3-T MR-guided brachytherapy for gynecologic malignancies

Catheter reconstruction and dosimetric verification of MRI-only treatment planning (MRTP) for interstitial HDR brachytherapy using PETRA sequence

Objective. The feasibility of MRI-only treatment planning (MRTP) for interstitial high-dose rate (HDR) brachytherapy (BT) was investigated for patients diagnosed with gynecologic cancer.Approach. A clinical MRTP workflow utilizing a 'pointwise encoding time reduction with radial acquisition (PETRA)' sequence was proposed. This is a clinically available MRI sequence optimized to improve interstitial catheter-tissue contrast. Interstitial needles outside the obturator region were reconstructed using MR images only. For catheters penetrating through the obturator, a library-based reconstruction was proposed. In this work, dwell coordinates from the clinical CT-based reconstruction were used as the surrogate for the library-based approach. For MR-only plan, dwell times were activated and assigned as in the clinical plans. The catheter reconstruction was assessed by comparing dwell position coordinates. The dosimetric comparisons between a clinical plan and MR-only plan were assessed for physical and EQD2 dose and volume parameters forD₉₀,D₅₀andD₉₈for clinical target volume (CTV) andD_2cc,D_0.1ccandD_5ccfor OARs.Main results. Catheter reconstruction was possible using the optimized PETRA sequence on MR images. An overall reconstruction difference of 1.7 ± 0.5 mm, attributed to registration-based errors, was found compared to the CT-based reconstruction. The MRTP workflow has the potential to generate a treatment plan with an equivalent dosimetric quality compared to the conventional CT/MRI-based approach. For CTVD₉₀, physical and EQD2 dose and volume parameter differences were 1.5 ± 1.9% and 0.7 ± 1.0 Gy, respectively. ForD_2ccOARs, DVH (EQD2) differences were -0.4 ± 1.1% (-0.2 ± 0.5 Gy), 0.5 ± 2.8% (0.2 ± 1.3 Gy) and -0.5 ± 1.4% (-0.2 ± 0.5 Gy) for rectum, bladder, and sigmoid, respectively.Significance. With the proposed MRTP approach, CT imaging may no longer be needed in HDR BT for interstitial gynecologic treatment. A proof-of-concept study was conducted to demonstrated that MRTP using PETRA is feasible, with comparable dosimetric results to the conventional CT/MRI-based approach.

A new technique for performing interstitial implants for gynecologic malignancies using transvaginal ultrasound guidance

Objectives

This study concerns a new technique that aims to achieve precise interstitial brachytherapy of pelvic recurrent tumors under transvaginal ultrasound (US) guidance, enhance the conformity index of the brachytherapy (BT), and improve the curative effect of radiotherapy for gynecological oncology patients with pelvic relapse.

Methods

A real-time transvaginal US-guided interstitial implant device was developed to assist in implant BT. Prior to implant brachytherapy, the size and location of the tumor in the pelvis and the interrelationship with adjacent organs were first assessed with intracavitary ultrasound. The transvaginal US-guided interstitial implant device was then placed on the endoluminal ultrasound probe, the probe was oriented intravaginally to determine a safe needle path, the implant needle was placed into the needle passage of the device, and the implant needle was inserted into the tumor tissue in the direction guided by the ultrasound puncture guide line. After the implant needle was placed in place, the cover of the transvaginal US-guided interstitial implant device was opened perpendicular to the ultrasound probe, and the needle was separated from the ultrasound probe smoothly, and then the cover was re-covered for subsequent implantation.

Results

In this study, 56 patients who underwent real-time transvaginal ultrasound-guided implantation for gynecologic oncology were enrolled, and insertion of 736 implant needles was completed. Among them, 13 patients had recurrent pelvic tumors after cervical cancer surgery and 6 patients had recurrent pelvic tumors after endometrial cancer surgery. Thirty-two patients who underwent radical radiation therapy for cervical cancer did not have adequate regression of parametrial invaded tissue after completion of standard EBRT treatment; and 5 patients had recurrent tumors in the radiation field after previous standard course of pelvic radiotherapy. The accuracy of the implant therapy was improved. The radiotherapy dose for recurrent pelvic masses was successfully increased, and the cumulative dose of external irradiation combined with BT was augmented to 80–100 Gy. The use of a new device for transvaginal implant for recurrent masses located in the lateral wall of the pelvic cavity was successful.

Conclusion

This intravascular US-guided interstitial implant device can realize interstitial implant with the shortest path under transvaginal US guidance. With convenient operation, high precision, and good security, the device not only improves the accuracy of implant therapy, but it also reduces the risks of anesthesia and organ injury, so it is suitable for widespread promotion and use.

AAPM Task Group Report 303 endorsed by the ABS: MRI Implementation in HDR Brachytherapy-Considerations from Simulation to Treatment

The Task Group (TG) on Magnetic Resonance Imaging (MRI) Implementation in High Dose Rate (HDR) Brachytherapy - Considerations from Simulation to Treatment, TG 303, was constituted by the American Association of Physicists in Medicine's (AAPM's) Science Council under the direction of the Therapy Physics Committee, the Brachytherapy Subcommittee, and the Working Group on Brachytherapy Clinical Applications. The TG was charged with developing recommendations for commissioning, clinical implementation, and on-going quality assurance (QA). Additionally, the TG was charged with describing HDR brachytherapy (BT) workflows and evaluating practical consideration that arise when implementing MR imaging. For brevity, the report is focused on the treatment of gynecologic and prostate cancer. The TG report provides an introduction and rationale for MRI implementation in BT, a review of previous publications on topics including available applicators, clinical trials, previously published BT related TG reports, and new image guided recommendations beyond CT based practices. The report describes MRI protocols and methodologies, including recommendations for the clinical implementation and logical considerations for MR imaging for HDR BT. Given the evolution from prescriptive to risk-based QA,¹ an example of a risk-based analysis using MRI-based, prostate HDR BT is presented. In summary, the TG report is intended to provide clear and comprehensive guidelines and recommendations for commissioning, clinical implementation, and QA for MRI-based HDR BT that may be utilized by the medical physics community to streamline this process. This report is endorsed by the American Brachytherapy Society (ABS). This article is protected by copyright. All rights reserved.

Intraoperative MR Imaging during Glioma Resection

One of the major issues in the surgical treatment of gliomas is the concern about maximizing the extent of resection while minimizing neurological impairment. Thus, surgical planning by carefully observing the relationship between the glioma infiltration area and eloquent area of the connecting fibers is crucial. Neurosurgeons usually detect an eloquent area by functional MRI and identify a connecting fiber by diffusion tensor imaging. However, during surgery, the accuracy of neuronavigation can be decreased due to brain shift, but the positional information may be updated by intraoperative MRI and the next steps can be planned accordingly. In addition, various intraoperative modalities may be used to guide surgery, including neurophysiological monitoring that provides real-time information (e.g., awake surgery, motor-evoked potentials, and sensory evoked potential); photodynamic diagnosis, which can identify high-grade glioma cells; and other imaging techniques that provide anatomical information during the surgery. In this review, we present the historical and current context of the intraoperative MRI and some related approaches for an audience active in the technical, clinical, and research areas of radiology, as well as mention important aspects regarding safety and types of devices.

