Recommendations from Gynaecological (GYN) GEC-ESTRO Working Group (IV): Basic principles and parameters for MR imaging within the frame of image based adaptive cervix cancer brachytherapy

Diffusion-weighted magnetic resonance imaging during radiotherapy of locally advanced cervical cancer--treatment response assessment using different segmentation methods

BACKGROUND

Diffusion-weighted magnetic resonance imaging (DW-MRI) and the derived apparent diffusion coefficient (ADC) value has potential for monitoring tumor response to radiotherapy (RT). Method used for segmentation of volumes with reduced diffusion will influence both volume size and observed distribution of ADC values. This study evaluates: 1) different segmentation methods; and 2) how they affect assessment of tumor ADC value during RT.

MATERIAL AND METHODS

Eleven patients with locally advanced cervical cancer underwent MRI three times during their RT: prior to start of RT (PRERT), two weeks into external beam RT (WK2RT) and one week prior to brachytherapy (PREBT). Volumes on DW-MRI were segmented using three semi-automatic segmentation methods: "cluster analysis", "relative signal intensity (SD4)" and "region growing". Segmented volumes were compared to the gross tumor volume (GTV) identified on T2-weighted MR images using the Jaccard similarity index (JSI). ADC values from segmented volumes were compared and changes of ADC values during therapy were evaluated.

RESULTS

Significant difference between the four volumes (GTV, DWIcluster, DWISD4 and DWIregion) was found (p < 0.01), and the volumes changed significantly during treatment (p < 0.01). There was a significant difference in JSI among segmentation methods at time of PRERT (p < 0.016) with region growing having the lowest JSIGTV (mean± sd: 0.35 ± 0.1), followed by the SD4 method (mean± sd: 0.50 ± 0.1) and clustering (mean± sd: 0.52 ± 0.3). There was no significant difference in mean ADC value compared at same treatment time. Mean tumor ADC value increased significantly (p < 0.01) for all methods across treatment time.

CONCLUSION

Among the three semi-automatic segmentations of hyper-intense intensities on DW-MR images implemented, cluster analysis and relative signal thresholding had the greatest similarity to the clinical tumor volume. Evaluation of mean ADC value did not depend on segmentation method.

Review of advanced catheter technologies in radiation oncology brachytherapy procedures

The development of new catheter and applicator technologies in recent years has significantly improved treatment accuracy, efficiency, and outcomes in brachytherapy. In this paper, we review these advances, focusing on the performance of catheter imaging and reconstruction techniques in brachytherapy procedures using magnetic resonance images and electromagnetic tracking. The accuracy of catheter reconstruction, imaging artifacts, and other notable properties of plastic and titanium applicators in gynecologic treatments are reviewed. The accuracy, noise performance, and limitations of electromagnetic tracking for catheter reconstruction are discussed. Several newly developed applicators for accelerated partial breast irradiation and gynecologic treatments are also reviewed. New hypofractionated high dose rate treatment schemes in prostate cancer and accelerated partial breast irradiation are presented.

Outpatient combined intracavitary and interstitial cervical brachytherapy: barriers and solutions to implementation of a successful programme - a single institutional experience

Involvement of parametrial disease in locally advanced cervical patients poses a challenge for women undergoing brachytherapy. Current use of the Fletcher suit applicator may not adequately cover the high risk clinical target volume (HR CTV), especially in the parametrial region due to the physical qualities of brachytherapy from the inverse square law and the need to respect organs at risk (OAR) constraints, and leads to lower local control rates. Combined intracavitary and interstitial brachytherapy with the use of 1 or 2 interstitial needles allows adequate coverage of the HR CTV and the clinical evidence have demonstrated a correlation with better clinical results. This procedure is often resource intensive, requiring inpatient stay and magnetic resonance imaging (MRI) planning. In departments where such resources are limited, there is a poor uptake of interstitial brachytherapy. This article discusses the technique of combined intracavitary and interstitial brachytherapy in an outpatient setting, and explores the issues and barriers for implementation and suggestions to overcome such barriers.

Three-dimensional dose accumulation in pseudo-split-field IMRT and brachytherapy for locally advanced cervical cancer

PURPOSE

Dose accumulation of split-field external beam radiotherapy (EBRT) and brachytherapy (BT) is challenging because of significant EBRT and BT dose gradients in the central pelvic region. We developed a method to determine biologically effective dose parameters for combined split-field intensity-modulated radiation therapy (IMRT) and image-guided BT in locally advanced cervical cancer.

METHODS AND MATERIALS

Thirty-three patients treated with split-field-IMRT to 45.0-51.2 Gy in 1.6-1.8 Gy per fraction to the elective pelvic lymph nodes and to 20 Gy to the central pelvis region were included in this study. Patients received six weekly fractions of high-dose rate BT to 6.5-7.3 Gy per fraction. A dose tracker software was developed to compute the equivalent dose in 2-Gy fractions (EQD2) to gross tumor volume (GTV), organs-at-risk and point A. Total dose-volume histogram parameters were computed on the 3D combined EQD2 dose based on rigid image registration. The dose accumulation uncertainty introduced by organ deformations between IMRT and BT was evaluated.

RESULTS

According to International Commission on Radiation Unit and Measurement and GEC European Society for Therapeutic Radiology and Oncology recommendations, D98, D90, D50, and D2cm3 EQD2 dose-volume histogram parameters were computed. GTV D98 was 84.0 ± 26.5 Gy and D2cc was 99.6 ± 13.9 Gy, 67.4 ± 12.2 Gy, 75.0 ± 10.1 Gy, for bladder, rectum, and sigmoid, respectively. The uncertainties induced by organ deformation were estimated to be -1 ± 4 Gy, -3 ± 5 Gy, 2 ± 3 Gy, and -3 ± 5 Gy for bladder, rectum, sigmoid, and GTV, respectively.

CONCLUSIONS

It is feasible to perform 3D EQD2 dose accumulation to assess high and intermediate dose regions for combined split-field IMRT and BT.

