Presentation Time Research Articles

PO50 Presentation Time: 10:00 AM: Long-Term Results of Salvage High Dose-Rate Brachytherapy with or without Pelvic External Beam Radiotherapy in Patients with Palpable Local Recurrence of Prostate Cancer After Radical Prostatectomy

<h3>Purpose</h3> This study aims to evaluate the long term outcomes and toxicities in patients with clinically apparent, gross local recurrence of prostate cancer after radical prostatectomy, treated with salvage high dose-rate brachytherapy (HDR-BT) with or without pelvic external beam radiotherapy (EBRT). <h3>Materials and Methods</h3> Retrospective chart review was performed to identify patients with clinically apparent, gross local recurrence of prostate cancer after radical prostatectomy who underwent salvage HDR-BT at a single institution between 2002 and 2020. HDR-BT regimens included 950 cGy x 2 (N=4), 1500 cGy x 1 (N=2), 950 cGy x 4 (N=1), and 800 cGy x 2 (N=1). Pelvic EBRT was allowed at the discretion of the treating physician. Treatment and clinical characteristics were obtained for each patient, and outcome and toxicity data were collected. Toxicity was graded according to Common Toxicity criteria for Adverse Events Version 5.0. Descriptive analysis was performed. <h3>Results</h3> A total of 8 patients were included in analysis with a median follow-up of 49 months (range: 9 to 223 months). Five (63%) patients presented with a biochemical recurrence, and 3 patients (38%) presented with symptoms including hematuria and urinary obstruction. Seven patients underwent TRUS-guided biopsy which confirmed recurrent adenocarcinoma. The remaining patient underwent a PSMA PET/CT scan revealing a PET-avid soft tissue lesion in the prostate bed, but declined biopsy and proceeded with treatment without pathologic confirmation. Median age at time of salvage brachytherapy was 68 years (range: 59 to 85 years). Median time from prostatectomy to salvage HDR-BT was 95 months (range: 19 to 207 months). Median PSA at time of HDR brachytherapy was 2.32 ng/ml (range: undetectable on ADT to 13 ng/ml). Median lesion size was 2.5 cm (range: 1 to 3.6 cm). Six patients (75%) received adjuvant pelvic EBRT, 45-50 Gy in 25 fractions. Seven out of 8 patients received ADT after salvage brachytherapy for a median duration of 12 months (range: 8 to 24 months). The remaining patient did not receive ADT due to cardiac comorbidities. Seven out of 8 patients were alive at last follow-up. There have been no locoregional recurrences. Three patients developed distant metastatic disease. One patient, who had negative conventional staging scans 3 months prior to brachytherapy, was found to have distant metastatic disease only 2 months after salvage brachytherapy and died due to metastatic prostate cancer 9 months after HDR-BT. The other 2 patients developed distant metastases at 14 and 27 months after brachytherapy. One patient developed late grade 3 urinary incontinence requiring artificial urinary sphincter (AUS) placement 18 months after brachytherapy. This patient had the largest tumor size, 3.6 cm in longest dimension, and received pelvic EBRT in addition to HDR-BT. He is now more than 10 years out from HDR-BT with undetectable PSA and doing well with his AUS. There were no other grade 2 or higher genitourinary or gastrointestinal toxicities. <h3>Conclusions</h3> This study demonstrates the long-term safety and efficacy of salvage HDR brachytherapy in the setting of clinically apparent local recurrence of prostate cancer after radical prostatectomy, with durable locoregional control and acceptable rates of toxicity. HDR-BT should be further explored as an option for dose-escalated salvage radiotherapy in patients with gross local recurrences after radical prostatectomy.

GPP06 Presentation Time: 8:50 AM: Enhanced Recovery Pathway (ERP) in Patients Undergoing Brachytherapy for Gynecologic Cancer (GYN-BT)

<h3>Purpose</h3> ERPs have been adopted by many surgical specialties and have demonstrated improved outcomes, including shorter hospital stay, decreased healthcare costs, improved time to functional recovery and patient satisfaction.¹ There is no current literature evaluating ERP for patients undergoing brachytherapy as part of their radiation treatment. We plan to implement an ERP to standardize and optimize the peri-operative phase and to determine the impact on patient outcomes. <h3>Methods</h3> A single institution, prospective study evaluating the outcomes of patients undergoing GYN-BT before (33 patients) and after (33 patients) the implementation of an ERP. The ERP will include multidisciplinary interventions that span the pre-, intra-, and post-operative phases; including pre-habilitation, early referral to social work and psychiatric services, patient/caregiver education, pre-operative carbohydrate-loading, goal directed fluids, and opioid-sparing analgesia. Questionnaires (MDASI-PeriOp-GYN, EORTC QLQ-C30, and EORTC QLQ-CX24) to assess patient reported outcomes (PROs) at baseline, post-brachytherapy, and 60-day follow-up are collected. MDASI-PeriOp-GYN consists of 28 questions, scored from 0 to 10, with a score ≥7, considered severe. <h3>Results</h3> Twenty patients have enrolled and completed baseline PROs, of these 7 have completed post-brachytherapy surveys. Baseline mean total score was 3.07 (range, 1.3-7.9) and post-BT was 2.78 (range, 0.1-5.5). Mean number of severe events at baseline was 7 vs. 5.7 after brachytherapy. Independent symptom scores for the baseline population were worse for distress (3.7 vs 3), sadness (3.9 vs 2.4), ability to work (4.9 vs 4.4), relations with others (2.7 vs 2.1), pain (2.6 vs 2.0), constipation (3.1 vs 2.0) and bloating (3.1 vs 1.9); while post-BT scores were worse for dysuria (1.4 vs 0), diarrhea (4.6 vs 4.1), vomiting (1.4 vs 1.1), dizziness (2.1 vs 1.4), fatigue (6.1 vs 5.6), and hot flashes (2.9 vs 1.7) (Figure 1). <h3>Conclusion</h3> Female patients with gynecologic malignancies represent a population with high-symptom burden and social stress throughout treatment. Baseline data show that patient experience may be improved through early focus on social support and pain control and optimization of symptom management after brachytherapy; including nausea/vomiting, diarrhea, dehydration, and urinary toxicity. Our proposed ERP plans to address both of these initiatives.

