High Dose Rate Source Research Articles

A Novel Positive-Contrast Magnetic Resonance Imaging Line Marker for High-Dose-Rate (HDR) MRI-Assisted Radiosurgery (MARS).

Magnetic resonance imaging (MRI) can facilitate accurate organ delineation and optimal dose distributions in high-dose-rate (HDR) MRI-Assisted Radiosurgery (MARS). Its use for this purpose has been limited by the lack of positive-contrast MRI markers that can clearly delineate the lumen of the HDR applicator and precisely show the path of the HDR source on T1- and T2-weighted MRI sequences. We investigated a novel MRI positive-contrast HDR brachytherapy or interventional radiotherapy line marker, C4:S, consisting of C4 (visible on T1-weighted images) complexed with saline. Longitudinal relaxation time (T1) and transverse relaxation time (T2) for C4:S were measured on a 1.5 T MRI scanner. High-density polyethylene (HDPE) tubing filled with C4:S as an HDR brachytherapy line marker was tested for visibility on T1- and T2-weighted MRI sequences in a tissue-equivalent female ultrasound training pelvis phantom. Relaxivity measurements indicated that C4:S solution had good T1-weighted contrast (relative to oil [fat] signal intensity) and good T2-weighted contrast (relative to water signal intensity) at both room temperature (relaxivity ratio > 1; r2/r1 = 1.43) and body temperature (relaxivity ratio > 1; r2/r1 = 1.38). These measurements were verified by the positive visualization of the C4:S (C4/saline 50:50) HDPE tube HDR brachytherapy line marker on both T1- and T2-weighted MRI sequences. Orientation did not affect the relaxivity of the C4:S contrast solution. C4:S encapsulated in HDPE tubing can be visualized as a positive line marker on both T1- and T2-weighted MRI sequences. MRI-guided HDR planning may be possible with these novel line markers for HDR MARS for several types of cancer.

Evaluation of a Balloon Implant for Simultaneous Magnetic Nanoparticle Hyperthermia and High-Dose-Rate Brachytherapy of Brain Tumor Resection Cavities

Previous work has reported the design of a novel thermobrachytherapy (TBT) balloon implant to deliver magnetic nanoparticle (MNP) hyperthermia and high-dose-rate (HDR) brachytherapy simultaneously after brain tumor resection, thereby maximizing their synergistic effect. This paper presents an evaluation of the robustness of the balloon device, compatibility of its heat and radiation delivery components, as well as thermal and radiation dosimetry of the TBT balloon. TBT balloon devices with 1 and 3 cm diameter were evaluated when placed in an external magnetic field with a maximal strength of 8.1 kA/m at 133 kHz. The MNP solution (nanofluid) in the balloon absorbs energy, thereby generating heat, while an HDR source travels to the center of the balloon via a catheter to deliver the radiation dose. A 3D-printed human skull model was filled with brain-tissue-equivalent gel for in-phantom heating and radiation measurements around four 3 cm balloons. For the in vivo experiments, a 1 cm diameter balloon was surgically implanted in the brains of three living pigs (40–50 kg). The durability and robustness of TBT balloon implants, as well as the compatibility of their heat and radiation delivery components, were demonstrated in laboratory studies. The presence of the nanofluid, magnetic field, and heating up to 77 °C did not affect the radiation dose significantly. Thermal mapping and 2D infrared images demonstrated spherically symmetric heating in phantom as well as in brain tissue. In vivo pig experiments showed the ability to heat well-perfused brain tissue to hyperthermic levels (≥40 °C) at a 5 mm distance from the 60 °C balloon surface.

A Novel Brachytherapy Needle Design to Reduce Urethra Dose in HDR Prostate Brachytherapy.

Ultrasound-guided high-dose-rate (HDR) prostate brachytherapy is a safe and effective treatment option for prostate cancer patients; however, some patients still experience acute and late genitourinary (GU) toxicity. It has been reported that urethra dose is associated with the incidence and severity of GU toxicity. Therefore, a technique that can further spare the urethra while ensuring adequate target coverage is highly desirable. Intensity modulated brachytherapy (IMBT) designs, such as rotating shield brachytherapy (RSBT), offer ideal dosimetry on-paper but are challenging to implement clinically due to the need for high precision in moving mechanisms and the use of non-conventional HDR sources, such as 153Gd, electronic, and 169Yb. In this study, we propose a novel clinically implementable solution based on the direction modulated brachytherapy (DMBT) design concept, which has no moving parts and works effectively with the commercially available 192Ir sources. The widely used GammaMedPlus (GMP) 192Ir sources, with outer diameters of 0.9 mm, was simulated using the GEANT4 Monte Carlo (MC) simulation code. The novel DMBT needle concept consists of a 14-gauge nitinol needle with an outer diameter of 2.1 mm and a crust thickness of 0.1 mm, which housed a platinum shield inside. A single groove, consistent with the outer diameter of each source, was incorporated inside the platinum shield to accommodate the HDR source. The maximum thickness of the shield was 0.8 mm. To evaluate the effectiveness of the DMBT needle concept in reducing urethra dose, two proof-of-concept in silico DMBT plans were created from the standard clinical plan by replacing two needles close to the urethra with the DMBT needles. The dosimetrical comparisons between the two DMBT plans, and the clinical BT plan were done by assessing the target coverage, and urethral, bladder and rectum dose. The MC results showed that the use of the novel DMBT needle could reduce the radiation dose by approximately 35% at 1 cm distance from the needle behind the platinum shield, as compared to the unshielded side. Additionally, when using the same dose volume histogram (DVH) planning criteria as the original plan, the DMBT plan reduced the maximum urethral dose at the pre-apical region by 16% and 28% for 0 mm and 2 mm planning organ at risk (PRV) margins, respectively, while maintaining equivalent V100 and D90 target coverage. The novel DMBT needle design offers a promising solution for reducing the dose to the pre-apical region of the urethra without compromising target coverage, increasing the dose to other organs-at-risk, or increasing the treatment time.

