Viscous Aqueous Gel Illustrating Natural Anatomy: The VAGINA method in gynaecological MRI simulation.

Accurately defining gross tumour volume (GTV) and organs at risk (OAR) is key to successful radiation therapy (RT) treatment outcomes for patients with gynaecological cancers. With improved access to magnetic resonance imaging (MRI) for RT simulation and planning, the optimisation and tailoring of proven diagnostic MRI techniques towards RT specific planning goals is fast evolving. Modifying MRI techniques for radiation oncology (RO) with the priority of anatomy visualisation and spatial location over diagnosis and disease characterisation relies heavily on successful collaboration between radiology and radiation oncology staff. This 'How I Do It' paper describes a qualitative analysis of the adaptation of a diagnostic MRI vaginal opacification technique into an RT specific MRI simulation procedure using aqueous ultrasound gel for improving natural anatomical visualisation of the vaginal canal. This technique is explained and could be introduced in other RO departments for dedicated RT planning scans in MR-Sim sessions with minimal difficulty. We found 10-15 cc of aqueous gel delivered vaginally produced optimal MRI planning images for most patients. With this small amount of gel and careful application technique, the full extent of the vaginal vault and cervix can be well visualised on T2 Weighted (T2W) imaging, while tending not to unfold the natural fornices of the collapsed vagina, representing a significant improvement in image quality from the outdated tampon procedure.

Validation of an MRI-only planning workflow for definitive pelvic radiotherapy.

PURPOSE: Previous work on Magnetic Resonance Imaging (MRI) only planning has been applied to limited treatment regions with a focus on male anatomy. This research aimed to validate the use of a hybrid multi-atlas synthetic computed tomography (sCT) generation technique from a MRI, using a female and male atlas, for MRI only radiation therapy treatment planning of rectum, anal canal, cervix and endometrial malignancies. PATIENTS AND METHODS: Forty patients receiving radiation treatment for a range of pelvic malignancies, were separated into male (n = 20) and female (n = 20) cohorts for the creation of gender specific atlases. A multi-atlas local weighted voting method was used to generate a sCT from a T1-weighted VIBE DIXON MRI sequence. The original treatment plans were copied from the CT scan to the corresponding sCT for dosimetric validation. RESULTS: The median percentage dose difference between the treatment plan on the CT and sCT at the ICRU reference point for the male cohort was - 0.4% (IQR of 0 to - 0.6), and - 0.3% (IQR of 0 to - 0.6) for the female cohort. The mean gamma agreement for both cohorts was > 99% for criteria of 3%/2 mm and 2%/2 mm. With dose criteria of 1%/1 mm, the pass rate was higher for the male cohort at 96.3% than the female cohort at 93.4%. MRI to sCT anatomical agreement for bone and body delineated contours was assessed, with a resulting Dice score of 0.91 ± 0.2 (mean ± 1 SD) and 0.97 ± 0.0 for the male cohort respectively; and 0.96 ± 0.0 and 0.98 ± 0.0 for the female cohort respectively. The mean absolute error in Hounsfield units (HUs) within the entire body for the male and female cohorts was 59.1 HU ± 7.2 HU and 53.3 HU ± 8.9 HU respectively. CONCLUSIONS: A multi-atlas based method for sCT generation can be applied to a standard T1-weighted MRI sequence for male and female pelvic patients. The implications of this study support MRI only planning being applied more broadly for both male and female pelvic sites. Trial registration This trial was registered in the Australian New Zealand Clinical Trials Registry (ANZCTR) ( www.anzctr.org.au ) on 04/10/2017. Trial identifier ACTRN12617001406392.

Adjuvant radiotherapy for endometrial cancer with cervical stromal involvement: A patterns of practice survey in Australia and New Zealand.

INTRODUCTION: The purpose of this study is to describe the patterns of practice in Australia and New Zealand for post-operative radiotherapy in endometrial cancer with cervical stromal involvement. METHODS: A ten-item survey including five clinical case scenarios in endometrial cancer with cervical stromal invasion was emailed to Royal Australian and New Zealand College of Radiologists (RANZCR) radiation oncologists in 2018. Responses were analysed to determine relative frequency distributions and preferred adjuvant treatment modalities for the clinical case scenarios. RESULTS: A total of 65 respondents initiated the survey with 27 respondents treating more than 11 endometrial cancer cases annually. Only 31 respondents answered all five clinical case scenarios. Preferred adjuvant radiotherapy modalities varied for the Stage II cases between vault brachytherapy (VB), pelvic external beam radiotherapy (EBRT) or a combination. For the stage IIIA and IIIC1 cases, the majority recommended pelvic EBRT with or without VB boost (79% and 77%), and of these, most combined with chemotherapy (61% and 88%). For 4 of the 5 case scenarios, when pelvic EBRT was offered, most recommended a VB boost. CONCLUSION: This patterns of practice survey suggests variability in adjuvant radiotherapy recommendations in endometrial cancer with cervical involvement, particularly in cases where there is lack of randomised data and discrepancies in consensus guidelines.