PO26 Presentation Time: 7:40 AM: Dosimetry Accuracy of a Model-Based Dose Calculation Algorithm in Modeling a Novel Direction Modulated Brachytherapy Tandem Applicator for the Cervical Cancer

<h3>Purpose</h3> A novel shielded tandem applicator for the direction modulated brachytherapy (DMBT) was previously introduced, which showed capability to improve the coverage of nonuniform targets and organs at risk in cervical cancer. This applicator has been recently modeled in a commercial treatment planning system (TPS - BrachyVision ACUROS^TM (BVA)), a Model based Dose Calculation algorithm (MBDCA), for the clinical research. In this study, we aim to benchmark the accuracy of the TPS in modeling the DMBT tandem using Monte Carlo (MC) simulations. <h3>Materials and Methods</h3> The DMBT tandem applicator, made of an MR compatible tungsten alloy with six symmetrical grooves covered by a sheath of PEEK plastic, was simulated in GEANT4 MC code. Subsequently, two scenarios were created using the BVA TPS and reproduced by GEANT4 MC simulations, including ‘source at the center of the water phantom' and ‘source at the middle of the applicator' for the cubical phantoms with dimensions of (20 cm)³, (30 cm)³, and (40 cm)³. A track length estimator (TLE) was then utilized to estimate the dose deposited inside the water phantoms and 2D/3D scoring were performed. Volumetric dose comparisons of the TPS against MC results were further implemented. <h3>Results</h3> There were different level of agreements between the TPS and MC results for the different phantom sizes. The best agreement, however, was achieved for the phantom (40 cm)³, such that the dose difference fell in the intervals [0% 8.5%] and [-6.5% 6.5%] in 95% of the voxels, for the ‘source at the center of the water phantom' and ‘source at the middle of the applicator', respectively. In addition, the dose difference was within for all phantoms, within 5 cm from the center of the HDR sources. <h3>Conclusions</h3> The results of this study indicated that the accuracy of the TPS in dose calculation depends on the phantom size. Nevertheless, it seems the TPS could still provide satisfactory accuracy inside the area of clinical importance.

PO43 Presentation Time: 4:45 PM: Reduced Duration Intracavitary Brachytherapy in Cervix Malignancies: A Comparative Analysis from Single Institute

<h3>Purpose</h3> The on-going pandemic has impacted the use of anesthesia and the operating room frequency thereby affecting the brachytherapy treatment in various institutions due to the COVID-19 protocols. This has led to single applications of Intracavitary brachytherapy (ICRT) being used to deliver entire treatment boost in cervix cancer. We present our dosimetric and early clinical outcomes comparing traditional weekly three-fractions ICRT with single application/ two-applications ICRT <h3>Materials and Methods</h3> In this retrospective analysis conducted in our department, a total of 39 cases, treated between January 2021 to January 2022 were evaluated for the study. Of these, 15 cases were treated with the traditional once a week applicator insertion for 3 fractions and 24 cases underwent lesser application - 20 cases underwent 2 insertions and 4 cases single insertion (all receiving total 3 fractions of 7Gy each). The dosimetric parameters were compared including CTV D90 and D95 along with rectum, sigmoid and bladder D2cc, 1cc and 0.1cc respectively. The acute toxicity assessment was done using the RTOG scale. The follow-up was undertaken as per the institutional protocol and Mann-Whitney U-test were applied to compare the cohorts. <h3>Results</h3> With a median follow-up of 6 months, the median CTV was D90%: 81.2 vs. 80.9 Gy and the median CTV volume was 44.3 vs 42.9 cc respectively. The 0.1 cm³ and 2 cm³ to bladder, rectum, and sigmoid were 105.6 vs 104.2 Gy and 85.5 vs 85.9Gy, 89.4Gy vs 88.7Gy and 69.1 vs 67.8Gy, and 84.7 vs 84.1Gy and 71.7 vs 69.9Gy, respectively suggesting no significant difference in the dosimetric outcomes with the two forms of applications. The less than three applications had a shorter overall treatment time with median OTT of 43 days vs. 55 days (p = 0.02). On completion of treatment and 6 months follow-up, local control was achieved in all patients. There was no significant difference in the acute toxicities in terms of cystitis and proctitis in both forms of the application. <h3>Conclusion</h3> The single application/ twice application ICRT procedure showed similar outcomes as the traditional three-week duration treatment in terms of dosimetric outcomes and acute toxicities and ultimately leading to shortened overall treatment time. It also helped reduce the anesthesia burden and various resources associated with the procedure.

Friday, June 17, 202212:30 PM - 1:30 PM PHSOR01 Presentation Time: 12:30 PM: Characterization of a Novel Multi-Modality Imaging Phantom for Ultrasound Interstitial Needle Guidance for High Dose Rate Gynecological Brachytherapy

<h3>Purpose</h3> To design, manufacture, and validate a realistic female pelvic phantom for multi-modality imaging on CT, MRI, and transrectal ultrasound (TRUS) to guide and track interstitial needles during an HDR gynecological procedure using a commercial needle tracking system. <h3>Materials and Methods</h3> The pelvic phantom was designed using 3D Slicer and Autodesk Fusion360 to model an average uterus from a 50 patient data study¹, a vaginal canal from KleenSpec speculum dimensions, and a rectum to accommodate a BK 8848 endocavity biplane US probe. A 1.5 cm x 3.0 cm x 1.25 cm (WxLxH) half ellipsoid CTV_HR was also designed. Modeled anatomy was Boolean subtracted from rectangular solids to create a negative space mold. An Ultimaker S3 printer was used to print the 3D molds using polylactic acid. Smooth-On Silicone 20T was used as a casting agent for the uterus, cervix, vaginal canal, and rectum based on their similar mechanical properties. A 3D printed box was constructed to house the designed anatomy to provide structural integrity and allow the insertion of a speculum, tandem and ovoid applicator, needles, and TRUS probe. Agarose gelatin with glycerol and cellulose was used as a background medium to surround and support the pelvic anatomy and to allow for US propagation. After manufacturing, the phantom was imaged with CT to identify potential imperfections that might impact its visualization on US images. Following initial CT validation, the tracking system with the endorectal probe was used to image the phantom. US images from a 180 degree sweep were acquired and a 3D US volume was generated that allowed uterus contouring to aid in real-time insertion of 2 needles (Needle1 in CTV_HR, Needle2 in uterus). After insertion, the phantom was imaged with a Siemens Biograph mCT using a slice thickness of 0.6 mm and with a Siemens Skyra 3T MRI using the institutional HDR brachytherapy MR imaging protocol with T1 and T2 weighted sequences. The CTV_HR and uterus were contoured on CT and MR images and their dimensions were checked against the CAD model. <h3>Results</h3> Fig. 1a shows the CAD model for the anatomy (uterus dimensions of 7.87 cm x 4.45 cm, rectum diameter of 2 cm), the encasing box, and the casting mold used to fabricate the phantom. The volumes of the CTV_HR and uterus reconstructed from the CAD model were 3 cm³ and 76.8 cm³, respectively. Figs. 1b-c show sagittal CT and US images of the phantom. The measurements of uterus dimensions (7.87 cm x 4.4 cm) and rectum diameter (2 cm) on the sagittal CT image demonstrated a high degree of fidelity with the CAD model. The uterus volume (77.1 cm³) reconstructed from CT images was also very similar to that from the CAD model. Fig. 1d shows the phantom setup for US imaging using the needle tracking system and BK 8848 endorectal probe. Representative sagittal images through the phantom at the location of the 2 implanted needles are shown in Figs. 1e-h (CT, T1w MRI, T2w MRI, and US, respectively). The overall volumes CTV_HR (3.2 cm³) and uterus (82.9 cm³) reconstructed from the T2w MR images also agreed with those from the CAD model. Fig. 1f shows axial and sagittal images of the 3D US volume from the tracking software (uterus contour in green). The generated volume allowed for intraoperative needle insertion guidance. <h3>Conclusions</h3> The manufactured pelvic phantom allows for accurate visualization with multiple imaging modalities and is conducive to applicator and needle insertion. The phantom is low cost and can be reproducibly manufactured with the 3D molding process. Our initial experiments demonstrate the ability to integrate the phantom with the commercial tracking system for future needle tracking validation studies. 1. Campelo, et al. (2020). Brachytherapy, 19(6), 767-776

