In global cancer statistics, cervical cancer ranks fourth for both incidence and mortality in women (1). In China, cervical cancer had a significant upward trend in age-standardized incidence rates (2).

Stages IB2, IIA2, IIB, IIIA, IIIB, and IVA (FIGO 2009) cervical cancers are all locally advanced cervical cancer (LACC). To treat this type of cervical cancer, the National Comprehensive Cancer Network (NCCN) guidelines recommend the external beam radiotherapy (EBRT), concurrent platinum-containing chemotherapy, and brachytherapy (category 1) (3). As a critical component of the definitive radiation therapy, brachytherapy technology has been rapidly developing in recent years. In consideration of significant changes in the tumor regresses and the topography of the target and organs at risk during the course of treatment (4), image-guided adaptive brachytherapy (IGABT) became an individualized treatment method for patients with LACC. IGABT improves overall survival (OS) and generates a high rate of local tumor control (LC) with a moderate rate of treatment-related morbidity (5–8). IGABT has been developing particularly in Europe, North America, and Asia (9).

The preferred imaging technologies for IGABT for LACC are CT and MRI. Compared with CT, advantages of MRI lie in the soft tissue contrast and in discrimination of cervical cancer from normal uterine and adjacent tissue (10). This helps to define the tumor shrinkage and topography after EBRT (11). The NCCN guidelines recommend MRI as the best imaging modality to determine soft tissue and parametrial involvement in patients with advanced tumors (3). Even so, it is difficult for every institution to gain MRI access for each individual brachytherapy fraction (7, 12–17). Due to the limited MRI availability, some institutions use MRI only in some of the brachytherapy fractions (12, 16–18). The use of MRI-guided adaptive brachytherapy (MR-IGABT) in each fraction is still limited (18). The aim of this study was to evaluate the clinical outcomes of MR-IGABT in each fraction for Chinese patients with LACC.

A total of 97 consecutive patients were included in this study, treated between September 2014 and April 2019. The median age at diagnosis was 54 (range 30~79) years. The median overall treatment time (OTT) was 63 days (range 40~141 days). Table 1 shows patients and treatment characteristics. For stages IIA2~IVA tumors, IC/IS and IS brachytherapy techniques were used in a higher proportion of 65%, 84%, 81%, 100%, and 94%, respectively.

MRI has been recommended as gold standard imaging for cervical cancer contours, with some comparative studies previously published (14, 23, 24), and for MR-IGABT (repetitive MRI during complete brachytherapy treatment), several studies reported its clinical efficacy for LACC patients in Europe (7, 25) and North America (26). This study aimed to report the treatment outcomes of MR-IGABT for 97 Chinese LACC patients.

Whether MR-IGABT brings satisfactory clinical outcomes for cervical cancer, it has been a research priority of many radiotherapy centers in recent years. Lindegaard et al. (6) compared outcomes of LACC between 2D (X-ray)-guided brachytherapy and MR-IGABT. The 3-year OS of MR-IGABT showed a significant improvement (79% vs. 63%, p = 0.005), and 3-year LC of MR-IGABT was achieved in 91% of patients. Moreover, the moderate and severe late morbidity were both reduced by about 50% (p = 0.02). Kamran et al. (27) compared outcomes of LACC of MR-IGABT versus CT-guided brachytherapy. OS was significantly improved in MR-IGABT (84% vs. 56%, p = 0.036), and 2-year LC were 96% and 87% (p = 0.65), respectively. A large multicenter cohort study of Retro EMBRACE (28) included 731 LACC patients showed the efficacy and safety of MR-IGABT. Five hundred and ninety-two (80.9%) patients used MR-IGABT for at least one brachytherapy fraction, and 168 (23.0%) patients used IC/IS technique. The 3/5-year actuarial OS and LC were 74%/65% and 91%/89%, respectively. The 3/5-year grades 3–5 late morbidity was 4%/5% and 6%/7% for bladder and gastrointestinal tract, respectively. These excellent outcomes of MR-IGABT have been demonstrated in the western world. For Chinese patients with LACC, Wu et al. (18) recently evaluated the clinical outcomes of MR-IGABT where MRI was repeated at each implant (with implant in situ), in limited patient numbers (49 Chinese patients), with the first and the third brachytherapy fractions using MR-IGABT and other brachytherapy fractions were planned on CT imaging. Two-year OS and LC were both achieved in 90% of the patients with no severe late toxicity.

