Potential role of ultrasound imaging in interstitial image based cervical cancer brachytherapy

Imaging to optimize gynecological radiation oncology

Gynecological cancers have particularly benefited from the increasing use of imaging to guide radiation treatment planning for both external beam radiation and brachytherapy. While the different gynecological cancers have varying use of imaging, certain trends predominate. CT represents an economical choice for evaluating initial disease extent or potential metastasis at follow-up, particularly for endometrial and ovarian cancers. F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT is particularly useful for assessing the initial disease extent and longer term treatment response of squamous predominant cancers, including cervical, vaginal, and vulvar cancers. With its excellent pelvic soft tissue discrimination, MRI provides the greatest assistance in evaluating the local extent of gynecological tumors, including initial evaluation for non-operative endometrial and vulvar cancer, and assessment before, after and during brachytherapy for cervix, locally recurrent endometrial, and primary vaginal cancers. With more limited availability of MRI, ultrasound can also help guide brachytherapy, particularly during procedures. The benefits of using imaging to better spare bone marrow or earlier assessment of treatment response are topics still being explored, in particular for cervical cancer. As imaging along with radiation oncology technologies continue to evolve and develop, such as with MRI-linacs and ultra high dose rate (FLASH) radiation, we may continue to see increasing use of imaging for advancing gynecological radiation oncology.

Ultrasound guidance for cervical implantation

Ultrasound can provide real-time imagery without the risk of radiation exposure, and it is widely available at a relatively low cost. It can provide updated three-dimensional information that can improve the physician's spatial awareness during a brachytherapy procedure for cervical cancer. There is mounting evidence demonstrating the numerous benefits of ultrasound-guided brachytherapy in the published literature. This evidence supports its routine use to improve the safety and the effectiveness of cervical brachytherapy. In this report we will review various methods in which ultrasound imaging has been used during cervical brachytherapy. We also include a description of our own institutional approach to ultrasound-guided cervical implementation that has been in use for all cervical brachytherapy procedures over the past two decades.

Evaluation of sociodemographic and baseline patient characteristic differences in cervical cancer patients treated with either external beam or brachytherapy boost

PURPOSE

Chemoradiation is considered the standard of care for locally advanced cervical cancer. While brachytherapy (BT) boost is associated with improved survival and less toxicity compared to external beam radiation therapy (EBRT) boost, it is unclear why many patients do not receive a BT boost. In this study, we compared sociodemographic and baseline patient characteristics between patients receiving EBRT boost versus BT boost.

METHODS

We analyzed patients in the National Cancer Database diagnosed between 2004 and 2016 with FIGO stage IIB-IVA cervical cancer treated with nonpalliative doses of chemoradiation. Logistic regression analysis was utilized to evaluate BT utilization over time and by other clinicopathological and sociodemographic factors.

RESULTS

Overall, 5764 patients were evaluated, of which 4937 (86%) underwent BT boost. Using multivariable logistic regression, higher FIGO stage was a significant predictor for utilization of EBRT versus BT boost, with odds ratio 2.92 (95% confidence interval [CI] 2.04-4.16; p < 0.001), 2.68 (95%CI 2.22-3.24; p < 0.001), and 4.51 (95%CI 3.05-6.67; p < 0.001) for IIIA, IIIB, and IVA, respectively, compared to IIB. Increased utilization of EBRT boost was also associated with community cancer facility types, lower income (based on zip code), earlier year of diagnosis, and higher comorbidity score.

CONCLUSIONS

In FIGO stage IIB-IVA cervical cancer patients treated with nonpalliative doses of chemoradiation, overall utilization of BT is 86%. Higher FIGO stage, community cancer facilities, lower income, earlier year of diagnosis, and higher comorbidity score were significant predictors of EBRT boost utilization. Future studies are needed to better understand reasons for this as higher FIGO stage patients are the mostly likely to benefit from a BT boost.

Clinical values of transrectal ultrasound in judging GTV of cervical cancer

PURPOSE

To investigate the clinical value of transrectal ultrasound in judging the Gross Target Volume (GTV) of cervical cancer (CC).

METHODS

A total of 196 CC patients admitted to the Department of Radiotherapy, China-Japan Union Hospital, Jilin University, from January 2016 to June 2019 were selected as the study subjects. The GTVs before and after applicator insertion were determined by transrectal ultrasound and compared with those judged by MRI.

