Brachytherapy System Research Articles

Intra-operative radiation therapy as salvage treatment option for recurrent glioblastoma multiforme.

2535 Background: Glioblastoma multiforme (GBM) is an extremely aggressive cerebral tumor with poor prognosis. The majority of patients relapse after the initial surgery plus adjuvant radiation and chemotherapy. In case of recurrence there is no established standard therapy. The optimal techniques for salvage re-irradiation are unclear, so that procedure poses a challenge. In contrast to traditional external beam radiotherapy (EBRT) intra-operative radiotherapy (IORT) may improve patient’s outcome at the cost of minimal side effects and short treatment duration. Methods: A total of 30 patients were treated with recurrent GBM between August 2016 and June 2019. All patients underwent maximal safe resection; patients were divided into IORT and EBRT groups. 15 patients were included in each group with similar clinical characteristics. All patients in IORT group underwent maximal safe microsurgical resection with subsequent intraoperative balloon electronic brachytherapy (IBEB) and no further adjuvant treatment. IBEB was performed using Axxent electronic brachytherapy device (Xoft Electronic Brachytherapy (eBx) System, USA. Patients in EBRT group underwent same surgery followed by external beam radiotherapy. Contrast-enhanced brain MRI with perfusion was performed within 24 hours of surgery +/- brain PET-CT with 18-FDOPA and then every 3 months. Both groups were also assigned to subgroups (≤ 2.5cm3 and > 2.5cm3) based on post-operative contrast-enhancing volume (POCEV). Median overall survival (OS) since diagnosis and local progression-free survival (locPFS) following the second surgery were analyzed. Possible toxicities and prognostic factors were also evaluated. Results: Median OS was 27 months in IORT group and 21 months in EBRT group. The locPFS range between 3.5 to 39 months in IORT group and only 2 to 10 months in group with EBRT. Kaplan-Meier OS curves in patients with POCEV ≤ 2.5cm3 showed more favorable outcomes for patients in the IORT group (p < 0.05). In patients with POCEV > 2.5cm3 the median OS was 17 months in IORT group and 13.5 months in EBRT group. Conclusions: IORT of recurrent GBM is feasible and provides encouraging local progression-free and overall survival; no high-grade radiation induced toxicities occur and further studies to establish this method are mandatory. The toxicity profile of additional IBEB was manageable. Maximal safe microsurgical resection is the most important prognostic factor and could determine the effectiveness of post-surgical IBEB.

Dose-rate considerations for the INTRABEAM electronic brachytherapy system: Report from the American association of physicists in medicine task group no. 292.

The purpose of this report is to provide detailed guidance on the dosimetry of the INTRABEAM® (Carl Zeiss Medical AG, Jena, Germany) electronic brachytherapy (eBT) system as it stands at the present time. This report has been developed by the members of American Association of Physicists in Medicine (AAPM) Task Group 292 and endorsed by the AAPM. Members of AAPM Task Group 292 on Electronic-Brachytherapy Dosimetry have reviewed pertinent publications and user manuals regarding the INTRABEAM system dosimetry and manufacturer-supplied dose calculation protocols. Formal written correspondence with Zeiss has also provided further clarification. Dose-rate calculations for the INTRABEAM system are highly dependent on choice of dosimetry protocol. Even with careful protocol selection, large uncertainties remain due to the incomplete characterization of the ionization chambers used for verification with respect to their energy dependence as well as manufacturing variations. There are two distinct sets of dose-rate data provided by Zeiss for the INTRABEAM system. One dataset (Calibration V4.0) is representative of the physical dose surrounding the source and the other dataset (TARGIT) has been adjusted to be consistent with a clinical trial named TARGIT (TARGeted Intraoperative RadioTherapy). The adjusted TARGIT doses are quite dissimilar to the physical doses, with differences ranging from 14% to 30% at the surface of a spherical applicator, depending on its diameter, and up to a factor of two at closer distances with the smaller needle applicators. In addition, ion chamber selection and associated manufacturing tolerances contribute to significant additional uncertainties. With these substantial differences in dose rates and their associated uncertainties, it is important for users to be aware of how each value is calculated and whether it is appropriate to be used for the intended treatment. If users intend to deliver doses that are the same as they were in 1998 at the onset of the TARGIT trial, then the TARGIT dose-rate tables should be used. The Calibration V4.0 dose rates may be more appropriate to use for applications other than TARGIT trial treatments, since they more closely represent the physical doses being delivered. Users should also be aware of the substantial uncertainties associated with the provided dose rates, which are due to beam hardening, chamber geometry, and selection of the point-of-measurement for a given ionization chamber. This report serves to describe the details and implications of the manufacturer-recommended dosimetry formalism for users of the INTRABEAM system.