Estimation of the total rectal dose of radical external beam and intracavitary radiotherapy for uterine cervical cancer using the deformable image registration method

We adapted the deformable image registration (DIR) technique to accurately calculate the cumulative intracavitary brachytherapy (ICBT) and external beam radiotherapy (EBRT) rectal dose for treating uterine cervical cancer. A total of 14 patients with primary cervical cancer radically treated with ICRT and EBRT were analysed using the Velocity AI(TM) software. Computed tomography (CT) images were registered, and EBRT and ICBT dose distributions were determined. Cumulative D2cm (3), D1cm (3) and D0.1cm (3) were calculated by simple addition of fractional values or by DIR. The accuracy of DIR was evaluated by means of a virtual phantom mimicking the rectum. The dice similarity coefficient (DSC) was calculated to evaluate rectal contour concordance between CT images before and after DIR. Virtual phantom analysis revealed that the average difference between the DIR-based phantom Dmean and the simple phantom Dmean was 1.9 ± 2.5 Gy (EQD2), and the DIR method included an uncertainty of ∼8.0%. The mean DSC between reference CT and CT was significantly improved after DIR (EBRT: 0.43 vs 0.85, P < 0.005; ICBT: 0.60 vs 0.87, P < 0.005). The average simple rectal D2cm (3), D1cm (3) and D0.1cm (3) values were 77.6, 81.6 and 91.1 Gy (EQD2), respectively; the DIR-based values were 76.2, 79.5 and 87.6 Gy, respectively. The simple addition values were overestimated, on average, by 3.1, 3.7 and 5.5 Gy, respectively, relative to the DIR-based values. In conclusion, the difference between the simple rectal dose-volume histogram (DVH) parameter addition and DIR-based cumulative rectal doses increased with decreasing DVH parameters.

Review of potential improvements using MRI in the radiotherapy workflow

The goal of modern radiotherapy is to deliver a lethal amount of dose to tissue volumes that contain a significant amount of tumour cells while sparing surrounding unaffected or healthy tissue. Online image guided radiotherapy with stereotactic ultrasound, fiducial-based planar X-ray imaging or helical/conebeam CT has dramatically improved the precision of radiotherapy, with moving targets still posing some methodical problems regarding positioning. Therefore, requirements for precise target delineation and identification of functional body structures to be spared by high doses become more evident. The identification of areas of relatively radioresistant cells or areas of high tumor cell density is currently under development. This review outlines the state of the art of MRI integration into treatment planning and its importance in follow up and the quantification of biological effects. Finally the current state of the art of online imaging for patient positioning will be outlined and indications will be given what the potential of integrated radiotherapy/online MRI systems is.

Local experience in cervical cancer imaging: Comparison in tumour assessment between TRUS and MRI

OBJECTIVE

The aim of study was to analyze the accuracy of TRUS (transrectal ultrasound) vs. MRI (magnetic resonance imaging) and clinical gynecological examination estimation in the evaluation of tumor dimensions.

METHODS

The patients inclusion criterion included primarily pathologically squamous cell carcinoma, but excluded were patients who had not undergone BT (brachytherapy) and treated with palliative intent. We offer two types of treatment for locally advanced cervical cancer: (a) radiochemotherapy followed by surgery and (b) exclusive radiochemotherapy. Imaging tests follow the presence of tumor and tumor size (width and thickness). Each examination was performed by a different physician who had no knowledge of the others' findings. All patients underwent MRI prior to EBRT (external beam radiation therapy) while 18 of them also at the time of the first brachytherapy application. For the analysis we used the r-Pearson correlation coefficient.

RESULTS

In 2013, 26 patients with cervical cancer were included. A total of 44 gynecological examinations were performed, 44 MRIs and 18 TRUSs. For the comparisons prior to EBRT the correlation coefficient between TRUS vs. MRI was r = 0.79 for AP and r = 0.83 for LL, for GYN vs. MRI was r = 0.6 for AP and r = 0.75 for LL. Prior to BT for GYN vs. MRI, r values were 0.60 and 0.63 for AP and LL, respectively; for GYN vs. TRUS, r values were 0.56 and 0.78 for AP and LL, respectively.

CONCLUSIONS

A high correlation between the three examinations was obtained. As such, TRUS can be considered a suitable method in the evaluation of tumor dimensions.

Magnetic resonance image guided brachytherapy

The application of magnetic resonance image (MRI)-guided brachytherapy has demonstrated significant growth during the past 2 decades. Clinical improvements in cervix cancer outcomes have been linked to the application of repeated MRI for identification of residual tumor volumes during radiotherapy. This has changed clinical practice in the direction of individualized dose administration, and resulted in mounting evidence of improved clinical outcome regarding local control, overall survival as well as morbidity. MRI-guided prostate high-dose-rate and low-dose-rate brachytherapies have improved the accuracy of target and organs-at-risk delineation, and the potential exists for improved dose prescription and reporting for the prostate gland and organs at risk. Furthermore, MRI-guided prostate brachytherapy has significant potential to identify prostate subvolumes and dominant lesions to allow for dose administration reflecting the differential risk of recurrence. MRI-guided brachytherapy involves advanced imaging, target concepts, and dose planning. The key issue for safe dissemination and implementation of high-quality MRI-guided brachytherapy is establishment of qualified multidisciplinary teams and strategies for training and education.

Optimizing packing contrast for MRI-based intracavitary brachytherapy planning for cervical cancer

PURPOSE

We prospectively tested five variations in vaginal gauze packing in an effort to improve contrast between the packing, cervix, and applicator for MRI-based intracavitary brachytherapy planning.

METHODS AND MATERIALS

Five patients enrolled on a prospective study from May 2013 to October 2013 received MRI-based intracavitary brachytherapy for cervical cancer with variations of impregnated gauze packing. Substances tested included antibiotic cream alone, antibiotic cream mixed with ultrasound gel, conjugated estrogens cream mixed with ultrasound gel, ultrasound gel alone, and gadolinium. Images from the T2-weighted pelvic MRI were used to obtain signal intensity measurements at points within the packing, cervix, and applicator. Signal intensity values were normalized using the signal-to-noise ratio and compared using an unpaired t-test.

RESULTS

Ultrasound gel-impregnated gauze allowed for the greatest contrast between the packing and the cervix with a difference in mean normalized signal intensity of 38.2 (p < 0.01). Conjugated estrogens cream mixed with ultrasound gel and gadolinium also provided contrast when compared with cervix, with differences in mean normalized signal intensity of 25.3 and -16.2, respectively (p < 0.01 for both). For all variations but gadolinium, the normalized mean signal intensity of the packing was found to be significantly different from the applicator, with the ultrasound gel again demonstrating the greatest contrast with a difference of 42.5 (p < 0.01).

CONCLUSIONS

Gauze impregnated with ultrasound gel, conjugated estrogens cream mixed with ultrasound gel, and gadolinium allowed for a significant difference in MRI signal intensity between the packing and the cervix. With respect to both the cervix and the applicator, ultrasoundgel-impregnated gauze provided the best contrast overall.

