Rectal Cancer: CT Localisation Flashcards
Contrast:
-oral contrast
-IV contrast
-Rectal contrast:
-Gastrograffin (20ml/L)
- visualise the internal iliac arteries
- produce systematic error in position of all organs
contrast:
-Radio-opaque marker
-post op contrast
-at anal verge
- radio-opaque marker on perineal scar
CT Scan Parameters
L2/3 to 4cm below the radio-opaque marker (anal verge) or the inferior extend of the tumour, which ever is lower
Imaging for Target Volume Delineation
-Planning CT
-Diagnostic MRI/MRI Fusion
-PET Fusion
function of MRI and PET
reduce the size of the contoured GTV
Pre-op Clinical Target Volume
RTOG consensus : CTV A
◦ Perirectal region (mesorectum)
◦ Presacral region
◦ Internal iliac region
Pre-op Clinical Target Volume
RTOG consensus : CTV B
For T4 disease involving gyn or GU structures
CTV B (External iliac region) + CTV A
Pre-op Clinical Target Volume
RTOG consensus : CTV C
tumours that extend to the anal verge, perianal skin, or lower third of the vaginal canal (Inguinal nodal region)
Post-Op CTV
Includes
◦ Surrounding safety margin beyond the mesorectum
◦ Nodal groups at risk
-Surgical clips aid in localising at risk areas of local
recurrence
Pre-op and Post-op PTV
CTV (CTV A +/- CTV B +/- CTV C) + margin= PTV
margin accounts for random and systematic errors ~ 8-10mm
Dose Pre-op:
Long course
50.4Gy in 28# , 1.8Gy
+/- Boost of 5.4Gy in 3 fractions if CRM threatened
Dose Pre-op:
short course
25Gy in 5 fractions
Dose Post-Op
50.4-54Gy in 28-30 fractions 1.8
OR
45Gy in 25# 1.8 +/- boost of 5.4-9Gy in 3/5#
Treatment Delivery:
3DCRT
SABR
-Significant acute and late effects
-re-irradiation setting
Treatment Delivery:
IMRT
-◦ Lower dose to small bowel
◦ Potential for dose escalation
