Objective To study the iso-center point coincidence of two accelerators with treatment planning system (TPS) based on γ passing rates of intensity-modulated radiotherapy (IMRT) plan verification.Methods Twenty-one IMRT plans were verified by Varian accelerator and twenty by Elekta accelerator with a gamma criterion of 3 mm/3％.The passing rates were measured when the iso-center point of TPS had-2,-1,0,1,and 2 mm shift in the x or y direction.A binomial curve of γwas fit to figure out the values of the two accelerators on the x and y axes when γ value reached the maximum.The γ pass rate difference was analysed by x2 test.Results The mean values of γ-2,γ-1,γ0,γ1,and γ2 in the x direction were (92.56±3.27) ％,(96.53± 1.82) ％,(96.13± 1.41) ％,(90.14± 2.87) ％,and (82.28± 4.69) ％ for Varian accelerator,and (94.82± 2.04) ％,(97.05± 2.02) ％,(98.38± 1.33) ％,(97.96± 1.44) ％,and (94.49±2.34)％ for Elekta accelerator.There was no significant difference in the mean value of γ0between the two accelerators (P=0.332).When γvalue reached the maximum,the values on the x and y axes were0.65 and-0.30 mm for Varian accelerator and 0.01 and 0.30 mm for Elekta accelerator,respectively.Conclusions In the same TPS,different accelerators have different degrees of coincidence of the actual field center point with the iso-center point of TPS,to which more attention should be paid in clinical practice.

Objective The aim of this study was to explore the effectiveness of self-made oral humidity detection device to assist in evaluating the degree of parotid gland damage in radiotherapy for nasopharyngeal carcinoma,so as to guide doctors to change the radiotherapy plan in time,reduce the radiation dose to parotid gland,and reduce the incidence of xerostomia after radiotherapy.Methods A retrospective analysis was conducted on the relationship between oral humidity and parotid gland dose of radiotherapy in 60 patients with nasopharyngeal carcinoma using oral detection devices in the Department of Oncology of Southwest Medical University Affiliated Hospital from January 1,2022 to December 31,2022.According to the method of changing the radiotherapy plan,patients were divided into experimental group(n=30)and control group(n=30).The patients in the experimental group used a self-made oral humidity detection device to detect oral humidity,when 30 patients with oral relative humidity below 65%underwent CT simulation positioning and changed the radiotherapy plan to reduce the dose of parotid gland;The control group patients collected oral humidity but did not interfere in the radiotherapy plan,and only underwent CT positioning during the mid-term radiotherapy.The average oral humidity,parotid gland,and target area dose parameters of patients were analyzed after radiotherapy.The follow-up questionnaire was conducted to evaluate the life quality of patients in terms of dry mouth,decreased taste,difficulty opening mouth,and dental caries in two groups.Results The average oral humidity(t=2.938,P<0.05),the Dmean of average dose of bilateral parotid glands(tleft=-2.076,tright=-2.094,P<0.05),the D50 for dose of 50%volume of bilateral parotid glands(tleft=-2.123,tright=-2.230,P<0.05),and the volume percentage V30 of bilateral parotid gland dose(tleft=-2.505,tright=-2.491,P<0.05)in patients were significantly re-duced in the experimental group compared to the control group,while there was no statistically significant differences in target area do-simetric parameters(P>0.05).The dry mouth and taste loss in the experimental group were lower than those of the control group(P<0.05),and the difficulty in opening the mouth and caries scores were lower than those of the control group,but the difference was not statistically significant(P>0.05).Conclusion The oral humidity detection device can detect the oral humidity of radiotherapy pa-tients in time,objectively evaluate the impact of radiation on patient's parotid gland,guide doctors to change the radiotherapy treatment plan in a timely manner,minimize the degree of parotid gland damage,and improve their quality of life in nasopharyngeal carcinoma radiotherapy patients.At the same time,the device is easy to operate,time-consuming,and non-invasive,which improves the effec-tiveness and safety of radiotherapy technology and is worth promoting this device.

Objective To analyze the effect of needle arrangement on the lung dose in interstitial brachytherapy for lung cancer. Methods For 15 patients undergoing interstitial brachytherapy for lung cancer, a virtual radiotherapy plan in which needle arrangement was not restricted by the ribs was designed and compared with the original plan. For the two plans, V5, V20, V30, and mean lung dose(MLD)of the whole lung were determined when the prescribed doses were 10,30, 60, and 120 Gy, respectively. The data were analyzed by Wilcoxon signed-rank test. Results The lung V5,V20, V30, and MLD were significantly smaller in the virtual plan than in the actual plan(all P<0.05). Conclusions Irregular needle arrangement prevents a further reduction in the lung dose in interstitial brachytherapy for lung cancer. In the implantation surgery, therefore, the needles should be arranged as regularly as possible.