Brachytherapy Quality Assurance Research Articles

Electromagnetic tracking for integrated quality assurance in breast interstitial brachytherapy: The impact of registration method.

Electromagnetic tracking (EMT) has great potential as a quality assurance tool in interstitial brachytherapy. Since its clinical application in most cases comprises a comparison with brachytherapy plan data, EMT registration and plan data are crucial. Registration uncertainties influence EMT outcomes and further decision-making processes. The impact of registration using four algorithms on the resulting data was investigated. Registration abilities of four sub-algorithms, which share the same principle of an iterative closest point approach were considered. Sub-algorithms differ regarding underlying mathematical norms, and also include a non-geometric implementation focusing on stochastic optimization. This study focused on the registration of point clouds originating from data obtained during treatment with interstitial brachytherapy in breast cancer patients. Data were acquired from a hybrid device prototype, capable of EMT measurements and data extracted from treatment plan. Main criteria for good registration performance were good geometric agreement, including low Euclidean distances between registered data sets as well as short registration time. In addition, previously published patient data with different than employed in the original publication algorithm were re-analyzed to further investigate the impact of registration method on clinically influential results. The stochastic algorithm presented much higher registration times, and earliest implementation of geometric approaches occasionally misaligned patient data. The remaining two algorithms performed almost identically resulted in sufficiently accurate registration performance. The re-analysis of previously published data demonstrated minor inconsistencies between former registration method and different algorithm; however, the overall trends with almost identical mean Euclidean distance of 2.22 mm (2.19 mm in the original work) could be reproduced. The choice of registration algorithm can influence the quality of registration. Therefore, it is advised to regularly examine the registration performance, especially in in-house programs.

Feasibility of using micro silica bead TLDs for in-Vivo dosimetry of CT-based HDR prostate brachytherapy: An experimental and simulation study

PurposeFeasibility of silica-based dosimeters for IVD of HDR prostate brachytherapy. Material and methodsPlastic dosimeter holders and a water-fillable prostate phantom were built in-house. Interstitial prostate brachytherapy and Monte Carlo simulations were performed. The treatment planning, Monte-Carlo simulation, and dosimetry results were compared. ResultsThe relative differences between TLD-TPS, TLD-MCNP, and TPS-MCNP were 0.2–6.9 %, 0.5–6.5 %, and 0.6–6.3 %, respectively. ConclusionMicro-silica bead dosimeters can perform offline in situ quality assurance in HDR prostate brachytherapy.

A comparative study on the accuracy of an automated multi-parameter high-dose-rate brachytherapy quality assurance system

This study aims to explore the measuring accuracy of an automated high-dose-rate brachytherapy (HDR BT) quality assurance system (hereinafter referred to as OriQA system) that could provide simultaneous measurements of dwell position, dwell time and source strength in a single test. Elekta-Flexitron was selected as the HDR BT afterloader, and measured the farthest transmission distance by source position simulator. Within the effective distance, we set dwell positions in two groups, specifically, plan_1 with an interval of 2.00 cm: 106.00 cm, 108.00 cm, 110.00 cm, 102.00 cm, 104.00 cm, 106.00 cm, 108.00 cm, and plan_2 with an interval of 0.20 cm: 111.40 cm, 111.60 cm, 111.80 cm, 112.00 cm, 112.20 cm, 112.40 cm, 112.60 cm. The measured values collected from OriQA device were compared with the data from traditional HDR BT QA tool (source position check ruler). Three groups of dwell time were set, specifically, plan_1: with fixed dwell time 2.00 s, plan_3 with interval 0.10 s: 3.70 s, 3.80 s, 3.90 s, 4.00 s, 4.10 s, 4.20 s, 4.30 s, and plan_4: fixed dwell time 5.00 s. Source strength was also measured continuously for a period of 10 weeks, and compared with the data collected from the well-chamber. The OriQA system showed reliable performance in the evaluation of measuring accuracy. The adjusted farthest transmission distance was 119.33 cm. And according to the time-position graph, the maximum deviation of dwell position between the measured and planned data was 0.34 mm, which was smaller than that between the ruler and planed data (0.75 mm). The maximum deviation of dwell time between the measured and planned data was 0.05 s. Fitting analysis revealed linear relationship between source strength Sk and the intensity detector response, with R2 = 0.9877, and intensity deviation fluctuated between 1.14% and 2.19%. Compared with the traditional QA tool, the OriQA device provided improved measuring accuracy and efficiency QA procedure for HDR BT.

