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Objective. Intensity modulated high dose rate brachytherapy (IMBT) is a rapidly developing application of brachytherapy where anisotropic dose distributions can be produced at each source dwell position. This technique is made possible by placing rotating metallic shields inside brachytherapy needles or catheters. By dynamically directing the radiation towards the tumours and away from the healthy tissues, a more conformal dose distribution can be obtained. The resulting treatment planning involves optimizing dwell position and shield angle (DPSA). The aim of this study was to investigate the column generation method for IMBT treatment plan optimization. Approach. A column generation optimization algorithm was developed to optimize the dwell times and shield angles. A retrospective study was performed on 10 prostate cases using RapidBrachyMCTPS. At every iteration, the plan was optimized with the chosen DPSA which would best improve the cost function that was added to the plan. The optimization process was stopped when the remaining DPSAs would not add value to the plan to limit the plan complexity. Main results. The average number of DPSAs and voxels were 2270 and 7997, respectively. The column generation approach yielded near-optimal treatment plans by using only 11% of available DPSAs on average in ten prostate cases. The coverage and organs at risk constraints passed in all ten cases. Significance. The column generation method produced high-quality deliverable prostate IMBT plans. The treatment plan quality reached a plateau, where adding more DPSAs had a minimal effect on dose volume histogram parameters. The iterative nature of the column generation method allows early termination of the treatment plan creation process as soon as the dosimetric indices from dose volume histogram satisfy the clinical requirements or if their values stabilize., (Creative Commons Attribution license.)

Purpose/objectives: There is a clinical need to develop anatomic phantoms for simulation-based learning in gynecological brachytherapy. Here, we provide a step-by-step approach to build a life-sized gynecological training phantom based on magnetic resonance imaging (MRI) of an individual patient. Our hypothesis is that this phantom can generate convincing ultrasound (US) images that are similar to patient scans., Methods: Organs-at-risk were manually segmented using patient scans (MRI). The gynecological phantom was constructed using positive molds from 3D printing and polyvinyl chloride (PVC) plastisol. Tissue texture/acoustic properties were simulated using different plastic softener/hardener ratios and microbead densities. Nine readers (residents) were asked to evaluate 10 cases (1 ultrasound image per case) and categorize each as a "patient" or "phantom" image. To evaluate whether the phantom and patient images were equivalent, we used a multireader, multicase equivalence study design with two composite null hypotheses with proportion (p r ) at H 01 : p r ≤ 0.35 and H 02 : p r ≥ 0.65. Readers were also asked to review US videos and identify the insertion of an interstitial needle into the pelvic phantom. Computed Tomography (CT) and magnetic resonance (MR) images of the phantom were acquired for a feasibility study., Results: Readers correctly classified "patient" and "phantom" scans at p r  = 53.3% ± 6.2% (p values 0.013 for H 01 and 0.054 for H 02 , df = 5.96). Readers reviewed US videos and identified the interstitial needle 100% of the time in transabdominal view, and 78% in transrectal view. The phantom was CT and MR safe., Conclusions: We have outlined a manufacturing process to create a life-sized, gynecological phantom that is compatible with multi-modality imaging and can be used to simulate clinical scenarios in image-guided brachytherapy procedures., (Copyright © 2022 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.)

