High Dose Rate Treatment Research Articles

Curvilinear catheter implantation in HDR prostate brachytherapy: feasibility study.

High-dose-rate (HDR) brachytherapy (BT) has been acknowledged as a widely utilized treatment for patients with intermediate- and high-risk prostate cancer, despite its side effects such as edema, incontinence, and impotence. Nevertheless, the treatment is consistently limited by the potential danger of excessive irradiation to organs-at-risk (OARs) like the urethra, bladder, and rectum. This study aims to introduce curvilinear catheter implantation in the prostate gland for HDR treatment. The objective is to improve the radiation dose distribution by offering access channels conformal to the prostate anatomy. This approach seeks to minimize toxicity to nearby OARs while utilizing a reduced number of needles, potentially leading to improved clinical outcomes. Curvilinear catheters were first pre-planned for an anonymized patient using Oncentra treatment planning system (TPS) and hybrid inverse planning optimization (HIPO) algorithm. The trajectories of the catheters were then analyzed using MATLAB to extract their radius of curvature. Tendon-driven active needles were then used to implant curvilinear catheters inside an anthropomorphic phantom. Proposed curvilinear catheter implantation resulted in significant improvement in terms of dosimetric constraints to the OARs and coverage to the prostate. Tendon-driven active needles were shown to be capable of realizing the required pre-planned curvatures inside prostate. It was shown that the active needle can realize a desired radius of curvature and a desired trajectory with an average accuracy of 9.1±8.6 and 1.27±0.50mm in air and inside a tissue-mimicking phantom, respectively. This work demonstrates the feasibility of using tendon-driven active curvilinear catheter implantation in prostate to improve the outcomes of HDR-BT via improved radiation dose distribution to the prostate and reduced toxicity to the OARs.

Characterization of a flexible a-Si:H detector for in vivo dosimetry in therapeutic x-ray beams.

The increasing use of complex and high dose-rate treatments in radiation therapy necessitates advanced detectors to provide accurate dosimetry. Rather than relying on pre-treatment quality assurance (QA) measurements alone, many countries are now mandating the use of in vivo dosimetry, whereby a dosimeter is placed on the surface of the patient during treatment. Ideally, in vivo detectors should be flexible to conform to a patient's irregular surfaces. This study aims to characterize a novel hydrogenated amorphous silicon (a-Si:H) radiation detector for the dosimetry of therapeutic x-ray beams. The detectors are flexible as they are fabricated directly on a flexible polyimide (Kapton) substrate. The potential of this technology for application as a real-time flexible detector is investigated through a combined dosimetric and flexibility study. Measurements of fundamental dosimetric quantities were obtained including output factor (OF), dose rate dependence (DPP), energy dependence, percentage depth dose (PDD), and angular dependence. The response of the a-Si:H detectors investigated in this study are benchmarked directly against commercially available ionization chambers and solid-state diodes currently employed for QA practices. The a-Si:H detectors exhibit remarkable dose linearities in the direct detection of kV and MV therapeutic x-rays, with calibrated sensitivities ranging from (0.580±0.002) pC/cGy to (19.36±0.10) pC/cGy as a function of detector thickness, area, and applied bias. Regarding dosimetry, the a-Si:H detectors accurately obtained OF measurements that parallel commercially available detector solutions. The PDD response closely matched the expected profile as predicted via Geant4 simulations, a PTW Farmer ionization chamber and a PTW ROOS chamber. The most significant variation in the PDD performance was 5.67%, observed at a depth of 3mm for detectors operated unbiased. With an external bias, the discrepancy in PDD response from reference data was confined to±2.92% for all depths (surface to 250mm) in water-equivalent plastic. Very little angular dependence is displayed between irradiations at angles of 0° and 180°, with the most significant variation being a 7.71% decrease in collected charge at a 110° relative angle of incidence. Energy dependence and dose per pulse dependence are also reported, with results in agreement with the literature. Most notably, the flexibility of a-Si:H detectors was quantified for sample bending up to a radius of curvature of 7.98mm, where the recorded photosensitivity degraded by (-4.9±0.6)% of the initial device response when flat. It is essential to mention that this small bending radius is unlikely during in vivo patient dosimetry. In a more realistic scenario, with a bending radius of 15-20mm, the variation in detector response remained within±4%. After substantial bending, the detector's photosensitivity when returned to a flat condition was (99.1±0.5)% of the original response. This work successfully characterizes a flexible detector based on thin-film a-Si:H deposited on a Kapton substrate for applications in therapeutic x-ray dosimetry. The detectors exhibit dosimetric performances that parallel commercially available dosimeters, while also demonstrating excellent flexibility results.