A novel direction modulated brachytherapy technique for urethra sparing in high-dose-rate brachytherapy of prostate cancer

PurposeImage-guided high-dose-rate (HDR) prostate brachytherapy is a safe and effective treatment option for prostate cancer patients; however, some patients still experience acute and late genitourinary (GU) toxicity. Studies have shown that urethral dose is associated with the incidence and severity of GU toxicity. Therefore, a technique that can further spare the urethra while ensuring adequate target coverage is highly desirable. Intensity modulated brachytherapy (IMBT) designs, such as rotating shield brachytherapy (RSBT), offer ideal dosimetry theoretically but are challenging to implement clinically due to the need for high precision in moving the treatment delivery mechanisms synchronized with the source loading. In this study, we propose a novel relatively easy-to-implement solution based on the direction modulated brachytherapy (DMBT) design concept, which does not involve moving parts and works effectively with the ubiquitous 192Ir source. Materials and MethodsThe popular Varian VS2000 (VS) and GammaMedPlus (GMP) 192Ir sources, with outer diameters of 0.6 mm and 0.9 mm, respectively, were simulated using the GEANT4 Monte Carlo (MC) simulation code. The novel DMBT needle concept consists of a 14-gauge nitinol needle, which houses a platinum shield inside. A single groove, consistent with the outer diameter of each source, was incorporated inside the platinum shield to accommodate the HDR source. The maximum thickness of the shield was 1.1 mm (0.8 mm) for the VS (GMP) source. To evaluate the effectiveness of the DMBT needle concept in reducing urethral dose, 6 patient cases were studied and DMBT plans were created by replacing two needles close to the urethra with the DMBT needles. The dosimetric comparisons between the DMBT and reference clinical plans were done by assessing the dose-volume histogram (DVH) planning criteria for the target coverage and organs-at-risk. ResultsThe MC results showed that the use of the novel DMBT needle design with the VS source (GMP source) could reduce the dose by 49.6% (39.2%) at 1 cm from the needle behind the platinum shield, as compared to the unshielded side. Additionally, when using the same DVH planning criteria as the original plan, the DMBT plan with the VS (GMP) source reduced the maximum urethral dose by 10.3% ± 5.6% (8.1% ± 5.0%) and 17.7% ± 14.2% (16.6% ± 13.3%) for 0 mm and 2 mm margins, respectively, while maintaining equivalent V90% and D100 target coverage. ConclusionThe novel DMBT technique offers a promising clinically implementable solution for sparing urethra, particularly in pre-apical region, without compromising the target coverage or increasing treatment time.

Feasibility of 4D HDR brachytherapy source tracking using x-ray tomosynthesis: Monte Carlo investigation.

High dose rate (HDR) brachytherapy rapidly delivers dose to targets with steep dose gradients. This treatment method must adhere to prescribed treatment plans with high spatiotemporal accuracy and precision, as failure to do so may degrade clinical outcomes. One approach to achieving this goal is to develop imaging techniques to track HDR sources in vivo in reference to surrounding anatomy. This work investigates the feasibility of using an isocentric C-arm x-ray imager and tomosynthesis methods to track Ir-192 HDR brachytherapy sources in vivo over time (4D). A tomosynthesis imaging workflow was proposed and its achievable source detectability, localization accuracy, and spatiotemporal resolution were investigated in silico. An anthropomorphic female XCAT phantom was modified to include a vaginal cylinder applicator and Ir-192 HDR source (0.5 × 0.5 × 5.0 mm3 ), and the workflow was carried out using the MC-GPU Monte Carlo image simulation platform. Source detectability was characterized using the reconstructed source signal-difference-to-noise-ratio (SDNR), localization accuracy by the absolute 3D error in its measured centroid location, and spatiotemporal resolution by the full-width-at-half-maximum (FWHM) of line profiles through the source in each spatial dimension considering a maximum C-arm angular velocity of 30° per second. The dependence of these parameters on acquisition angular range (θtot = 0°-90°), number of views, angular increment between views (Δθ = 0°-15°), and volumetric constraints imposed in reconstruction was evaluated. Organ voxel doses were tallied to derive the workflow's attributable effective dose. The HDR source was readily detected and its centroid was accurately localized with the proposed workflow and method (SDNR: 10-40, 3D error: 0-0.144 mm). Tradeoffs were demonstrated for various combinations of image acquisition parameters; namely, increasing the tomosynthesis acquisition angular range improved resolution in the depth-encoded direction, for example from 2.5 mm to 1.2 mm between θtot = 30o and θtot = 90o , at the cost of increasing acquisition time from 1 to 3 s. The best-performing acquisition parameters (θtot = 90o , Δθ = 1°) yielded no centroid localization error, and achieved submillimeter source resolution (0.57 × 1.21 × 5.04 mm3 apparent source dimensions, FWHM). The total effective dose for the workflow was 263 µSv for its required pre-treatment imaging component and 7.59 µSv per mid-treatment acquisition thereafter, which is comparable to common diagnostic radiology exams. A system and method for tracking HDR brachytherapy sources in vivo using C-arm tomosynthesis was proposed and its performance investigated in silico. Tradeoffs in source conspicuity, localization accuracy, spatiotemporal resolution, and dose were determined. The results suggest this approach is feasible for localizing an Ir-192 HDR source in vivo with submillimeter spatial resolution, 1-3 second temporal resolution and minimal additional dose burden.

