Retrospective assessment of HDR brachytherapy dose calculation methods in locally advanced cervical cancer patients: AcurosBV vs. AAPM TG43 formalism.

PURPOSE: This retrospective analysis was completed to investigate the use of a model-based dose calculation algorithm (MBDCA) AcurosBV, for use in HDR BT treatments for locally advanced cervical cancer treated with tandem and ovoid applicators with interstitial needles. METHODS: A cohort of 32 patients receiving post-EBRT HDR brachytherapy boost with a prescription dose of 5.5 Gy × 5 fractions to the high-risk clinical target volume (CTVHR) were selected for this study. For standard TG43 dose calculation, applicators were manually digitized on the planning images, while for AcurosBV calculations, solid renderings of Titanium Fletcher Suite Delclos (FSD) applicators included in BrachyVision were matched to those used clinically and Ti needles were manually digitized. The dose was recalculated using Varian's AcurosBV 13.5 and dose-to-medium-in-medium (Dm,m) was reported. EQD2 values for targets and organs at risk were compared between dose calculation formalisms. D90% and D98% values were reported for the high and intermediate-risk CTVs, and D 2 c m 3 ${\mathrm{\ D}}_{{\mathrm{2\ c}}{{\mathrm{m}}}^{\mathrm{3}}}$ values were reported for OARs including bladder, rectum, sigmoid, bowel, and vagina. Due to variability within the patient cohort, the dosimetric impact of AcurosBV was investigated corresponding to planning image modality (CT vs. CBCT), presence of Ti needles, and contrast within vaginal balloons used to stabilize implants. AcurosBV showed lower dosimetric values for all plans compared to TG43. RESULTS: The average ± standard deviation of dosimetric reduction in D90% was 4.33 ± 0.09% for CTVHR and 4.12 ± 0.09% for CTVIR. The reduction to OARs D 2 c m 3 ${\mathrm{\ D}}_{{\mathrm{2\ c}}{{\mathrm{m}}}^{\mathrm{3}}}$ was: 4.99 ± 0.15% for bladder, 7.87 ± 0.16% for rectum, 5.79 ± 0.17% for sigmoid, 6.91 ± 0.14% for bowel, and 4.55 ± 0.14% for vagina. CONCLUSIONS: AcurosBV should be utilized for HDR BT GYN cases, treated with tandem and ovoid applicators, with high degrees of heterogeneity and calculated in tandem with TG43.

Yttrium-90 (90Y) brachytherapy for squamous carcinoma: Treatment of the conjunctiva, cornea, and sclera.

Purpose: Patients with conjunctival squamous cell carcinoma that present with persisting disease or recurrence following topical chemotherapy and/or surgery especially when invading the sclera are challenging to treat. Herein, we describe the use of high-dose-rate (HDR), FDA-cleared, yttrium-90 (90Y) plaque brachytherapy for such lesions. Observation: Three cases of invasive conjunctival squamous cell carcinoma that had exhibited a poor response or recurrence following topical chemotherapy and/or surgery are described. As treatment, HDR 90Y beta-radiation was applied to the tumor and margins for a single, continuous duration. In contrast to low-dose-rate (LDR) plaque, HDR 90Y brachytherapy did not require episcleral sutures, amniotic membrane buffering of the cornea, a Gunderson flap, outpatient dwell time, or second surgery. Radiation safety was improved by eliminating LDR-implant related post-operative radiation exposure to health care personnel, the community, family, and pets. Follow-up examination at one month revealed complete tumor resolution in all patients. At last follow-up (8, 11 and 18 months) all patients remained clinically tumor-free as confirmed by slit-lamp biomicroscopy, anterior segment optical coherence tomography, and high-frequency ultrasound imaging. There were no acute complications (e.g., corneal edema, iridocyclitis, scleropathy, keratopathy or cataract). Conclusion and Importance: 90Y brachytherapy demonstrated efficacy as a single-surgery, minimally invasive, outpatient irradiation for squamous carcinoma of the ocular surface. While short-term results were promising, long-term follow-up monitoring for side-effects and recurrence are essential.

A novel multi-modality imaging phantom for validating interstitial needle guidance for high dose rate gynecological brachytherapy.