A two-center experience: The impact of COVID-19 on two brachytherapy programs in Ontario - virtual care, service suspension and radiation therapy workflow

IntroductionMost brachytherapy (BT) procedures require general anesthesia and are therefore considered aerosol generating medical procedures (AGMPs). The COVID-19 pandemic impacted BT as services were prioritized by balancing the harm associated with COVID-19 infection versus the effect of delay of potentially curative treatment. This article summarizes the impact of the pandemic on BT programs in two cancer centers in a Canadian province. MethodsAs part of a quality assurance project, a retrospective study was conducted for the first five months of the pandemic (March 1 to July 31, 2020). Chart review and COVID-19 related mitigation strategies were identified by BT Clinical Specialist Radiation Therapists (bCSRT) in each center using electronic medical records, departmental reports, policies and procedures. ResultsImpact included start of virtual care (VC), shortened fractionation, suspension of services and workflow changes. Both centers implemented VC strategies to reduce clinic visits: “same-day size and treat” strategy for post-operative endometrial cancer patients and virtual patient education for all patients. BT services that were suspended were low-dose-rate and high-dose-rate (HDR) prostate treatments (Center 1), lung and esophagus HDR treatments (Center 2). Workflow changes that affected staff and patients in both centers included COVID-19 screening and the use of personal protective equipment. The centers were marginally different in workflow adjustments for AGMP procedures. Those considered high-risk AGMP and low-risk cancer were suspended temporarily with alternate treatment strategies sought for some patients. Others had temporizing treatment such as androgen deprivation therapy to facilitate oncological safe deferral of procedures. ConclusionBoth BT programs delivered treatment to most patients with minimal delays and cancellations, where feasible. Some of the pandemic workflow changes continued to the current state of the pandemic. Long-term follow-up is needed to assess the impact of COVID-19 and treatment interruptions on oncologic outcomes.

Treatment verification in high dose rate brachytherapy using a realistic 3D printed head phantom and an imaging panel

Even though High Dose Rate (HDR) brachytherapy has good treatment outcomes in different treatment sites, treatment verification is far from widely implemented because of a lack of easily available solutions. Previously it has been shown that an imaging panel (IP) near the patient can be used to determine treatment parameters such as the dwell time and source positions in a single material pelvic phantom. In this study we will use a heterogeneous head phantom to test this IP approach, and simulate common treatment errors to assess the sensitivity and specificity of the error-detecting capabilities of the IP. A heterogeneous head-phantom consisting of soft tissue and bone equivalent materials was 3D-printed to simulate a base of tongue treatment. An High Dose Rate treatment plan with 3 different catheters was used to simulate a treatment delivery, using dwell times ranging from 0.3 s to 4 s and inter-dwell distances of 2 mm. The IP was used to measure dwell times, positions and detect simulated errors. Measured dwell times and positions were used to calculate the delivered dose. Dwell times could be determined within 0.1 s. Source positions were measured with submillimeter accuracy in the plane of the IP, and average distance accuracy of 1.7 mm in three dimensions. All simulated treatment errors (catheter swap, catheter shift, afterloader errors) were detected. Dose calculations show slightly different distributions with the measured dwell positions and dwell times (gamma pass rate for 1 mm/1% of 96.5%). Using an IP, it was possible to verify the treatment in a realistic heterogeneous phantom and detect certain treatment errors.

PO09: Treatment of Facial Folliculotropic Mycosis Fungoides with High Dose Rate Brachytherapy in Two Fractions

<h3>Purpose</h3> To describe the treatment and outcomes for the treatment of folliculotropic mycosis fungoides (FMF) with high dose rate (HDR) brachytherapy in the facial area with complex topography. <h3>Materials and Methods</h3> A 68-year-old male with past medical history of morbid obesity status post gastric bypass, diabetes mellitus, hypertension, and atrial fibrillation was diagnosed with FMF of the face, scalp, trunk and extremities. Patient was referred to radiation therapy due to severe burning pain and pruritus of facial lesions on the nose, upper lip, and left temple after no response with UVA therapy. Electron beam therapy was initially chosen with a prescription of 3600 cGy in 20 fractions, but the resulting treatment plans were highly non-conformal with large dose heterogeneity and poor target coverage. HDR brachytherapy was pursued as an alternate treatment option with a prescription dose of 800 cGy in 2 fractions. Patient setup for simulation included a custom Freiburg flap applicator on an Aquaplast mask using 18 catheters to cover all lesions. Patient was scanned with pink bolus in the nostrils, a lead shield under the lip, and a bite block. Treatment planning was performed using Oncentra (Elekta, Stockholm, Sweden). HDR treatment was delivered using an Elekta Flexitron remote afterloader unit. Bilateral internal tungsten eye shields (Civco, Orange City, IA) were placed prior to treatment to reduce ocular dose. <h3>Results</h3> The drawn target was 25.2cc along the upper lip, bilateral nose, right medial canthus, and left temple. Achieved target coverage was V90% = 98.6%, D90% = 100.5%, and D95% = 95.9%. Skin V150% was 0.12cc. Without eye shield placement, right and left eye D0.01cc were 117.9% and 78.2%, respectively. Right and left lens doses were 99.1% and 69.4%, respectively. Average fractional delivery time was 603.5 seconds with an air kerma strength of 39.0 mGy*m²/s (apparent activity 9.7 Ci). Patient tolerated treatment without complications. At two week follow up, patient showed grade 1 dermatitis of the treatment area with erythema and mild desquamation. Patient has been asymptomatic six months post treatment. <h3>Conclusions</h3> Low dose HDR brachytherapy can be an effective treatment for facial FMF lesions with complex topography. It allows for suitable target coverage and normal tissue sparing, a shorter treatment course when compared to electron beam radiotherapy, and is associated with minimal adverse effects and rapid clinical response. It also allows sparing total skin electron therapy for the future in case of disease progression as the volume of tissue receiving radiation is very small. Figure 1a: Oncentra treatment plan in axial, sagittal, and coronal planes, with 3D rendering show in bottom right. Target volume in light blue, right eye in green, and left eye in blue. 1b shows wires outlining the target volume (top); pre-mask setup with pink bolus, bite block, gauze in the nostrils, and bilateral eye shields (middle); and final treatment setup with mask (bottom). 1c shows the pre-treatment lesions, and 1d shows the same area four months post treatment.

