MRI-Based Evaluation of the Vaginal Cuff in Brachytherapy Planning: Are We Missing the Target?

doi:10.1016/j.ijrobp.2016.01.042

International Journal of Radiation OncologyBiologyPhysics

Volume 95, Issue 2, 1 June 2016, Pages 743-750

This work was presented previously in part at the American Brachytherapy Society Annual Meeting, April 10, 2015, Orlando, FL.

https://doi.org/10.1016/j.ijrobp.2016.01.042 Get rights and content

Purpose

Although recurrences and toxicity occur after vaginal cuff (VC) brachytherapy, little is known about dosimetry due to the inability to clearly visualize the VC on computed tomography (CT). T2-weighted (T2W) magnetic resonance imaging (MRI) is superior to CT in this setting, and we hypothesized that it could provide previously unascertainable dosimetric information.

Methods and Materials

In a cohort of 32 patients who underwent cylinder-based brachytherapy for endometrial cancer with available MR simulation images, the VC was retrospectively contoured on T2W images, and cases were replanned to treat the upper VC to a dose of 7 Gy/fraction prescribed to 5 mm. Relevant dose-volume parameters for the VC were calculated.

Results

T2W MRI identified significant underdosing not observed on CT or T1-weighted imaging. Over two-thirds (69%) of patients had at least 1 cm³ of VC that received less than 75% of the prescription dose and half (50%) of patients had a least 1 cm³ of VC that received less than 50% of the prescription dose. The mean minimum point dose to the VC was 2.4 Gy, or 34% of the intended prescription dose (range: 0.53-6.4 Gy).

Conclusions

We identified previously unreported VC underdosing in over two-thirds of our patients, with most of these patients having volumes of undistended VC that received less than half of the prescription dose. The maximum dimension was along the craniocaudal axis in some patients or left-right/anterior-posterior axis in others, suggesting that suture material may be restricting access to the vaginal apex and that alternative applicators may be needed when the diameter of the apex is larger than the introitus. Additional follow-up will be needed to determine whether underdosing is associated with isolated VC failure or whether low failure rates across the cohort suggest that some patients are being exposed to excessive dose and unnecessary risk of toxicity.

Introduction

Endometrial carcinoma is the most common gynecologic malignancy in the United States, with 54,870 new cases estimated in 2015 (1). After surgical management, 70% of failures occur in the vaginal cuff (VC) (2). Although external beam radiation therapy (EBRT) decreases risk of these failures 2, 3, brachytherapy alone achieves similar VC control in appropriately selected patients with less gastrointestinal and genitourinary toxicity 4, 5, 6.

Unique dosimetric challenges exist in brachytherapy for endometrial cancer given that the VC is both the clinical target volume (CTV) and an organ at risk. Although trials of vaginal brachytherapy required a uniform dose and prescription depth, the dose distribution to the VC CTV has historically been impossible to calculate because computed tomography (CT) or fluoroscopic imaging was used, neither of which allows for adequate delineation of the VC from surrounding tissue (7). Because VC failures are uncommon after brachytherapy 4, 8, 9, it is assumed that the at-risk tissue is being sufficiently covered. However, insufficient coverage might be the cause of failures that do occur, and this can only be investigated using imaging modalities that allow for direct visualization of the VC. Furthermore, inability to directly visualize the vaginal cuff suggests a missed opportunity to minimize toxicity by delivering only the minimum dose necessary to achieve an acceptable rate of VC control.

VC can be visualized using T2-weighted (T2W) magnetic resonance imaging (MRI) 10, 11, which provides better soft tissue contrast than CT (12) and is already used in other gynecologic cancers for defining gross disease 13, 14. This supports a novel application in endometrial cancer treatment. We hypothesize that there is significant post-operative anatomic variation in VC anatomy, and that T2W MRI can be used to provide a full and nuanced quantification of VC dosimetry.

