Search

Purpose: To develop a novel decision-support system for radiation oncology that incorporates clinical, treatment and outcome data, as well as outcome models from a large clinical trial on magnetic resonance image-guided adaptive brachytherapy (MR-IGABT) for locally advanced cervical cancer (LACC)., Methods: A system, called EviGUIDE, was developed that combines dosimetric information from the treatment planning system, patient and treatment characteristics, and established tumor control probability (TCP), and normal tissue complication probability (NTCP) models, to predict clinical outcome of radiotherapy treatment of LACC. Six Cox Proportional Hazards models based on data from 1341 patients of the EMBRACE-I study have been integrated. One TCP model for local tumor control, and five NTCP models for OAR morbidities., Results: EviGUIDE incorporates TCP-NTCP graphs to help users visualize the clinical impact of different treatment plans and provides feedback on achievable doses based on a large reference population. It enables holistic assessment of the interplay between multiple clinical endpoints and tumour and treatment variables. Retrospective analysis of 45 patients treated with MR-IGABT showed that there exists a sub-cohort of patients (20%) with increased risk factors, that could greatly benefit from the quantitative and visual feedback., Conclusion: A novel digital concept was developed that can enhance clinical decision- making and facilitate personalized treatment. It serves as a proof of concept for a new generation of decision support systems in radiation oncology, which incorporate outcome models and high-quality reference data, and aids the dissemination of evidence-based knowledge about optimal treatment and serve as a blueprint for other sites in radiation oncology., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Purpose: To provide educational support to brachytherapy users during the COVID-19 pandemic, online workshops were developed and implemented by BrachyAcademy, non-profit peer-to-peer educational initiative in Elekta., Methods and Materials: In 2021-2022 two online workshops were organized. Participating teams had to send a clinical case of locally advanced cervical cancer (LACC) including brachytherapy Digital Imaging and Communications in Medicine (DICOM) files and questions to the faculty. During the workshop, feedback was given to each clinical case by five faculty members (two Radiation Oncologists, one Radiologist, two Medical Physicists). Participants competed a post-workshop questionnaire which included combination of qualitative and quantitative questions via yes/no responses, Likert scale, and 1 to 10 scale., Results: Twenty-one teams from eight countries (Europe, Asia, Latin America) participated in two online workshops. The total number of participants was 49. The clinical cases represented LACC with The International Federation of Gynecology and Obstetrics (FIGO) stages from IB3 to IVA. During both, Workshop1 (W1) and Workshop 2 (W2) the following areas of improvement were identified: familiarity with the GEC ESTRO and The International Commission on Radiation Units & Measurements, Report 89 (ICRU 89) recommendations for contouring and planning based on clinical drawings and MRI sequencing choice; appropriate applicator selection; experience with interstitial needles; appropriate applicator reconstruction; dose optimization. The participants rated both workshops with overall scores 8,3 for W1, and 8,5 for W2. In 82% participants the training course fully met expectations for W1, and in 76% in W2., Conclusions: We successfully implemented the online workshops on image-guided adaptive brachytherapy (IGABT) in LACC. Main performance issues and areas for improvement were identified based on multidisciplinary discussion of participant's clinical cases through all steps of the brachytherapy procedure. We encourage teams to consider online workshops in addition to hands-on training., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Purpose: To report clinical and treatment characteristics, remission and failure patterns, and risk factors for local failure (LF) from the EMBRACE-I