MRI-guided HDR prostate brachytherapy in standard 1.5T scanner

169Yb-based high dose rate intensity modulated brachytherapy for focal treatment of prostate cancer

PURPOSE

This study compares conventional 192Ir-based high dose rate brachytherapy (HDR-BT) with 169Yb-based HDR intensity modulated brachytherapy (IMBT) for focal prostate cancer treatment. Additionally, the study explores the potential to generate less invasive treatment plans with IMBT by reducing the number of catheters needed to achieve acceptable outcomes.

METHODS AND MATERIALS

A retrospective dosimetric study of ten prostate cancer patients initially treated with conventional 192Ir-based HDR-BT and 5-14 catheters was employed. RapidBrachyMCTPS, a Monte Carlo-based treatment planning system was used to calculate and optimize dose distributions. For 169Yb-based HDR IMBT, a custom 169Yb source combined with 0.8 mm thick platinum shields placed inside 6F catheters was used. Furthermore, dose distributions were investigated when iteratively removing catheters for less invasive treatments.

RESULTS

With IMBT, the urethra D10 and D0.1cc decreased on average by 15.89 and 15.65 percentage points (pp) and the rectum V75 and D2cc by 1.53 and 11.54 pp, respectively, compared to the conventional clinical plans. Similar trends were observed when the number of catheters decreased. On average, there was an observed increase in PTV V150 from 2.84 pp with IMBT when utilizing all catheters to 8.83 pp when four catheters were removed. PTV V200 increased from 0.42 to 2.96 pp on average. Hotspots in the body were however lower with IMBT compared to conventional clinical plans.

CONCLUSIONS

169Yb-based HDR IMBT for focal treatment of prostate cancer has the potential to successfully deliver clinically acceptable, less invasive treatment with reduced dose to organs at risk.

Rapid multi-catheter segmentation for magnetic resonance image-guided catheter-based interventions

BACKGROUND

Magnetic resonance imaging (MRI) is the gold standard for delineating cancerous lesions in soft tissue. Catheter-based interventions require the accurate placement of multiple long, flexible catheters at the target site. The manual segmentation of catheters in MR images is a challenging and time-consuming task. There is a need for automated catheter segmentation to improve the efficiency of MR-guided procedures.

PURPOSE

To develop and assess a machine learning algorithm for the detection of multiple catheters in magnetic resonance images used during catheter-based interventions.

METHODS

In this work, a 3D U-Net was trained to retrospectively segment catheters in scans acquired during clinical MR-guided high dose rate (HDR) prostate brachytherapy cases. To assess confidence in segmentation, multiple AI models were trained. On clinical test cases, average segmentation results were used to plan the brachytherapy delivery. Dosimetric parameters were compared to the original clinical plan. Data was obtained from 35 patients who underwent HDR prostate brachytherapy for focal disease with a total of 214 image volumes. 185 image volumes from 30 patients were used for training using a five-fold cross validation split to divide the data for training and validation. To generate confidence measures of segmentation accuracy, five trained models were generated. The remaining five patients (29 volumes) were used to test the performance of the trained model by comparison to manual segmentations of three independent observers and assessment of dosimetric impact on the final clinical brachytherapy plans.

RESULTS

The network successfully identified 95% of catheters in the test set at a rate of 0.89 s per volume. The multi-model method identified the small number of cases where AI segmentation of individual catheters was poor, flagging the need for user input. AI-based segmentation performed as well as segmentations by independent observers. Plan dosimetry using AI-segmented catheters was comparable to the original plan.

CONCLUSION

The vast majority of catheters were accurately identified by AI segmentation, with minimal impact on plan outcomes. The use of multiple AI models provided confidence in the segmentation accuracy and identified catheter segmentations that required further manual assessment. Real-time AI catheter segmentation can be used during MR-guided insertions to assess deflections and for rapid planning of prostate brachytherapy.

US-guided EM tracked system for HDR brachytherapy: A first in-men randomized study for whole prostate treatment

PURPOSE

An electromagnetic tracking device (EMT) has been integrated in an HDR 3D ultrasound guidance system for prostate HDR. The aim of this study was to compare the efficiency of HDR workflows with and without EM tracking.

METHODS AND MATERIALS

A total of 58 patients with a 15 Gy HDR prostate boost were randomized in two arms and two operation room (OR) procedures using: (1) the EMT investigational device, and (2) the Oncentra prostate system (OCP). OR times were compared for both techniques.

RESULTS

The overall procedure median time was about 20% shorter for EMT (63 min) compared to OCP (79 min). The US acquisition and contouring was longer for OCP compared to EMT (23 min vs. 16 min). The catheter reconstruction's median times were 23 min and 13 min for OCP and EMT respectively. For the automatic reconstruction with EMT, 62% of cases required no or few manual corrections. Using the EM technology in an OR environment was challenging. In some cases, interferences or the stiffness of the stylet introduced errors in the reconstruction of catheters. The last step was the dosimetry with median times of 11 min (OCP) and 15.5 min (EMT). Finally, it was observed that there was no learning curve associated with the introduction of this new technology.

CONCLUSIONS

The EMT device offers an efficient solution for automatic catheter reconstruction for HDR prostate while reducing the possibility of mis-reconstructed catheters caused by issues of visualization in the US images. Because of that, the overall OR times was shorter when using the EMT system.

Toward mechatronic MRI-guided focal laser ablation of the prostate: Robust registration for improved needle delivery

BACKGROUND

Multiparametric MRI (mpMRI) is an effective tool for detecting and staging prostate cancer (PCa), guiding interventional therapy, and monitoring PCa treatment outcomes. MRI-guided focal laser ablation (FLA) therapy is an alternative, minimally invasive treatment method to conventional therapies, which has been demonstrated to control low-grade, localized PCa while preserving patient quality of life. The therapeutic success of FLA depends on the accurate placement of needles for adequate delivery of ablative energy to the target lesion. We previously developed an MR-compatible mechatronic system for prostate FLA needle guidance and validated its performance in open-air and clinical 3T in-bore experiments using virtual targets.

PURPOSE

To develop a robust MRI-to-mechatronic system registration method and evaluate its in-bore MR-guided needle delivery accuracy in tissue-mimicking prostate phantoms.

