Imaging
Outline - MRI - CT - US - Combinations of imaging modalities for treatment planning
Imaging Part 1: MRI
MRI for cervical cancer high soft tissue contrast multiplanar imaging
MRI anatomy: the normal uterus Endometrium Junctional zone Myometrium Cervical canal Cervical stroma T2-weighted, sagittal
MRI anatomy: the normal uterus Cervical stroma: low SI = dark Cervical canal: high SI = bright T2-weighted, transversal
MRI anatomy: the parametria Borders Anterior: urinary bladder Lateral: pelvic wall Posterior: mesorectal fascia T2-weighted, transversal
MRI anatomy: the vagina Use gel!!! Don t forget the clinical examination! T2-weighted, sagittal
MRI anatomy: cervix cancer T2-weighted, sagittal
MRI anatomy: cervix cancer GTV at diagnosis: macroscopic tumour extension at time of diagnosis High signal intensity mass(es) (FSE, T2) in cervix/corpus, parametria, vagina, bladder and rectum
MRI anatomy: signs of parametrial invasion Parametria involved? Disruption of the cervical ring Complete loss of cervical stroma, tumor in the parametria present T2-weighted, sagittal
Findings at time of diagnosis (GTV D ) High signal intensity tumor mass invasion into the parametria necrosis corpus invasion vaginal invasion
MRI anatomy: tumor regression Before treatment
MRI anatomy: tumor regression Radiochemotherapy: Week 2
MRI anatomy: tumor regression Radiochemotherapy: Week 5
MRI anatomy: tumor regression Changes in signal intensity Changes in volume Changes in shape
MRI anatomy: tumor regression Changes in signal intensity Intermediate / low SI High SI Intermediate SI
MRI anatomy: tumor regression Intermediate / low SI = recovering cervical stroma Grey zones? High SI = residual GTV Changes in signal intensity Regions with intermediate SI in the parametria within the initial tumor extension Sign of tumor response -> fibrosis, edema, tumor (?) Intermediate SI = grey zones
MRI anatomy: tumor regression N=175, median values Changes in volume At diagnosis At brachytherapy GTV at diagnosis: 44,4cm³ Residual GTV at brachytherapy: 8,2cm³ Res. GTV at BT + grey zones: 20,3cm³ High Risk CTV: 34cm³ Tumour regression without grey zones 78,5% Tumour regression with grey zones 50,1% GTV at diagnosis Residual GTV at brachytherapy Residual GTV at BT + grey zone
MRI anatomy: tumor regression Changes in shape Residual tumor in parametria: predominantly expansive vs predom. infiltrative: 43% vs 88% (p<0.001)
Contouring in IGABT: MRI HR-CTV: includes gtv, whole cervix, and presumed extracervical tumour extension. Pathologic residual tissue(s) as defined by palpable indurations and/or grey zones in parametria, uterine corpus, vagina or rectum and bladder are included in HR-CTV. No safety margin are added. GTV HRCTV Grey zone Cervix
MRI for IGABT: Imaging recommendations Tipps and tricks: Image orientation in the axis of the uterus Use vaginal gel Use all (multiplanar) image sets for evaluation
Imaging Part 2: CT
Comparison of MRI and CT Overestimation of HRCTV by CT
CT for IGABT Challenges: No GTV - vaginal involvement - corpus invasion Reasonable discrimination of cervical outline BUT: Overestimation of HRCTV by CT
MRI- vs. CT-based contouring: results HR CTV Example is not from cited publication Example is not from cited publication
OAR contouring on CT Rectum and bladder CT and MRI useful for delineation of outer organ boundaries
MRI- vs. CT-based contouring: results Organs at risk Similar values of DVH parameters
MRI- vs. CT-based contouring: results Common interpretation: CT is OK for OAR, but suboptimal for HR CTV and IR CTV...oversimplification for the OAR? Viswanathan AN, et al. Radiother Oncol 2007
How to improve CT imaging for BT Adapt your application technique! Avoid thick stainless steel applicators / accessories Use CT compatible equipment Avoid non-diluted contrast (packing, Foley ballon, bladder...) Consider marking vaginal extension (i.e. radio-opaque suture)
How to improve CT imaging for BT
How to improve CT imaging for BT Use bladder contrast!