MR-guided 125I seed implantation treatment for maxillofacial malignant tumor

PURPOSE

This study assessed the therapeutic efficacy of postoperative magnetic resonance (MR)-guided interstitial 125 I seed implantation for treatment of oral and maxillofacial malignant tumors.

METHODS AND MATERIALS

A total of 127 patients with oral or maxillofacial malignant tumors were included in this study who received interstitial 125 I treatment after the surgery resection. Before implantation, all the patients received MR scans to assess the lesion scope, extent, and nature. 125 I implantation target regions were based on the pre-operative imaging. 125 I seeds were delivered to target regions via puncture needles under the real-time guidance of MR. Computed tomography (CT)or MR was performed immediately after implantation and again every 3 months later.

RESULTS

After successful 125 I implantation, all patients were also examined regularly to detect tumor recurrence, lymphatic, and distant metastases. To date, CT or MR verification showed that 13/127 patients experienced tumor recurrence or lymphatic metastasis or distant metastasis. No seeds migration was observed, no serious treatment-related complications affected patient quality of life, and no important organ (such as major cervical vessels, spinal cord, etc.) injuries were observed.

CONCLUSION

Our results show that MR-guided 125 I implantation is an effective approach to site-specific treatment for oral and maxillofacial tumor, which could potentially reduce postoperative complications and tumor recurrence rates, increase patient survival, and improve quality of life.

Aiming for 100% Local Control in Locally Advanced Cervical Cancer: The Role of Complex Brachytherapy Applicators and Intraprocedural Imaging

The use of brachytherapy for the treatment of gynecologic malignancies, particularly cervical cancer, has a long and rich history that is nearly as long as the history of radiation oncology itself. From the first gynecologic brachytherapy treatments in the early 20th century to the modern era, significant transformation has occurred driven largely by advancements in technology. The development of high-dose rate sources, remote afterloaders, novel applicators, and 3-dimensional image guidance has led to improved local control, and thus improved survival, solidifying the role of brachytherapy as an integral component in the treatment of locally advanced cervical cancer. Current research efforts examining novel magnetic resonance imaging sequences, active magnetic resonance tracking, and the application of hydrogel aim to further improve local control and reduce treatment toxicity.

A Review on Advances in Intra-operative Imaging for Surgery and Therapy: Imagining the Operating Room of the Future

With the advent of Minimally Invasive Surgery (MIS), intra-operative imaging has become crucial for surgery and therapy guidance, allowing to partially compensate for the lack of information typical of MIS. This paper reviews the advancements in both classical (i.e. ultrasounds, X-ray, optical coherence tomography and magnetic resonance imaging) and more recent (i.e. multispectral, photoacoustic and Raman imaging) intra-operative imaging modalities. Each imaging modality was analyzed, focusing on benefits and disadvantages in terms of compatibility with the operating room, costs, acquisition time and image characteristics. Tables are included to summarize this information. New generation of hybrid surgical room and algorithms for real time/in room image processing were also investigated. Each imaging modality has its own (site- and procedure-specific) peculiarities in terms of spatial and temporal resolution, field of view and contrasted tissues. Besides the benefits that each technique offers for guidance, considerations about operators and patient risk, costs, and extra time required for surgical procedures have to be considered. The current trend is to equip surgical rooms with multimodal imaging systems, so as to integrate multiple information for real-time data extraction and computer-assisted processing. The future of surgery is to enhance surgeons eye to minimize intra- and after-surgery adverse events and provide surgeons with all possible support to objectify and optimize the care-delivery process.

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.

Technical assessment of a mobile CT scanner for image-guided brachytherapy

PURPOSE

The imaging performance and dose of a mobile CT scanner (Brainlab Airo®, Munich, Germany) is evaluated, with particular consideration to assessment of technique protocols for image-guided brachytherapy.

METHOD

Dose measurements were performed using a 100-mm-length pencil chamber at the center and periphery of 16- and 32-cm-diameter CTDI phantoms. Hounsfield unit (HU) accuracy and linearity were assessed using materials of specified electron density (Gammex RMI, Madison, WI), and image uniformity, noise, and noise-power spectrum (NPS) were evaluated in a 20-cm-diameter water phantom as well as an American College of Radiology (ACR) CT accreditation phantom (Model 464, Sun Nuclear, Melbourne, FL). Spatial resolution (modulation transfer function, MTF) was assessed with an edge-spread phantom and visually assessed with respect to line-pair patterns in the ACR phantom and in structures of interest in anthropomorphic phantoms. Images were also obtained on a diagnostic CT scanner (Big Bore CT simulator, Philips, Amsterdam, Netherlands) for qualitative and quantitative comparison. The manufacturer's metal artifact reduction (MAR) algorithm was assessed in an anthropomorphic body phantom containing surgical instrumentation. Performance in application to brachytherapy was assessed with a set of anthropomorphic brachytherapy phantoms - for example, a vaginal cylinder and interstitial ring and tandem.

RESULT

Nominal dose for helical and axial modes, respectively, was 56.4 and 78.9 mGy for the head protocol and 17.8 and 24.9 mGy for the body protocol. A high degree of HU accuracy and linearity was observed for both axial and helical scan modes. Image nonuniformity (e.g., cupping artifact) in the transverse (x,y) plane was less than 5 HU, but stitching artifacts (~5 HU) in the longitudinal (z) direction were observed in axial scan mode. Helical and axial modes demonstrated comparable spatial resolution of ~5 lp/cm, with the MTF reduced to 10% at ~0.38 mm-1 . Contrast-to-noise ratio was suitable to soft-tissue visualization (e.g., fat and muscle), but windmill artifacts were observed in helical mode in relation to high-frequency bone and metal. The MAR algorithm provided modest improvement to image quality. Overall, image quality appeared suitable to relevant clinical tasks in intracavitary and interstitial (e.g., gynecological) brachytherapy, including visualization of soft-tissue structures in proximity to the applicators.

CONCLUSION

The technical assessment highlighted key characteristics of dose and imaging performance pertinent to incorporation of the mobile CT scanner in clinical procedures, helping to inform clinical deployment and technique protocol selection in brachytherapy. For this and other possible applications, the work helps to identify protocols that could reduce radiation dose and/or improve image quality. The work also identified areas for future improvement, including reduction of stitching, windmill, and metal artifacts.

