MRI-based interstitial brachytherapy for vaginal tumors: A multi-institutional study on practice patterns, contouring, and consensus definitions of target volumes

Salvage interstitial brachytherapy for treatment of recurrent endometrial cancers in the vagina: Seven-year single institution experience and review of second recurrence patterns

INTRODUCTION

Interstitial brachytherapy (ISBT) is a known treatment for vaginal recurrence of endometrial cancer. This study reviews a large tertiary institution's ISBT experience and outcomes for vaginal recurrences.

MATERIAL AND METHODS

Patients who underwent salvage ISBT for vaginal recurrence of endometrial cancer from January 1, 2014 to August 31, 2021, were identified. Initial and salvage disease factors and treatments were recorded. Outcomes were calculated including overall survival, local, and distant failure.

RESULTS

Thirty-nine patients were included; thirty received external beam radiotherapy and interstitial brachytherapy (EBRT + ISBT) while 9 received ISBT alone. At initial diagnosis, the ISBT alone group had an older median age, with stage IA-IV disease, frequently receiving adjuvant treatment, compared to the EBRT with ISBT group with mainly stage IA disease who did not. Median follow up was 22 months and median time to recurrence 14 months (16.5 months in EBRT + ISBT group and 14 in the ISBT alone group). Two-year overall survival was 85% for all patients, 85.6% and 83.3%in the EBRT + ISBT and ISBT alone groups, respectively. Local failure was 22.7% for all patients, 16.7% in the EBRT + ISBT group and 11.1% in the ISBT alone group. Median HRCTV D90 (EQD2) was 76.8 Gy in the EBRT + ISBT group, and 57.9 Gy in the ISBT alone group. Late grade 3 or higher toxicity occurred in only 3 patients.

CONCLUSIONS

EBRT + ISBT is an effective treatment for endometrial cancer vaginal recurrence, with acceptable toxicity. ISBT alone is an option for patients with contraindications to or with previous treatment of pelvic radiation.

Patient-specific cylinder templates for hybrid interstitial vaginal brachytherapy: Feasibility of automated 3-D design, 3D printing, and dosimetric outlook

PURPOSE

Delivering highly conformal treatment plans for high-dose rate vaginal brachytherapy using commercially available applicators can be challenging. A partially automated workflow is presented for the in-house modeling and 3D printing of patient-specific cylindrical templates (PSCTs), which facilitate placement of flexible intracavitary and interstitial needles. To demonstrate feasibility, we compare PSCT treatment plans to retrospective interstitial brachytherapy plans delivered at our center. PSCTs derived from these plans were 3D printed to test the validity of the auto-design process. To facilitate clinical implementation, we validated the steam sterilization compatibility of PSCTs printed using polyetheretherketone (PEEK).

METHODS AND MATERIALS

Plans for ten patients treated using a combination of vaginal cylinder and interstitial needles were compared to PSCT-based plans created for the same patient. DVH parameters for the HRCTV (V100, V150, V200, D90) and OARs (D2 cm3) were evaluated, as well as the number of needles used and the total interstitial length. Each planned PSCT was printed and compared to the intended needle geometry. 3D printed models were sterilization validated by an independent contractor for an autoclave protocol.

RESULTS

PSCT plans demonstrated advantages over template based perineal BT in reducing the total interstitial needle length required while preserving or improving HRCTV and OAR dosimetry. All printed PSCTs matched planned geometry.

CONCLUSIONS

PSCTs stand to be an alternative to current HDR-BT templates/applicators for patients with vaginal and locally recurrent endometrial cancers. Clinically equivalent or improved treatment plans can be created and devices to deliver these plans can be accurately printed and sterilized.

Recommendations of the Spanish brachytherapy group of the Spanish Society of Radiation Oncology and the Spanish Society of Medical Physics for interstitial high-dose-rate brachytherapy for gynaecologic malignancies

The present document includes consensus-based recommendations from the Brachytherapy Group (GEB) of the Spanish Society of Radiation Oncology (SEOR) and the Spanish Society of Medical Physics (SEFM) for interstitial high-dose-rate (HDR) brachytherapy (BT) for gynaecologic malignancies. A nine-item survey-which included questions on experience with interstitial BT; indications and technique; applicator type; magnetic resonance imaging (MRI)-based planning; dose; fractionation schedule; and treatment planning-was sent to all radiation oncology departments (n = 174) in Spain in 2021. Responses were received from 36 centres (50% of all centres [n = 72] with a BT unit). The consensus-based recommendations presented here are based on a review of the available literature, professional experience among the group of experts, and in-person discussions held during the annual meeting of these two societies. We describe the results of the survey and the following: indications; contraindications; patient selection; description of applicators; role of imaging in planning; contouring; dose prescription; dosimetric reconstruction; optimisation; and dose indications for cancers of the cervix, vagina, and vulva. The various clinical scenarios in which interstitial BT is used in the treatment of gynaecological tumours are described in detail, including cervix intracavitary/interstitial hybrid HDR-BT; cervix perineal templates/freehand implants; primary vaginal malignancies/vaginal recurrences; and vulvar interstitial implants.