Characterization of an x-ray source with a partitioned diamond-tungsten target for electronic brachytherapy with 3D beam directionality

The Sculptura™ is a new high-dose-rate electronic brachytherapy system developed by Sensus Healthcare. By combining a steerable electron beam with a partitioned diamond-tungsten x-ray target, the x-ray source of the Sculptura™ is capable of producing highly anisotropic dose distributions, thus achieving true 3D beam directionality. This article reports the spectral and dosimetric characterization of the Sculptura™ x-ray source through a combination of measurements and Monte Carlo simulations for operating points between 50–100 kV. Excellent agreement (~5% discrepancy) between the simulations and measurements was obtained for in-air dose rate characterization. The validated simulations were then used to calculate the dose distribution in water. Dose rates of >2 cGy/min/μA can be produced at 100 kV, thus delivering 10 Gy in 1 min for typical operating conditions. The dose distributions are sharply peaked, with a full-width at half-maximum azimuth of about 100°.

Intraoperative radiotherapy with balloon-based electronic brachytherapy system – First Bulgarian experience in breast cancer patients

Intraoperative radiotherapy with balloon-based electronic brachytherapy system – First Bulgarian experience in breast cancer patients

A novel quality assurance system for eye plaque brachytherapy.

Eye Plaque brachytherapy pre-treatment quality assurance (QA) conducted clinically involves an activity verification of individual seeds via well chamber and does not include a physical measurement of dose-rate of the final assembly. A novel spectroscopic, dose-rate detection system, was evaluated for pre-treatment QA of eye plaque brachytherapy. The system includes a water phantom with sterility management. The system was calibrated using a known-activity I-125 seed, measured at 1cm in water along the radial axis, compared to TG-43 U1 calculations and verified over a number of distances. A depth dose curve was acquired for a clinical, mixed activity eye plaque and two 'error' plaques. The probe was stepped from a water equivalent source to a detector distance (SDD) of 2.5 to 12mm along the plaque central axis. The latter measurements aimed to characterise the sensitivity of the system. The calculated and measured single-seed dose-rates agreed to within 0.5cGy/h from a SDD of 3mm and above. The clinical plaque showed agreement between measured and treatment planning system (TPS) calculated dose-rates within 2%. Sensitivity testing resulted in a maximum deviation from TPS data of 18%, therefore was able to detect the presence of packing errors. The dose-rate detection system was successfully evaluated for verification of I-125 based eye plaques without compromising sterility, allowing for quick pre-treatment, dose-rate verification of patient-ready plaques. Its agreement with TPS data for the unmodified plaque and its deviation when introducing errors confirms the approach suggested is a viable QA tool.

Design and validation of a surgical navigation system for brachytherapy based on mixed reality.

An accurate position of the needle is vitally important in low-dose-rate seed implantation brachytherapy. Our paper aims to implement a mixed reality navigation system to assist with the placement of the I125 seed implantation thoracoabdominal tumor brachytherapy needle and to validate the accuracy and quality of this type of method. With the surgical navigation system, based on mixed reality through a novel modified multi-information fusion method, the fusion of virtual organs and a preoperative plan for a real patient and the tracking of surgical tools in real time were achieved. Personalized image recognition and pose estimation were used to track needle punctures in real time and to perform registration processes. After a one-time registration with a hexagonal prism tracker that used an iterative closest point algorithm, all information, including medical images and volume renderings of organs, needles, and seeds, was precisely merged with the patient. Doctors were able to observe the tumor target and to visualize the preoperative plan. This system was validated in both phantom and animal experiments. The accuracy of this system was validated by calculating the positional and rotational error of each needle insertion. The accuracy of implantation of each seed was determined in an animal experiment to test the accuracy in low-dose-rate brachytherapy. The efficiency of this system was also validated through time consumption assessments. In the phantom experiment, the average error of the needle locations was 0.664mm and the angle error was 4.74°, average time consumption was 16.1min with six needles inserted. Based on the results of the animal experiment, the accuracy of the needle insertion was 1.617mm, while the angle error was 5.574° and the average error of the seed positions was 1.925mm. This paper describes the design and experimental validation of a novel surgical navigation system based on mixed reality for I125 seed brachytherapy for thoracoabdominal tumors. This system was validated through a series of experiments, including phantom experiments and animal experiments. Compared with the traditional image-guided system, the procedure presented here is convenient, displays clinically acceptable accuracy and reduces the number of CT scans, allowing doctors to perform surgery based on a visualized plan. All the experimental results indicated that the procedure is ready to be applied in further clinical studies.