Concurrent kilovoltage CBCT imaging and megavoltage beam delivery: suppression of cross-scatter with 2D antiscatter grids and grid-based scatter sampling

Objective. The concept of using kilovoltage (kV) and megavoltage (MV) beams concurrently has potential applications in cone beam computed tomography (CBCT) guided radiation therapy, such as single breath hold scans, metal artifact reduction, and simultaneous imaging during MV treatment delivery. However, MV cross-scatter generated during MV beam delivery degrades CBCT image quality. To address this, a 2D antiscatter grid and a cross-scatter correction method were investigated in the context of high dose MV treatment delivery. Approach. A 3D printed, tungsten 2D antiscatter grid prototype was utilized in kV CBCT scans to reduce MV cross-scatter fluence during concurrent MV beam delivery. Remaining cross-scatter in projections was corrected by using the 2D grid itself as a cross-scatter intensity sampling device, referred to as grid-based scatter sampling (GSS). To test this approach, kV CBCT acquisitions were performed while delivering 6 and 10 MV beams, mimicking high dose rate treatment delivery scenarios. kV and MV beam deliveries were not synchronized to eliminate MV beam delivery interruption. MV cross-scatter suppression performance of the proposed approach was evaluated in projections and CBCT images of phantoms. Main results. 2D grid reduced the intensity of MV cross-scatter in kV projections by a factor of 3 on the average, when compared to conventional antiscatter grid. Remaining cross scatter as measured by the GSS method was within 7% of measured reference intensity values, and subsequently corrected. CBCT image quality was improved substantially during concurrent kV–MV beam delivery. Median Hounsfield Unit (HU) inaccuracy was up to 182 HU without our methods, and it was reduced to a median 6.5 HU with our 2D grid and scatter correction approach. Our methods provided a factor of 2–6 improvement in contrast-to-noise ratio. Significance. This investigation demonstrates the utility of 2D antiscatter grids and grid-based scatter sampling in suppressing MV cross-scatter. Our approach successfully minimized the effects of MV cross-scatter in concurrent kV CBCT imaging and high dose MV treatment delivery scenarios. Hence, robust MV cross-scatter suppression is potentially feasible without MV beam delivery interruption or compromising kV image acquisition rate.

Incorporating Treatment Time into Butterfly Optimization to Reduce Total Treatment Time for Vaginal Cylinder Brachytherapy.

PurposeFor patient comfort and safety, irradiation times should be kept at a minimum while maintaining high treatment quality. In this study of high dose rate (HDR) therapy with a vaginal cylinder, we used the butterfly optimization algorithm (BOA) to simultaneously optimize individual dwell times for precise dose conformity and for the reduction of total dwell time.Material and methodsBOA is a population-based, meta-heuristic algorithm that averts local minima by conducting intensive local and global searching based on switching probability. We constructed an objective function (a stimulus intensity function) that consisted of two components. The first one was the root-mean-squared dose error (RMSE) defined as the square root of the sum of squared differences between the prescribed and delivered dose at the constraint points. The second component was weighted total treatment time. Eight previously treated cases were retrospectively reviewed by re-optimizing the clinical treatment plans with BOA. ResultsCompared to the eight original plans generated with the commercial adaptive volume optimization algorithm (AVOA), the BOA-optimized plans reduced treatment times by 5.4% to 8.9%, corresponding to a time-saving of 13.1 to 47.7 seconds with the activities on the treatment day and saving from 29.3 to 64.6 seconds if treated with an activity of 5 CI. Dose deviations from the prescription were smaller than in the original plans.Conclusion Dose optimizations based on the BOA algorithm yield closer dose conformity in vaginal HDR treatment than AVOA. Incorporating total treatment time into the optimization algorithm reduces the delivery time while having only a small effect on dose conformity.