PO18: An Efficient and Reproducible Autoradiography Technique for HDR-Gynecological Applicators Commissioning

<h3>Purpose</h3> High Dose Rate (HDR) brachytherapy commissioning of Elekta's gynecological (Gyn) applicator sets include a large inventory of CT/MR compatible plastic, applicator tubes of varying shapes and sizes. This often present a challenge to the efficiency of source autoradiography - an essential test to determine and verify final dwell position of the HDR source and its positioning/stepping accuracy. We present a technique of acquiring radiograph-autoradiograph combinations of HDR-Gyn applicators that allows testing of several applicators simultaneously, in a rigid and reproducible set-up. <h3>Materials Methods</h3> Elekta provides x-ray catheter (marker) sets as a required accessory to verify source positioning inside Gyn applicators. Once the markers are calibrated & Final Marker Position (FMP) characterized, using Elekta's Source Position Check Ruler & CT-scans, the technique of radiograph-autoradiograph superposition is recommended for determination of final dwell position (FDP) & verification of source positioning accuracy. To ensure a rigid & reproducible set-up, template trays to hold multiple applicator tubes & Gafochromic EBT3 film for recording multiple radiographs in unison were built using Styrofoam. Channels were carved in styrofoam creating tight narrow groves fitting applicators in place. Applicators were taped with tips laid flat & flush with the film secured to styrofoam base independently. Primary advantage of using styrofoam is that it offers no backscatter to radiography as well as gamma photons from the Ir-192 source. Additionally, it is readily available and easy to work with. Each tray held 4-6 applicators with markers allowing a simultaneous radiograph acquisition, &∼ 5 cm lateral spacing enabled independent images. Truebeam^TM Linear accelerator was used for radiography. Multiple pre-prepared template trays with applicators were exposed at a source-to-film-distance of 100 cm with 400 monitor units using 2.5 MV imaging beam. This technique provided best visualization of the plastic applicator & marker on a gafochromic EBT3 film. Once the multiple-applicator-radiograph is acquired, templates were transported to adjacent HDR suite, set on a rigid couch, markers carefully removed & transfer tube connected for acquisition of autoradiograph coincident with recently acquired radiograph, using Flexitron afterloader. For Ir-192 source's autoradiograph, a 10-15 seconds dwell time is adequate to darken film with marker visualization reasonably intact for analysis. Pre-prepared templates and availability of personnel allowed simultaneous use of linear accelerator & afterloader, for radiograph & autoradiograph acquisition, adding further efficiency. Source positioning & stepping accuracy was verified by coincidence of center of darkening at the exposed dwell-position & center of visualized markers, on a viewbox illuminator. <h3>Results</h3> Using techniques and workflow developed, 60 CT/MR compatible HDR-Gyn plastic applicators were commissioned. Autoradiography-radiography superposition with x-ray markers enabled verification of Elekta specified distances between the outer tip of the IU/ovoid tubes, inner tip & the final dwell position, & HDR source positioning & stepping accuracy within 1 mm. Figure 1-A shows Styrofoam templates with multiple channels for affixing applicators over EBT3 Gafochromic film for radiography, 1-B is HDR room setup for autoradiography and 1-C shows images of multiple different applicator tubes depicting the radiograph-autoradiograph overlay with marker visualization and HDR source positioning. <h3>Conclusion</h3> We present an efficient autoradiography technique for commissioning of a large inventory HDR-Gyn plastic applicators using a linear accelerator & HDR afterloader.