Fully automatic catheter segmentation in MRI with 3D convolutional neural networks: application to MRI-guided gynecologic brachytherapy

External-beam radiotherapy followed by high dose rate (HDR) brachytherapy is the standard-of-care for treating gynecologic cancers. The enhanced soft-tissue contrast provided by magnetic resonance imaging (MRI) makes it a valuable imaging modality for diagnosing and treating these cancers. However, in contrast to computed tomography (CT) imaging, the appearance of the brachytherapy catheters, through which radiation sources are inserted to reach the cancerous tissue later on, is often variable across images. This paper reports, for the first time, a new deep-learning-based method for fully automatic segmentation of multiple closely spaced brachytherapy catheters in intraoperative MRI. Represented in the data are 50 gynecologic cancer patients treated by MRI-guided HDR brachytherapy. For each patient, a single intraoperative MRI was used. 826 catheters in the images were manually segmented by an expert radiation physicist who is also a trained radiation oncologist. The number of catheters in a patient ranged between 10 and 35. A deep 3D convolutional neural network (CNN) model was developed and trained. In order to make the learning process more robust, the network was trained 5 times, each time using a different combination of shown patients. Finally, each test case was processed by the five networks and the final segmentation was generated by voting on the obtained five candidate segmentations. 4-fold validation was executed and all the patients were segmented. An average distance error of 2.0  ±  3.4 mm was achieved. False positive and false negative catheters were 6.7% and 1.5% respectively. Average Dice score was equal to 0.60  ±  0.17. The algorithm is available for use in the open source software platform 3D Slicer allowing for wide scale testing and research discussion. In conclusion, to the best of our knowledge, fully automatic segmentation of multiple closely spaced catheters from intraoperative MR images was achieved for the first time in gynecological brachytherapy.

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.

Accurate model-based segmentation of gynecologic brachytherapy catheter collections in MRI-images

The gynecological cancer mortality rate, including cervical, ovarian, vaginal and vulvar cancers, is more than 20,000 annually in the US alone. In many countries, including the US, external-beam radiotherapy followed by high dose rate brachytherapy is the standard-of-care. The superior ability of MR to visualize soft tissue has led to an increase in its usage in planning and delivering brachytherapy treatment. A technical challenge associated with the use of MRI imaging for brachytherapy, in contrast to that of CT imaging, is the visualization of catheters that are used to place radiation sources into cancerous tissue. We describe here a precise, accurate method for achieving catheter segmentation and visualization. The algorithm, with the assistance of manually provided tip locations, performs segmentation using image-features, and is guided by a catheter-specific, estimated mechanical model. A final quality control step removes outliers or conflicting catheter trajectories. The mean Hausdorff error on a 54 patient, 760 catheter reference database was 1.49  mm; 51 of the outliers deviated more than two catheter widths (3.4  mm) from the gold standard, corresponding to catheter identification accuracy of 93% in a Syed-Neblett template. In a multi-user simulation experiment for evaluating RMS precision by simulating varying manually-provided superior tip positions, 3σ maximum errors were 2.44  mm. The average segmentation time for a single catheter was 3 s on a standard PC. The segmentation time, accuracy and precision, are promising indicators of the value of this method for clinical translation of MR-guidance in gynecologic brachytherapy and other catheter-based interventional procedures.

Prospective Clinical Implementation of a Novel Magnetic Resonance Tracking Device for Real-Time Brachytherapy Catheter Positioning

PURPOSE

We designed and built dedicated active magnetic resonance (MR)-tracked (MRTR) stylets. We explored the role of MRTR in a prospective clinical trial.

METHODS AND MATERIALS

Eleven gynecologic cancer patients underwent MRTR to rapidly optimize interstitial catheter placement. MRTR catheter tip location and orientation were computed and overlaid on images displayed on in-room monitors at rates of 6 to 16 frames per second. Three modes of actively tracked navigation were analyzed: coarse navigation to the approximate region around the tumor; fine-tuning, bringing the stylets to the desired location; and pullback, with MRTR stylets rapidly withdrawn from within the catheters, providing catheter trajectories for radiation treatment planning (RTP). Catheters with conventional stylets were inserted, forming baseline locations. MRTR stylets were substituted, and catheter navigation was performed by a clinician working inside the MRI bore, using monitor feedback.

RESULTS

Coarse navigation allowed repositioning of the MRTR catheters tips by 16 mm (mean), relative to baseline, in 14 ± 5 s/catheter (mean ± standard deviation [SD]). The fine-tuning mode repositioned the catheter tips by a further 12 mm, in 24 ± 17 s/catheter. Pullback mode provided catheter trajectories with RTP point resolution of ∼1.5 mm, in 1 to 9 s/catheter.

CONCLUSIONS

MRTR-based navigation resulted in rapid and optimal placement of interstitial brachytherapy catheters. Catheters were repositioned compared with the initial insertion without tracking. In pullback mode, catheter trajectories matched computed tomographic precision, enabling their use for RTP.

MR- versus CT-based high-dose-rate interstitial brachytherapy for vaginal recurrence of endometrial cancer

PURPOSE

To compare clinical outcomes of MR-based versus CT-based high-dose-rate interstitial brachytherapy (ISBT) for vaginal recurrence of endometrioid endometrial cancer (EC).

METHODS AND MATERIALS

We reviewed 66 patients with vaginal recurrent EC; 18 had MR-based ISBT on a prospective clinical trial and 48 had CT-based treatment. Kaplan-Meier survival modeling was used to generate estimates for local control (LC), disease-free interval (DFI), and overall survival (OS), and multivariate Cox modeling was used to assess prognostic factors. Toxicities were evaluated and compared.

RESULTS

Median followup was 33 months (CT 30 months, MR 35 months). Median cumulative equivalent dose in 2-Gy fractions was 75.5 Gy for MR-ISBT and 73.8 Gy for CT-ISBT (p = 0.58). MR patients were older (p = 0.03) and had larger tumor size (>4 cm vs. ≤ 4 cm) compared to CT patients (p = 0.04). For MR-based versus CT-based ISBT, 3-year KM rate for local control was 100% versus 78% (p = 0.04), DFI was 69% versus 55% (p = 0.1), and OS was 63% versus 75% (p = 0.81), respectively. On multivariate analysis, tumor Grade 3 was associated with worse OS (HR 3.57, 95% CI 1.25, 11.36) in a model with MR-ISBT (HR 0.56, 95% CI 0.16, 1.89). Toxicities were not significantly different between the two modalities.

CONCLUSION

Despite worse patient prognostic features, MR-ISBT was associated with a significantly better (100%) 3-year local control, comparable survival, and improved DFI rates compared to CT. Toxicities did not differ compared to CT-ISBT patients. Tumor grade contributed as the most significant predictor for survival. Larger prospective studies are needed to assess the impact of MR-ISBT on survival outcomes.

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.

Magnetic resonance imaging basics for the prostate brachytherapist

Magnetic resonance imaging (MRI) is increasingly being used in radiation therapy, and integration of MRI into brachytherapy in particular is becoming more common. We present here a systematic review of the basic physics and technical aspects of incorporating MRI into prostate brachytherapy. Terminology and MRI system components are reviewed along with typical work flows in prostate high-dose-rate and low-dose-rate brachytherapy. In general, the brachytherapy workflow consists of five key components: diagnosis, implantation, treatment planning (scan + plan), implant verification, and delivery. MRI integration is discussed for diagnosis; treatment planning; and MRI-guided brachytherapy implants, in which MRI is used to guide the physical insertion of the brachytherapy applicator or needles. Considerations and challenges for establishing an MRI brachytherapy program are also discussed.