Feasibility of magnetic resonance-only high-dose-rate surface brachytherapy for clinical application.

In this article, we investigate the feasibility of magnetic resonance (MR)-only imaging for high-dose-rate (HDR) surface brachytherapy (SABT). We examined whether a standard CT-based planning can be replaced with an MR-only planning. For this purpose, the MRI digitization and plan quality check processes were compared against the standard CT-based processes. A prospective clinical implementation of the MR-only planning was evaluated on a clinical data set. A pointwise encoding time reduction with radial acquisition (PETRA) sequence was optimized for visualization of Freiburg flap (FF) on MR images. MR and conventional CT images were acquired with a FF applicator (Elekta, Stockholm, Sweden) placed on the following phantoms: (1) flat styrofoam (FST), FF locked-in placed with supporting structure; (2) cast-made facemask, and (3) porcine leg (PL). Catheters were digitized and activated with 10mm step size on Oncentra Brachy 4.5.3 Treatment Planning System. The CT-only and MR-only treatment plans were generated by optimizing the dose to the target defined as volume at 3mm skin depth. To compare the plans, the MRI-to-CT alignment was performed via rigid registration. Positional displacements of dwell positions between CT and MR plans were compared on the FST phantom and the relative percent dose difference in 2210 different points from CT or MR-only plans was compared. For all three phantoms, the comparabilities between CT and MR-only plans were assessed by calculating dice similarity coefficient (DSC) for volumes enclosing 150%, 125%, 100%, 95%, 90%, 80%, and 65% isodose lines (V150 -V65 ). The MR images of FF placed on the forearm of a healthy subject were acquired with this optimized PETRA sequence and used for treatment planning. The relative percent dose was calculated on 140 representative points placed at 3mm skin depth to evaluate the dose to the skin. Using the optimized PETRA sequence, MRTP digitization accuracy was<1mm in each dimension and on three-dimensional (3D) displacement for the FST phantom. In each phantom and clinical data set, it was possible to generate MR-only treatment plans with the 3mm skin depth prescription. In the FST phantom, the mean relative dose at the points was not significantly different(<0.1% difference) for CT or MR-based plans. The assessment of similarities in dose profiles between CT and MR-only plans' provided DSC values greater than 0.96, 0.92, and 0.73 for all volumes enclosing up to 100%, 125%, and 150% isodose lines, respectively. The feasibility of generating a HDR treatment plan with FF using MR-only has been evaluated in phantoms with varying geometry and for a clinical data set. The optimization of a standard MRI sequence-PETRA-implemented in this study showed that FF-based catheters can be digitized and a plan can be generated using only MRI. The resulting MR-only plans were comparable to the conventional CT-based plans, suggesting that MRI alone can generate clinically acceptable plans for FF in phantoms and on a clinical data set. Reliable MR-only treatment planning could improve treatment prescription through more accurate characterization of soft tissue targets.

Catheter position prediction using deep-learning-based multi-atlas registration for high-dose rate prostate brachytherapy.

High-dose-rate (HDR) prostate brachytherapy involves treatment catheter placement, which is currently empirical and physician dependent. The lack of proper catheter placement guidance during the procedure has left the physicians to rely on a heuristic thinking-while-doing technique, which may cause large catheter placement variation and increased plan quality uncertainty. Therefore, the achievable dose distribution could not be quantified prior to the catheter placement. To overcome this challenge, we proposed a learning-based method to provide HDR catheter placement guidance for prostate cancer patients undergoing HDR brachytherapy. The proposed framework consists of deformable registration via registration network (Reg-Net), multi-atlas ranking, and catheter regression. To model the global spatial relationship among multiple organs, binary masks of the prostate and organs-at-risk are transformed into distance maps, which describe the distance of each local voxel to the organ surfaces. For a new patient, the generated distance map is used as fixed image. Reg-Net is utilized to deformably register the distance maps from multi-atlas set to match this patient's distance map and then bring catheter maps from multi-atlas to this patient via spatial transformation. Several criteria, namely prostate volume similarity, multi-organ semantic image similarity, and catheter position criteria (far from the urethra and within the partial prostate), are used for multi-atlas ranking. The top-ranked atlas' deformed catheter positions are selected as the predicted catheter positions for this patient. Finally, catheter regression is used to refine the final catheter positions. A retrospective study on 90 patients with a fivefold cross-validation scheme was used to evaluate the proposed method's feasibility. In order to investigate the impact of plan quality from the predicted catheter pattern, we optimized the source dwell position and time for both the clinical catheter pattern and predicted catheter pattern with the same optimization settings. Comparisons of clinically relevant dose volume histogram (DVH) metrics were completed. For all patients, on average, both the clinical plan dose and predicted plan dose meet the common dose constraints when prostate dose coverage is kept at V100=95%. The plans from the predicted catheter pattern have slightly higher hotspot in terms of V150 by 5.0% and V200 by 2.9% on average. For bladder V75, rectum V75, and urethra V125, the average difference is close to zero, and the range of most patients is within ±1 cc. We developed a new catheter placement prediction method for HDR prostate brachytherapy based on a deep-learning-based multi-atlas registration algorithm. It has great clinical potential since it can provide catheter location estimation prior to catheter placement, which could reduce the dependence on physicians' experience in catheter implantation and improve the quality of prostate HDR treatment plans. This approach merits further clinical evaluation and validation as a method of quality control for HDR prostate brachytherapy.

