HDR BT Research Articles

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

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. A cohort of 32 patients receiving post-EBRT HDR brachytherapy boost with a prescription dose of 5.5Gy × 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 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. 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 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. 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.

Single–dose high-dose-rate brachytherapy versus two and three fractions for locally advanced prostate cancer

BackgroundSingle-dose high-dose-rate brachytherapy (SD-HDR-BT) was compared to two or three fraction HDR BT in intermediate and high-risk localized prostate cancer with median follow-up of 10 years. Materials and methods293 patients received 1 × 19Gy or 1 × 20Gy (Group A = 49), 2 × 13Gy (Group B = 138), or 3 × 10.5 Gy (Group C = 106) HDR BT. The primary endpoint was biochemical relapse-free interval (bRFI). Late genitourinary (GU) and gastrointestinal (GI) morbidity used RTOG scales and the International Prostate Symptom Score (IPSS). Freedom from biochemical relapse (bRFI), overall survival (OS) and GU, GI and IPSS morbidity were calculated using Kaplan-Meier (K-M) method and log-rank test. Univariate and multivariate hazard ratios (HR) were obtained using Cox’s proportional hazard. ResultsAt 10 years, K-M estimates of bRFI were 64 % (Group A), 72 % (Group B), and 76 % (Group C) (p = 0.2). No statistically significant difference was seen in OS. In multivariate analysis risk-category and ADT administration, but not dose, were significant predictors of relapse (p = 0.0003 and 0.03, respectively). At ten years, GU grade 3 events were 8 % (A), 2 % (B) and 13 % (C); (p = 0.01). IPSS ≥ 20 was 31 % (A), 20 % (B) and 23 % (C); (p = 0.6) and grade 3 GI was 0 % in groups A and B and 2 % in C; (p = 0.3). No GU or GI grade-4 events were observed. Pre-treatment IPSS was a highly significant predictor of failure in multivariate analysis. ConclusionsLong-term outcome data show reduced but not statistically significant difference in PSA control, and no difference in overall survival, between SD-HDR-BT and 2 or 3 fractions of HDR-BT.

Deep learning for high-resolution dose prediction in high dose rate brachytherapy for breast cancer treatment

Objective. Monte Carlo (MC) simulations are the benchmark for accurate radiotherapy dose calculations, notably in patient-specific high dose rate brachytherapy (HDR BT), in cases where considering tissue heterogeneities is critical. However, the lengthy computational time limits the practical application of MC simulations. Prior research used deep learning (DL) for dose prediction as an alternative to MC simulations. While accurate dose predictions akin to MC were attained, graphics processing unit limitations constrained these predictions to large voxels of 3 mm × 3 mm × 3 mm. This study aimed to enable dose predictions as accurate as MC simulations in 1 mm × 1 mm × 1 mm voxels within a clinically acceptable timeframe. Approach. Computed tomography scans of 98 breast cancer patients treated with Iridium-192-based HDR BT were used: 70 for training, 14 for validation, and 14 for testing. A new cropping strategy based on the distance to the seed was devised to reduce the volume size, enabling efficient training of 3D DL models using 1 mm × 1 mm × 1 mm dose grids. Additionally, novel DL architecture with layer-level fusion were proposed to predict MC simulated dose to medium-in-medium (D m,m ). These architectures fuse information from TG-43 dose to water-in-water (D w,w ) with patient tissue composition at the layer-level. Different inputs describing patient body composition were investigated. Main results. The proposed approach demonstrated state-of-the-art performance, on par with the MC D m,m maps, but 300 times faster. The mean absolute percent error for dosimetric indices between the MC and DL-predicted complete treatment plans was 0.17% ± 0.15% for the planning target volume V 100, 0.30% ± 0.32% for the skin D 2cc , 0.82% ± 0.79% for the lung D 2cc , 0.34% ± 0.29% for the chest wall D 2cc and 1.08% ± 0.98% for the heart D 2cc . Significance. Unlike the time-consuming MC simulations, the proposed novel strategy efficiently converts TG-43 D w,w maps into precise D m,m maps at high resolution, enabling clinical integration.

A deep learning-based 3D Prompt-nnUnet model for automatic segmentation in brachytherapy of postoperative endometrial carcinoma.

