Intraluminal brachytherapy using a balloon applicator for superficial esophageal carcinoma: importance of applicator confirmation by computed tomography

Intraluminal brachytherapy using a balloon applicator has been the treatment of choice for superficial esophageal carcinomas. During treatment, the applicator is made to expand to be cylindrical as determined from an AP radiograph. However, optimal expansion of the applicator is not usually confirmed by computed tomography (CT). Therefore, this study was conducted to assess the shape of the balloon applicator by CT. Ten patients with superficial esophageal carcinoma were treated with intraluminal brachytherapy using a balloon applicator. The applicators were expanded properly in all patients as viewed from the AP radiograph. In seven of 10 patients, optimal expansion of the applicator was observed on CT. However, in the remaining three patients, applicators were found to be distorted presumably not only by primary tumor and mediastinal lymph nodes but also by neighboring organs. These results indicate that, when treating superficial esophageal carcinoma using a balloon applicator, there may be risks of applicator distortion in some cases. Assessment by CT should be done to precisely confirm the shape of the applicator.     

A new applicator for the intraluminal high-dose-rate irradiation of esophageal carcinoma

Within the framework of multimodal treatment (radiation, chemotherapy) of esophageal carcinoma high dose rate intracavitary irradiation is used either as a boost or with a palliative intention. By use of a set of four tubes of different thickness (diameter 6, 8, 10, 14 mm) it is possible to adapt the diameter of the applicator to the remaining esophageal lumen. Thereby the radioactive source is placed centrally in the esophagus. The distance between the source and the mucosa is maximized and the radiation dose to the mucosa is reduced in comparison to a normal tube with a diameter of 4 to 6 mm. Better depth penetration of the dose can be achieved in deeper parts of the esophageal wall. The applicators are placed using a guide wire during endoscopy. If the malignant stenosis is endoscopically impassable, an intraluminal reduction of the tumours mass is performed by laser therapy or bougienage.     

CT computer-optimized high-dose-rate brachytherapy with surface applicator technique for scar boost radiation after breast reconstruction surgery

PURPOSE: Immediate breast reconstruction has become increasingly prevalent after mastectomy for breast cancer. Postoperative scar boost radiation for the reconstructed breast presents many planning challenges due to the shape, size, and curvature of the scar. High-dose-rate (HDR) surface applicator brachytherapy is a novel and effective method of delivering scar boost radiation. Two cases, one with a saline implant and one with a transverse rectus abdominis musculocutaneous flap reconstruction, illustrate the method and advantages of HDR optimization of surface applicators. METHODS AND MATERIALS: For 2 patients a mold of the breast was made with Aquaplast sheets. A reproducible system was used for arm positioning. Skin fiducials, including tattoos from external beam planning, were matched to fiducials on the mold. HDR catheters were sited on the mold at 1cm intervals, with the central catheter situated along the scar. Topographically, both scars demonstrated extreme curvature in both craniocaudal and mediolateral directions. A CT computer-optimized HDR plan was developed, with the reference dose prescribed at the skin surface. The dosimetry was compared to single-field and matched-field electron plans. RESULTS: This surface applicator technique provided a uniform skin dose of 100% to the entire clinical target volume (CTV) without hot spots in both patients. The patient position and surface applicator setup were consistently reproducible. The patients tolerated the treatment well with minimal skin erythema. In the single-field electron plan, skin dose was decreased to 50% at the periphery of the scar. Matching fields addressed this depth dose decrement, but resulted in large localized hot spots of more than 200% centrally in each field. CONCLUSION: CT computer-optimized HDR surface applicator brachytherapy provided a reproducible homogeneous method of treating highly curved scars on the reconstructed breast. Electron beam treatment would result in longer and more complex treatments yet still provide a less homogeneous dose than this surface applicator technique.     

Dosimetric effects of saline- versus water-filled balloon applicators for IORT using the model S700 electronic brachytherapy source