METHODS

The improved registration multifiducial assembly houses thirty-six aqueous gadolinium-filled spheres distributed over a 7.3 × 7.3 × 5.2 cm volume. MRI-guided needle guidance accuracy was quantified in agar-based tissue-mimicking prostate phantoms on trajectories (N = 44) to virtual targets covering the mechatronic system's range of motion. 3T gradient-echo recalled (GRE) MRI images were acquired after needle insertions to each target, and the air-filled needle tracks were segmented. Needle guidance error was measured as the shortest Euclidean distance between the target point and the segmented needle trajectory, and angular error was measured as the angle between the targeted trajectory and the segmented needle trajectory. These measurements were made using both the previously designed four-sphere registration fiducial assembly on trajectories (N = 7) and compared with the improved multifiducial assembly using a Mann-Whitney U test.

RESULTS

The median needle guidance error of the system using the improved registration fiducial assembly at a depth of 10 cm was 1.02 mm with an interquartile range (IQR) of 0.42-2.94 mm. The upper limit of the one-sided 95% prediction interval of needle guidance error was 4.13 mm. The median (IQR) angular error was 0.0097 rad (0.0057-0.015 rad) with a one-sided 95% prediction interval upper limit of 0.022 rad. The median (IQR) positioning error using the previous four-sphere registration fiducial assembly was 1.87 mm (1.77-2.14 mm). This was found to be significantly different (p = 0.0012) from the median (IQR) positioning error of 0.28 mm (0.14-0.95 mm) using the new registration fiducial assembly on the same trajectories. No significant difference was detected between the medians of the angular errors (p = 0.26).

CONCLUSION

This is the first study presenting an improved registration method and validation in tissue-mimicking phantoms of our remotely actuated MR-compatible mechatronic system for delivery of prostate FLA needles. Accounting for the effects of needle deflection, the system was demonstrated to be capable of needle delivery with an error of 4.13 mm or less in 95% of cases under ideal conditions, which is a statistically significant improvement over the previous method. The system will next be validated in a clinical setting.

Rapid variable flip angle positive susceptibility contrast imaging for clinical metal seeds

Positive susceptibility contrast imaging (PSCI) based on susceptibility mapping exhibits excellent efficacy for visualizing magnetic resonance (MR)-compatible metallic devices because of their high magnetic susceptibility compared to that of human tissues. However, the long-acquisition time required by the two-dimensional fast spin echo (2D FSE)-based PSCI approach, impedes its practical applications in 3D imaging. In this study, a three-dimensional (3D) susceptibility-based variable flip angle (vFA) FSE sequence was proposed to accelerate data acquisition in the clinical radiotherapy applications of ex vivo and in vivo rapid 3D PSCI for the imaging of metal seeds. Here, the proposed scheme applied a 3D modulated vFA technique for refocused imaging with an extended echo-train sequence for sampling data. The scheme integrated the projection-onto-dipole fields (PDF) to remove the background field and accelerate PSCI by using a compressive sensing framework with a variable-densitysampling mask. The experiments involved some gelatin phantoms, porcine tissues and patients with scapular tumors and brachytherapy seeds. All of the experimental results showed that the proposed scheme could accelerate data acquisition of 3D PSCI at the reduction factors of 2 ∼ 5 while accurately localizing the actual positions of the brachytherapy seeds in the ex vivo and in vivo applications. The results were compared with those of the existing methods, including susceptibility gradient mapping using the original resolution (SUMO) and gradient echo acquisition for superparamagnetic particle (GRASP).

Investigation the effect of a magnetic field on the dose distribution of I-125, Ir-192, Yb-169, and Co-60 brachytherapy sources by Monte Carlo simulation

Magnetic resonance imaging (MRI) during brachytherapy may alter the dose distribution of radioactive sources implanted in the tumor. This study investigates the impact of a magnetic field of 1.5 T, 3 T, and 7 T strengths on the dose distribution of high dose rate Co-60, Ir-192, and Yb-169, and low dose rate I-125 sources, using Geant4 Monte Carlo toolkit. After validating the simulation results by calculating the AAPM-TG43 dosimetric parameters, seven sources of each radioisotope were simulated in a water phantom, and their dose distributions were compared under the influence of a magnetic field. The simulation results indicate that using Co-60 brachytherapy under the MRI guidance is not recommended. Furthermore, the impact of a magnetic field of up to 7 T strength on the dose distribution of Ir-192, Yb-169, and I-125 sources is negligible, provided that there is no air pocket near brachytherapy sources.

Preliminary Study of a Modular MR-Compatible Robot for Image-Guided Insertion of Multiple Needles

Percutaneous needle-based interventions such as transperineal prostate brachytherapy require the accurate placement of multiple needles to treat cancerous lesions within the target organ. To guide needle placement, magnetic resonance imaging (MRI) offers excellent visualization of the target lesion without the need for ionizing radiation. To date, multi-needle insertion relies on a grid template, which limits the ability to steer individual needles. This work describes an MR-compatible robot designed for the sequential insertion of multiple non-parallel needles under MR guidance. The 6-DOF system is designed with an articulated arm to extend the reach of the robot. This strategy presents a novel approach enabling the robot to maneuver around existing needles while minimizing the footprint of the robot. Forward kinematics as well as optimization-based inverse kinematics are presented. The impact of the robot on image quality was tested for four sequences (T1w-TSE, T2w-TSE, THRIVE and EPI) on a 3T Philips Achieva system. Quantification of the signal-to-noise ratio showed a 46% signal loss in a gelatin phantom when the system was powered on but no further adverse effects when the robot was moving. Joint level testing showed a maximum error of 2.10 ± 0.72°s for revolute joints and 0.31 ± 0.60 mm for prismatic joints. The theoretical workspace spans the proposed clinical target surface of 10 x 10 cm. Lastly, the feasibility of multi-needle insertion was demonstrated with four needles inserted under real-time MR-guidance with no visible loss in image quality.

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.

Commissioning of an intra-operative US guided prostate HDR system integrating an EM tracking technology

PURPOSE

Ultrasound-based planning for high-dose-rate prostate brachytherapy is commonly used in the clinic, mainly because it offers fast real-time image-guided capability at a relatively low cost. The main difficulty with US planning is the catheter reconstruction due to artefacts (from multiple catheters) and echogenicity. Electromagnetic tracking (EMT) system offers a fast and accurate solution for automatic reconstruction of catheters using the EMT technology. In this study, the commissioning and performance evaluation of the new real-time prostate high-dose-rate brachytherapy investigational system from Philips Disease Management Solutions integrating EMT was performed before its clinical integration.

