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The in vivo dosimetric monitoring in HDR brachytherapy is important for improving patient safety. However, there are very limited options available for clinical application. In this study, we present a new in vivo dose measurement system with a plastic scintillating detector (PSD) for GYN HDR brachytherapy. An FDA approved PSD system, called OARtrac (AngioDynamics, Latham, NY), was used with various applicators for in vivo dose measurements for GYN patients. An institutional workflow was established for the clinical implementation of the dosimetric system. Action levels were proposed based on the measurement and system uncertainty for measurement deviations. From October 2018 to September 2019, a total of 75 measurements (48 fractions) were acquired from 14 patients who underwent HDR brachytherapy using either a multichannel cylinder, Venezia applicator, or Syed-Neblett template. The PSDs were placed in predetermined catheters/channels. A planning CT was acquired for treatment planning in Oncentra (Elekta, Version-4.5.2) TPS. The PSDs were contoured on the CT images, and the PSD D 90% values were used as the expected doses for comparison with the measured doses. The mean difference from patient measurements was −0.22% ± 5.98%, with 26% being the largest deviation from the expected value (Syed case). Large deviations were observed when detectors were placed in the area where dose rates were less than 1 cGy/s. The establishment of clinical workflow for the in vivo dosimetry for both the intracavitary and interstitial GYN HDR brachytherapy will potentially improve the safety of the patient treatment. [ABSTRACT FROM AUTHOR]

Simulation-based education has been previously demonstrated to be efficacious for teaching intracavitary (IC) brachytherapy. In principle, the success of this "hands-on" approach could be extended to interstitial (IS) and/or hybrid IC/IS brachytherapy. Yet, this education technique has not been adopted and one reason may be the shortcomings of current simulation models. Highly-desirable features which were not available in current simulation models included: non-stylized realistic anatomical representation, compatibility with image-guidance (ultrasound, CT, and/or MRI), practical material for needle placement, and commercial availability. Our work presents results from our evaluation of the physical, radiographic, and imaging characteristics of a new commercial prototype phantom designed for simulation-based education. The SIM (Simulated Inanimate Models, Pittsford, NY) gynecological trainer prototype phantom was constructed based on a representative female pelvis CT imageset to provide physically realistic anatomy within a block of tissue-like material. The original CT imageset was truncated to a region of interest with dimensions of 160 × 160 × 220 mm. To provide a planning imageset, the phantom was imaged using CT with 1 mm slice reconstruction and using an axial T2 MRI sequence with 1.5 mm slice reconstruction. We assessed the anatomic dimensions of the model, physical compatibility with different hybrid applicators, and the quality of the radiographic model on imaging. After the implant was approved, a planning CT was taken, an HR-CTV was drawn, and the plan quality was evaluated. After clinical assessment, feedback was provided to the manufacturer for consideration in future designs. The phantom consisted of a 15 mm introitus which preceded a cylindrical air cavity with length of 75 mm and average diameter of 20 mm with irregular ridges intended to represent a vaginal canal which was capped by a pliable opening of 3 mm intended to represent an intact cervical os. Near the cervical region, the cylindrical air cavity widened from 20 to 28 mm. Proximal to the cervical os, there was a conical air cavity 80 mm in length which represented an intrauterine canal. In addition to the air cavities and tissue, the phantom was composed of three other distinct materials designed to represent bones, bladder, and rectum - each of which was distinguishable on US-, CT- and MR-based imaging. Within the phantom, an experienced physician was able to place a tandem-and-ovoid (TO) applicator with a 30 degree curved tandem, but was restricted to ovoid sizes ≤ 20 mm. To supplement the TO, the physician was able to place three IS needles to produce a realistic hybrid IC/IS implant intended to cover a hypothetical 35 × 35 × 40 mm3 HR-CTV. Coronal and sagittal views of the phantom post-implant planning CT imageset with in situ hybrid IC/IS equipment are shown in Figure 1. Figure 1 also contains the final plan with