Assessing cumulative dose distributions in combined radiotherapy for cervical cancer using deformable image registration with pre-imaging preparations

Background

The purpose of the study was to evaluate the feasibility of deformable image registration (DIR) in assessing cumulative dose distributions of the combination of external beam radiotherapy (EBRT) and fractionated intracavitary brachytherapy (ICBT) for cervical cancer.

Materials and methods

Three-dimensional image data sets of five consecutive patients were used. The treatment plan consisted of whole pelvic EBRT (total dose: 45 Gy in 25 fractions) combined with computed tomography (CT)-based high-dose rate ICBT (≥24 Gy in 4 fractions to the high risk clinical target volume (HR-CTV)). Organs at risk and HR-CTV were contoured on each CT images and dose-volume parameters were acquired. Pre-imaging preparations were performed prior to each ICBT to minimize the uncertainty of the organ position. Physical doses of each treatment were converted to biologically equivalent doses in 2 Gy daily fractions by the linear quadratic model. Three-dimensional dose distributions of each treatment were accumulated on CT images of the first ICBT using DIR with commercially available image registration software (MIM Maestro®). To compare with DIR, 3D dose distributions were fused by rigid registration based on bony structure matching. To evaluate the accuracy of DIR, the Dice similarity coefficient (DSC) was measured between deformed contours and initial contours.

Results

The cumulative dose distributions were successfully illustrated on the CT images using DIR. Mean DSCs of the HR-CTV, rectum, and bladder were 0.46, 0.62 and 0.69, respectively, with rigid registration; and 0.78, 0.76, and 0.87, respectively, with DIR (p <0.05). The mean DSCs derived from our DIR procedure were comparable to those of previous reports describing the quality of DIR algorithms in the pelvic region. DVH parameters derived from the 2 methods showed no significant difference.

Conclusions

Our results suggest that DIR-based dose accumulation may be acceptable for assessing cumulative dose distributions to assess doses to the tumor and organs at risk in combined radiotherapy for cervical cancer under pre-imaging preparations.

Extended field chemoradiation for cervical cancer patients with histologically proven para-aortic lymph node metastases after laparaoscopic lymphadenectomy

BACKGROUND AND PURPOSE

The purpose of this work was to evaluate the use of extended-field chemoradiation (EFRT) with concomitant chemotherapy in patients with histologically confirmed para-aortic metastases after laparoscopic para-aortic and pelvic lymphadenectomy (LAE) with regard to oncologic results and treatment-related toxicity.

PATIENTS AND METHODS

A total of 44 women with squamous cell carcinoma (82 %) and adenocarcinoma (18 %) of the cervix in FIGO stages IIA (n = 3), IIB (n = 29); IIIB (n = 9), and IVA (n = 3) and histologically proven para-aortic metastases underwent EFRT and chemotherapy. Laparoscopic LAE was performed in 40 patients. Patients underwent chemoradiation with conventional fractionation of 1.8-50.4 Gy to the para-aortic and pelvic region. In addition, MRI-guided brachytherapy was performed to the cervix with 5-6 single doses of 5 Gy for a total dose of 25-30 Gy.

RESULTS

The mean number of harvested lymph nodes was 17 in the pelvic as well as para-aortic regions, respectively. Laparoscopic intervention did not delay chemoradiation. Follow-up was 6-76 months (mean 25.1 months). There was no grade 4 or 5 acute radiation toxicity. In all, 8, 4, and 11 % grade 1, 2, and 3 gastrointestinal late toxicities and 7, 11, and 19 % grade 1, 2 and 3 genitourinary late toxicities were recorded. Despite the excellent locoregional (pelvic) control rates of 89.1 and 82.8 % after 2 and 5 years, respectively, the overall survival rates were 68.4 and 54.1 % after 2 and 5 years, respectively. Of the 44 patients, 43 remained tumor free in the para-aortic region.

CONCLUSION

In patients with proven para-aortic disease, excellent pelvic and para-aortic control could be achieved by laparoscopic LAE followed by EFRT. More than half of the patients were long-term survivors. The high risk of distant metastases should be addressed by further improving systemic treatment.

Parametrial boosting in locally advanced cervical cancer: combined intracavitary/interstitial brachytherapy vs. intracavitary brachytherapy plus external beam radiotherapy

PURPOSE

Parametrial boost (PB) with external beam radiotherapy (EBRT) aims to increase the dose in the parametrial regions where the contribution from intracavitary brachytherapy (IC BT) is insufficient. An alternative technique for parametrial boosting is combined intracavitary and interstitial (IC-IS) BT. We compared doses delivered by IC BT plus EBRT PB with doses delivered by IC-IS BT.

METHODS AND MATERIALS

We reviewed 51 consecutive patients with locally advanced cervical cancer with parametrial involvement at diagnosis. At BT, 23 patients had persistent parametrial involvement and were treated with IC-IS BT. For the 23 patients, we simulated a treatment of IC BT combined with EBRT PB and compared it with the delivered IC-IS BT. Equivalent total doses in 2-Gy fractions of the target and organs at risk were evaluated, and the normal tissue volume irradiated to at least 60 Gy (V60).

RESULTS

The mean high-risk clinical target volume D90 was comparable (p = 0.8) for both techniques. However, with the EBRT PB scenario, 3 patients received high-risk clinical target volume D90 of <79 Gy, whereas IC-IS BT resulted in D90 of >84 Gy for all patients. Organs at risk D(2cm(3)) were significantly higher by a mean of 4-6 Gy (p < 0.001) with EBRT PB. The PB scenario resulted in a significantly higher V60 of 594 ± 596 cm(3) as compared with 228 ± 82 cm(3) with IC-IS BT (p = 0.004).

CONCLUSIONS

Combined IC-IS BT is superior than IC BT + EBRT PB both in terms of organ sparing and target coverage. The IC-IS BT was more conformal with less normal tissue exposure to intermediate doses (V60).

Brachytherapy in cancer cervix: Time to move ahead from point A?