PHSOR11 Presentation Time: 1:20 PM: Verify the Transit Time Correction Accuracy of the Bravos Afterloader System Using a Novel Scintillation-Based Brachytherapy Quality Assurance Device

<h3>Purpose</h3> Compared to the older generations, the new Bravos high dose rate (HDR) afterloader offers the function to automatically correct dwell time to compensate the transit dose effect. To our best knowledge, there is no QA attempt to verify the accuracy of this correction. To address this issue, a new transit time measurement module has been developed and included in the OriQA HDR QA device, an autonomous phantom for HDR brachytherapy quality assurance. In this work, we employ the OriQA system to verify the transit time correction accuracy of the Bravos afterloader system. <h3>Method</h3> The OriQA device utilizes radioluminescence imaging technique to accurately measure HDR source strength, dwell time, and dwell position. It consists of a 20 cm needle applicator insert, a radioluminescence phosphor sheet placed directly atop the applicator, a digital camera, and software for signal processing and displaying results. Radiation-induced luminescence photons are emitted from the phosphor sheet and captured by the camera. The signal intensity and location are processed to yield relative source strength and dwell information. For the verification test, one of the Bravos channels was connected to the OriQA applicator using a one-meter transfer tube. After specific plan delivery, the raw data of OriQA measurement including source position and time was exported to Matlab for further analysis. The real dwell time at each dwell position and the transit time between dwells during cable extension and retraction were extracted. The transit time correction method provided by the vendor was applied to the measurement, yielding the delivered dwell time. The percentage difference between the delivered and planned dwell time was calculated and used as an indicator of the transit time correction accuracy. Several verification plans were created including seven with fixed dwell steps, one with variable dwell steps, and one with variable dwell time. Plans with fixed dwell steps were delivered three times. The rest were delivered once. Plan details are listed in table 1. For each plan, the mean and standard deviation of the difference between planned and delivered dwell time were calculated from all dwell positions and deliveries. <h3>Results</h3> The deviations between the planned and delivered dwell time are listed in table 1. For plans with less than 4 cm dwell step, the accuracy of transit time correction is, on average, less than 1.2% of the dwell time. For plans with 4 cm and 9 cm dwell step, the accuracy is 1.5% and 2.85%, on average, respectively. Dwell time variation does not affect the correction accuracy, as shown in plan 9. Standard deviations of plan 3, 4, and 9 are greater than 1% due to the relatively large difference at the proximal dwell. <h3>Conclusion</h3> This is the first study that successfully verifies the transit time correction accuracy of the Bravos system. Less than 2% accuracy is observed for clinically relevant dwell steps (0.3 cm to 4 cm). Variations in dwell step, dwell position, and dwell time do not worsen the accuracy.

The design of a novel direction modulated brachytherapy vaginal cylinder applicator for optimizing coverage of the apex

High-dose-rate (HDR) vaginal cuff brachytherapy is an effective adjuvant therapy for women with stage I endometrial cancer. Although infrequent, failures do occur, most frequently at the vaginal vault. A potential cause of failure is insufficient dosimetric coverage at the vaginal apex due to cold spots from the anisotropic dose distribution of the source. Here, we propose a novel direction modulated brachytherapy (DMBT)-concept vaginal cylinder (VC) applicator that resolves this dosimetric issue. The novel DMBT-VC applicator was designed and simulated with the GEANT4 Monte Carlo code. The outer cylinder material chosen was polyphenylsulfone (PPSU) plastic, and the central part was a detachable rod, housing a single lumen made of either polyether ether ketone (PEEK) plastic or an MR-compatible tungsten alloy. The PPSU-based outer cylinder, together with the inner PEEK rod provides the dose distribution of a conventional VC applicator. The PEEK rod is then replaced with an MR-compatible tungsten alloy rod of the same dimensions to generate directional "pencil-like" beams to compensate for the anisotropic cold spots. Two widely used 192 Ir HDR sources, VS2000 and GammaMedPlus, were also simulated. The novel DMBT-VC applicator was able to remove the underdosage at the apex due to the anisotropy effect regardless of the HDR sources without unnecessarily increasing the dose to the periphery of the applicator. Also, further directional modulation to reach deeper in the apex by up to 14mm beyond the VC surface was achievable, again without increasing the peripheral doses. Total treatment dwell times increased only by 7-13%. The novel DMBT-VC applicator provides improved dose coverage at the vaginal apex by overcoming the classical anisotropy issue ubiquitous to all HDR brachytherapy sources. The next step in development of the device is manufacturing a prototype for clinical testing.

BEBIG 60Co HDR brachytherapy source dosimetric parameters validation using GATE Geant4-based simulation code