To create and evaluate a three-dimensional (3D) Prompt-nnUnet module that utilizes the prompts-based model combined with 3D nnUnet for producing the rapid and consistent autosegmentation of high-risk clinical target volume (HR CTV) and organ at risk (OAR) in high-dose-rate brachytherapy (HDR BT) for patients with postoperative endometrial carcinoma (EC). On two experimental batches, a total of 321 computed tomography (CT) scans were obtained for HR CTV segmentation from 321 patients with EC, and 125 CT scans for OARs segmentation from 125 patients. The numbers of training/validation/test were 257/32/32 and 87/13/25 for HR CTV and OARs respectively. A novel comparison of the deep learning neural network 3D Prompt-nnUnet and 3D nnUnet was applied for HR CTV and OARs segmentation. Three-fold cross validation and several quantitative metrics were employed, including Dice similarity coefficient (DSC), Hausdorff distance (HD), 95th percentile of Hausdorff distance (HD95%), and intersection over union (IoU). The Prompt-nnUnet included two forms of parameters Predict-Prompt (PP) and Label-Prompt (LP), with the LP performing most similarly to the experienced radiation oncologist and outperforming the less experienced ones. During the testing phase, the mean DSC values for the LP were 0.96±0.02, 0.91±0.02, and 0.83±0.07 for HR CTV, rectum and urethra, respectively. The mean HD values (mm) were 2.73±0.95, 8.18±4.84, and 2.11±0.50, respectively. The mean HD95% values (mm) were 1.66±1.11, 3.07±0.94, and 1.35±0.55, respectively. The mean IoUs were 0.92±0.04, 0.84±0.03, and 0.71±0.09, respectively. A delineation time<2.35s per structure in the new model was observed, which was available to save clinician time. The Prompt-nnUnet architecture, particularly the LP, was highly consistent with ground truth (GT) in HR CTV or OAR autosegmentation, reducing interobserver variability and shortening treatment time.

A comparative study on the accuracy of an automated multi-parameter high-dose-rate brachytherapy quality assurance system

This study aims to explore the measuring accuracy of an automated high-dose-rate brachytherapy (HDR BT) quality assurance system (hereinafter referred to as OriQA system) that could provide simultaneous measurements of dwell position, dwell time and source strength in a single test. Elekta-Flexitron was selected as the HDR BT afterloader, and measured the farthest transmission distance by source position simulator. Within the effective distance, we set dwell positions in two groups, specifically, plan_1 with an interval of 2.00 cm: 106.00 cm, 108.00 cm, 110.00 cm, 102.00 cm, 104.00 cm, 106.00 cm, 108.00 cm, and plan_2 with an interval of 0.20 cm: 111.40 cm, 111.60 cm, 111.80 cm, 112.00 cm, 112.20 cm, 112.40 cm, 112.60 cm. The measured values collected from OriQA device were compared with the data from traditional HDR BT QA tool (source position check ruler). Three groups of dwell time were set, specifically, plan_1: with fixed dwell time 2.00 s, plan_3 with interval 0.10 s: 3.70 s, 3.80 s, 3.90 s, 4.00 s, 4.10 s, 4.20 s, 4.30 s, and plan_4: fixed dwell time 5.00 s. Source strength was also measured continuously for a period of 10 weeks, and compared with the data collected from the well-chamber. The OriQA system showed reliable performance in the evaluation of measuring accuracy. The adjusted farthest transmission distance was 119.33 cm. And according to the time-position graph, the maximum deviation of dwell position between the measured and planned data was 0.34 mm, which was smaller than that between the ruler and planed data (0.75 mm). The maximum deviation of dwell time between the measured and planned data was 0.05 s. Fitting analysis revealed linear relationship between source strength Sk and the intensity detector response, with R2 = 0.9877, and intensity deviation fluctuated between 1.14% and 2.19%. Compared with the traditional QA tool, the OriQA device provided improved measuring accuracy and efficiency QA procedure for HDR BT.

High-Dose Rate Brachytherapy Alone for Treatment of Unfavorable Intermediate Risk Prostate Cancer: A Propensity-Score Matched Analysis.