Brachytherapy forms an integral part of the radiation therapy in cancer cervix. The dose prescription for intracavitary brachytherapy (ICBT) in cancer cervix is based on Tod and Meredith's point A and has been in practice since 1938. This was proposed at a time when accessibility to imaging technology and dose computation facilities was limited. The concept has been in practice worldwide for more than half a century and has been the fulcrum of all ICBT treatments, strategies and outcome measures. The method is simple and can be adapted by all centres practicing ICBT in cancer cervix. However, with the widespread availability of imaging techniques, clinical use of different dose-rates, availability of a host of applicators fabricated with image compatible materials, radiobiological implications of dose equivalence and its impact on tumour and organs at risk; more and more weight is being laid down on individualised image based brachytherapy. Thus, computed tomography, magnetic-resonance imaging and even positron emission computerized tomography along with brachytherapy treatment planning system are being increasingly adopted with promising outcomes. The present article reviews the evolution of dose prescription concepts in ICBT in cancer cervix and brings forward the need for image based brachytherapy to evaluate clinical outcomes. As is evident, a gradual transition from "point" based brachytherapy to "profile" based image guided brachytherapy is gaining widespread acceptance for dose prescription, reporting and outcome evaluation in the clinical practice of ICBT in cancer cervix.

[Pulsed-dose rate brachytherapy in cervical cancers: why, how?]

The end of the production of 192 iridium wires terminates low dose rate brachytherapy and requires to move towards pulsed-dose rate or high-dose rate brachytherapy. In the case of gynecological cancers, technical alternatives exist, and many teams have already taken the step of pulsed-dose rate for scientific reasons. Using a projector source is indeed a prerequisite for 3D brachytherapy, which gradually installs as a standard treatment in the treatment of cervical cancers. For other centers, this change implies beyond investments in equipment and training, organizational consequences to ensure quality.

Tracer kinetic model selection for dynamic contrast-enhanced magnetic resonance imaging of locally advanced cervical cancer

BACKGROUND

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) offers a unique capability to probe tumour microvasculature. Different analysis of the acquired data will possibly lead to different conclusions. Therefore, the objective of this study was to investigate under which conditions the Tofts (TM), extended Tofts (ETM), compartmental tissue uptake model (C-TU) and 2-compartment exchange model (2CXM) were the optimal tracer kinetic models (TKMs) for the analysis of DCE-MRI in patients with cervical cancer.

MATERIAL AND METHODS

Ten patients with locally advanced cervical cancer (FIGO: IIA/IIB/IIIB/IVA - 1/5/3/1) underwent DCE-MRI prior to radiotherapy. From the two-parameter TM it was possible to extract the forward volume transfer constant (K(trans)) and the extracellular-extravascular volume fraction (ve). From the three-parameter ETM, additionally the plasma volume fraction (vp) could be extracted. From the three-parameter C-TU it was possible to extract information about the blood flow (Fp), permeability-surface area product (PS) and vp. Finally, the four-parameter 2CXM extended the C-TU to include ve. For each voxel, corrected Akaike information criterion (AICc) values were calculated, taking into account both the goodness-of-fit and the number of model parameters. The optimal model was defined as the model with the lowest AICc.

RESULTS

All four TKMs were the optimal model in different contiguous regions of the cervical tumours. For the 24 999 analysed voxels, the TM was optimal in 17.0%, the ETM was optimal in 2.2%, the C-TU in 23.4% and the 2CXM was optimal in 57.3%. Throughout the tumour, a high correlation was found between K(trans)(TM) and Fp(2CXM), ρ = 0.91.

CONCLUSION

The 2CXM was most often optimal in describing the contrast agent enhancement of pre-treatment cervical cancers, although this model broke down in a subset of the tumour voxels where overfitting resulted in non-physiological parameter estimates. Due to the possible overfitting of the 2CXM, the C-TU was found more robust and when 2CXM was excluded from comparison the C-TU was the preferred model.

MRI-assisted cervix cancer brachytherapy pre-planning, based on application in paracervical anaesthesia: final report

Background

Optimal applicator insertion is a precondition for the success of cervix cancer brachytherapy (BT). We aimed to assess feasibility and efficacy of MRI-assisted pre-planning, based on applicator insertion in para-cervical anaesthesia (PCA).

Patients and methods.

Five days prior to BT, the pre-planning procedure was performed in 18 cervix cancer patients: tandem-ring applicator was inserted under PCA, pelvic MRI obtained and applicator removed. Procedure tolerability was assessed. High risk clinical target volume (HR CTV) and organs at risk were delineated on the pre-planning MRI, virtual needles placed at optimal positions, and dose planning performed. At BT, insertion was carried out in subarachnoidal anaesthesia according to pre-planned geometry. Pre-planned and actual treatment parameters were compared.

Results

Pre-planning procedure was well tolerated. Median difference between the pre-planned and actual needle insertion depth and position were 2 (0–10) mm and 4 (0–30) degrees, respectively. The differences between the pre-planned and actual geometric and dosimetric parameters were statistically non-significant. All actual needles were positioned inside the HR CTV and outside the organs at risk (OAR).

Conclusions

Our pre-planning approach is well tolerated and effective. Pre-planned geometry and dose distribution can be reproduced at BT.

In vivo dosimetry: trends and prospects for brachytherapy

The error types during brachytherapy (BT) treatments and their occurrence rates are not well known. The limited knowledge is partly attributed to the lack of independent verification systems of the treatment progression in the clinical workflow routine. Within the field of in vivo dosimetry (IVD), it is established that real-time IVD can provide efficient error detection and treatment verification. However, it is also recognized that widespread implementations are hampered by the lack of available high-accuracy IVD systems that are straightforward for the clinical staff to use. This article highlights the capabilities of the state-of-the-art IVD technology in the context of error detection and quality assurance (QA) and discusses related prospects of the latest developments within the field. The article emphasizes the main challenges responsible for the limited practice of IVD and provides descriptions on how they can be overcome. Finally, the article suggests a framework for collaborations between BT clinics that implemented IVD on a routine basis and postulates that such collaborations could improve BT QA measures and the knowledge about BT error types and their occurrence rates.

Inter-application displacement of brachytherapy dose received by the bladder and rectum of the patients with inoperable cervical cancer

BACKGROUND

The aim of the study was to examine on the CT basis the inter-application displacement of the positions D0.1cc, D1cc and D2cc of the brachytherapy dose applied to the bladder and rectum of the patients with inoperable cervical cancer.

PATIENTS AND METHODS

This prospective study included 30 patients with cervical cancer who were treated by concomitant chemo-radiotherapy. HDR intracavitary brachytherapy was made by the applicators type Fletcher tandem and ovoids. For each brachytherapy application the position D0.1cc was determined of the bladder and rectum that receive a brachytherapty dose. Then, based on the X, Y, and Z axis displacement, inter-application mean X, Y, and Z axis displacements were calculated as well as their displacement vectors (R). It has been analyzed whether there is statistically significant difference in inter-application displacement of the position of the brachytherapy dose D0.1cc, D1cc and D2cc of the bladder and rectum. The ANOVA test and post-hoc analysis by Tukey method were used for testing statistical importance of differences among the groups analyzed. The difference among the groups analyzed was considered significant if p < 0.05.

