Dosimetric feasibility of iterative kV CBCT for radiation therapy planning for pelvis
10.3760/cma.j.issn.0254-5098.2021.11.010
- VernacularTitle:基于盆腔迭代锥形束CT图像的剂量学可行性分析
- Author:
Bo YANG
1
;
Zhiqun WANG
;
Wenbo LI
;
Qizhen ZHU
;
Rui LI
;
Xin ZHANG
;
Junsheng PAN
;
Ke HU
;
Fuquan ZHANG
;
Jie QIU
Author Information
1. 中国医学科学院北京协和医学院北京协和医院放疗科 100730
- Keywords:
Iterative cone beam CT;
Radiation therapy planning;
Dose;
Gamma pass rate
- From:
Chinese Journal of Radiological Medicine and Protection
2021;41(11):851-855
- CountryChina
- Language:Chinese
-
Abstract:
Objective:To study the feasibility of using pelvic iterative cone beam CT images for dose calculation of radiation therapy planning, so as to provide support for adaptive radiotherapy.Methods:The CIRS 062 M phantom was scanned by Varian Halcyon v2.0 o-ring accelerator, and the average CT number under different scattering conditions was calculated, and then the ICBCT-ED conversion curve was established. CT images of CIRS 002PRA pelvic IMRT phantom and ICBCT images at different positions were collected. Treatment plan using VMAT technique based on CT image was designed and transplanted into ICBCT image with dose recalculated. The differences of gamma passing rate among target volume, organs at risk and 3-dimensional dose were compared. Based on the actual treatment plan of patients, the differences of 3-dimensional dose gamma passing rate in 10 pelvic patients were analyzed retrospectively.Results:There was a large CT value deviation at central position between the isolated no-scattering condition and the full-scattering condition, and the maximum deviation was 144 HU. The CT values of other positions in full-scattering condition were similar to those of the central position, and the maximum deviation was less than 50 HU. Based on the calculated result of ICBCT images at different positions of the pelvic phantom, the dose deviation of the target volume or organs at risk was less than 1 Gy. Compared with the plan based on CT images, the average 3-dimensional dose gamma passing rate under the criteria of 1% dose difference (DD)/1 mm distance-to-agreement (DTA) and 2% DD/2 mm DTA in plan based on ICBCT images were (88.86 ±1.18)% and (98.38±0.89)%, respectively. The ranges of average 3-dimensional dose gamma passing rate under the criteria of 2% DD/2 mm DTA and 3% DD/3 mm DTA in 10 patients with pelvic tumors were 90.03%-95.43% and 93.58%-97.78%, respectively, and the worst result was only 85.90% and 92.90%, respectively. The main reason of the worst result was the dose difference caused by large variation of bladder contour due to over-filling.Conclusions:Under comprehensive scattering conditions, the ICBCT-ED conversion curve is reconstructed and the treatment plan can be designed by using the ICBCT image of Halcyon v2.0 linear accelerator. The accuracy meets the standards of clinical application, which provides assurance for adaptive radiotherapy in the future.