METHOD AND MATERIALS

The Philips' clinical investigational system includes a treatment planning software (TPS) that was commissioned based on AAPM TG53 and TG56 recommendations for the use of TPS in brachytherapy. First, the CIRS - model 045A - QA phantom was used to evaluate the ultrasound (US) image quality and 3D image handling. Distances, volumes, and dimensions of the structures inside the phantom were measured and compared to the actual values. The calibration reproducibility and accuracy of the electromagnetic (EM) sensor used to track the US probe (rotation and translation) were performed using a specifically designed QA tool mounted on the probe and immersed in a salted water tank. This was performed for 3 different B&K 8848 US probes to evaluate the sensitivity of EM calibration to the probe geometric properties (manufacturing process). The new TPS performance was compared to that in OncentraBrachy (OcB) V4.5.5 (Elekta) using 30 clinical cases as part of a retrospective study. Following the system commissioning, clinical workflows were explored; tests were performed with the brachytherapy team on phantoms and finally implemented in the clinic.

RESULTS

US image quality evaluation showed a mean difference with actual dimensions (lengths, widths and distances) of 0.4 mm (±0.3 mm) and mean difference in volume sizes of 0.2 cc (±0.2 cc). Then, the calibration of the US-to-EM coordinate system was performed for 3 different probes. For each probe, 3 measurements were acquired for every position of the calibration tool and measurements were repeated 3 times for a total of 27 measurements per probe per plane. The error was slightly higher in transverse mode compared to sagittal mode with mean values of 0.6 ± 0.2 mm and 0.3 ± 0.1 mm respectively. 30 clinical cases were used to compare the new TPS performance to OcB (IPSA). Optimized plans obtained with both systems were all clinically acceptable, but the plans from the Philips system have slightly higher V150% values, V200% values and dose to organs at risk. In the case of organs at risk, plans could have been manually modified to reduce the dose. Philips' system had a larger number of active dwell positions and longer treatment times.

CONCLUSIONS

The first clinical version of Philips' system was proven to be stable, accurate and precise. The fully integrated EM tracking technology opens the way for automated catheter reconstruction and on-the-fly dynamical replanning.

Design and validation of an MRI-compatible mechatronic system for needle delivery to localized prostate cancer

PURPOSE

Prostate cancer is the most common non-cutaneous cancer among men in the United States and is the second leading cause of cancer death in American men. (Siegel et al. [2019] CA: A Cancer J Clin.69(1):7-34.) Focal laser ablation (FLA) has the potential to control small tumors while preserving urinary and erectile function by leaving the neurovascular bundles and urethral sphincters intact. Accurate needle guidance is critical to the success of FLA. Multiparametric magnetic resonance images (mpMRI) can be used to identify targets, guide needles, and assess treatment outcomes. The purpose of this work was to design and evaluate the accuracy of an MR-compatible mechatronic system for in-bore transperineal guidance of FLA ablation needles to localized lesions in the prostate.

METHODS

The mechatronic system was constructed entirely of non-ferromagnetic materials, with actuation controlled by piezoelectric motors and optical encoders. The needle guide hangs between independent front and rear two-link arms, which allows for horizontal and vertical translation as well as pitch and yaw rotation of the guide with a 6.0 cm range of motion in each direction. Needles are inserted manually through a chosen hole in the guide, which has been aligned with the target in the prostate. Open-air positioning error was evaluated using an optical tracking system (0.25 mm RMS accuracy) to measure 125 trajectories in free space. Correction of systematic bias in the system was performed using 85 of the trajectories, and the remaining 40 were used to estimate the residual error. The error was calculated as the horizontal and vertical displacement between the axis of the desired and measured trajectories at a typical needle insertion depth of 10 cm. MR-compatibility was evaluated using a grid phantom to assess image degradation due to the presence of the system, and induced force, heating, and electrical interference in the system were assessed qualitatively. In-bore positioning error was evaluated on 25 trajectories.

RESULTS

Open-air mean positioning error at the needle tip was 0.80 ± 0.36 mm with a one-sided 95% confidence interval of 1.40 mm. The mean deviation of needle trajectories from the planned direction was 0.14 ± 0.06^∘ . In the MR bore, the mean positioning error at the needle tip was 2.11 ± 1.05 mm with a one-sided 95% prediction interval of 3.84 mm. The mean angular error was 0.49 ± 0.26^∘ . The system was found to be compatible with the MR environment under the specified gradient-echo sequence parameters used in this study.

CONCLUSION

A complete system for delivering needles to localized prostate tumors was developed and described in this work, and its compatibility with the MR environment was demonstrated. In-bore MRI positioning error was sufficiently small for targeting small localized prostate tumors.

Magnetic resonance biomarkers in radiation oncology: The report of AAPM Task Group 294

A magnetic resonance (MR) biologic marker (biomarker) is a measurable quantitative characteristic that is an indicator of normal biological and pathogenetic processes or a response to therapeutic intervention derived from the MR imaging process. There is significant potential for MR biomarkers to facilitate personalized approaches to cancer care through more precise disease targeting by quantifying normal versus pathologic tissue function as well as toxicity to both radiation and chemotherapy. Both of which have the potential to increase the therapeutic ratio and provide earlier, more accurate monitoring of treatment response. The ongoing integration of MR into routine clinical radiation therapy (RT) planning and the development of MR guided radiation therapy systems is providing new opportunities for MR biomarkers to personalize and improve clinical outcomes. Their appropriate use, however, must be based on knowledge of the physical origin of the biomarker signal, the relationship to the underlying biological processes, and their strengths and limitations. The purpose of this report is to provide an educational resource describing MR biomarkers, the techniques used to quantify them, their strengths and weakness within the context of their application to radiation oncology so as to ensure their appropriate use and application within this field.

HDR brachytherapy boost using MR-only workflow for intermediate- and high-risk prostate cancer: 8-year results of a pilot study

PURPOSE

To report 8-year clinical outcome with high-dose-rate brachytherapy (HDRBT) boost using MRI-only workflow for intermediate (IR) and high-risk (HR) prostate cancer (PC) patients.