Comparative evaluation of radiation detection capabilities of CsPbI2Br and CsPbIBr2 materials for the development of QA relative dosimeter for brachytherapy

High-dose-rate brachytherapy is a cancer treatment that intensively irradiates tumors by inserting radioactive isotopes with high dose rates into the body. For this treatment, it is necessary to deliver an appropriate dose to the tumor tissue through an accurate treatment plan but only deliver the minimum dose to the normal tissue. Therefore, it is imperative to verify the positional accuracy of the source through accurate quality assurance (QA) in clinical practice. However, in clinical practice, the position of the source is visually determined using rulers, automatic radiographers, video monitors, and other devices, yielding inaccurate results. In this study, a semiconductor dosimeter using either CsPbI2Br or CsPbIBr2 was manufactured. The radiation detectability of both materials was tested and compared to evaluate which of the two materials would be more suitable as the QA relative dosimeter for brachytherapy. The reproducibility, linearity, and percentage interval distance (PID) of the two materials were analyzed to evaluate the radiation detectability and applicability of the relative dosimeter. In the reproducibility evaluation, the relative standard deviation (RSD) of CsPbI2Br was 0.98%, and the RSD of CsPbIBr2 was 3.45%. In the linearity evaluation, the coefficient of determination (R2) of CsPbI2Br was 0.9998, and the R2 of CsPbIBr2 was 0.9994. In the PID evaluation, both materials showed an exponential and constant decrease in measured signal sizes as the distance from the source increased. As a result of the evaluations, the CsPbI2Br dosimeter showed greater stability in detecting radiation and satisfied the evaluation criteria. In conclusion, CsPbI2Br shows promise as a digital relative dosimeter for brachytherapy QA.

Suitability Assessment of CsPbI_3 Dosimeter with ^192Ir Source for Brachytherapy Quality Assurance

In brachytherapy, quality assurance (QA) is a prerequisite to minimize the dose irradiation to the healthy tissues in patients during treatment, as it evaluates the accuracy of the dose applied to the patients as well as the accuracy of the position of the irradiation. Therefore, a strong emphasis has been placed on brachytherapy QA in clinical practice. This study assessed the suitability of a CsPbI3 dosimeter for the brachytherapy QA system. To verify the reliability of the unit cell sensor fabricated with CsPbI3, the electrical parameters were evaluated, after which the position dependence of the sensor was analyzed. A high level of reliability (R 2 > 0.99) and reproducibility (relative standard deviation < 1.5%) were observed. The maximal value measured at the isocenter of the sensor as the distance of the dosimeter from the irradiation source was gradually decreased. When the optimal angle was assessed, the variation was as high as 5.01 nC depending on the form of the 192Ir source. Therefore, the CsPbI3 dosimeter fabricated in this study is a suitable substitute for the conventional QA dosimeter.

Determining The Accuracy of Dwell Position by Using Electron Energy with Gafchromic Film in High Dose Rate Brachytherapy Systems

Due to the general lack of darkroom and film processing equipment in many clinics, it is no longer possible to use radiation sensitive Xomat V radiographic film for High Dose Rate brachytherapy quality assurance. An alternative is to use radio chromic film that does not require processing. The aim of this study is to develop and clinically test the GafChromic film-based brachytherapy Quality Assurance (QA) system using different electron energies. As an electron source (6 MeV-9 MeV-12 MeV -15 MeV -18 MeV) (Elekta Synergy® Platform linear accelerator, Varian GM plus IX (Varian Medical Systems, Inc.USA), Varian brand cylinder, ring and tandem double ovoid applicators, RTQA2 and EBT3 GafChromic film were used. In RTQA2 films, images are obtained at high electron energies (12 MeV and above) at 300 Monitor Unit (MU), while images are obtained at all energies at 700 MU in irradiation using different electron energies and MUs. For the desired image quality depending on the material of the applicator used, it was determined that the image clarity increased as the energy, field size and MUs increased. In EBT3, the desired image could be obtained at 18 MeV and 2500 MU. It is possible to obtain the desired image quality by using high-energy electrons, especially RTQA2 Gafchromic film, in determining the accuracy of the dwell position in brachytherapy. Since it has been determined that this method can be used easily in quality control tests, we think that this method is suitable for clinical use when necessary.