Imaging of Ir-192 source using a high energy gamma camera for high-dose-rate brachytherapy

We developed a small field-of-view (FOV) high energy gamma camera and measured the gamma photons from an Ir-192 source for imaging of the source. The developed gamma camera consists of a 10 mm thick GAGG pixel scintillator block optically coupled to a position sensitive photomultiplier (PSPMT). It was encased in a 2 cm thick tungsten shield and a 1 mm diameter pinhole collimator was mounted in its head. The gamma camera was positioned 1 m from the Ir-192 source delivered from the brachytherapy system and imaged the Ir-192 source while the source changed dwell positions in the FOV of the gamma camera. We could image the source with 1 s interval and observed the source changed its position in the images. The spatial resolution of the gamma camera system at 1 m from the Ir-192 source was 28 mm FWHM and position accuracy was 5 mm. With the 10 cm thick water phantom positioned between the source and gamma camera, the counts were decreased to half, but the Ir-192 source images could still be observed clearly. We conclude that the developed gamma camera system is promising for the imaging of the Ir-192 source during high-dose-rate brachytherapy pending future improvements in spatial resolution.

Comprehensive external audit for HDR brachytherapy systems – the national experience

On-site audits in brachytherapy are performed for all HDR units after commissioning in the Czech Republic. Air-kerma strength, source positioning accuracy, dose calculation accuracy by treatment planning system, and reconstruction algorithm in terms of geometry accuracy are verified. Results obtained in 2003 – 2018 for 24 audited HDR brachytherapy sources are described in the paper. Weak points in HDR brachytherapy process are emphasized. The audited centres often failed in good knowledge of applicators, especially of needles with different blind tip lengths.

Clinical and Dosimetric Comparison of Interstitial Applications Using Martinez Universal Perineal Interstitial Template (MUPIT) and Syed–Neblett Template for Carcinoma Cervix

MUPIT and Syed–Neblett Template are the two commonly used systems for interstitial brachytherapy for gynecological cancers in India. A retrospective study was done to compare and evaluate the outcome, dosimetric data and the toxicities of the two perineal template-based high dose rate brachytherapies in patients diagnosed of cervical cancer and vaginal carcinoma. Between January 2010 and January 2013, 62 patients treated with interstitial transperineal brachytherapy using MUPIT and Syed–Neblett Template at a tertiary care center of Eastern India were included in the study. The median EBRT dose was 50 Gy; ISRT (interstitial brachytherapy) dose was 21 Gy. The dosimetric data and clinical outcome and the toxicity profile were obtained from our file archive and TPS archives. These were correlated with follow-up status regarding toxicity and locoregional recurrence and control. During the study period, 62 patients received ISRT of which 8 were of vault recurrence. Of these 62 patients, 37 were treated using Syed–Neblett and 25 using MUPIT. Median age was 45 years; ISRT dose was similar in both groups (21 Gy in 3 fractions once a week). The mean EQD2 to the 2 cc bladder and 2 cc rectum was 75.4 Gy and 72.21 Gy in the Syed cohort and 76.83 Gy and 75.38 Gy in the MUPIT cohort, respectively (p = 0.12 and 0.09). Acute toxicity was mostly grade 1 and 2 genitourinary (%) or grade 1 and 2 rectal (%). Most common late toxicity was gastrointestinal bleeding and dysuria: 16.22% and 8.35% in the Neblett arm and 18.18 and 9% in the MUPIT arm. With a median follow-up of 27 months, the local control rate was 53% in the Neblett arm and 67% in the MUPIT arm (p = .32). Though there were differences between the dose volumes received by the OAR and the target, the local control rates and long-term normal tissue toxicity were found to be not significantly different between the two systems of transperineal brachytherapy for cervical cancers.