HR-CTV D 90% = 102% with the purple HR-CTV contour and red 100% isodose line. The primary clinical feedback provided to the manufacturer on this prototype phantom included: enlarging the vaginal canal dimensions to physically accommodate larger IC applicators; adding a visual/palpable cervical tumor to provide a target and recreate the needle-placement decision-making process. We report the basic characteristics of a novel gynecologic phantom prototype which intended for simulation-based training. This phantom provided an anatomically-realistic "hand-on" tool composed of various materials which were each distinguishable on three modalities: US, CT, MR. Clinical feedback was provided to the manufacturer for consideration in the next generation of this phantom. [ABSTRACT FROM AUTHOR]

Brachytherapy is an essential component of curative treatment for cervical cancer. Simulation-based education using models is an effective method for teaching intracavitary (IC) brachytherapy skills. While the use of interstitial (including hybrid) applications is increasing among physicians, simulation training for gynecologic interstitial brachytherapy has been unsatisfactory. This is in part due to the limitations of current simulation models, including unsuitable material for needle placement and incompatibility with ultrasound (US), CT and/or MRI imaging. We present here the results from a simulation-based hybrid brachytherapy workshop held in March 2022, in which we seek to validate a novel, commercially available US/CT/MRI-compatible gynecologic phantom for its use in gynecologic brachytherapy training. The SIM (Simulated Inanimate Models, Pittsford, NY) gynecological trainer phantom modeled a uterus, cervix, and vaginal canal within a block of tissue-like colloid material. The model also contained a gel-filled bladder and air-filled rectum. The phantom was US, CT, and MRI-compatible with realistic visualization of the pelvic organs, pubic bones, and sacral bones on imaging due to variable physical and hydrogen densities. We CT simulated the phantom with a tandem-and-ovoid applicator with 20 mm ovoids and a 30-degree curved tandem in place. We segmented the bladder and rectum and created a cervical HR-CTV with dimensions of 35 × 35 × 40 mm3. We then simulated the model again with 2 free-hand interstitial needles alongside the tandem-and-ovoids to improve geographic coverage of the HR-CTV. We designed a workshop incorporating the phantom and simulated datasets, during which trainees performed the following elements: 1- IC placement; 2- review of the IC-alone optimized plan treatment planning system; 3- schematic mapping on 3D diagrams of the HR-CTV in axial, coronal, and sagittal orientations; 4- pre-planning of location and depth of desired interstitial needles; 5- interstitial needle labeling and placement; 6- evaluation and modification of needle placement with imaging; 7- plan review and DVH comparison of HR-CTC coverage and organ-at-risk limits with and without the supplemental needles. Pre- and post-workshop surveys with Likert-style questions were administered. A Wilcoxon matched-pairs signed-rank test was used to assess statistical differences between pre- and post-workshop responses. Thirteen residents (PGY 2-5) participated in the workshops over the course of 3 separate 1-hour sessions. Seven residents reported performing 2 or more intracavitary procedures, and 6 reported performing 2 or more interstitial gynecologic procedures prior to workshop participation. All eligible residents completed each component of the workshop. Responses to questions ascertaining knowledge, preparedness, comfort, confidence, and ability in planning and executing IC and hybrid interstitial brachytherapy procedures all demonstrated significant improvement from pre- to post-workshop (Figure 1). In response to whether the session was an effective learning experience, all 13 residents rated the workshop with a score of 9 (n=1) or 10 (n=12) out of 10, with a score of 10 indicating 'strongly agree.' Suggested improvements to the model included increasing dimensions of the vagina, angling of the cervix/uterus, and adding a visible/palpable tumor. The novel gynecologic phantom simulates live tissue, permits needle placement, is US/CT/MR-compatible, and is commercially available. The improvements seen in trainee knowledge, skills, and confidence validate the novel gynecologic phantom for interstitial brachytherapy skills training. Based on responses from the workshop, improvements to the model are currently in progress, with modified model expected by the ABS annual meeting. [ABSTRACT FROM AUTHOR]