study., Materials and Methods: EMBRACE-I was a prospective, observational, multicenter cohort study on magnetic resonance imaging-based image-guided adaptive brachytherapy (MR-IGABT) in locally advanced cervical cancer. Treatment consisted of external beam radiotherapy, concurrent chemotherapy, and MR-IGABT. LF was defined as progressive or recurrent disease in the cervix, uterus, parametria, pelvic wall, or vagina. Competing risk analysis was used to estimate local tumor control (LC) and Cox proportional regression models for multivariable analysis and dose-response analysis., Results: One thousand three hundred eighteen patients with a median follow-up of 52 months were available for this analysis. Eighty-one patients had persistent disease 3 months after end of treatment. Of those, 60 patients achieved LC at 6-9 months without further treatment, whereas 21 patients had progressive disease. In addition, 77 patients developed a local recurrence after complete remission comprising a total number of 98 LFs. LFs were located inside the MR-IGABT target volumes in 90% of patients with LF. In multivariable analysis, histology, minimal dose to 90% of high-risk clinical target volume (CTV HR ), maximum tumor dimension, CTV HR > 45 cm 3 , overall treatment time, tumor necrosis on magnetic resonance imaging at diagnosis, uterine corpus infiltration at diagnosis and at MR-IGABT, and mesorectal infiltration at MR-IGABT had significant impact on LF. Dose-response analysis showed that a minimal dose to 90% of 85 Gy to the CTV HR led to 95% (95% CI, 94 to 97) LC 3 years postintervention for squamous cell in comparison to 86% (95% CI, 81 to 90) for adeno/adenosquamous carcinoma histology., Conclusion: The present study demonstrates the safety and validity of the GYN GEC-ESTRO/ICRU-89 target concept and provides large-scale evidence for dose prescription and new risk factors for LF in MR-IGABT in locally advanced cervical cancer., Competing Interests: Maximilian P. SchmidHonoraria: ElektaResearch Funding: Elekta (Inst), Varian Medical Systems (Inst)Patents, Royalties, Other Intellectual Property: Patent: US20170120072 Umesh MahantshettyConsulting or Advisory Role: AstraZenecaResearch Funding: Varian Medical Systems (Inst) Kari TanderupResearch Funding: Varian Medical Systems (Inst), Elekta (Inst) Peter HoskinResearch Funding: Varian Medical Systems (Inst), Astellas Pharma (Inst), Bayer (Inst), Roche (Inst), Pfizer (Inst), Elekta (Inst), Bristol Meyers (Inst) Bradley R. PietersConsulting or Advisory Role: BD Bard (Inst)Research Funding: ElektaTravel, Accommodations, Expenses: BD BardOther Relationship: Elekta (Inst) Remi NoutConsulting or Advisory Role: Merck KGaA (Inst)Research Funding: Varian Medical Systems (Inst), Elekta (Inst), Accuray (Inst) Nicole NesvacilHonoraria: ElektaConsulting or Advisory Role: ElektaTravel, Accommodations, Expenses: Elekta Richard PötterResearch Funding: Elekta (Inst), Varian Medical Systems (Inst) Christian KirisitsHonoraria: ElektaResearch Funding: Elekta (Inst), Varian Medical (Inst)Patents, Royalties, Other Intellectual Property: Patent WO2015181632A1 on Methods and Systems for Brachytherapy Planning Based on Imaging DataNo other potential conflicts of interest were reported.

Background: The concept of the use of MRI for image-guided adaptive brachytherapy (IGABT) in locally advanced cervical cancer was introduced 20 years ago. Here, we report on EMBRACE-I, which aimed to evaluate local tumour control and morbidity after chemoradiotherapy and MRI-based IGABT., Methods: EMBRACE-I was a prospective, observational, multicentre cohort study. Data from patients from 24 centres in Europe, Asia, and North America were prospectively collected. The inclusion criteria were patients older than 18 years, with biopsy-proven squamous cell carcinoma, adenocarcinoma, or adenosquamous carcinoma of the uterine cervix, The International Federation of Gynecology and Obstetrics (FIGO) stage IB-IVA disease or FIGO stage IVB disease restricted to paraaortic lymph metastasis below the L1-L2 interspace, suitable for curative treatment. Treatment consisted of chemoradiotherapy (weekly intravenous cisplatin 40 mg/m 2 , 5-6 cycles, 1 day per