PURPOSE: To design, manufacture, and validate a female pelvic phantom for multi-modality imaging (CT, MRI, US) to benchmark a commercial needle tracking system with application in HDR gynecological (GYN) interstitial procedures. MATERIALS AND METHODS: A GYN needle-tracking phantom was designed using CAD software to model an average uterus from a previous patient study, a vaginal canal from speculum dimensions, and a rectum to accommodate a transrectal ultrasound (TRUS) probe. A target volume (CTVHR ) was designed as an extension from the cervix-uterus complex. Negative space molds were created from modeled anatomy and 3D printed. Silicone was used to cast the anatomy molds. A 3D printed box was constructed to house the manufactured anatomy for structural integrity and to accommodate the insertion of a speculum, tandem, needles, and TRUS probe. The phantom was CT-imaged to identify potential imperfections that might impact US visualization. Free-hand TRUS was used to guide interstitial needles into the phantom. The commercial tracking system was used to generate a 3D US volume. After insertion, the phantom was imaged with CT and MR and the uterus and CTVHR dimensions were verified against the CAD model. RESULTS/CONCLUSIONS: The manufactured phantom allows for accurate visualization with multiple imaging modalities and is conducive to applicator and needle insertion. The phantom dimensions from the CAD model were verified with those from each imaging modality. The phantom is low cost and can be reproducibly manufactured with the 3D printing and molding processes. Our initial experiments demonstrate the ability to integrate the phantom with a commercial tracking system for future needle tracking validation studies.

Transitioning from a COMS-based plaque brachytherapy program to using eye physics plaques and plaque simulator treatment planning system: A single institutional experience.

The aim of this work is to describe the implementation and commissioning of a plaque brachytherapy program using Eye Physics eye plaques and Plaque Simulator treatment planning system based on the experience of one institution with an established COMS-based plaque program. Although commissioning recommendations are available in official task groups publications such as TG-129 and TG-221, we found that there was a lack of published experiences with the specific details of such a transition and the practical application of the commissioning guidelines. The specific issues addressed in this paper include discussing the lack of FDA approval of the Eye Physics plaques and Plaque Simulator treatment planning system, the commissioning of the plaques and treatment planning system including considerations of the heterogeneity corrected calculations, and the implementation of a second check using an FDA-approved treatment planning system. We have also discussed the use of rental plaques, the analysis of plans using dose histograms, and the development of a quality management program. By sharing our experiences with the commissioning of this program this document will assist other institutions with the same task and act as a supplement to the recommendations in the recently published TG-221.

What is appropriate target delineation for MRI-based brachytherapy for medically inoperable endometrial cancer?

PURPOSE: For medically inoperable endometrial cancer (MIEC), the volumetric target of image-guided brachytherapy (IGBT) techniques is not well established. We propose a high-risk CTV (HRCTV) concept and report associated rates of local control and toxicity. METHODS AND MATERIALS: For all MIEC patients receiving definitive external beam radiotherapy (EBRT) followed by MRI-based IGBT at a single institution, BT dose was prescribed to HRCTV defined as GTV plus endometrial cavity with a planning goal of a summed EQD2 D90 of ≥85 Gy. Freedom from local progression (FFLP) and overall survival (OS) were estimated via Kaplan Meier method. RESULTS: Thirty two MIEC patients received EBRT followed by MRI-based IGBT between December 2015 and August 2020. Median follow up was 19.8 months. A total of 75% of patients had FIGO stage I/II disease, 56% endometrioid histology, and 50% grade 3 disease. OS was 73.6% (95% CI 57.8%-89.3%) at 12 months and 65.8% (95% CI 48.4%-83.2%) at 24 months. FFLP was 93.8% (95% CI 85.3%-100%) at 12 months and 88.8% (95% CI 86.6%-91.0%) at 24 months. 23 (72%) patients experienced no RT-related toxicity, while 2 of 32 patients (6%) experienced late grade 3+ toxicities (grade 3 refractory vomiting; grade 5 GI bleed secondary to RT-induced proctitis). CONCLUSIONS: Patients with MIEC receiving definitive EBRT followed by MRI-based IGBT prescribed to the MRI-defined HRCTV demonstrated favorable long-term local control with an acceptable toxicity profile.