To demonstrate the feasibility of high-dose rate brachytherapy (HDR BT) as monotherapy for unfavorable intermediate risk (UIR) prostate cancer by comparing survival outcomes of HDR BT alone against external beam radiation therapy (EBRT) + HDR BT boost, +/- androgen deprivation therapy (ADT) using propensity-score matched (PSM) data. This retrospective study queried two data registries collecting patient data from 1991 to present. 633 patients with UIR prostate cancer treated with HDR BT alone, HDR BT+EBRT or HDR+EBRT+ADT were included. HDR BT patients received 42-45Gy/6 fractions (fx) or 27 Gy/2 fx. For HDR BT+EBRT, the HDR dose was 20-24 Gy/2 fx, 24 Gy/4 fx, or 15 Gy/1 fx. EBRT patients received 45 Gy/25 fx to the prostate +/- pelvic nodes. GU/GI toxicities were graded according to the Common Terminology Criteria for Adverse Events (CTCAE) v5.0. Time-to-event analyses were carried out to evaluate the relationship between treatments and five primary endpoints of interest: freedom from biochemical recurrence (FFBC), freedom from distant metastasis (FFDM), freedom from local failure (FFLF), cancer specific survival (CSS), and overall survival (OS) at 5 years. PSM was performed with one-to-n matching. Logistic regression was used to estimate the respective propensity scores. The five potential confounders identified were T-stage, Gleason score, pre-treatment PSA, age, and percent positive cores. Balance was checked using the standardized mean difference of covariates. Univariate and multivariate analyses were conducted on the matched data. Toxicity analysis was performed via association between a change in pre- and post-treatment GU/GI toxicity status and the treatment group, as well as incidence of post-treatment severe GI/GU toxicity (grade 3 or higher) and the treatment group. Univariate analysis with Kaplan-Meier method and log rank test comparison between the three cohorts demonstrated no significant difference in all survival outcomes FFBC, FFDM, FFLF, CSS, OS (p = 0.15, 0.19, 0.29, 0.57, 0.28, respectively). Multivariate analysis with Cox proportional hazard regression showed no differences in HR for FFBC and OS (p = 0.95, 0.11) with addition of EBRT, or with EBRT+ADT (p = 0.17, 0.24); no fit was obtainable for FFDM, CSS, FFLF. Toxicities between the three cohorts were not significantly different when comparing post-treatment and baseline GI/GU symptoms (p = 0.53/1). No Grade 2 or 3 GI toxicities were identified, while 8%/1% HDR patients, 10%/1% HDR+EBRT patients, and 12%/2% HDR+EBRT+ADT patients experienced Grade 2/3 GU toxicities. The incidence of grade 3 or higher GU toxicities between the three groups was not significantly different (p = 0.91). This propensity-score matched study demonstrates the feasibility of HDR BT alone for effective treatment of UIR prostate cancer when compared to HDR+EBRT or HDR+EBRT+ADT, while potentially minimizing the added toxicities of EBRT and the undesirable side effect profile of ADT.

Single Dose vs. Fractionated High-Dose Rate Brachytherapy in Localized Prostate Cancer: Long Term Results

To evaluate long-term freedom from biochemical relapse (FFbR) and overall survival (OS) after single-dose high-dose-rate brachytherapy (HDR-BT) compared with 2 or 3 fraction schedules. HDR-BT, delivering 1 × 19 Gy or 1 × 20 Gy (A = 49), 2 × 13 Gy (B = 138) or 3 × 10.5 Gy (C = 106), was given to patients with intermediate or high-risk prostate cancer as their sole treatment. Patients were staged with pelvic MRI and isotope bone scan. Transperineal transrectal ultrasound guided implantation was followed by MRI based CTV definition based on GEC ESTRO guidelines. Biochemical relapse was assessed using the Phœnix definition (PSA nadir plus 2 µg/L). Patients were evaluated prospectively from 6 months after implant and bi-annually thereafter. Estimates of freedom from biochemical relapse, and overall survival (OS) were calculated using the Kaplan-Meier (K-M) method and the log-rank test to test for significance. Univariate and multivariate hazard ratios (HR) were obtained using Cox's proportional hazard model. For multivariate modelling a stepwise reduction method was used. Median follow-up was 123, 116 and 120 months (p = 0.4), (A, B, C, respectively). Neo-adjuvant and adjuvant androgen deprivation treatment was given to 80% of all patients, median duration was 9 months for A and 6 months for B and C. K-M estimates of FFbR, at 8 and 10 years, were 67% and 64% (Group A), 78% and 72% (Group B), and 80% and 76% (Group C). Differences in FFbR between dose groups was not significant (p = 0.2). Similarly, no significant difference was seen in OS. Eight and 10-year estimates were 81% and 75% (A), 85% and 74% (B), and 90% and 83% (C); p = 0.5. Hazard Ratios for risk of biochemical recurrence were significant for ADT administration (yes/no) and overall risk category, in multivariate analyses. Only the latter was significant in univariate analysis for risk of death, Gleason risk (low, intermediate, high), MRI tumor stage risk and overall risk category were significant in univariate analyses. Only tumor stage and Gleason risk were significant in multivariate analyses. Concerns around the efficacy of 19-20 Gy single dose HDR BT as monotherapy, based on early data, may have been unfounded. Long-term outcome data up to 10 years show no significant difference in PSA control and overall survival compared to 2 and 3 fractions of HDR-BT.

