Place of modern imaging in brachytherapy planning

Imaging has probably been the most important driving force for the development of brachytherapy treatments the last 20 years. Due to implementation of three-dimensional imaging, brachytherapy is nowadays a highly accurate and reliable treatment option for many cancer patients. To be able to optimize the dose distribution in brachytherapy the anatomy and the applicator(s) or sources should be correctly localised in the images. For computed tomography (CT) the later criteria is easily fulfilled for most brachytherapy sites. However, for many sites, like cervix and prostate, CT is not optimal for delineation since soft tissue is not adequately visualized and the tumor is not well discriminated. For cervical cancer treatment planning based on magnetic resonance imaging (MRI) is recommended. Some centres also use MRI for postimplant dosimetry of permanent prostate seed implant and high dose rate prostate brachytherapy. Moreover, in so called focal brachytherapy where only a part of the prostate is treated, multiparametric MRI is an excellent tool that can assist in defining the target volume. Applicator or source localization is challenging using MRI, but tolls exist to assist this process. Also, geometrical distortions should be corrected or accounted for. Transrectal ultrasound is considered to be the gold standard for high dose rate prostate brachytherapy and transrectal ultrasound -based brachytherapy procedure offers a method for interactive treatment planning. Reconstruction of the needles is sometimes challenging, especially to identify the needle tip. The accuracy of the reconstruction could be improved by measuring the residuals needle length and by using a bi-planar transducer. The last decade several groups worldwide have explored the use of transrectal and transabdominal ultrasound for cervical cancer brachytherapy. Since ultrasonography is widely available, offers fast image acquisition and is a rather inexpensive modality such development is interesting. However, more work is needed to establish this as an adequate alternative for all phases of the treatment planning process. Studies using positron emission tomography imaging in combination with brachytherapy treatment planning are limited. However, development of new tracers may offer new treatment approaches for brachytherapy in the future. Combination of several image modalities will be the optimal solution in many situations, either during the same session or for different fractions. When several image modalities are combined so called image registration procedures are used and it is important to understand the principles and limitations of such procedures.     

The Role of Magnetic Resonance Imaging in Brachytherapy

The application of magnetic resonance imaging (MRI) in image-guided brachytherapy has expanded rapidly over the past two decades. In cervix cancer, significant improvements in overall survival, local control and long-term morbidity have been shown in patients treated with MRI-guided brachytherapy, changing clinical practice and directing an international approach to standardise the technique; unifying adaptive target volume definition and dose reporting. MRI-guided prostate brachytherapy has significantly improved the accuracy of tumour and organ-at-risk delineation, facilitating targeted implantation and dose optimisation. It also has potential to improve clinical outcomes through enhancement of the therapeutic ratio and the identification of dominant lesions that can be the targets of sub-volume boosting and salvage therapy. However, MRI-guided brachytherapy presents a number of logistical and financial challenges in modern healthcare systems, requiring technologically advanced imaging and planning techniques, as well as robust safety and quality assurance procedures. A collaborative, multidisciplinary approach involving clinical oncologists, radiologists, medical physicists, therapy radiographers, nurses and technical staff is therefore critical to its successful incorporation into any clinical brachytherapy workflow. In this overview we evaluate the current role of MRI in image-guided brachytherapy, primarily in cervix and prostate cancer, but also in other tumour sites, and review its potential future developments in the context of both clinical and research spheres.     

ORIGINAL ARTICLE: Use of 3D imaging and awareness of GEC-ESTRO recommendations for cervix cancer brachytherapy throughout Australia and New Zealand

Introduction: A 2005 survey of practices indicated limited use of three-dimensional (3D) imaging modalities and planning methods in cervix cancer brachytherapy in Australia and New Zealand. However, advancing technologies and published recommendations are influencing change. This survey aims to identify both changes in practice and awareness and uptake of Groupe European de Curietherapie of the European Society for Therapeutic Radiology and Oncology (GEC-ESTRO) recommendations. Methods: A survey was emailed to all radiotherapy departments with brachytherapy facilities. Twenty departments practise brachytherapy for cancer of the cervix. The survey consisted of five questions enquiring about use and type of 3D imaging; rate of reimaging and replanning; and contouring, prescribing and reporting practices. Results: A 100% response rate was obtained. Sixty-five per cent of departments use 3D CT imaging to plan brachytherapy insertions. Thirty per cent of departments use two-dimensional (2D) x-rays. Four departments (20%) use a combination of imaging modalities including CT, ultrasound and MRI. Sixty-five per cent of departments reimage and replan for each insertion. Four departments (20%) contour, prescribe dose and report treatment according to GEC-ESTRO recommendations. Conclusions: There has been a marked increase in the use of 3D imaging and awareness of GEC-ESTRO recommendations. Implementation and reporting of image-based gynaecological brachytherapy is strongly dependent on local resources and infrastructure.     