GSOR16 Presentation Time: 11:45 AM: Financial Toxicity in Patients Undergoing Brachytherapy for Gynecologic Cancers

<h3>Purpose</h3> Financial toxicity (FT) affects about 50% of patients with gynecologic cancer. Brachytherapy (BT) is an important component of treatment for many of these patients. We aimed to assess factors that contribute to FT in patients with gynecologic cancer who undergo BT. <h3>Materials and Methods</h3> Gynecologic oncology patients undergoing BT from October 2017-February 2021 completed a survey that included demographics, the EQ-5D-3L to measure quality of life, and Comprehensive Score for Financial Toxicity (COST) tool to measure economic burden. High FT was defined as a COST score ≤23. We stratified patients into 3 groups: vaginal BT (VBT) only, VBT with external beam radiation therapy (EBRT + VBT), or "other" types of BT with external beam radiation therapy (EBRT + other BT). "Other" types of BT included tandem and ovoids, tandem and ring, and interstitial implants. Data presented as percent or median (interquartile range) and compared with Chi-square/Fisher's exact test and Wilcoxon rank-sum test, respectively. We used modified Poisson regression to calculate risk ratios (RR) and 95% confidence intervals (CI) with high FT as the outcome and type of BT as the exposure. <h3>Results</h3> Among 101 respondents, median COST score was 30 (IQR 21-35); 28% had high FT [median COST: 14 (IQR 9-19)] and 72% had low FT [median COST: 32 (IQR 28-37)]. Respondents were white (81%), 9% Black, and 7% Asian. Median age was 63 (57-71), with a younger age in the high FT group [59 (49-62)] compared to the low FT group [67 (61-72), p<0.01]. Patients in the high FT group were more likely to be single (32%) compared to those in the low FT group (10%, p=0.01). In the high FT group, 68% of patients had private insurance, whereas 38% had private insurance in the low FT group (p<0.01). Most patients (71%) had uterine cancer, followed by cervical (23%) and vaginal/vulvar (6%) cancer. The majority (69%) of the entire group had stage I disease, with more patients in the low FT cohort having stage I disease (75%) compared to the high FT cohort (54%, p=0.03). Within the treatment groups, 51% received VBT alone, 29% received EBRT + VBT, and 21% received EBRT + other BT. The type of BT was significantly associated with FT. VBT alone was more common in the low FT group (58%) than the high FT group (32%), and EBRT + VBT was less common in the low FT group (21%) than the high FT group (50%, p=0.01). Patients who had EBRT + VBT were 2.8 times (95%, CI 1.2-6.5) more likely to have high FT compared to VBT patients; this association was attenuated when adjusting for age and insurance (RR 2.0; 95%, CI 0.84-4.7). Of the assessed cost-coping strategies, borrowing money was reported by 31% of the EBRT + VBT, 24% of the EBRT + other BT, and 2% of the VBT groups (p<0.01), and reduced leisure spending was reported by 31% of the EBRT + VBT, 5% of the EBRT + other BT, and 16% of the VBT groups (p<0.01). <h3>Conclusions</h3> A substantial proportion of patients going through BT have high FT. Younger age, being single, having private insurance, and higher stage disease were associated with higher FT. There is a higher risk of FT associated with undergoing EBRT. Patients who go through only VBT were least likely to have high FT. Patients going through EBRT were more likely to borrow money and reduce leisure spending as cost-coping strategies. Further research is needed to understand specific drivers of high FT for patients receiving EBRT and BT and to evaluate FT over time.

GSOR20 Presentation Time: 12:05 PM: Vaginal Cuff Brachytherapy versus External Beam in High Risk (T1b Grade 3) Endometrioid Endometrial Cancer: An NCDB Analysis

<h3>Purpose</h3> The optimal adjuvant management of localized, resected high risk (HR) Stage I endometrioid endometrial cancer (i.e. FIGO grade 3 with > 50% myometrial invasion) remains unclear. A Cochrane meta-analysis showed a 10% overall survival (OS) benefit when EBRT (external beam radiation therapy) was given versus no radiation treatment. However, no randomized trials have compared adjuvant EBRT to VCB (vaginal cuff brachytherapy) without chemotherapy. A SEER analysis from 2012 showed reported that in women with lymph node dissection, there was no difference in OS between EBRT and VCB in patients with HR Stage I endometrial cancer. We hypothesized that adjuvant EBRT or VCB would both be equally associated with improved OS in HR Stage I endometrial cancer in a large, modern database. <h3>Materials and Methods</h3> The National Cancer Database (NCDB) was queried for women diagnosed with endometrioid endometrial cancer from 2004-2017, who had undergone total hysterectomy or greater, and lymph node dissection revealing a pathologic stage of IB (AJCC Edition 6) or IC (AJCC Edition 7), and FIGO Grade of 3. Women were grouped by receipt of multiagent chemotherapy (MCT), VCB (without EBRT), EBRT (without VCB), or EBRT+VCB. OS was measured by Kaplan-Meier estimator, and compared using log rank test. Cox proportional hazard modeling was done, using as additional covariates tumor size, lymphovascular space invasion (LVSI), margin status, age, extent of comorbidities, treatment year, and several demographic factors (race, insurance status, educational and income level of zip code, urban versus rural location). A propensity score weighted analysis was performed, using the above covariates. <h3>Results</h3> 10,357 women were analyzed. As adjuvant treatment, 22% received EBRT alone, 26% received VCB alone, 11% received EBRT+VCB, and 42% received no radiation. 30% received adjuvant chemotherapy. Median OS for the entire group was 11.0 years. For the whole group, median OS times were 12.8 years with VCB alone, 11.3 years for EBRT alone, and 11.5 years with EBRT+brachytherapy, which were not significantly different (p > 0.05). However, median OS was only 8.6 years in patients not receiving any radiation, (p <0.0001 compared to receipt of each of the radiation modalities). For patients receiving no adjuvant chemotherapy, median OS was 12.3 years for EBRT alone, 12.8 years with VCB alone, 11.9 years with EBRT+brachytherapy (p > 0.05), but was only 9.6 years in patients not receiving any radiation (p < 0.00001). On multivariate analysis, receipt of radiation (but not receipt of multiagent chemotherapy), smaller tumor size, absence of LVSI, less comorbidities, younger age, and white race were associated with improved overall survival (p <0.003). Propensity score weighted analysis confirmed the OS benefit for women who received any RT. <h3>Conclusions</h3> In this large database, VCB and EBRT had comparable effectiveness in improving OS for HR Stage I endometrial cancer. With equal effect, VCB is favored given the more convenient schedule and decreased side effects as shown in previous randomized trials. The results of this study give impetus for a randomized trial comparing EBRT and VCB without chemotherapy in women with HR endometrioid endometrial cancer. In addition, a large percentage of women with HR disease who did not receive any radiation, despite this being the standard of care with known survival advantage, which reveals likely deficiencies in health care delivery.