A Plan Quality Assurance (QA) Method for HDR Breast Brachytherapy with Multi-Lumen Balloon Applicator and HDR Interstitial Prostate Brachytherapy

A challenge facing the physics community has been quick plan quality checks for high-dose-rate (HDR) brachytherapy treatment planning. This study aims to develop a QA method of manually verifying the planned treatment time from treatment planning system (TPS) for HDR breast brachytherapy using multi-lumen balloon applicators and HDR interstitial prostate brachytherapy.

130P - Intraoperative radiotherapy with electronic brachytherapy system in breast cancer patients: Systematic review

130P - Intraoperative radiotherapy with electronic brachytherapy system in breast cancer patients: Systematic review

EP-1749 Relation between depth dose and HVL for electronic brachytherapy systems: a Monte Carlo study

EP-1749 Relation between depth dose and HVL for electronic brachytherapy systems: a Monte Carlo study

A preliminary study on a real-time dose monitoring system based on scintillating fibers for brachytherapy

Abstract Purpose: We developed and evaluated a preliminary scintillating fiber-based real-time dose monitoring system (SRDMS) for brachytherapy . Materials and methods: The SRDMS consisted of a detector section with 10 scintillating fibers (BCF-12, Saint Gobain Inc., S.A. France) inserted into a long barrel cylinder and a readout system comprising a photo-multiplier tube (PMT H12428-203 MOD, Hamamatsu Photonics , Shizuoka, Japan) and National Instrument Measurement & Automation Explorer (NI MAX, National Instruments, TX, USA). Basic system performance was estimated by measuring the dwell position and time for various patterns of source motion. Signal output response with data sampling, linearity, and reproducibility was also evaluated. In addition, dwell position and time measurement via the SRDMS were compared across three treatment plans, which were applied to a silicone-based human phantom to evaluate the system’s response to more complex and realistic situations. Results: The difference between the measured source dwell position and plan was -0.52 ± 0.53 mm. The difference between the measured dwell time and plan was 7 ± 5 ms. For signal output verification, the signal-to-SD ratio was less than 1.5%. The signal output linearity was maintained at -0.43 ± 0.50%, and reproducibility was 1.35 ± 1.44%. Conclusions: In this study, we demonstrated that the SRDMS can accurately detect relative dwell positions and dwell times. In further studies, we plan to verify the accuracy of relative source strength, and update the SRDMS with real-time monitoring. The SRDMS could be used for real-time dose monitoring during brachytherapy.

Brachytherapy utilising miniaturised X-ray tubes – clinical implementation and future applications

Electronic brachytherapy is an advanced radiation treatment technique specifically designed to deliver high doses of radiation inside or very close to the tumor-bearing tissues. Unlike the traditional radionuclide-based brachytherapy, electronic brachytherapy uses a miniaturised x-ray tube that can produce radiation when energised. Most of the electronic brachytherapy systems operate at 50 kVp, therefore posing less radiation exposure to both patients and staff when compared to the standard Cobalt-60 or Iridium-192 based brachytherapy systems. Electronic brachytherapy systems have broader applications that include the treatment of skin, brain, breast, spinal metastasis, endometrium, and cervix. The Axxent Xoft brachytherapy system is a unique system which houses a miniature X-ray tube of 2.25 mm diameter at the tip of a flexible catheter. As a mobile unit, the Xoft system requires less shielding and can be operated in remote centres with minimal radiation shielding facilities. The dose fall-off characteristics mimic those of the low energy isotopes, yet the unit still maintains the high dose rate property of an Ir-192 source. This study details the implementation and commissioning aspects of the Axxent system for intra-operative radiotherapy in Breast Cancer and future applications. Electronic brachytherapy systems have the potential to replace conventional radionuclide-based brachytherapy sources and systems.