Curiethérapie guidée par imagerie multimodale : l’exemple du cancer du col utérin

Image-guided brachytherapy is crucial in the management of locally advanced cervical cancers and has benefited from advances in imaging over recent decades. The recommendations of the European Brachytherapy - European Society for Radiation Oncology (GEC-ESTRO) have resulted in harmonized practices and improved clinical outcomes in terms of efficacy and toxicity. Post-implant magnetic resonance imaging (MRI) has become the reference imaging modality to guide brachytherapy. There is an increasing interest for other multimodal imaging in these patients. The metabolic information provided by Positrons Emission Tomography/computed tomodensitometry (PET/CT) is also very promising approach to guide personalized dose escalation strategies. The prognostic values of MRI and PET scanner before brachytherapy make it possible to consider personalizing the dose delivered in brachytherapy and to propose a dose escalation to patients who really need it and to possibly consider a deescalation strategy in patients with a very good prognosis. However, further studies are needed to confirm this approach.     

Brachytherapy for cancer of the cervix: An Australian and New Zealand survey of current treatment techniques

Establishing guidelines for the practice of brachytherapy throughout Australia and New Zealand is one of the goals of the Australasian Brachytherapy Group. To better appreciate Australasian resources and conditions, the group conducted a survey in early 2005. The aims were to survey current practices, to emphasize variations in practice and to determine the availability of advanced imaging and treatment methods to assess resources. A survey was sent to all Australian and New Zealand radiotherapy departments. The survey requested details of treatment with respect to external beam radiotherapy, brachytherapy, optimization methods, reporting methods, scheduling brachytherapy and access to imaging and methods of work‐up. Thirty‐four departments were contacted with 27 (79%) responses returned. Twenty‐one departments use brachytherapy. Doses and fractionation schedules varied and use of sectional imaging was minimal. Individualized dosimetry is practised in a limited fashion by 60% of the surveyed departments. There is high compliance with International Commission on Radiation Units 38 dose reporting recommendations. All brachytherapy units identified have access to CT and 85% to MRI within the hospital settings. Brachytherapy for cancer of the cervix is, currently, largely based on the Manchester system. The survey did emphasize considerable variation in dose and fractionation schemes between departments. The Australasian Brachytherapy Group subgroup intends to proceed with the process of formulating recommendations for cervix brachytherapy. It is intended that these will cover the use of image‐based planning and treatment, target definition(s), verification of brachytherapy treatments and a uniform dose‐reporting mechanism.     

Treatment planning for MRI assisted brachytherapy of gynecologic malignancies based on total dose constraints

PURPOSE: To develop a method for treatment planning and optimization of magnetic resonance imaging (MRI)-assisted gynecologic brachytherapy that includes biologically weighted total dose constraints. METHODS AND MATERIALS: The applied algorithm is based on the linear-quadratic model and includes dose, dose rate, and fractionation of the whole radiotherapy setting, consisting of external beam therapy plus high-dose-rate (HDR), low-dose-rate (LDR) or pulsed-dose rate (PDR) brachytherapy. Biologically effective doses (BED) are converted to more familiar isoeffective (equivalent) doses in 2-Gy fractions. For individual treatment planning of each brachytherapy fraction, the algorithm calculates the physical dose per brachytherapy fraction that corresponds to a predefined isoeffective total dose constraint. Achieved target dose and sparing of organs at risk of already delivered brachytherapy fractions are incorporated. RESULTS: Since implementation for use in clinical routine in 2001, MRI assisted treatment plans of 216 gynecologic patients (161 HDR, 55 PDR brachytherapy) were prospectively optimized taking into account isoeffective dose-volume histogram-based total dose constraints for high-risk clinical target volume (HR CTV) and organs at risk (bladder, rectum, sigmoid). The algorithm is implemented in a spreadsheet and the procedure is fast and efficient. An uncertainty analysis of the isoeffective total doses based on variations of tissue parameters shows that confidence intervals are larger for PDR compared with HDR brachytherapy. For common treatment schedules, overall uncertainties of high-risk clinical target volume and organs at risk are within 8 Gy, except for the bladder when using the PDR technique. CONCLUSION: The presented method to respect total dose constraints is reliable and efficient and an essential tool when aiming to increase local control and minimize side effects.     