PO-2196 Dosimetric results of a randomised trial of HDR vs. LDR single dose BT of localised prostate cancer

PO-2196 Dosimetric results of a randomised trial of HDR vs. LDR single dose BT of localised prostate cancer

Prospective analysis of the impact of adjuvant treatment with external beam radiation therapy and vaginal brachytherapy on health-related quality of life in patients with early-stage endometrioid endometrial carcinoma.

Our study evaluates the impact of adjuvant treatment with external beam radiotherapy (EBRT) combined with vaginal high dose rate brachytherapy (HDR BT) on health related quality of life (HRQL) in patients with early stage endometrioid endometrial carcinoma. From March 2019 to February 2021, 60 patients were enrolled with early stage endometrioid endometrial carcinoma, and qualified to adjuvant treatment after hysterectomy. HRQL was assessed using the EORTC QLQ-C30 questionnaire, with the endometrial cancer-specific HRQL module EORTC QLQ-EN24. Questionnaires were completed in four timepoints during adjuvant radiotherapy. A significant decrease in mean global health status / quality of life (p < 0.001) and role functioning (p = 0.028) was noted, as assessed in EORTC QLQ-C30 scale. Among the EORTC QLQ-C30 symptoms scales, significant differences were noted in the fatigue scale (p = 0.003), pain scale (p = 0.001), constipation scale (p < 0.001) and diarrhea scale (p < 0.001) over time. The EORTC QRQ-EN24 analysis showed significant deterioration in the urological symptoms scale (p < 0.001), gastrointestinal symptoms scale (p < 0.001) and in the mean pain in back and pelvis scale (p = 0.003). Adjuvant radiotherapy in patients with early-stage endometrioid endometrial cancer after hysterectomy is associated with worse quality of life, especially due to the toxicity of the treatment in relation to the gastrointestinal tract and urinary system.

Technical note: Evaluation of a spatial optimization model for prostate high dose-rate brachytherapy in a clinical treatment planning system.

Spatial properties of a dose distribution, such as volumes of contiguous hot spots, are of clinical importance in treatment planning for high dose-rate brachytherapy (HDRBT). We have in an earlier study developed an optimization model that reduces the prevalence of contiguous hot spots by modifying a tentative treatment plan. The aim of this study is to incorporate the correction of hot spots in a standard inverse planning workflow and to validate the integrated model in a clinical treatment planning system. The spatial function is included in the objective function for the inverse planning, as opposed to in the previous study where it was applied as a separate post-processing step. Our aim is to demonstrate that fine-adjustments of dose distributions, which are often performed manually in today's clinical practice, can be automated. A spatial optimization function was introduced in the treatment planning system RayStation (RaySearch LaboratoriesAB, Stockholm, Sweden) via a research interface. A series of 10 consecutive prostate patients treated with HDRBT was retrospectively replanned with and without the spatial function. Optimization with the spatial function decreased the volume of the largest contiguous hot spot by on average 31%, compared to if the function was not included. The volume receiving at least 200% of the prescription dose decreased by on average 11%. Target coverage, measured as the fractions of the clinical target volume (CTV) and the planning target volume (PTV) receiving at least the prescription dose, was virtually unchanged (less than a percent change for both metrics). Organs-at-risk received comparable or slightly decreased doses if the spatial function was included in the optimization model. Optimization of spatial properties such as the volume of contiguous hot spots can be integrated in a standard inverse planning workflow for brachytherapy, and need not be conducted as a separate post-processing step.

Dosimetric impact of a robust optimization approach to mitigate effects from rotational uncertainty in prostate intensity modulated brachytherapy.

Intensity modulated brachytherapy (IMBT) is an emerging technology for cancer treatment, in which radiation sources are shielded to shape the dose distribution. The rotatable shields provide an additional degree of freedom, but also introduce an additional, directional, type of uncertainty, compared to conventional high dose-rate brachytherapy (HDR BT). We propose and evaluate a robust optimization approach to mitigate the effects of rotational uncertainty in the shields with respect to planningcriteria. A previously suggested prototype for platinum-shielded prostate 169 Yb-based dynamic IMBT is considered. We study a retrospective patient data set (anatomical contours and catheter placement) from two clinics, consisting of six patients that had previously undergone conventional 192 Ir high dose-rate brachytherapy treatment. The Monte Carlo based treatment planning software RapidBrachyMCTPS is used for dose calculations. In our computational experiments, we investigate systematic rotational shield errors of ±10 and ±20degrees, and the same systematic error is applied to all dwell positions in each scenario. This gives us three scenarios, one nominal and two with errors. The robust optimization approach finds a compromise between the average and worst-case scenariooutcomes. We compare dose plans obtained from standard models and their robust counterparts. With dwell times obtained from a linear penalty model, for 10degrees errors, the dose to urethra (D0.1cc ) and rectum (D0.1cc and D1cc ) increase with up to 5% and 7%, respectively, in the worst-case scenario, while with the robust counterpart, the corresponding increases were 3% and 3%. For all patients and all evaluated criteria, the worst-case scenario outcome with the robust approach had lower deviation compared to the standard model, without compromising target coverage. We also evaluated shield errors up to 20degrees and while the deviations increased to a large extent with the standard models, the robust models were capable of handling even such largeerrors. We conclude that robust optimization can be used to mitigate the effects from rotational uncertainty and to ensure the treatment plan quality ofIMBT. This article is protected by copyright. All rights reserved.