RESULTS

All 196 patients were successfully undergoing applicator insertion according to the pretreatment plan. The GTV doses reached the clinical requirements during treatment. There was no significant difference between the GTVs judged by MRI and ultrasound before insertion in terms of upper/lower diameter (MRI Before 1 vs. Ultrasound Before 1) (MB1 vs. UB1), left/right diameter (MB2 vs. UB2), or ventral/dorsal diameter (MB3 vs. UB3), and the intragroup correlation coefficients (ICC) were 0.59, 0.77, and 0.66, respectively; moreover, there was no significant difference between the GTVs judged by MRI and ultrasound after insertion in terms of MRI After one vs. Ultrasound After one (MA1 vs. UA1), MA2 vs. UA2, and MA3 vs. UA3, and the ICC values were 0.62, 0.79, and 0.76, respectively.

CONCLUSIONS

Transrectal ultrasound can satisfactorily determine the GTV of CC and has certain value in brachytherapy for CC.

Feasibility of fusing three-dimensional transabdominal and transrectal ultrasound images for comprehensive intraoperative visualization of gynecologic brachytherapy applicators

PURPOSE

In this study, we propose combining three-dimensional (3D) transrectal ultrasound (TRUS) and 3D transabdominal ultrasound (TAUS) images of gynecologic brachytherapy applicators to leverage the advantages of each imaging perspective, providing a broader field-of-view and allowing previously obscured features to be recovered. The aim of this study was to evaluate the feasibility of fusing these 3D ultrasound (US) perspectives based on the applicator geometry in a phantom prior to clinical implementation.

METHODS

In proof-of-concept experiments, 3D US images of application-specific multimodality pelvic phantoms were acquired with tandem-and-ring and tandem-and-ovoids applicators using previously validated imaging systems. Two TRUS images were acquired at different insertion depths and manually fused based on the position of the ring/ovoids to broaden the TRUS field-of-view. The phantom design allowed "abdominal thickness" to be modified to represent different body habitus and TAUS images were acquired at three thicknesses for each applicator. The merged TRUS images were then combined with TAUS images by rigidly aligning applicator components and manually refining the registration using the positions of source channels and known tandem length, as well as the ring diameter for the tandem-and-ring applicator. Combined 3D US images were manually, rigidly registered to images from a second modality (magnetic resonance (MR) imaging for the tandem-and-ring applicator and X-ray computed tomography (CT) for the tandem-and-ovoids applicator (based on applicator compatibility)) to assess alignment. Four spherical fiducials were used to calculate target registration errors (TREs), providing a metric for validating registrations, where TREs were computed using root-mean-square distances to describe the alignment of manually identified corresponding fiducials. An analysis of variance (ANOVA) was used to identify statistically significant differences (p < 0.05) between the TREs for the three abdominal thicknesses for each applicator type. As an additional indicator of geometric accuracy, the bladder was segmented in the 3D US and corresponding MR/CT images, and volumetric differences and Dice similarity coefficients (DSCs) were calculated.

RESULTS

For both applicator types, the combination of 3D TRUS with 3D TAUS images allowed image information obscured by the shadowing artifacts under single imaging perspectives to be recovered. For the tandem-and-ring applicator, the mean ± one standard deviation (SD) TREs from the images with increasing thicknesses were 1.37 ± 1.35 mm, 1.84 ± 1.22 mm, and 1.60 ± 1.00 mm. Similarly, for the tandem-and-ovoids applicator, the mean ± SD TREs from the images with increasing thicknesses were 1.37 ± 0.35 mm, 1.95 ± 0.90 mm, and 1.61 ± 0.76 mm. No statistically significant difference was detected in the TREs for the three thicknesses for either applicator type. The mean volume differences for the bladder segmentations were 3.14% and 2.33% and mean DSCs were 87.8% and 87.7% for the tandem-and-ring and tandem-and-ovoids applicators, respectively.

CONCLUSIONS

In this proof-of-concept study, we demonstrated the feasibility of fusing 3D TRUS and 3D TAUS images based on the geometry of tandem-and-ring and tandem-and-ovoids applicators. This represents a step toward an accessible and low-cost 3D imaging method for gynecologic brachytherapy, with the potential to extend this approach to other intracavitary configurations and hybrid applicators.