Quality Assurance in Clinical Trials Requiring Radiation Therapy in Sub-Saharan Africa

Given the increasing availability of radiation therapy in sub-Saharan Africa, clinical trials that include radiation therapy are likely to grow. Ensuring appropriate delivery of radiation therapy through rigorous quality assurance is an important component of clinical trial execution. We reviewed the process for credentialing radiation therapy sites and radiation therapy quality assurance through the Imaging and Radiation Oncology Core (IROC) Houston Quality Assurance Center for AIDS Malignancy Consortium (AMC)-081, a multicenter study of cisplatin and radiation therapy for women with locally advanced cervical cancer living with HIV, conducted by the AIDS Malignancy Consortium at 2 sites in South Africa and Zimbabwe. Women living with HIV with newly diagnosed stage IB2, IIA (>4 cm), IIB-IVA cervical carcinoma (per the 2009 International Federation of Gynecology and Obstetrics [FIGO] staging classifications) were enrolled in AMC-081. They received 3-dimensional conformal external beam radiation therapy (EBRT) to the pelvis (41.4-45 Gy) using a linear accelerator, high-dose-rate brachytherapy (6-9 Gy to point A with each fraction and up to 4 fractions), and concurrent weekly cisplatin (40 mg/m2). IROC reviewed EBRT and brachytherapy quality assurance records after treatment. All of the 38 women enrolled in AMC-081 received ±5% of the protocol-specified prescribed dose of EBRT. Geometry of brachytherapy applicator placement was scored as per protocol in all implants. Doses to points A and B, International Commission on Radiation Units and Measurements (ICRU) bladder, or ICRU rectum required correction by IROC in >50% of the implants. In the final evaluation, 58% of participants (n=22) were treated per protocol, 40% (n=15) had minor protocol deviations, and 3% (n=1) had major protocol deviations. No records were received within 60 days of treatment completion as requested in the protocol. Major radiation therapy deviations were low, but timely submission of radiation therapy data did not occur. Future studies, especially those that include specialized radiation therapy techniques such as stereotactic or intensity-modulated radiation therapy, will require pathways to ensure timely and adequate quality assurance.

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.

On the potential of 2D ion chamber arrays for high-dose rate remote afterloading brachytherapy quality assurance

Objective. To investigate the potential of 2D ion chamber arrays to serve as a standalone tool for the verification of source strength, positioning and dwell time, within the framework of 192Ir high-dose rate brachytherapy device quality assurance (QA). Approach. A commercially available ion chamber array was used. Fitting of a 2D Lorentzian peak function to experimental data from a multiple source dwell position irradiation on a frame-by-frame basis, facilitated tracking of the source center orthogonal projection on the array plane. For source air kerma strength verification, Monte Carlo simulation was employed to obtain a chamber array- and source-specific correction factor of calibration with a 6 MV photon beam. This factor converted the signal measured by each ion chamber element to air kerma in free space. A source positioning correction was also applied to lift potential geometry mismatch between experiment and Monte Carlo simulation. Main results. Spatial and temporal accuracy of source movement was verified within 0.5 mm and 0.02 s, respectively, in compliance with the test endpoints recommended by international professional societies. The source air kerma strength was verified experimentally within method uncertainties estimated as 1.44% (k = 1). The source positioning correction method employed did not introduce bias to experimental results of irradiations where source positioning was accurate. Development of a custom jig attachable to the chamber array for accurate and reproducible experimental set up would improve testing accuracy and obviate the need for source positioning correction in air kerma strength verification. Significance. Delivery of a single irradiation plan, optimized based on results of this work, to a 2D ion chamber array can be used for concurrent testing of source position, dwell time and air kerma strength, and the procedure can be expedited through automation. Chamber arrays merit further study in treatment planning QA and real time, in vivo dose verification.