METHODS AND MATERIALS

Fifty-two patients were treated with 46-60 Gy of 3D conformal radiotherapy preceded and/or followed by a single dose of 8-10 Gy MRI-guided HDRBT. Interventions were performed in a 0.35 T MRI scanner. Trajectory planning, navigation, contouring, catheter reconstruction, and dose calculation were exclusively based on MRI images. Biochemical relapse-free- (BRFS), local relapse-free- (LRFS), distant metastasis-free- (DMFS), cancer-specific-(CCS) and overall survival (OS) were analyzed. Late morbidity was scored using the Common Terminology Criteria for Adverse Events (CTCAE 4.0) combined with RTOG (Radiation Therapy Oncology Group) scale for urinary toxicity and rectal urgency (RU) determined by Yeoh.

RESULTS

Median follow-up time was 107 (range: 19-143) months. The 8-year actuarial rates of BRFS, LRFS, DMFS, CSS and OS were 85.7%, 97%, 97.6%, and 77.6%, respectively. There were no Gr.3 GI side effects. The 8-year actuarial rate of Gr.2 proctitis was 4%. The 8-year cumulative incidence of Gr.3 GU side effects was 8%, including two urinary stenoses (5%) and one cystitis (3%). EPIC urinary and bowel scores did not change significantly over time.

CONCLUSIONS

MRI-only HDR-BT boost with moderate dose escalation provides excellent 8-year disease control with a favorable toxicity profile for IRPC and HRPC patients. Our results support the clinical importance of MRI across the BT workflow.

Impact of a 1.5 T magnetic field on DNA damage in MRI-guided HDR brachytherapy

PURPOSE

Some studies have suggested that the presence of a static magnetic field (SMF) during irradiation alters biological damage. Since MRI-guided radiotherapy is becoming increasingly common, we constructed a DNA-based detector to assess the effect of a 1.5 T SMF on DNA damage during high dose rate (HDR) brachytherapy irradiation.

METHODS

Block phantoms containing a small cavity for the placement of plasmid DNA (pBR322) samples were 3-D printed with biocompatible tissue equivalent material. The phantom was CT scanned and an HDR brachytherapy treatment plan was designed to deliver 20 Gy and 30 Gy doses to the DNA samples in the presence and absence of a 1.5 T SMF. Relative yields of single- and double-strand breaks (SSBs and DSBs, respectively) were computed from gel electrophoresis images of the DNA band intensities and averaged over sample sizes ranging from 12 to 30. Radiation dose was also measured in the presence and absence of the 1.5 T SMF using GafChromic™ EBT3 film placed in the coronal, sagittal, and axial planes.

RESULTS

The average yield of DNA with SSBs and DSBs in the presence and absence of the SMF showed no statistically significant differences (all p ≥ 0.17). Differences in the net optical densities of the EBT3 films for each plane were within experimental uncertainty, suggesting no dose difference in the presence and absence of the SMF.

CONCLUSIONS

HDR irradiation in the presence of the 1.5 T SMF did not alter dose deposition to the DNA cavity nor change SSB and DSB DNA damage.

Image guidance in radiation therapy for better cure of cancer

The key goal and main challenge of radiation therapy is the elimination of tumors without any concurring damages of the surrounding healthy tissues and organs. Radiation doses required to achieve sufficient cancer-cell kill exceed in most clinical situations the dose that can be tolerated by the healthy tissues, especially when large parts of the affected organ are irradiated. High-precision radiation oncology aims at optimizing tumor coverage, while sparing normal tissues. Medical imaging during the preparation phase, as well as in the treatment room for localization of the tumor and directing the beam, referred to as image-guided radiotherapy (IGRT), is the cornerstone of precision radiation oncology. Sophisticated high-resolution real-time IGRT using X-rays, computer tomography, magnetic resonance imaging, or ultrasound, enables delivery of high radiation doses to tumors without significant damage of healthy organs. IGRT is the most convincing success story of radiation oncology over the last decades, and it remains a major driving force of innovation, contributing to the development of personalized oncology, for example, through the use of real-time imaging biomarkers for individualized dose delivery.

Automatic multi-catheter detection using deeply supervised convolutional neural network in MRI-guided HDR prostate brachytherapy

PURPOSE

High-dose-rate (HDR) brachytherapy is an established technique to be used as monotherapy option or focal boost in conjunction with external beam radiation therapy (EBRT) for treating prostate cancer. Radiation source path reconstruction is a critical procedure in HDR treatment planning. Manually identifying the source path is labor intensive and time inefficient. In recent years, magnetic resonance imaging (MRI) has become a valuable imaging modality for image-guided HDR prostate brachytherapy due to its superb soft-tissue contrast for target delineation and normal tissue contouring. The purpose of this study is to investigate a deep-learning-based method to automatically reconstruct multiple catheters in MRI for prostate cancer HDR brachytherapy treatment planning.

METHODS

Attention gated U-Net incorporated with total variation (TV) regularization model was developed for multi-catheter segmentation in MRI. The attention gates were used to improve the accuracy of identifying small catheter points, while TV regularization was adopted to encode the natural spatial continuity of catheters into the model. The model was trained using the binary catheter annotation images offered by experienced physicists as ground truth paired with original MRI images. After the network was trained, MR images of a new prostate cancer patient receiving HDR brachytherapy were fed into the model to predict the locations and shapes of all the catheters. Quantitative assessments of our proposed method were based on catheter shaft and tip errors compared to the ground truth.

RESULTS

Our method detected 299 catheters from 20 patients receiving HDR prostate brachytherapy with a catheter tip error of 0.37 ± 1.68 mm and a catheter shaft error of 0.93 ± 0.50 mm. For detection of catheter tips, our method resulted in 87% of the catheter tips within an error of less than ± 2.0 mm, and more than 71% of the tips can be localized within an absolute error of no >1.0 mm. For catheter shaft localization, 97% of catheters were detected with an error of <2.0 mm, while 63% were within 1.0 mm.

CONCLUSIONS

In this study, we proposed a novel multi-catheter detection method to precisely localize the tips and shafts of catheters in three-dimensional MRI images of HDR prostate brachytherapy. It paves the way for elevating the quality and outcome of MRI-guided HDR prostate brachytherapy.

Impact of magnetic fields on calculated AAPM TG-43 parameters for 192Ir and 60Co HDR brachytherapy sources: A Monte Carlo study

PURPOSE

The aim of this work is to investigate the influence of an external magnetic field (MF) on The American Association of Physicists in Medicine (AAPM) No. 43 Report (TG-43) parameters for ¹⁹²Ir and ⁶⁰Co high dose rate (HDR) brachytherapy sources using Monte Carlo (MC) simulation methods.