Section snippets

Methods and Materials

The records of 42 patients treated with postoperative high-dose-rate (HDR) brachytherapy using vaginal cylinders at the University of Michigan from August 2013 to January 2015 were reviewed with institutional review board approval. Surgery consisted of total hysterectomy and bilateral salpingoophorectomy with or without lymphadenectomy. Eligible patients underwent vaginal cylinder–based brachytherapy with or without EBRT and had at least 1 simulation MRI. Ten patients who underwent CT-based

Qualitative assessment of VC

On T2W images, structures had the following appearances: vaginal cylinder-black/hypointense, lubricant, and fluid in vaginal canal-white/hyperintense, and VC-intermediate signal, hyperintense to cylinder but hypointense compared with surrounding pelvic fat. Like other muscular structures in the pelvis, the cuff had a typical striated or multilayered morphology. Normal structures were easily identified, including the bladder, urethra/Foley catheter, and rectosigmoid. Areas of undistended vaginal

Discussion

This study used emerging MRI simulation techniques to evaluate VC dosimetry in adjuvant brachytherapy for endometrial cancer. Our study has several novel findings. First, many patients had large areas of VC that were underdosed. Two-thirds of patients had at least 1 cm³ of VC that received less than 75% of the prescription dose, and half of patients had at least 1 cm³ of VC that received less than 50% of the prescription dose.

Second, there was significant heterogeneity with respect to VC

Conclusions

In conclusion, we identified frequent and substantial VC underdosing using MRI simulation and retrospective dosimetry in women undergoing cylinder-based HDR brachytherapy after hysterectomy for endometrial cancer. The clinical implications of these findings necessitate further investigation, including associations with failure rates and toxicity. We suggest that ongoing and future prospective studies of vaginal cylinder–based brachytherapy should consider MR-based VC dosimetry to firmly

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Cited by (21)

