Cervical cancer is a prevalent gynecological malignancy in China that poses a significant threat to women's health [1]. For patients with stage IIB-IVA primary cervical cancer, radical chemoradiotherapy is the treatment of choice [2]. Still, the risk of recurrence after treatment is high, with a median recurrence time of 7–36 months, a recurrence rate between 8–26%, pelvic recurrence in 14–57% of patients and distant or multiple sites in 15–61% of patients [8]. For patients with stage IIB-IVA after radical radiotherapy, the 3-year PFS rate was 74.4% (95% CI, 68.0%-79.8%) [3], and the 5-year overall survival rate was approximately 70% [2]. A recent study found that patients with cervical cancer who underwent radical radiotherapy for stage IB1-IIIB had a local PFS rate of 70%-80% at two years [9]. Unfortunately, there is no standard treatment for recurrent cervical cancer and the prognosis is poor [10]. These studies suggest that while radical radiotherapy can help control cervical cancer, it is not always effective in preventing pelvic recurrence, which is a significant factor in treatment failure.

Numerous studies indicate that the presence of LNM and parametrial infiltration are significant factors that affect the prognosis of cervical cancer. In a retrospective analysis conducted by McComas et al., it was found that LNM negatively affected survival (IIIC1 Hazard Ratio [HR] = 2.0, p < 0.001, IIIC2 HR = 3.9, p < 0.001) [11].In a study conducted by Wang et al., 1433 patients with cervical cancer who underwent radical radiotherapy were reviewed. The study found that the 3-year disease-free survival (DFS) for patients with local LNM was 58.0%, while the DFS for patients without LNM was 81.8% [12]. The prognosis of cervical cancer patients is not solely determined by the presence or absence of lymph node metastases, but also by the number and size of the metastases [13, 14]. PET/CT is currently the most accurate test available for detecting metastatic lymph nodes with noperable people, however, it has limitations. In one of the most recent collaborative studies, the sensitivity, specificity, positive predictive value, and negative predictive value of PET/CT were 33.3%, 94.2%, 53.8%, and 87.5%, respectively, for the detection of microscopic lymph node metastases [15]. To reduce the risk of lymphatic metastases, increasing the dose of irradiation to the area of positive lymph node drainage may be necessary. The degree of parametrial infiltration also has significant prognostic significance. In their study, Wright et al. utilized data from the US National Cancer Database to analyze the 5-year overall survival rates of patients with stage IIIA (40.7%), IIIB (41.4%), IIIC1 (60.8%), and IIIC2 (37.5%). Their findings indicated that patients with stage IIIC1 had a significantly better prognosis compared to those with stage IIIA and IIB [16]. Grigsby et al. reported that the 5-year PFS rates were 52%, 63%, and 36% for stage IIIB, IIIC1, and IIIC2, respectively. Notably, patients with stage IIIC1 had a better prognosis than those with stage IIIB [17]. The findings indicate that the new staging system contradicts the previously held principle that higher stage indicates worse prognosis. The presence of a large localised tumour (stage IIIB) may have more clinical relevance to prognosis than lymph node metastases. These results provide theoretical support for using IMRT-SIB to parametrial areas and positive lymph node drainage.

According to the NCCN guidelines, the current radiotherapy regimen for cervical cancer combines ERBT and ICBT [18]. ICBT, in particular, is a crucial part of radical radiotherapy and used in conjunction with high-dose radiation at the end of external irradiation, greatly enhancing the local control rate and surviva lrate in advanced cervical cancer [19]. The intracavitary rear-mounted radiation source's fixed location can cause issues such as inadequate radiation to the tumor and excessive radiation to surrounding normal tissues, which can result in severe complications [20]. Improving the effectiveness of cervical cancer treatment while minimizing side effects is crucial in reducing recurrence rates. While some studies have attempted to increase overall radiation dose to improve local control rates in the pelvis, research has shown that this approach does not lead to further improvements in local control rates but increases the risk of late complications [21]. However, traditional supplemental dosing techniques are limited to two-dimensional imaging which can lead to unpredictable dose distribution to both the tumor and surrounding OARs [22].So is a method available that allows for a more rational target area dose distribution and simpler target area dose calculation? IMRT-SIB, derived from IMRT, is an irradiation method that simultaneously delivers split doses to different target areas within the same irradiation field. This method has demonstrated better outcomes in breast, rectal, and head and neck squamous cell carcinomas [23,24,25], and has also been reported to be effective in treating cervical cancer. The National Comprehensive Cancer Network (NCCN) has recently updated its guidelines to include sib to positive lymph nodes and parametrial areas as a new treatment option for cervical cancer. This provides patients with more options for managing their condition [18].