PHSOR06 Presentation Time: 10:25 AM: A Novel Gamma Camera-Based System for Real-Time Visualization of 192Ir Source Position in High Dose Rate Brachytherapy

Purpose: The physical location of the 192Ir source in high-dose-rate (HDR) brachytherapy is currently invisible to the treatment team during treatment delivery. Although the in-room radiation monitor(s) can indicate whether the source is inside or outside the afterloader, the inability to easily visualize the physical source location makes it difficult in responding to radiation safety events and in treatment delivery verification. The purpose of this work was to develop a gamma camera-based imaging system for real-time visualization of the 192Ir source position during the HDR treatment delivery.

The combined use of 2D scout and 3D axial CT images to accurately determine thecathetertips for high-dose-rate brachytherapy plans.

PurposeTo develop a method combining CT scout images with axial images to improve the localization accuracy of catheter tips in high‐dose‐rate (HDR) brachytherapy treatments.Materials and MethodsCT scout images were utilized along with conventionally reconstructed axial images to aid the localization of catheter tips used during HDR treatment planning. A method was developed to take advantage of the finer image resolution of the scout images to more precisely identify the tip coordinates. The accuracies of this method were compared with the conventional method based on the axial CT images alone, for various slice thicknesses, in a computed tomography dose index (CTDI) head phantom. A clinical case which involved multiple interstitial catheters was also selected for the evaluation of this method. Locations of the catheter tips were reconstructed with the conventional CT‐based method and this newly developed method, respectively. Location coordinates obtained via both methods were quantitatively compared.ResultsCombination of the scout and axial CT images improved the accuracy of identification and reconstruction of catheter tips along the longitudinal direction (i.e., head‐to‐foot direction, more or less parallel to the catheter tracks), compared to relying on the axial CT images alone. The degree of improvement was dependent on CT slice thickness. For the clinical patient case, the coordinate differences of the reconstructed catheter tips were 2.6 mm ± 0.9 mm in the head‐to‐foot direction, 0.4 mm ± 0.2 mm in the left‐to‐right direction, and 0.6 mm ± 0.2 mm in the anterior‐to‐posterior direction, respectively.ConclusionCombining CT scout and axial images demonstrates the ability to provide a more accurate identification and reconstruction of the interstitial catheter tips for HDR brachytherapy treatment, especially in the longitudinal direction. The method developed in this work has the potential to be implemented clinically together with automatic segmentation in modern brachytherapy treatment planning systems, in order to improve the reconstruction accuracy of HDR catheters.

Reproducibility of vaginal immobilization balloons in situ overnight for cervical cancer brachytherapy.

PurposeThe use of vaginal immobilization balloons placed into the vagina for immobilization of tandem and ovoid (T+O) applicator during high-dose-rate (HDR) brachytherapy delivery has been used at our institution, and seems to have improved our patient comfort, decreased procedure time, and minimized applicator misplacement. We aimed to show that these balloons, while originally marketed for single-day use, are safe and maintain applicator positioning/dosimetry when left in situ overnight for treatment delivery on sequential days.Material and methodsForty-two paired computed tomography (CT) scans from thirteen patients who underwent T+O HDR treatments on sequential days with vaginal immobilization balloons in situ overnight were retrospectively compared to calculate mean change of balloon volumes and balloon/T+O distance to bony landmarks. Dosimetric planning was retroactively performed on day 2 using CT scan of each pair, and the change in estimated radiation delivery to the bladder and rectum was compared.ResultsNo statistically significant overnight changes were found in balloon volumes or anterior balloon positioning. The posterior balloon shifted –0.29 ±0.46 cm (p = 0.03) to the anterior public symphysis and 0.32 ±0.50 cm (p = 0.01) to the right femoral head. The tandem shifted 0.37 ±0.39 cm (p = 0.002) to the pubic symphysis. There was no significant difference found in radiation delivered to the bladder or rectum between the paired scans.ConclusionsThis study showed minimal change in balloon volumes, balloons/T+O positioning, or in radiation dose to bladder and rectum when the applicator remained overnight. These findings support that inflatable vaginal immobilization balloons remaining in situ overnight for additional HDR T+O treatments on sequential days, is safe and provides stable dosimetry.