cycle, plus 45-50 Gy external-beam radiotherapy delivered in 1·8-2 Gy fractions) followed by MRI-based IGABT. The MRI-based IGABT target volume definition and dose reporting was according to Groupe Européen de Curiethérapie European Society for Radiation Oncology recommendations. IGABT dose prescription was open according to institutional practice. Local control and late morbidity were selected as primary endpoints in all patients available for analysis. The study was registered with ClinicalTrials.gov, NCT00920920., Findings: Patient accrual began on July 30, 2008, and closed on Dec 29, 2015. A total of 1416 patients were registered in the database. After exclusion for not meeting patient selection criteria before treatment, being registered but not entered in the database, meeting the exclusion criteria, and being falsely excluded, data from 1341 patients were available for analysis of disease and data from 1251 patients were available for assessment of morbidity outcome. MRI-based IGABT including dose optimisation was done in 1317 (98·2%) of 1341 patients. Median high-risk clinical target volume was 28 cm 3 (IQR 20-40) and median minimal dose to 90% of the clinical target volume (D 90% ) was 90 Gy (IQR 85-94) equi-effective dose in 2 Gy per fraction. At a median follow-up of 51 months (IQR 20-64), actuarial overall 5-year local control was 92% (95% CI 90-93). Actuarial cumulative 5-year incidence of grade 3-5 morbidity was 6·8% (95% CI 5·4-8·6) for genitourinary events, 8·5% (6·9-10·6) for gastrointestinal events, 5·7% (4·3-7·6) for vaginal events, and 3·2% (2·2-4·5) for fistulae., Interpretation: Chemoradiotherapy and MRI-based IGABT result in effective and stable long-term local control across all stages of locally advanced cervical cancer, with a limited severe morbidity per organ. These results represent a positive breakthrough in the treatment of locally advanced cervical cancer, which might be used as a benchmark for clinical practice and all future studies., Funding: Medical University of Vienna, Aarhus University Hospital, Elekta AB, and Varian Medical Systems., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Objective: To prospectively compare the interobserver variability of combined transrectal ultrasound (TRUS)/computed tomography (CT)- vs. CT only- vs. magnetic resonance imaging (MRI) only-based contouring of the high-risk clinical target volume (CTV HR ) in image-guided adaptive brachytherapy (IGABT) for locally advanced cervical cancer (LACC)., Methods: Five patients with LACC (FIGO stages IIb-IVa) treated with radiochemotherapy and IGABT were included. CT, TRUS, and T2-weighted MRI images were performed after brachytherapy applicator insertion. 3D-TRUS image acquisition was performed with a customized ultrasound stepper device and software. Automatic applicator reconstruction using optical tracking was performed in the TRUS dataset and TRUS and CT images were fused with rigid image registration with the applicator as reference structure. The CTV HR (based on the GEC-ESTRO recommendations) was contoured by five investigators on the three modalities (CTV HR _CT, CTV HR _TRUS-CT, and CTV HR _MRI). A consensus reference CTV HR _MRI (MRIref) was defined for each patient. Descriptive statistics and overlap measures were calculated using RTslicer (SlicerRT Community and Percutaneous Surgery Laboratory, Queen's University, Canada), comparing contours of every observer with one another and with the MRIref., Results: The interobserver coefficient of variation was 0.18 ± 0.05 for CT, 0.10 ± 0.04 for TRUS-CT, and 0.07 ± 0.03 for MRI. Interobserver concordance in relation to the MRIref expressed by the generalized conformity index was 0.75 ± 0.04 for MRI, 0.51 ± 0.10 for TRUS-CT, and 0.48 ± 0.06 for CT. The mean CTV HR _CT volume of all observers was 71% larger than the MRIref volume, whereas the mean CTV HR _TRUS-CT volume was 15% larger., Conclusion: Hybrid TRUS-CT as an imaging modality for contouring the CTV HR in IGABT for LACC is feasible and reproducible among multiple observers. TRUS-CT substantially reduces overestimation of the CTV HR volume of CT alone while maintaining similar interobserver variability.