PurposeThis study aims to validate the dosimetric characteristics of High Dose Rate (HDR) 60Co source (Co0.A86 model) using GATE Geant4-based Monte Carlo code. According to the recommendation of the American Association of Physicists in Medicine (AAPM) task group report number 43, the dosimetric parameters of a new brachytherapy source should be verified either experimentally or by Monte Carlo calculation before clinical applications. The validated 60Co source in this study will be used for the simulation of intensity-modulated brachytherapy (IMBT) of vaginal cancer using the same GATE Geant4-based Monte Carlo code in the future. Materials and methodsGATE (version 9.0) simulation code was used to model and calculate the required TG-43U1 dosimetric data of the 60Co HDR source. DoseActors were defined for calculation of dose rate constant, radial dose function, and anisotropy function in a water phantom with an 80 cm radius. ResultsThe dose rate constant was obtained as 1.070±0.008cGy.h−1.U−1 which shows a relative difference of 2.01% compared to the consensus value, 1.092 ​cGy.h−1.U−1. The calculated results of anisotropy and radial dose functions starting from 0.1 cm to 10 cm around the source showed excellent agreement with the results of published studies. The mean variation of the radial dose and anisotropy functions values from the consensus data were 1% and 0.9% respectively. ConclusionFindings from this investigation revealed that the validation of the HDR 60Co source is feasible by the GATE Geant4-based Monte Carlo code. As a result, the GATE Monte Carlo code can be used for the verification of the brachytherapy treatment planning system.

Intensity Modulated High Dose Rate (HDR) Brachytherapy Using Patient Specific 3D Metal Printed Applicators: Proof of Concept.

PurposeIn high-dose-rate (HDR) brachytherapy, an anisotropic dose distribution may be desirable for achieving a higher therapeutic index, particularly when the anatomy imposes challenges. Several methods to deliver intensity-modulated brachytherapy (IMBT) have been proposed in the literature, however practical implementation is lacking due to issues of increased delivery times and complicated delivery mechanisms. This study presents the novel approach of designing a patient-specific inner shape of an applicator with 3D metal printing for IMBT using an inverse plan optimization model.MethodsThe 3D printed patient-specific HDR applicator has an external shape that resembles the conventional brachytherapy applicator. However, at each dwell position of the HDR source, the shielding walls in the interior are divided into six equiangular sections with varying thicknesses. We developed a mathematical model to simultaneously optimize the shielding thicknesses and dwell times according to the patient’s anatomical information to achieve the best possible target coverage. The model, which is a bi-convex optimization problem, is solved using alternating minimization. Finally, the applicator design parameters were input into 3D modeling software and saved in a 3D printable file. The applicator has been tested with both a digital phantom and a simulated clinical cervical cancer patient.ResultsThe proposed approach showed substantial improvements in the target coverage over the conventional method. For the phantom case, 99.18% of the target was covered by the prescribed dose using the proposed method, compared to only 58.32% coverage achieved by the conventional method. For the clinical case, the proposed method increased the coverage of the target from 56.21% to 99.92%. In each case, both methods satisfied the treatment constraints for neighboring OARs.ConclusionThe study simulates the concept of the IMBT with inverse planning using the 3D printed applicator design. The non-isotropic dose map can be produced with optimized shielding patterns and tailored to individual patient’s anatomy, to plan a more conformal plan.

The Design of an Audit Test for 60Co Brachytherapy Treatment Planning System.

Background:Auditing the treatment planning system (TPS) software for a radiotherapy unit is of paramount importance in any radiation therapy department. A Plexiglas phantom was proposed to measure the ionization of 60Co high dose rate (HDR) source and compare dose points in the planning system for auditing and verifying TPS.Methods:Auditing was performed using a Plexiglas phantom in an end-to-end test, and relative dose points were detected by a farmer-type ionization chamber and compared with the relative dose of similar points in TPS. The audit results were determined as pass optimal level (<3.3%), pass action level (between 3.3% and 5%), and out of tolerance (>5%).Results:The comparison of the collected data revealed that 80% of the measured values were ≤5% in the pass level, and 20% of the points were out of tolerance (between 5% and 6.99%).Conclusion:This study documented the appropriateness of the dosimetry audit test and this phantom design for the HDR brachytherapy TPS.

CONTEMPORARY APPROACHES TO PROGNOSTICATION AND MANAGEMENT OF PELVIC RADIATION INJURIES IN GYNECOLOGICAL CANCER PATIENTS.

Rapid development of radiotherapeutic techniques and implementation of radiation therapy (RT) nanotechnologies in practice, taking into account principles of radiobiology, ensures that the planned dose will bedelivered to the target volume with minimal irradiation of healthy tissues while maintaining the guaranteed RTquality. Therefore, further advance of RT involves not only implementation of the new technologies in radiationpractice, but also the intensive developments in fields of radiation medicine and clinical radiobiology. search for optimal models of the high-energy (HDR - high dose rate) brachytherapy (BT) using the 192Irsource in comparison with effects of the reference gamma radiation from 60Co, thereby, to increase the effectivenessof chemoradiation therapy (CRT) of gynecological cancer patients (GCPs) with minimal radiation loads on criticalorgans and tissues in the tumor environment. The radiobiological study was aimed to determine the feasibility ofusing the transmembrane potential (TMP) and intensity of reactive oxygen species (ROS) production in peripheralblood lymphocytes (PBL) as predictors of radiosensitivity of non-malignant cells from the tumor environment or itsbed in order to minimize the RT complications in GCPs. Patients (n = 115) with cancer stages II-III, T2-3N0-1M0 were managed with comprehensiveconservative treatment. Three groups of patients were selected depending on the applied HDR BT method against abackground of the administered chemosensitizing agents. Blood samples of GCPs (n = 24) before the RT initiationand of apparently healthy individuals (AHIs, i.e. the control group, n = 18) were taken for the radiobiologicalresearch. Review of the direct results of 60Co or 192Ir sources use in HDR BT and of the follow-up data showed theincreased tumor positive response in the main study groups after CRT course by respectively 16.6 % and 20.1 % incomparison with 60Со HDR BT administration. Concerning local reactions it was noted that grade II radiation reactions were almost absent in the main groups. According to the results of radiobiological studies, it was establishedthat TMP level in PBL of GCPs was 1.36 times higher than in AHIs. Thus, the emerging of late radiation injuries depended on the accuracy of of individual computer planning and correct reproduction of the planned RT course, timely correction of treatment programs, use of a complexof rational medical prophylaxis, severity of tumor process and concomitant disorders, as well as on the used type ofHDR radiation sources (192Ir and 60Co). Changes in TMP values and intensity of ROS production in PBL of GCPs in comparison with AHIs, and the high values of these parameters in PBL of individual patients are a rationale to specifythem as additional indicators characterizing the possibility of radiation complications before the RT planning.