Impact of High-Dose-Rate Brachytherapy Training via Telehealth in Low- and Middle-Income Countries.

PURPOSEOur objective was to demonstrate the efficacy of a telehealth training course on high-dose-rate (HDR) brachytherapy for gynecologic cancer treatment for clinicians in low- and middle-income countries (LMICs)METHODSA 12-week course consisting of 16 live video sessions was offered to 10 cancer centers in the Middle East, Africa, and Nepal. A total of 46 participants joined the course, and 22 participants, on average, attended each session. Radiation oncologists and medical physicists from 11 US and international institutions prepared and provided lectures for each topic covered in the course. Confidence surveys of 15 practical competencies were administered to participants before and after the course. Competencies focused on HDR commissioning, shielding, treatment planning, radiobiology, and applicators. Pre- and post-program surveys of provider confidence, measured by 5-point Likert scale, were administered and compared.RESULTSForty-six participants, including seven chief medical physicists, 16 senior medical physicists, five radiation oncologists, and three dosimetrists, representing nine countries attended education sessions. Reported confidence scores, both aggregate and paired, demonstrated increases in confidence in all 15 competencies. Post-curriculum score improvement was statistically significant (P < .05) for paired respondents in 11 of 15 domains. Absolute improvements were largest for confidence in applicator commissioning (2.3 to 3.8, P = .009), treatment planning system commissioning (2.2 to 3.9, P = .0055), and commissioning an HDR machine (2.2 to 4.0, P = .0031). Overall confidence in providing HDR brachytherapy services safely and teaching other providers increased from 3.1 to 3.8 and 3.0 to 3.5, respectively.CONCLUSIONA 12-week, low-cost telehealth training program on HDR brachytherapy improved confidence in treatment delivery and teaching for clinicians in 10 participating LMICs.

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

High-dose-rate (HDR) brachytherapy is an established technique to be used as monotherapy option or focal boost in conjunction with external beam radiation therapy (EBRT) for treating prostate cancer. Radiation source path reconstruction is a critical procedure in HDR treatment planning. Manually identifying the source path is labor intensive and time inefficient. In recent years, magnetic resonance imaging (MRI) has become a valuable imaging modality for image-guided HDR prostate brachytherapy due to its superb soft-tissue contrast for target delineation and normal tissue contouring. The purpose of this study is to investigate a deep-learning-based method to automatically reconstruct multiple catheters in MRI for prostate cancer HDR brachytherapy treatment planning. Attention gated U-Net incorporated with total variation (TV) regularization model was developed for multi-catheter segmentation in MRI. The attention gates were used to improve the accuracy of identifying small catheter points, while TV regularization was adopted to encode the natural spatial continuity of catheters into the model. The model was trained using the binary catheter annotation images offered by experienced physicists as ground truth paired with original MRI images. After the network was trained, MR images of a new prostate cancer patient receiving HDR brachytherapy were fed into the model to predict the locations and shapes of all the catheters. Quantitative assessments of our proposed method were based on catheter shaft and tip errors compared to the ground truth. Our method detected 299 catheters from 20 patients receiving HDR prostate brachytherapy with a catheter tip error of 0.37±1.68mm and a catheter shaft error of 0.93±0.50mm. For detection of catheter tips, our method resulted in 87% of the catheter tips within an error of less than±2.0mm, and more than 71% of the tips can be localized within an absolute error of no >1.0mm. For catheter shaft localization, 97% of catheters were detected with an error of <2.0mm, while 63% were within 1.0mm. In this study, we proposed a novel multi-catheter detection method to precisely localize the tips and shafts of catheters in three-dimensional MRI images of HDR prostate brachytherapy. It paves the way for elevating the quality and outcome of MRI-guided HDR prostate brachytherapy.

Fast and fully-automated multi-criterial treatment planning for adaptive HDR brachytherapy for locally advanced cervical cancer