PO25 Presentation Time: 7:40 AM: A Web-Based Data Recording and Patient Tracking System for Cervical Cancer Patients Treated with Combined Treatment in Different Centers: BrachydATA

<h3>Purpose</h3> This study aims to create a web-based data recording and patient tracking system for cervical cancer patients treated with combined treatment in different centers: BrachydATA. <h3>Materials and Methods</h3> For this purpose, first of all, domain and hosting SSL for website were purchased, and then special software was purchased for data entry, storage, and processing. The patient, disease, treatment, treatment response, and toxicity characteristics that we planned to enter the system were determined following the literature review. <h3>Results</h3> The web address is http://www.brachydata.com/cervix/. The patient, disease, treatment, treatment response, and toxicity characteristics that we planned to enter the system as 4 main steps are shown in Table 1. It has been settled the system can automatically calculate EQD2 values for target and organs at-risk using the entered dose information, and the system can export the entered data as an excel table. Usernames will be given to enter the data from each center, and all users will be able to see the data only from their centers. <h3>Conclusions</h3> For now, only data entry could be made into the system, and the system will be developed by testing it by different centers and enabling artificial intelligence and machine learning algorithms to work in the background.

PHSPP02 Presentation Time: 2:40 PM: Automated Channel Identification for Efficient Brachytherapy Treatment Planning

<h3>Purpose</h3> For interstitial brachytherapy, channel reconstruction during the process of brachytherapy treatment planning can be an arduous and time-consuming task, which becomes more difficult and error-prone when 20 to 30 different catheters with curvatures are involved and overlap in 3D in the patient anatomy. The goal of this project is to develop an artificial intelligence-based approach for automated channel identification using patient CT scans, reducing both the time and potential for human error in brachytherapy treatment planning. <h3>Materials and Methods</h3> Three sets of CT scans were used as well as a baseline model for training, which were acquired with a set of binary-coded "dummy wires" markers <i>in situ</i>. Each of the 12 available dummy wires was designed with a unique pattern of radio-opaque markers and/or spacing strands which was mapped to a channel identification array. An identification algorithm was developed which involved first manually specifying the 3D DICOM coordinates of the centroids of each of the marker strands within the dummy wires. A nearest neighbor search was performed using a k-d tree method for each centroid acting as a potential starting point within a channel. Using the knowledge from the baseline model of each of the 12 potential dummy wire markers, the system predicted the most probable trajectory through the centroids. Then, to assign the proper channel number, the identified pattern of the applicable neighboring points was correlated with the channel identification array defined previously. This process was repeated until the entire configuration of channel identities was determined. Finally, a process of elimination was used to output the correct channel labels and locations. <h3>Results</h3> In this feasibility study, the developed algorithm was able to suitably provide channel identities and return the locations to the user when the proper centroid locations were input into the model. The model ran within seconds and required no training data other than the layout and spacing of the strands within the coded dummy-wire marker system. The final output was able to be graphically represented as labeled reconstructions of the catheters in a 3D space. <h3>Conclusions</h3> The outcomes of this preliminary work suggested that there is a future for automated aid in the channel identification process based on coded dummy-wire markers for more efficient treatment planning in brachytherapy. Using only the centroids of the markers, the channels could be accurately reconstructed. Future work will involve creating a 3D CT scan-based image detection algorithm to automate the process of defining the centroid locations without any <i>a priori</i> knowledge.

Saturday, June 18, 20227:40 AM - 5:00 PMPO22 Presentation Time: 7:40 AM: A Novel Algorithm for Automatic Interstitial Needle Tracking on PETRA MRI for HDR Brachytherapy

<h3>Purpose</h3> Current practice for interstitial high-dose-rate (HDR) brachytherapy treatment planning involves manual tracking of needle positions on CT images. Recently, PETRA MRI showed the potential to detect empty interstitial gynecological brachytherapy needles owing to low needle signal, intermediate tissue contrast and high spatial resolution. We aimed to develop an algorithm for automatic interstitial needle tracking on PETRA images by employing their negative contrast against surrounding tissue. <h3>Materials and Methods</h3> Fourteen ProGuide Sharp Needles 6Fx294mm were implanted in an endometrial adenocarcinoma patient using a Syed-Neblett template. One of the needles lay in the obturator center, and six inside the obturator slots. The patient underwent standard CT imaging with copper-filled needles. After marker removal, 3D PETRA images of the patient's pelvis (TR\TE 3.32\0.07 ms, voxel size 0.9 mm³ isotropic, 416 slices) were acquired on a 3T Siemens Vida MR scanner. PETRA MR images were analyzed for interstitial needle detection using custom code in MATLAB R2022a. A rectangular part of all axial slices where needles may be contained (slices 149-310) was selected. For each slice part, corner points were extracted from the original part and from its sharpened gradient magnitude image by detecting Harris features. Points found within Euclidean distance (ED) of 3 pixels on both images were matched, and the pixel with minimum signal intensity closest to each such point on the original part was selected. Minimum intensity points lying within 2 pixels ED between subsequent slices were considered as possible catheter coordinates. Such points appearing on at least 10 continuous slices were designated as true catheters, and their positions were compared to those visible on CT. <h3>Results</h3> Figure 1a) displays the selected MR image parts for two example slices. Pixels with detected Harris features and their closest signal minima are marked by red and green crosses, respectively, in b). Pixels accepted as needle positions are shown as magenta crosses in c). Matching CT image parts with bright marker-filled needles are displayed in d). Empty interstitial catheters on PETRA images corresponded to local minima of signal intensity, located near Harris features. The assumption of needle position continuity within an allowed distance along subsequent slices helped avoid spurious signal minima, while following needle position variations caused by different deflection angles. Needles guided through the obturator grooves and the central needle were detected only after they became detached from the obturator (ex. figure left). All 14 needles were tracked along their visible length inside tissue (ex. figure right). Visual comparison to CT images confirmed interstitial catheter detection on MRI. Selecting a range of slices and zooming on a part of each slice for analysis reduced computational time and output data size. <h3>Conclusions</h3> Automated detection of interstitial needles is feasible on PETRA MR images and may facilitate MR-only treatment planning in interstitial HDR brachytherapy. The newly developed algorithm was able to track all needles inside tissue based on their signal intensity characteristics, without requiring manual seed position placement.