First clinical experience with a novel, mobile cone-beam CT system for treatment quality assurance in brachytherapy

Background and purposeOn-site cone-beam computed tomography (CBCT) has gained in importance in adaptive brachytherapy during recent years. Besides treatment planning, there is increased need particularly for image-guidance during interventional procedures and for image-guided treatment quality assurance (QA). For this purpose, an innovative CBCT device was rolled out at our hospital as the first site worldwide. We present the first clinical images and experiences.Materials and methodsThe novel CBCT system is constructed of a 121 cm diameter ring gantry, and features a 43.2 × 43.2 cm2 flat-panel detector, wireless remote-control via tablet-PC, and battery-powered maneuverability. Within the first months of clinical operation, we performed CBCT-based treatment QA for a total of 26 patients (8 with breast, 16 with cervix, and 2 with vaginal cancer). CBCT scans were analyzed regarding potential movements of implanted applicators in-situ during the brachytherapy course.ResultsWith the presented device, treatment QA was feasible for the majority of patients. The CBCT scans of breast patients showed sufficient contrast between implanted catheters and tissue. For gynecologic patients, a distinct visualization of applicators was achieved in general. However, reasonable differentiations of organic soft tissues were not feasible.ConclusionThe CBCT system allowed basic treatment QA measures for breast and gynecologic patients. For image-guidance during interventional brachytherapy procedures, the current image quality is not adequate. Substantial performance enhancements are required for intraoperative image-guidance.

Influence and compensation of patient motion in electromagnetic tracking based quality assurance in interstitial brachytherapy of the breast.

Electromagnetic tracking (EMT) is a versatile and viable technique for various quality assurance (QA) tasks in interstitial brachytherapy (iBT). As the duration of EMT measurements in iBT is on the order of minutes, they can be strongly affected by patient motion, especially breathing, which gives rise to motion artefacts. Since the centrepiece of EMT-related QA in iBT is to assess the geometry of the iBT implant or applicator, the absence of adequate motion compensation techniques could impede the use of EMT for QA purposes. A common way to compensate for this is to reference the data to either external or internal reference sensors (ERS, IRS) which are fixated on the patient's body or inside the applicator and therefore move with the patient. The purpose of the presented study is to provide a quantitative and in-depth analysis on the use of reference sensors for motion compensation. First, the need for adequate motion compensation is identified both qualitatively and quantitatively using a phantom subjected to simulated breathing motion. An evaluation routine is developed to assess the influence of motion compensation using reference sensors on the acquired EMT data. The evaluation metric is based on the observed displacement of the EMT sensor from its mean position while dwelling at a dwell position (DP) for a dwell time of 1 s. After that, the routine is applied to a cohort of 54 breast cancer patients treated with iBT, and the quality of an ERS based compensation approach is assessed. In a subgroup of four patients, an IRS is inserted into the iBT implant and IRS-based compensation is compared to the ERS-based approach. Moreover, a correlation analysis of the ERS and IRS approach is performed, also including respiratory signals derived from the trajectories of the different reference sensors. It was found that motion compensation with ERS effectively reduced the mean sensor displacement per DP to median values as low as 0.11 mm in both phantom and patient measurements, which is below the precision of the EMT system (0.48 mm). Compensation using the IRS yielded comparable results and was as good as compensation with ERS. The results obtained from both approaches showed a strong correlation. Also the respiratory signals calculated from the different reference sensors were well correlated in most cases. These results indicate that motion compensation with ERS can effectively remove motion artefacts in EMT data. While compensation with an IRS leads to comparable results, the IRS occupies one catheter whose geometry hence cannot be assessed. The use of ERS has proven to be both effective and practical in clinical routine.

Development and evaluation of lead(II) iodide-based polycrystalline digital dosimeter for quality assurance in brachytherapy

Brachytherapy is a cancer treatment that involves intensively irradiating a tumor by placing a sealed radioactive isotope inside the body. Determining the position of the source through accurate quality assurance (QA) is important, because brachytherapy uses radioactive isotope sources with high dose rates. However, in clinical practice, the source position is determined with the naked eye through the use of a ruler, autoradiograph, video monitor, etc., which yields inaccurate results. Therefore, in this study, a lead (II) iodide (PbI2) based polycrystalline digital dosimeter that can measure the relative dose was developed for the QA of the brachytherapy device, and its applicability was evaluated in terms of reproducibility, linearity, percentage interval distance (PID), and angular dependence. Reproducibility evaluation yielded a relative standard deviation value of 1.41%, which satisfied the evaluation criterion of 1.5%. The linearity evaluation yielded an R2 value of 0.9993, which satisfied the evaluation criterion of 0.9990. The PID evaluation revealed that, as the distance from the source increased, the signal decreased according to the inverse-square law. When the PbI2-based digital dosimeter was rotated up to 45°, a difference of up to 13.20% in the angular dependence was observed. Thus, the dosimeter fabricated in this experiment met all the criteria of the aforementioned evaluations. Therefore, it is considered to be highly applicable as a dosimeter for the QA of brachytherapy devices.