Background and Aim: External beam radiotherapy (EBRT) combined with brachytherapy has an essential role in the curative treatment of primary vaginal cancer. EBRT is associated with significant tumour shrinkage, making primary vaginal cancer suitable for image guided adaptive brachytherapy (IGABT). The aim of these recommendations is to introduce an adaptive target volume concept for IGABT of primary vaginal cancer., Methods: In December 2013, a task group was initiated within GYN GEC-ESTRO with the purpose to introduce an IGABT target concept for primary vaginal cancer. All participants have broad experience in IGABT and vaginal cancer brachytherapy. The target concept was elaborated as consensus agreement based on an iterative process including target delineation and dose planning comparison, retrospective analysis of clinical data and expert opinions., Results: Gynaecological examination and MR imaging are the modalities of choice for local tumour assessment. A specific template for standardised documentation with clinical drawings for vaginal cancer was developed. The adaptive target volume concept comprises different response-related target volumes. For EBRT these are related to the primary tumour and the lymph nodes, while for IGABT these are related to the primary tumour and are consisting of the residual gross tumour volume (GTV-T res ) and the high-, and intermediate risk clinical target volumes (CTV-T HR , CTV-T IR )., Conclusion: This target concept for IGABT of primary vaginal cancer defines adaptive target volumes for volumetric dose prescription and should improve comparability of different radiotherapy schedules of this rare disease. A prospective evaluation of the target volume concept within a multicentre study is planned., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Primary vaginal cancer is a rare cancer and clinical evidence to support recommendations on its optimal management is insufficient. Because primary vaginal cancer resembles cervical cancer in many aspects, treatment strategies are mainly adopted from evidence in locally advanced cervical cancer. To date, the organ-sparing treatment of choice is definitive radiotherapy, consisting of external beam radiotherapy and brachytherapy, combined with concurrent chemotherapy. Brachytherapy is an important component of the treatment and its steep dose gradient enables the delivery of high doses of radiation to the primary tumour, while simultaneously sparing the surrounding organs at risk. The introduction of volumetric CT or MRI image-guided adaptive brachytherapy in cervical cancer has led to better pelvic control and survival, with decreased morbidity, than brachytherapy based on x-ray radiographs. MRI-based image-guided adaptive brachytherapy with superior soft-tissue contrast has also been adopted sporadically for primary vaginal cancer. This therapy has had promising results and is considered to be the state-of-the-art treatment for primary vaginal cancer in standard practice., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Purpose: To describe the evolution of external beam radiation therapy (EBRT) from EMBRACE-I (general guidelines for EBRT) to the initial phase of the EMBRACE-II study (detailed protocol for EBRT)., Methods and Materials: EMBRACE-I enrolled 1416 locally advanced cervical cancer patients treated with chemoradiation including image-guided adaptive brachytherapy during 2008 to 2015. From March 2016 until March 2018, 153 patients were enrolled in the ongoing EMBRACE-II study, which involves a comprehensive detailed strategy and accreditation procedure for EBRT target contouring, treatment planning, and image guidance. EBRT planning target volumes (PTVs), treated volumes (V43 Gy), and conformity index (CI; V43 Gy/PTV) were evaluated in both studies and compared., Results: For EMBRACE-I, conformal radiation therapy (60% of patients) or intensity-modulated radiation therapy (IMRT) and volumetric arc therapy (VMAT; 40%) was applied with 45 to 50 Gy over 25 to 30 fractions to the elective clinical target volume (CTV). For pelvic CTVs (82%), median PTV and V43 Gy volumes were 1549 and 2390 mL, respectively, and CI was 1.54. For pelvic plus paraortic nodal (PAN) CTVs (15%), median PTV and V43 Gy volumes were 1921 and 2895 mL, and CI was 1.51. For pelvic CTVs treated with 45 to 46 Gy, the use of conformal radiation therapy was associated with a median V43 Gy volume that was 546 mL larger than with IMRT/VMAT. For pelvic CTVs treated with IMRT, the use of a dose prescription ≥48 Gy was associated with a median V43 Gy volumes that was 428 mL larger than