Saturday, June 18, 20223:45 PM - 4:45PM MSS01 Presentation Time: 3:45 PM: A Single-Institution Retrospective Study of Three-Fraction HDR Accelerated Partial Breast Irradiation

<h3>Purpose</h3> Accelerated partial breast irradiation (APBI) delivered with high-dose-rate brachytherapy is a standard of care treatment which is typically delivered over 8-10 fractions. The TRIUMPH-T multi-institutional study recently demonstrated promising results using a shorter three fraction regimen. However, there are limited additional published series using this regimen. Here, we report our experience and outcomes for patients treated as per the TRIUMPH-T regimen. <h3>Materials and Methods</h3> Retrospective single-institution analysis of patients who underwent lumpectomy followed by APBI (22.5 Gy in 3 fractions delivered over 2-3 days) using a SAVI applicator between November 2016 and January 2021. Per the TRIMPH-T protocol guidelines, the planning treatment volume (PTV) was 1 cm beyond the surgical cavity, limited to 0.5 cm from the skin surface, and subtracted from chest wall and SAVI cavity. Dose-volume metrics were obtained from the clinically treated plan. Chart review was performed to determine locoregional recurrence and toxicities according to CTCAEv5.0. <h3>Results</h3> From 2016-2021, 31 patients were treated per the TRIUMPH-T protocol. The median age was 64 years (range 46-82). 77% of patients had invasive ductal carcinoma, median tumor size was 1.2 cm (range 0.4-2.0), 84% were Grade 1-2, 90% were N0 (3 DCIS patients were Nx), and 100% were ER+. Median follow-up was 31 months (range 6-62 months) from completion of brachytherapy. PTV median dose metrics were as follows: D90: 94.6% (range 90-110%), V150: 22.0cc (range 12.5-38.2cc), V200: 11.0cc (range 3.5-21.2cc), and DHI: 0.51 (range 0.36-0.68). Median D0.03cc for the skin (3 mm inner margin on body) and rib were 68.3% (range 29.9-91.6%) and 70.6% (range 15.7-124.2%), respectively. There were no acute/late grade 3 or higher toxicities. Cumulative late Grade 1 and 2 toxicities were seen in 58% and 6% of patients, respectively. Grade 1-2 fibrosis was seen in 32% of patients. Other toxicities included grade 1 breast pain (26%), grade 1-2 seroma formation (23%), grade 1 hyperpigmentation (6%), symptomatic fat necrosis (6%), and breast infection (3%). Of note, four patients experienced locoregional recurrence: three ipsilateral breast tumor recurrences (two in the same quadrant as the lumpectomy cavity), and one nodal recurrence (patient was cN0/pN0). All three ipsilateral breast tumor recurrences occurred in patients who would be classified as "cautionary" based on ASTRO consensus guidelines due to age ≤50, lobular histology, or high grade. There were no distant recurrences or deaths of any cause. <h3>Conclusions</h3> Three-fraction HDR brachytherapy APBI delivered per the TRIMUPH-T protocol was well-tolerated in our cohort with no grade 3 or higher toxicities and an acceptably small percentage of grade 2 toxicities. Given the small sample size, the number of recurrences suggests that attention to appropriate patient selection is necessary until more long-term follow-up data is available.

PHSOR07 Presentation Time: 1:00 PM: Feasibility of Using Dual-Activity Seed Loading When Using Eye Physics Eye Plaques and Plaque Simulator Treatment Planning in Eye Plaque Brachytherapy

<h3>Purpose</h3> Uveal melanoma is a tumor of the eye commonly treated with the application of gold plaques loaded with radioactive I-125 seeds. This study evaluates the dosimetric impact of incorporating dual-activity seed loading in Eye Physics eye plaques under two clinical scenarios that may benefit from this dual-activity approach. <h3>Materials and Methods</h3> Plaque Simulator (Eye Physics, LLC, Los Alamitos, CA) was used to retrospectively re-plan 10 clinical cases for two clinical scenarios: 1) shallow (<5.5 mm) tumors with large base dimensions (16 mm - 19 mm) planned with the largest plaque available from Eye Physics (EP2342 in Fig.1), and 2) tumors very near the optic nerve planned with EP2029N notched plaque (Fig. 1). Five clinical plans were selected for each clinical scenario. The clinical plans chosen were prescribed to at least 2 mm deeper depth than the tumor apex in order to achieve target (base + 2 mm margin) coverage of at least 95%. In the replanning, some of seeds in the plaque were replaced with higher activity seeds. For Scenario 1), EP2342 plaques were planned with the outer ring of sources at twice the activity of the inner sources. For Scenario 2), EP2029N plaques were planned with the 6 seeds closest to the notch at twice the activity of the other sources. Seed loading was kept symmetric for ease of loading, QA, and plaque placement. Plans were based on retinal sketches rather than digitized directly from retinal imaging, so the exact dose to critical structures is an estimate, but the direction and approximate magnitude of the dose change can be analyzed. <h3>Results</h3> In all the cases of large shallow tumors for Scenario 1), the dual-activity plan was able to decrease the prescription depth by 0.8 mm to 1.3 mm. Therefore, doses to all critical structures were consistently lower in dual-activity plans: inner sclera -24.6% ± 1.6%, optic disc -6.5% ± 2.5%, fovea -6.0% ± 3.3% (average ± standard deviation). In 3 out of 5 tumors close to the optic nerve for Scenario 2), the dual-activity plan was able to decrease the prescription depth by 0.5 mm to 0.7 mm. In all 5 of these cases, dose to inner sclera was consistently lower in the re-plans by 20.9%±5.6% and dose to the optic disc and fovea were consistently higher by 19.3%±7% and 21.8%±11.4% respectively. <h3>Conclusions</h3> For large shallow tumors, critical structure dosimetrics were constantly improved due to shallower prescription depth by partially loading with higher activity seeds. The largest dose reduction occurs to the inner sclera since it is close to the plaque, but changes in other critical structures were patient-specific depending the location of the tumor in the eye. It may be beneficial to always plan tumors such as these with dual activities. As this is the largest plaque offered by Eye Physics, this planning approach may allow it to be used for larger tumors while still maintaining reasonable dose to critical structures. For tumors near the optic nerve, the results showed that although scleral dose was decreased, dose to optic disc and fovea were increased. As this difference is due to the location of the tumor relative to the optic nerve and the fovea, it may be beneficial to investigate dual activity plans on a case-by-case basis if scleral dose is a concern for that particular patient.