Advantages of real-time transabdominal ultrasound guidance in combined interstitial/intracavitary cervical brachytherapy: a case-based review

Sub-optimal placement of both intracavitary devices and interstitial needles is a relatively common occurrence in cervical brachytherapy, which may reduce the accuracy of dose distribution and contribute to adverse toxicities. To mitigate complications, improve target dose coverage, and verify proper device placement, implants may be placed under real-time image guidance. Traditionally, transrectal ultrasound has been used for needle guidance. However, we have utilized transabdominal ultrasound (TA-US) in our brachytherapy center. The purpose of this pictorial essay was to provide a pictorial description of TA-US technique, present a retrospective review of our preliminary outcomes adopting TA-US into routine practice, and to discuss the advantages of real-time ultrasound image guidance for placement of intrauterine tandem and interstitial needles.

Interstitial brachytherapy for gynecologic malignancies: Complications, toxicities, and management

From both a disease and management perspective, locally advanced gynecologic cancers present a significant challenge. Dose escalation with brachytherapy serves as a key treatment, providing conformal radiation while sparing at-risk organs. Intracavitary brachytherapy techniques have been shown to be effective, with improving tumor control and toxicity profiles with the advent of three-dimensional image planning. Despite this, the variations in tumor size, location, and pelvic anatomy may lead to suboptimal dosimetry with standard intracavitary applicators in some clinical scenarios. The addition of interstitial needles (interstitial brachytherapy (ISBT)) can improve the conformality of brachytherapy treatments by adding needles to peripheral (and central) regions of the target volume, improving the ability to escalate doses in these undercovered regions while sparing organs at risk. Interstitial brachytherapy can be delivered by intracavitary and interstitial hybrid applicators (ICBT/ISBT), perineal template (P-ISBT), or by free-hand technique. ISBT has however yet to be widely available because of concerns of complications and toxicities from this specialized treatment. However, with the increasing use of three-dimensional image-guided brachytherapy, there is an opportunity to increase the level of expertise in the gynecologic radiation oncology community with an improved understanding of the potential complications and morbidity. In this article, we review the acute and long-term toxicity in both ICBT/ISBT and P-ISBT using image-guided brachytherapy.

Imaging-guided brachytherapy for locally advanced cervical cancer: the main process and common techniques

Brachytherapy (BT) delivers integrated boost doses to the central tumor while sparing the surrounding organs at risk (OARs) efficiently. It's a mandatory treatment component for locally advanced cervical cancer (LACC) because it results in excellent overall survival and local control compared with other dose boosting modalities. Currently, BT is undergoing a transition from 2-dimensional (2D) to 3-dimensional (3D) treatment planning. Imaging-guided BT (IGBT) employing computed tomography (CT) or magnetic resonance imaging (MRI) can provide exact individual delineation of target and OARs meanwhile prescribe the dose to the target volume instead of "point A" for X-ray-based BT. There are three main techniques for BT: intracavitary (IC), interstitial (IS), and intracavitary/interstitial (IC/IS) combination. The applicator choice depends on the specific tumor extension. The real-time transabdominal ultrasound (US)-guided applicator placement technique is strongly recommended to ensure ideal applicator positioning. MRI is the ideal standard imaging for BT owing to its superior soft tissue visualization than CT. However, CT-based BT is more often performed because of the availability. In developing countries, US-based BT can be adopted. For treatment planning, the applicator reconstruction is easier on CT than on MRI, because the applicator image is more clearly visible. Individual treatment planning should be performed for every single applicator insertion to ensure dose accuracy. In this review article, we explain the main clinical process and common techniques, including the applicator choice and placement, imaging techniques, target delineation, and treatment planning; asthose will help to improve the efficiency of 3D BT.

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.