According to the NCCN guidelines, a dose of external radiation of around 40–45 Gy is needed to cover minimally diseased lymph nodes. For large unresected limited lymph node lesions, an additional dose of 10–20 Gy can be administered. However, it is important to take into account the dose of brachytherapy [18].In a study conducted by Yunzhi Dang et al., 74 patients with stage IIB-IVB cervical cancer underwent IMRT with simultaneous dose increments for pelvic lymph nodes, pelvic field doses of 45–50 Gy/25 f,positive lymph nodes of 62.5 Gy/25 f and intracavitary brachytherapy of 24 Gy/3 f to 42 Gy/6 f. The study found that the 3-year local control, distant metastasis-free survival, and overall survival rates were 91.7%, 75.7%, and 71.4%, respectively. Additionally, there were no significant differences in side effects observed [26]. Patients with locally advanced cervical cancer were treated with a combination of IMRT/VMAT (45 Gy/25f), weekly cisplatin chemotherapy, and pushes to LNM (60 Gy/25f), followed by ICRT(28 Gy/4f). The 3-year OS rate, local recurrence-free survival rate, regional recurrence-free survival rate, and distant recurrence-free survival rate were 69%, 91%, 79%, and 77% in 23 patients, not statistically significant when compared to patients without LNM [27]. In a prospective study by Beriwal et al., 36 patients with stage IB2-IVA cervical cancer were treated with IMRT and concurrent cisplatin chemotherapy. The metastatic lymph node area received a synchronous increase to 55-60 Gy, and high-dose-rate ICBT was implemented simultaneously. 34 patients achieved CR, 11 experienced recurrences, 2 had in-field recurrences, and 9 developed out-field recurrences [28]. Most studies suggest that simultaneous boost to positive lymph nodes can improve the control rate of cervical cancer. However, it has not been confirmed whether this treatment can improve the prognosis of cervical cancer.

According to the NCCN guidelines, in cases where large parametrial/pelvic sidewall tumors are not adequately covered by ICBT, parametrial boost of 5–10 Gy may be considered at the end of total pelvic radiotherapy, but only in selected cases [18]. According to some scholars, interstitial brachytherapy (IB) is an effective treatment for cervical cancer. It can increase the dose of the cancerous area while decreasing the dose of nearby OARs [29]. In a study evaluating the efficacy of IB for patients with bulky (≥ 4 cm) and high-risk, stage IIB-IVB advanced cervical cancer, the four-year rates of local control, pelvic control, DFS, and OS were 100%, 100%, 81.6%, and 87.8%, respectively [30]. Although IB is a viable medical procedure, it should be noted that it is invasive and carries a significant risk of complications, including but not limited to infection and haemorrhage. Marnitz et al.reported on the feasibility of using helical tomotherapy with the SIB technique to enhance radiation dose. Their study demonstrated a low rate of acute toxic reactions [31]. Building upon the success of helical tomotherapy with SIB, we believe that using IMRT-SIB is feasible.

In this study, a new target range of CTV-hr was defined to reduce the recurrence rate of patients by increasing the radiation dose to high recurrence sites without changing the total cervical radiation dose. In our study, implementing a CTV-hr and performing IMRT-SIB can lead to a significant improvement in the PFS and OS rates of patients with stage IIB-IVA cancer. we conducted a stratified analysis and found a significant increase in the 3-year OS rate, PFS rate, in-field PFS rate, and out-field PFS rate in patients with IIB-IIIC1 compared to the control group. However, no significant difference was observed in patients with stage IIIC2 and IVA. One possible explanation for this phenomenon is that patients in this stage may have already developed metastasis to the para-aortic lymph nodes or infiltration of the pelvic organs beyond the true pelvic area. This can ultimately result in distant metastases occurring in a shorter period of time, leading to a poor prognosis.

The study has a few limitations that should be noted. Firstly, it is a retrospective study. Secondly, the FIGO 2018 staging system has revised lymph node metastasis, but some of the data and references in this study are based on the previous 2009 FIGO staging system. Thirdly, since the patient did not undergo lymph node biopsy, it is necessary to verify whether the lymph nodes were indeed metastatic. Therefore, a prospective trial is needed to confirm these findings.