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Appendix C

Appendix C. Gynaecological Module. Disclaimer. This learning module was created as starting point for each cancer centre to implement as part of IGRT Education in their radiation department. The material included may not be suitable in every clinical environment.

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Appendix C

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  1. Appendix C Gynaecological Module

  2. Disclaimer • This learning module was created as starting point for each cancer centre to implement as part of IGRT Education in their radiation department. • The material included may not be suitable in every clinical environment. • This module is designed to be adjusted to include your centre’s site specific policies and procedures. • This material was developed by members of the Radiation Therapy Community of Practice – IGRT Education Group.

  3. Introduction • This module has been created to provide an overview of the anatomy, machine parameters, matching considerations & trouble shooting in regards to gynaecological IGRT • IGRT is a method used on treatment units to improve the delivery of IMRT & Rapid Arc plans • Allows better targeting of the tumour location while avoiding nearby healthy tissue immediately prior to radiation treatment each day

  4. Cross Sectional Anatomy • Bladder* • Rectum • Small Bowel* • Common Iliac Nodes • External/Internal Iliac Nodes • Pre-sacral Nodes • Ilium (ASIS, Iliac Crest, Pelvic Brim) • Ischium • Obturator Foramen • L1-L5 • Sacrum • Sacroiliac Joint • Coccyx • Pubic Symphysis • Acetabulum • Femur • Uterus (Fundus, Body & Isthmus)* • Cervix* • Ovaries* • Endometrium* • Myometrium • Vagina* * Regions of Interest

  5. Varian kV imaging CBCT Elekta kV imaging CBCT Machine Parameters

  6. Machine Parameters - Varian • kV/kV matching • Orthogonal images taken using kV imager • CBCT matching • Full scan vs. half scan, using kV source & detector • Bowtie filter kV source kV detector EPI

  7. kV Imaging - Varian • Daily kV/kV orthogonal imaging: • May be used in conjunction with CBCT (depending on centre protocols) • 2D/2D matching can be done using the dynamic or optimized filter to best view the anatomy • Manual or Auto Match to bony anatomy

  8. CBCT Imaging - Varian • Daily CBCT imaging: • May be used in conjunction with kV/kV matching (depending on centre protocols) • 3D Match is used, a half scan or full scan can be used depending on what anatomy needs to be visualized • Matching to bony anatomy (centre specific)

  9. CBCT Imaging Parameters - Varian • The following are CBCT preset options used for pelvis scans: • Pelvis: • Half fan • Full 360º scan • Pelvis Spotlight: • Full fan • Half scan (22º→178Eº or 178Eº → 22º) • Depending on the centre, a manual or automatch (usually to bony anatomy) with a clipbox can be done

  10. Clipbox - Varian • A clipbox can be used for an automatch to outline the area of interest that will be matched. The settings for the clipbox will be centre specific. The following example is an auto-match to bony anatomy, setting the clipbox around the pelvic bones in all 3 dimensions

  11. CBCT Imaging Parameters - Varian • The type of CBCT scan used will vary from centre to centre depending on the anatomy that needs to be visualized. A full scan of the pelvis will produce better visualization of any peripheral structures, while a half scan captures a smaller area of interest and has a ring artefact peripherally. Half scan (full bowtie) vs. Full scan (half bowtie: Gyne (same patient), note the ring artefact on the left diagram caused by the steep dose gradient from the x-ray beam going through two areas on the filter vs. the better visualization of peripheral structures and patient contour in the full scan on the right.

  12. Machine Parameters- Elekta KV/KV matching • Orthogonal images taken using KV imager CBCT matching • Full Scan vs Half Scan, using KV source & detector • 1 minute scans or 2 minute scans can be used depending on gantry speed • Various filters and collimators can be used.