Comparison of outcomes for MR-guided versus CT-guided high-dose-rate interstitial brachytherapy in women with locally advanced carcinoma of the cervix

OBJECTIVE

The purpose was to compare local control (LC), overall survival (OS) and dose to the organs at risk (OAR) in women with locally advanced cervical cancer treated with MR-guided versus CT-guided interstitial brachytherapy (BT).

METHODS

56 patients (29 MR, 27 CT) were treated with high-dose-rate (HDR) interstitial BT between 2005-2015. The MR patients had been prospectively enrolled on a Phase II clinical trial. Data were analyzed using Kaplan-Meier (K-M) and Cox proportional hazards statistical modeling in JMP® & R®.

RESULTS

Median follow-up time was 19.7months (MR group) and 18.4months (CT group). There were no statistically significant differences in patient age at diagnosis, histology, percent with tumor size >4cm, grade, FIGO stage or lymph node involvement between the groups. Patients in the MR group had more lymphovascular involvement compared to patients in the CT group (p<0.01). When evaluating plans generated, there were no statistically significant differences in median cumulative dose to the high-risk clinical target volume or the OAR. 2-year K-M LC rates for MR-based and CT-based treatments were 96% and 87%, respectively (log-rank p=0.65). At 2years, OS was significantly better in the MR-guided cohort (84% vs. 56%, p=0.036). On multivariate analysis, squamous histology was associated with longer OS (HR 0.23, 95% CI 0.07-0.72) in a model with MR BT (HR 0.35, 95% CI 0.08-1.18). There was no difference in toxicities between CT and MR BT.

CONCLUSION

In this population of locally advanced cervical-cancer patients, MR-guided HDR BT resulted in estimated 96% 2-year local control and excellent survival and toxicity rates.

Outcomes with volume-based dose specification in CT-planned high-dose-rate brachytherapy for stage I-II cervical carcinoma: A 10-year institutional experience

OBJECTIVE

To determine prognostic factors for progression-free survival (PFS) and overall survival (OS) for stage I-II cervical-cancer patients treated using computed-tomography (CT)-planned high-dose-rate (HDR) intracavitary brachytherapy (BT).

METHODS

A total of 150 patients were treated for Stage I-II cervical cancer using CT-planned BT between 4/2004 and 10/2014. Of these, 128 were eligible for inclusion. Kaplan-Meier local control (LC), pelvic control (PC), overall survival (OS), and PFS estimates were calculated.

RESULTS

After a median follow-up of 30months, the 2-year LC rate was 96%, PFS was 88%, and OS was 88%. Overall, 18 patients (14%) experienced any recurrence (AR), 8 had distant recurrence only and 10 had a combination of local, pelvic, regional, and distant recurrence. No patients had LR only. A prognostic factor for AR was tumor size >4cm (p=0.01). Patients with tumors >4cm were 3.3 times more likely to have AR than those with tumors ≤4cm (hazard ratio [HR]=3.3; 95% confidence interval [CI] 1.28-9.47). Point A was 85% of prescription for tumors < 4 cm and decreased approximately 3% over 5 fractions compared to 90% of prescription for tumors > 4 cm that decreased approximately 4% over 5 fractions. Two patients (2%) experienced grade≥2 late toxicity. There were no acute or late grade≥3 toxicities.

CONCLUSION

CT-planned BT resulted in excellent local control and survival. Large tumor size was associated with an increased risk of recurrence outside the radiation field and worse PFS and OS. A volume-optimized plan treated a smaller area than a point A standard plan for patients with Stage I-II cervical cancer that have received chemoradiation. Given the outstanding LC achieved with modern therapy including chemoradiation, HDR, and image-based BT, further efforts to combat spread outside the radiation field with novel therapies are warranted.

Cervical cancer brachytherapy in Canada: A focus on interstitial brachytherapy utilization

PURPOSE

Brachytherapy (BT) techniques for cervical cancer in Canada have changed over the last decade, with evolution to high-dose-rate and image-guided BT. However, there are currently no national data on the use of interstitial BT (IBT). The purpose of this study was to document IBT utilization in Canadian centers, as well as update details of cervical cancer BT practices.

METHODS AND MATERIALS

All Canadian centers with gynecologic BT services (n = 33) were identified, and one gynecology radiation oncologist per center was sent a 33-item e-mail questionnaire regarding their center's practice for cervical cancer BT in 2015. Responses were reported and compared with practice patterns identified in a 2012 Canadian survey.

RESULTS

The response rate was 85% (28/33 centers). The majority (93%) of respondents used high-dose-rate BT, similar to the 2012 survey; 96% of centers had transitioned to three-dimensional (MRI/CT)-based planning in 2015 vs. 75% in 2012 (p = 0.03); 57% centers incorporated MRI for treatment planning in 2015 compared to 38% in 2012 (p = 0.15); the majority (13/16) using a combination of MRI and CT; 50% (14/28 centers) had the capacity to perform IBT, whereas 71% of those that did not referred patients to other centers. Of centers performing IBT, the majority (11/14) used template-based techniques with a median of 6 (range 2-20) needles/catheters and an average of 4 (range 1-5) fractions. Catheters were placed using: strategy based on pre-op imaging (21%), intra-op ultrasound (50%), intra-op MRI (7%), and intra-op CT (21%). The most common dose/fractionation schedules were 6 Gy × 5 fractions (40%), 8 Gy × 3 fractions (19%), and 7 Gy × 4 fractions (15%).

CONCLUSIONS

In Canada, treatment of cervical cancer continues to evolve. IBT has been adopted by half of the responding centers. As more centers move to MRI-based image-guided treatment planning, IBT will become an even more integral part of cervical cancer treatment.

Evaluation of an active magnetic resonance tracking system for interstitial brachytherapy

PURPOSE

In gynecologic cancers, magnetic resonance (MR) imaging is the modality of choice for visualizing tumors and their surroundings because of superior soft-tissue contrast. Real-time MR guidance of catheter placement in interstitial brachytherapy facilitates target coverage, and would be further improved by providing intraprocedural estimates of dosimetric coverage. A major obstacle to intraprocedural dosimetry is the time needed for catheter trajectory reconstruction. Herein the authors evaluate an active MR tracking (MRTR) system which provides rapid catheter tip localization and trajectory reconstruction. The authors assess the reliability and spatial accuracy of the MRTR system in comparison to standard catheter digitization using magnetic resonance imaging (MRI) and CT.

METHODS

The MRTR system includes a stylet with microcoils mounted on its shaft, which can be inserted into brachytherapy catheters and tracked by a dedicated MRTR sequence. Catheter tip localization errors of the MRTR system and their dependence on catheter locations and orientation inside the MR scanner were quantified with a water phantom. The distances between the tracked tip positions of the MRTR stylet and the predefined ground-truth tip positions were calculated for measurements performed at seven locations and with nine orientations. To evaluate catheter trajectory reconstruction, fifteen brachytherapy catheters were placed into a gel phantom with an embedded catheter fixation framework, with parallel or crossed paths. The MRTR stylet was then inserted sequentially into each catheter. During the removal of the MRTR stylet from within each catheter, a MRTR measurement was performed at 40 Hz to acquire the instantaneous stylet tip position, resulting in a series of three-dimensional (3D) positions along the catheter's trajectory. A 3D polynomial curve was fit to the tracked positions for each catheter, and equally spaced dwell points were then generated along the curve. High-resolution 3D MRI of the phantom was performed followed by catheter digitization based on the catheter's imaging artifacts. The catheter trajectory error was characterized in terms of the mean distance between corresponding dwell points in MRTR-generated catheter trajectory and MRI-based catheter digitization. The MRTR-based catheter trajectory reconstruction process was also performed on three gynecologic cancer patients, and then compared with catheter digitization based on MRI and CT.