High-risk CTV delineation for cervix brachytherapy: Application of GEC-ESTRO guidelines in Australia and New Zealand.

INTRODUCTION: Image-based brachytherapy for cervical cancer using MRI has been implemented in Australia and New Zealand. The aims of this study were to measure variability in High-risk CTV (HR-CTV) delineation and evaluate dosimetric consequences of this. METHODS: Nine radiation oncologists, one radiation therapist and two radiologists contoured HR-CTV on 3T MRI datasets from ten consecutive patients undergoing cervical brachytherapy at a single institution. Contour comparisons were performed using the Dice Similarity Coefficient (DSC) and Mean Absolute Surface Distance (MASD). Two reference contours were created for brachytherapy planning: a Simultaneous Truth and Performance Level Estimation (STAPLE) and a consensus contour (CONSENSUS). Optimized plans (8 Gy) for both these contours were applied to individual participant's contours to assess D90 and D100 coverage of HR CTV. To compare variability in dosimetry, relative standard deviation (rSD) was calculated. RESULTS: Good concordance (mean DSC≥0.7, MASD≤5 mm) was achieved in 8/10 cases when compared to the STAPLE reference and 6/10 cases when compared to the CONSENSUS reference. Greatest variation was visually seen in the cranio-caudal direction. The average mean rSD across all patients was 27% and 34% for the STAPLE HR-CTV D90 and D100, respectively, and 28% and 35% for the CONSENSUS HR-CTV D90 and D100. Delineation uncertainty resulted in an average dosimetric uncertainty of ±1.5-1.6 Gy per fraction based on an 8 Gy prescribed fraction. CONCLUSIONS: Delineation of HR-CTV for cervical cancer brachytherapy was consistent amongst observers, suggesting similar interpretation of GEC-ESTRO guidelines. Despite the good concordance, there was dosimetric variation noted, which could be clinically significant.

Implications for dosimetric changes when introducing MR-guided brachytherapy for small volume cervix cancer: a comparison of CT and MR-based treatments in a single centre.

To evaluate cervix brachytherapy dosimetry with the introduction of magnetic resonance (MR) based treatment planning and volumetric prescriptions and propose a method for plan evaluation in the transition period. The treatment records of 69 patients were reviewed retrospectively. Forty one patients were treated using computed tomography (CT)-based, Point A-based prescriptions and 28 patients were treated using magnetic resonance (MR)-based, volumetric prescriptions. Plans were assessed for dose to Point A and organs at risk (OAR) with additional high-risk clinical target volume (HR-CTV) dose assessment for MR-based brachytherapy plans. ICRU-38 point doses and GEC-ESTRO recommended volumetric doses (D2cc for OAR and D100, D98 and D90 for HR-CTV) were also considered. For patients with small HR-CTV sizes, introduction of MR-based volumetric brachytherapy produced a change in dose delivered to Point A and OAR. Point A doses fell by 4.8 Gy (p = 0.0002) and ICRU and D2cc doses for OAR also reduced (p < 0.01). Mean Point A doses for MR-based brachytherapy treatment plans were closer to those of HR-CTV D100 for volumes less than 20 cm(3) and HR-CTV D98 for volumes between 20 and 35 cm(3), with a significant difference (p < 0.0001) between Point A and HR-CTV D90 doses in these ranges. In order to maintain brachytherapy dose consistency across varying HR-CTV sizes there must be a relationship between the volume of the HR-CTV and the prescription dose. Rather than adopting a 'one size fits all' approach during the transition to volume-based prescriptions, this audit has shown that separating prescription volumes into HR-CTV size categories of less than 20 cm(3), between 20 and 35 cm(3), and more than 35 cm(3) the HR-CTV can provide dose uniformity across all volumes and can be directly linked to traditional Point A prescriptions.

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.