PSOR3 Presentation Time: 11:40 AM: The Role of CAPRA Score as a Predictor of Outcomes in High-Risk Prostate Cancer Patients Treated with EBRT Plus HDR Brachytherapy Boost: A 20-year Single-Institution Experience

<h3>Purpose</h3> The study aimed to report clinical outcomes of high-risk prostate cancer (PCa) patients treated with external beam radiation therapy (EBRT) and high dose-rate boost (HDRB) according to CAPRA score. <h3>Material and Methods</h3> The study sample consisted of 361 high-risk PCa patients stratified according to D'Amico classification and treated with EBRT and HDRB and antiandrogen therapy (ADT) between 1999 and 2016. We conducted retrospective competing-risk survival analyses to compare individuals with a CAPRA score lesser than or equal to five and greater than five on biochemical recurrence (BCR) and metastasis incidence. Kaplan-Meier analysis was performed to assess overall survival (OS). Subsequently, we used ROC curves to compare the performance of the CAPRA model to the MSKCC stratification tool on BCR and metastasis incidence. <h3>Results</h3> The mean age of the patients at treatment time was 69.6±7.3 years. The median follow-up was 55.5 months. Of the 361 individuals, 52,4 % (n=189) had a CAPRA score above five. In comparison to individuals with a CAPRA score lesser than or equal to five, individuals with a CAPRA score above five were deemed at higher risk of BCR (sHR = 2.74, 95% CI: 1.12-6.66, p=0.027) and demonstrated a tendency towards significance in their metastasis incidence trend (sHR 2.33 95% CI: 0.89-6.12, p = 0.085). For 10-year OS, there was a HR for mortality of 1.89 (95% CI: 1.04-3.43, p=0.036) for individuals with a CAPRA score above five. There was no significant difference between either risk stratification strategy in ROC curves analysis. <h3>Conclusions</h3> The data suggest that patients' tumours classified as high-risk using the CAPRA score correlated with a higher risk of BCR, metastasis, and mortality when compared to lower-risk tumours. Further studies are needed to validate the use of the CAPRA score to predict cancer-specific mortality (CSM) as an initial risk stratification tool.

GSOR25 Presentation Time: 12:30 PM: Interim Pre-Brachytherapy Magnetic Resonance Imaging (MRpb) Response as Predictor of Local Control in the Definitive Treatment of Cervical Cancer

<h3>Background</h3> External beam radiotherapy (EBRT) followed by brachytherapy is standard of care in the management of cervical cancer. Whether early imaging response can predict longer term outcome is unclear. In this study, we investigated the role of interim pelvic magnetic resonance imaging (MRI), done prior to brachytherapy (BT) in predicting local tumor control. <h3>Methods</h3> We identified 87 consecutive patients who underwent definitive EBRT followed by BT for FIGO IIB-IVA cervical cancer at our institution between 2012 and 2020. The median age was 54 years (range, 23-81 years). Most patients had squamous cell carcinoma (77%), advanced stage disease (57.5% stage IIIA and higher, 51.7% nodal disease) and received concurrent cisplatin (98.8%). All patients had an MRI at baseline (MRb) and prior to brachytherapy boost (MRpb). The median time from completion of EBRT to MRpb was 3 days (IQR: -14d to +1d). EBRT included the regional LNs and primary site (median dose 45Gy, range 45-54Gy). Node positive patients also received a boost (median 5.4Gy, range 5.4-14.4Gy) Fifty-seven patients (65.5%) had intracavitary brachytherapy (median dose 28Gy, range 2-28Gy) and 30 (34.5%) had an interstitial BT (median dose 24Gy, range 20-28Gy). Adjuvant chemotherapy was delivered in 24 cases (27.6%). Patients were followed post-treatment with pelvic exams/cytology every 3 months for years 1-2 and every 6 months thereafter. PET/CT and a pelvic MRI were done 3 months posttreatment and as clinically indicated thereafter. Median follow up time was 35.5 months (range 3.8-114.2 months). Response to EBRT on MRpb was defined as residual disease > 2 cm, residual disease ≤ 2 cm and no measurable disease (complete response, CR). Local failure was defined as recurrent or persistent tumor in the cervix following all treatment and confirmed pathologically. Chi square test was used to compare categorical data. <h3>Results</h3> Overall, 19.5% of patients had a CR, 22.9% had residual disease ≤2cm and 57.5% had residual disease >2cm noted on MRpb. No patients who achieved a CR on MRpb had local recurrence. Of patients with residual disease ≤2 cm on MRpb, 19/20 patients (95%) ultimately achieved CR on subsequent imaging (median time to CR 3.1 months; range, 2.7-8.6 months), none of whom had a local failure. Of patients with residual disease >2 cm on MRpb, 40/50 (80%) ultimately achieved CR on subsequent imaging (median time to CR, 3.6 months; range, 2.1 - 18.6 months). Of the 10 patients with residual disease >2 cm on MRpb who did not achieve a CR, 4 had local failure, 1 had local and distant failure and 5 had regional or distant failure only. Overall, 6/50 (15%) patients with persistent disease >2 cm had local failure, compared with none of the patients who had more profound responses. Local disease response on MRpb did not predict regional or distant failure (p=0.35). <h3>Conclusions</h3> Interim pre-BT MRI seems promising in predicting local tumor control in the definitive management of cervical cancer and could be instrumental in dose intensification/de-escalation efforts. Further investigation of various MRI sequences in predicting response and long-term control is ongoing.

PO39 Presentation Time: 4:45 PM: Medical Comorbidities in Cervical Cancer Treated with External Beam Radiotherapy and Brachytherapy: A Single Institutional Study

<h3>Purpose</h3> There are limited studies on the association between medical comorbidities and cervical cancer. This study aimed to elucidate the incidence, spectrum, and impact of medical comorbidities on clinical outcomes in patients with cervical cancer treated by external beam radiotherapy (EBRT) and intracavitary brachytherapy (ICBT). <h3>Materials and Methods</h3> From October 2015 to September 2018, data of 100 cervical cancer patients were collected from our institute. These patients were treated with EBRT with concurrent chemotherapy followed by brachytherapy. The following important information was extracted: age, disease stage, comorbidities, treatment, follow-up, disease status, and radiation toxicities. <h3>Result</h3> Median age of patients with and without comorbidities were 52.5 and 47.5years. A total of 39 medical disorders were found in 28 patients. The distribution as per comorbidities was as follows: Hypertension, 17 patients; diabetes mellitus, 7 patients; hypothyroidism, 3 patients; cardiovascular disease, 3 patients, and others 9 patients. Out of 28 patients with comorbidities, 10 patients were stage IIIB, 10 were IIB, 4 were stage IB2 and the rest were other stages. Of them, 24 patients completed the prescribed treatment, and the remaining 4 patients did not complete ICBT. Median survival among patients with and without comorbidities was 28 and 26.5 months respectively. The 3-year overall survival rate in patients with and without comorbidities was 84.6% vs 89% (p-value, 0.56). There was no correlation between comorbidity and late radiation morbidity. <h3>Conclusion</h3> Results of our study show that the incidence of medical comorbidities can be as high as 28% in cervical cancer patients. Hypertension and diabetes are the commonest comorbidities associated with cervical cancer. There was no impact of comorbidities on clinical outcomes in cervical cancer patients.