Dose to pelvic lymph nodes during brachytherapy of locally advanced cervical cancer with 60Co HDR source

PURPOSEThis study investigated the correlation between the prescription dose and dose to the Manchester and International Commission on Radiation Units and Measurements-report 38 (ICRU-38) lymphatic trapezoid points during high-dose-rate (HDR) brachytherapy of locally advanced cervical cancer with (Cobalt-60) 60Co . METHODS AND MATERIALSA retrospective study was designed for; patients with locally advanced cervical cancer, treated by external beam radiotherapy and concurrent weekly Cisplatin-based chemotherapy, had no extended parametrial invasion and was treated by tandem-ovoid set, from 2017 to 2020. Groupe Européen de Curiethérapie-European Society for Radiotherapy and Oncology (GEC-ESTRO) based target's volume, ICRU-89 revised version of Manchester points A and B, and ICRU-38 lymph node surrogate points were determined, and their dose was recorded. Paired sample t-test, linear regression analysis, and Pearson correlation analyses were done considering a statistical significance level of 0.05 and using IBM SPSS statistics (Version 23, IBM Crop.). RESULTSSeventy-four brachytherapy cases were included. A positive and strong correlation was observed between D90 of clinical target volume (CTVHR) and points A and B dose for CTVHR〈 15 cc and 〉 35 cc. Strong and significant (p < 0.05) correlations were achieved between pelvic wall points dose and D90 and D100 of the obturator and between D50 and hot points of internal iliac lymph nodes. A strong correlation was obtained between D50 and D90 of external iliac lymph nodes and their ICRU points. CONCLUSIONSStrong correlations were obtained between dose to the pelvic lymphatic chains and their historical ICRU-38 surrogate points during HDR brachytherapy of locally advanced cervical cancer patients with 60Co tandem-ovoid applicator sets. The correlation strength between point A and prescription dose highly depends on the CTVHR volume.

‘End to end’ dosimetry audit for HDR brachytherapy

Purpose: A dosimetric audit of Ir-192 high dose rate (HDR) brachytherapy remote afterloading units was carried out in 2019. All six brachytherapy departments on the island of Ireland participated in an end-to-end test and in a review of local HDR dosimetry procedures. Materials and methods: A 3D-printed customised phantom was created to position the following detectors at known distances from the HDR source: a Farmer ionization chamber, GafChromic film and thermoluminescent dosimeters (TLDs). Dedicated HDR applicator needles were used to position an Ir-192 source at 2 cm distance from these detectors. The end-to-end dosimetry audit pathway was performed at each host site and included the stages of imaging, applicator reconstruction, treatment planning and delivery. Deviations between planned and measured dose distributions were quantified using gamma analysis methods. Local procedures were also discussed between auditors and hosts.

End-to-end dosimetric audit: A novel procedure developed for Irish HDR brachytherapy centres.

A dosimetric audit of Ir-192 high dose rate (HDR) brachytherapy remote after-loading units was carried out in 2019. All six brachytherapy departments on the island of Ireland participated in an end-to-end test and in a review of local HDR dosimetry procedures. A 3D-printed customised phantom was created to position the following detectors at known distances from the HDR source: a Farmer ionization chamber, GafChromic film and thermoluminescent dosimeters (TLDs). Dedicated HDR applicator needles were used to position an Ir-192 source at 2cm distance from these detectors. The end-to-end dosimetry audit pathway was performed at each host site and included the stages of imaging, applicator reconstruction, treatment planning and delivery. Deviations between planned and measured dose distributions were quantified using gamma analysis methods. Local procedures were also discussed between auditors and hosts. The mean difference between Reference Air Kerma Rate (RAKR) measured during the audit and RAKR specified by the vendor source certificate was 1.3%. The results of end-to-end tests showed a mean difference between calculated and measured dose of 2.5% with TLDs and less than 0.5% with Farmer chamber measurements. GafChromic films showed a mean gamma passing rates of >95% for plastic and metal applicators with 2%/1 mm global tolerance criteria. The results of this audit indicate dosimetric consistency between centres. The 'end to end' dosimetry audit methodology for HDR brachytherapy has been successfully implemented in a multicentre environment, which included different models of Ir-192 sources and different treatment planning systems. The ability to create a 3D-printed water-equivalent phantom customised to accurately position all three detector types simultaneously at controlled distances from the Ir-192 source under evaluation gives good reproducibility for end-to-end methodology.