PurposeTo develop and evaluate a fast, automated multi-criterial treatment planning approach for adaptive high-dose-rate (HDR) intracavitary + interstitial brachytherapy (BT) for locally advanced cervical cancer. Methods and materialsTwenty-two previously delivered single fraction MRI-based HDR treatment plans (SFclin) were used to guide training of our in-house system for multi-criterial autoplanning, aiming for an autoplan quality superior to the training plans, while respecting the clinically desired “pear-shaped” dose distribution. Next, the configured algorithm was used to automatically generate treatment plans for 63 other fractions (SFauto). The SFauto plans were compared to the corresponding SFclin plans in blind pairwise comparisons by an expert clinician. Then, the effect of adaptive autoplanning on total treatment (TT) plans (external beam + 3 BT fractions) was evaluated for 16 patients by simulating the clinically applied adaptive strategy to generate TTauto plans and compare them with the corresponding clinical treatments (TTclin). ResultsIn the blind comparisons, all SFauto plans were considered clinically acceptable. In 62/63 comparisons, SFauto plans were considered at least as good as, or better than the corresponding SFclin. The average optimization time for autoplanning was 20.5 ± 19.2 s (range 4.4–106.4 s) per plan. In 14 of 16 TTauto plans, the desired total dose of 90 Gy (EQD2) was obtained, compared to only 9 in the corresponding TTclin, while autoplanning also decreased bladder and rectum doses. ConclusionsFast, fully-automated multi-criterial treatment planning for adaptive HDR-BT for locally advanced cervical cancer is feasible. Autoplans were superior to corresponding clinical plans.

Effect of general ion recombination on dose measurement for high dose rate carbon-ion scanning beam

We confirmed the effect of ion recombination using a parallel-plate ionization chamber: dose monitor for clinical use and the Advanced Markus chamber. A 290 MeV/u carbon-ion beam was irradiated using the continuous spot-scanning method in a field size of 5 cm by 5 cm with 2 mm spacing. We tested three beam intensities (1.35 × 108, 2.69 × 109, and 4.03 × 109 particle per second (pps)) at two linear energy transfers (12 keV/μm and 200 keV/μm). The charge (Q) was measured by changing the voltage of the Advanced Markus chamber and that of the dose monitor. Then, Boag’s method was used to calculate the saturated charge (Qsat). For the Advanced Markus chamber, 300 V is a sufficient potential to collect charge. For the dose monitor, Qsat/Q at 2500 V was 1.024 for 4.03 × 109 pps, indicating that the general recombination correction cannot be ignored when high dose rate treatment is performed using a carbon-ion scanning beam.

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

PurposeThe aim of this work is to investigate the influence of an external magnetic field (MF) on The American Association of Physicists in Medicine (AAPM) No. 43 Report (TG-43) parameters for 192Ir and 60Co high dose rate (HDR) brachytherapy sources using Monte Carlo (MC) simulation methods. Materials and methodsWe used the Geant4 toolkit (version 10.1. p01) to simulate the geometry of 192Ir and 60Co brachytherapy sources. AAPM TG-43 parameters (the radial dose function, g(r), and the anisotropy function, F (r, θ)) of both 192Ir and 60Co sources were calculated in the presence of a magnetic field with strengths of 1.5T, 3T, and 7T in the X, Y, and Z directions in a voxelized water phantom. ResultsFor the 192Ir source, the calculated values g(r) and F (r, θ) remained nearly unaffected by the magnetic field for all investigated strengths.For the 60Co source, the differences for the g(r) and F (r,θ) under the 1.5T, 3T, and 7T magnetic field strengths along the direction parallel with the MF were found to be an increase of up to 5%, 15%, and 33%, respectively. However, for the directions perpendicular with the magnetic field, there was a decrease of up to 3%, 6% and 15% under 1.5T, 3T and 7T strengths, respectively. ConclusionOur results highlight the necessity of a Monte Carlo-based treatment planning system (TPS) if cobalt HDR treatments are performed under a magnetic field, especially for strengths greater than 1.5T.

Evaluation of exit skin dose for intra-cavitary brachytherapy treatments by the BEBIG 60Co machine using thermoluminescent dosimeters

AbstractPurpose:This study aims to evaluate the application of the exit skin dose (ESD) in verifying the accuracy of intra-cavitary brachytherapy treatments performed by the BEBIG 60Co machine using thermoluminescent dosimeters (TLDs).Materials and methods:Eleven patients who were treated for gynaecological (GYN) malignancy by high-dose-rate (HDR) brachytherapy machine have been considered in this study. A combination of tandem, cylinder and interstitial needles was applied for eight patients while tandem ovoid (TO) applicators were used for the rest (three patients). In order to measure ESD, thermoluminescent dosimetry was performed for each patient. TLDs were placed precisely on the patient’s skin along her symphysis pubis bone (anterior) and left (L)/right (R) sides of her pelvic. Positioning of the dosimeter was accurately determined using fiducial markers in computed tomography (CT) scan imaging, prior to the treatment. Finally, a comparison was made between the calculated dose from the treatment planning system (TPS) and the dose measured by TLDs.Results:About 90% of all cases showed a good agreement (while considering TLD uncertainty ∼5·5%) between TPS dose calculations and TLD measurements. The measured mean values of ESD received to anterior, left and right positions were 56·72, 12·18 and 12·82 cGy, respectively. For three patients, differences up to 11·9% were detected.Conclusion:To conclude, ESD measurement method can be a suitable practical approach for verifying the accuracy of GYN HDR treatment delivery.

