Multichannel vaginal cylinder brachytherapy—Impact of tumor thickness and location on dose to organs at risk

Can an in-person hands-on applicator-based teaching session improve trainee knowledge and comfort with complex gynecologic brachytherapy?

INTRODUCTION

With the emergence of imaged-based planning and hybrid applicators the complexity of gynecologic brachytherapy has dramatically increased. Despite the known advantages of brachytherapy, notable national declines in utilization of brachytherapy have been documented. Clearly improved education in the sphere of gynecologic brachytherapy is needed. We hypothesize that a hands-on applicator-based training session would improve trainee comfort with gynecologic brachytherapy.

METHODS AND MATERIALS

An in-person, applicator-based, hands-on training session was held with trainees from both radiation and gynecologic oncology programs. Trainees practiced assembling and handling applicators while receiving instruction on clinical scenarios in which various applicators are used in gynecologic cancer brachytherapy. Pre- and post-session, participants were administered an objective test of 10 pictorial-based case vignettes to quantify ability to select the correct applicator based on the interpretation of T2-weighted MR images. Participants additionally received a subjective survey to quantify comfort and experience with gynecologic brachytherapy using Likert-type question formatting.

RESULTS

A total of 14 trainees participated. Most common case volume experience was 0-10 intracavitary (57%), 0-10 hybrid (71%), and 0-10 interstitial (71%). Pre-session, the most common answer to comfort level was "not comfortable still learning" for all brachytherapy types, and most common answer to largest gap in knowledge was all facets of brachytherapy. Average case-based test score was 3.5/10 pre-session versus 5.3/10 post-session (p = 0.028). Post-session, all respondents reported improved comfort level with brachytherapy. Post-session, most common answer to largest gap in knowledge was applicator/patient selection, and applicator/patient selection was also the largest area of identified improvement. 100% of participants felt repeating the session in the future would be helpful.

CONCLUSIONS

Hands-on training with applicators improves both subjective and objective comfort with gynecologic brachytherapy. With 100% of participants requesting to implement this session into resident training, we suggest national opportunities might exist to expand educational processes and improve utilization of complex gynecologic brachytherapy in practice.

Risk-Tailoring Radiotherapy for Endometrial Cancer: A Narrative Review

Endometrial cancer is the most common gynecologic cancer in the United States and it contributes to the second most gynecologic cancer-related deaths. With upfront surgery, the specific characteristics of both the patient and tumor allow for risk-tailored treatment algorithms including adjuvant radiotherapy and systemic therapy. In this narrative review, we discuss the current radiation treatment paradigm for endometrial cancer with an emphasis on various radiotherapy modalities, techniques, and dosing regimens. We then elaborate on how to tailor radiotherapy treatment courses in combination with other cancer-directed treatments, including chemotherapy and immunotherapy. In conclusion, this review summarizes ongoing research that aims to further individualize radiotherapy regimens for individuals in an attempt to improve patient outcomes.

Quantification of Artifacts and Image Distortions in 1.5 Tesla Magnetic Resonance Images of a Commercial Multi-Channel Vaginal Cylinder Brachytherapy Applicator Set

Background

The BEBIG Portio multi-channel applicator provides better target dose coverage and sparing organs-at-risk compared to a single-channel cylinder. However, artifacts and distortions of Portio in magnetic resonance images (MRI) have not yet been reported.

Objective

We aimed to quantify the artifacts and distortions in its 1.5-Tesla MR images before clinical use.

Material and Methods

In this experimental study, we employed a gelatin-filled phantom to conduct our measurements. T2-weighted (T2W) images were examined for artifacts and distortions. Computed tomography (CT) images were used as a reference to assess image distortions. Artifact severity was measured by recording the full-width-at-half-maximum (FWHM) image pixel values at various positions along the length of the applicator/channels. CT and MRI-based applicator reconstruction accuracy were then compared, and signal-to-noise ratio (SNR) and contrast were also determined for the applicator images.

Results

The applicator distortion level for the Portio applicator was less than the image spatial resolution (0.5±0.5 pixels). The average FWHM for the tandem applicator images was 5.23±0.39 mm, while it was 3.21±0.37 mm for all channels (compared to their actual diameters of 5.0 mm and 3.0 mm, respectively). The average applicator reconstruction difference between CT and MR images was 0.75±0.30 mm overall source dwell positions. The image SNR and contrast were both acceptable.