Purpose: To develop an endovaginal MRI array that provides signal enhancement forward into the posterior parametrium and sideways into the vaginal wall, accelerating multiple-contrast detection of residual tumors that survive external beam radiation. The array's enclosure should form an obturator for cervical cancer brachytherapy, allowing integration with MRI-guided catheter placement, CT, and interstitial radiation dose delivery., Methods: The endovaginal array consisted of forward-looking and sideways-looking components. The forward-looking element imaged the cervix and posterior endometrium, and the sideways-looking elements imaged the vaginal wall. Electromagnetic simulation was performed to optimize the geometry of a forward-looking coil placed on a conductive-metallic substrate, extending the forward penetration above the coil's tip. Thereafter, an endovaginal array with one forward-looking coil and four sideways-looking elements was constructed and tested at 1.5 Tesla in saline and gel phantoms, and three sexually mature swine. Each coil's tuning, matching, and decoupling were optimized theoretically, implemented with electronic circuits, and validated with network-analyzer measurements. The array enclosure emulates a conventional brachytherapy obturator, allowing use of the internal imaging array together with tandem coils and interstitial catheters, as well as use of the enclosure alone during CT and radiation delivery. To evaluate the receive magnetic field ( B 1 - ) spatial profile, the endovaginal array's specific absorption-rate (SAR) distribution was simulated inside a gel ASTM phantom to determine extreme heating locations in advance of a heating test. Heating tests were then performed during high SAR imaging in a gel phantom at the predetermined locations, testing compliance with MRI safety standards. To assess array imaging performance, signal-to-noise-ratios (SNR) were calculated in a saline phantom and in vivo. Swine images were acquired with the endovaginal array combined with the scanner's body and spine arrays., Results: Simulated B 1 - profiles for the forward-looking lobe pattern, obtained while varying several geometric parameters, disclosed that a forward-looking coil placed on a metal-backed substrate could double the effective forward penetration from approximately 25 to ∼40 mm. An endovaginal array, enclosed in an obturator enclosure was then constructed, with all coils tuned, matched, and decoupled. The ASTM gel-phantom SAR test showed that peak local SAR was 1.2 W/kg in the forward-looking coil and 0.3 W/kg in the sideways-looking elements, well within ASTM/FDA/IEC guidelines. A 15-min 4 W/kg average SAR imaging experiment resulted in less than 2 o C temperature increase, also within ASTM/FDA/IEC heating limits. In a saline phantom, the forward-looking coil and sideways-looking array's SNR was four to eight times, over a 20-30 mm field-of-view (FOV), and five to eight times, over a 15-25 mm FOV, relative to the spine array's SNR, respectively. In three sexually mature swine, the forward-looking coil provided a 5 + 0.2 SNR enhancement factor within the cervix and posterior endometrium, and the sideways-looking array provided a 4 + 0.2 SNR gain factor in the vaginal wall, relative to the Siemens spine array, demonstrating that the array could significantly reduce imaging time., Conclusions: Higher SNR gynecological imaging is supported by forward-looking and sideways-looking coils. A forward-looking endovaginal coil for cervix and parametrium imaging was built with optimized metal backing. Array placement within an obturator enhanced integration with the brachytherapy procedure and accelerated imaging for detecting postexternal-beam residual tumors., (© 2021 American Association of Physicists in Medicine.)

Purpose: The purpose of this study was to evaluate the impact of dose reporting schemes and tissue/applicator heterogeneities for 192 Ir-, 75 Se-, and 169 Yb-based MRI-guided conventional and intensity-modulated brachytherapy., Methods and Materials: Treatment plans using a variety of dose reporting and tissue/applicator segmentation schemes were generated for a cohort (n = 10) of cervical cancer patients treated with 192 Ir-based Venezia brachytherapy. Dose calculations were performed using RapidBrachyMCTPS, a Geant4-based research Monte Carlo treatment planning system. Ultimately, five dose calculation scenarios were evaluated: (a) dose to water in water (D w,w ); (b) D w,w taking the applicator material into consideration (D w,wApp ); (c) dose to water in medium (D w,m ); (d and e) dose to medium in medium with mass densities assigned either nominally per structure (D m,m (Nom) ) or voxel-by-voxel (D m,m )., Results: Ignoring the plastic Venezia applicator (D w,wApp ) overestimates D m,m by up to 1% (average) with high energy source ( 192 Ir and 75 Se) and up to 2% with 169 Yb. Scoring dose to water (D w,wApp or D w,m ) generally overestimates dose and this effect increases with decreasing photon energy. Reporting dose other than D m,m (or D m,m Nom ) for 169 Yb-based conventional and intensity-modulated brachytherapy leads to a simultaneous overestimation (up to 4%) of CTV HR D 90 and underestimation (up to 2%) of bladder D 2cc due to a significant dip in the mass-energy absorption ratios at the depths of nearby targets and OARs. Using a nominal mass-density assignment per structure, rather than a CT-derived voxel-by-voxel assignment for MRI-guided brachytherapy, amounts to a dose error up to 1% for all radionuclides considered., Conclusions: The effects of the considered dose reporting schemes trend correspondingly between conventional and intensity-modulated brachytherapy. In the absence of CT-derived mass densities, MRI-only-based dosimetry can adequately approximate D m,m by assigning nominal mass densities to structures. Tissue and applicator heterogeneities do not significantly impact dosimetry for 192 Ir and 75 Se, but do for 169 Yb; dose reporting must be explicitly defined since D w,m and D w,w may overstate the dosimetric benefits., (© 2021 American Association of Physicists in Medicine.)

