Effects of gas cavity in rectum on radiotherapy plan for prostate cancer(PDF)
《中国医学物理学杂志》[ISSN:1005-202X/CN:44-1351/R]
- Issue:
- 2018年第8期
- Page:
- 879-884
- Research Field:
- 医学放射物理
- Publishing date:
Info
- Title:
- Effects of gas cavity in rectum on radiotherapy plan for prostate cancer
- Author(s):
- JU Mengyang1; SHI Yujing1; LI Jinkai2; TIAN Tian2; ZHENG Hailun2; SUN Xinchen2
- 1. Department of Medicine in Specific Environments, Nanjing Medical University, Nanjing 210009, China; 2. Department of Radiation Oncology, the First Affiliated Hospital of Nanjing Medical University, Nanjing 210009, China
- Keywords:
- ; Keywords: prostate cancer; gas cavity; volumetric modulated arc therapy; dosimetric difference; conformity index; homogeneity index
- PACS:
- R815.6；R737.25
- DOI:
- DOI:10.3969/j.issn.1005-202X.2018.08.003
- Abstract:
- Abstract: Objective To define the structure of gas cavity and investigate the effect of gas cavity in rectum on radiotherapy plan for prostate cancer. Methods Twelve patients with prostate cancer were selected. The target volume was delineated and gas cavity was defined in cone beam computed tomography (CBCT) images obtained before the first treatment. The gas cavity in CBCT images was mapped into CT images. The electron density was determined based on the CT value of gas cavity, and then the electron density value of gas cavity was changed for recalculating the radiotherapy plan. The mean dose (Dmean) and maximum dose (Dmax) of planning target volume (PTV), the Dmean and Dmax of target area corresponding to gas cavity (PTVg), the variations of Dmean, V30, V40, V50, V70 of rectum and bladder, the variations of V30 of femoral head were compared. Furthermore, the differences in conformity index and homogeneity index were also compared. Results A total of 24 treatment plans were designed. In the present of gas cavity, both Dmean and Dmax of PTV were decreased compared to those without gas cavity, without statistical significance (P>0.05). The Dmean and Dmax of PTVg also decreased, without statistical differences (P>0.05). With the existence of gas cavity, the conformability (conformity index decreased) and homogeneity (homogeneity index increased) of the plans were decreased. For organs-at-risk, the Dmean, V5, V30, V40 of rectal was increased by 0.4 Gy, 0.5%, 0.8%, 1.7%, respectively, and the differences were statistically significant (P<0.05), but the variations of rectum V50 didn’t showed any statistical significant (P=0.310). The Dmean, V5, V30, V40, V50 of bladder were decreased, without statistical differences (P>0.05). The V30 of both sides of the femur was increased by 0.1% and 0.2%, respectively. The monitor units and segments didn’t changes even with the presence of gas cavity. Conclusion In prostate radiotherapy plans, gas cavity increases the target dose to rectum, but has little effects on the target area and other organs at risk. Therefore, it is significant to monitor the presence of gas cavity in the rectum before retreatment.
Last Update: 2018-07-26