Intraoperative 360-deg three-dimensional transvaginal ultrasound during needle insertions for high-dose-rate transperineal interstitial gynecologic brachytherapy of vaginal tumors

Brachytherapy, a type of radiotherapy, may be used to place radioactive sources into or in close proximity to tumors, providing a method for conformally escalating dose in the tumor and the local area surrounding the malignancy. High-dose-rate interstitial brachytherapy of vaginal tumors requires precise placement of multiple needles through holes in a plastic perineal template to deliver treatment while optimizing dose and avoiding overexposure of nearby organs at risk (OARs). Despite the importance of needle placement, image guidance for adaptive, intraoperative needle visualization, allowing misdirected needles to be identified and corrected during insertion, is not standard practice. We have developed a 360-deg three-dimensional (3-D) transvaginal ultrasound (TVUS) system using a conventional probe with a template-compatible custom sonolucent vaginal cylinder and propose its use for intraoperative needle guidance during interstitial gynecologic brachytherapy. We describe the 3-D TVUS mechanism and geometric validation, present mock phantom procedure results, and report on needle localization accuracy in patients. For the six patients imaged, landmark anatomical features and all needles were clearly visible. The implementation of 360-deg 3-D TVUS through a sonolucent vaginal cylinder provides a technique for visualizing needles and OARs intraoperatively during interstitial gynecologic brachytherapy, enabling implants to be assessed and providing the potential for image guidance.

Review of strategies for MRI based reconstruction of endocavitary and interstitial applicators in brachytherapy of cervical cancer

Brachytherapy plays an essential role in the curative intent management of locally advanced cervical cancer. The introduction of the magnetic resonance (MR) as a preferred image modality and the development of new type of applicators with interstitial components have further improved its benefits. The aim of this work is to review the current status of one important aspect in the cervix cancer brachytherapy procedure, namely catheter reconstruction. MR compatible intracavitary and interstitial applicators are described. Considerations about the use of MR imaging (MRI) regarding appropriate strategies for applicator reconstruction, technical requirements, MR sequences, patient preparation and applicator commissioning are included. It is recommendable to perform the reconstruction process in the same image study employed by the physician for contouring, that is, T2 weighted (T2W) sequences. Nevertheless, a clear identification of the source path inside the catheters and the applicators is a challenge when using exclusively T2W sequences. For the intracavitary component of the implant, sometimes the catheters may be filled with some substance that produces a high intensity signal on MRI. However, this strategy is not feasible for plastic tubes or titanium needles, which, moreover, induce magnetic susceptibility artifacts. In these situations, the use of applicator libraries available in the treatment planning system (TPS) is useful, since they not only include accurate geometrical models of the intracavitary applicators, but also recent developments have made possible the implementation of the interstitial component. Another strategy to improve the reconstruction process is based on the incorporation of MR markers, such as small pellets, to be used as anchor points. Many institutions employ computed tomography (CT) as a supporting image modality. The registration of CT and MR image sets should be carefully performed, and its uncertainty previously assessed. Besides, an important research work is being carried out regarding the use of ultrasound and electromagnetic tracking technologies.

Correlation analysis between the parameters of contrast-enhanced ultrasonography in evaluating cervical cancer metastasis and expression of E-cadherin

The study aims to investigate the correlation between the parameters of contrast-enhanced ultrasonography in evaluating cervical cancer metastasis and expression of E-cadherin. All 120 patients with cervical cancer underwent contrast-enhanced ultrasonography. According to the results of postoperative pathological examination, patients were divided into distant metastasis group (group A), lymph node metastasis without distant metastasis group (group B) and no metastasis group (group C). Expression of E-cadherin in cervical cancer tissues was detected by enzyme-linked immunosorbent assay (ELISA). Correlations between the parameters of contrast-enhanced ultrasonography in evaluating cervical cancer metastasis and expression of E-cadherin were analyzed by Pearsons correlation analysis. Comparison of parameters of contrast-enhanced ultrasonography showed that, the baseline intensity of group A was 11.9±2.2 dB, which was significantly lower than that of group B and C. Baseline intensity of group B was significantly lower than that of group C (13.0±2.4 vs. 15.3±3.6 dB), significant differences were found among three groups (P<0.05). The sensitivity and specificity of the use of enhanced intensity ~83.7 dB in evaluating tumor metastasis of patients with cervical cancer were 82.42 and 79.32%, respectively. Expression level of E-cadherin protein in group A was 0.030±0.003 ng/ml, which was significantly lower than that in group B and C (P<0.05), expression level of E-cadherin protein in group A was significantly lower than that in group C (0.037±0.007 vs. 0.045±0.012 ng/ml), significant differences in the expression level of E-cadherin protein were found among the three groups of cervical cancer patients (P<0.05). Pearsons correlation analysis showed that there was a positive correlation between the baseline intensity of contrast-enhanced ultrasonography and the expression level of E-cadherin (P<0.05), while there was a negative correlation between the enhanced intensity of contrast-enhanced ultrasonography and the expression level of E-cadherin (P<0.05). Contrast-enhanced ultrasonography can be used to determine the tumor metastasis of cervical cancer patients, in addition, the combined use of contrast-enhanced ultrasonography and E-cadherin protein expression can significantly improve the diagnosis and treatment of cervical cancer.