GEC-ESTRO (ACROP)-ABS-CBG Consensus Brachytherapy Target Definition Guidelines for Recurrent Endometrial and Cervical Tumors in the Vagina

PURPOSE

Representatives from the Gynecologic Groupe European de Curietherapie-European Society for Radiation Therapy and Oncology (GYN GEC-ESTRO), the American Brachytherapy Society (ABS), and the Canadian Brachytherapy Group (CBG) met to develop international consensus recommendations for target definitions for image-guided adaptive brachytherapy for vaginal recurrences of endometrial or cervical cancer.

METHODS AND MATERIALS

Seventeen radiation oncologists and 2 medical physicists participated. Before an in-person meeting each participant anonymously contoured 3 recurrent endometrial/cervical cancer cases. Participants contoured the residual gross primary tumor volume (GTV-T_res), a high-risk clinical target volume (CTV-T_HR), and an intermediate-risk clinical target volume (CTV-T_IR), on T2-weighted magnetic resonance images (MRIs). All contours were drawn using Falcon EduCase. Contours were reviewed at an in-person meeting during which a consensus document was created defining agreed-upon target definitions (Trial 1). After establishing these definitions, the group was sent one of the cases again (recurrent cervical cancer vaginal recurrence) and asked to contour the targets again (Trial 2). The Computerized Environment for Radiation Research (CERR) software (The Mathworks, Natwick, MA) was used to analyze the contours. Kappa statistics were generated to assess level of agreement between contours. A conformity index (CI), defined as the ratio between the intersection and union volume of a given pair of contours, was calculated. A simultaneous truth and performance level estimation (STAPLE) contour was created for the CTV-T_HR and CTV-T_IR for the postmeeting case.

RESULTS

Consensus definitions for GTV-T_res, CTV-T_HR, and CTV-T_IR were established. Kappa statistics (Trial 1/Trial 2) for GTV-T_res, CTV-T_HR, and CTV-T_IR were 0.536/0.583, 0.575/0.743 and 0.522/0.707. Kappa statistics for Trial 2 for the CTV-T_HR and CTV-T_IR showed "substantial" agreement while the GTV-T_res remained at moderate agreement.

CONCLUSIONS

This consensus provides recommendations to facilitate future collaborations for MRI-guided adaptive brachytherapy target definitions in endometrial/cervical vaginal recurrences.

An endovaginal MRI array with a forward-looking coil for advanced gynecological cancer brachytherapy procedures: Design and initial results

PURPOSE

To develop an endovaginal MRI array that provides signal enhancement forward into the posterior parametrium and sideways into the vaginal wall, accelerating multiple-contrast detection of residual tumors that survive external beam radiation. The array's enclosure should form an obturator for cervical cancer brachytherapy, allowing integration with MRI-guided catheter placement, CT, and interstitial radiation dose delivery.

METHODS

The endovaginal array consisted of forward-looking and sideways-looking components. The forward-looking element imaged the cervix and posterior endometrium, and the sideways-looking elements imaged the vaginal wall. Electromagnetic simulation was performed to optimize the geometry of a forward-looking coil placed on a conductive-metallic substrate, extending the forward penetration above the coil's tip. Thereafter, an endovaginal array with one forward-looking coil and four sideways-looking elements was constructed and tested at 1.5 Tesla in saline and gel phantoms, and three sexually mature swine. Each coil's tuning, matching, and decoupling were optimized theoretically, implemented with electronic circuits, and validated with network-analyzer measurements. The array enclosure emulates a conventional brachytherapy obturator, allowing use of the internal imaging array together with tandem coils and interstitial catheters, as well as use of the enclosure alone during CT and radiation delivery. To evaluate the receive magnetic field ( B 1 - ) spatial profile, the endovaginal array's specific absorption-rate (SAR) distribution was simulated inside a gel ASTM phantom to determine extreme heating locations in advance of a heating test. Heating tests were then performed during high SAR imaging in a gel phantom at the predetermined locations, testing compliance with MRI safety standards. To assess array imaging performance, signal-to-noise-ratios (SNR) were calculated in a saline phantom and in vivo. Swine images were acquired with the endovaginal array combined with the scanner's body and spine arrays.