Preliminary Results of Uveal Melanoma Treated With Iodine-125 Plaques: Analysis of Disease Control and Visual Outcomes With 63 Gy to the Target Volume.

Purpose: Our purpose was to review the preliminary outcomes of patients with uveal melanoma treated with iodine-125 plaques using a novel treatment planning approach. Methods and Materials: This was a single institution, retrospective review of patients treated with iodine-125 brachytherapy for uveal melanoma from November 2016 to February 2019. We used 3-dimensional treatment planning with the Eye Physics Plaque Simulator to ensure that a minimum of 63 Gy covered a 2-mm circumferential tumor margin and the apex height of the tumor over 94 hours. Primary endpoints were local failure, systemic metastasis, final visual acuity (VA), and radiation retinopathy. Associations between primary endpoints and tumor characteristics/radiation dose were performed using univariate analysis. Results: Sixty-nine patients were included in the analysis. Mean largest basal diameter was 11.67 mm (range, 6-18; median, 12), and the average tumor thickness to the inner sclera was 3.18 mm (range, 0.5-9.3; median, 2.8). Molecular testing that was successfully performed in 59 patients revealed that 27% (16 of 59) had class 2 gene expression profile designation. Average follow-up posttreatment was 28.3 months (range, 4-46; median, 29), with 6% (4 of 69) developing local failure and 6% (4 of 69) developing metastasis over this duration. Average final VA (0.57 logMAR [Snellen 20/74]; range, 0-2.9; median, 0.3) was decreased from baseline (0.34 logMAR [Snellen 20/44]; range, 0-2.3; median, 0.1), and 48% (33 of 69) developed radiation retinopathy. Fifty percent of patients had a final VA 20/40 or better and 22% had a final VA 20/200 or worse. Conclusions: In patients with uveal melanoma, preliminary results with brachytherapy using Eye Physics plaques with a treatment plan that delivers 63 Gy to a 2-mm circumferential tumor margin and the tumor apex suggest effective disease control and favorable VA outcomes.

Dual-source strength seed loading for eye plaque brachytherapy using eye physics eye plaques: A feasibility study.

Purpose: This study quantifies the dosimetric impact of incorporating two iodine-125 (125I) seed source strengths in Eye Physics eye plaques for treatment of uveal melanoma. Material and methods: Plaque Simulator was used to retrospectively plan 15 clinical cases of three types: (1) Shallow tumors (< 5.5 mm) with large base dimensions (range, 16-19 mm); (2) Tumors near the optic nerve planned with notched plaques; and (3) Very shallow (< 3.0 mm) tumors with moderate base dimensions (range, 13.5-15.5 mm) planned with larger plaques than requested by the ocular oncologist. Circular plaques were planned with outer ring sources twice the source strength of inner sources, and notched plaques with the six seeds closest to the notch at twice the source strength. Results: In cases of type (1), the dual-source strength plan decreased prescription depth, and doses to critical structures were lower: inner sclera -25% ±2%, optic disc -7% ±3%, and fovea -6% ±3%. In four out of five cases of type (2), the dual-source strength plan decreased prescription depth, and dose to inner sclera was lower (-22% ±5%), while dose to optic disc (17% ±7%) and fovea (20% ±12%) increased. In cases of type (3), a smaller dual-source strength plaque was used, and scleral dose was lower (-45% ±3%), whereas dose to optic disc (1% ±14%) and fovea (5% ±5%) increased. Conclusions: Dual-source strength loading as described in this study can be used to cover tumor margins and decrease dose to sclera, and therefore the adjacent retina, but can either decrease or increase radiation dose to optic disc and fovea depending on location and size of the tumor. This technique may allow the use of a smaller plaque, if requested by the ocular oncologist. Clinical determination to use this technique should be performed on an individual basis, and additional QA steps are required. Integrating the use of volumetric imaging may be warranted.

Recommendations on the practice of calibration, dosimetry, and quality assurance for gamma stereotactic radiosurgery: Report of AAPM Task Group 178.