MATERIALS AND METHODS

We used the Geant4 toolkit (version 10.1. p01) to simulate the geometry of ¹⁹²Ir and ⁶⁰Co brachytherapy sources. AAPM TG-43 parameters (the radial dose function, g(r), and the anisotropy function, F (r, θ)) of both ¹⁹²Ir and ⁶⁰Co sources were calculated in the presence of a magnetic field with strengths of 1.5T, 3T, and 7T in the X, Y, and Z directions in a voxelized water phantom.

RESULTS

For the ¹⁹²Ir source, the calculated values g(r) and F (r, θ) remained nearly unaffected by the magnetic field for all investigated strengths. For the ⁶⁰Co source, the differences for the g(r) and F (r,θ) under the 1.5T, 3T, and 7T magnetic field strengths along the direction parallel with the MF were found to be an increase of up to 5%, 15%, and 33%, respectively. However, for the directions perpendicular with the magnetic field, there was a decrease of up to 3%, 6% and 15% under 1.5T, 3T and 7T strengths, respectively.

CONCLUSION

Our results highlight the necessity of a Monte Carlo-based treatment planning system (TPS) if cobalt HDR treatments are performed under a magnetic field, especially for strengths greater than 1.5T.

MARBLES - Metal Artifact Based Landmark Enhanced Susceptibility Weighted Imaging For Interventional Device Localization In MRI

Susceptibility Weighted Imaging (SWI) is a method extensively studied for its application to improve contrast in MR imaging modality. The method enhances the visualization of magnetically susceptible content such as iron, calcium and zinc in the tissues by using the susceptibility differences in tissues to generate a unique image contrast. In this study, we propose an SWI based approach to improve the visualization of interventional devices in MRI data. Results obtained from two datasets (biopsy needle and brachytherapy seeds), indicate SWI to be suitable for visualization of the interventional devices, while also being computationally faster when compared with quantitative susceptibility mapping (QSM).

MRI artifact simulation for clinically relevant MRI sequences for guidance of prostate HDR brachytherapy

For the purpose of magnetic resonance imaging (MRI) guidance of prostate high-dose-rate (HDR) brachytherapy, this paper presents a study on the potential of clinically relevant MRI sequences to facilitate tracking or localization of brachytherapy devices (HDR source/titanium needle), and which could simultaneously be used to visualize the anatomy. The tracking or localization involves simulation of the MRI artifact in combination with a template matching algorithm. Simulations of the MRI artifacts induced by an HDR brachytherapy source and a titanium needle were implemented for four types of sequences: spoiled gradient echo, spin echo, balanced steady-state free precession (bSSFP) and bSSFP with spectral attenuated inversion recovery (SPAIR) fat suppression. A phantom study was conducted in which mentioned sequences (in 2D) as well as the volumetric MRI sequences of the current clinical scan protocol were applied to obtain the induced MRI artifacts for an HDR source and a titanium needle. Localization of the objects was performed by a phase correlation based template matching algorithm. The simulated images demonstrated high correspondences with the acquired MR images, and allowed localization of the objects. A comparison between the object positions obtained for all applied MRI sequences showed deviations (from the average position) of 0.2-0.3 mm, proving that all MRI sequences were suitable for localization of the objects, irrespective of their 2D or volumetric nature. This study demonstrated that the MRI artifact induced by an HDR source or a titanium needle could be simulated for the four investigated types of MRI sequences (spoiled gradient echo, spin echo, bSSFP and bSSFP-SPAIR), valuable for real-time object localization in clinical practice. This leads to more flexibility in the choice of MRI sequences for guidance of HDR brachytherapy, as they are suitable for both object localization and anatomy visualization.

Accelerated positive contrast MRI of interventional devices using parallel compressed sensing imaging

Susceptibility-based magnetic resonance imaging (MRI) method can image small MR-compatible devices with positive contrast. However, the relatively long data acquisition time required by the method hinders its practical applications. This study presents a parallel compressive sensing technique with a modified fast spin echo to accelerate data acquisition for the susceptibility-based positive contrast MRI. The method integrates the generalized autocalibrating partially parallel acquisitions and the compressive sensing techniques in the reconstruction algorithm. MR imaging data acquired from several phantoms containing interventional devices such as biopsy needles, stent, and brachytherapy seeds, used for validating the proposed technique. The results show that it can speed up data acquisition by a factor of about five while preserving the quality of the positive contrast images.

MR-based source localization for MR-guided HDR brachytherapy

For the purpose of MR-guided high-dose-rate (HDR) brachytherapy, a method for real-time localization of an HDR brachytherapy source was developed, which requires high spatial and temporal resolutions. MR-based localization of an HDR source serves two main aims. First, it enables real-time treatment verification by determination of the HDR source positions during treatment. Second, when using a dummy source, MR-based source localization provides an automatic detection of the source dwell positions after catheter insertion, allowing elimination of the catheter reconstruction procedure. Localization of the HDR source was conducted by simulation of the MR artifacts, followed by a phase correlation localization algorithm applied to the MR images and the simulated images, to determine the position of the HDR source in the MR images. To increase the temporal resolution of the MR acquisition, the spatial resolution was decreased, and a subpixel localization operation was introduced. Furthermore, parallel imaging (sensitivity encoding) was applied to further decrease the MR scan time. The localization method was validated by a comparison with CT, and the accuracy and precision were investigated. The results demonstrated that the described method could be used to determine the HDR source position with a high accuracy (0.4-0.6 mm) and a high precision (⩽0.1 mm), at high temporal resolutions (0.15-1.2 s per slice). This would enable real-time treatment verification as well as an automatic detection of the source dwell positions.