High-Dose-Rate Brachytherapy as an Organ-Sparing Treatment for Early Penile Cancer.

Low-dose-rate brachytherapy is an effective organ-sparing treatment for patients with early-stage penile cancer. However, only limited data are available on the role of high-dose-rate brachytherapy (HDR-BT) in this clinical setting. Between 2002 and 2020, 31 patients with early penile cancer were treated at our center with interstitial HDR BT at a dose of 18 × 3 Gy twice daily. A breast brachytherapy template was used for the fixation of stainless hollow needles. The median follow-up was 117.5 months (range, 5-210). Eight patients (25.8%) developed a recurrence; of these, seven were salvaged by partial amputation. Six patients died of internal comorbidities or a second cancer. The probability of local control at 5 and 10 years was 80.7% (95% CI: 63.7-97.7%) and 68.3% (95% CI: 44.0-92.6%), respectively. Cause-specific survival was 100%. Only one case of radiation-induced necrosis was observed. The probability of penile sparing at 5 and 10 years was 80.6% (95% CI: 63.45-97.7%) and 62.1% (95% CI: 34.8-89.4%), respectively. These results show that HDR-BT for penile cancer can achieve results comparable to LDR-BT with organ sparing. Despite the relatively large patient cohort-the second largest reported to date in this clinical setting-prospective data from larger samples are needed to confirm the role of HDR-BT in penile cancer.

Friday, June 17, 20229:00 AM - 10:00 AM PP01 Presentation Time: 9:00 AM: Propensity-Matched Analysis of High-Dose-Rate Brachytherapy in Intermediate Risk Prostate Cancer: Monotherapy or Boost?

<h3>Purpose</h3> High-Dose-Rate Brachytherapy (HDR BT) either as monotherapy or boost has excellent reported prostate cancer control outcomes. Monotherapy is more commonly used for those with favorable risk features, while HDR tends to be combined with external beam radiotherapy (EBRT) for those with higher risk disease. Patients with intermediate risk prostate cancer (IR-PCa) can be managed either with monotherapy or boost. In the absence of randomized data, our objective is to compare biochemical response and oncological outcomes for patients with intermediate risk prostate cancer treated with either HDR as monotherapy or as a boost in combination with EBRT. <h3>Materials and Methods</h3> A propensity score matching analysis was performed of IR-PCa patients treated with either HDR monotherapy (27 Gy in 2 fractions), or HDR boost (15 Gy followed by EBRT; 37.5 Gy in 15 fractions delivered with Intensity modulated radiotherapy). The former patients were included in a prospective clinical trial whereas the latter were selected from a retrospective institutional database. Matching was based on age, baseline PSA, T stage, grade group, perineural invasion, and percentage of positive cores. No patient received androgen deprivation therapy. The primary outcome was biochemical disease-free survival (bDFS) defined as time from treatment to PSA nadir +2 or death. Secondary outcomes included PSA nadir and incidence of grade (G) ≥3 genitourinary (GU) and gastrointestinal (GI) toxicities measured using CTCAE v.4. A General Linear Mixed Model and Analysis of Covariance was used to investigate changes in PSA over time. <h3>Results</h3> A total of 132 patients were matched, 66 in each cohort with a median age of 66 years (range: 48-80). Median follow up was 59 months (interquartile range (IQR) 54, 62) for the HDR monotherapy cohort and 63 months (IQR 42, 81) for the boost BT group. They were well matched with a Propensity Score of 0.4615 and 0.4612, respectively. Thirty-eight percent of patients had unfavorable intermediate risk disease. Patients treated with monotherapy had slightly higher PSA in the first 4 years, Figure 1 (p=0.034), although by 5-years median PSA was 0.14 ng/ml (IQR 0.06, 0.34) with monotherapy and 0.15 ng/ml (IQR 0.07, 0.51) with boost. At 4 years, 24 (36%) monotherapy patients and 26 (44%) boost patients had PSA <0.2 ng/ml. Among all patients, 7% (10 of 132) experienced biochemical failure: six patients in the HDR monotherapy group and four in the boost group, resulting in 5-year bDFS of 93.5% and 93.3%, respectively. Favorable and Unfavorable IR-PCa had similar risk of recurrence. Late G3 GU toxicity occurred in 2 out of 66 boost patients and was not seen in the monotherapy patients. <h3>Conclusions</h3> Although limited by small sample size, we report high efficacy of HDR brachytherapy as either monotherapy or boost for all patients with intermediate risk disease. Boost patients had a lower PSA value in the first 4 years, although with a suggestion of greater G3 urinary toxicity.