影像学技术在图像引导宫颈癌近距离放射治疗中的应用

图像引导放射治疗是一种很有前途的放射治疗技术,可以提高宫颈癌患者的局部控制率,降低并发症发生率。MRI软组织分辨率高,是图像引导宫颈癌近距离放射治疗公认的金标准。CT软组织分辨率虽不及MRI,但更易识别施源器、源和源路径,在宫颈癌的放疗计划中,CT的使用率远远高于MRI。新的成像技术,如PET和MRI,改善了放疗计划中靶区的勾画,特别是PET联合CT、MRI,在功能成像方面也显得越来越重要。在病人初始分期方面,超声已经被MRI取代,但在图像引导妇科插植和腔内近距离治疗中起重要作用。本综述的目的是评估各种影像技术在图像引导宫颈癌近距离放射治疗中的应用。     

Systematic evaluation of MRI findings in different stages of treatment of cervical cancer: potential of MRI on delineation of target, pathoanatomic structures, and organs at risk

PURPOSE: To compare magnetic resonance imaging (MRI) findings at different stages of cervix cancer treatment and to define the potential of MRI to delineate the gross tumor volume (GTV), clinical target volume (CTV), pathoanatomic structures, and organs at risk (OAR) in brachytherapy. METHODS AND MATERIALS: Forty-nine patients underwent MRI at diagnosis and at brachytherapy. The ability to discriminate anatomic structures on MRI was assessed (quality factor: 0 = inability to discriminate; 1 = fair discrimination; 2 = good discrimination; 3 = excellent discrimination). The overall ability to visualize (percentage of patients with quality factors greater than 0) and the overall discrimination quality score (mean quality factors of all patients) were estimated for the applicator, GTV at diagnosis (GTV(D)), GTV at brachytherapy (GTV(BT))/"gray zones," cervix rim/uterine corpus, OAR, vaginal wall, and parametria. RESULTS: The overall ability to visualize the applicator on MRI at brachytherapy was 100%; for the GTV(BT)/"gray zones," cervix rim/uterine corpus, OAR, and vaginal wall, visualization was 98% (overall discrimination quality factors: 1.2, 2.9, 2.1, 1.9, 1.7, and 2.6). Three of 4 borders of parametrial space were defined in more than 98% (discrimination quality factors: 2.9, 2.1, and 1.2). CONCLUSION: Magnetic resonance imaging provides appropriate information for definition of the applicator, GTV, CTV, pathoanatomic structures, and OAR that enables precise delineation for cervix cancer brachytherapy.     

A novel MRI marker for prostate brachytherapy

PURPOSE: Magnetic resonance imaging (MRI) is the optimal imaging modality for the prostate and surrounding critical organ structures. However, on MRI, the titanium radioactive seeds used for brachytherapy appear as black holes (negative contrast) and cannot be accurately localized. We sought to develop an encapsulated contrast agent marker (ECAM) with high-signal intensity on MRI to permit accurate localization of radioactive seeds with MRI during and after prostate brachytherapy. METHODS AND MATERIALS: We investigated several agents with paramagnetic and superparamagnetic properties. The agents were injected into titanium, acrylic, and glass seeds, which were linked together in various combinations and imaged with MRI. The agent with the greatest T1-weighted signal was tested further in a canine prostate and agarose phantom. Studies were performed on a 1.5-T clinical MRI scanner. RESULTS: The cobalt-chloride complex contrast (C4) agent with stoichiometry (CoCl(2))(0.8)(C(2)H(5)NO(2))(0.2) had the greatest T1-weighted signal (positive contrast) with a relaxivity ratio >1 (r(2)/r(1) = 1.21 +/- 0.29). Acrylic-titanium and glass-titanium seed strands were clearly visualized with the encapsulated contrast agent marker. CONCLUSION: We have developed a novel ECAM that permits positive identification of the radioactive seeds used for prostate brachytherapy on MRI. Preclinical in vitro phantom studies and in vivo canine studies are needed to further optimize MRI sequencing techniques to facilitate MRI-based dosimetry.     