MR elastography to measure the effects of cancer and pathology fixation on prostate biomechanics, and comparison with T 1, T 2 and ADC

MRI is under evaluation for image-guided intervention for prostate cancer. The sensitivity and specificity of MRI parameters is determined via correlation with the gold-standard of histopathology. Whole-mount histopathology of prostatectomy specimens can be digitally registered to in vivo imaging for correlation. When biomechanical-based deformable registration is employed to account for deformation during histopathology processing, the ex vivo biomechanical properties are required. However, these properties are altered by pathology fixation, and vary with disease. Hence, this study employs magnetic resonance elastography (MRE) to measure ex vivo prostate biomechanical properties before and after fixation. A quasi-static MRE method was employed to measure high resolution maps of Young's modulus (E) before and after fixation of canine prostate and prostatectomy specimens (n  =  4) from prostate cancer patients who had previously received radiation therapy. For comparison, T ₁, T ₂ and apparent diffusion coefficient (ADC) were measured in parallel. E (kPa) varied across clinical anatomy and for histopathology-identified tumor: peripheral zone: 99(±22), central gland: 48(±37), tumor: 85(±53), and increased consistently with fixation (factor of 11  ±  5; p  <  0.02). T ₂ decreased consistently with fixation, while changes in T ₁ and ADC were more complex and inconsistent. The biomechanics of the clinical prostate specimens varied greatly with fixation, and to a lesser extent with disease and anatomy. The data obtained will improve the precision of prostate pathology correlation, leading to more accurate disease detection and targeting.

Magnetic Resonance Spectroscopy and its Clinical Applications: A Review

In vivo NMR spectroscopy is known as magnetic resonance spectroscopy (MRS). MRS has been applied as both a research and a clinical tool in order to detect visible or nonvisible abnormalities. The adaptability of MRS allows a technique that can probe a wide variety of metabolic uses across different tissues. Although MRS is mostly applied for brain tissue, it can be used for detection, localization, staging, tumour aggressiveness evaluation, and tumour response assessment of breast, prostate, hepatic, and other cancers. In this article, the medical applications of MRS in the brain, including tumours, neural and psychiatric disorder studies, breast, prostate, hepatic, gastrointestinal, and genitourinary investigations have been reviewed.

MR-safe personal radiation dosimeters

Magnetic resonance imaging (MRI) is being rapidly integrated for cancer treatments—such systems are referred to as MRI‐guided radiation therapy (MRIgRT). As the magnet of an MRI scanner is always on, the presence of a strong static magnetic field from the MRI scanner during radiotherapy delivery presents new challenges. One of the challenges is that a personal radiation dosimeter used to estimate the radiation dose deposited in an individual wearing the device must be MR‐safe. No such devices, however, are currently available. In this work we first modified an existing personal dosimeter (by removing a metal clip) to make it MR‐safe and then investigated potential effects of magnetic field on dosimeter readings, i.e., optically stimulated luminescent dosimeter (OSLD) readings. We found that the effect of magnetic field on OSLD sensitivity was within radiation protection tolerance levels. OSLD personal dosimeters can be directly used in conjunction with MRIgRT radiation protection purposes.

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.

Simultaneous automatic segmentation of multiple needles using 3D ultrasound for high-dose-rate prostate brachytherapy

PURPOSE

Sagittally reconstructed 3D (SR3D) ultrasound imaging shows promise for improved needle localization for high-dose-rate prostate brachytherapy (HDR-BT); however, needles must be manually segmented intraoperatively while the patient is anesthetized to create a treatment plan. The purpose of this article was to describe and validate an automatic needle segmentation algorithm designed for HDR-BT, specifically capable of simultaneously segmenting all needles in an HDR-BT implant using a single SR3D image with ~5 mm interneedle spacing.

MATERIALS AND METHODS

The segmentation algorithm involves regularized feature point classification and line trajectory identification based on the randomized 3D Hough transform modified to handle multiple straight needles in a single image simultaneously. Needle tips are identified based on peaks in the derivative of the signal intensity profile along the needle trajectory. For algorithm validation, 12 prostate cancer patients underwent HDR-BT during which SR3D images were acquired with all needles in place. Needles present in each of the 12 images were segmented manually, providing a gold standard for comparison, and using the algorithm. Tip errors were assessed in terms of the 3D Euclidean distance between needle tips, and trajectory error was assessed in terms of 2D distance in the axial plane and angular deviation between trajectories.

RESULTS

In total, 190 needles were investigated. Mean execution time of the algorithm was 11.0 s per patient, or 0.7 s per needle. The algorithm identified 82% and 85% of needle tips with 3D errors ≤3 mm and ≤5 mm, respectively, 91% of needle trajectories with 2D errors in the axial plane ≤3 mm, and 83% of needle trajectories with angular errors ≤3°. The largest tip error component was in the needle insertion direction.

CONCLUSIONS

Previous work has indicated HDR-BT needles may be manually segmented using SR3D images with insertion depth errors ≤3 mm and ≤5 mm for 83% and 92% of needles, respectively. The algorithm shows promise for reducing the time required for the segmentation of straight HDR-BT needles, and future work involves improving needle tip localization performance through improved image quality and modeling curvilinear trajectories.

The utilization of magnetic resonance imaging in the operating room

Online image guidance in the operating room using ultrasound imaging led to the resurgence of prostate brachytherapy in the 1980s. Here we describe the evolution of integrating MRI technology in the brachytherapy suite or operating room. Given the complexity, cost, and inherent safety issues associated with MRI system integration, first steps focused on the computational integration of images rather than systems. This approach has broad appeal given minimal infrastructure costs and efficiencies comparable with standard care workflows. However, many concerns remain regarding accuracy of registration through the course of a brachytherapy procedure. In selected academic institutions, MRI systems have been integrated in or near the brachytherapy suite in varied configurations to improve the precision and quality of treatments. Navigation toolsets specifically adapted to prostate brachytherapy are in development and are reviewed.

Clinical use of magnetic resonance imaging across the prostate brachytherapy workflow

MRI produces better soft tissue contrast than does ultrasonography or computed tomography for visualizing male pelvic anatomy and prostate cancer. Better visualization of the tumor and organs at risk could allow better conformation of the dose to the target volumes while at the same time minimizing the dose to critical structures and the associated toxicity. Although the use of MRI for prostate brachytherapy would theoretically result in an improved therapeutic ratio, its implementation been slow, mostly because of technical challenges. In this review, we describe the potential role of MRI at different steps in the treatment workflow for prostate brachytherapy: for patient selection, treatment planning, in the operating room, or for postimplant assessment. We further present the current clinical experience with MRI-guided prostate brachytherapy, both for permanent seed implantation and high-dose-rate brachytherapy.

Magnetic resonance imaging-guided functional anatomy approach to prostate brachytherapy

PURPOSE

To provide an MRI based functional anatomy guide to prostate brachytherapy.

METHODS AND MATERIALS

We performed a narrative review of periprostatic functional anatomy and the significance of this anatomy in prostate brachytherapy treatment planning.