Focal MR-Guided High-Dose-Rate Brachytherapy for Localized Prostate Cancer: A Prospective Clinical Trial

<h3>Purpose/Objective(s)</h3> Focal therapy has gained traction in the management of localized prostate cancer (PCa) based on the promise of equivalent oncologic outcomes with minimal toxicity compared to whole gland therapy. However, 20-45% of patients have persistent/recurrent disease within the first 2-5 years after most commonly-used ablative methods (e.g., HIFU, cryotherapy). Based on brachytherapy's (BT) well-established and long track-record of efficacy for PCa, we sought to test the focal therapy hypothesis in a prospective clinical trial of MR-guided HDR for men with localized PCa. <h3>Materials/Methods</h3> This prospective trial was approved in 2016 (UHN IRB# 16-5490; NCT02918253) for patients with clinically low- and favorable intermediate-risk prostate cancer, and a conspicuous lesion on mpMRI consistent with the area of pathological involvement. The CTV was derived from the mpMRI-defined GTV plus a 7 mm isotropic expansion, with 2 mm sup/inf added for the PTV. Implant and planning were performed with an MR-only workflow, and delivery with HDR BT. Treatment consisted of two separate implants within 14 days, to a prescription dose of 33-36 Gy in 2 sessions (BED ≥ 200 Gy). Biochemical recurrence (BCR), defined as > 2ng/mL above nadir was calculated using the Kaplan Meier method. Local failure, distant metastasis (DM) and toxicity events are reported as absolute rates. <h3>Results</h3> Nineteen patients have been treated, with a median age of 73 years (range 48-84), and median follow-up of 24 months (8-63). Median PSA was 6.1 ng/mL and 17/19 patients had Grade Group 2 disease. On average, the GTV and PTV corresponded to 3.56% (1.58-12.07) and 23.16% (13.71-40.75) of the median prostatic volume (40.49 cc [25.57-97.6]). Median number of catheters was 7 (4-11). Median GTV D₉₉ and PTV D₉₅ per fraction were 23.82 Gy (18.50-31.89) and 18.71 Gy (16.01-20.64), respectively. Nine patients have undergone the 2-yr local control ascertainment; 7 with mpMRI plus biopsies, and 2 with mpMRI only. At 2-years, local control and BCR-free survival were 100%; a single BCR event has been recorded 34 months after treatment. No DM or death events have occurred. The rate of treatment-related acute and late toxicities that were graded ≥ 2 was 0%. <h3>Conclusion</h3> Focal MRI-guided HDR brachytherapy as monotherapy appears to have a high therapeutic ratio and is a promising technique for localized PCa. Further follow-up will determine the durability of outcomes with this approach and the need for collaborative randomized studies.

Outcomes of 3D MRI Based HDR Brachytherapy with Hybrid Multichannel Vaginal Cylinder Applicator and Freehand Needles for Treatment of Vaginal Disease

