Throwing the dart blind-folded: comparison of computed tomography versus magnetic resonance imaging-guided brachytherapy for cervical cancer with regard to dose received by the ‘actual’ targets and organs at risk

Abstract

PurposeComputed tomography (CT) is inferior to magnetic resonance imaging (MRI) in cervical tumor delineation, but similar in identification of organs at risk (OAR). The trend to over-estimate high-risk and low-risk clinical target volume (HRCTV, IRCTV) on CT can lead to under-estimation of dose received by 90% (D90) of the ‘actual’ CTV. This study aims to evaluate whether CT-guided planning delivers adequate dose to the ‘actual’ targets while spares the OAR similarly.Material and methodsMRI-guided high-dose-rate image-guided brachytherapy (IGBT) was performed in 11 patients. The pre-brachytherapy CTs were retrospectively contoured to generate CT-guided plans. MRI-based contours (HRCTVmri, IRCTVmri, bladdermri, rectummri, and sigmoidmri) were fused to CT plans for dosimetric comparison with MRI-guided plans. Paired 2-tailed t-test and Wilcoxon signed-rank test were used to analyze data.Results63.6% of CT plans achieved the HRCTVmriD90 constraint (≥ 7.2 Gy in one fraction), compared with 90.9% for MRI plans. > 90% of both modalities achieved the OAR’s constraints (EMBRACE). The percentage of CT and MRI plans that achieved the aims (EMBRACE II) for bladder, rectum, and sigmoid were 36.4% vs. 81.8%, 63.6% vs. 63.6%, and 72.7% vs. 72.7%, respectively. There were no statistically significant differences in HRCTVmriD90, IRCTVmriD90, or dose received by the most exposed 2 cm3 (D2cc) of OARmri between the modalities. Excluding the CT plans not achieving HRCTVmriD90 constraint, there were significant increase in bladdermriD2cc, rectummriD2cc, and sigmoidmriD2cc, compared with MRI plans (0.9 Gy/Fr, 95% CI 0.2-1.5, p = 0.018; 0.9 Gy/Fr, 95% CI 0.3-1.4, p = 0.009; 0.5 Gy/Fr, 95% CI 0.2-0.9, p = 0.027, respectively).ConclusionsMRI-based IGBT remains the gold standard. CT planning may compromise HRCTVmriD90 or increase OARmriD2cc, which could decrease local control or increase treatment toxicity.

Comparison of accuracy and long‐term prognosis between computed tomography‐based and magnetic resonance imaging‐based brachytherapy for cervical cancer: A meta‐analysis

“…Among them, two studies compared MRI‐ and hybrid (MRI/CT) imaging‐based BT therapies, while two other studies compared the effects of CT vs MRI vs hybrid imaging‐based BT . Another nine studies were performed to compare CT‐ and MRI‐based BT in cervical cancer patients . Among the included studies, the sample size ranged from 5 to 76 participants.…”

Impact of intracavitary brachytherapy technique (2D versus 3D) on outcomes of cervical cancer: a systematic review and meta-analysis

“…In addition, ~ 40% of patients included in the present meta-analysis received CT based 3D-BT. MRI provides superior soft tissue delineation compared with CT, so that there has been a concern that target volume might different between CT and MRI (29,30). A previous planning study compared CT and MRI guided brachytherapy, and resulted in that CT planning may compromise target volume coverage and increase OAR dose (29).…”

“…MRI provides superior soft tissue delineation compared with CT, so that there has been a concern that target volume might different between CT and MRI (29,30). A previous planning study compared CT and MRI guided brachytherapy, and resulted in that CT planning may compromise target volume coverage and increase OAR dose (29). Increasing the use of MRI based brachytherapy also could lead the improvement of survival and toxicities.…”

Comparison of impact of target delineation of computed tomography- and magnetic resonance imaging-guided brachytherapy on dose distribution in cervical cancer

“…Their accuracy of the target volume and all OAR delineations effectively deliver more tumor-specific high doses, with less adverse effects on the surrounding normal tissues [ 3 , 4 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ]. However, with CT, it is very difficult to identify the cervix and parametrium, and cause the tumor volume delineation to be overestimated, which results in a reduced dose coverage for the tumor volume and increased doses to OAR [ 7 , 8 , 9 , 10 , 26 , 27 ]. On the other hand, MRI-based planning provides better accuracy for the HRCTV and all OAR delineations.…”