with a dose prescription of 45 to 46 Gy. For EMBRACE-II, all patients were treated with: IMRT/VMAT, daily IGRT, 45 Gy over 25 fractions for the elective CTV, and simultaneously integrated boost for pathologic lymph nodes. For pelvic CTVs (61%), median PTV and V43 Gy volumes were 1388 and 1418 mL, and CI was 1.02. For pelvic plus PAN CTVs (32%), median PTV and V43 Gy volumes were 1720 and 1765 mL, and CI was 1.03. From EMBRACE-I to initial II, median V43 Gy was decreased by 972 mL (41%) and 1130 mL (39%), and median CI decreased from 1.54 to 1.02 and 1.51 to 1.03 for pelvic and pelvic plus PAN irradiation, respectively., Conclusions: Application of IMRT/VMAT, IGRT, and a 45-Gy dose provides the potential of higher conformality inducing significant reduction of treated volume. Adherence to a detailed protocol including comprehensive accreditation, as in EMBRACE-II, reduces considerably V43 Gy and V50 Gy and improves conformality and interinstitutional consistency., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Purpose: To investigate the isodose surface volumes (ISVs) for 85, 75 and 60 Gy EQD2 for locally advanced cervix cancer patients., Materials and Methods: 1201 patients accrued in the EMBRACE I study were analysed. External beam radiotherapy (EBRT) with concomitant chemotherapy was followed by MR based image-guided adaptive brachytherapy (MR-IGABT). ISVs were calculated using a predictive model based on Total Reference Air Kerma and compared to Point A-standard loading systems. Influence of fractionation schemes and dose rates was evaluated through comparison of ISVs for α/β 10 Gy and 3 Gy., Results: Median V85 Gy , V75 Gy and V60 Gy EQD2 10 were 72 cm 3 , 100 cm 3 and 233 cm 3 , respectively. Median V85 Gy EQD2 10 was 23% smaller than in standard 85 Gy prescription to Point A. For small (<25 cm 3 ), intermediate (25-35 cm 3 ) and large (>35 cm 3 ) CTV HR volumes, the V85 Gy was 57 cm 3 , 70 cm 3 and 89 cm 3 , respectively. In 38% of EMBRACE patients the V85 Gy was similar to standard plans with 75-85 Gy to Point A. 41% of patients had V85 Gy smaller than standard plans receiving 75 Gy at Point A, while 21% of patients had V85 Gy larger than standard plans receiving 85 Gy at Point A., Conclusions: MR-IGABT and individualized dose prescription during EMBRACE I resulted in improved target dose coverage and decreased ISVs compared to standard plans used with classical Point A based brachytherapy. The ISVs depended strongly on CTV HR volume which demonstrates that dose adaptation was performed per individual tumour size and response during EBRT., (Copyright © 2018 Elsevier B.V. All rights reserved.)

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.

Background and Purpose: To compare the dosimetric impact of organ and target variations relative to the applicator for intracavitary brachytherapy by a multicentre analysis with different application techniques and fractionation schemes., Material and Methods: DVH data from 363 image/contour sets (120 patients, 6 institutions) were included for 1-6 fractions per patient, with imaging intervals ranging from several hours to ∼20 days. Variations between images acquired within one (intra-application) or between consecutive applicator insertions (inter-application) were evaluated. Dose plans based on a reference MR or CT image series were superimposed onto subsequent image sets and D(2cm(3)) for the bladder, rectum and sigmoid and D(90) for HR CTV were recorded., Results: For the whole sample, the systematic dosimetric variations for all organs at risk, i.e. mean variations of D(2cm(3)), were found to be minor (<5%), while random variations, i.e. standard deviations were found to be high due to large variations in individual cases. The D(2cm(3)) variations (mean±1SD) were 0.6±19.5%, 4.1±21.7% and 1.6±26.8%, for the bladder, rectum and sigmoid. For HR CTV, the variations of D90 were found to be -1.1±13.1% for the whole sample. Grouping of the results by intra- and inter-application variations showed that random uncertainties for bladder and sigmoid were 3-7% larger when re-implanting the applicator for individual fractions. No statistically significant differences between the two groups were detected in dosimetric variations for the HR CTV. Using 20% uncertainty of physical dose for OAR and 10% for HR CTV, the effects on total treatment dose for a 4 fraction HDR schedule at clinically relevant dose levels were found to be 4-8 Gy EQD2 for OAR and 3 Gy EQD2 for HR CTV., Conclusions: Substantial variations occur in fractionated cervix cancer BT with higher impact close to clinical threshold levels. The treatment approach has to balance uncertainties for individual cases against the use of repetitive imaging, adaptive planning and dose delivery., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

