Robustness of postoperative intensity-modulated radiotherapy plan for cervical cancer(PDF)
《中国医学物理学杂志》[ISSN:1005-202X/CN:44-1351/R]
- Issue:
- 2020年第1期
- Page:
- 22-28
- Research Field:
- 医学放射物理
- Publishing date:
Info
- Title:
- Robustness of postoperative intensity-modulated radiotherapy plan for cervical cancer
- Author(s):
- ZHU Zhipeng; LIU Wenqi; ZHU Huijun; HUANG Jiqin; LIAO Xihong; LI Guihua
- Department of Radiation Oncology, the Second Affiliated Hospital of Guangxi Medical University, Nanning 530000, China
- Keywords:
- Keywords: cervical cancer; robustness; setup error; intensity-modulated radiotherapy
- PACS:
- R730.55；R815
- DOI:
- DOI:10.3969/j.issn.1005-202X.2020.01.005
- Abstract:
- Abstract: Objective To discuss the sensitivity of dose distribution of postoperative intensity-modulated radiotherapy (IMRT) plan for cervical cancer to setup errors which were simulated by shifting the isocenter. Methods Postoperative IMRT plan was designed for 30 cases of cervical cancer. Assuming that all the systematic errors were in the same direction, the isocenter was shifted by ±3.0, ±5.0 and ±7.0 mm along the original axes of x, y and z to simulate the setup errors in left-right, abdomen-back, and head-feet directions, respectively, and the effects of setup errors on dose distribution were analyzed. After the recalculation of dose distribution without changing optimization conditions, the dose-volume histogram parameters of 30 reference plans and 540 recalculated plans were obtained. The differences in different directions were analyzed by paired t-test. Results When the error was 3, 5 and 7 mm, the average deviations of declines of CTV D98 and PTV V95 were 0.16% and 0.55%, 0.44% and 1.72%, 0.89% and 3.41%, respectively, and the frequency of excess V50 of small intestine, rectum, bladder, left femoral head and right femoral head were 2.22%, 0.00%, 0.00%, 0.00%, 0.00%; 11.11%, 2.22%, 0.00%, 4.44%, 4.44%; 15.56%, 6.67%, 2.78%, 13.33% and 14.44%, respectively. The results of paired t-test showed that compared with the setup errors in x and z axes, the setup error in y direction had greater effects on CTV D98 and PTV V95 (P<0.05, P<0.05); and that the V50 of small intestine and bladder was more affected by the setup error in back direction than the setup errors in the other directions (P<0.05, P<0.05). Moreover, the effect of the setup error in abdomen direction on the V50 of rectum was the greatest (P<0.05); the V50 of left femoral head was more affected by the setup error in right direction than the setup errors in the other directions (P<0.05), and the V50 of right femoral head was more affected by the setup error in the left direction (P<0.05). Conclusion When the setup error was smaller than 5 mm, the setup error has insignificant effects on target doses and the V50 of small intestine, bladder, rectum, left femoral head and right femoral head, which indicates the postoperative IMRT for cervical cancer was robust. However, with larger setup errors, the plans were no longer robust. The reason for that must be found before treatment, and if necessary, the device for positioning needed to be remade.
Last Update: 2020-01-14