Commission and preliminary validation of in-room CT in proton and heavy ion radiotherapy
10.3760/cma.j.cn113030-20240828-00336
- VernacularTitle:滑轨CT应用于质子重离子放疗的调试和初步验证
- Author:
Yanyan WEN
1
;
Jingfang ZHAO
;
Yinxiangzi SHENG
Author Information
1. 上海市质子重离子医院放射物理科，上海市放射肿瘤学重点实验室，上海质子重离子放射治疗工程技术研究中心，上海 201315
- Publication Type:Journal Article
- Keywords:
Radiotherapy, image-guided;
In-room on-rails computed tomography;
Radiotherapy, adaptive;
Radiotherapy, proton and heavy ion
- From:
Chinese Journal of Radiation Oncology
2025;34(6):576-584
- CountryChina
- Language:Chinese
-
Abstract:
Objective:To explore the accuracy of in-room on-rails CT (IRCT) for image-guided radiotherapy (IGRT) and adaptive radiotherapy (ART) during proton and heavy-ion radiotherapy.Methods:The positioning accuracy and registration accuracy of IRCT were tested by using the spherical phantom and multiple imaging modality iso-centricity, and the positioning accuracy of isocenter geometric mapping and 3D-3D registration accuracy were evaluated when the phantoms were applied to IGRT. Standard water-aluminum phantom and ACR467 phantom were utilized to establish and evaluate the HU value-relative linear stopping power to water (RLSP) conversion curve. By scanning the same rigid phantom images on both IRCT and planned CT, followed by dose calculation and comparison of dose differences, the consistency of dose distribution between 2 modalities was evaluated when applied to ART in relation to the planned CT. Pre-treatment CT of patient was acquired using IRCT scan before treatment. Online qualitative analysis and offline quantitative analysis were performed. A case of prostate cancer was selected, and its online qualitative analysis ability was tested by evaluating whether IRCT could effectively identify changes in the position of clinical target volume (CTV) and critical organs at risk. One case of prostate cancer and 1 case of breast cancer were selected, and the offline quantitative analysis ability was tested by the key dose volume histogram parameters of dose recalculation on CT before treatment.Results:In IGRT application, the isocenter geometric mapping positioning accuracy was 0.1 mm. The displacement accuracy for 3D-3D registration was 0.8 mm, with a rotational accuracy of 0.6°. In ART application, a CT HU value-RLSP conversion curve was established using standard methods. The RLSP variation range for 24 representative tissues was -3.91% to 1.49%, with an average variation of -0.75%±0.95%. Calculation results performed on rigid phantoms for head, chest, and abdominal-pelvic regions showed that compared to the planned CT, the γ pass rate for proton plan dose distribution consistency on IRCT was>97%, and >95% for carbon-ion plan, both using 2%/2 mm criteria with a 10% threshold. The results of 2 representative clinical applications showed that online qualitative analysis of carbon-ion plans for prostate cancer could identify changes in patient soft tissue position relative to the planned CT, CTV, and critical organs at risk before treatment. Offline quantitative analysis could quantify dose changes in patients undergoing treatment. In the prostate cancer original plan for prostate cancer, the relative volume of CTV receiving 95% (V 95%) of the prescribed dose was 100%, which were 97.63% and 99.91% before different fractions of treatment, respectively. For the bladder and rectum, V 95% was 3.00% and 3.80%, which were changed to 0.75% and 12.36% for one session of treatment, and 2.76% and 3.08% for another session of treatment, aligning with the results of online qualitative analysis. In the original plan for breast cancer, tumor bed CTV and breast CTV V 95% were 99.93% and 99.93%, which were 100.00% and 99.57% for one session of treatment and 92.32% and 93.13% for another session of treatment, triggering re-planning. The re-planned results were improved to 99.82% and 99.93%. Conclusions:IRCT can be applied to IGRT and ART in proton and heavy-ion radiotherapy, enabling accurate patient positioning verification and adjustment, as well as online anatomical qualitative analysis and offline dose quantitative analysis.
