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Contouring rectal cancers

Learning to contour rectal cancer patient image sets for radiotherapy planning

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Contouring rectal cancers

  1. 1. CONTOURING FOR RECTAL CANCERS Dr. Ashutosh Mukherji Additional Professor Department of Radiotherapy, Regional Cancer Centre, JIPMER
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  6. 6. 6 Importance of Depth of invasion Kikuchi R, Dis Colon Rectum, 1995 (12):1286-95
  7. 7. Role of imaging in early lesions • Confirm that muscularis propria thickness is preserved • Identify sites of disease within the mesorectum • Final decision regarding appropriateness of local excision is driven by Histopathology assessment of risk factors of the excised lesion 7
  8. 8. • Location of tumour – anterior, posterior, r or l lateral • Morphology: annular, semi annular, polypoidal, ulcerating, mucinous, villous • For annular/ulcerating – location of central invasive portion vs raised edges • For polypoidal/villous lesions – site of stalk • Invasive margin: nodular infiltrating, broad based pushing margin 8 • Submucosa visible at invasive edge? – T1 • Submucosa not visible at invasive edge but good thickness of muscularis propria visible? T1 (sm3)/early T2 • Part of muscularis propria visible? = T2 • No muscularis propria visible but intermediate signal intensity does not project beyond contour of bowel = T2 full thickness/T3a • Tumour projecting beyond muscularis propria = T3
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  10. 10. 10 Finding the nodes
  11. 11. How MR Imaging helps in contouring rectal cancers • To assess bulky polyps >5mm thick • Initial assessment of disease remote from the lumen within entire mesorectum • Identification of pelvic sidewall disease • Identify site location of stalk or invasive border and relationship to puborectalis sling, peritoneal reflection, mesorectal or intersphincteric border • Identification of high risk patients with extramural venous invasion 11
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  13. 13. Rectal Cancer Radiotherapy Contouring Guideline for clinical target volumes (CTV) for neoadjuvant chemoradiotherapy in locally advanced rectal cancer: gross tumor, peri-rectal, pre-sacral, internal iliac and external iliac. NTUH practice: • GTV: main tumor mass + involved lymph nodes • CTV: – GTV with 15 mm expansion – Distal 20 mm margin to GTV for CTV – Vessels with 7 mm expansion – Contour CTV to include mesorectum and pre-sacrum – Avoid bone and small bowel Int J Radiat Oncol Biol Phys. 2009 Jul 1;74(3):824-30. doi: 10.1016/j.ijrobp.2008.08.070.
  14. 14. RTOG CONSENSUS PANEL RECOMMENDATIONS • Risk volumes defined as CTVs: these were local and nodal. • Local CTV included mesorectum, presacrum, scar tissue and anastomosis. • Nodal CTV included perirectal, iliac (external and internal) and inguinal. • Nodal CTVs: – CTVA: internal iliac, presacral and peri-rectal – CTVB: external iliac – CTVC: inguinal 14 https://www.rtog.org/CoreLab/ContouringAtlases/Anorectal.aspx; Myerson et al. IJROBP 2009
  15. 15. International consensus guidelines on Clinical Target Volume delineation in rectal cancer • Consensus was obtained for delineation of the CTV for elective irradiation of all regional lymph node levels. • Seven subsites at risk were identified: presacral space (PS), mesorectum (M), lateral lymph nodes (LLN), external iliac nodes (EIN), inguinal nodes (IN), ischiorectal fossa (IRF) and sphincter complex (SC). 15 Radiotherapy and Oncology 120 (2016) 195–201 http://dx.doi.org/10.1016/j.radonc.2016.07.017
  16. 16. IMMOBILIZATION DEVICES • BELLY BOARD
  17. 17. Schematic presentation of belly board surface • Belly board : in region of pelvis, the board has raised surface …. To separate pelvic and abdominal structures • Abdominal area has depression : to accommodate the bowel loops……so that the intestines do not displace pelvic structures.