(Potential) Mishaps of High-Dose-Rate Vaginal Cuff Brachytherapy
2023, Practical Radiation Oncology
Considering how commonly vaginal cuff brachytherapy is used, there is relatively little literature regarding the potential, albeit low, risk for complications. We present 3 potentially serious mishaps involving cylinder misplacement, dehiscence, and excessive normal tissue irradiation due to unique anatomy. Three patients with potentially serious treatment errors were encountered in the authors’ usual clinical practice. Each patient's records were reviewed for this report. For patient 1, computed tomography (CT) simulation revealed grossly inadequate cylinder insertion, which was most obvious on the sagittal view. For patient 2, CT simulation revealed that the cylinder extended beyond the perforated vaginal cuff and was surrounded by bowel. For patient 3, CT images were used only to verify cylinder depth. A standard library plan based on cylinder diameter and active length was used. In retrospect, the images revealed an unusually thin rectovaginal septum, with the lateral and posterior vaginal wall thickness estimated to be <2 mm. This patient's fractional normal tissue doses were calculated for this report, revealing a rectal maximum dose (per fraction) of 10.8 Gy, maximum dose that 2 cc of the organ receives of 7.4 Gy, and volume of the organ that receives the prescription dose or higher of 2.8 cc. All doses were far in excess of those anticipated for a minimal 0.5-cm vaginal wall depth. Vaginal cuff high-dose-rate brachytherapy is a high-volume, routine procedure. Even in experienced hands, however, it carries a risk of improper cylinder placement, cuff dehiscence, and excessive normal tissue dose, all of which could seriously affect outcomes. These potential mishaps would be better appreciated and avoided with more extensive use of CT-based quality assurance measures.
Evaluating the relationship between vaginal apex “dog ears” and patterns of recurrence in endometrial cancer following adjuvant image guided vaginal cuff brachytherapy
2023, Brachytherapy
The aim of this investigation is to characterize vaginal apex “dog ears” and their association with patterns of treatment failure in patients with endometrial cancer treated with adjuvant high-dose-rate (HDR) single-channel vaginal cuff brachytherapy (VCB).
A retrospective review of patients treated with HDR VCB from 2012 to 2021 for medically operable endometrial cancer at a single institution was conducted. Dog ears, defined as tissue at the apex extending at least 10 mm from the brachytherapy applicator were identified on CT simulation images. Fisher exact test and a multivariate logistic regression model evaluated the association between factors of interest with treatment failure. Vaginal cuff failure free survival (VCFFS) was calculated from first brachytherapy to vaginal cuff recurrence (VCR).
A total of 219 patients were reviewed. In this sample, 57.5% of patients met criteria for having dog ears. In total, 13 patients (5.9%) developed a VCR. There was no statistically significant difference in the rate of VCR between patients with and without dog ears (7.1% vs. 4.3%, p = 0.56). There was a trend toward increased risk of recurrence with higher grade histology identified in the multivariate logistic regression model (p = 0.085). The estimated 3-year probability of VCFFS was 86%.
Vaginal apex dog ears are prevalent but are not found to statistically increase the risk of VCR after VCB in our single institution experience. However, while local failure remains low in this population, we report an absolute value of over twice as many VCRs in patients with dog ears, indicating that with improved dog ear characterization this may remain a relevant parameter for consideration in treatment planning.
Do air gaps with image-guided vaginal cuff brachytherapy impact failure rates in patients with high-intermediate risk FIGO Stage I endometrial cancer?
2021, Brachytherapy
Citation Excerpt :
Because the submucosal lymphatic channels that are the target of VCBT lie in a relatively narrow window a few millimeters deep to the vaginal mucosa and dose distribution in modern optimization algorithms is driven primarily by distance from the source, the question has been raised as to whether these air gaps are detrimental to target coverage (5,6). Multiple studies have been performed to quantify air gaps and their dosimetric impact, finding a mean dose reduction to the vaginal mucosa of 26–27% (7–18). However, none have assessed the impact of these air gaps on the rate of VCF after IGBT.
The aim of this study was to assess the impact of air gaps at the cylinder surface on the rate of vaginal cuff failure (VCF) after image-guided adjuvant vaginal cuff brachytherapy (VCBT) in the treatment of high-intermediate risk (HIR) FIGO (Fédération Internationale de Gynécologie et d'Obstétrique (International Federation of Gynecology and Obstetrics)) Stage I endometrial cancer.
A retrospective review of patients treated with image-guided VCBT from 2009 to 2016 for HIR FIGO Stage I endometrial cancer was performed. Air gaps present at the applicator surface on the first postinsertion CT were contoured. Vaginal cuff failure–free survival (VCFFS) was measured from the first fraction of VCBT to VCF.
A total of 234 patients were identified. Air gaps were present on the first postinsertion CT scan in 82% of patients. The median number of air gaps was 2 (interquartile range [IQR] 1–3), median depth of the largest air gap was 2.7 mm (IQR 2.1–3.4 mm), and the median cumulative volume of air gaps was less than 0.1 cm³ (range < 0.1–0.7 cm³). At a median followup of 56 months (IQR 41–69), 12 patients (5%) experienced VCF, of which 4 had isolated VCF and 8 had synchronous pelvic or distant failure. Five-year VCFFS and isolated VCFFS were 96% (95% confidence interval 93–98%) and 98% (95% confidence interval 96–100%), respectively. On univariate analysis, no factors, including the presence, number, maximum depth, or cumulative volume of air gaps, were predictive for VCFFS.
In this population, VCFFS remained high despite most patients having air gaps present on postinsertion CT scan.
NRG Oncology/RTOG Consensus Guidelines for Delineation of Clinical Target Volume for Intensity Modulated Pelvic Radiation Therapy in Postoperative Treatment of Endometrial and Cervical Cancer: An Update
2021, International Journal of Radiation Oncology Biology Physics