PurposeThe Xoft Axxent Electronic Brachytherapy System (Xoft, Inc., San Jose, CA) is a viable option for intraoperative radiation therapy (IORT) treatment of early-stage breast cancer. The low-energy (50-kVp) X-ray source simplifies shielding and increases relative biological effectiveness but increases dose distribution sensitivity to medium composition. Treatment planning systems typically assume homogenous water for brachytherapy dose calculations, including precalculated atlas plans for Xoft IORT. However, Xoft recommends saline for balloon applicator filling. This study investigates dosimetric differences due to increased effective atomic number (Z_eff) for saline (Z_eff = 7.56) versus water (Z_eff = 7.42).MethodsBalloon applicator diameters range from 3 to 6 cm. Monte Carlo N-Particle software is used to calculate dose at the surface (D_s) of and 1 cm away (D_1cm) from the water-/saline-filled balloon applicator using a single dwell at the applicator center as a simple estimation of the dosimetry and multiple dwells simulating the clinical dose distributions for the atlas plans.ResultsSingle-dwell plans show a 4.4–6.1% decrease in D_s for the 3- to 6-cm diameter applicators due to the saline. Multidwell plans show similar results: 4.9% and 6.4% D_s decrease, for 4-cm and 6-cm diameter applicators, respectively. For the single-dwell plans, D_1cm decreases 3.6–5.2% for the 3- to 6-cm diameter applicators. For the multidwell plans, D_1cm decreases 3.3% and 5.3% for the 4-cm and 6-cm applicators, respectively.ConclusionsThe dosimetric effect introduced by saline versus water filling for Xoft balloon applicator–based IORT treatments is ∼5%. Users should be aware of this in the context of both treatment planning and patient outcome studies.     

Techniques for and uncertainties of MRI-based reconstruction of titanium tandem and ring brachytherapy applicators

PurposeEliminating patient computed tomography (CT) scans for tandem and ring (T&R) brachytherapy can reduce overall procedure time and eliminates imaging dose. However, reconstructing titanium applicators in magnetic resonance imaging (MRI) is challenging. We evaluated the uncertainty of different applicator reconstruction workflows in MR-guided brachytherapy, and assessed the clinical impact of reconstruction uncertainties.Methods and materialsTitanium MRI-compatible T&Rs with aqueous gel in the buildup cap were reconstructed on CTs and MRIs to assess the uncertainties of four different workflows. Reconstruction was performed using (1) proton density–weighted MRIs with solid applicator from a library, (2) applicator-only reference CT fused with MRIs, (3) T2-weighted (T2W) MRIs following GEC-ESTRO guidelines, and (4) patient CTs fused with patient MRIs with in situ applicators. We evaluated dwell positions and plan quality differences using high-risk clinical target volume coverage, and EQD2 D_2cc of rectum, sigmoid, bladder, and small bowel.ResultsThe 2σ uncertainty for dwell positions for each workflow were (1) 2.7 mm for both ring and tandem, (2) 1.4 mm ring and 0.8 mm tandem, (3) 0.2 mm ring and 0.8 mm tandem, and (4) 1.9 mm ring and 0.4 mm tandem. Reconstruction uncertainties resulted in dose variations within acceptable levels (below 10%) except for (1) which resulted in larger dose to the rectum (20%). Dose uncertainties were similar between reference CT and patient CT.ConclusionsReconstruction with a reference CT results in similar uncertainty to a patient CT. T2W MRI plans have acceptable uncertainty levels for the applicator reconstruction and resulting dose distributions.     

Skin dose estimation using virtual structures for Contura Multi-Lumen Balloon breast brachytherapy

PurposeTo propose a workflow that uses ultrasound (US)-measured skin–balloon distances and virtual structure creations in the treatment planning system to evaluate the maximum skin dose for patients treated with Contura Multi-Lumen Balloon applicators.Methods and MaterialsTwenty-three patients were analyzed in this study. CT and US were used to investigate the interfractional skin–balloon distance variations. Virtual structures were created on the planning CT to predict the maximum skin doses. Fitted curves and its equation can be obtained from the skin–balloon distance vs. maximum skin dose plot using virtual structure information. The fidelity of US-measured skin distance and the skin dose prediction using virtual structures were assessed.ResultsThe differences between CT- and US-measured skin–balloon distances values had an average of −0.5 ± 1.1 mm (95% confidence interval [CI] = −1.0 to 0.1 mm). Using virtual structure created on CT, the average difference between the predicted and the actual dose overlay maximum skin dose was −1.7% (95% CI = −3.0 to −0.4%). Furthermore, when applying the US-measured skin distance values in the virtual structure trendline equation, the differences between predicted and actual maximum skin dose had an average of 0.7 ± 6.4% (95% CI = −2.3% to 3.7%).ConclusionsIt is possible to use US to observe interfraction skin–balloon distance variation to replace CT acquisition. With the proposed workflow, based on the creation of virtual structures defined on the planning CT- and US-measured skin–balloon distances, the maximum skin doses can be reasonably estimated.     