Conclusion

These findings indicate that the Portio applicator has a satisfactory low level of artifacts and image distortions in 1.5-Tesla, T2W images. It may, therefore, be a promising option for MRI-guided multi-channel vaginal brachytherapy.

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.

Dosimetric study of Varian Universal Multi-Channel Cylinder System for High-Dose-Rate 192Ir Brachytherapy

PURPOSE

Recently, the Varian multichannel vaginal cylinder (MCVC) set for high-dose-rate ¹⁹²Ir brachytherapy was commercially released. This MCVC was distinct from our existing MCVC in its peripheral channel layout and tip design. This investigation sought to assess the dosimetric impact of these changes.

METHODS AND MATERIALS

The dimensions of the virtual model for each applicator were compared against both physical and radiographic measurements. Volumetric dose distributions were generated in silico using a model-based dose calculation algorithm (MBDCA). To characterize the effects of the new peripheral channel layout on dose to adjacent areas ("dose-spill"), point doses were compared using two sets of applicator-based reference points: at surface or 5 mm radially from surface. To evaluate the dose-shaping capabilities, a dose distribution was generated for the new applicator and assessed against a representative dose distribution for a patient previously treated with existing equipment.

RESULTS

Based on both physical and radiographic measurements, virtual models were representative of each applicator within ±1 mm. Commissioning of the MBDCA was benchmarked based on AAPM Working Group on Dose Calculation Algorithms in Brachytherapy. The layout of the new applicator reduced dose-spill to other reference points significantly, as much as a factor of 16.3, compared with the existing equipment. The rounded tip shape and curve of the peripheral channels in the new applicator produced more conformity to its HR-CTV than existing equipment.

CONCLUSIONS

Compared with our existing equipment, the design changes in the new Varian MCVC set offered improved control of dose spill and better conformality to HR-CTV.

Manufacturing and evaluation of multi-channel cylinder applicator with 3D printing technology

Purpose

This study was designed to assess dosimetric characteristics of 3D-printed personalized multi-channel cylinder applicator (MCCA).

Material and methods

UnionTech RS Pro 600 (UnionTech, Inc., Shanghai, China) 3D printer was used for manufacturing MCCA. The geometry of MCCA was designed with Fusion 360 v.2.0.5827 (Autodesk, Inc.) software. The designed file was exported to Meshmixer v.3.5 (Autodesk, Inc.) to create three-dimensional model in stereolithography (STL) file format, which is the common file format for inputting data to 3D printers. We used high-temp resin, FLHTAM02 model (Formlabs Inc., MA, USA), as material in 3D printing process. This resin model has good resistance to high temperature and compatibility with various solvents. We created a simple cubic shape phantom for dosimetric evaluation of the applicator with Gafchromic EBT3 films. Also, Monte Carlo method was applied to simulate MCCA in the same configuration as in experimental test.

Results

The mean ± standard deviation (SD) difference between measured and calculated doses in treatment planning system (TPS) for all control points was 0.0860 ±0.0393 Gy, corresponding to 4.01 ±1.21%. The mean ±SD difference between doses calculated by Monte Carlo simulation and TPS for all control points was 0.0996 ±0.0471 Gy, corresponding to 4.58 ±1.05%. The mean ±SD of dose difference between film measurement and Monte Carlo simulation for all control points was 0.0136 ±0.0200 Gy, corresponding to 0.60 ±0.69%. P-value for dose difference between film measurement and TPS, Monte Carlo and TPS, and film measurement and Monte Carlo were 0.7, 0.66, and 0.95, respectively.

Conclusions

Dosimetric results and mechanical accuracy of MCCA show that high-temp resin with SLA 3D printing technique can be used for producing patient-specific MCCA in brachytherapy.