Expert consensus on computed tomography-assisted three-dimensional-printed coplanar template guidance for interstitial permanent radioactive 125I seed implantation therapy.

Interstitial permanent radioactive seed implantation delivers a high local dose to tumors and sharply drops off at surrounding normal tissues. Radioactive seeds implanted via ultrasound or computed tomography (CT) guidance are minimally invasive and facilitate quick recovery. Transrectal ultrasound-guided 125I seed implantation assisted by a transperineal plane template is standard for early-stage prostate carcinoma, with a highly consistent target volume dose distribution. The postplan dose evaluation is consistent with the preplan evaluation. Until now, there was no workflow for seed implantation elsewhere in the body, and it was difficult to effectively preplan for seed implantation because of patients' position changes, organ movement, and bone structure interference. Along with three-dimensional (3D) printing techniques and seed implantation planning systems for brachytherapy, coplanar and X Y axis coordinate templates were created, referred to as 3D-printed coplanar templates (3D-PCT). 125I seed implantation under CT guidance with 3D-PCT assistance has been very successful in some carcinomas. Preplanning was very consistent with postplanning of the gross tumor volume. All needles are kept parallel for 3D-PCT, with no coplanar needle rearrangement. No standard workflow for 3D-PCT-assisted seed implantation exists at present. The consensus topics for CT-assisted guidance compared to 3D-PCT-assisted guidance for seed implantation are as follows: Indications for seed implantation, preplanning, definition of radiation doses and dosimetry evaluation, 3D-PCT workflow, radiation protection, and quality of staff. Despite current data supporting 125I seed implantation for some solid carcinomas, there is a need for prospectively-randomized multicenter clinical trials to gather strong evidence for using 125I seed implantation in other solid carcinomas.

Individualized and inverse optimized needle configuration for combined intracavitary-interstitial brachytherapy in locally advanced cervical cancer.

The aim of this study is to address the limitation of combined intracavitary-interstitial (IC/IS) brachytherapy (BT) in locally advanced cervical cancer using standardized applicators and to determine the optimal dose distribution in patients with challenging tumors, innovative methods of customizing and optimizing the IS needle configuration for combined IC/IS BT are proposed and investigated. A software module that could customize the IS needle configuration and subsequently generate the digital model of guiding template for three-dimensional printing was developed and integrated into our in-house treatment planning system for BT. The inverse optimization method based on the technique of mixed-integer linear programming was introduced to determine the needle tracks out of a candidate pool and dwell times at corresponding locations to best meet dose objectives. A treatment planning study was conducted to evaluate the feasibility and performance of the proposed methods. The workflow for combined IC/IS BT with customized and inverse optimized IS needle configuration was presented. Dosimetric results of the treatment planning study showed that sufficient target coverage could be obtained with the customized IS needle configuration for challenging cases. The proposed dose-based optimization method for IS needle configuration was feasible and effective. Improved target coverage and organ-at-risk sparing were achieved using the inverse planning method. Using the proposed methods of customizing and optimizing the IS needle configuration, the limitation in the standardized design of combined IC/IS applicators can be addressed, and sufficient target coverage is obtained in cervical cancer patients with unfavorable tumor topography and/or extra lateral expansion.

Monte Carlo investigation on precise dosimetry of HDR breast brachytherapy with Accuboost

Introduction: Accuboost is a HDR brachytherapy system in early stages breast cancer treatment. This device provides a completely noninvasive procedure with parallel-opposed radiation from two immobilizing peripheral applicators that caused it a preferred option of modalities to choose. In most commercial treatment planning systems, tissues are considered as a simple water phantom. Inaccuracies arised from geometry and compositions can lead to deviations in interested dose distribution. This study intends to simulate HDR breast brachytherapy with Accuboost device in order to consider requirement corrections to have an accurate treatment dosimetry. Materials and Methods: MCNP5 simulation is employed to model phantoms in dosimetric measurements. We tried to take geometrical corrections into account in three phantoms. Dose distributions as dose volume histogram parameters and isodose plots obtained from these phantoms are compared to those of water. Corrections are included using real breast tissue with ICRU-44 breast composition, chest defined with an air cavity as lung and a curved surface to introduce a more realistic contour for breast skin. Accuboost is simulated with radiations from eighteen HDR 192-Ir sources on each applicator with appropriate tungsten shields. Results: Differences in most regions with less than 1% to water and maximum value about 5 % have been observed in phantom with ICRU-44 breast material compared to the water. Lung presence have increased deviations a few percent but it has not significantly differed. In phantom with all corrections maximum differences are almost the same as both earlier and deviations with about 5-7% are found near the chest and around the breast skin not in contact to applicators. Conclusion: Based on the results, although discrepancies between corrected phantom and water phantom are in areas near the skin the main differences are in clinical accepted uncertainties and other points of tissue have shown accommodatian. Therefore essential correction may be not needed.