RESULTS

The catheter tip localization error increased as the MRTR stylet moved further off-center and as the stylet's orientation deviated from the main magnetic field direction. Fifteen catheters' trajectories were reconstructed by MRTR. Compared with MRI-based digitization, the mean 3D error of MRTR-generated trajectories was 1.5 ± 0.5 mm with an in-plane error of 0.7 ± 0.2 mm and a tip error of 1.7 ± 0.5 mm. MRTR resolved ambiguity in catheter assignment due to crossed catheter paths, which is a common problem in image-based catheter digitization. In the patient studies, the MRTR-generated catheter trajectory was consistent with digitization based on both MRI and CT.

CONCLUSIONS

The MRTR system provides accurate catheter tip localization and trajectory reconstruction in the MR environment. Relative to the image-based methods, it improves the speed, safety, and reliability of the catheter trajectory reconstruction in interstitial brachytherapy. MRTR may enable in-procedural dosimetric evaluation of implant target coverage.

Comparison of image-based three-dimensional treatment planning using AcurosTM BV and AAPM TG-43 algorithm for intracavitary brachytherapy of carcinoma cervix

Aim

To compare the image-based three-dimensional treatment planning using AcurosTM BV and AAPM TG-43 algorithm for intracavitary brachytherapy of carcinoma cervix.

Materials and methods

Twenty-seven patients with cancer cervix, stage IIB or IIIB with vaginal involvement limited to the upper third of the vagina was included into the study. Intracavitary treatments with the patient in this study done with computed tomography and magnetic resonance imaging compatible ring applicator. Groupe European de Curietherapie and European Society for Therapeutic Radiology and Oncology recommended doses to target volumes and organs at risk compared using dose volume histogram.

Results

The mean value of Point ‘A’ dose was compared between AcurosTM BV and TG-43, which indicates 0·13% difference. The differences in the mean dose to gross tumour volume for various volumes are V100% 0·28%, V150% 1·22% and V200% 1·03%; all volumes showed small difference but statistical significant (p<0·05). The mean dose of high-risk clinical target volume (HRCTV) D90 using AcurosTM BV was 8·47 Gy, which was 1·63% less compared with TG-43. The mean point A dose using AcurosTM BV is 1·04 times the dose to D90 of mean HRCTV. The same difference was observed in comparison with TG43. D2cc and D0·1cc of the bladder, rectum and sigmoid showed a statistically significant difference (p<0·05) in comparison with TG-43.

Conclusion

The differences in dosimetric parameters between the AcurosTM BV and TG-43 proved to be statistically significant. The difference is very small, and they are clinically insignificant.

Metal artefacts in MRI-guided brachytherapy of cervical cancer

The importance of assessing the metal-induced artefacts in magnetic resonance imaging (MRI)-guided brachytherapy is growing along with the increasing interest of integrating MRI into the treatment procedure of cervical cancer. Examples of metal objects in use include intracavitary cervical applicators and interstitial needles. The induced artefacts increase the uncertainties in the clinical workflow and can be a potential obstacle for the accurate delivery of the treatment. Overcoming this problem necessitates a good understanding of its originating sources. Several efforts are recorded in the literature to quantify the extent of such artefacts, in phantoms and in clinical practice. Here, we elaborate on the origin of metal-induced artefacts in the light of brachytherapy applications, while summarizing recent efforts that have been made to assess and overcome the induced distortions.

Iterative-cuts: longitudinal and scale-invariant segmentation via user-defined templates for rectosigmoid colon in gynecological brachytherapy

Among all types of cancer, gynecological malignancies belong to the fourth most frequent type of cancer among women. In addition to chemotherapy and external beam radiation, brachytherapy is the standard procedure for the treatment of these malignancies. In the progress of treatment planning, localization of the tumor as the target volume and adjacent organs of risks by segmentation is crucial to accomplish an optimal radiation distribution to the tumor while simultaneously preserving healthy tissue. Segmentation is performed manually and represents a time-consuming task in clinical daily routine. This study focuses on the segmentation of the rectum/sigmoid colon as an organ-at-risk in gynecological brachytherapy. The proposed segmentation method uses an interactive, graph-based segmentation scheme with a user-defined template. The scheme creates a directed two-dimensional graph, followed by the minimal cost closed set computation on the graph, resulting in an outlining of the rectum. The graph's outline is dynamically adapted to the last calculated cut. Evaluation was performed by comparing manual segmentations of the rectum/sigmoid colon to results achieved with the proposed method. The comparison of the algorithmic to manual result yielded a dice similarity coefficient value of [Formula: see text], in comparison to [Formula: see text] for the comparison of two manual segmentations by the same physician. Utilizing the proposed methodology resulted in a median time of [Formula: see text], compared to 300 s needed for pure manual segmentation.

Direction Modulated Brachytherapy for Treatment of Cervical Cancer. II: Comparative Planning Study With Intracavitary and Intracavitary-Interstitial Techniques

PURPOSE

To perform a comprehensive comparative planning study evaluating the utility of the proposed direction modulated brachytherapy (DMBT) tandem applicator against standard applicators, in the setting of image guided adaptive brachytherapy of cervical cancer.

METHODS AND MATERIALS

A detailed conceptual article was published in 2014. The proposed DMBT tandem applicator has 6 peripheral grooves of 1.3-mm width, along a 5.4-mm-thick nonmagnetic tungsten alloy rod of density 18.0 g/cm(3), capable of generating directional dose profiles. We performed a comparative planning study with 45 cervical cancer patients enrolled consecutively in the prospective observational EMBRACE study. In all patients, MRI-based planning was performed while utilizing various tandem-ring (27 patients) and tandem-ring-needles (18 patients) applicators, in accordance with the Groupe Européen de Curiethérapie-European Society for Radiotherapy and Oncology recommendations. For unbiased comparisons, all cases were replanned with an in-house-developed inverse optimization code while enforcing a uniform set of constraints that are reflective of the clinical practice. All plans were normalized to the same high-risk clinical target volume D90 values achieved in the original clinical plans.

RESULTS

In general, if the standard tandem was replaced with the DMBT tandem while maintaining all other planning conditions the same, there was consistent improvement in the plan quality. For example, among the 18 tandem-ring-needles cases, the average D2cm(3) reductions achieved were -2.48% ± 11.03%, -4.45% ± 5.24%, and -5.66% ± 6.43% for the bladder, rectum, and sigmoid, respectively. An opportunity may also exist in avoiding use of needles altogether for when the total number of needles required is small (approximately 2 to 3 needles or less), if DMBT tandem is used.

