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

IMRT as an Alternative Technique for Intracavitary Brachytherapy in Patients with Carcinoma of the Cervix: A Feasibility Study Using Unified Dosimetric Index

OBJECTIVE

Intracavitary brachytherapy (ICBT) plays an important role in the management of carcinoma of the cervix. This study attempts to find the feasibility of intensity-modulated radiation therapy (IMRT) as a boost for patients who are not suitable for ICBT in order to improve their disease-free and overall survival.

METHODS

Twenty patients with carcinoma of the cervix were included in this study. Nine fields of IMRT and ICBT plans were generated for PTVBoost. Various dosimetric indices like coverage, conformity, homogeneity, and gradient index were calculated, and the corresponding unified dosimetric index (UDI) values were generated. Plans were classified based on combined UDI, and the UDI values were compared with those of ICBT. In addition, rectum and bladder doses were compared.

RESULTS

All the dosimetric indices were within acceptable limits except for the gradient index. The gradient index of the IMRT and ICBT plans were 8.77 ± 0.26 and 1.33 ± 0.06 respectively (p < 0.0001). The mean of combined UDI with standard deviation was 32.557 ± 8.940 and plan quality was calculated from these values. Rectum and bladder doses for ICBT were lesser than IMRT (p < 0.0001).

CONCLUSION

ICBT is the gold standard for boost RT in carcinoma of the cervix patients. IMRT boost is feasible for patients who are unsuitable on medical grounds for brachytherapy.

Application of three-dimensional multi-imaging combination in brachytherapy of cervical cancer

BACKGROUND

Three-dimensional (3D) imaging has an important role in brachytherapy and the treatment of cervical cancer. The main imaging methods used in the cervical cancer brachytherapy include magnetic resonance imaging (MRI), computer tomography (CT), ultrasound (US), and positron emission tomography (PET). However, single-imaging methods have certain limitations compared to multi-imaging. The application of multi-imaging can make up for the shortcomings and provide a more suitable imaging selection for brachytherapy.

PURPOSE

This review details the situation and scope of existing multi-imaging combination methods in cervical cancer brachytherapy and provides a reference for medical institutions.

MATERIALS AND METHODS

Searched the literature related to application of three-dimensional multi-imaging combination in brachytherapy of cervical cancer in PubMed/Medline and Web of Science electronic databases. Summarized the existing combined imaging methods and the application of each method in cervical cancer brachytherapy.

CONCLUSION

The current imaging combination methods mainly include MRI/CT, US/CT, MRI/US, and MRI/PET. The combination of two imaging tools can be used for applicator implantation guidance, applicator reconstruction, target and organs at risk (OAR) contouring, dose optimization, prognosis evaluation, etc., which provides a more suitable imaging choice for brachytherapy.

Clinical Outcomes of MRI-Guided Adaptive Brachytherapy for Each Fraction in Locally Advanced Cervical Cancer: A Single Institution Experience

Purpose

This study aims to evaluate clinical outcomes of MRI-guided adaptive brachytherapy (MR-IGABT) for each brachytherapy fraction in patients with locally advanced cervical cancer (LACC).

Methods and Materials

A retrospective analysis was performed on 97 consecutive patients with LACC treated with 44.0–50.4 Gy external beam radiotherapy (EBRT) ± concurrent platinum-containing chemotherapy followed by 4 × 7 Gy MR-IGABT between September 2014 and April 2019. Intracavitary (IC)/interstitial (IS)/hybrid intracavitary and interstitial (IC/IS) brachytherapy was used in MR-IGABT. Brachytherapy planning and dose reporting followed the GEC-ESTRO recommendations. Clinical outcomes including overall survival (OS), cancer-specific survival (CSS), progression-free survival (PFS), local control (LC), and treatment-related toxicity evaluated by the RTOG criteria were analyzed. Kaplan–Meier and univariable and multivariable Cox regression analyses were used to analyze the prognostic factor.

Results

Median follow-up was 21.1 months. Median dose to 90% (D₉₀) of the high-risk clinical target volume (HR-CTV) was 91.7 Gy (range 76.7~107.2 Gy). Two-year OS, CSS, PFS, and LC were 83.5%, 84.1%, 71.1%, and 94.8%, respectively. Four patients (4.1%) suffered from grade 3 late gastrointestinal radiation toxicity, and no other grade 3 or greater radiation toxicity occurred. Initial HR-CTV was an independent factor of OS (p = 0.001, HR = 1.018/cm³), PFS (p = 0.012, HR = 1.012/cm³), and LC (p = 0.011, HR = 1.028/cm³). The HR-CTV D₉₀ (p = 0.044, HR = 0.923/Gy) was an independent factor of PFS. Age was an independent factor of LC (p = 0.010, HR = 1.111/year).

Conclusion

For patients with LACC, MR-IGABT was effective and safe. It showed favorable LC, OS, and minimal toxicity. Moreover, initial HR-CTV, HR-CTV D₉₀, and age were significant prognostic factors.