Performance evaluation of lead-monoxide dosimeter with parylene coating for quality assurance of brachytherapy devices

The source position of irradiation is identified using a method that uses rulers and films for quality assurance (QA) in brachytherapy. However, this method involves a high probability of errors, because the scales are checked using the naked eye, and QA is indirectly performed using photographs. Lead monoxide (PbO) is widely used as a semiconductor dosimeter, because it is a photoconductor that generates electrons in response to electromagnetic waves. Moreover, PbO has excellent sensitivity to reflected rays, owing to its high atomic number (Z Pb: 82, Z O: 8) and density (ρPbO: 9.53 g/cm3). We applied PbO to a dosimeter for QA in a brachytherapy device and attempted to increase the signal stability with a parylene coating for performance improvement. Subsequently, a comparative analysis was performed with a PbO dosimeter that was not coated with parylene to determine whether the fabricated dosimeter is applicable as a dosimeter for QA of the brachytherapy device, by analyzing the reproducibility, linearity, percentage interval distance (PID), and angular dependence in the 192Ir source used for brachytherapy. The RSD of the non-parylene PbO dosimeter was 0.85%, and the RSD of the parylene PbO dosimeter was 0.40% in the reproducibility results. In the linearity evaluation results, the R 2 value of the non-parylene PbO dosimeter was 0.9996, and that of the parylene PbO dosimeter was 0.9997 In the PID evaluation results, the difference in the intensity distribution measured according to the distance due to the dose was attenuated at the coated parylene in the case of the parylene PbO dosimeter. Therefore, adjustments using correction coefficients are required for suitable performance. In the angular dependence evaluation results, the parylene PbO dosimeter had 3.44% less angular dependence than the non-parylene dosimeter at an angle of 45°. The parylene-coated PbO dosimeter showed better performance than the non-parylene-coated PbO dosimeter in terms of the reproducibility, linearity, and angular dependence. Therefore, it is considered that the parylene-coated PbO dosimeter can be implemented for QA of brachytherapy devices.

A Machine-Learning Based Method for Inter-Institutional QA of MR-Based Brachytherapy Treatment Planning in Cervical Cancer

Inter-institutional quality assurance (QA) of brachytherapy (BT) treatment planning is often based on expert judgment of a limited number of treatment plans. Cohort comparisons are of limited value as patient anatomy has a major impact on organs-at-risk (OAR) dose. Therefore, the aim of this study was to develop and test a QA tool that predicts OAR dose based on patient anatomy.60 Patients (120 plans) from institute A (data A) and 14 patients (32 plans) from institute B (data B) were included, treated in accordance with EMBRACE II guidelines. Additionally, 71 MR-guided BT pre-EMBRACE II plans (71 patients) from institute B were included (data B'). Histograms of the overlap (OVHs) between delineated OARs and the high-risk CTV were used to objectify patient anatomy. Dimensionality of the OVH data was reduced by principal component analysis. A random-forest model was fitted to training OVHs and DVHs. Model performance was evaluated using leave-one-out cross-validation for data A. Then, different models were created and tested based on data splits according to institute (A versus B and A versus B'), applicator type (ovoid versus ring), application type (IC versus IC+IS). The models predict DVHs from OVHs, from which the D2cm3 of the OARs was computed. Model performance based on data A was evaluated by calculating the distribution (σ) of the difference between planned and predicted D2cm3 values (D2cm3, pl-pr), and the Pearson correlation coefficient (r) of these values. For the models based on the data splits it was tested if the D2cm3, pl-pr values fell within the 95%-confidence interval (CI) of the D2cm3, pl-pr values from data A.Leave-one-out validation of the model based on data A demonstrated predictability of the D2cm3 values for all OARs (bladder r = 0.64, rectum r = 0.75, sigmoid r = 0.88, small bowel r = 0.92). The distribution of D2cm3, pl-pr values was relatively constant for all OARs (bladder σ = 0.61 Gy, rectum σ = 0.56 Gy, sigmoid σ = 0.48 Gy, small bowel σ = 0.53 Gy). For the different data splits, models trained on one applicator or application type could predict D2cm3 values for the other applicator or application type within the CI. Training on data A and testing on data B resulted in predicted bladder D2cm3-values within the CI for 30/32 plans. In contrast, only 42/71 plans of data B' fit within the CI (Chi-squared test, P < 0.001).Our OVH-based model can predict D2cm3 values for all applicable OARs in a multi-center setting. The models are robust against differences in applicator and application type, and are sufficiently sensitive to distinguish differences in planning protocols. We believe that OVH-based QA can play an important role to assure treatment plan quality in multi-institutional studies.