Accurate target definition is critical for the appropriate application of radiation therapy. In 2008, the Radiation Therapy Oncology Group (RTOG) published an international collaborative atlas to define the clinical target volume (CTV) for intensity modulated pelvic radiation therapy in the postoperative treatment of endometrial and cervical cancer. The current project is an updated consensus of CTV definitions, with removal of all references to bony landmarks and inclusion of the para-aortic and inferior obturator nodal regions.
An international consensus guideline working group discussed modifications of the current atlas and areas of controversy. A document was prepared to assist in contouring definitions. A sample case abdominopelvic computed tomographic image was made available, on which experts contoured targets. Targets were analyzed for consistency of delineation using an expectation-maximization algorithm for simultaneous truth and performance level estimation with kappa statistics as a measure of agreement between observers.
Sixteen participants provided 13 sets of contours. Participants were asked to provide separate contours of the following areas: vaginal cuff, obturator, internal iliac, external iliac, presacral, common iliac, and para-aortic regions. There was substantial agreement for the common iliac region (sensitivity 0.71, specificity 0.981, kappa 0.64), moderate agreement in the external iliac, para-aortic, internal iliac and vaginal cuff regions (sensitivity 0.66, 0.74, 0.62, 0.59; specificity 0.989, 0.966, 0.986, 0.976; kappa 0.60, 0.58, 0.52, 0.47, respectively), and fair agreement in the presacral and obturator regions (sensitivity 0.55, 0.35; specificity 0.986, 0.988; kappa 0.36, 0.21, respectively). A 95% agreement contour was smoothed and a final contour atlas was produced according to consensus.
Agreement among the participants was most consistent in the common iliac region and least in the presacral and obturator nodal regions. The consensus volumes formed the basis of the updated NRG/RTOG Oncology postoperative atlas. Continued patterns of recurrence research are encouraged to refine these volumes.
Brachytherapy Future Directions
2020, Seminars in Radiation Oncology
Citation Excerpt :
In gynecological cancer, several applicators are ubiquitous. However, poor applicator fit during vaginal brachytherapy can lead to air gaps and underdosing of the target volume.21 For interstitial implants, poor applicator fit or placement may result in poor implant geometry and increased interfraction variability when multiple fractions are delivered with a single implant.22
Brachytherapy has advanced dramatically in the last decade due largely to improvements in applicators, imaging, treatment planning, and use of clinical trials. In addition, current research in brachytherapy technology continues to change how we deliver this treatment modality. The future of brachytherapy lies in the ability of new technologies to overcome real or perceived barriers. The focus for this manuscript is on specific tools that have or are near to being introduced in the clinic. First, we explore the impact electromagnetic tracking technologies can have on brachytherapy implants and planning workflow. This is followed by an overview of the use of 3D printing and its ability to help tailor brachytherapy implants. Next, we discuss advances in self-shielded applicators and intensity-modulated brachytherapy technology. The manuscript closes out with 2 sections on treatment planning. First is a discussion of biological optimization and its potential as compared with current techniques (eg, based on physical dosimetry). And lastly, a section on optimization treatment planning efficiencies in which we explore the potential for machine learning in brachytherapy. As recent clinical evidence continues to show excellent outcomes, this is an exciting time to practice brachytherapy. With the new technologies presented here, the future is even brighter.
Clinical Outcome of Exclusively Radiographer-led Delivery of Postoperative Vaginal Vault Brachytherapy for Endometrial Cancer – The Addenbrooke's Experience
2019, Clinical Oncology
Citation Excerpt :
More recently, MRI-guided VBT has been adopted by some centres in view of the superior soft tissue contrast compared with computed tomography. One study of MRI-guided VBT reported air gaps in 48% of patients, resulting in 75% of patients in this study receiving <50% dose to the vaginal cuff [16]. The solution for air gaps identified on imaging remains uncertain.
Postoperative vaginal vault brachytherapy (VBT) reduces local recurrence in operable endometrial cancer. Radiographer-led delivery of VBT, carried out without image guidance, was implemented at Addenbrooke's in 2010 to maximise skills mix and to improve service delivery. The purpose of this study was to evaluate the safety and effectiveness of this service.
This was a single-centre retrospective study of endometrial cancer patients treated with postoperative high dose rate VBT ± external beam radiotherapy (EBRT) between January 2010 and December 2016.
In total, 414 patients were analysed: 307 received adjuvant VBT alone and 107 patients received pelvic EBRT followed by VBT. Thirty-seven per cent of patients receiving VBT alone were high risk according to ESMO-ESGO-ESTRO criteria. After a median follow-up of 59 months (range 2–118), 9/414 (2.2%) patients had isolated vaginal recurrences, 15/414 (3.6%) had locoregional recurrence (vaginal, pelvic node or both), whereas 62/414 (15%) patients had distant recurrence. The 5-year actuarial isolated vaginal recurrence rate was 2.3% (VBT alone 2.1%, EBRT + VBT 3.0%). Grade 3 urinary or bowel toxicity occurred in 2/414 (0.6%) patients treated with EBRT and VBT. None of the patients treated with VBT alone had grade 3 complications.
Radiographer-led delivery of VBT, without the use of image guidance, is a safe and effective service.

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: Conflict of interest: none.

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Clinical InvestigationMRI-Based Evaluation of the Vaginal Cuff in Brachytherapy Planning: Are We Missing the Target?

Purpose

Methods and Materials

Results

Conclusions

Introduction

Section snippets

Methods and Materials

Qualitative assessment of VC

Discussion

Conclusions

Int J Radiat Oncol Biol Phys

Gynecol Oncol

Lancet

Eur J Cancer

Gynecol Oncol

Pract Radiat Oncol

Gynecol Oncol

Int J Radiat Oncol Biol Phys

Clin Radiol

Radiother Oncol

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Clinical Investigation
MRI-Based Evaluation of the Vaginal Cuff in Brachytherapy Planning: Are We Missing the Target?