Use of ultrasound in image-guided high-dose-rate brachytherapy: enumerations and arguments

Inherently, brachytherapy is the most conformal radiotherapeutic technique. As an aid to brachytherapy, ultrasonography (USG) serves as a portable, inexpensive, and simple to use method allowing for accurate, reproducible, and adaptive treatments. Some newer brachytherapy planning systems have incorporated USG as the sole imaging modality. Ultrasonography has been successfully used to place applicator and dose planning for prostate, cervix, and anal canal cancers. It can guide placement of brachytherapy catheters for all other sites like breast, skin, and head and neck cancers. Traditional USG has a few limitations, but recent advances such as 3-dimensional (3D) USG and contrast USG have enhanced its potential as a dependable guide in high-dose-rate image-guided brachytherapy (HDR-IGBT). The authors in this review have attempted to enumerate various aspects of USG in brachytherapy, highlighting its use across various sites.

Toward a 3D transrectal ultrasound system for verification of needle placement during high-dose-rate interstitial gynecologic brachytherapy

PURPOSE

Treatment for gynecologic cancers, such as cervical, recurrent endometrial, and vaginal malignancies, commonly includes external-beam radiation and brachytherapy. In high-dose-rate (HDR) interstitial gynecologic brachytherapy, radiation treatment is delivered via hollow needles that are typically inserted through a template on the perineum with a cylinder placed in the vagina for stability. Despite the need for precise needle placement to minimize complications and provide optimal treatment, there is no standard intra-operative image-guidance for this procedure. While some image-guidance techniques have been proposed, including magnetic resonance (MR) imaging, X-ray computed tomography (CT), and two-dimensional (2D) transrectal ultrasound (TRUS), these techniques have not been widely adopted. In order to provide intra-operative needle visualization and localization during interstitial brachytherapy, we have developed a three-dimensional (3D) TRUS system. This study describes the 3D TRUS system and reports on the system validation and results from a proof-of-concept patient study.

METHODS

To obtain a 3D TRUS image, the system rotates a conventional 2D endocavity transducer through 170 degrees in 12 s, reconstructing the 2D frames into a 3D image in real-time. The geometry of the reconstruction was validated using two geometric phantoms to ensure the accuracy of the linear measurements in each of the image coordinate directions and the volumetric accuracy of the system. An agar phantom including vaginal and rectal canals, as well as a model uterus and tumor, was designed and used to test the visualization and localization of the interstitial needles under idealized conditions by comparing the needles' positions between the 3D TRUS scan and a registered MR image. Five patients undergoing HDR interstitial gynecologic brachytherapy were imaged using the 3D TRUS system following the insertion of all needles. This image was manually, rigidly registered to the clinical postinsertion CT scan based on the vaginal cylinder of the needle template. The positions of the tips and the trajectory of the needle paths were compared between the modalities.

RESULTS

The observed geometric errors of the system were ≤ 0.3 mm in each of the three coordinate planes of the 3D US image and the mean measured volumetric error was 0.10 cm³ . In the phantom study, the mean needle tip difference was 1.54 ± 0.71 mm and the mean trajectory difference was 0.94 ± 0.89 degrees (n = 14). In the in vivo study, a total of 73 needles were placed, of which 88% of needles were visible and 79% of tips were identifiable in the 3D TRUS images. Six of the nine needles that were not visible were due to shadowing artifacts created by the presence of the vaginal cylinder of the needle template. The mean distance between corresponding needle tips in the two modalities was 3.82 ± 1.86 mm and the mean trajectory difference was 3.04 ± 1.63 degrees for the five patients.