Purpose: To investigate dosimetric uncertainties of MRI-based cervix cancer brachytherapy, when applying two HDR fractions for each applicator insertion and their clinical relevance., Methods: 21 patients with 84 MRI-examinations and fractions were investigated. After insertion of the MRI compatible tandem-ring applicator, an MRI-set was recorded and the treatment plan optimised for the first fraction. Prior to the second fraction 16-20 h later a second MRI-set was recorded, and the dose distribution from the plan of the previous day superimposed and analysed. The same procedure was repeated for fractions 3 and 4. Dose from EBRT and brachytherapy was normalised to 2 Gy-fractionation (EQD2), added up to a total dose, and compared to a calculated total dose if only 1 MRI-examination per insertion is available., Results: The total D(90) for High risk (HR) CTV was 1.2±2.7 Gy(αβ10) (1±3%) (mean±1SD) lower by individual MRI-evaluation of each fraction compared to 1 MRI per insertion. The D(2cm(3)) increased by 0.7±4.7 Gy(αβ3) (1±6%) for bladder, 1.1±2.4 Gy(αβ3) (2±4%) for rectum and decreased by 0.8±3.4 Gy(αβ3) (1±5%) for sigmoid. For HR CTV the individual approach did not identify any case with a decrease of D(90) >5 Gy(αβ10). For the bladder 3 cases, for the rectum no case and for the sigmoid 1 case was identified with an increase of D(2cm(3)) >5 Gy(αβ3). For the bladder all dose variations of more than 5 Gy(αβ3) could have been avoided by ensuring a constant bladder filling. Individual MRI-evaluation did not determine any case where dose constraints were not fulfilled., Conclusions: For the treatment schedule as applied in this study, geometric differences between applicator, target and OAR result in overall dosimetric changes, which seem to be of minor relevance in regard to clinical dose volume constraints applied at present., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

Purpose: To investigate and test the feasibility of adaptive 3D image based BT planning for cervix cancer patients in settings with limited access to MRI, using a combination of MRI for the first BT fraction and planning of subsequent fractions on CT., Material and Methods: For 20 patients treated with EBRT and HDR BT with tandem/ring applicators two sets of treatment plans were compared. Scenario one is based on the "gold standard" with individual MRI-based treatment plans (applicator reconstruction, target contouring and dose optimization) for two BT applications with two fractions each. Scenario two is based on one initial MRI acquisition with an applicator in place for the planning of the two fractions of the first BT application and reuse of the target contour delineated on MRI for subsequent planning of the second application on CT. Transfer of the target from MRI of the first application to the CT of the second one was accomplished by use of an automatic applicator-based image registration procedure. Individual dose optimization of the second BT application was based on the transferred MRI target volume and OAR structures delineated on CT. DVH parameters were calculated for transferred target structures (virtual dose from MRI/CT plan) and CT-based OAR. The quality of the MRI/CT combination method was investigated by evaluating the CT-based dose distributions on MRI-based target and OAR contours of the same application (real dose from MRI/CT plan)., Results: The mean difference between the MRI based target volumes (HR CTVMRI2) and the structures transferred from MRI to CT (HR CTVCT2) was -1.7±6.6 cm(3) (-2.9±20.4%) with a median of -0.7 cm(3). The mean difference between the virtual and the real total D90, based on the MRI/CT combination technique was -1.5±4.3 Gy EQD2. This indicates a small systematic underestimation of the real D90., Conclusions: A combination of MRI for first fraction and subsequent CT based planning is feasible and easy when automatic applicator-based image registration and target transfer are technically available. The results show striking similarity to fully MRI-based planning in cases of small tumours and intracavitary applications, both in terms of HR CTV coverage and respecting of OAR dose limits. For larger tumours and complex applications, as well as situations with unfavourable OAR topography, especially for the sigmoid, MRI based adaptive BT planning remains the superior method., (Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.)