Diffusion-weighted MRI in image-guided adaptive brachytherapy: Tumor delineation feasibility study and comparison with GEC-ESTRO guidelines

Integration of functional imaging in brachytherapy

Functional imaging allows the evaluation of numerous biological properties that could be considered at all steps of the therapeutic management of patients treated with brachytherapy. Indeed, it enables better initial staging of the disease, and some parameters may also be used as predictive biomarkers for treatment response, allowing better selection of patients eligible for brachytherapy. It may also improve the definition of target volumes with the aim of dose escalations by dose-painting. Finally, it could be useful during the follow-up to assess response to treatment. In this review, we report how functional imaging is integrated at the present time during the brachytherapy procedure, and what are its potential future contributions in the main tumour locations where brachytherapy is recommended. Functional imaging has great potential in the contact of brachytherapy, but still, several issues remain to be resolved before integrating it into clinical practice, especially as a biomarker or in dose painting strategies.

Evaluation and evolution of apparent diffusion coefficient (ADC) in image-guided adaptive brachytherapy (IGABT) for cervical cancer

PURPOSE

Image-guided adaptive brachytherapy (IGABT) recently has shown excellent clinical outcomes with superior local control and less toxicity. For IGABT, T2W (T2-weighted) MRI is the gold standard. However, studies have shown that target delineation with the same results in uncertainties, poor interobserver variabilities, and low conformity indices for high-risk clinical target volume contours. In this study, we investigate the role of diffusion-weighted imaging-derived apparent diffusion coefficient (ADC) maps to aid in IGABT. We also evaluated ADC from the baseline to brachytherapy.

METHODS AND MATERIALS

Thirty selected patients were enrolled for this study, and two MRIs were taken at diagnosis and before brachytherapy. Patients were divided into two groups, Group 1 being patients with parametrial involvement before external beam radiotherapy and no parametrial involvement before brachytherapy. Group 2 included patients with parametrial involvement before external beam radiotherapy and persistent parametrial involvement before brachytherapy. ADC was measured at the center, edge, and 1 cm from the edge.

RESULTS

The measured ADC increased from diagnosis to brachytherapy, and this increase was more for the patients in Group 1 than in Group 2. The mean TDadc (diagnosis ADC, center), TEadc (tumor edge ADC diagnosis), and T1cmDadc (1 cm from edge at diagnosis) were 0.884, 1.45, and 1.9 × 10^-3 mm²/s, respectively. The TBadc (ADC at brachytherapy, center), TEBadc (tumor edge ADC at brachytherapy), and TE1cmBadc (1 cm from edge brachytherapy) were 1.2, 1.8, and 2.3 × 10^-3 mm²/s, respectively, p-value <0.00001. No abnormal ADC was present outside the high-risk clinical target volume contours.

CONCLUSION

MRI-based IGABT using T2W imaging essentially covers all functionally abnormal zones at brachytherapy. Diffusion-weighted imaging, along with ADC maps, should only be used as a supplement for target delineation.

Diffusion MRI: Technical principles and application to uterine cervical cancer

Imaging is involved in the management of uterine cervical cancer with several objectives: 1/to assess local and lymph node extension of the initial disease; 2/evaluate treatment response to conservative therapy; 3/detect recurrences. Pelvic MRI is the first-line examination in all these indications. It is the key element for delineation after image fusion when the indication of chemoradiation therapy is made. It is also essential for guiding the placement of applicators and optimising the dosimetry of brachytherapy. The diffusion-weighted acquisition is a sequence sensitive to the motion of water molecules. It allows distinguishing water molecules with free diffusion from water molecules with diffusion restricted by obstacles such as cell membranes or the cytoskeleton. The diffusion is thus connected to the cellularity of the explored tissue, and the cancers, being hypercellular, will present a high signal. It thus provides additional information thanks to a high contrast between the tumour and the surrounding tissues, facilitating detection, evaluation of the volume and extent of the disease.

Image-Guided Gynecologic Brachytherapy for Cervical Cancer

The incorporation of magnetic resonance imaging in brachytherapy has resulted in an increased use of interstitial catheters in order to create a comprehensive treatment plan that covers the visualized tumor. However, the insertion with passive, image-guidance requires estimating the location of the tumor during the insertion process, rather than visualizing and inserting the catheters directly to the desired location under active tracking. In order to treat residual disease, multiparametric MR sequences can enhance the information available to the clinician. The precision availed by MR-guided brachytherapy results in substantial improvements in needle positioning, and resulting treatment plans.

Imaging for Target Delineation and Treatment Planning in Radiation Oncology: Current and Emerging Techniques

Imaging in radiation oncology has a wide range of applications. It is necessary not only for tumor staging and treatment response assessment after therapy but also for the treatment planning process, including definition of target and organs at risk, as well as treatment plan calculation. This article provides a comprehensive overview of the main imaging modalities currently used for target delineation and treatment planning and gives insight into new and promising techniques.

Potentials and challenges of diffusion-weighted magnetic resonance imaging in radiotherapy

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Discussion of DW imaging protocols and imaging setup.

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Discussion of mono- and bi-exponential models for quantitative parameter extraction.

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Review of recent publications investigating potential benefits of using DWI in RT, including detailed synoptic table.

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Detailed discussion of geometric and quantitative accuracy of DW imaging and DW-derived parameters.

Purpose

To review the potential and challenges of integrating diffusion weighted magnetic resonance imaging (DWI) into radiotherapy (RT).

Content

Details related to image acquisition of DWI for RT purposes are discussed, along with the challenges with respect to geometric accuracy and the robustness of quantitative parameter extraction. An overview of diffusion- and perfusion-related parameters derived from mono- and bi-exponential models is provided, and their role as potential RT biomarkers is discussed. Recent studies demonstrating potential of DWI in different tumor sites such as the head and neck, rectum, cervix, prostate, and brain, are reviewed in detail.

Conclusion

DWI has shown promise for RT outcome prediction, response assessment, as well as for tumor delineation and characterization in several cancer types. Geometric and quantification robustness is challenging and has to be addressed adequately. Evaluation in larger clinical trials with well designed imaging protocol and advanced analysis models is needed to develop the optimal strategy for integrating DWI in RT.

A national survey of AIRO (Italian Association of Radiation Oncology) brachytherapy (Interventional Radiotherapy) study group

Purpose

To review brachytherapy resources and to explore current practice patterns in Italy.

Material and methods

In 2016, on behalf of the Italian Association of Radiation Oncology (AIRO), the Brachytherapy Study Group proposed conducting a survey in order to identify brachytherapy practice patterns. An electronic questionnaire was sent to all radiotherapy centres in Italy, asking for: 1. General information on the Radiation Oncology Centre (affiliation, whether brachytherapy was delivered or not); 2. Brachytherapy equipment and human resources; 3. Brachytherapy procedures; 4. Brachytherapy assessment (number of patients treated annually, treated sites, and different modalities of treatments).

Results

A total of 66 questionnaires were returned (33.5% of all brachytherapy centers in Italy), out of which 48 (74%) from non-academic hospitals, 6 (10%) from academic hospitals, and 12 (16%) from private institutions. Most centers (84%) had only one brachytherapy machine; 44% did not deliver brachytherapy treatments or delivered less than demanded because of the lack of staff or expertise, need of modernization, or other reasons. The majority of treatments were administered to outpatients for gynecological tumors.

Conclusions

This survey illustrates the current status of brachytherapy in Italy and should encourage collaboration to develop, implement, and monitor its use when appropriate.