Friday, June 17, 20224:00 PM - 5:00 PM MSPP01 Presentation Time: 4:00 PM: A Feasibility Study on Utilizing Cadaveric Models at a Network of Brachytherapy Research and Training Centers to Encourage Development and Widespread Use of Novel Robotic Bladder Cancer Brachytherapy Techniques

<h3>Purpose</h3> This feasibility study outlines a proof-of-concept model – the Houston Methodist Institute for Technology, Innovation & Education (MITIE) – for the use of cadaveric models at research centers to encourage development and training of novel robotic brachytherapy techniques, thereby expediting the incorporation of brachytherapy into the standard of care for muscle-invasive bladder cancer (MIBC). <h3>Materials and Methods</h3> Catheter insertion sites were marked on a male cadaver, and the da Vinci Surgical System(R) (Intuitive Surgical, Inc., Sunnyvale, CA) was docked. A modified catheter-needle system was assembled since pre-assembled bladder-specific catheter-needle systems are not compatible with all brachytherapy afterloaders. Closed-end catheters were inserted into 17-gauge curved needles. The first catheter was placed into the right lateral hypogastric abdominal wall, through the bladder dome wall, and out the opposing side. A single plane implant was completed with 1 cm spacing with the two other catheters (Figure 1a). Catheters were secured with nylon retaining buttons (Figure 1b). A CT simulation scan confirmed placement and a plan was developed for simulated brachytherapy delivery (Figure 1c). <h3>Results</h3> Cadaveric models enable physicians to develop new brachytherapy procedures in a controlled and simulated surgical environment without affecting operative time. Physicians can gain familiarity with the procedure and practice alterations to surgical equipment, including the catheter-needle system, which may prevent complications peri- and postoperatively. The proof-of-concept trial in MITIE shows how research and training centers can serve as incubators for the development of brachytherapy techniques. With a network of these centers, experts across the country can collaborate to test new techniques on cadaveric models and accelerate developments in bladder brachytherapy. This network would provide training opportunities for physicians, especially residents, which can familiarize physicians with brachytherapy techniques, promoting their use and providing clinical data to support these techniques as a new standard of care. Currently, institutes like MITIE are limited in number, necessitating travel and coordination of attending and resident physicians' schedules. Although an expanded network of these institutes would alleviate this issue, these training centers are associated with high operating costs, including the acquisition costs and high turnover rate required of cadaveric training models. Therefore, cost may impede scalability and must be considered alongside the benefits of establishing a widespread network of research and training programs for brachytherapy. <h3>Conclusions</h3> Robotic brachytherapy is a rarely utilized, minimally invasive treatment modality for MIBC. Innovation-focused facilities with cadaveric models can provide simulated surgical environments for the research, development, and training of robotic brachytherapy techniques and applicators, accelerating the acceptance of brachytherapy as the standard of care for MIBC.

PO38 Presentation Time: 4:45 PM: Dose at PIBS Point: A Predictor for Vaginal Stricture in Cervical Cancer

<h3>Purpose</h3> To co-relate vaginal stricture with the radiotherapy dose at the posterior inferior border of symphysis (PIBS) points in the patients with locally advanced cervical cancer. <h3>Material and Methods</h3> A total of 45 untreated patients, with ECOG 0-2 registered from January 2020 to March 2021 with histopathologically proven carcinoma cervix from stage IIB to IVA were included in the study. All the patients received external beam radiation therapy (EBRT) on 6 MV Linear Accelerator with Volumetric modulated arc therapy (VMAT) to a dose of 45 Gy in 25 fractions to the pelvis and 55 Gy in 25 fractions to the positive nodal disease (Pelvic & Paraaortic) with simultaneous integrated boost (SIB) along with weekly concurrent cisplatin at 40 mg/m². Twenty-three patients were treated with Intracavitary Brachytherapy (ICRT) with a dose of 7 Gy per fraction for three weekly fractions. All the patients were scanned with 1 mm slice thickness & 3-D planning was done on Oncentra treatment planning system. The contouring of targets was done as per ICRU 89 in case of ISBT. Twenty-two patients were treated with interstitial brachytherapy (ISBT), with 6 Gy per fraction for four fractions. The dose was prescribed to HR CTV and point A for ISBT and ICRT respectively. The time gap between two fractions for patients treated with ISBT was at least six hours. Evaluation of disease status and treatment response was done with Functional MRI Pelvis before, during, and 3 months after completion of radiotherapy. Late vaginal morbidity was assessed as per CTCAE v5.0. <h3>Results</h3> The mean duration of follow-up was 12.17 months (1-24.3 months).35.6 % of patients had vaginal stricture with a mean duration of appearance at 7.55 months and a median duration of 8.0 months (3.9-12 months). 24.4% had grade 1 vaginal toxicity, 6.7% had grade 2 vaginal toxicity, 4.4% had grade 3 toxicity. Doses at PIBS 0, PIBS minus points had no correlation with vaginal toxicity, however, dose at PIBS plus 2 was significantly associated with vaginal stricture (p =0.03). Threshold doses and time of appearance of vaginal toxicity are shown in table 1. <h3>Conclusion</h3> Dose at PIBS + 2 is a strong predictor for vaginal stricture. Efforts during brachytherapy planning should be taken to reduce the dose to PIBS +2 so as to reduce the probability of vaginal stricture.