MRI引导下的宫颈癌三维后装治疗进展

宫颈癌是造成全球女性肿瘤患者死亡的主要原因之一,放疗是宫颈癌的主要治疗手段,而后装治疗是宫颈癌放疗不可缺少的组成部分,外照射联合后装治疗适用于无远处转移的各期初治或复发宫颈癌患者。MRI具有良好的软组织分辨率,在精确靶区范围、保护OAR以及改善患者临床结局等方面有着独特优势;近来许多研究证实了MRI引导下的宫颈癌三维后装的可行性及优越性。本文主要从相关MR成像技术、施源器选择、靶区勾画与评估以及MRI引导下的三维后装治疗所带来的临床效应等方面进行阐述。     

Curiethérapie de la prostate : évolutions des indications et des techniques

Prostate brachytherapy has been for a long time one of the standard treatments for low risk prostate cancer, with high rates of biochemical control and low levels of urinary and sexual late toxicity compared to other available techniques, namely external beam radiotherapy and radical prostatectomy. The aim of this article is to review the recent innovations of prostate brachytherapy, which suggest a bright future for the technique. We will discuss the extension of indications of permanent implant brachytherapy to favorable intermediate-risk patients, the use of novel isotopes such as Palladium 103 and Cesium 131, and the benefit of brachytherapy as a boost following external beam radiotherapy for intermediate and high-risk patients. We will also discuss the rise of high dose rate brachytherapy, as a boost or monotherapy, the increasing use of MRI for patient selection and treatment planning, as well as the development of brachytherapy as a means of focal therapy.     

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.     

3D brachytherapy for cervical cancer: New optimization ways

Brachytherapy has known major improvements in recent decades. It represents an essential component of local treatment of cervix cancers. One major breakthrough was the advent of 3D imaging for image-guided brachytherapy. Doses could be prescribed to volumes. This allows better delineation and coverage of target volumes, as well as organs at risk (bladder, rectum, sigmoid) protection. Local recurrences have been consequently reduced and survival has been improved. In addition, improvement and development of new applicators have facilitated the delivery of interstitial treatments. Afterloading applicators, associated with 3D imaging, allow dosimetry optimization in order to improve the coverage of the target volumes (dose in 90% of the high risk clinical target volume) and to limit dose to the organs at risk. In the future, more personalized treatments will be achieved through more advanced applicators and/or by improving the accuracy of imaging at the time of brachytherapy.     

Ultrasound-guided Brachytherapy for Cervix Cancer

Radiotherapy and brachytherapy are the definitive treatments for locally advanced cervix cancer. The use of soft-tissue imaging, particularly magnetic resonance imaging, has enhanced their effectiveness and improved clinical outcomes. However, the use of magnetic resonance imaging is largely restricted to well-resourced centres in both the first and developing world and remains elusive to many less advantaged centres, particularly those in areas with a high burden of cervix cancer. Ultrasound is an accessible, affordable and accurate imaging modality that can be used throughout the brachytherapy procedure. Ultrasound is primarily used to ensure safe insertion of the applicator but can also be used to guide planning. The methods used to utilise ultrasound images for planning are described. Ultrasound is particularly useful as a verification aid to confirm applicator placement after patients are moved and transferred around the radiotherapy department. It can also be used to verify the dimensions of treatment volumes over the course of brachytherapy. There is a crucial unmet need for an accessible economical soft-tissue imaging modality in cervical brachytherapy. Ultrasound has the potential to meet this need.     

Advanced imaging applications for locally advanced cervical cancer

Advanced imaging approaches (computed tomography, CT; magnetic resonance imaging, MRI; 18F-fluorodeoxyglucose positron emission tomography, FDG PET) have increased roles in cervical cancer staging and management. The recent FIGO (International Federation of Gynecology and Obstetrics) recommendations encouraged applications to assess the clinical extension of tumors rather than relying on clinical examinations and traditional non-cross sectional investigations. MRI appears to be better than CT for primary tumors and adjacent soft tissue involvement in the pelvis. FDG-PET/CT has increased in usage with a particular benefit for whole body evaluation of tumor metabolic activity. The potential benefits of advanced imaging are assisting selection of treatment based upon actual disease extent, to adequately treat a tumor with minimal normal tissue complications, and to predict the treatment outcomes. Furthermore, sophisticated external radiation treatment and brachytherapy absolutely require advanced imaging for target localization and radiation dose calculation.     