Patient and physician reported toxicity with two-fraction definitive high-dose-rate prostate brachytherapy: the impact of implant interval

PurposeHigh-dose-rate (HDR) brachytherapy is an effective method of treating localized prostate cancer. There are limited data on the relationship between implant interval and outcomes. This study aims to assess if the implant interval between HDR treatments has an impact on patient-reported health-related quality of life (QOL) and physician-graded toxicity in men treated for localized prostate cancer.Material and methodsPatients were treated with HDR brachytherapy as monotherapy with 27 Gy in 2 fractions, given over two implants, performed 1-2 weeks apart. Patients were dichotomized into one-week and two-week cohorts. Patient-reported EPIC-26 genitourinary (GU), gastrointestinal (GI), and sexual QOL were assessed. Linear regression, chi-squared testing, and generalized linear mixed effect models were used to assess the differences in patient characteristics, patient-reported QOL, and physician-graded toxicity.ResultsOutcomes of 122 patients were analyzed. Median follow-up was 18 months. Patient-reported GU and GI QOL worsened after treatment with a return towards baseline over time, while patient-reported sexual QOL worsened after treatment, but did not return towards baseline. There were no differences in patient-reported health related QOL as a function of implant interval. Maximum physician-graded GU, GI, and sexual toxicity rates of grade 2 or 3 were 68%, 3%, and 53%, respectively. There was no difference in rates of grade 2 or 3 toxicity as a function of implants interval.ConclusionsHDR brachytherapy for prostate cancer is a well-tolerated treatment. The interval between treatments is not associated with differences in patient-reported QOL or physician-graded toxicities.

A Phase I/II trial of MRI-based Focal Salvage High Dose Rate Brachytherapy in Locally Radiorecurrent Prostate Cancer: Initial Dosimetric Feasibility and Preliminary Experience from the FSHARP Trial

Salvage high dose rate (HDR) brachytherapy for radiorecurrent disease results in biochemical control of ∼50-70%, but has an ∼10-20% risk of grade ≥3 toxicity. Historically, salvage HDR has, but recently, advances in imaging have allowed for improved intraprostatic recurrence localization. We hypothesized that by using diagnostic multiparametric MRI and fluciclovine PET with MRI-based treatment planning, the salvage HDR therapeutic ratio could be improved by targeting the focal lesion in a single fraction. The FSHARP trial is currently studying this approach and we report the initial dosimetry and preliminary experience of patients enrolled on this study. FSHARP (NCT0331297) is a Phase I/II trial of salvage focal single fraction HDR for radiorecurrent prostate cancer in patients with locally recurrent prostate cancer after any form of definitive radiotherapy. The primary endpoint is 3-month RT-related CTCAE v4.03 grade ≥3 genitourinary or gastrointestinal toxicity, with an initial 7 patient safety lead-in. Eligibility criteria include: initial diagnosis of cT1-T3a N0 M0 prostate adenocarcinoma, no evidence of metastases, and biopsy-proven local recurrence. All patients require a multiparametric MRI and biopsy of any target lesions. Patients undergo transrectal ultrasound-guided catheter placement followed by MRI-based treatment planning and HDR treatment. The planning target volume (PTV) is a 0-5 mm expansion around the gross tumor volume (GTV) avoiding surrounding critical structures. The prescription is to the periphery with the highest dose possible up to 30 Gy while not violating critical structure constraints and prioritizing GTV > PTV coverage. We performed a descriptive analysis of patient characteristics, dosimetry, and the acute EPIC-26 patient-reported quality of life of patients currently enrolled on the trial. 11 of a planned 24 patients have been treated on trial and the initial safety lead-in has been completed, with enrollment ongoing. Prior definitive treatment included external beam radiotherapy (n=8), low dose rate brachytherapy (n=2), and stereotactic body radiotherapy (n=1), with a median of 67 months from the completion of prior radiotherapy. Median pre-salvage PSA was 6.3 (range: 2.6-13.5). The median number of HDR catheters was 17 (range: 13-22), and the median prescribed peripheral dose was 19 Gy (19-22). Median GTV was 5.4 cc (2.01-44.72). Median PTV was 23.7 cc (8.78-76.69). Median GTV D90 was 21.3 Gy (17.13-35.91), PTV D90 was 19.6 Gy (16.3-23.9) Accrual to the FSHARP trial is ongoing. Future studies will correlate dosimetric findings with clinical outcomes. The table describes the baseline and follow-up median EPIC-26 scores up to 6 months with median follow-up of 6.23 months (0.8-12.2).Abstract 2706; Table 1Baseline (n=11)1 month (n=8)3 months (n=7)6 months (n=6)Urinary Obstructive/Irritative81.257587.593.75Urinary Incontinence100.0082.3879.2592.75Bowel95.8393.7591.67100Sexual54.1723.081848.67 Open table in a new tab