  18. 18. Simulation Protocol • Full bladder • Prone on bowel displacement device (if can do daily OBI or equivalent) • Anal marker & wire on distal edge of tumor if possible • IV & oral contrast • 2.5 to 5 mm CT slices 18
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  20. 20. 20 Contouring the GTV • Scroll through slices to view extent of tumor. • Start your contour where the tumor is obvious • Check your volume against exam / colonoscopy findings since imaging is less sensitive
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  22. 22. Lowest boundary of GTV 22
  23. 23. 23 Measure the distance from the GTV to anal verge
  24. 24. 24 In the SAGITTAL view, use the measuring tool to check the vertical extent of the GTV contour.
  25. 25. Differentiating a lymph node from a vessel 1. Use MRI overlay 2. Scroll up and down: nodes will be rounded structures that disappear then reappear 3. Contour the vessels before contouring the GTV 4. Sub-centimeter perirectal nodes are contoured in the GTV to show you they are in the standard CTV. These DO NOT need to be contoured unless grossly enlarged. 25
  26. 26. 26 Enlarged perirectal lymph node
  27. 27. • Now turn off ALL contours • Start at abdominal aorta • Scroll inferiorly, following branches • Lymph nodes sit on vessels. This is why we contour vessels in nodal CTV • Sequence of vessels: – Aorta (artery) or IVC (vein)  Common Iliacs (R and L)  Internal iliac (go posterior/in front of sacrum) and External Iliacs (go anterior  become inguinal/femoral when exit pelvis) 27 Review anatomy of pelvic vessels
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  31. 31. • Lymph node metastasis 31
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  33. 33. • Lymph node metastasis, bifurcation of iliacs 33
  34. 34. • Common iliacs 34
  35. 35. What is the CTV? 35 This is the RTOG 2009 Consensus Recommendation
  36. 36. Caudal (inferior) extent of CTV (Muscles and connective tissue of pelvic floor are better visualized with MRI) 1. CTV should extend at least to the pelvic floor, even if upper rectal cancer 2. Extend to a minimum of 2cm caudad to GTV 36 Mesorectum (peri-rectal) Pelvic floor, Levator ani
  37. 37. • Lower boundary of CTV 37
  38. 38. CTV in the lower pelvis 38 Posterior and lateral margins: Extend to lateral pelvic muscles or bone Anterior margin: Extend into prostate/seminal vesicles in a male (vagina for female)
  39. 39. CTV IN Lower Pelvis 39
  40. 40. CTV in Mid-pelvis 40 CTVA covers: Rectum, Mesorectum, Internal iliac vessels, Presacral space Mesorectum Presacral space Anterior margin: Extends 1 cm into Posterior bladder wall
  41. 41. CTV IN Mid-Pelvis 41
  42. 42. CTV in Upper-pelvis 42 DO NOT include muscle or boneInclude internal iliac arteries and veins; posterior border of CTV abuts external iliac vessels (which we do NOT include unless T4 tumor invading prostate or vaginal anteriorly) Presacral space Lymph Nodes
  43. 43. Superior Extent of CTV 43 Continue contour up to where the common iliacs bifurcate OR L5/S1 interspace
  44. 44. CTV IN Upper Pelvis 44
  45. 45. Designation of regions at risk of recurrence and their contouring • The International working group identified following subsites for risk of nodal recurrence: – Presacral nodes (PN), – Mesorectum (M), – Lateral lymph nodes (LLN), – External iliac nodes (EIN), – Ischio-rectal fossa (IRF), – Sphincter complex (SC), – Inguinal Nodes (IN) 45
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  49. 49. 49 Anterior border of the posterior lateral node (purple), when the ureters join the bladder (red line)
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  52. 52. 52 Caudal border of the external iliac nodes (orange), where the deep circumflex vein crosses the external iliac artery
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  55. 55. 55 Cranial border of the ischio-rectal fossa (blue), where the inferior pudendal artery leaves the pelvis going into the Alcock’s canal