Complications of intracavitary brachytherapy for gynecologic cancers and their management: A comprehensive review

Intracavitary gynecologic brachytherapy in the form of tandem-based brachytherapy and vaginal cylinder-based brachytherapy represents a fundamental component of the treatment of women with cervical or uterine cancer due to the ability to deliver a therapeutic dose of radiation with sharp dose falloff. This results in highly effective treatment in terms of oncologic outcomes with an overall favorable toxicity profile. Still, complications and side effects of brachytherapy do exist. While advances in brachytherapy techniques have led to a significant decrease in the rates of toxicity, a thorough understanding of the potential complications is crucial to ensuring optimal outcomes for women with gynecologic cancer undergoing brachytherapy. Use of equivalent dose at 2 Gy per fraction (EQD2) models has allowed incorporation of external beam radiotherapy dose to the brachytherapy dose leading to development of consolidated dose constraints for organs-at-risk in the modern era. This manuscript offers a comprehensive review of potential complications associated with intracavitary brachytherapy for gynecologic cancer including predictive factors, mitigation tactics, and management strategies.

Preliminary results of modified interstitial MIAMI brachytherapy applicator for treatment of upper and apical vaginal tumors

Purpose

Intracavitary vaginal brachytherapy (VBT) cylinders are limited in treating upper/apical vaginal disease due to the distance between the target and radiation source positions. Interstitial brachytherapy devices directly expose the vaginal mucosa to radiation sources, increasing morbidity. To target apical disease while limiting excessive treatment to the vaginal mucosa and organs at risk, we modified the commercially available multichannel MIAMI applicator, allowing the direct extension of needles into the apex with the protection of cylinder.

Material and methods

The device has one central plastic core with six peripheral channels. The modified device permits titanium needles to surpass the apical surface into vaginal tissue. A retrospective analysis on thirteen patients treated with this device was conducted. Patient demographics, gross tumor volume (GTV)/clinical target volume (CTV), initial diagnosis and management, toxicity data, and EQD₂ data for the bladder and rectum were obtained.

Results

There were ten patients with vaginal recurrences and three with primary vaginal/cervical cancers. Mean dosage of VBT treatment was 25.5 Gy in 3-5 fractions. Mean dosage of external beam radiation therapy (EBRT) treatment was 44 Gy. Common acute toxicities included diarrhea, fatigue, cystitis, and nausea. Common chronic toxicities were pelvic pain, vaginal stenosis, and skin telangiectasia. Mean EQD₂ dose for bladder and rectum were 72.3 Gy and 62.3 Gy, respectively. Ten patients had no evidence of relapse, two suffered from distant metastases, and one patient with stage IIIA cervical adenocarcinoma had loco-regional recurrence seventeen months after radiation treatment.

Conclusions

Our data suggests that the custom applicator is associated with robust dosimetric coverage, good loco-regional control, acceptable toxicity, and reduced tissue trauma. This device allows treatment of apically located vaginal tumors without significant damage to the vaginal vault and organs at risk. Additionally, it provides the flexibility to treat multiple patients with variable vaginal diameters and sizes/depths of apical tumors using a single device.

Image-based multichannel vaginal cylinder brachytherapy for the definitive treatment of gynecologic malignancies in the vagina

PURPOSE

Brachytherapy is integral to vaginal cancer treatment and is typically delivered using an intracavitary single-channel vaginal cylinder (SCVC) or an interstitial brachytherapy (ISBT) applicator. Multi-channel vaginal cylinder (MCVC) applicators allow for improved organ-at-risk (OAR) sparing compared to SCVC while maintaining target coverage. We present clinical outcomes of patients treated with image-based high dose-rate (HDR) brachytherapy using a MCVC.

METHODS AND MATERIALS

Sixty patients with vaginal cancer (27% primary vaginal and 73% recurrence from other primaries) were treated with combination external beam radiotherapy (EBRT) and image-based HDR brachytherapy utilizing a MCVC if residual disease thickness was 7 mm or less after EBRT. All pts received 3D image-based BT to a total equivalent dose of 70-80 Gy.

RESULTS

The median high-risk clinical target volume was 24.4 cm³ (interquartile range [IQR], 14.1), with a median dose to 90% of 77.2 Gy (IQR, 2.8). After a median follow-up of 45 months (range, 11-78), the 4-year local-regional control, distant control, DFS, and OS rates were 92.6%, 76.1%, 64.0%, and 67.2%, respectively. The 4-year LRC rates were similar between the primary vaginal (92%) and recurrent (93%) groups (p = 0.290). Pts with lymph node positive disease had a lower rate of distant control at 4 years (22.7% vs. 89.0%, p < 0.001). There were no Grade 3 or higher acute complications. The 4-year rate of late Grade 3 or higher toxicity was 2.7%.