RESULTS

There are significant inter-application displacements of the position of the brachytherapy dose D0,1cc, D1cc and D2cc of the bladder and rectum.

CONCLUSIONS

When we calculate the cumulative brachytherapy dose by summing up D0,1cc, D1cc and D2cc of the organs at risk for all the applications, we must bear in mind their inter-application displacement, and the fact that it is less likely that the worst scenario would indeed happen.

Ultrasound guided conformal brachytherapy of cervix cancer: survival, patterns of failure, and late complications

Objective

The aim of this study was to report on the long-term results of transabdominal ultrasound guided conformal brachytherapy in patients with cervical cancer with respect to patterns of failures, treatment related toxicities and survival.

Methods

Three hundred and nine patients with cervical cancer who presented to Institute between January 1999 and December 2008 were staged with magnetic resonance imaging and positron emission tomography and treated with external beam radiotherapy and high dose rate conformal image guided brachytherapy with curative intent. Follow-up data relating to sites of failure and toxicity was recorded prospectively.

Results

Two hundred and ninety-two patients were available for analyses. The median (interquantile range) follow-up time was 4.1 years (range, 2.4 to 6.1 years). Five-year failure free survival and overall survival (OS) were 66% and 65%, respectively. Primary, pelvic, para-aortic, and distant failure were observed in 12.5%, 16.4%, 22%, and 23% of patients, respectively. In multivariate analysis, tumor volume and nodal disease related to survival, whereas local disease control and point A dose did not.

Conclusion

Ultrasound guided conformal brachytherapy of cervix cancer has led to optimal local control and OS. The Melbourne protocol compares favorably to the more technically elaborate and expensive GEC-ESTRO recommendations. The Melbourne protocol's technical simplicity with real-time imaging and treatment planning makes this a method of choice for treating patients with cervical cancer.

MRI findings at image guided adaptive cervix cancer brachytherapy: radiation oncologist's perspective

Magnetic resonance imaging (MRI) represents the reference imaging modality for image guided adaptive brachytherapy (IGABT) of cervix cancer. Accurate interpretation of pre-treatment MRI is required for proper understanding of the tumor extent and topography at IGABT. Planning and optimal timing of the application begins already before treatment, and may need to be adapted during external beam irradiation (EBRT) according to additional clinical and/or radiological findings. The level of MRI utilization in IGABT depends on the infrastructural capabilities of individual centers, ranging from no use at all to repetitive imaging during EBRT and each IGABT fraction. In this article, we summarize the role of different imaging modalities and practical aspects of MRI interpretation in cervix cancer IGABT, concentrating on the systematic evaluation of post-insertion images. MRI with the applicator in place from the radiation oncologist’s perspective should begin with immediate identification of eventual complications of the application procedure and assessment of the implant adequacy, followed by appropriate corrective measures in case of adverse findings. Finally, the tumor extent, topography, and treatment response should be evaluated in the context of initial clinical and radiological findings to allow for an appropriate selection and delineation of the target volumes.

Brachytherapy in the treatment of cervical cancer: a review

Dramatic advances have been made in brachytherapy for cervical cancer. Radiation treatment planning has evolved from two-dimensional to three-dimensional, incorporating magnetic resonance imaging and/or computed tomography into the treatment paradigm. This allows for better delineation and coverage of the tumor, as well as improved avoidance of surrounding organs. Consequently, advanced brachytherapy can achieve very high rates of local control with a reduction in morbidity, compared with historic approaches. This review provides an overview of state-of-the-art gynecologic brachytherapy, with a focus on recent advances and their implications for women with cervical cancer.

Direction-modulated brachytherapy for high-dose-rate treatment of cervical cancer. I: theoretical design

PURPOSE

To demonstrate that utilization of the direction-modulated brachytherapy (DMBT) concept can significantly improve treatment plan quality in the setting of high-dose-rate (HDR) brachytherapy for cervical cancer.

METHODS AND MATERIALS

The new, MRI-compatible, tandem design has 6 peripheral holes of 1.3-mm diameter, grooved along a nonmagnetic tungsten-alloy rod (ρ = 18.0 g/cm(3)), enclosed in Delrin tubing (polyoxymethylene, ρ = 1.41 g/cm(3)), with a total thickness of 6.4 mm. The Monte Carlo N-Particle code was used to calculate the anisotropic (192)Ir dose distributions. An in-house-developed inverse planning platform, geared with simulated annealing and constrained-gradient optimization algorithms, was used to replan 15 patient cases (total 75 plans) treated with a conventional tandem and ovoids (T&O) applicator. Prescription dose was 6 Gy. For replanning, we replaced the conventional tandem with that of the new DMBT tandem for optimization but left the ovoids in place and kept the dwell positions as originally planned. All DMBT plans were normalized to match the high-risk clinical target volume V100 coverage of the T&O plans.

RESULTS

In general there were marked improvements in plan quality for the DMBT plans. On average, D2cc for the bladder, rectum, and sigmoid were reduced by 0.59 ± 0.87 Gy (8.5% ± 28.7%), 0.48 ± 0.55 Gy (21.1% ± 27.2%), and 0.10 ± 0.38 Gy (40.6% ± 214.9%) among the 75 plans, with best single-plan reductions of 3.20 Gy (40.8%), 2.38 Gy (40.07%), and 1.26 Gy (27.5%), respectively. The high-risk clinical target volume D90 was similar, with 6.55 ± 0.96 Gy and 6.59 ± 1.06 Gy for T&O and DMBT, respectively.

CONCLUSIONS

Application of the DMBT concept to cervical cancer allowed for improved organ at risk sparing while achieving similar target coverage on a sizeable patient population, as intended, by maximally utilizing the anatomic information contained in 3-dimensional imaging. A series of mechanical and clinical validations are to be followed.

Optimal single 3T MR imaging sequence for HDR brachytherapy of cervical cancer

Purpose

The superior image quality of 3 tesla (3T) magnetic resonance (MR) imaging in cervical cancer offers the potential to use a single image set for brachytherapy. This study aimed to determine a suitable single sequence for contouring tumour and organs at risk, applicator reconstruction, and treatment planning.