Table 7 (5–8, 17, 18, 25–30) summarizes the clinical outcomes of IGABT mentioned in this study and/or other studies recently published. The clinical outcomes of MR-IGABT, including the present study, show favorable OS, LC, and limited severe morbidity. The 2-year rates for OS and LC were achieved in 83.5% and 94.8% in the present study. Studies (8, 31) showed most local failures occurring less than 2 years after treatment. Tan et al. (32) summarized the distribution of local failure by time: 44.9% (year 1), 29.0% (year 2), 8.7% (year 3), 8.7% (year 4), 2.9% (year 5), 1.4% (years 6–10), and 4.3% (>10 years).

PFS is another important clinical outcome. Two-year PFS in the present study was 71.1%. A total of 20 distant metastasis occurred, which was the largest share of PFS (20/29). This was similar to other studies (7, 32, 33). Potter et al. (7) reported that IGABT technology significantly reduces local failure, which will further make distant metastases the predominant failure pattern. In order to reduce the risk of distant metastases and improve PFS, intensified chemoradiotherapy (34) or other therapy (such as molecular targeted therapy or immunotherapy) should be taken into account.

The most common radiation toxicity that occurred was grade 1 acute mucous membrane radiation toxicity (58.1%). Other incidences of radiation toxicity (acute bladder, acute lower gastrointestinal, late bladder, and late gastrointestinal) were all less than 20% (19.4%, 9.2%, 17.3%, and 19.4%, respectively). Only 4 patients (4.1%) showed grade 3 late gastrointestinal radiation toxicity. After symptomatic treatment, 2 patients fell to grade 1 and 2 patients fell to grade 0. ABS guideline (35) recommended the D_2cc to the bladder, rectum, and sigmoid are ≤90, ≤75, and ≤75 Gy, respectively. In this study, only 2 (2%) patients had a rectum D_2cc higher than 75 Gy. The interstitial-related side effect (such as pain, bleeding, infection) was settled with symptomatic treatment. MR-IGABT with interstitial technique can fully conform to dose limits for OARs, which will further lead to a well- tolerated treatment.

In the present study, the larger initial HR-CTV (per cm³) was an independent factor for worse OS, PFS, and LC. We investigated the correlations between initial HR-CTV and other dose–volume parameters. The initial HR-CTV was negatively correlated with HR-CTV D₉₀ (p = 0.002), HR-CTV D₉₈ (p = 0.016), and HR-CTVD₁₀₀ (p = 0.006) and positively correlated with bladder D_0.1cc (p = 0.047), bladder D_1cc (p < 0.001), bladder D_2cc (p < 0.001), rectum D_0.1cc (p = 0.027), rectum D_1cc (p < 0.001), rectum D_2cc (p < 0.001). The initial HR-CTV showed no correlation between the dose to sigmoid and small bowel. The probable cause is the geometrical uncertainties in OARs (36) (e.g., filling status and motion in relation to the radiation sources). These uncertainties are highly related to the motility of the organs, such as, the sigmoid and small bowel. The high dose of HR-CTV D₉₀ was an independent prognostic factor for improved PFS. Furthermore, we found that age was an independent factor for LC. A large national cohort analysis (37), which included 24,126 patients found that age was an independent predictor for the receipt of complete treatment (concurrent chemotherapy with combination external beam radiation and brachytherapy to total dose ≥70 Gy) for cervical cancer. Its multivariable analysis showed age groups of women older than 61 (group 61–70, group 71–80, group 80+) were less likely to be treated with complete treatment. In the present study, age was significantly different (p = 0.016) between patients with and without concurrent chemotherapy [median age was 53 (range 30–76) vs. 61.5 (range 33–79)]. The older age resulted in incomplete treatment, which may influence the LC.

