ABSTRACT
Objective This study is aimed to compare the CT number and volume of the parotid of the NPC patients between the first CT scan and the rescanning after 20 fractions.Method 14 NPC patients who had been treated were selected for analysis. Each patient was rescanned after the treatment of 20 fractions as the same protocol of the first CT sim for replanning. The CT number and volume change of the Parotid were compared and the CT number and volume change of the brain stem were also evaluated as a reference data. The results were analyzed with SPPS19, The results were analyzed with SPPS19 for t test. Results Mean right parotid CT number of the 14 patients for pre treatment and re-plan(after 20 fractions) was 6.4 and-0.5 ( =0.02) separately, the mean stand deviation was 26.5 and 35.6 ( = 0.04) separately、the mean volume was 24.6 cm3 and 16.1 cm 3 ( = 0.002) separately. Mean left parotid CT number of the 14 patients for pre treatment and re-plan was 4.4 and-1.8 ( =0.024) separately, the mean stand deviation is 29.7 and 35.5 ( =0.026) separately、the mean volume was 24.1 cm3 and 16.7 cm3 ( =0.001) separately. The Mean brain stem CT number of the 14 patients for pre-treatment and re-plan was 28.7 cm3 and 28.9 cm3 ( =0.887) separately. Conclusion After the treatment of 20 fractions , the volume of the parotid was significantly shrinked, the CT number was significantly decreased and the SD of CT number was significantly increased. The volume, CT number and SD of the Brain stem did not have significant changes. The change of the CT number could be a new observed data for the adaptive plan during the treatment as the tumor response.