超声图像引导宫颈癌近距离治疗的研究进展

近距离治疗是宫颈癌根治性放疗不可或缺的治疗方法。随着影像技术的快速发展,三维图像引导已应用到宫颈癌近距离治疗中。三维超声凭借其优越的软组织成像特点,兼具经济、高效、便捷等优势,继CT和MRI后逐渐应用于引导宫颈癌近距离治疗。本综述通过查阅大量相关文献,总结了超声图像引导宫颈癌近距离治疗的研究进展,以供研究参考。     

超声图像引导宫颈癌近距离治疗的研究进展

近距离治疗是宫颈癌根治性放疗不可或缺的治疗方法。随着影像技术的快速发展,三维图像引导已应用到宫颈癌近距离治疗中。三维超声凭借其优越的软组织成像特点,兼具经济、高效、便捷等优势,继CT和MRI后逐渐应用于引导宫颈癌近距离治疗。本综述通过查阅大量相关文献,总结了超声图像引导宫颈癌近距离治疗的研究进展,以供研究参考。     

MRI-guided HDR prostate brachytherapy in standard 1.5T scanner

PURPOSE: Magnetic resonance imaging (MRI) provides superior visualization of the prostate and surrounding anatomy, making it the modality of choice for imaging the prostate gland. This pilot study was performed to determine the feasibility and dosimetric quality achieved when placing high-dose-rate prostate brachytherapy catheters under MRI guidance in a standard "closed-bore" 1.5T scanner. METHODS AND MATERIALS: Patients with intermediate-risk and high-risk localized prostate cancer received MRI-guided high-dose-rate brachytherapy boosts before and after a course of external beam radiotherapy. Using a custom visualization and targeting program, the brachytherapy catheters were placed and adjusted under MRI guidance until satisfactory implant geometry was achieved. Inverse treatment planning was performed using high-resolution T(2)-weighted MRI. RESULTS: Ten brachytherapy procedures were performed on 5 patients. The median percentage of volume receiving 100% of prescribed minimal peripheral dose (V(100)) achieved was 94% (mean, 92%; 95% confidence interval, 89-95%). The urethral V(125) ranged from 0% to 18% (median, 5%), and the rectal V(75) ranged from 0% to 3.1% (median, 0.3%). In all cases, lesions highly suspicious for malignancy could be visualized on the procedural MRI, and extracapsular disease was identified in 2 patients. CONCLUSION: High-dose-rate prostate brachytherapy in a standard 1.5T MRI scanner is feasible and achieves favorable dosimetry within a reasonable period with high-quality image guidance. Although the procedure was well tolerated in the acute setting, additional follow-up is required to determine the long-term safety and efficacy of this approach.     

Curiethérapie prostatique de rattrapage : solution pour les rechutes localisées après irradiation ?

Salvage brachytherapy after a first prostate radiation therapy is an emerging technique, which has to be considered in the therapeutic armamentarium in the clinically challenging context of patients with isolated local failure from prostate cancer who may still be considered for cure. These occult failures are more and more frequently diagnosed at an early stage, thanks to targeted biopsies and advances in imaging modalities, such as multiparametric MRI and PET-CT. Salvage brachytherapy benefits from the implantation accuracy of brachytherapy procedures using 3D dosimetry and has resulted in more than 50% tumour control rates with long-term. Incontinence rates are always below those of other salvage treatments such as radical prostatectomy, HIFU or cryotherapy. Today, a consensus has been reached to better define good candidates for salvage brachytherapy with respect to disease characteristics at baseline and at failure. No consensus has been clearly defined yet regarding the choice of the technique (low or high dose rate), the total dose to be delivered, or the volume to be implanted (whole gland or focal). While we await robust data from recently completed phase II studies and given the heterogeneous results in the literature, this technique (although already included in the last 2016 NCCN guidelines) remains to be precisely evaluated, optimally within the frame of controlled trials.