The American Association of Physicists in Medicine (AAPM) formed Task Group 178 (TG-178) to perform the following tasks: review in-phantom and in-air calibration protocols for gamma stereotactic radiosurgery (GSR), suggest a dose rate calibration protocol that can be successfully utilized with all gamma stereotactic radiosurgery (GSR) devices, and update quality assurance (QA) protocols in TG-42 (AAPM Report 54, 1995) for static GSR devices. The TG-178 report recommends a GSR dose rate calibration formalism and provides tabulated data to implement it for ionization chambers commonly used in GSR dosimetry. The report also describes routine mechanical, dosimetric, and safety checks for GSR devices, and provides treatment process quality assurance recommendations. Sample worksheets, checklists, and practical suggestions regarding some QA procedures are given in appendices. The overall goal of the report is to make recommendations that help standardize GSR physics practices and promote the safe implementation of GSR technologies.

Multimaterial three-dimensional printing in brachytherapy: Prototyping teaching tools for interstitial and intracavitary procedures in cervical cancers.

PURPOSE: As the utilization of brachytherapy procedures continues to decline in clinics, a need for accessible training tools is required to help bridge the gap between resident comfort in brachytherapy training and clinical practice. To improve the quality of intracavitary and interstitial high-dose-rate brachytherapy education, a multimaterial, modular, three-dimensionally printed pelvic phantom prototype simulating normal and cervical pathological conditions has been developed. METHODS AND MATERIALS: Patient anatomy was derived from pelvic CT and MRI scans from 50 representative patients diagnosed with localized cervical cancer. Dimensions measured from patients' uterine body and uterine canal sizes were used to construct a variety of uteri based off of the averages and standard deviations of the subjects in our study. Soft-tissue anatomy was three-dimensionally printed using Agilus blends (shore 30 and 70) and modular components using Vero (shore 85). RESULTS: The kit consists of four uteri, a standard bladder, a standard rectum, two embedded gross tumor volumes, and four clip-on gross tumor volume attachments. The three anteverted uteri in the kit are based on the smallest, the average, and the largest dimensions from our patient set, whereas the retroverted uterus assumes average dimensions. CONCLUSIONS: This educational high-dose-rate gynecological pelvic phantom is an accessible and cost-effective way to improve radiation oncology resident training in intracavitary/interstitial brachytherapy cases. Implementation of this phantom in resident education will allow for more thorough and comprehensive physician training through its ability to transform the patient scenario. It is expected that this tool will help improve confidence and efficiency when performing brachytherapy procedures in patients.

Practice Patterns for the Treatment of Uveal Melanoma with Iodine-125 Plaque Brachytherapy: Ocular Oncology Study Consortium Report 5.

BACKGROUND: Treatment planning for I-125 plaque therapy for uveal melanoma has advanced significantly since the Collaborative Ocular Melanoma Study trial, with more widely available image-guided planning and improved dosimetry. OBJECTIVE: We evaluated real-world practice patterns for I-125 plaque brachytherapy in the United States by studying practice patterns at centers that comprise the Ocular Oncology Study Consortium (OOSC). METHODS: The OOSC database and responses to a treatment practice survey were evaluated. The database contains treatment information from 9 institutions. Patients included in the database were treated between 2010 and 2014. The survey was conducted in 2018 and current treatment planning methods and prescriptions were queried. RESULTS: Examination of the OOSC database revealed that average doses to critical structures were highly consistent, with the exception of one institution. Survey responses indicated that most centers followed published guidelines regarding dose and prescription point. Dose rate ranged from 51 to 118 cGy/h. As of 2018, most institutions use pre-loaded plaques and fundus photographs and/or computed tomography or magnetic resonance imaging in planning. CONCLUSIONS: While there were differences in dosimetric practices, overall agreement in plaque brachytherapy practices was high among OOSC institutions. Clinical margins and planning systems were similar among institutions, while prescription dose, dose rates, and dosimetry varied.

Vaginal Dose Is Associated With Toxicity in Image Guided Tandem Ring or Ovoid-Based Brachytherapy.

