Cervix Delineation
Cervix Delineation
Cervix Delineation
Cervix
Target Volume
delineation
For definitive treatment of carcinoma cervix with conformal radiation
techniques, accurate target delineation is vitally important,
Various guidelines for CTV delineation are published in the literature yet a
consensus definition of clinical target volume (CTV) remains variable
Clinical judgement remains the most important aspect of determining the
target volumes
Contourin
g contouring guidelines available for CTV
Several
Taylor et al pelvic nodal delineation (CT based)
Toita et al for CTV delineation in intact cervix EBRT (CT based)
Lim et al for CTV delineation in intact cervix IMRT (MRI based)
Small et al for CTV delineation in post operative IMRT (CT based)
PGI literature review & guidelines for delineation of CTV for intact carcinoma cervix (CT based)
CTV
CTV Pelvic Nodes:
o Obturator, internal and external and common iliac nodes up to the bifurcation of the aorta using blood vessels as a
surrogate with a 7 mm margin modified.
o
CTV Tumour:
o Gross tumour, uterus and parametrium and upper third of vagina (unless there is involvement by disease, in which case a 2
cm margin below apparent disease should be used). Consider inclusion of proximal half of utero-sacral ligaments. Cervix
and uterus can be outlined as a separate volume from parametruim and upper vagina unless the INTERLACE guidelines are
being followed.
PTV
PTV Nodes = CTV Pelvic Nodes + 7- 8mm
PTV parametrium and upper vagina = CTV Tumour + 7mm
PTV cervix and uterus lateral margins 7mm. Sup/Inf and Ant/Post 12-18mm
However, there is an alternative by INTERLACE guidelines which produce PTV1, PTV2, and PTV3 as per table below:
2
Clinical Target Volume 1 CTV1 should include the whole cervical tumour
(CTV1) and its local extension (GTV). Also, the cervix and uterus.
Planning guidelines and expansions from INTERLACE trial
Clinical Target Volume 2 Proximal half of the uterosacral ligament,
(CTV2) bilateral parametria and upper half of the vagina, or 2 cm below known vaginal disease.
If there is uterosacral involvement, the entire ligament needs to be encompassed.
The external iliac, obturator, internal iliac and common iliac nodes are also included in
this volume. The superior extent is at the aortic bifurcation. The nodal areas are defined
by using a 7mm around blood vessels. It should be extended to include visible disease
and lymphoceles.
It should be modified to exclude bone, psoas muscle, bladder and bowel. The subaortic
presacral nodes can be covered by connecting the nodal areas either side of S1 and S2
with a 10 mm strip volume.
Where nodes at the aortic bifurcation or at the level of the common iliac vessels are
positive (histology/CT PET /> 15mm on imaging) the most superior extent of CTV3 will
be at the renal hilum. In general, a margin of at least 2cm should be added above the
highest involved lymph node region.
3
Normal Tissue Delineation
(RTOG)
• Bowel: The small and large bowel can be contoured together as a Bowel-Bag.
• Inferiorly, the bowel bag should begin with the first small or large bowel loop or
above the ano-rectum, whichever is most inferior.
• The contours should end 1 cm. above the PTV .
• Ano-Rectum: Ano-Rectum should be contoured from the level of the anus to the
sigmoid flexure. It should extend from the anal verge (marked by a radiopaque marker
at simulation) to superiorly where it loses its round shape in the axial plane and
connects anteriorly with the sigmoid.
• Bladder: Contoured inferiorly from its base, and superiorly to the dome.
• Femoral Heads:The ball of the femur, trochanters, and proximal shaft to the level
of the bottom of ischial tuberosities
Gay HA, Barthold HJ, O′Meara E, Bosch WR, El Naqa I, Al-Lozi R, et al. Pelvic normal tissue contouring guidelines
for radiation therapy: A Radiation Therapy Oncology Group consensus panel atlas. Int J Radiat Oncol Biol Phys
2012;83:e353-62.
Problems with contouring for gynaec
cancer
on CT images
• The GTV itself may/ may not be well seen
• The parametrial disease is usually not visualized
• Though pelvic nodal contouring is systematic, but we still tend to end up
replicating the traditional cranio-caudal boundaries of a 4-field box
• MR based guidelines are difficult to implement on CT
• It is expensive to do routine MR-based planning
• Problems with the availability of MR-based TPS