1 kHz laser accelerated electron beam feasible for radiotherapy uses: A PIC–Monte Carlo based study

Laser wakefield acceleration (LWFA) offers a promising compact solution for the production of high and very high energy electron (VHEE) beams, which have an ultrashort pulse duration with a high instantaneous dose rate and small source size. These unique properties are of radiobiological as well as clinical interest. In this paper we focus on the potential application of high repetition rate LWFA electron beams for radiobiology and radiotherapy. On the basis of particle-in-cell (PIC) and Monte Carlo simulations we propose that, using a commercially available 1kHz laser system one can generate electron beams with 35.7MeV mean energy and 3pC electron bunch charge at 1kHz repetition rate to deliver a dose rate of 18Gy/min, which could be extremely useful for real radiotherapy applications. Thanks to the high repetition rate, dose delivery can be performed with high precision making this system a potential alternative to conventional clinical electron accelerators.

Positional and angular tracking of HDR 192 Ir source for brachytherapy quality assurance using radiochromic film dosimetry.

To quantify and verify the dosimetric impact of high-dose rate (HDR) source positional uncertainty in brachytherapy, and to introduce a model for three-dimensional (3D) position tracking of the HDR source based on a two-dimensional (2D) measurement. This model has been utilized for the development of a comprehensive source quality assurance (QA) method using radiochromic film (RCF) dosimetry including assessment of different digitization uncertainties. An algorithm was developed and verified to generate 2D dose maps of the mHDR-V2 192 Ir source (Elekta, Veenendaal, Netherlands) based on the AAPM TG-43 formalism. The limits of the dosimetric error associated with source (0.9mm diameter) positional uncertainty were evaluated and experimentally verified with EBT3 film measurements for 6F (2.0mm diameter) and 4F (1.3mm diameter) size catheters at the surface (4F, 6F) and 10mm further (4F only). To quantify this uncertainty, a source tracking model was developed to incorporate the unique geometric features of all isodose lines (IDLs) within any given 2D dose map away from the source. The tracking model normalized the dose map to its maximum, then quantified the IDLs using blob analysis based on features such as area, perimeter, weighted centroid, elliptic orientation, and circularity. The Pearson correlation coefficients (PCCs) between these features and source coordinates (x, y, z, θy , θz ) were calculated. To experimentally verify the accuracy of the tracking model, EBT3 film pieces were positioned within a Solid Water® (SW) phantom above and below the source and they were exposed simultaneously. The maximum measured dosimetric variations on the 6F and 4F catheter surfaces were 39.8% and 36.1%, respectively. At 10mm further, the variation reduced to 2.6% for the 4F catheter which is in agreement with the calculations. The source center (x, y) was strongly correlated with the low IDL-weighted centroid (PCC=0.99), while the distance to source (z) was correlated with the IDL areas (PCC=0.96) and perimeters (PCC=0.99). The source orientation θy was correlated with the difference between high and low IDL-weighted centroids (PCC=0.98), while θz was correlated with the elliptic orientation of the 60-90% IDLs (PCC=0.97) for a maximum distance of z=5mm. Beyond 5mm, IDL circularity was significant, therefore limiting the determination of θz (PCC≤0.48). The measured positional errors from the film sets above and below the source indicated a source position at the bottom of the catheter (-0.24±0.07mm). Isodose line features of a 2D dose map away from the HDR source can reveal its spatial coordinates. RCF was shown to be a suitable dosimeter for source tracking and dosimetry. This technique offers a novel source QA method and has the potential to be used for QA of commercial and customized applicators.

Technical Note: Scintillation markers for real-time visual source tracking during skin high dose rate brachytherapy.

Treatment misadministration during high dose rate (HDR) brachytherapy is mainly caused due to gross errors in incorrect manual entry of catheter length and manual connection of hardware. The probability of these errors increases with increasing complexity of a surface applicator. A simple, real-time visual verification method was developed using a scintillator to enhance quality assurance (QA) measures for HDR surface brachytherapy and thus reduce manual errors and improve patient safety. Scintillation markers were fabricated from cerium-doped lutetium yttrium orthosilicate (LYSO) embedded in a polymer compound to form 5-mm diameter markers. To verify catheter-transfer tube connections, markers were attached to each channel of a Freiburg flap and irradiated with an 192 Ir source. To determine if the source reached the edge of a target, markers were placed along the periphery. The HDR source was visually tracked by following the illumination from the markers. The response of the markers was also verified in the presence of thermoplastic material overlaid on the Freiburg applicator. Scintillation markers emitted intense blue visible light upon irradiation when the HDR source was beneath the marker, verifying the source's presence in the correct catheter. The signal was clearly visible even when the marker was placed on top of the thermoplastic material covering the Freiburg Flap. Crosstalk from adjacent catheters was <50% of the maximum light intensity. Scintillation markers and paint were developed to successfully meet the challenge of visually tracking of HDR source during brachytherapy by surface applicators. This direct visualization of source allows real-time catheter verification during treatment, and correct superficial target coverage, thus preventing a medical event. It can easily be integrated into pre-existing QA program.

