MRI guided online adaptive radiotherapy and the dosimetric impact of inter- and intrafractional motion in patients with cervical cancer

Shouliang Ding; Zun Piao; Meining Chen; Fanghua Li; Yongbao Li; Biaoshui Liu; Hongdong Liu; Xiaoyan Huang; Junyun Li

doi:10.1016/j.ctro.2024.100881

MRI guided online adaptive radiotherapy and the dosimetric impact of inter- and intrafractional motion in patients with cervical cancer

Clin Transl Radiat Oncol. 2024 Oct 29:50:100881. doi: 10.1016/j.ctro.2024.100881. eCollection 2025 Jan.

Authors

Shouliang Ding^{1

2}, Zun Piao¹, Meining Chen¹, Fanghua Li¹, Yongbao Li¹, Biaoshui Liu¹, Hongdong Liu¹, Xiaoyan Huang^{1

2}, Junyun Li¹

Affiliations

¹ State Key Laboratory of Oncology in South China, Guangdong Provincial Clinical Research Center for Cancer, Sun Yat-sen University Cancer Center, Guangzhou 510060, PR China.
² United Laboratory of Frontier Radiotherapy Technology of Sun Yat-sen University & Chinese Academy of Sciences Ion Medical Technology Co., Ltd, Guangzhou 510060, PR China.

Abstract

Purpose: The aim of this study was to evaluate the inter- and intrafractional organs motions and dosimetric advantages of MRI guided online adaptive radiotherapy for cervical cancer.

Methods: A total of 150 fractions treated on the 1.5 T Unity MR-Linac were included in this study. Each fraction, pre-treatment, position validation and post-treatment MRI scans were obtained. Structures including CTV, rectum and bladder were delineated by the same radiation oncologists on each MRI. The inter- and intrafractional changes of contours were assessed by Hausdorff distance (HD), dice similarity coefficient (DSC), relative volume difference (ΔV) and the relative positions of the geometric center. The non-ART plans and online adaptive plans were obtained by recalculating or re-optimizing from reference plans on daily MRI, respectively. CTV coverage and OARs constraints were evaluated between ART and non-ART plans.

Results: For each fraction, the interfractional changes of HD, ΔV and DSC for CTV, bladder and rectum were significant. Our study also examined the relationship of bladder and rectum filling on CTV position. For 150 non-ART plans, CTV coverage constraints (D_98% ≥ 45 Gy) were not met by 45 %, while 15 % were not covered by more than 5 % of the prescribed dose. Compared to the non-ART plans, the ART plans had higher CTV coverage and lower dose to the bladder and rectum (P < 0.05). During the treatment, the intrafractional changes of bladder, rectum and CTV may affect actual dose delivery. And we observed an intrafractional time trend in the motion of the CTV. There were 15 % fractions failing the CTV coverage constraints in post-MRI due to intrafractional motion. The adaptive plans optimized with 3 mm margin could cover CTV of post-MRI in 98 % fractions.

Conclusions: Considerable inter- and intrafractional CTV and OARs changes were observed in cervical cancer patients treated on MR-Linac. MRI guided online ART has significant dosimetric advantages in cervical cancer and is an ideal approach for achieving individualized and precise radiotherapy.

Keywords: Cervical cancer; MR-Linac; MRI; Online adaptive radiotherapy.