The Change Of Tumor Target Volume During Waiting Times For Intensity-modulated Radiotherapy (IMRT) In Nasopharyngeal Carcinoma (NPC)

Purpose: To determine the influence of waiting times for intensity-modulatedradiotherapy (IMRT) in tumor target volume of nasopharyngeal carcinoma (NPC).Methods and Materials: From March 2005 to April 2007, 49 patients withnasopharyngeal carcinoma received IMRT as the initial treatment at the cancer hospitalof Chinese Academic of Medical Science. The original simulating CT scan wasacquired before IMRT plan, and a second CT scan was acquired before the start ofradiotherapy. Waiting time was defined as time between CT simulation and start ofradiotherapy. CT-CT fusion was used to reduce error of delineation between the firsttumor target volume (GTV) and the second tumor target volume (sGTV). Tumor targetvolume was calculated by treatment planning system. Analysis of the change betweenGTV and sGTV and its influence factor were carried out.Results: Median waiting time was 17 days (range, 7-27 days). There were significantdifferences between GTV and sGTV of both primary tumor (p=0.000) and metastasislymphomas (p=0.000). Multivariate analysis showed that the change of primary tumortarget volume had significant correlation with the first tumor target volume, and thechange of metastasis lymphomas had significant correlation with the first volume,necrosis of lymphoma and waiting time.Conclusion: Within the range of the waiting time observed in our study, primary tumorwith large volume would have had a significant increase in volume, but whether thetherapeutic effect would be influenced or not would be needed to prove by study withlarge cases. Patients with large volume tumor should be considered to reduce theinfluence of waiting time by enlarging clinical target volume and by neoadjuvantchemotherapy. For avoiding the unnecessary high-dose to normal tissue, the later maybe better.