CONCLUSIONS

Integrating the novel DMBT tandem onto both intracavitary and intracavitary-interstitial applicator assembly enabled consistent improvement in the sparing of the OARs, over a standard "single-channel" tandem, though individual variations in benefit were considerable. Although at an early stage of development, the DMBT concept design is demonstrated to be useful and pragmatic for potential clinical translation.

Outcomes with image-based interstitial brachytherapy for vaginal cancer

PURPOSE

To compare clinical outcomes of image-based versus non-image-based interstitial brachytherapy (IBBT) for vaginal cancer.

METHODS AND MATERIALS

Of 72 patients with vaginal cancer treated with brachytherapy (BT), 47 had image guidance (CT=31, MRI=16) and 25 did not. Kaplan-Meier (KM) estimates were generated for any recurrence, local control (LC), disease-free interval (DFI), and overall survival (OS) and Cox models were used to assess prognostic factors.

RESULTS

Median age was 66 and median follow-up time was 24months. Median cumulative EQD2 dose was 80.8Gy in the non-IBBT group and 77Gy in the IBBT group. For non-IBBT versus IBBT, the 2-year KM LC was 71% vs. 93% (p=0.03); DFI was 54% vs. 86% (p=0.04); and OS 52% vs. 82% (p=0.35). On multivariate analysis, IBBT was associated with better DFI (HR 0.24, 95% CI 0.07-0.73). Having any 2 or more of chemotherapy, high-dose-rate (HDR) BT or IBBT (temporally correlated variables) significantly reduced risk of relapse (HR=0.33, 95% CI=0.13-0.83), compared to having none of these factors.

CONCLUSION

Over time, the use of chemotherapy, HDR, and IBBT has increased in vaginal cancer. The combination of these factors resulted in the highest rates of disease control. Image-guided brachytherapy for vaginal cancer patients maximizes disease control.

Characterizing gradient echo signal decays in gynecologic cancers at 3T using a Gaussian augmentation of the monoexponential (GAME) model

PURPOSE

To assess whether R2* mapping with a standard Monoexponential (ME) or a Gaussian Augmentation of the Monoexponential (GAME) decay model better characterizes gradient-echo signal decays in gynecological cancers after external beam radiation therapy at 3T, and evaluate implications of modeling for noninvasive identification of intratumoral hypoxia.

MATERIALS AND METHODS

Multi-gradient-echo signals were acquired on 25 consecutive patients with gynecologic cancers and three healthy participants during inhalation of different oxygen concentrations at 3T. Data were fitted with both ME and GAME models. Models were compared using F-tests in tumors and muscles in patients, muscles, cervix, and uterus in healthy participants, and across oxygenation levels.

RESULTS

GAME significantly improved fitting over ME (P < 0.05): Improvements with GAME covered 34% of tumor regions-of-interest on average, ranging from 6% (of a vaginal tumor) to 68% (of a cervical tumor) in individual tumors. Improvements with GAME were more prominent in areas that would be assumed hypoxic based on ME alone, reaching 90% as ME R2* approached 100 Hz. Gradient echo decay parameters at different oxygenation levels were not significantly different (P = 0.81).

CONCLUSION

R2* may prove sensitive to hypoxia; however, inaccurate representations of underlying data may limit the success of quantitative assessments. Although the degree to which R2 or σ values correlate with hypoxia remains unknown, improved characterization with GAME increases the potential for determining any correlates of fit parameters with biomarkers, such as oxygenation status. J. MAGN. RESON. IMAGING 2016;44:1020-1030.

Magnetic resonance imaging-guided brachytherapy for cervical cancer: initiating a program

Over the past decade, the application of magnetic resonance imaging (MRI) has increased, and there is growing evidence to suggest that improvements in accuracy of target delineation in MRI-guided brachytherapy may improve clinical outcomes in cervical cancer. To implement a high quality image guided brachytherapy program, a multidisciplinary team is required with appropriate expertise as well as an adequate patient load to ensure a sustainable program. It is imperative to know that the most important source of uncertainty in the treatment process is related to target delineation and therefore, the necessity of training and expertise as well as quality assurance should be emphasized. A short review of concepts and techniques that have been developed for implementation and/or improvement of workflow of a MRI-guided brachytherapy program are provided in this document, so that institutions can use and optimize some of them based on their resources to minimize their procedure times.

Review of advanced catheter technologies in radiation oncology brachytherapy procedures

The development of new catheter and applicator technologies in recent years has significantly improved treatment accuracy, efficiency, and outcomes in brachytherapy. In this paper, we review these advances, focusing on the performance of catheter imaging and reconstruction techniques in brachytherapy procedures using magnetic resonance images and electromagnetic tracking. The accuracy of catheter reconstruction, imaging artifacts, and other notable properties of plastic and titanium applicators in gynecologic treatments are reviewed. The accuracy, noise performance, and limitations of electromagnetic tracking for catheter reconstruction are discussed. Several newly developed applicators for accelerated partial breast irradiation and gynecologic treatments are also reviewed. New hypofractionated high dose rate treatment schemes in prostate cancer and accelerated partial breast irradiation are presented.

A system to use electromagnetic tracking for the quality assurance of brachytherapy catheter digitization

PURPOSE

To investigate the use of a system using electromagnetic tracking (EMT), post-processing and an error-detection algorithm for detecting errors and resolving uncertainties in high-dose-rate brachytherapy catheter digitization for treatment planning.

METHODS

EMT was used to localize 15 catheters inserted into a phantom using a stepwise acquisition technique. Five distinct acquisition experiments were performed. Noise associated with the acquisition was calculated. The dwell location configuration was extracted from the EMT data. A CT scan of the phantom was performed, and five distinct catheter digitization sessions were performed. No a priori registration of the CT scan coordinate system with the EMT coordinate system was performed. CT-based digitization was automatically extracted from the brachytherapy plan DICOM files (CT), and rigid registration was performed between EMT and CT dwell positions. EMT registration error was characterized in terms of the mean and maximum distance between corresponding EMT and CT dwell positions per catheter. An algorithm for error detection and identification was presented. Three types of errors were systematically simulated: swap of two catheter numbers, partial swap of catheter number identification for parts of the catheters (mix), and catheter-tip shift. Error-detection sensitivity (number of simulated scenarios correctly identified as containing an error/number of simulated scenarios containing an error) and specificity (number of scenarios correctly identified as not containing errors/number of correct scenarios) were calculated. Catheter identification sensitivity (number of catheters correctly identified as erroneous across all scenarios/number of erroneous catheters across all scenarios) and specificity (number of catheters correctly identified as correct across all scenarios/number of correct catheters across all scenarios) were calculated. The mean detected and identified shift was calculated.