Performance Evaluation of Lead (II) Oxide Dosimeter for Digital Quality Assurance in Brachytherapy

Performance Evaluation of Lead (II) Oxide Dosimeter for Digital Quality Assurance in Brachytherapy

Automated multi-parameter high-dose-rate brachytherapy quality assurance via radioluminescence imaging

The purpose of this study is to leverage radioluminescence imaging for the development of an automated high-dose-rate (HDR) brachytherapy quality assurance (QA) system that enables simultaneous measurements of dwell position, dwell time, wire velocity, and relative source strength in a single test. The system consists of a radioluminescence phosphor sheet (a mixture of Gd2O2S:Tb and PDMS) positioned atop a HDR needle applicator, a complementary metal-oxide-semiconductor digital camera used to capture the emitted radioluminescence signals from the scintillator sheet, and an in-house graphical user interface for signal processing. The signal processing was used to extract source intensity, location, and elapsed time, yielding the final measurements on dwell position, dwell time, and wire velocity. The source strength relative to the well chamber calibration (in unit of Air-Kerma strength, Sk ) is measured by establishing a calibration curve that correlates Sk with the detector response. Validation experiments are performed using three customized treatment plans. With these plans, the dwell position and dwell time are verified for a range of 110.0 cm–117.5 cm and 2 s–16 s, respectively, and the linear correlation with Sk is demonstrated for the source strength varying between 28 348 U (cGy cm2 h−1) and 41 906 U. The wire velocity, i.e. the speed of the radioactive source averaged over the distance in between dwell positions, is calculated for various distances ranging from 5 mm to 50 mm. Results show that the mean deviations of the measured dwell position and dwell time are 0.1 mm (range from 0 to 0.2 mm) and 32.5 ms (range from 0 to 60.0 ms) with respect to the planned values, respectively, and the system response is highly linear with Sk ( R2 = 0.998). Moreover, the measured wire velocities are comparable to previously reported values. Benefitting from the compact hardware design and image processing algorithms, the system provides a practical, reliable, and comprehensive solution for HDR QA.

Brachytherapy quality assurance in the PORTEC-4a trial for molecular-integrated risk profile guided adjuvant treatment of endometrial cancer

ObjectiveThe PORTEC-4a trial investigates molecular-integrated risk profile guided adjuvant treatment for endometrial cancer. The quality assurance programme included a dummy run for vaginal brachytherapy prior to site activation, and annual quality assurance to verify protocol adherence. Aims of this study were to evaluate vaginal brachytherapy quality and protocol adherence. MethodsFor the dummy run, institutes were invited to create a brachytherapy plan on a provided CT-scan with the applicator in situ. For annual quality assurance, institutes provided data of one randomly selected brachytherapy case. A brachytherapy panel reviewed and scored the brachytherapy plans according to a checklist. ResultsAt the dummy run, 15 out of 21 (71.4%) institutes needed adjustments of delineation or planning. After adjustments, the mean dose at the vaginal apex (protocol: 100%; 7 Gy) decreased from 100.7% to 99.9% and range and standard deviation (SD) narrowed from 83.6–135.1 to 96.4–101.4 and 8.8 to 1.1, respectively. At annual quality assurance, 22 out of 27 (81.5%) cases had no or minor and 5 out of 27 (18.5%) major deviations. Most deviations were related to delineation, mean dose at the vaginal apex (98.0%, 74.7–114.2, SD 7.6) or reference volume length. ConclusionsMost feedback during the brachytherapy quality assurance procedure of the PORTEC-4a trial was related to delineation, dose at the vaginal apex and the reference volume length. Annual quality assurance is essential to promote protocol compliance, ensuring high quality vaginal brachytherapy in all participating institutes.