How to improve CT imaging for BT Use i.v. contrast!
How to improve CT imaging for BT Use 2-3mm slice thickness over the region of interest!
How to improve CT imaging for BT Sometimes it is still difficult!
How to improve CT based contouring How to overcome limitations of CT: No GTV, Overestimation of HR CTV Use anatomical landmarks! Use additional information!
Inferior and superior extent cervical borders Superior: Where uterus indents, contour the next 1 cm - pointed shape (cone) HR CTV contouring on CT: tips Uppermost contour Uterine vessels abutting (i. v. contrast) Inferior: ring / ovoids level Cervical length: 2.5 3 cm Vaginal involvement: add vaginal tissue involved clinically at BT. Uterine involvement: more challenging. Clinical / radiological information into account
HR CTV contouring on CT: tips Lateral borders of HR-CTV: Clinical examination & imaging No parametrial invasion: lateral cervical borders Parametrial invasion: grey structures in parametria (density of cervix)
How to improve CT based contouring At DG Pre BT MRI? At (each) BT
Incorporation of pre-bt MRI information Initial MRI EBRT Pre-BT MRI 1. CT MRI based BT 2. CT MRI based BT Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Week 7 Pre-BT MRI improves the ability to contour on CT! HR CTV FIGO HR CTV Clinical Drawings HR CTV Pre-BT MRI Federico M, et al. 2012 (published as abstract)
SUMMARY & CONCLUSIONS MRI-based approach: Gold Standard CT-based approach: feasible, provided: - Experience with MRI-Based Approach - Pre-therapy MRI available - Standardized CT protocol used - Clinical findings incorporated - Pre BT MRI facilitates CT contouring
Imaging Part 3: Ultrasound
Ultrasound probes for IGABT Transabdominal Ultrasound (TAUS) Transrectal Ultrasound (TRUS) (Transvaginal Ultrasound)
TAUS
TAUS High correlation of MRI and TAUS for uterine corpus Differences of >1cm for width of cervix Uncertainties for assessment of parametrial infiltration Mahanshetty U et al Radiother Oncol 2011
Treatment planning with TAUS Van Dyk S et al IJROBP 2009
What are the most important aspects in IGABT for local tumour control?
What are the most important aspects in IGABT for local tumour control? Schmid MP et al Radiother Oncol 2011
TRUS? Transrectal ultrasonography is a low cost imaging modality is widely available has direct contact to the target volume has a reasonable soft tissue contrast allows dynamic real time imaging is already implemented in prostate cancer brachytherapy
TRUS for guidance during implantation of applicator Stock et al 1997 Int J Rad Oncol Biol Phys: TRUS feasible for the visualisation of needles allowing accurate needle placement in interstitial gynecologic brachytherapy
TRUS Prospective multicenter trial: TRUS vs. MRI vs. histology N=182 (early stage cervical cancer) High correlation (US significantly better (!!!) than MRI in assessent residual tumour and parametrial invasion (!!!)
Comparison of maximum target width between MRI, TRUS and CT for 21 consecutive patients Blinded analysis of consecutive patients at defined time points with prospective imaging protocol N= 21 Schmid MP unpublished data
GTV assessment by power doppler Provided by Anastazija Aleksandrova
BOWEL
ARTIFACTS
How TRUS could be used? Preplanning Guidance of application Target definition Treatment planning
Applicator visibility
Applicator reconstruction - all 3 views necessary!
Needles / applicator template - useful for correct identification of needles on live image, and applicator rotation, all 3 views used
Target definition
Target definition and applicator reconstruction