CONCLUSIONS

In this proof-of-concept study, the 3D TRUS system allowed for localization of needles not obscured by shadowing artifacts, providing a method for visualizing needles intra-operatively during HDR interstitial brachytherapy of gynecologic cancers and providing the potential for 3D image-guidance.

Long term results from a prospective database on high dose rate (HDR) interstitial brachytherapy for primary cervical carcinoma

OBJECTIVE

Present long-term outcomes in primary cervical cancer treated with external beam and high dose rate interstitial brachytherapy.

METHODS

High dose rate (HDR) interstitial (IS) brachytherapy (BT) and external beam (EBRT) were administered from 1992 to 2009 to 315 patients who were unsuitable for intracavitary (IC) BT alone. Histology was 89% squamous cell, 8% adenocarcinoma, and 3% adenosquamous. FIGO stage was I-14%, II-47%, III-34%, and IVA-5%. Median tumor size was 6cm. Lymph node metastases were 26% pelvic and 9.5% para-aortic. Treatment planning was 49% 2D and 51% 3D-CT. The mean doses were central EBRT EQD210 37.3±4.3Gy (sidewall 49.2±3.6Gy) and HDR EQD210 42.3±5.3Gy (nominal 5.4Gy×6 fractions using a mean of 24 catheters and 1 tandem). Total EQD210 mean target dose was 79.5±5.4Gy. Standardized planned dose constraints were ICRU points or D0.1cc bladder 80%, rectum 75% and urethra 90% of the HDR dose per fraction. Morbidity assessment was CTCAEv3. Median and mean follow-up were 50 and 61months (3-234).

RESULTS

The 10-year actuarial local control was 87%, regional control 84%, and loco-regional control 77%. Distant metastasis free survival was 66%, cause specific survival 56%, disease free survival 54%, and overall survival 40%. The rates of late grade GU and GI toxicities were 4.8% G3 and 5.4% G4.

CONCLUSIONS

Template-guided interstitial can be safely performed to successfully deliver high radiation dose to locally advanced cervix cancer and avoid excessive dose and injury to adjacent vital pelvic organs. We achieved high tumor control with low morbidity in patients who were poor candidates for intracavitary brachytherapy.

Potential role of TRAns Cervical Endosonography (TRACE) in brachytherapy of cervical cancer: proof of concept

PURPOSE

Magnetic resonance imaging (MRI) is the gold standard for image guided adaptive brachytherapy (BT) of cervical cancer. Ultrasound is an attractive alternative with reasonable costs and high soft tissue depiction quality. This technical note aims to demonstrate the proof of principle for use of TRAns Cervical Endosonography with rotating transducer in the context of brachytherapy (TRACE BT).

MATERIAL AND METHODS

TRACE BT presentation is based on a single stage IIB cervical cancer patient. Prior to second BT implant, rotating US transducer (6.9 mm diameter) was inserted in cervical canal and axial images obtained at 10 MHz, focal range of 30 mm, and axial resolution of 0.4 mm. Size and topography of hypo-echoic areas were assessed and optimal positions of interstitial needles were determined. Finally, intracavitary applicator was placed and needles inserted through vaginal ring-template according to TRACE pre-plan. MRI-based high risk clinical target volume (CTVHR) dimensions were compared with hypoechoic areas on TRACE. Topography of parametrial needles on post-insertion MRI was compared with TRACE pre-plan.

RESULTS

Insertion of rotating mechanism into cervico-uterine cavity was safe, feasible and fast. The 360° imaging in axial plane enabled real-time assessment of cervix, uterus, and adjacent parametria. Qualitative comparison of TRACE with post-insertion MRI revealed favorable agreement of findings. In-plane size of CTVHR on MRI was comparable to hypoechoic areas on TRACE. Needle positions on post-insertion MRI corresponded to TRACE-based pre-plan. Main limitation of TRACE was gradual deterioration of image quality due to coupling gel removal.

CONCLUSIONS

Present proof of concept demonstrates potential role of TRACE-BT for cervical cancer as an attractive high-tech approach with reasonable costs. Prior to investigation of its clinical role, further development of TRACE methodology is needed. This includes reliable transducer-tissue coupling, applicator reconstruction, imaging range, limitations in extensive tumors, US-based contouring concepts, registration with other imaging methods, organ dose-assessment, real-time dosimetry, etc.