  13. kV Imaging - Elekta • Daily kV/kV orthogonal imaging: • May be used in conjunction with CBCT (depending on centre protocols) • 2D/2D matching can be done using template matching with Elekta’s iView software and other programs such as MOSAIQ. • Programs may offer manual and automatic matches • kV matching is limited to bony anatomy

  14. CBCT Imaging - Elekta • Daily CBCT imaging: • May be used in conjunction with kV/kV matching (depending on the centre protocols) • 3D match is used with a half scan or full scan, depending on what anatomy needs to be visualized. • Full scans allow for improved image quality for soft tissue definition. Gantry speed can be increased (1 minute vs. 2 minutes) to reduce dose to patient and time required to scan patient • Matching to bony anatomy or soft tissue (centre specific)

  15. CBCT Imaging Parameters-Elekta Filters • F0: no filter • F1: bowtie filter (decreases dose to patient) • Centre-specific

  16. CBCT Imaging Parameters-Elekta • Collimators: determine the Field of View (FOV) and axial field length to be scanned • FOV: small (S), medium (M), large (L) • Panel positioning depends on FOV chosen • Lengths: machine specific: 10, 15 or 20 represent lengths of 10cm, 15cm, 20cm

  17. CBCT Imaging Parameters-Elekta • XVI requires users to create a 1) Clipbox: to define the 3D volume to be registered. This can be around the spine or another area of interest. 2) Correction reference point 3) Alignment method: Bone or Grey Value

  18. Matching Considerations • Organs at Risk: • Small Bowel • Rectum • Bladder • Priorities & Special Considerations (centre/case specific) • Bony match to bony anatomy (CBCT or kV/kV) • Soft tissue specifications covered by specific isodose lines

  19. Matching Considerations • CBCT matching: soft tissue and/or bony match • Auto or manual match to bony anatomy can be done • Window levels can be set to bone of soft tissue depending on what needs to be visualized • An auto match can also measure the rotation of the patient which can be useful when matching • Isodose lines can be visualized to check proximity to OARs • Contours can be visualized on CBCT (i.e. to ensure the target is within the PTV contour) • Any changes in patient anatomy/target volume can be seen and reported

  20. Matching Considerations • kV image matching: bony match only • A bony match to the pelvic bones can be performed if CBCT is not an option • To assess the match, the following structures can be used: • Superiorly/Inferiorly: L5/S1, iliac crests, pelvic brim • Anteriorly/Posteriorly: sacrum, pubic bone • Laterally: SI joint, pelvic brim, symphysis pubis

  21. Trouble Shooting • Common issues imaging gynaecological patients: • Empty bladder (if full bladder required) • Variation of rectal filling • Target volume not covered by specific isodose line • Pelvic Tilt

  22. Empty Bladder(Full bladder required) • A full bladder is typically required to decrease bladder toxicities as well as reduce dose to small bowel • With gynaecological patients, if they have had surgery, sometimes it can be difficult to hold a full bladder for treatment • The case on the right, demonstrates a patient towards the end of her treatment having difficulty holding a full bladder • RO was consulted and ok to continue with treatment with satisfactory bladder filling • Patient discontinued her last week of treatment (and last brachytherapy fraction) due to severe cystitis

  23. Rectal Filling • Rectal filling can vary day to day and may differ significantly from the CT simulation scan. • This can affect PTV coverage • Centres may set limitations for rectal diameter at the time of CT simulation

  24. Variation of Rectal Fullness • This patient’s rectum was larger at the time of CT simulation which created challenges for PTV coverage when the rectum was smaller on treatment days.

  25. Target Volume Coverage • Isodose lines can be converted into contours to ensure coverage of a specific target volume (or avoidance) • The case on the right demonstrates how bladder fullness affected the position of the patient’s uterus. If not full enough, the uterus fell anteriorly and outside of the 90% isodose line. • In this case, the patient was taken off the couch to fill her bladder more

  26. Pelvic Tilt • A pelvic rotation is another common problem with pelvis set-ups • Shown in this case, the sacrum and pubic bone could not be properly aligned on the right lateral image & the ischial tuberosities were not matching with the pelvic brim on the AP image • Therapists in this case repositioned the patient shifting the pubic bone in an anterior/superior direction

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