<h3>Purpose/Objective(s)</h3> Multichannel vaginal cylinder (MCVC) is unable to cover residual vaginal cancer >7 mm thick or with supra-vaginal extension. Freehand needles inserted directly into areas of disease can extend isodose lines to allow for better coverage of disease if clinically indicated. We report outcomes of use of MCVC with freehand needles at our institution. <h3>Materials/Methods</h3> All patients with malignancies involving vagina treated from 2014-2021 with HDR BT at our institution with MCVC with freehand needles were identified. Clinical characteristics including primary malignancy, initial stage, date of diagnosis and recurrence (if applicable), prior RT, use of EBRT, and BT dose and fractionation were collected. Number of freehand needles used per fraction, 3D imaging used for planning, high-risk clinical target volume (HR-CTV) at each fraction, dose to 2cc (D2cc) of organs at risk, and HR-CTV D90 were recorded. Initial response based on examination and imaging and overall local control outcomes were recorded. Local failure was defined as time to recurrence either within HR-CTV or marginal failure, calculated from date of last BT fraction, with censorship at date of last follow-up. Local control was analyzed via Kaplan-Meier method. <h3>Results</h3> 33 patients were identified with median follow-up 1.9 years (IQR 1.0-2.9 years). 19 patients (57.6%) had primary endometrial cancer with vaginal recurrence/disease. Remaining patients had primary vaginal cancer or involvement secondary to other primaries. 8 patients had recurrent disease after previous course of RT. 24 patients received EBRT with median dose of 45 Gy in 25 fractions, with remaining patients treated with BT alone. BT prescription dose ranged from 20-36 Gy in 3-7 fractions, with a total of 168 BT fractions delivered. Median number of freehand needles utilized was 3, with freehand needles utilized in 157/168 total fractions. MRI-based plan was done for at least 1 fraction in 30 patients (90.9%). Median HR-CTV at time of BT was 19.7cc. Median D2cc to the bladder, rectum, and sigmoid were 56.4 Gy, 55.7 Gy, and 45.4 Gy, respectively. Median D90 to the HR-CTV for pts treated with EBRT plus BT was 76.7 Gy and for BT alone was 48.8 Gy. 29 patients (87.9%) had complete local response to BT on initial examination and/or follow-up imaging. 1 and 2-year local control rates for those who did not have prior RT was 89.5% and 89.5%, respectively. 1 and 2-year local control rates for those who had previous RT was 58.3% and 29.2%, respectively. 1 patient had vaginal laceration requiring surgical repair and 1 patient with disease progression developed small bowel obstruction 1 month after BT, with no additional acute grade 3+ toxicities identified. <h3>Conclusion</h3> Our approach with MCVC plus freehand needles with MRI-based planning was feasible and safe. Initial local response is excellent, with acceptable local control rates and low rate of serious acute toxicities. Multi-institutional experiences are needed to further validate this approach for treatment of vaginal disease.

Outcomes of 3D MRI based HDR brachytherapy with hybrid multichannel vaginal cylinder applicator and freehand needles for treatment of vaginal disease

Freehand needles can be used with multichannel vaginal cylinders (MCVC) to cover vaginal cancer >7 mm thick or with supra-vaginal extension. We report our institutional outcomes using this novel hybrid technique.Patients with vaginal malignancies treated with HDR BT using MCVC plus freehand needles from 2014-2021 at our institution were identified. Clinical characteristics, details of brachytherapy, initial response, and overall local control (LC) outcomes were recorded. LC was analyzed via Kaplan-Meier method.34 patients were identified with median follow-up 1.9 years. 19 patients had primary endometrial cancer with vaginal recurrence/disease, and remaining had primary vaginal cancer or other primaries. 7 patients had recurrence after previous RT course. 25 patients received EBRT with median dose 45 Gy in 25 fractions, and rest received BT alone. Median HR-CTV D90 for patients treated with EBRT plus BT was 77.4 Gy.30 patients had complete local response to BT on initial examination and/or follow-up imaging. 1 and 2-year LC rates in patients without prior RT treated with EBRT + BT were 94.1% and 94.1%, respectively. 1 and 2-year LC rates for those without prior RT were 88.1% and 76.4%, respectively. 1 and 2-year LC rates for those with prior RT were 68.6% and 34.3%, respectively. 1 patient had vaginal laceration requiring surgical repair, and 1 patient developed small bowel obstruction 1 month after BT, with no additional acute grade 3+ toxicities identified.Our approach with MCVC plus freehand needles with MRI-based planning was feasible and safe, with excellent initial local response and low rate of serious toxicities.

The impact of adjuvant treatment with external beam radiotherapy and vaginal brachytherapy on health-related quality of life in patients with early-stage endometrioid endometrial carcinoma - initial results of a prospective study.