Comparison of computed tomography- and magnetic resonance imaging-based target delineation for cervical cancer brachytherapy

Purpose

The objective of this study was to compare and assess the accuracy of computed tomography (CT)-based target delineation with that of magnetic resonance imaging (MRI)-based on high-dose-rate brachytherapy (HDR-BT) for patients with cervical cancer.

Material and methods

Data of 20 patients with locally advanced cervical cancer were collected and evaluated. Dimensions, conformity, and dose parameters of high-risk clinical target volume (CTV_HR) as well as D_0.1cc, D_1cc, and D_2cc of organs at risk (OARs) based on MRI were compared with those based on CT.

Results

Average age of 20 patients included was 57.8 years. Width, thickness, and volumes of CT-based CTV_HR (CTV_HR-CT) were significantly overestimated compared with those of MRI-based CTV_HR (CTV_HR-MR). Mean values of dice similarity coefficient (DSC), Hausdorff distance (HD), and centroid distance (ΔV) of CTV_HR were 0.82 cm, 0.96 cm, and 0.35 cm, respectively. Dose values of CTV_HR-CT were significantly lower compared with those of CTV_HR-MR. Concerning OARs, geometrical and dosimetric values on CT were comparable to those on MRI.

Conclusions

The delineated ranges of CTV_HR were significantly over-estimated on CT compared with MRI. D₉₈ and D₉₀ of CTV_HR-CT were lower than CTV_HR-MR. DSC and ΔV of CTV_HR and CTV_IR were similar to each other; however, there was a difference in terms of HD. CT images regarding pre-BT MR images for delineating were not enough and MRI fusion is still required.

Inter-observer and intra-observer variability in reporting vaginal dose points for cervical cancer in high-dose-rate brachytherapy

Purpose

The ICRU 89 recommends reporting a set of vaginal dose points for cervical cancer treatments in order to quantify the goodness of implant. This vaginal dose reporting method for combined external beam radiotherapy and brachytherapy has been adopted by the EMBRACE II study protocol. Large variations in dose between patients and centers have been reported. The aim of this study was to determine possible discrepancies with consensus observers from the same institution. Therefore, the inter- and intra-observer variability were analyzed.

Material and methods

For five patients, five experienced observers reported dose at the proposed vaginal points twice. The effect of inter- and intra-observer variations on total dose was analyzed by estimating biologically equivalent dose EQD₂ (α/β = 3 Gy). Coefficient of variation (CV) was used to provide a measure of data dispersion as a proportion to the mean.

Results

The maximum inter-observer deviation among all patients and all points ranged from 0.5 Gy to 24.1 Gy in EQD₂. The higher inter-observer discrepancies were found at points at 3 o’clock and at 6 o’clock, with respect to ovoids. In case of the maximum intra-observer deviation, it ranged from 0.5 Gy to 14.2 Gy, with higher deviation points at 12 o’clock and 9 o’clock, with respect to ovoids.

Conclusions

There is a need to ensure consistency in vaginal points reporting. The impact of the dosimetric inter- and intra-observer variability should also be considered when dealing with dose tolerances and limits due to the potential dose gradient.

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.

Dosimetric comparison of graphical optimization and inverse planning simulated annealing for brachytherapy of cervical cancer

Purpose

Graphical optimization (GO) and inverse planning simulated annealing (IPSA) are the main treatment planning optimization techniques used in patients undergoing 3D brachytherapy treatment. This study aims to compare the dosimetric difference of plans optimized by GO and IPSA in cervical cancer brachytherapy.

Material and methods

21 cervical cancer patients data sets consisted of computed tomography (CT) and magnetic resonance imaging (MRI), acquired with the Fletcher applicator in situ were transferred to the Oncentra brachytherapy planning system. For each patient, the treatment plan was initially optimized with GO to reach a maximal D₉₀ tumor dose (6 Gy/fraction, 5 fractions), while keeping the dose to organs at risk (OARs) as low as possible. A second plan was then optimized with IPSA on the same CT images and data set (i.e., contours, catheters, and location of dwell points). Targets and OARs dose volume histograms and irradiation time were compared; data were analyzed with paired t-test; p value < 0.05 was considered statistically significant.

Results

The plans with both optimizations meet the clinical requirements. The mean D₉₀ of the clinical target volume was comparable for GO and IPSA. Similar values (p > 0.05) of target V₁₀₀, V₁₅₀, V₂₀₀, HI, and CI were registered for GO and IPSA optimizations. Bladder and rectum D_1cc and D_2cc obtained by GO resulted in larger values than those obtained by IPSA (p = 0.002). V₇₅ for bladder and rectum were slightly higher for IPSA, but without statistical difference (p > 0.05). The irradiation time was comparable (p > 0.05).

Conclusions

In 3D brachytherapy of cervical cancer, GO and IPSA optimizations do not present a significant difference in target dose coverage; nevertheless, IPSA may reduce the maximum dose to normal tissue when compared with GO.