Brachytherapy using Ru-106 applicators in ophthalmology

Two Ru-106 applicators of the type CCB as manufactured by the "Zentralinstitut für Isotopen- und Strahlenforschung" (Berlin, GDR) were investigated. The homogeneity of the relative dose distribution at the surface of the applicators was determined. For the evaluation of the data extremely small TLD crystals (2 x 1 x 1 mm) had to be manufactured as well as an almost tissue equivalent acrylic eye phantom. In order to assure reproducibility of the applicator positioning, the plaque suture eyelets had to be placed on locating pins. 120 points of measurements located within the active plaque area of 20 mm diameter were evaluated. The results show that the area to be used in tumor treatment is about 20 to 25% less than expected. One plaque shows a considerable inhomogeneity with respect to dose distribution (up to 40%). A modified eye phantom was used for the determination of the central axis depth dose distribution.     

Application of optical photogrammetry in radiation oncology: HDR surface mold brachytherapy

PurposeWe propose a novel method of designing surface mold brachytherapy applicators using optical photogrammetry. The accuracy of this technique for the purpose of 3D-printing surface mold brachytherapy applicators is investigated.Methods and MaterialsPhotogrammetry was used to generate a 3D model of a patient's right arm. The geometric accuracy of the model was evaluated against CT in terms of volume, surface area, and the Hausdorff distance. A surface mold applicator was then 3D printed using this reconstructed model. The accuracy was evaluated by analyzing the displacement and air-gap volumes between the applicator and plaster cast on a CT image. This technique was subsequently applied to generate a 3D-printed applicator of the author's hand directly, as a proof of principle, using only photographic images.ResultsThe volume and surface area of the model were within 0.1% and 2.6% of the CT-obtained values, respectively. Using the Hausdorff distance metric, it was determined that 93% of the visible vertices present in the CT-derived model had a matching vertex on the photogrammetry-derived model within 1 mm, indicating a high level of similarity. The maximum displacement between the plaster cast of the patient's arm and the photo-derived 3D-printed applicator was 1.2 mm with a total air-gap volume of approximately 0.05 cm³.ConclusionsPhotogrammetry has been applied to the task of generating 3D-printed brachytherapy surface mold applicators. The current work demonstrates the feasibility and accuracy of this technique and how it may be incorporated into a 3D-printing brachytherapy workflow.     

Comparison of dose delivered to vagina using two different intracavitary brachytherapy applicators for carcinoma cervix

PURPOSEThe aim of the study was to compare the dose to vaginal points between two intracavitary applicators used for HDR brachytherapy in Carcinoma CervixMETHODS AND MATERIALSPatients reporting to our center for Carcinoma cervix intracavitary brachytherapy were randomly allocated to treatment with either Manchester or Fletcher Suit Delclos (FSD) applicator. All patients received an EBRT dose of 50 Gy in 25 fractions along with weekly Cisplatin (40 mg/m²). Brachytherapy was administered using CT based planning. All patients received a dose of 7 Gy to Point A one week apart for a total of three fractions. For vaginal dose reporting, the PIBS points (PIBS, PIBS+1, PIBS+2, PIBS-1, PIBS-2) and dose to vagina at the level of ovoids was compared between the two applicatorsRESULTSA total of 30 Carcinoma cervix patients were randomly allocated to receive intracavitary brachytherapy with either Manchester or FSD applicator. The mean vaginal reference length for patients treated with Manchester applicator was 4.3 and for patients treated with FSD applicator was 4.4. On analyzing dose to different vaginal points, patients treated with Manchester applicator received significantly higher mean and median doses to all PIBS points (except PIBS-2 cm) as compared to FSD applicator. On analyzing dose to the upper vagina at the level of the ovoids, the Manchester applicator delivered higher antero-posterior doses as compared to FSD applicator.CONCLUSIONSManchester applicator gives higher dose to the vagina as compared to FSD applicator for intracavitary brachytherapy in Carcinoma Cervix. The choice of using a particular applicator depends on the residual disease at the time of brachytherapy and patient anatomy     

婴儿食管吻合口狭窄球囊扩张术

目的：本文报告４例婴儿食管吻合口狭窄使用球囊扩张术治疗。材料和方法：４例女婴均为食物闭锁术后２￣１５个月出现吻合口狭窄，狭窄内径３￣６ｍｍ。采用球囊导管分次扩张，球囊直径６￣１５ｍｍ。结果：４例共进行球囊扩张１２次，保持临床无症状期４￣６个月。无食管穿孔并发症。结论：球囊扩张术简单、安全、有效，为婴儿食物吻合口狭窄的首选治疗方法。     