Development of an HDR-BT QA tool for source position verification.

PurposeThis study aimed to develop a high‐dose‐rate brachytherapy (HDR‐BT) quality assurance (QA) tool for verification of source positions, and to report on its effectiveness.MethodsWe fabricated a cuboid phantom measuring 30 × 30×3 cm3 with spaces to embed Fletcher‐Williamson tandem and ovoid applicators. Lead‐based, cylindrically shaped radiopaque markers, which scatter radiation and blacken the Gafchromic® RTQA2 films placed on the applicators, were inserted into the phantom to determine the applicator tip and reference source positions. A three‐dimensional image‐guided brachytherapy (3D‐IGBT) plan was generated, and the source positions on the film and radiation treatment planning system (RTPS) were verified with the tool. Source position errors were evaluated as the distance in the applicator axis direction between the source position and the center position of two radiopaque marker pairs.ResultsSource position errors on the film and RTPS were in good agreement with one another and were all within 0.5 mm for all applicators. Offset values of each applicator were in good agreement with the value determined in treatment planning (6 mm). The expanded measurement uncertainty of our QA tool was estimated to be 0.87 mm, with a coverage factor k of 2.ConclusionsOur new HDR‐BT QA tool developed for comprehensive source position verification will be useful for cross checking actual source positions and planned source positions on the RTPS.

End-to-end delivery quality assurance of computed tomography–based high-dose-rate brachytherapy using a gel dosimeter

PurposeThe purpose of this study was to develop a novel quality assurance (QA) program to check the entire treatment chain of image-guided brachytherapy with dose distribution evaluation in a single setup and irradiation using a gel dosimeter. Methods and MaterialsA polymer gel was used, and the readout was performed by magnetic resonance scanning. A CT-based treatment plan was generated using the Oncentra planning system (Elekta, Sweden), and irradiation was performed three times using an afterloading device with an Ir-192 source. The dose-response curve of the gel was created using 6-MV X-ray, which is independent of the source beams. Planar gamma images on a coronal plane along the source transport axis were calculated using the measured dose as a reference, and the calculated doses were used in several error simulations (no error; 2.0 or 2.5 mm systematic and random source dwell mispositioning; and dose error of 2%, 5%, 10%, and 20%). ResultsThe dose-R2 (spin-spin relaxation rate) conversion table revealed that the uncertainty and dose resolution of 6-MV X-ray were better than those of Ir-192 and also constant between the three measurements. With the 3%/1 mm criteria, there were statistically significant differences between each pair of settings except dose error of 2% and 5%. ConclusionThis work depicts a simple and efficient end-to-end test that can provide a clinically useful tool for QA of image-guided brachytherapy. In this QA program, air kerma strength and dwell position setting could also be verified. This test can also distinguish between different types of error.

Error detection using an electromagnetic tracking system in multi-catheter breast interstitial brachytherapy

The hybrid treatment delivery system (HTDS) has been proposed as a possible option for a quality assurance in the multi-catheter interstitial brachytherapy for breast cancer patients. The system, which consists out of a prototype afterloader with an integrated electromagnetic tracking (EMT) sensor and an EMT system, allows the automatic measurement of implanted catheters.To test the feasibility of the system for error detection, possible treatment planning errors and treatment delivery errors were simulated. Planning errors such as an incorrect offset value, an incorrect indexer length, tip/connector end swaps, and partial swaps, and; treatment delivery errors such as catheter shifts and catheter connection swaps were manually simulated using phantoms. An in-house Matlab routine was used to assess geometrical deviations between the dwell positions defined based on CT and EMT measurement. Additionally, the influence of implant motion on the detection ability of the system was assessed. An algorithm for the detection and specification of errors based on the error simulation results was developed. At the University Hospital Erlangen, a patient study is ongoing, where errors in patient data were analyzed using the proposed algorithm.All simulated planning errors were detected. Catheter connection swaps can be detected 100% of the time. A shift detection rate of >97% was observed for shifts larger than 1.1 mm, both in the static and the motion measurements. Catheter reconstruction uncertainties and catheter shifts <2 mm were found to be the most common treatment planning and delivery errors in patient data. HTDS proved to be a reliable method for error detection.