼ˆPï¼œ0.001ï¼‰ and 37.5%ï¼ˆPï¼œ0.001ï¼‰compared with CT1,respectively. The dose-volume on GTV and PGTV has mild variation between Plan1 and Plan2. The V30 of parotid gland and the Dmax of brainstem, eyeball, lens, and optic nerve all in Plan2 were lower than Plan1 (average decrease was 17.0% to 60.1%). The differences of some dose-volume parameters (It includes Dmean and D99 of GTV and PGTV, Dmean of parotid gland and Dmax of eyeball and optic nerve.) between Plandef and Plan1 were less than 5%. The Dyce Similarity Coefficient of target volume and OARs after deformation registration were higher than that after rigid registration.
Conclusion: The volume of GTV and parotid gland decreased significantly during IMRT for NPC. The dose-volume indexes of the GTV and the OARs in Plandef were similar as which in Plan1. Therefore, the dose-volume index of Plan1 can be used to evaluate the efficacy of radiotherapy and to predict radioactive damage.