Modeling study for optimization of skin dose for partial breast irradiation using Xoft Axxent electronic brachytherapy applicator

PurposeBalloon brachytherapy with the MammoSite system (Hologic Inc., Bedford, MA) is a widely used approach for accelerated partial breast irradiation. Inherent to this approach, high skin doses can occur if the balloon to skin distance is small. This has been associated with late skin toxicity, particularly telangiectasia. The Xoft Axxent electronic brachytherapy balloon applicator (Xoft, Fremont, CA) is a novel device for accelerated partial breast irradiation. It is unique in that it uses an electronic 50-kV source. This source has a pronounced anisotropy with constriction of isodose distribution at the proximal end of the catheter. This anisotropy can be considered as an advantage to optimize skin dose when the cavity to skin distance is small. In this study, we simulated various balloon-insertion orientations to optimized skin surface dose.MethodsBreast phantoms were constructed of tissue-equivalent material. Xoft Axxent balloon catheters were inserted at a distance of 6 mm from the surface. The catheter was placed at three different catheter to surface orientations: (1) perpendicular to the surface, (2) oblique to the surface (45°), and (3) parallel to the surface. Three-dimensional treatment planning was then performed using Nucletron's Plato planning system (Nucletron, Columbia, MD). Multiple dwell positions were used, and the dose was optimized to the target volume. The target volume was defined as volume from the balloon surface to 1-cm distance from the balloon surface or to the phantom surface (if less then 1 cm from the balloon surface). Target volume coverage was compared between plans using dose–volume histograms. Surface doses were compared using isodose line distribution and surface point doses. Plato planned surface doses were then verified by direct measurement using Landauer Dot InLight dosimeters (Landauer, Glenwood, IL).ResultsExcellent target coverage was obtained for all three catheter orientations with a D₉₅ of ≥95%. Surface dose was lowest for the perpendicular orientation with a calculated dose of 99%. The parallel orientation had the highest surface dose of 164%. The oblique orientation showed intermediate results with a surface dose of 117%. Measured surface doses were reproducible and correlated well with calculated values.ConclusionOptimized Xoft Axxent balloon catheter orientation using source anisotropy and multiple dwell positions can be used to minimize excessive skin dose and yet maintain optimal tumor cavity coverage when the cavity to skin distance is small. This has the potential to decrease skin late effects and improve cosmetic outcome. Further clinical study is warranted.     

Image-guided cervix high-dose-rate brachytherapy treatment planning: Does custom computed tomography planning for each insertion provide better conformal avoidance of organs at risk?

PURPOSE: Intracavitary high-dose-rate (HDR) brachytherapy (BT) for cervical cancer involves multiple applicator insertions. Our study addresses whether customized three-dimensional plans generated for the first insertion (using computed tomography [CT] planning) can be applied to subsequent insertions without significant changes in dose distributions if identical applicators are used. METHODS AND MATERIALS: Twenty-seven patients were treated with external-beam radiotherapy, platinum-based chemotherapy, and HDR BT. Either tandem and ovoids (TO, n=12) or tandem and ring (TR, n=15) applicators were used, based on clinical indications. Postimplant CT scans were acquired and custom plans generated for each insertion. Dose parameters for organs at risk (OARs) from the second insertion were retrospectively compared to those that would have been delivered using the initial plan. RESULTS: Overall, we observed a significant increase (p<0.038) in dose to International Commission on Radiation Units and Measurement points and 2cm(3) volumes of bladder and rectum when a single plan was used. The sigmoid and small bowel exhibited a more variable increase in dose. Applicator-specific results revealed a significant increase (p<0.030) to dose points and volumes for the rectum and bladder for TR applicators. Conversely, dose values from the more flexible TO did not show any significant trend, exhibiting large interpatient variations. CONCLUSIONS: A duplication of planned dwell times and positions from one insertion to the next does not duplicate dose distributions in HDR cervix applications. A single plan used for an entire course of BT can result in significant increases to OAR doses for TR and unpredictable OAR doses for TO applicators. Treatment plans should be tailored for each insertion to reflect current applicator and anatomical geometry.     

