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

High-Dose-Rate Three-Dimensional Image-Guided Adaptive Brachytherapy (3D IGABT) for Locally Advanced Cervical Cancer (LACC): A Narrative Review on Imaging Modality and Clinical Evidence

Background: Brachytherapy (BT) is a critical component of radiotherapy for locally advanced cervical cancer (LACC), and it has rapidly developed in recent decades. Since the advent of three-dimensional image-guided adaptive brachytherapy (3D-IGABT), magnetic resonance imaging (MRI) has emerged as the primary modality for image guidance. Meanwhile, other imaging modalities, such as computed tomography, 18F-fluorodeoxyglucose positron emission tomography, ultrasound, and their combinations have also been widely studied. Materials and methods: We reviewed studies on different imaging modalities utilized for target delineation and planning. Emerging techniques in IGABT like real-time image guidance and 3D printing were also included. We summarized research on their feasibility and concentrated on their clinical outcomes. Results: MRI-guided BT was the gold standard, and CT-guided BT was the most widely applied. Other modalities have shown feasibility and promising efficacy in dosimetry studies and preliminary outcomes. The longer-term clinical outcomes associated with these approaches require further elucidation. Conclusions: As 3D-IGABT was validated by promising clinical outcomes, the future of BT for LACC is expected to progress toward the refinement of more effective image-guided procedures. Moreover, achieving operational consensus and driving technological advancements to mitigate the inherent limitations associated with different imaging modes remain essential.

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

High-dose-rate brachytherapy (HDR-BT) has been shown to play an important role in the treatment of cervical cancer patients. The aim of this systematic review and meta-analysis was to compare the dose parameters and long-term effects of MRI-based, CT-based and hybrid imaging (MRI/CT)-based volumetric planning. A systematic search was conducted to identify the clinical studies of BT treatment on cervical cancer patients. After study selection, a total of 13 clinical studies were enrolled for further analysis. No obvious differences were observed among the treatment parameters and the patients included. In detail, no significant difference was observed among these three techniques of volumetric planning in the parameters of high-risk clinical target volume (HR-CTV), total dose of D90 or mean fraction dose of D90. Meanwhile, MRI-based planning was superior to CT-based treatment in the total dose D2cc to organs at risk (OAR) for the bladder, rectum and sigmoid. Furthermore, no significant difference was observed among MRI-, CT- or hybrid-based treatments with the mean fraction dose D2cc to OAR for the bladder, rectum or sigmoid. In conclusion, MRI provides good anatomical delineation of the relevant HR-CTV and OAR, and performed better in the analyses of dose parameters compared with CT. At least one MR image is required to assess the tumour extension, with clinical findings and MRI information facilitating much more accurate CT-based contouring.

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

Purpose

The dose distributions obtained from three imaging approaches for target delineation in cervical cancer using high-dose-rate (HDR) brachytherapy were investigated.

Material and methods

Ten cervical cancer patients receiving four fractions of HDR brachytherapy were enrolled. Based on different imaging approaches, three brachytherapy plans were developed for each patient: with the high-risk clinical target volume (HRCTV) delineated on magnetic resonance (MRI) images for every fraction (approach A; MRI-only); on MRI for the first fraction and computed tomography (CT) images for the subsequent fractions (approach B; MRI_1st/CT); and on CT images for all fractions (approach C; CT-only). The volume, height, width at point A, width at maximum level, and dosimetric parameters (D₁₀₀, D₉₈, D₉₅, and D₉₀ of the HRCTV; and D_0.1cc, D_1cc, and D_2cc of all organs at risk, or organ at risk – OAR: bladder, rectum, sigmoid colon, and bowel) provided by each approach were compared.

Results

The mean HRCTV volume, width, and height obtained from approach C (CT-only) were overestimated compared to those from approaches A (MRI-only) and B (MRI_1st/CT). The doses to the HRCTV for approaches A and B were similar. However, the HRCTV doses for approach C were significantly lower than those for approaches A and B for all parameters (D₉₅-D₁₀₀). As to the OAR, the three approaches showed no differences.

Conclusions

A combination of MRI and CT is a safe alternative approach for cervical cancer HDR brachytherapy. The technique provides comparable dosimetric outcomes to MRI-based planning, while being more cost-effective.

Off-line magnetic resonance imaging navigation of cervix cancer brachytherapy in patients with risk factors for uterine perforation

Purpose

There are no reports on pre-insertion identification of cervix cancer patients at risk for uterine perforation during brachytherapy (BT). Our aim was to assess the incidence of risk factors in our patient cohort, and assess feasibility of a novel technique of magnetic resonance imaging (MRI)-guided navigation for applicator insertion (NAI) in high-risk cases.

Material and methods

All patients with locally advanced cervical cancer, treated with image guided adaptive BT at our department between October 2013 and June 2017 were considered for analysis. Tumor characteristics on initial MRI (MRI_initial), pre-BT MRI (MRI_pre-BT), and BT MRI (MRI_BT) were assessed. Frequency of risk factors (age above 60 years, retroverted/retroflected uterus, tumor necrosis, non-visible cervical orifice, distorted cervical canal) was recorded. Patients with two or more factors underwent MRI guided NAI. Time needed for NAI was estimated and procedure feasibility score assigned using a three-tiered scoring system.

Results

Twenty-seven patients (98 insertions) were included. Mean tumor volume was 70.2 (± 47.9), 17.8 (± 18.9), and 10.3 (± 9.1) cm³ on MRI_initial, MRI_pre-BT, and MRI_BT1, respectively (p < 0.05). In 16 (59%) cases, ≥ 1 perforation risk factor was found on MRI_pre-BT: distorted canal in 12 (44%), necrosis in 9 (33%), retroverted/retroflected uterus in 8 (30%) cases. Nine (33%) patients had ≥ 2 risk factors and underwent MRI guided NAI. Additional time to perform NAI was estimated at 105 minutes, and feasibility score was 1 in all cases. There were no cases of uterine perforation.

Conclusions

Using pre-insertion MRI, we found ≥ 2 risk factors for uterine perforation in 1/3 of patients. Off-line MRI navigation was feasible and enabled non-complicated insertion in all cases. Further studies with larger sample size are warranted to assess its clinical efficacy.