RESULTS

MRI has improved delineation of gross tumor and critical periprostatic structures that have been implicated in toxicity. Furthermore, MRI has revealed the significant anatomic variants and the dynamic nature of these structures that can have significant implications for treatment planning and dosimetry.

CONCLUSIONS

The MRI-based functional anatomy approach to prostate brachytherapy takes into account extent of disease, its relation to the patient's individual anatomy, and functional baseline to optimize the therapeutic ratio of prostate cancer treatment.

Technical Note: Method to correlate whole-specimen histopathology of radical prostatectomy with diagnostic MR imaging

PURPOSE

Validation of MRI-guided tumor boundary delineation for targeted prostate cancer therapy is achieved via correlation with gold-standard histopathology of radical prostatectomy specimens. Challenges to accurate correlation include matching the pathology sectioning plane with the in vivo imaging slice plane and correction for the deformation that occurs between in vivo imaging and histology. A methodology is presented for matching of the histological sectioning angle and position to the in vivo imaging slices.

METHODS

Patients (n = 4) with biochemical failure following external beam radiotherapy underwent diagnostic MRI to confirm localized recurrence of prostate cancer, followed by salvage radical prostatectomy. High-resolution 3-D MRI of the ex vivo specimens was acquired to determine the pathology sectioning angle that best matched the in vivo imaging slice plane, using matching anatomical features and implanted fiducials. A novel sectioning device was developed to guide sectioning at the correct angle, and to assist the insertion of reference dye marks to aid in histopathology reconstruction.

RESULTS

The percentage difference in the positioning of the urethra in the ex vivo pathology sections compared to the positioning in in vivo images was reduced from 34% to 7% through slicing at the best match angle. Reference dye marks were generated, which were visible in ex vivo imaging, in the tissue sections before and after processing, and in histology sections.

CONCLUSIONS

The method achieved an almost fivefold reduction in the slice-matching error and is readily implementable in combination with standard MRI technology. The technique will be employed to generate datasets for correlation of whole-specimen prostate histopathology with in vivo diagnostic MRI using 3-D deformable registration, allowing assessment of the sensitivity and specificity of MRI parameters for prostate cancer. Although developed specifically for prostate, the method is readily adaptable to other types of whole tissue specimen, such as mastectomy or liver resection.

American Brachytherapy Society Task Group Report: Combination of brachytherapy and external beam radiation for high-risk prostate cancer

PURPOSE

To review outcomes for high-risk prostate cancer treated with combined modality radiation therapy (CMRT) utilizing external beam radiation therapy (EBRT) with a brachytherapy boost.

METHODS AND MATERIALS

The available literature for high-risk prostate cancer treated with combined modality radiation therapy was reviewed and summarized.

RESULTS

At this time, the literature suggests that the majority of high-risk cancers are curable with multimodal treatment. Several large retrospective studies and three prospective randomized trials comparing CMRT to dose-escalated EBRT have demonstrated superior biochemical control with CMRT. Longer followup of the randomized trials will be required to determine if this will translate to a benefit in metastasis-free survival, disease-specific survival, and overall survival. Although greater toxicity has been associated with CMRT compared to EBRT, recent studies suggest that technological advances that allow better definition and sparing of critical adjacent structures as well as increasing experience with brachytherapy have improved implant quality and the toxicity profile of brachytherapy. The role of androgen deprivation therapy is well established in the external beam literature for high-risk disease, but there is controversy regarding the applicability of these data in the setting of dose escalation. At this time, there is not sufficient evidence for the omission of androgen deprivation therapy with dose escalation in this population. Comparisons with surgery remain limited by differences in patient selection, but the evidence would suggest better disease control with CMRT compared to surgery alone.

CONCLUSIONS

Due to a series of technological advances, modern combination series have demonstrated unparalleled rates of disease control in the high-risk population. Given the evidence from recent randomized trials, combination therapy may become the standard of care for high-risk cancers.

Image-guided high-dose-rate brachytherapy boost to the dominant intraprostatic lesion using multiparametric magnetic resonance imaging including spectroscopy: Results of a prospective study

PURPOSE

To evaluate the long-term outcomes of image-guided high-dose-rate (HDR) brachytherapy boost to the dominant intraprostatic lesion (DIL) using multiparametric magnetic resonance imaging (MRI), including spectroscopy (MRI/magnetic resonance spectroscopy [MRS]).

METHODS AND MATERIALS

Between December 2009 and March 2011, 20 patients with intermediate-risk prostate cancer underwent multiparametric MRI/MRS protocol before treatment. All patients were treated with an external beam radiotherapy dose of 40 Gy, combined with an HDR brachytherapy boost of 15 Gy. Concurrently, the DIL received a boost of 18 Gy. Missing data during followup were handled with multiple imputations.

RESULTS

The median followup was 62 months (range, 23-71 months). Six patients (31%) were classified as favorable intermediate risk and 13 patients (69%) as unfavorable intermediate risk. One patient experienced a prostate-specific antigen biochemical failure, and the 5-year biochemical failure-free survival rate was of 94.7%. The mean International Prostate Symptom Score rose from 7, with respect to baseline, to 10.42 1 month after treatment, and rapidly decreased to 6.97 after 3 months. Grade 1, 2, and 3 acute genitourinary toxicities were reported in 13 (68%), 3 (16%), and 1 (5%) patients, respectively. Grade 1 and 2 late genitourinary toxicities were reported in 9 (53%) and 3 (18%) patients, respectively. Only grade 1 acute and late gastrointestinal toxicities were reported in 4 (21%) and 3 (18%) patients, respectively.

CONCLUSIONS

Delivering an HDR brachytherapy boost to the DIL using image-guided multiparametric MRI/MRS is feasible with good outcomes for biochemical control, acute and late toxicities, and dosimetric constraints for critical organs.

Image-Guided High-Dose-Rate (HDR) Boost Localization Using MRI/MR Spectroscopy: A Correlation Study with Biopsy

PURPOSE

The purpose of this study is to compare the blind interpretations of magnetic resonance imaging (MRI) sequences, diffusion-weighted imaging (DWI), apparent diffusion coefficient (ADC), mapping, and magnetic resonance spectroscopy (MRS) of the prostate, in comparison to prostate biopsy to identify a valid dominant intraprostatic lesion (DIL) for dose escalation using high-dose rate brachytherapy.