On the stability of well-type ionization chamber source strength calibration coefficients.

To investigate the variability and stability of brachytherapy source strength calibration coefficients for air-communicating and pressurized well-type ionization chambers among high-dose rate (HDR), low-dose rate (LDR), and electronic brachytherapy (EBT) source qualities. These qualities of an ionization chamber are important features to assess given their role in maintaining traceability to a primary national standards laboratory and facilitating efficacious patient care in brachytherapy. The calibration records from the University of Wisconsin Accredited Dosimetry Calibration Laboratory (UWADCL) customer well-type ionization chamber database were retrospectively analyzed for calibrations performed between 1996 and 2019. A statistical analysis was performed and differentiated among calibration type to quantify the distribution of chamber calibration coefficients among several chamber models. Distributions were quantified based on their moments and by quantile analysis. For LDR calibrations, chamber response was further differentiated by seed type to study the variability in seed dependence within and across chamber models. In addition to these metrics, the calibration lineage at the UWADCL was used to assess the stability of these calibration coefficients among chamber model and source type based on the ratio of subsequent calibration coefficients. The distribution of brachytherapy source strength calibration coefficients for a particular chamber model is not necessarily normally distributed and is sensitive to changes in the machining tolerances or design of the chamber model. Calibration source quality also influenced the distributions of calibration coefficients for a chamber model; the air-kerma rate calibration coefficients for EBT sources were the most variable followed by LDR and then HDR source types. The stability of a chamber's source strength calibration coefficient exhibited a similar dependence on the source quality. Air-communicating and pressurized chambers exhibited an average stability between subsequent calibrations of 0.2% and 3.0%, respectively, for HDR calibrations, but could exhibit more than double this variability characteristic of their leptokurtic distributions. For LDR calibrations, the spread and stability in a model's calibration ratio toward another seed type is extensive and notable. For some seed types and chamber models exhibit variations of <0.5% while others exceeded 2.0%. Furthermore, the magnitude of this dependence is outside the variability of the source's source strength due to manufacturing, which was determined from the manufacturer and NIST source strength intercomparison records at the UWADCL. As a result, establishing and disseminating calibration conversion factors among different source and chamber models is not advised as it would substantially increase the uncertainty in a clinical user's determination of source strength. The calibration of a well-type ionization chamber is unique to the chamber, source, and source holder. Attempting to generalize source strength calibration coefficients among chambers of the same model or source type is impractical given the variation in response observed across the calibration history of the UWADCL. Attempting to quantitate and transfer calibration coefficients in such a relative sense may significantly degrade the uncertainty relative to specifically calibrating a chamber for an individual source.

Estimation and comparison of integral dose to target and organs at risk in three-dimensional computed tomography image-based treatment planning of carcinoma uterine cervix with two high-dose-rate brachytherapy sources: 60Co and 192Ir.

Iridium-192 (192Ir) has been a widely accepted radioisotope for high-dose-rate (HDR) brachytherapy. Recently, Cobalt-60 (60Co) radioisotope with a longer half-life (5.26 years) has been gaining popularity due to economic and logistical reasons as compared with the traditional 192Ir. This study aimed to evaluate and compare the integral dose (ID) to the target and organs at risk (OARs) with two HDR brachytherapy sources in brachytherapy treatment of carcinoma uterine cervix to find appropriate HDR radioisotopes for clinical benefit. This is a retrospective analysis of 52 computed tomography image-based brachytherapy plans of 52 patients who have received intracavitary treatment with 192Ir HDR source. For each patient plan, one additional set of plan was created using 60Co source in place of 192Ir source keeping the same dwell position, and again dose was optimized. The volume and mean dose for target, OARs, and volume structures of 400%, 200%, 150%, 100%, and 50% were recorded for the estimation and comparison of ID. The mean ID to high-risk clinical target volume was significantly higher by 5.84% in 60Co plan than that in 192Ir plan. For OARs, the mean ID to the rectum was significantly higher by 2.60% in 60Co plan as compared to 192Ir plan, whereas for bladder and sigmoid colon, it was lower in 60Co plan than that in 192Ir plan. The mean ID of central dose volume structures of 400%, 200%, 150%, 100%, and 50% was higher by 12.97%, 9.77%, 8.16%, 6.10%, and 3.22%, respectively, in 60Co plan than that of 192Ir plan. The results of our study concluded that 192Ir HDR radioisotope should be preferred for intracavitary brachytherapy due to its ideal physical characteristics for better clinical outcomes.