RESULTS

Simulated B 1 - profiles for the forward-looking lobe pattern, obtained while varying several geometric parameters, disclosed that a forward-looking coil placed on a metal-backed substrate could double the effective forward penetration from approximately 25 to ∼40 mm. An endovaginal array, enclosed in an obturator enclosure was then constructed, with all coils tuned, matched, and decoupled. The ASTM gel-phantom SAR test showed that peak local SAR was 1.2 W/kg in the forward-looking coil and 0.3 W/kg in the sideways-looking elements, well within ASTM/FDA/IEC guidelines. A 15-min 4 W/kg average SAR imaging experiment resulted in less than 2^o C temperature increase, also within ASTM/FDA/IEC heating limits. In a saline phantom, the forward-looking coil and sideways-looking array's SNR was four to eight times, over a 20-30 mm field-of-view (FOV), and five to eight times, over a 15-25 mm FOV, relative to the spine array's SNR, respectively. In three sexually mature swine, the forward-looking coil provided a 5 + 0.2 SNR enhancement factor within the cervix and posterior endometrium, and the sideways-looking array provided a 4 + 0.2 SNR gain factor in the vaginal wall, relative to the Siemens spine array, demonstrating that the array could significantly reduce imaging time.

CONCLUSIONS

Higher SNR gynecological imaging is supported by forward-looking and sideways-looking coils. A forward-looking endovaginal coil for cervix and parametrium imaging was built with optimized metal backing. Array placement within an obturator enhanced integration with the brachytherapy procedure and accelerated imaging for detecting postexternal-beam residual tumors.

Clinical outcomes of distal vaginal and vulvar cancer treated with image-guided brachytherapy

Purpose

To evaluate treatment outcomes with image-guided brachytherapy (IGBT) for distal vaginal and vulvar cancers.

Material and methods

Women treated for distal vaginal or vulvar malignancies utilizing IGBT were retrospectively reviewed, and acute and late toxicities were retrospectively graded. Descriptive statistical analysis was performed.

Results

Eighteen patients were included, out of which, twelve patients (66.7%) were with primary disease of the distal vagina and vulva, most commonly squamous cell carcinoma of the vulva (n = 8, 66.7%), and six with recurrent disease, most commonly recurrent endometrial carcinoma (n = 5, 83.3%). All patients received external beam radiation (EBRT) to a median dose of 45 Gy in 25 fractions, followed by IGBT (range of 15 to 27.5 Gy in 3 to 5 fractions). Mean follow-up was 20.6 months. Mean dose to high-risk clinical target volume (HR-CTV) D₉₀ was 72.4 Gy. Mean D_2cc for the rectum, bladder, and urethra were 50 Gy, 50.6 Gy, and 62.9 Gy, respectively. Five patients (27.8%) recurred. Three patients (16.7%) had local recurrence, 1 patient (5.6%) had distant recurrence only, and 1 patient (5.6%) had simultaneous regional and distant recurrence. Grade 3 acute toxicities included 1 (5.6%) vaginal stenosis, 6 (33.3%) dermatitis/mucositis, 2 (11.1%) vaginal pain, and 1 (5.6%) vaginal/vulvar infection. Grade 3 late toxicities comprised 3 (17.7%) cases of vaginal pain and 1 (5.9%) skin/vaginal necrosis. There were no grade 4 or higher toxicities.

Conclusions

Definitive radiation therapy in the form of EBRT and IGBT provides meaningful loco-regional control in women with distal vaginal and vulvar cancers, with mainly skin and vaginal toxicity.

Method of computing direction-dependent margins for the development of consensus contouring guidelines

BACKGROUND

Clinical target volume (CTV) contouring guidelines are frequently developed through studies in which experts contour the CTV for a representative set of cases for a given treatment site and the consensus CTVs are analyzed to generate margin recommendations. Measures of interobserver variability are used to quantify agreement between experts. In cases where an isotropic margin is not appropriate, however, there is no standard method to compute margins in specified directions that represent possible routes of tumor spread. Moreover, interobserver variability metrics are often measures of volume overlap that do not account for the dependence of disagreement on direction. To aid in the development of consensus contouring guidelines, this study demonstrates a novel method of quantifying CTV margins and interobserver variability in clinician-specified directions.

METHODS

The proposed algorithm was applied to 11 cases of non-spine bone metastases to compute the consensus CTV margin in each direction of intraosseous and extraosseous disease. The median over all cases for each route of spread yielded the recommended margins. The disagreement between experts on the CTV margin was quantified by computing the median of the coefficients of variation for intraosseous and extraosseous margins.