Material and methods

A 3T (Skyra, Siemens Healthcare AG, Germany) MR imaging system with an 18 channel body matrix coil generated HDR cervical cancer brachytherapy planning images on 20 cases using plastic-based treatment applicators. Seven different T2-weighted Turbo Spin Echo (TSE) sequences including both 3D and contiguous 2D scans based on sagittal, axial (transverse), and oblique planes were analysed. Each image set was assessed for total scanning time and usefulness in tumour localization via inter- and intra-observer analysis of high-risk clinical target volume (HR CTV) contouring. Applicator reconstruction in the treatment planning system was also considered.

Results

The intra-observer difference in HR CTV volumes between 2D and 3D axial-based image sets was low with an average difference of 3.1% for each observer. 2D and 3D sagittal image sets had the highest intra- and inter observer differences (over 15%). A 2D axial ‘double oblique’ sequence was found to produce the best intra- (average difference of 0.6%) and inter-observer (mean SD of 9.2%) consistency and greatest conformity (average 0.80).

Conclusions

There was little difference between 2D and 3D-based scanning sequences; however the increased scanning time of 3D sequences have potential to introduce greater patient motion artifacts. A contiguous 2D sequence based on an axial T2-weighted turbo-spin-echo (TSE) sequence orientated in all planes of the treatment applicator provided consistent tumour delineation whilst allowing applicator reconstruction and treatment planning.

Comparative analysis of rectal dose parameters in image-guided high-dose-rate brachytherapy for cervical cancer with and without a rectal retractor

PURPOSE

The objective of this study was to determine if use of a rectal retractor (RR) in high-dose-rate intracavitary brachytherapy for cervical cancer reduces rectal dose parameters.

METHODS AND MATERIALS

We reviewed data obtained from patients treated with intracavitary brachytherapy for cervical cancer with and without an RR. Treatment plans for each brachytherapy fraction were separated into two groups; R group with use of an RR and P group with use of vaginal packing. Dose-volume parameters for high-risk clinical target volume (HR-CTV), rectum, sigmoid, small bowel, and vaginal surface were collected for each fraction. Rectal D2cc and International Commission on Radiation Units & Measurements (ICRU) rectal point doses were compared between groups using Student's t tests. Predictors of higher rectal D2cc were determined by univariate and multivariate regression analyses.

RESULTS

Four hundred sixty-three brachytherapy fractions from 114 patients were used for analysis, 377 fractions with a RR (R group) and 86 with vaginal packing only (P group). Both groups were similar except for slightly higher mean HR-CTV and mean bladder volume in P group. Both mean ICRU rectal point dose (241.1 vs. 269.9 cGy, p = 0.006) and rectal D2cc (240.6 vs. 283.6 cGy, p < 0.001) were significantly higher in P group. Point A dose, HR-CTV, stage, and use of an RR were significant predictors of rectal D2cc on multivariate analysis.

CONCLUSIONS

Our data show that use of an RR leads to lower rectal dose parameters compared with vaginal packing. Further study is needed to determine if this will lead to less long-term toxicity.

Comparison of measurements of the uterus and cervix obtained by magnetic resonance and transabdominal ultrasound imaging to identify the brachytherapy target in patients with cervix cancer

PURPOSE

To compare measurements of the uterus and cervix obtained with magnetic resonance imaging (MRI) and transabdominal ultrasound to determine whether ultrasound can identify the brachytherapy target and be used to guide conformal brachytherapy planning and treatment for cervix cancer.

METHODS AND MATERIALS

Consecutive patients undergoing curative treatment with radiation therapy between January 2007 and March 2012 were included in the study. Intrauterine applicators were inserted into the uterine canal while patients were anesthetized. Images were obtained by MRI and transabdominal ultrasound in the longitudinal axis of the uterus with the applicator in treatment position. Measurements were taken at the anterior and posterior surface of the uterus at 2.0-cm intervals along the applicator, from the external os to the tip of the applicator. Data were analyzed using Bland Altman plots examining bias and 95% limits of agreement.

RESULTS

A total of 192 patients contributed 1668 measurements of the cervix and uterus. Mean (± SD) differences of measurements between imaging modalities at the anterior and posterior uterine surface ranged from 1.5 (± 3.353) mm to 3.7 (± 3.856) mm, and -1.46 (± 3.308) mm to 0.47 (± 3.502) mm, respectively. The mean differences were less than 3 mm in the cervix. The mean differences were less than 1.5 mm at all measurement points on the posterior surface.

CONCLUSION

Differences in the measurements of the cervix and uterus obtained by MRI and ultrasound were within clinically acceptable limits. Transabdominal ultrasound can be substituted for MRI in defining the target volume for conformal brachytherapy treatment of cervix cancer.

Primary peritoneal clear cell carcinoma treated with IMRT and interstitial HDR brachytherapy: a case report

Primary peritoneal clear cell carcinoma (PP‐CCC), which is a rare tumor with poor prognosis, is typically managed with surgery and/or chemotherapy. We present a unique treatment approach for a patient with a pelvic PP‐CCC, consisting of postchemotherapy intensity‐modulated radiation therapy (IMRT) followed by interstitial high‐dose–rate (HDR) brachytherapy. A 54‐year‐old female with an inoperable pelvic‐supravaginal 5.6 cm T3N0M0 PP‐CCC tumor underwent treatment with 6 cycles of carboplatin and taxol chemotherapy. Postchemotherapy PET/CT scan revealed a residual 3.3 cm tumor. The patient underwent CT and MR planning simulation, and was treated with 50 Gy to the primary tumor and 45 Gy to the pelvis including the pelvic lymph nodes, using IMRT to spare bowel. Subsequently, the patient was treated with an interstitial HDR brachytherapy implant, planned using both CT and MR scans. A total dose of 15 Gy in 5 Gy fractions over two days was delivered with Ir‐192 HDR brachytherapy. The total prescribed equivalent 2 Gy dose (EQD2) to the HDR planning target volume (PTV) from both the EBRT and HDR treatments ranged between 63 and 68.8Gy2 due to differential dosing of the primary and pelvic targets. The patient tolerated radiotherapy well, except for mild diarrhea not requiring medication. There was no patient‐reported acute toxicity one month following the radiotherapy course. At four months following adjuvant radiation therapy, the patient had near complete resolution of local tumor on PET/CT without any radiation‐associated toxicity. However, the patient was noted to have metastatic disease outside of the radiation field, specifically lesions in the liver and bone. This case report illustrates the feasibility of the treatment of a pelvic PP‐CCC with IMRT followed by interstitial HDR brachytherapy boost, which resulted in near complete local tumor response without significant morbidity.