Therapeutic effects of simultaneous intraluminal irradiation and intraluminal hyperthermia on oesophageal carcinoma

An applicator enabling simultaneous intraluminal radiotherapy and intraluminal hyperthermia delivery was developed to improve the treatment results for locally advanced oesophageal carcinoma. Eight inoperable cases were treated by this method. Six cases received 40 Gy external irradiation followed by simultaneous intraluminal hyperthermia and radiotherapy (3 Gy and 4 Gy in three cases each) once weekly for 3 weeks; the remaining two cases received 50 Gy external irradiation followed by simultaneous intraluminal hyperthermia and radiotherapy (4 Gy) once weekly for 2 weeks. Hyperthermia was delivered by a radiofrequency current thermotherapy instrument for 30 min at an output that raised the oesophageal mucosal surface temperature to 42-43 degrees C. Intraluminal radiotherapy was delivered with a microSelectron to a submucosal depth of 5 mm after the first 15 min of hyperthermia. Four cases achieved complete response, with all demonstrating local control. Partial response was obtained in four cases, and three of these patients died of local recurrence. There were no significant adverse side effects apart from fistula in one case. In conclusion, simultaneous intraluminal radiotherapy and hyperthermia may improve the current treatment results for locally advanced oesophageal carcinoma.     

Quantitative CT assessment of a novel direction-modulated brachytherapy tandem applicator

PurposeThe purpose of this study was to quantitatively assess the CT metal-induced artifacts from a novel direction-modulated brachytherapy (DMBT) tandem applicator prototype, recently designed for cervical cancer treatments.Methods and materialsA water-based pelvic phantom was constructed for CT scanning. The DMBT applicator was imaged using our institutional protocol, one with higher kVp and mAs settings, and repetition of these protocols using 3-mm slices. A conventional stainless steel applicator was also scanned. In addition to the standard reconstructed images, applicator images were reconstructed using a commercial metal artifact-reduction (MAR) algorithm and an in-house–developed research algorithm. Subsequently, image quality and artifact severity were evaluated.ResultsArtifact severity, measured in terms of SDs in CT numbers, decreased asymptotically to background water levels with the distance away from the applicator. Artifact-reduction algorithms lead to significant and visible improvements in image quality, with >50% and >20% decrease in artifact severity achieved at a 10-mm distance for the DMBT and stainless steel applicators, respectively. Differences in artifact severity were minimal between the four imaging protocols. DMBT dimensions were the same on images with and without the commercial MAR algorithm, within <1 mm of the theoretical value. Both the commercial and in-house algorithms restored the CT numbers outside the applicator, albeit a better performance was achieved by the in-house algorithm.ConclusionsThe artifacts produced by both applicators were minimized with the use of MAR algorithms. Adoption of the DMBT and stainless steel applicators for CT-guided brachytherapy is anticipated as MAR algorithms are widely available on CT scanners.     

Custom 3D-printed applicators for high dose-rate brachytherapy in skin cancer

PURPOSEThis paper describes the protocol for the development of 3D-printed custom applicators in treating skin carcinoma, the evaluation of the materials used, and the methods for segmentation and rendering of the applicators.MATERIAL AND METHODSThe segmentation and rendering process for the applicator had six phases: (i) determination of the volume of the lesion using a computed tomography (CT) scan; (ii) delineation of the patient surface, using the same CT images; (iii) creation of the applicator in the planner and segmentation of the mold; (iv) preliminary dosimetry and establishment of the route of the catheter from the brachytherapy unit; (v) creation of the 3D applicator using specialized software; and (vi) applicator printing. Following this process, the patient returned for a second CT to undergo the definitive dosimetry with the applicator in place. Radiation therapy was then administered.RESULTSWe made a total of 16 applicators. Only three applicators had to be remade, two due to an error in the infill and the other due to incorrect catheter geometry. In all cases, correct coverage of the planning target volume was achieved with the prescribed isodose.CONCLUSIONSThe creation of custom molds in plesiotherapy for skin cancer with 3D printing is feasible. Compared to manual methods, 3D printing increases precision in applicator geometry and optimization of the dosimetry.     

Thin CaSO4:Dy thermoluminescent dosimeters for calibration of Sr+Y applicators

Clinical applicators are used in brachytherapy to treat superficial lesions of skin and eye. They should be periodically calibrated according to quality control programs and international recommendations. Thin CaSO₄:Dy thermoluminescent dosimeters were used to calibrate various applicators with a dermatological applicator as a reference. The obtained absorbed dose rates were compared with those quoted in their calibration certificates. Depth-dose curves were constructed for all the applicators. A mail dosimetry system was developed for calibration of clinical applicators.