RESULTS

The recommended intraosseous and extraosseous margins were 7.0 mm and 8.0 mm, respectively. The median coefficient of variation quantifying the margin disagreement between experts was 0.59 and 0.48 for intraosseous and extraosseous disease.

CONCLUSIONS

The proposed algorithm permits the generation of margin recommendations in relation to adjacent anatomy and quantifies interobserver variability in specified directions. This method can be applied to future consensus CTV contouring studies.

3D image-guided interstitial brachytherapy for primary vaginal cancer: A multi-institutional experience

PURPOSE/OBJECTIVES

High dose rate (HDR) interstitial brachytherapy (ISBT) boost is integral for definitive radiation treatment of primary vaginal cancer. Technological advances with CT or MRI guidance provide improved precision and ability to treat more extensively invasive tumors over historical techniques, but reported experience is limited. We sought to provide updated outcome and toxicity data for women with primary vaginal cancer undergoing treatment with a modern ISBT technique.

MATERIAL/METHODS

Databases of primary vaginal carcinoma patients treated at two Canadian academic cancer institutions were combined including patient, tumor and treatment characteristics, and survival outcomes and toxicity data. Descriptive statistics, survival estimates based on the Kaplan-Meier method, and univariable/multivariable Cox proportional hazards regression analyses are reported.

RESULTS

Between 2002 and 2017, 67 women with primary vaginal cancer were treated with 3D HDR ISBT. FIGO stage distribution was I (22.4%), II (50.8%), III (17.9%), IVa (9.0%). All patients received external beam radiotherapy and HDR ISBT of 500-750 cGy per fraction over 2-4 fractions. Median follow-up was 2.68 years (95% confidence interval: 2.04-6.04). Cumulative rate of grade 3-4 genitourinary/gastrointestinal toxicity was 10.4%. Four patients developed vaginal fistula. Progression-free survival at 2 and 3 years was 73.5% and 66.4% for all patients, 78.3% and 75.0% for stage I-II and 61.6% and 46.2% for stage III-IVa, respectively (log-rank p = 0.252).

CONCLUSIONS

Use of 3D image-guided HDR ISBT boost was safe and resulted in improved survival outcomes compared to historical rates in this series of primary vaginal cancer patients. Prospective study is warranted to better define clinical and dosimetric predictors of local control.

Salvage Re-irradiation With Single-modality Interstitial Brachytherapy for the Treatment of Recurrent Gynaecological Tumours in the Pelvis: A Multi-institutional Study

AIMS

Recurrent gynaecological tumours can cause significant morbidity with limited salvage options. This study investigates the strategy of salvage single-modality interstitial brachytherapy (SM-ISBT) for recurrent gynaecological pelvic cancer at two specialised ISBT centres.

MATERIALS AND METHODS

Patients who had received salvage SM-ISBT for pelvic recurrence of gynaecological cancers from September 2008 to January 2017 were included. None had distant metastasis at the time of recurrence. Local control, progression-free and overall survival and long-term toxicities were evaluated.

RESULTS

Twenty-six patients with a median follow-up of 24 months (range 2.5-106.3 months) after SM-ISBT were included. Primary cancer sites were endometrium (20), cervix (4), vulva (1) and vagina (1). All patients had prior whole-pelvic external beam irradiation and 16 had prior brachytherapy. The median disease-free survival prior to SM-ISBT was 20.3 months (interquartile range 9.9-30.5). SM-ISBT was delivered with high dose rate technique over three to six fractions. The median high-risk clinical target volume was 34.6 cm3, with a median D90 of 29.1 Gy (range 16.1-64.6). The median bladder, rectum and sigmoid D2cm3 were 15.5, 18.7 and 3.7 Gy, respectively. After SM-ISBT, complete and partial responses were achieved in 17 (64%) and 5 (19%) patients, respectively. Two (7.4%) patients had grade 3 toxicities (both vaginal stenosis), with no grade 4 complications. Eighteen patients (69%) recurred, including local, regional and metastatic in 14 (54%), 8 (30%) and 5 (19%) patients, respectively. Two-year local control, progression-free survival and overall survival were 50, 38 and 78%, respectively. In follow-up, 12 patients (46%) remained in local control.

CONCLUSIONS

Salvage SM-ISBT re-irradiation for pelvic recurrence of gynaecological malignancies was feasible and safe. With limited salvage options, the local control obtained in more than a quarter of patients seems reasonable. Further efforts are needed to establish a consensus about the optimal patient selection, dose fractionation, implant technique and combination with systemic therapies.