ABSTRACT
Objective@#To study the more safe and accurate guidance scheme of cone beam computed tomography (CBCT) in nasopharyngeal carcinoma.@*Methods@#CBCT was regularly performed on 87 patients with nasopharyngeal carcinoma in Meizhou People's Hospital from November 2014 to August 2015. For each patient, 10 times CBCT scans were obtained pre-treatment. All the setup errors were obtained and analysed on the orientation X (left and right), Y (head and foot) and Z (vertical) axis.@*Results@#With the increase of the number of CBCT scans, there was no statistically significant difference among the mean setup errors of the 10 times scans in X (left and right) and Y (head and foot) directions (all P > 0.05). And there was no statistically significant difference among the mean setup errors of 6 times scans in Z (vertical) direction, but from the beginning of the 7th, the systematic error in Z direction was increasing, the system error of the 7th, 8th, 9th, 10th time was 0.140, 0.292, 0.461, and 0.640 mm. Moreover, the difference of the mean systematic errors among the first 7 times was statistically significant (H = 15.232, P = 0.019), and the differences of the mean systematic errors among the first 8, 9 and 10 times were statistically significant (all P < 0.05).@*Conclusions@#Non-consecutive scans of CBCT could reduce the systematic and random errors. The appropriate frequency of application of CBCT based on the change law of setup errors is an ideal CBCT guidance scheme for nasopharyngeal carcinoma.
ABSTRACT
Objective To analyze set-up errors for irradiation of nasopharyngeal carcinoma by using kilo-voltage cone beam computed tomography (kV-KBCT) scanning, and to calculate the external margin from planning target volume (PTV) of nasopharyngeal carcinoma. Methods A total of 150 nasopharyngeal carcinoma patients in Meizhou People's Hospital from December 2014 to November 2016 were treated by image-guided radiation therapy (IGRT), kV-KBCT, CT image scanning matcthed by bone and grey alignment. PTV of nasopharyngeal carcinoma was also calculated. Results According to PTV formula, the external distance before radiotherapy guided by grey alignment was 0.5 mm in X-axis, 0.4 mm in Y-axis, 0.8 mm in Z-axis. While the distance was 0.1 mm in X-axis, 0.5 mm in Y-axis, 1.7 mm in Z-axis guided by bone alignment. After radiotherapy, the external distance guided by grey alignment was 0.4 mm in X-axis, 0.5 mm in Y-axis, 0.9 mm in Z-axis. While the distance was 0.1 mm in X-axis, 0.9 mm in Y-axis, 2.0 mm in Z-axis guided by bone alignment. There was no significant difference in set-up errors of 3 directions and 2 aligned ways before and after treatment.Conclusions The PTV within 3 mm is safe when IGRT is used for directing radiotherapy of nasopharyngeal carcinoma,and kV-KBCT is an effective image equipment.