PACS number: 87.55.‐x

High-risk clinical target volume delineation in CT-guided cervical cancer brachytherapy: impact of information from FIGO stage with or without systematic inclusion of 3D documentation of clinical gynecological examination

PURPOSE

The aim of the study was to improve computed tomography (CT)-based high-risk clinical target volume (HR CTV) delineation protocols for cervix cancer patients, in settings without any access to magnetic resonance imaging (MRI) at the time of brachytherapy. Therefore the value of a systematic integration of comprehensive three-dimensional (3D) documentation of repetitive gynecological examination for CT-based HR CTV delineation protocols, in addition to information from FIGO staging, was investigated. In addition to a comparison between reference MRI contours and two different CT-based contouring methods (using complementary information from FIGO staging with or without additional 3D clinical drawings), the use of standardized uterine heights was also investigated.

MATERIAL AND METHODS

Thirty-five cervix cancer patients with CT- and MR-images and 3D clinical drawings at time of diagnosis and brachytherapy were included. HR CTV(stage) was based on CT information and FIGO stage. HR CTV(stage + 3Dclin) was contoured on CT using FIGO stage and 3D clinical drawing. Standardized HR CTV heights were: 1/1, 2/3 and 1/2 of uterine height. MRI-based HR CTV was delineated independently. Resulting widths, thicknesses, heights, and volumes of HR CTV(stage), HR CTV(stage + 3Dclin) and MRI-based HR CTV contours were compared.

RESULTS

The overall normalized volume ratios (mean ± SD of CT/MRI(ref) volume) of HR CTV(stage) and HR stage + 3Dclin were 2.6 (± 0.6) and 2.1 (± 0.4) for 1/1 and 2.3 (± 0.5) and 1.8 (± 0.4), for 2/3, and 1.9 (± 0.5) and 1.5 (± 0.3), for 1/2 of uterine height. The mean normalized widths were 1.5 ± 0.2 and 1.2 ± 0.2 for HR CTV(stage) and HR CTV(stage + 3Dclin), respectively (p < 0.05). The mean normalized heights for HR CTV(stage) and HR CTV(stage + 3Dclin) were both 1.7 ± 0.4 for 1/1 (p < 0.05.), 1.3 ± 0.3 for 2/3 (p < 0.05) and 1.1 ± 0.3 for 1/2 of uterine height.

CONCLUSION

CT-based HR CTV contouring based on FIGO stage alone leads to large overestimation of width and volume. Target delineation accuracy can systematically improve through incorporation of additional information from comprehensive 3D documentation of repetitive gynecological examination in the contouring protocol, and thus help to improve the accuracy of dose optimization in settings with limited access to imaging facilities at the time of brachytherapy. If CT information is only available, minimum 2/3 of uterine height may be a good surrogate for the height of HR CTV.

Voxelwise comparison of perfusion parameters estimated using dynamic contrast enhanced (DCE) computed tomography and DCE-magnetic resonance imaging in locally advanced cervical cancer

PURPOSE

Dynamic contrast enhanced (DCE) imaging has gained interest as an imaging modality for assessment of tumor characteristics and response to cancer treatment. However, for DCE-magnetic resonance imaging (MRI) tissue contrast enhancement may vary depending on imaging sequence and temporal resolution. The aim of this study is to compare DCE-MRI to DCE-computed tomography (DCE-CT) as the gold standard.

MATERIAL AND METHODS

Thirteen patients with advanced cervical cancer were scanned once prior to chemo-radiation and during chemo-radiation with DCE-CT and -MRI in immediate succession. A total of 22 paired DCE-CT and -MRI scans were acquired for comparison. Kinetic modeling using the extended Tofts model was applied to both image series. Furthermore the similarity of the spatial distribution was evaluated using a Γ analysis. The correlation between the two imaging techniques was evaluated using Pearson's correlation and the parameter means were compared using a Student's t-test (p < 0.05).

RESULTS

A significant positive correlation between DCE-CT and -MRI was found for all kinetic parameters. The results showing the best correlation with the DCE-CT-derived parameters were obtained using a population-based input function for MRI. The median Pearson's correlations were: volume transfer constant K(trans) (r = 0.9), flux rate constant kep (r = 0.77), extracellular volume fraction ve (r = 0.58) and blood plasma volume fraction vp (r = 0.83). All quantitative parameters were found to be significantly different as estimated by DCE-CT and -MRI. The Γ analysis in normalized maps revealed that 45% of the voxels failed to find a voxel with the corresponding value allowing for an uncertainty of 3 mm in position and 3% in value (Γ3,3). By reducing the criteria, the Γ-failure rates were: Γ3,5 (37% failure), Γ3,10 (26% failure) and at Γ3,15 (19% failure).

CONCLUSION

Good to excellent correlations but significant bias was found between DCE-CT and -MRI. Both the Pearson's correlation and the Γ analysis proved that the spatial information was similar when analyzing the two sets of DCE data using the extended Tofts model. Improvement of input function sampling is needed to improve kinetic quantification using DCE-MRI.

Magnetic resonance imaging for assessment of parametrial tumour spread and regression patterns in adaptive cervix cancer radiotherapy

PURPOSE

To investigate the impact of magnetic resonance imaging (MRI)-morphologic differences in parametrial infiltration on tumour response during primary radiochemotherapy in cervical cancer.

MATERIAL AND METHODS

Eighty-five consecutive cervical cancer patients with FIGO stages IIB (n = 59) and IIIB (n = 26), treated by external beam radiotherapy (± chemotherapy) and image-guided adaptive brachytherapy, underwent T2-weighted MRI at the time of diagnosis and at the time of brachytherapy. MRI patterns of parametrial tumour infiltration at the time of diagnosis were assessed with regard to predominant morphology and maximum extent of parametrial tumour infiltration and were stratified into five tumour groups (TG): 1) expansive with spiculae; 2) expansive with spiculae and infiltrating parts; 3) infiltrative into the inner third of the parametrial space (PM); 4) infiltrative into the middle third of the PM; and 5) infiltrative into the outer third of the PM. MRI at the time of brachytherapy was used for identifying presence (residual vs. no residual disease) and signal intensity (high vs. intermediate) of residual disease within the PM. Left and right PM of each patient were evaluated separately at both time points. The impact of the TG on tumour remission status within the PM was analysed using χ(2)-test and logistic regression analysis.

RESULTS

In total, 170 PM were analysed. The TG 1, 2, 3, 4, 5 were present in 12%, 11%, 35%, 25% and 12% of the cases, respectively. Five percent of the PM were tumour-free. Residual tumour in the PM was identified in 19%, 68%, 88%, 90% and 85% of the PM for the TG 1, 2, 3, 4, and 5, respectively. The TG 3-5 had significantly higher rates of residual tumour in the PM in comparison to TG 1 + 2 (88% vs. 43%, p < 0.01).