Our study evaluates the impact of adjuvant treatment with external beam radiotherapy (EBRT) combined with vaginal high-dose-rate brachytherapy (HDR BT) on health-related quality of life (HRQL) in patients with early-stage endometrioid endometrial carcinoma. We assessed HRQL of patients based on the EORTC QLQ-C30 questionnaire, with endometrial cancer specific HRQL module - EORTC QLQ-EN24. From March 2019 to April 2020 we enrolled 20 patients with early-stage endometrioid endometrial carcinoma, qualified for adjuvant treatment after hysterectomy. We compared the scores measured with the questionnaires at the beginning and at the end of the treatment. There was a statistically significant decrease in the mean of global health status/quality of life assessed according to the EORTC QLQ-C30 scale, from 62.25 ± 13.12 at the beginning of the adjuvant radiotherapy to 55.85 ± 14.68 at the end of the treatment (p = 0.047). The mean appetite loss score was higher at the onset of the treatment as compared to its value after EBRT, 19.9 ± 27.33 vs 11.6 ± 19.52 (p = 0.043). Similarly to the mean constipation score, which was 29.85 ± 30.40 vs 11.6 ± 19.52 (p = 0.013). The mean diarrhoea symptom scale increased from 16.55 ± 20.16 to 56.75 ± 36.10 (p = 0.001). In the EORTC QLQ-EN24 scales, gastrointestinal symptoms scores were higher at the end of the treatment, (with the mean of 26.45 ± 22.76) as compared to 14.30 ± 16.52 at the beginning of EBRT (p = 0.003). Patients who receive adjuvant radiotherapy have decreased quality of life during the treatment reporting more serious gastrointestinal symptoms. The potential risk of treatment-related toxicity should be taken into account during the treatment planning process in order to minimize the deterioration of HRQL.

Assessment of HDR brachytherapy-replicating prostate radiotherapy planning for tomotherapy, cyberknife and VMAT.

A dosimetric study was undertaken to assess the ability of Cyberknife (CK), Volumetric Modulated Arc Therapy (VMAT), and TomoTherapy (Tomo) to generate treatment plans that mimic the dosimetry of high dose-rate brachytherapy (HDR BT) for prostate cancer. The project aimed to assess the potential of using stereotactic body radiotherapy (SBRT) for boost treatment of high-risk prostate cancer patients where HDR BT in combination with conformal external beam radiotherapy (EBRT) is the standard of care. The datasets of 6 prostate patients previously treated with HDR BT were collated. VMAT, CK, and TomoTherapy treatment plans were generated for each dataset using the target and organ-at-risk structures as defined by the Radiation Oncologist during the HDR BT treatment process. The HDR BT plan isodoses were also converted into planning structures to assist the other modalities to achieve a HDR BT-like dose distribution. CK plans were created using both the iris collimator (IC) and a multileaf collimator (MLC). Comparison of the techniques was made based on dose-volume indices. Each plan was created at centres experienced using the respective treatment planning systems (TPS). Planning target volume (PTV V100%), i.e., the volume of the planning target volume (PTV) receiving 100% of the relative dose, in VMAT and TomoTherapy SBRT plans was higher than HDR BT plans. PTV V150% and V200%, i.e., volume of the PTV receiving 150% and 200% of the relative dose, were approached on all the CK MLC and TomoTherapy SBRT plans. However, it is not presently achievable for "virtual brachytherapy" SBRT to replicate the same high intraprostatic doses as HDR BT while meeting the constraints on the organs-at-risk (OARs). Half of the CK IC plans achieved PTV V150% but this was at the expense of high rectal dose. TomoTherapy and CK MLC plans achieved PTV V150% and V200% but the bladder dose was higher compared to CK IC plans. VMAT exhibited excellent PTV coverage based on V100 and OAR sparing, but without any ability to achieve the high intra-prostatic doses of HDR (V150% and V200%). SBRT techniques can be used to deliver hypofractionated radiotherapy to the PTV V100%. Based on the comparison of "physical" dose distributions, SBRT cannot presently achieve the same high intraprostatic doses as HDR BT while respecting the OAR constraints. SBRT still remains an attractive treatment option for delivering hypofractionated treatments for prostate cancer compared to HDR BT, in particular as it is less invasive and less resource intensive. Long-term outcomes of clinical trials comparing HDR BT and SBRT "prostate boosts" may show whether the high intraprostatic doses are clinically significant and correlate with outcomes.

Steering a Tendon-Driven Needle in High-Dose-Rate Prostate Brachytherapy for Patients with Pubic Arch Interference.

High-dose-rate brachytherapy (HDR BT) is a radiation therapy that places radioactive sources at cancerous tissue using needles. HDR BT offers better dose conformality and sparing of clinical structures, lower operator dependency, and fewer acute irritative symptoms compared to the other form of BT (low-dose-rate (LDR)). However, use of HDR BT is limited for patients with pubic arch interference, where the transperineal path to the prostate is blocked. This study aims to introduce a tendon-driven needle that can bend inside tissue to reach desired positions inside prostate. Initial experiments in a phantom tissue showed the feasibility of the needle to get around the pubic arch for placement at hard-to-reach target positions.

PP-0117 HDR BT in Non melanoma Skin Cancer: Results and toxicity with different techniques and applicators.

PP-0117 HDR BT in Non melanoma Skin Cancer: Results and toxicity with different techniques and applicators.