RESULTS

The maximum noise ±1 standard deviation associated with the EMT acquisitions was 1.0 ± 0.1 mm, and the mean noise was 0.6 ± 0.1 mm. Registration of all the EMT and CT dwell positions was associated with a mean catheter error of 0.6 ± 0.2 mm, a maximum catheter error of 0.9 ± 0.4 mm, a mean dwell error of 1.0 ± 0.3 mm, and a maximum dwell error of 1.3 ± 0.7 mm. Error detection and catheter identification sensitivity and specificity of 100% were observed for swap, mix and shift (≥2.6 mm for error detection; ≥2.7 mm for catheter identification) errors. A mean detected shift of 1.8 ± 0.4 mm and a mean identified shift of 1.9 ± 0.4 mm were observed.

CONCLUSIONS

Registration of the EMT dwell positions to the CT dwell positions was possible with a residual mean error per catheter of 0.6 ± 0.2 mm and a maximum error for any dwell of 1.3 ± 0.7 mm. These low residual registration errors show that quality assurance of the general characteristics of the catheters and of possible errors affecting one specific dwell position is possible. The sensitivity and specificity of the catheter digitization verification algorithm was 100% for swap and mix errors and for shifts ≥2.6 mm. On average, shifts ≥1.8 mm were detected, and shifts ≥1.9 mm were detected and identified.

Image-guided video assisted thoracoscopic surgery (iVATS) - phase I-II clinical trial

Purpose

To facilitate localization and resection of small lung nodules, we developed a prospective clinical trial (ClinicalTrials.govnumber NCT01847209) for a novel surgical approach which combines placement of fiducials using intra‐operative C‐arm computed tomography (CT) guidance with standard thoracoscopic resection technique using image‐guided video‐assisted thoracoscopic surgery (iVATS).

Methods

Pretrial training was performed in a porcine model using C‐arm CT and needle guidance software. Methodology and workflow for iVATS was developed, and a multi‐modality team was trained. A prospective phase I‐II clinical trial was initiated with the goal of recruiting eligible patients with small peripheral pulmonary nodules. Intra‐operative C‐arm CT scan was utilized for guidance of percutaneous marking with two T‐bars (Kimberly‐Clark, Roswell, GA) followed by VATS resection of the tumor.

Results

Twenty‐five patients were enrolled; 23 underwent iVATS, one withdrew, and one lesion resolved. Size of lesions were: 0.6–1.8 cm, mean = 1.3 ± 0.38 cm.. All 23 patients underwent complete resection of their lesions. CT imaging of the resected specimens confirmed the removal of the T‐bars and the nodule. Average and total procedure radiation dose was in the acceptable low range (median = 1501 μGy*m², range 665–16,326). There were no deaths, and all patients were discharged from the hospital (median length of stay = 4 days, range 2–12). Three patients had postoperative complications: one prolonged air‐leak, one pneumonia, and one ileus.

Conclusions

A successful and safe step‐wise process has been established for iVATS, combining intra‐operative C‐arm CT scanning and thoracoscopic surgery in a hybrid operating room. J. Surg. Oncol. 2015 111:18–25. © 2015 The Authors. Journal of Surgical Oncology Published by Wiley Periodicals, Inc.

Magnetic resonance image guided brachytherapy

The application of magnetic resonance image (MRI)-guided brachytherapy has demonstrated significant growth during the past 2 decades. Clinical improvements in cervix cancer outcomes have been linked to the application of repeated MRI for identification of residual tumor volumes during radiotherapy. This has changed clinical practice in the direction of individualized dose administration, and resulted in mounting evidence of improved clinical outcome regarding local control, overall survival as well as morbidity. MRI-guided prostate high-dose-rate and low-dose-rate brachytherapies have improved the accuracy of target and organs-at-risk delineation, and the potential exists for improved dose prescription and reporting for the prostate gland and organs at risk. Furthermore, MRI-guided prostate brachytherapy has significant potential to identify prostate subvolumes and dominant lesions to allow for dose administration reflecting the differential risk of recurrence. MRI-guided brachytherapy involves advanced imaging, target concepts, and dose planning. The key issue for safe dissemination and implementation of high-quality MRI-guided brachytherapy is establishment of qualified multidisciplinary teams and strategies for training and education.

Redesign of process map to increase efficiency: Reducing procedure time in cervical cancer brachytherapy

PURPOSE

To increase intraprocedural efficiency in the use of clinical resources and to decrease planning time for cervical cancer brachytherapy treatments through redesign of the procedure's process map.

METHODS AND MATERIALS

A multidisciplinary team identified all tasks and associated resources involved in cervical cancer brachytherapy in our institution and arranged them in a process map. A redesign of the treatment planning component of the process map was conducted with the goal of minimizing planning time. Planning time was measured on 20 consecutive insertions, of which 10 were performed with standard procedures and 10 with the redesigned process map, and results were compared. Statistical significance (p < 0.05) was measured with a two-tailed t test.

RESULTS

Twelve tasks involved in cervical cancer brachytherapy treatments were identified. The process map showed that in standard procedures, the treatment planning tasks were performed sequentially. The process map was redesigned to specify that contouring and some planning tasks are performed concomitantly. Some quality assurance tasks were reorganized to minimize adverse effects of a possible error on procedure time. Test dry runs followed by live implementation confirmed the applicability of the new process map to clinical conditions. A 29% reduction in planning time (p < 0.01) was observed with the introduction of the redesigned process map.

CONCLUSIONS

A process map for cervical cancer brachytherapy was generated. The treatment planning component of the process map was redesigned, resulting in a 29% decrease in planning time and a streamlining of the quality assurance process.

RFA-cut: Semi-automatic segmentation of radiofrequency ablation zones with and without needles via optimal s-t-cuts

In this contribution, we present a semi-automatic segmentation algorithm for radiofrequency ablation (RFA) zones via optimal s-t-cuts. Our interactive graph-based approach builds upon a polyhedron to construct the graph and was specifically designed for computed tomography (CT) acquisitions from patients that had RFA treatments of Hepatocellular Carcinomas (HCC). For evaluation, we used twelve post-interventional CT datasets from the clinical routine and as evaluation metric we utilized the Dice Similarity Coefficient (DSC), which is commonly accepted for judging computer aided medical segmentation tasks. Compared with pure manual slice-by-slice expert segmentations from interventional radiologists, we were able to achieve a DSC of about eighty percent, which is sufficient for our clinical needs. Moreover, our approach was able to handle images containing (DSC=75.9%) and not containing (78.1%) the RFA needles still in place. Additionally, we found no statistically significant difference (p<;0.423) between the segmentation results of the subgroups for a Mann-Whitney test. Finally, to the best of our knowledge, this is the first time a segmentation approach for CT scans including the RFA needles is reported and we show why another state-of-the-art segmentation method fails for these cases. Intraoperative scans including an RFA probe are very critical in the clinical practice and need a very careful segmentation and inspection to avoid under-treatment, which may result in tumor recurrence (up to 40%). If the decision can be made during the intervention, an additional ablation can be performed without removing the entire needle. This decreases the patient stress and associated risks and costs of a separate intervention at a later date. Ultimately, the segmented ablation zone containing the RFA needle can be used for a precise ablation simulation as the real needle position is known.