Purpose: To present a novel, MRI-compatible dynamicshield intensity modulated brachytherapy (IMBT) applicator and delivery system using 192 Ir, 75 Se, and 169 Yb radioisotopes for the treatment of locally advanced cervical cancer. Needle-free IMBT is a promising technique for improving target coverage and organs at risk (OAR) sparing., Methods and Materials: The IMBT delivery system dynamically controls the rotation of a novel tungsten shield placed inside an MRI-compatible, 6-mm wide intrauterine tandem. Using 36 cervical cancer cases, conventional intracavitary brachytherapy (IC-BT) and intracavitary/interstitial brachytherapy (IC/IS-BT) (10Ci 192 Ir) plans were compared to IMBT (10Ci 192 Ir; 11.5Ci 75 Se; 44Ci 169 Yb). All plans were generated using the Geant4-based Monte Carlo dose calculation engine, RapidBrachyMC. Treatment plans were optimized then normalized to the same high-risk clinical target volume (HR-CTV) D 90 and the D 2cc for bladder, rectum, and sigmoid in the research brachytherapy planning system, RapidBrachyMCTPS. Plans were renormalized until either of the three OAR reached dose limits to calculate the maximum achievable HR-CTV D 90 and D 98 ., Results: Compared to IC-BT, IMBT with either of the three radionuclides significantly improves the HR-CTV D 90 and D 98 by up to 5.2% ± 0.3% (P < 0.001) and 6.7% ± 0.5% (P < 0.001), respectively, with the largest dosimetric enhancement when using 169 Yb followed by 75 Se and then 192 Ir. Similarly, D 2cc for all OAR improved with IMBT by up to 7.7% ± 0.6% (P < 0.001). For IC/IS-BT cases, needle-free IMBT achieved clinically acceptable plans with 169 Yb-based IMBT further improving HR-CTV D 98 by 1.5% ± 0.2% (P = 0.034) and decreasing sigmoid D 2cc by 1.9% ± 0.4% (P = 0.048). Delivery times for IMBT are increased by a factor of 1.7, 3.3, and 2.3 for 192 Ir, 75 Se, and 169 Yb, respectively, relative to conventional 192 Ir BT., Conclusions: Dynamic shield IMBT provides a promising alternative to conventional IC- and IC/IS-BT techniques with significant dosimetric enhancements and even greater improvements with intermediate energy radionuclides. The ability to deliver a highly conformal, OAR-sparing dose without IS needles provides a simplified method for improving the therapeutic ratio less invasively and in a less resource intensive manner., (© 2020 American Association of Physicists in Medicine.)

Purpose: Intensity modulated brachytherapy (IMBT) with rotating metal shields enables dose modulation that can better conform to the tumor while reducing OAR doses. In this work, we investigate novel rotating shields, compatible with MRI-compatible tandems used for cervix brachytherapy. Three unique shields were evaluated using the traditional 192 Ir source. Additionally, 75 Se and 169 Yb isotopes were investigated as alternative sources., Methods: Three different IMBT shields were modeled and simulated in RapidBrachyMCTPS. Each tungsten shield was designed to fit inside a 6 mm-wide MRI-compatible tandem. The active core of the source was replaced with 192 Ir, 75 Se and 169 Yb. Transmission factors (TFs) were calculated and defined as the dose ratio at 1 cm on opposite sides of the shielded tandem on the transverse plane. Polar and azimuthal anisotropy plots were extracted from simulations. Dose homogeneities V 200% V 100% were calculated for all radionuclide-shield combinations., Results: TFs are favorable for IMBT and ranged between 12.9% and 32.2% for 192 Ir, 4.0%-16.1% for 75 Se and 1.2-6.4% for 169 Yb for all shield designs. Average beam-widths in the polar and azimuthal directions were reduced to the range of 42°-112° and 27°-107°, respectively, for all shield-radionuclide combinations. Dose homogeneities for all the radionuclide-shield combinations were within 12% of the non-IMBT tandem., Conclusions: This study has quantitatively assessed the influence of various rotating cervical cancer-specific IMBT tandem shields on dosimetry. The dynamic single-channel shields and narrow beam-widths in the polar and azimuthal direction give rise to highly anisotropic distributions. Intermediate-to-high energy radionuclides, 75 Se and 169 Yb substantially improve the modulation capacity of IMBT and pave the way for treating large and complex cervical cancer without interstitial needle implantation., (Copyright © 2020 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)

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., (Copyright © 2019 Elsevier Inc. All rights reserved.)

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., (© 2019 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.)