GSOR10 Presentation Time: 9:45 AM: Positron Emission Tomography (PET) versus Computed Tomography (CT)-Guided Intracavitary Brachytherapy for Locally Advanced Cervical Cancer: A Randomised Study

<h3>Purpose</h3> This study compared early clinical outcomes in locally advanced cervical cancer (LACC) treated with PET-CT guided intracavitary brachytherapy (ICBT) versus 3D CT guided ICBT after external beam radiation therapy (EBRT). <h3>Materials and Methods</h3> From September 2019 to April 2021, 50 patients with newly diagnosed LACC (FIGO stage IIB to IIIB) who received EBRT (50.4Gy in 28 fractions over 5.5 weeks) with concurrent weekly chemotherapy were randomized into two arms: PET/CT- guided ICBT arm (25 patients) and CT- guided ICBT arm (25 patients). High-risk clinical target volume (HRCTV) in PET-CT arm included cervix along with FDG avid lesion and in CT arm included cervix along with residual disease based on CT scan findings. The prescribed dose of ICRT was 7.0 Gy X 3 fractions (once a week fraction). Rectum, bladder, and sigmoid colon were contoured as organs at risk in both arms. Local control, overall survival, and dosimetry comparison between two arms were evaluated. Common Terminology Criteria for Adverse Events v.4.03 (CTCAE v4.03) was used for reporting early toxicity. <h3>Results</h3> Clinical characteristics like age, stage etc. were comparable in the two arms. The 2- year local control rate was 79.1% in PET-CT arm and 72.7% in CT arm (p-value, 0.3). The 2-year overall survival was 89% in CT arm and 82.9% in PET-CT arm (p-value, 0.6). The mean dose to HRCTV D90 and HRCTV D95 in PET CT arm was 87.7Gy (s=6.1Gy) and 83.04Gy (s=5.5Gy) and in CT arm was 85.6Gy (s=6.4Gy) and 80.6Gy (s=5.7Gy) (p-value, 0.13).The mean dose to bladder, rectum and sigmoid colon in PET-CT arm were 80.3Gy (s=8.2Gy), 70Gy (s=6.1Gy) and 66.2Gy (s=7.4Gy) and in CT arm were 79 Gy (s=6.9Gy), 70.2Gy (s=7.2Gy) and 64.9Gy (s=6.3Gy), (p-value:0.58, 0.88 and 0.55). No Grade III/IV OAR toxicity were reported in both arms. <h3>Conclusion</h3> Though the limited sample size, the results of our randomized study show that PET-CT guided ICBT is feasible in patients with LACC. The clinical outcome (overall survival, local control, and OAR toxicity) and dosimetry parameters were comparable in both arms. Based on marginally better local control in the PET-CT arm, though not statistically significant, we suggest further studies with a larger sample size to evaluate the role of PET-CT in LACC.

Sunday, June 19, 202210:00 AM - 10:15 AMPO47 Presentation Time: 10:00 AM: Dose Distribution of Permanent Interstitial Brachytherapy (Iodine-125) in Comparison to Temporary Interstitial Brachytherapy (Iridium-192) with a Hydrogel Spacer for Prostate Cancer

<h3>Purpose</h3> Brachytherapy (BT) for prostate cancer can be applied as permanent interstitial brachytherapy BT (LDR, low dose rate) and temporary interstitial brachytherapy BT (HDR, high dose rate), applied also alternatively in many centers. The aim of the study was to analyze the dose distribution in- and outside the prostate. <h3>Methods</h3> The intraoperative dose distribution of 102 LDR-BT patients was compared with the dose distribution of 109 HDR-BT patients (232 HDR-BT fractions). A hydrogel spacer (HS) (10ml) was only applied before HDR-BT. For the analysis of the dose coverage outside the prostate, a 5mm margin was added to prostate volume (PV+). Prostate V100 and V150 denote the PV covered by 100% and 150% of the prescription dose, while prostate D90 and urethra D30 denote the minimum dose in 90% of the PV and 30% of the urethral volume. <h3>Results</h3> The comparison of volume and dose values is shown in the table. HDR-BT patients had on average a slightly larger PV, but considerably larger PV+. The only not significantly different value comparing both methods was prostate V100. LDR-BT was characterized by a considerably more inhomogeneous dose distribution and higher doses to the urethra. However, the minimum dose in 90% of PV+ was lower. As a consequence of the HA in HDR-BT patients, the dose to the rectum was considerably lower. <h3>Conclusion</h3> In comparison to HDR-BT, LDR-BT is characterized by a more inhomogeneous dose inside the prostate, a higher dose to the urethra and a slightly less steep dose drop-off around the prostate. The dose to the rectal wall can be considerably reduced applying the HS.

GPP08 Presentation Time: 9:50 AM: From Learning Outcomes to Game Design: Basic Brickwork in Virtual Reality Simulation of Cervical Brachytherapy Procedures

<h3>Purpose</h3> Even before the pandemic, clinical training opportunity for brachytherapy (BT) procedures has been decreasing. In locally advanced cervix cancer (CC), this has been linked to declining BT utilization and poorer clinical outcomes. This work describes the culmination of our early exploration into how to augment resident training in CCBT, distilling and integrating educational keys for a first-in-kind immersive, hands-on, and interaction-enabled virtual reality (VR) simulator for CCBT applicator insertion procedures. <h3>Materials and Methods</h3> Informal needs assessment in consultation with frontline experts and novice stakeholders identified the basic competencies thought to be required to successfully execute a CCBT applicator insertion procedure according to local standards. There was early recognition that, even before a curricular intervention could be designed, a versatile training tool would be needed. After reviewing international guidelines relating to CCBT and BT training, procedure-based learning outcomes were articulated, then selected and simplified for programming a basic goal-oriented simulation (sim) in VR. A clinical vignette of a typical CC case was crafted, with specific narrative stops amenable to building knowledge, skills, and behaviors. Emphasis on the "why" and the "how" of certain BT steps was built in. Procedural milestones were generalizable to trainees with varying degrees of clinical BT experience, with some steps or ‘interactions' made evaluable (go, no go) in this linear design. Gamification expanded options for cross-linking and reinforcing learning concepts. To the extent feasible, realism was incorporated into the physical representation of sim objects, such as CT-scanned surgical instruments and an intracavitary/interstitial BT applicator (Elekta, Netherlands; with permission), extracted as user-configurable additions to the 3D immersive operating room (OR) environment coded on Unreal engine v. 2.46 (Epic Games, US). <h3>Results</h3> A working prototype was generated for a single-player VR sim, broadly mimicking the procedural steps for actual CCBT applicator insertion. Despite an estimated runtime of 20 minutes, depending on user proficiency with CCBT and with VR technology (headset, hand controllers), the sim can start/stop at user discretion, and be shown on-screen to non-playing observers in a classroom setting. The game can also be run iteratively offline, enabling self-paced study of CCBT procedural steps in sequence, repeated execution for kinesthetic learning, and easy focus on recurring problem areas. The user starts the sim in OR, with a computer-generated patient draped and BT instrument tray at the ready. The case vignette and step-by-step instructions trigger the user to complete specific procedural tasks in the correct order; sim will not advance otherwise. Hints are given when needed. Pop-up multiple choice questions, in between BT sim interactions, are formative, drawing on basic recall, understanding, and application, to strengthen learning of core concepts in CCBT. Further contextual information is given at end of sim, to better situate procedural learnings with post-procedure processes (e.g. applicator verification and BT planning). <h3>Conclusions</h3> A novel VRsim tool, inspired by educational design principles, was created as proof-of-concept for guided performance-oriented learning of CCBT procedural aspects. Broader range and complexity of simulated procedures is planned, with higher level of user interaction and realism. Prospective evaluation of face (realism) and content (usefulness) validity will inform on its potential, as part of comprehensive CCBT instructional programming.