CONCLUSION

MRI-morphologic features of PM infiltration appear to allow for prediction of tumour response during external beam radiotherapy and chemotherapy. A predominantly infiltrative tumour spread at the time of diagnosis resulted in a significantly higher rate of residual tumour in the PM at the time of brachytherapy in comparison to a predominantly expansive tumour spread.

The implementation of a PDR 3D-guided gynaecological brachytherapy service in a UK centre

Background

Due to the discontinuation of the widely used low-dose rate (LDR) Caesium afterloader units, many centres in the past 10 years have moved from LDR Selectron treatments to Iridium 192 afterloaders. While the majority of UK centres have opted for high-dose rate (HDR) units, the Christie have invested in two pulsed dose rate (PDR) afterloaders alongside a move to full 3D-planned gynaecological brachytherapy.

Purpose

To share the experience and learning curve involved in the implementation of a 3D-guided PDR brachytherapy service.

Methods

The specific logistical and practical challenges of implementing a PDR service are discussed alongside the more general challenges of implementing 3D-guided magnetic resonance (MR) based brachytherapy. A multidisciplinary approach was undertaken to streamline the patient pathway and give all disciplines a forum to discuss service improvements and resolve problems.

Conclusions

The lessons learned throughout this experience can inform the decisions of departments that may wish to implement a PDR service or indeed a 3D image-guided HDR brachytherapy service in the future. The focus on the utilisation of lean principles to the patient pathway, improved multidisciplinary working and enhancing service efficiency is of interest to all centres.

Commissioning of a grid-based Boltzmann solver for cervical cancer brachytherapy treatment planning with shielded colpostats

PURPOSE

We sought to commission a gynecologic shielded colpostat analytic model provided from a treatment planning system (TPS) library. We have reported retrospectively the dosimetric impact of this applicator model in a cohort of patients.

METHODS AND MATERIALS

A commercial TPS with a grid-based Boltzmann solver (GBBS) was commissioned for (192)Ir high-dose-rate (HDR) brachytherapy for cervical cancer with stainless steel-shielded colpostats. Verification of the colpostat analytic model was verified using a radiograph and vendor schematics. MCNPX v2.6 Monte Carlo simulations were performed to compare dose distributions around the applicator in water with the TPS GBBS dose predictions. Retrospectively, the dosimetric impact was assessed over 24 cervical cancer patients' HDR plans.

RESULTS

Applicator (TPS ID #AL13122005) shield dimensions were within 0.4 mm of the independent shield dimensions verification. GBBS profiles in planes bisecting the cap around the applicator agreed with Monte Carlo simulations within 2% at most locations; differing screw representations resulted in differences of up to 9%. For the retrospective study, the GBBS doses differed from TG-43 as follows (mean value ± standard deviation [min, max]): International Commission on Radiation units [ICRU]rectum (-8.4 ± 2.5% [-14.1, -4.1%]), ICRUbladder (-7.2 ± 3.6% [-15.7, -2.1%]), D2cc-rectum (-6.2 ± 2.6% [-11.9, -0.8%]), D2cc-sigmoid (-5.6 ± 2.6% [-9.3, -2.0%]), and D2cc-bladder (-3.4 ± 1.9% [-7.2, -1.1%]).

CONCLUSIONS

As brachytherapy TPSs implement advanced model-based dose calculations, the analytic applicator models stored in TPSs should be independently validated before clinical use. For this cohort, clinically meaningful differences (>5%) from TG-43 were observed. Accurate dosimetric modeling of shielded applicators may help to refine organ toxicity studies.

Evaluation of microscopic tumor extension in early-stage cervical cancer: quantifying subclinical uncertainties by pathological and magnetic resonance imaging findings

We performed a detailed analysis of hysterectomy specimens of uterine cervical cancer to determine the appropriate length of uterine body to include within the clinical target volume. Between 2008 and 2011, 54 patients with uterine cervical carcinoma underwent hysterectomy. Those with quality pre-operative magnetic resonance imaging (MRI) data were included for analysis. Tumor sizes measured by MRI and microscopy were compared with regard to brachytherapy-oriented parameters. Detailed descriptive analysis focusing on the extent of tumor involvement was also performed. A total of 31 specimens were analyzed. The median maximal tumor length measured by MRI was slightly shorter than microscopic length (19 vs. 24 mm, respectively), while the maximal radius was almost identical. No tumors with a maximal size <2 cm by MRI (n = 6) extended to the uterine body ≥ 1/3. The majority of maximal tumor length underestimation on MRI was within 1 cm. Precise tumor delineation can be made by MRI. For patients with tumors <2 cm on MRI, treating the entire uterine body length may not be necessary. A 1-cm margin around an MRI-based gross tumor seems to be adequate to cover the actual tumor involvement.

Vaginal dose point reporting in cervical cancer patients treated with combined 2D/3D external beam radiotherapy and 2D/3D brachytherapy

BACKGROUND AND PURPOSE

Traditionally, vaginal dose points have been defined at the vaginal source level, thus not providing dose information for the entire vagina. Since reliable vaginal dose volume/surface histograms are unavailable, a strategy for comprehensive vaginal dose reporting for combined EBRT and BT was established and investigated.

MATERIAL AND METHODS

An anatomical vaginal reference point was defined at the level of the Posterior-Inferior Border of Symphysis (PIBS), plus two points ±2 cm (mid/introitus vagina). For BT extra points were selected for the upper vagina at 12/3/6/9 o'clock, at the vaginal surface and 5 mm depth. A vaginal reference length (VRL) was defined from ring centre to PIBS. Fifty-nine patients treated for cervical cancer were included in this retrospective feasibility study.

RESULTS

The method was applicable to all patients. Total EQD2 doses at PIBS and ±2 cm were 36.7 Gy (3.1-68.2), 49.6 Gy (32.1-89.6) and 4.3 Gy (1.0-46.6). At the vaginal surface at ring level doses were respectively 266.1 Gy (67.6-814.5)/225.9 Gy (61.5-610.5) at 3/9 o'clock, and 85.1 Gy (55.4-140.3)/72.0 Gy (49.1-108.9) at 12/6 o'clock. Mean VRL on MRI was 5.6 cm (2.0-9.4).

CONCLUSIONS

With this novel system, a comprehensive reporting of vaginal doses is feasible. The present study has demonstrated large dose variations between patients observed in all parts of the vagina, resulting from different contributions from EBRT and BT.