CONCLUSIONS

Clinical outcomes of pts with primary and recurrent vaginal cancer treated definitively in a systematic manner with combination EBRT with image-guided HDR BT utilizing a MCVC applicator demonstrate high rates of local control and low rates of severe morbidity. The MCVC technique allows interstitial implantation to be avoided in select pts with ≤7 mm residual disease thickness following EBRT while maintaining excellent clinical outcomes with extended 4-year follow-up in this rare malignancy.

Dosimetric comparison of interstitial brachytherapy with multi-channel vaginal cylinder plans in patients with vaginal tumors

BACKGROUND

To evaluate the dosimetric performance of multi-channel vaginal cylinder (MCVC) against interstitial brachytherapy (ISBT) for the treatment of vaginal tumors.

METHODS

Vaginal tumors with extension of > 0.5 cm and ≤ 2 cm from the lateral vaginal wall and/or ≤ 1 cm in height above the vaginal vault were retrospectively selected from a ISBT registry trial database. The selected patients were treated with ISBT and targets included the intermediate (IRCTV) or high-risk (HRCTV) clinical target volumes. For technique comparison, a 35 mm MCVC was registered with the interstitial intra-vaginal cylinder. Bladder and rectum contours were transferred from the ISBT to the MCVC-BT plans. Vaginal mucosa was achieved by 3 mm uniform expansion from cylinder surface. Both the ISBT and MCVC-BT plans were optimized using the Inverse Planning Simulated Annealing optimization algorithm. After normalizing target D90 to 700 cGy, dose to organs at risk were measured and compared between ISBT and MCVC plans.

RESULTS

Six interstitial patient plans met the inclusion criteria for this study. Four patients had vaginal primaries and two recurrent cancers in the vagina. Lower doses to bladder and rectum were seen with ISBT plans. In half of the MCVC plans, the rectal dose met the recommended constraints. For plans in which the rectal constraint was not met, the target volumes were abutting the rectum and had a cranial-caudal length ≥ 5 cm. Dose to vaginal mucosa was lower in ISBT plans directed to the HRCTVs, although no difference was seen in circumferential IRCTVs.

CONCLUSIONS

Overall, ISBT results in decreased dose to OARs as compared to MCVC. However, MCVC BT results in acceptable doses to OARs with possible improvement in vaginal doses for circumferential targets. Careful consideration to tumor geometry and location may help guide optimal techniques in vaginal tumor brachytherapy.

American Brachytherapy Task Group Report: Adjuvant vaginal brachytherapy for early-stage endometrial cancer: A comprehensive review

This article aims to review the risk stratification of endometrial cancer, treatment rationale, outcomes, treatment planning, and treatment recommendations of vaginal brachytherapy (VBT) in the postoperative management of endometrial cancer patients. The authors performed a thorough review of the literature and reference pertinent articles pertaining to the aims of this review. Adjuvant VBT for early-stage endometrial cancer patients results in very low rates of vaginal recurrence (0-3.1%) with low rates of late toxicity which are primarily vaginal in nature. Post-Operative Radiation Therapy in Endometrial Cancer 2 (PORTEC-2) supports that VBT results in noninferior rates of vaginal recurrence compared to external beam radiotherapy for the treatment of high-intermediate risk patients. VBT as a boost after external beam radiotherapy, in combination with chemotherapy, and for high-risk histologies have shown excellent results as well though randomized data do not exist supporting VBT boost. There are many different applicators, dose-fractionation schedules, and treatment planning techniques which all result in favorable clinical outcomes and low rates of toxicity. Recommendations have been published by the American Brachytherapy Society and the American Society of Radiation Oncology to help guide practitioners in the use of VBT. Data support that patients and physicians prefer joint decision making regarding the use of VBT, and patients often desire additional treatment for a marginal benefit in risk of recurrence. Discussions regarding adjuvant therapy for endometrial cancer are best performed in a multidisciplinary setting, and patients should be counseled properly regarding the risks and benefits of adjuvant therapy.