METHODS

MRI/MRS were performed on 20 patients with intermediate risk adenocarcinoma of the prostate. T1W, T2W, DWI-ADC, and MRS sequences were performed at 1.5 T with pelvic and endorectal coils. An experienced radiologist rated the presence of cancer in each sextant by using a dichotomic approach, first on MR standard acquisitions (T1W and T2W), then on DWI-ADC mapping, and later on MRS images. Areas under the receiver's operating characteristic curve were calculated using a sextant as the unit of analysis. The transrectal ultrasonography-guided biopsy results were used as the reference standard. A table summarizing the MRI/MRS findings was made and compared to the corresponding area in the prostate biopsy report. A perfect match was defined to be the presence of cancer in the same sextant of the MRI/MRS exam and the prostate biopsy.

RESULTS

The interpretation of the MRI/MRS exams per sextant was compared to the diagnostic biopsy report. MRI readings were compared with the biopsy as a surrogate for the complete pathology specimen of the prostate. A sensitivity (Sn) of 98.6% (95% confidence interval, 92.2% - 99.9%) and specificity (Sp) of 60.8% (46.1% - 74.2%) were found. The positive and negative predictive values (PPV, NPV) were 77.3% (67.1% - 85.5%) and 96.9% (83.8% - 99.9%), respectively. When MRS readings were compared with biopsy, we found a Sn of 96.4% (87.7% - 99.6%) and Sp of 54.8% (38.7% - 70.2%). The PPV and NPV were 74% (62.4% - 83.6%) and 92% (74% - 99%), respectively. DWI-ADC mapping results were also compared with biopsy. We found a Sn and Sp of 93.7% (84.5% - 98.2%) and 82.1% (66.5% - 92.5%), respectively, and a PPV and NPV of 89.4% (79.4% - 95.6%) and 88.9% (73.9% - 96.9%), respectively. Finally, after combining MRI, MRS, and DWI-ADC mapping, compared with biopsy, we obtained a Sn, Sp, PPV, and NPV of 100% (94.8% - 100%), 49% (34.8% - 63.4%), 72.6% (62.5% - 81.3%), and 100% (86.3% - 100%), respectively.

CONCLUSIONS

The combination of MRI/MRS is a sensitive tool for both the structural and metabolic evaluation of prostate cancer location. MRI/MRS exams are useful to delineate a DIL for high-dose-rate (HDR) intraprostatic boost.

Trends in targeted prostate brachytherapy: from multiparametric MRI to nanomolecular radiosensitizers

The treatment of localized prostate cancer is expected to become a significant problem in the next decade as an increasingly aging population becomes prone to developing the disease. Recent research into the biological nature of prostate cancer has shown that large localized doses of radiation to the cancer offer excellent long-term disease control. Brachytherapy, a form of localized radiation therapy, has been shown to be one of the most effective methods for delivering high radiation doses to the cancer; however, recent evidence suggests that increasing the localized radiation dose without bound may cause unacceptable increases in long-term side effects. This review focuses on methods that have been proposed, or are already in clinical use, to safely escalate the dose of radiation within the prostate. The advent of multiparametric magnetic resonance imaging (mpMRI) to better identify and localize intraprostatic tumors, and nanomolecular radiosensitizers such as gold nanoparticles (GNPs), may be used synergistically to increase doses to cancerous tissue without the requisite hazard of increased side effects.

Learning curve of MRI-based planning for high-dose-rate brachytherapy for prostate cancer

PURPOSE

To evaluate introduction of MRI-based high-dose-rate brachytherapy (HDRBT), including procedure times, dose-volume parameters, and perioperative morbidity.

METHODS AND MATERIALS

Study included 42 high-risk prostate cancer patients enrolled in a clinical protocol, offering external beam radiotherapy + two HDRBT 8.5 Gy boosts. Time was recorded for initiation of anesthesia (A), fixation of needle implant (B), end of MR imaging (C), plan approval (D), and end of HDRBT delivery (E). We defined time A-E as total procedure time, A-B as operating room time, B-C as MRI procedure time, C-D as treatment planning time, and D to E as treatment delivery time. Dose-volume parameters were retrieved from the dose planning system. Results from the first 21 patients were compared with the last 21 patients.

RESULTS

Total procedure time, operating room time, MRI procedure time, and treatment planning time decreased significantly from average 7.6 to 5.3 hours (p < 0.01), 3.6 to 2.4 hours (p < 0.01), 1.6 to 0.8 hours (p < 0.01), and 2.0 to 1.3 hours (p < 0.01), respectively. HDRBT delivery time remained unchanged at 0.5 hours. Clinical target volume prostate+3mmD90 fulfilled planning aim in 92% of procedures and increased significantly from average 8.3 to 9.0 Gy (p < 0.01). Urethral D0.1 cm(3) and rectal D2 cm(3) fulfilled planning aim in 78% and 95% of procedures, respectively, and did not change significantly. Hematuria occurred in (95%), hematoma (80%), moderate to strong pain (35%), and urinary retention (5%) of procedures.

CONCLUSIONS

After introduction of MRI-based HDRBT, procedure times were significantly reduced. D90 Clinical target volumeprostate+3mm fulfilled constraints in most patients and improved over time, but not at expense of an increased urethral or rectal dose.

In-bore MRI interventions: current status and future applications

PURPOSE OF REVIEW

This review discusses the feasibility, recent advances and current status of in-bore MRI-guided interventional techniques for diagnosis and treatment of focal prostate cancer (PCa) and also explores the future applications, highlighting the emerging strategies for the treatment of PCa.

RECENT FINDINGS

Multiparametric MRI has opened up opportunities for diagnosis and targeted therapeutics to the site of disease within the organ wherein minimizing the incidence of treatment-related toxicity of whole gland therapy. MRI-guided targeted biopsy has a higher detection rate for significant cancer and lower rate of detection of insignificant cancer. In comparison to ultrasound-guided focal therapy, in-bore treatment provides the advantage of real time thermal monitoring during treatment and assessment of treatment coverage by an enhanced scan immediately post-treatment. Preliminary results of ongoing phase I and II in-bore focal PCa treatment trials via transperineal, transrectal and transurethral routes, using different energy modalities for the ablation, have shown promising results.

SUMMARY

Advances in multiparametric-MRI has opened up opportunities for in-bore targeted focal treatment of PCa in the correctly selected patient.