Comparison and consensus guidelines for delineation of clinical target volume for CT- and MR-based brachytherapy in locally advanced cervical cancer

OBJECTIVE

To create and compare consensus clinical target volume (CTV) contours for computed tomography (CT) and 3-Tesla (3-T) magnetic resonance (MR) image-based cervical-cancer brachytherapy.

METHODS AND MATERIALS

Twenty-three experts in gynecologic radiation oncology contoured the same 3 cervical cancer brachytherapy cases: 1 stage IIB near-complete response (CR) case with a tandem and ovoid, 1 stage IIB partial response (PR) case with tandem and ovoid with needles, and 1 stage IB2 CR case with a tandem and ring applicator. The CT contours were completed before the MRI contours. These were analyzed for consistency and clarity of target delineation using an expectation maximization algorithm for simultaneous truth and performance level estimation (STAPLE), with κ statistics as a measure of agreement between participants. The conformity index was calculated for each of the 6 data sets. Dice coefficients were generated to compare the CT and MR contours of the same case.

RESULTS

For all 3 cases, the mean tumor volume was smaller on MR than on CT (P<.001). The κ and conformity index estimates were slightly higher for CT, indicating a higher level of agreement on CT. The Dice coefficients were 89% for the stage IB2 case with a CR, 74% for the stage IIB case with a PR, and 57% for the stage IIB case with a CR.

CONCLUSION

In a comparison of MR-contoured with CT-contoured CTV volumes, the higher level of agreement on CT may be due to the more distinct contrast medium visible on the images at the time of brachytherapy. MR at the time of brachytherapy may be of greatest benefit in patients with large tumors with parametrial extension that have a partial or complete response to external beam. On the basis of these results, a 95% consensus volume was generated for CT and for MR. Online contouring atlases are available for instruction at http://www.nrgoncology.org/Resources/ContouringAtlases/GYNCervicalBrachytherapy.aspx.

Real-time active MR-tracking of metallic stylets in MR-guided radiation therapy

PURPOSE

To develop an active MR-tracking system to guide placement of metallic devices for radiation therapy.

METHODS

An actively tracked metallic stylet for brachytherapy was constructed by adding printed-circuit micro-coils to a commercial stylet. The coil design was optimized by electromagnetic simulation, and has a radio-frequency lobe pattern extending ∼5 mm beyond the strong B0 inhomogeneity region near the metal surface. An MR-tracking sequence with phase-field dithering was used to overcome residual effects of B0 and B1 inhomogeneities caused by the metal, as well as from inductive coupling to surrounding metallic stylets. The tracking system was integrated with a graphical workstation for real-time visualization. The 3 Tesla MRI catheter-insertion procedures were tested in phantoms and ex vivo animal tissue, and then performed in three patients during interstitial brachytherapy.

RESULTS

The tracking system provided high-resolution (0.6 × 0.6 × 0.6 mm(3) ) and rapid (16 to 40 frames per second, with three to one phase-field dithering directions) catheter localization in phantoms, animals, and three gynecologic cancer patients.

CONCLUSION

This is the first demonstration of active tracking of the shaft of metallic stylet in MR-guided brachytherapy. It holds the promise of assisting physicians to achieve better targeting and improving outcomes in interstitial brachytherapy.

Refinement-cut: user-guided segmentation algorithm for translational science

In this contribution, a semi-automatic segmentation algorithm for (medical) image analysis is presented. More precise, the approach belongs to the category of interactive contouring algorithms, which provide real-time feedback of the segmentation result. However, even with interactive real-time contouring approaches there are always cases where the user cannot find a satisfying segmentation, e.g. due to homogeneous appearances between the object and the background, or noise inside the object. For these difficult cases the algorithm still needs additional user support. However, this additional user support should be intuitive and rapid integrated into the segmentation process, without breaking the interactive real-time segmentation feedback. I propose a solution where the user can support the algorithm by an easy and fast placement of one or more seed points to guide the algorithm to a satisfying segmentation result also in difficult cases. These additional seed(s) restrict(s) the calculation of the segmentation for the algorithm, but at the same time, still enable to continue with the interactive real-time feedback segmentation. For a practical and genuine application in translational science, the approach has been tested on medical data from the clinical routine in 2D and 3D.

Brachytherapy in the treatment of cervical cancer: a review

Dramatic advances have been made in brachytherapy for cervical cancer. Radiation treatment planning has evolved from two-dimensional to three-dimensional, incorporating magnetic resonance imaging and/or computed tomography into the treatment paradigm. This allows for better delineation and coverage of the tumor, as well as improved avoidance of surrounding organs. Consequently, advanced brachytherapy can achieve very high rates of local control with a reduction in morbidity, compared with historic approaches. This review provides an overview of state-of-the-art gynecologic brachytherapy, with a focus on recent advances and their implications for women with cervical cancer.

Dosimetric consequences of interobserver variability in delineating the organs at risk in gynecologic interstitial brachytherapy

PURPOSE

To investigate the dosimetric variability associated with interobserver organ-at-risk delineation differences on computed tomography in patients undergoing gynecologic interstitial brachytherapy.

METHODS AND MATERIALS

The rectum, bladder, and sigmoid of 14 patients treated with gynecologic interstitial brachytherapy were retrospectively contoured by 13 physicians. Geometric variability was calculated using κ statistics, conformity index (CIgen), and coefficient of variation (CV) of volumes contoured across physicians. Dosimetric variability of the single-fraction D0.1cc and D2cc was assessed through CV across physicians, and the standard deviation of the total EQD2 (equivalent dose in 2 Gy per fraction) brachytherapy dose (SD(TOT)) was calculated.

RESULTS

The population mean ± 1 standard deviation of κ, CIgen, and volume CV were, respectively: 0.77 ± 0.06, 0.70 ± 0.08, and 20% ± 6% for bladder; 0.74 ± 06, 0.67 ± 0.08, and 20% ± 5% for rectum; and 0.33 ± 0.20, 0.26 ± 0.17, and 82% ± 42% for sigmoid. Dosimetric variability was as follows: for bladder, CV = 31% ± 19% (SD(TOT) = 72 ± 64 Gy) for D0.1cc and CV = 16% ± 10% (SD(TOT) = 9 ± 6 Gy) for D2cc; for rectum, CV = 11% ± 5% (SD(TOT) = 16 ± 17 Gy) for D0.1cc and CV = 7% ± 2% (SD(TOT) = 4 ± 3 Gy) for D2cc; for sigmoid, CV = 39% ± 28% (SD(TOT) = 12 ± 18 Gy) for D0.1cc and CV = 34% ± 19% (SD(TOT) = 4 ± 4 Gy) for D2cc.

CONCLUSIONS

Delineation of bladder and rectum by 13 physicians demonstrated substantial geometric agreement and resulted in good dosimetric agreement for all dose-volume histogram parameters except bladder D0.1cc. Small delineation differences in high-dose regions by the posterior bladder wall may explain these results. The delineation of sigmoid showed fair geometric agreement. The higher dosimetric variability for sigmoid compared with rectum and bladder did not correlate with higher variability in the total brachytherapy dose but rather may be due to the sigmoid being positioned in low-dose regions in the cases analyzed in this study.