A Monte Carlo-based dosimetric characterization of Esteya® , an electronic surface brachytherapy unit.

The purpose of this work is threefold: First, to obtain the phase space of an electronic brachytherapy (eBT) system designed for surface skin treatments. Second, to explore the use of some efficiency enhancing (EFEN) strategies in the determination of the phase space. Third, to use the phase space previously obtained to perform a dosimetric characterization of the Esteya eBT system. The Monte Carlo study of the 69.5 kVp x-ray beam of the Esteya® unit (Elekta Brachytherapy, Veenendaal, The Netherlands) was performed with PENELOPE2014. The EFEN strategies included the use of variance reduction techniques and mixed Class II simulations, where transport parameters were fine-tuned. Four source models were studied varying the most relevant parameters characterizing the electron beam impinging the target: the energy spectrum (mono-energetic or Gaussian shaped), and the electron distribution over the focal spot (uniform or Gaussian shaped). Phase spaces obtained were analyzed to detect differences in the calculated data due to the EFEN strategy or the source configuration. Depth dose curves and absorbed dose profiles were obtained for each source model and compared to experimental data previously published. In our EFEN strategy, the interaction forcing variance reduction (VRIF) technique increases efficiency by a factor ~20. Tailoring the transport parameters values (C1 and C2) does not increase the efficiency in a significant way. Applying a universal cutoff energy EABS of 10 keV saves 84% of CPU time while showing negligible impact on the calculated results. Disabling the electron transport by imposing an electron energy cutoff of 70 keV (except for the target) saves an extra 8% (losing in the process 1.2% of the photons). The Gaussian energy source (FWHM = 10%, centered at the nominal kVp, homogeneous electron distribution) shows characteristic K-lines in its energy spectrum, not observed experimentally. The average photon energy using an ideal source (mono-energetic, homogeneous electron distribution) was 36.19 ± 0.09 keV, in agreement with the published measured data of 36.2 ± 0.2 keV. The use of a Gaussian-distributed electron source (mono-energetic) increases the penumbra by 50%, which is closer to the measurement results. The maximum discrepancy of the calculated percent depth dose with the corresponding measured values is 4.5% (at the phantom surface, less than 2% beyond 1 mm depth) and 5% (for the 80% of the field) in the dose profile. Our results agree with the findings published by other authors and are consistent within the expected Type A and B uncertainties. Our results agree with the published measurement results within the reported uncertainties. The observed differences in PDD, dose profiles, and photon spectrum come from three main sources of uncertainty: intermachine variations, measurements, and Monte Carlo calculations. It has been observed that a mono-energetic source with a Gaussian electron distribution over the focal spot is a suitable choice to reproduce the experimental data.

Dosimetric and 7-Year Biochemical Results with a Robotic Prostate Brachytherapy System

Dosimetric and 7-Year Biochemical Results with a Robotic Prostate Brachytherapy System

A simulation study of BrachyShade, a shadow-based internal source tracking system for HDR prostate brachytherapy

This paper presents a simulation study of BrachyShade, a proposed internal source-tracking system for real time quality assurance in high dose rate prostate brachytherapy. BrachyShade consists of a set of spherical tungsten occluders located above a pixellated silicon photodetector. The source location is estimated by minimising the mean squared error between a parametric model of the shadow image and acquired images of the shadows projected on the detector plane. A novel algorithm is finally employed to correct the systemic error resulting from Compton scattering in the medium. The worst-case error obtained with BrachyShade for a 13.5 ms image acquisition is less than 1.3 mm in the most distant part of the treatment volume, while for 75% of source locations an error of less than 0.42 mm was achieved.