  56. 56. 56 Caudal border of the ischio-rectal fossa (blue), at the inferior level of the sphincter complex and the ischial tuberosity
  57. 57. 57 Elective subsites to be included in CTV according to stage and tumour location Mesorectum; PS = Pre-sacral space; LLN = Lateral lymph nodes
  58. 58. 58 EIN=External iliac nodes; IRF = Ischio-rectal fossa; SC = Sphincter complex Elective subsites to be included in CTV according to stage and tumour location
  59. 59. When a CTV Boost is required 59 Extend CTV to cover entire mesorectum and presacral region at level of GTV, with a minimum 2cm margin on GTV in the cephalad and caudad directions Add a margin of 7-10 mm for PTV to the various CTVs
  60. 60. PTV from the CTV 60 Add a margin of 7-10 mm for PTV to the various CTVs
  61. 61. 61 SAGITTAL VIEW CORONAL VIEW Always check final volumes in sagittal and coronal views to make that the contoured volume makes sense in 3 dimensions
  62. 62. 62 DOSE CONSTRAINTS
  63. 63. Pre-operative vs. Post-operative Therapy • Approach 1 – Post-operative radiation – Surgical resection – If T3/4 and/or N1/2  post-operative chemoradiation  chemotherapy • Approach 2 – Pre-operative radiation – U/S / MRI T3/4 cancer or clinical T4 – Pre-operative therapy  surgery  chemotherapy 63
  64. 64. 64 Effect of Field Volume: Short course versus Long Course RT
  65. 65. • Pre-operative radiotherapy has generally been better tolerated than postoperative. This was also seen in the single trial comparing pre- and postoperative radiotherapy. • In all pre-operative trials irrespective of whether conventional fractions of about 2 Gy or high fractions of 5 Gy were used, more perineal complications after an abdominoperineal resection were seen in irradiated patients • Increased risk of postoperative ileus has been seen in trials irradiating large volumes of small bowel, either pre-op or postop but not when smaller volumes were irradiated 65
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  68. 68. Post-operative Therapy: Who needs treatment? • T3 or greater Or N+ Gunderson LL, et al. JCO 2004;22:1785-96 68
  69. 69. • Low-risk patients (LRR <10%) are recommended TME alone, • intermediate-risk patients (LRR 10%–20%) are advised preoperative SCRT followed by TME and adjuvant chemotherapy as standard treatment, • high-risk patients (LRR >20%) are recommended preoperative CRT followed by TME and adjuvant chemotherapy. 69
  70. 70. TAKE HOME MESSAGE
  71. 71. Contouring guideline  GTV: main tumor mass + involved lymph nodes  CTV: – GTV with 15 mm expansion – Distal 20 mm margin to GTV for CTV – Vessels with 7 mm expansion – Contour CTV to include mesorectum, lateral nodes, External and internal iliac nodes, pre-sacrum, ischiorectal fossa, sphincter complex and inguinal nodes where required – Avoid bone and small bowel – Boost CTV where required with a minimum 2cm margin on GTV in the cephalad and caudad directions  PTV: 7-10 mm margin to the CTV 71
  72. 72. According to Roel’s: • The CTV should encompass the tumor, the MS, and the PPS in all cases. The Inferior pelvis is at risk if the tumor is located within 6 cm from the anal margin and the surgeon aims at a sphincter-saving procedure, or the tumor invades the anal sphincter and an APR is necessary. • MLN and the LLN are included into the CTV for all patients. • The obturator nodes should be included when the tumor is located <10 cm from the anal margin. • The External iliac LN should be part of the CTV only when anterior organ involvement is highly suspected • Inguinal LN should be part of the CTV only when the tumor invades the lower third of the vagina or there is major tumor extension into the internal and external anal sphincter. 72
  73. 73. Pertinent articles for reference 73
  74. 74. Thank you

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