Purpose: The MRI-guided cervical cancer brachytherapy provides unparalleled soft-tissue contrast for target and normal tissue contouring, but eliminates the ability to use conventional metallic fiducials for radiation source path reconstruction as required for treatment planning. Instead, the source path is reconstructed by manually aligning a library model to the signal void produced by the applicator, which takes time intraoperatively and precludes fully automated treatment planning. The purpose of this study is to present and validate an algorithm to automatically reconstruct tandem and ring applicators using MRI for cervical cancer brachytherapy treatment planning., Methods: Applicators were reconstructed using T2-weighted MR images acquired at 1.5 T from 33 brachytherapy fractions including 10 patients using a model-to-image registration algorithm. The algorithm involves (a) image filtering and maximum intensity projection to highlight the applicator, (b) ring center identification using the circular Hough transform, and (c) three-dimensional surface model registration, optimized by maximizing the image intensity gradient normal to the model surface. Two independent observers manually reconstructed all applicators, enabling the calculation of interobserver variability and establishing a ground truth. Algorithm variability was calculated by comparing algorithm results to each individual observer, and algorithm accuracy was calculated by comparing algorithm results to the ground truth. The algorithm variability and accuracy were compared to the interobserver variability using paired t-tests., Results: Mean ± SD interobserver variability was 0.83 ± 0.31 mm and 0.78 ± 0.29 mm for the ring and tandem, respectively. The algorithm had mean ± SD variability and accuracy of 0.72 ± 0.32 mm (P = 0.02) and 0.60 ± 0.24 mm (P = 0.0005) for the ring, and 0.70 ± 0.29 mm (P = 0.11) and 0.58 ± 0.24 mm (P = 0.004) for the tandem, respectively., Conclusions: The algorithm variability and accuracy were within the interobserver variability measured in this study. The algorithm accuracy and mean execution time of 10.0 s are sufficient for clinical tandem and ring reconstruction, and are a step toward fully automated tandem and ring brachytherapy treatment planning., (© 2019 American Association of Physicists in Medicine.)

Purpose: We investigate the effect of the GafChromic™ film EBT3 model absorbed dose energy response when used for dose measurements around low-energy photon sources. Monte Carlo based correction procedure in synergy with appropriate calibration curves was shown to provide more accurate absorbed dose (either relative or absolute). An assessment was made of possible dose errors that might be encountered if such energy dependent response is ignored., Methods: We measured PDDs in water from a Xoft 50 kVp source using EBT3 film, and compared to PDD measurements acquired with a PTW-TN34013 parallel-plate ionization chamber. For the x-ray source, we simulated spectra using the EGSnrc (BEAMnrc) Monte Carlo code, and calculated Half Value Layer (HVL) at different distances from the source in water. Measurement strips of EBT3 film were positioned at distances of 2-6 cm from the Xoft source in a water phantom using a custom-made holder and irradiated simultaneously., Results: Our results show that film calibration curves obtained at beam qualities near the effective energy of the Xoft 50 kVp source in water lead to variation in absorbed dose energy dependence of the response of around 5%. However, if the calibration curve was established in an MV beam quality, the error in absorbed dose could be as large as 20%., Conclusion: Accurate dose measurements using radiochromic films at low photon energies require that the radiochromic film dosimetry system be calibrated at appropriate corresponding low energies, as large absorbed dose errors are expected when film calibration is performed in MV beam qualities., (Copyright © 2019 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)

Purpose: As a core component of a new gynecologic cancer radiation program, we envisioned, structured, and implemented a novel Interventional Radiation Oncology (IRO) unit and magnetic resonance (MR)-brachytherapy environment in an existing MR simulator., Methods and Materials: We describe the external and internal processes required over a 6-8 month time frame to develop a clinical and research program for gynecologic brachytherapy and to successfully convert an MR simulator into an IRO unit., Results: Support of the institution and department resulted in conversion of an MR simulator to a procedural suite. Development of the MR gynecologic brachytherapy program required novel equipment, staffing, infrastructural development, and cooperative team development with anesthetists, nurses, therapists, physicists, and physicians to ensure a safe and functional environment. Creation of a separate IRO unit permitted a novel billing structure., Conclusions: The creation of an MR-brachytherapy environment in an MR simulator is feasible. Developing infrastructure includes several collaborative elements. Unique to the field of radiation oncology, formalizing the space as an Interventional Radiation Oncology unit permits a sustainable financial structure., (Copyright © 2018 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.)