The independent prognostic factors for LC in previous studies (26, 38, 39) where patients received MR-IGABT have reported stage, histology, HR-CTV D₉₀, and initial HR-CTV, OTT. Dimopoulos et al. (39) found that LC was clearly greater if the HR-CTV D₉₀ ≥87 Gy. Horne et al. (26) found that LC was affected by HR-CTV >40 cm³. In the present study, 2-year LC was 96.5% for HR-CTV D₉₀ ≥87 Gy versus 83.3% for HR-CTV D₉₀ <87 Gy (log-rank, p = 0.039) and 100% for initial HR-CTV ≤40 cm³ versus 84.8% for initial HR-CTV >40 cm³ (log-rank, p = 0.001). In addition, we found that 2-year LC was significantly different between CR and PR (98.4% for CR vs. 87.9% for PR, log-rank, p = 0.040), indicating the initial tumor response may influence LC.

Interstitial techniques including IC/IS and IS techniques were used as a dose-escalation method in 90 of 97 patients in this study, with 85 patients (87.6%) HR-CTV D₉₀ ≥87 Gy and 96 patients (99.0%) HR-CTV D₉₀ ≥80 Gy. The median HR-CTV D₉₀ was 91.7 Gy, which meet the ABS (35) and NCCN guidelines (3). Only 1 patient (1%) showed HR-CTV D₉₀ lower than 80 Gy, due to the large volume of initial HR-CTV (93.08 cm³). Compared with traditional IC brachytherapy alone, interstitial technique is more feasible with adequate coverage of disease in the vagina and parametrium (40).

In the present study, 69 patients (71.1%) had OTT longer than 8 weeks, which was suggested within 8 weeks (3). The main reason was patients did not receive timely brachytherapy treatment after the end of EBRT, which can be further optimized. The reduction of OTT to avoid repopulation in cervical cancer is known to be one of the ways to improve LC. Compared with the difficulty to deliver a higher dose of radiation to cervical cancer, OTT can be more easily kept within certain limits. Mazeron et al. (41) reported that the inverse correlation (probit model) between overall treatment time and local control and excessive OTT was an independent factor of LC for LACC treated by IGABT, with a cutoff of 55 days (Log-rank, p = 0.004, and Cox model, p = 0.047). Although, for OTT, there was no statistical significance in OS, PFS, and LC in the present study, we found OTT was significantly different (p = 0.035) between CR and PR [median OTT was 62 days (range 40–125 days) vs. 64 days (range 54–141 days)]. In consideration of the significant difference of 2-year LC between CR and PR in this study, the longer OTT results in a poorer initial tumor response, which further impacts LC. However, there is still insufficient high-level evidence with regard to OTT effects because OTT is closely related to many factors such as tumor response, dose, fractionation, and treatment-related side effects.

The major limitation of this study is its retrospective nature, with 23 patients receiving EBRT in other institutions before the MR-IGABT in our center. This results in a lack of unity in the EBRT dosimetric data and treatment characteristics. In addition, a longer follow-up may be required to obtain more meaningful results.

This retrospective study including 97 consecutive Chinese patients with LACC has shown that MR-IGABT was effective and safe. It showed favorable LC, OS, toxicity, and morbidity. Moreover, initial HR-CTV, HR-CTV D₉₀, and age were significant prognostic factors. Future investigations and systemic treatment need to be emphasized.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by the ethics committee of China-Japan Union Hospital of Jilin University. The patients/participants provided their written informed consent to participate in this study.

YC: manuscript writing, data collection, and data analysis. YP: protocol development. NZ: manuscript writing. DH: data management. XG: data analysis. ZM: data analysis. GC: protocol development and manuscript editing. All authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.

This work was partially supported by grants from the National Natural Science Foundation of China (grant numbers 82073331, 81201737, 31600679, 81703034, 82003208), Project of Science and Technology Department of Jilin Province (grant number 20190303151SF, 20210401138YY), and Horizontal Project of Jilin University (grant numbers 2019YX435, 2019155).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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