PURPOSE: To calculate vaginal doses during image guided brachytherapy with volume-based metrics and correlate with long-term vaginal toxicity. METHODS AND MATERIALS: In this institutional review board-approved study, institutional databases were searched to identify women undergoing computed tomography and/or magnetic resonance-guided brachytherapy at the Duke Cancer Center from 2009 to 2015. All insertions were contoured to include the vagina as a 3-dimensional structure. All contouring was performed on computed tomography or magnetic resonance imaging and used a 0.4-cm fixed brush to outline the applicator and/or packing, expanded to include any grossly visible vagina. The surface of the cervix was specifically excluded from the contour. High-dose-rate (HDR) and low-dose-rate (LDR) doses were converted to the equivalent dose in 2-Gy fractions using an α/ß of 3 for late effects. The parameters D0.1cc, D1cc, and D2cc were calculated for all insertions and summed with prior external beam therapy. Late and subacute toxicity to the vagina were determined by the Common Terminology Criteria for Adverse Events version 4.0 and compared by the median and 4th quartile doses, via the log-rank test. Univariate and multivariate hazard ratios were calculated via Cox regression. RESULTS: A total of 258 insertions in 62 women who underwent definitive radiation therapy including brachytherapy for cervical (n=48) and uterine cancer (n=14) were identified. Twenty HDR tandem and ovoid, 32 HDR tandem and ring, and 10 LDR tandem and ovoid insertions were contoured. The median values (interquartile ranges) for vaginal D0.1cc, D1cc, and D2cc were 157.9 (134.4-196.53) Gy, 112.6 (96.7-124.6) Gy, and 100.5 (86.8-108.4) Gy, respectively. At the 4th quartile cutoff of 108 Gy for D2cc, the rate of late grade 1 toxicity at 2 years was 61.2% (95% confidence interval [CI] 43.0%-79.4%) below 108 Gy and 83.9% (63.9%-100%) above (P=.018); grade 2 or greater toxicity was 36.2% (95% CI 15.8%-56.6%) below 108 Gy and 70.7% (95% CI 45.2%-96.2%) above (P=.004); and grade 3 or worse toxicity was 9.9% (95% CI 0.0%-23.6%) below 108 Gy and 30.0% (95% CI 4.7%-55.3%) above (P=.025). This association was maintained on multivariate analysis, independent of covariates such as applicator type, age, and dose rate. CONCLUSIONS: Vaginal dose was associated with all grades of vaginal toxicity. Confirmation at other sites using this methodology will be necessary to establish reproducibility; however, the integration of routine calculation of vaginal dose may be warranted.

Air kerma based dosimetry calibration for the Leksell Gamma Knife.

No accepted official protocol exists for the dosimetry of the Leksell Gamma Knife (GK) stereotactic radiosurgery device. Establishment of a dosimetry protocol has been complicated by the unique partial-hemisphere arrangement of 201 individual 60Co beams simultaneously focused on the treatment volume and by the rigid geometry of the GK unit itself. This article proposes an air kerma based dosimetry protocol using either an in-air or in-acrylic phantom measurement to determine the absorbed dose rate of fields of the 18 mm helmet of a GK unit. A small-volume air ionization chamber was used to make measurements at the physical isocenter of three GK units. The absorbed dose rate to water was determined using a modified version of the AAPM Task Group 21 protocol designed for use with 60Co-based teletherapy machines. This experimentally determined absorbed dose rate was compared to the treatment planning system (TPS) absorbed dose rate. The TPS used with the GK unit is Leksell GammaPlan. The TPS absorbed dose rate at the time of treatment is the absorbed dose rate determined by the physicist at the time of machine commissioning decay corrected to the treatment date. The TPS absorbed dose rate is defined as absorbed dose rate to water at the isocenter of a water phantom with a radius of 8 cm. Measurements were performed on model B and C Gamma Knife units. The absorbed dose rate to water for the 18 mm helmet determined using air-kerma based calculations is consistently between 1.5% and 2.9% higher than the absorbed dose rate provided by the TPS. These air kerma based measurements allow GK dosimetry to be performed with an established dosimetry protocol and without complications arising from the use of and possible variations in solid phantom material. Measurements were also made with the same ionization chamber in a spherical acrylic phantom for comparison. This methodology will allow further development of calibration methods appropriate for the smaller fields of GK units to be compared to a well established standard.