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Fundamentals of Contouring
eContour has partnered with the Radiation Oncology Education
Collaborative Study Group(ROECSG) to bring together contouring resources for trainees. Please do not hesitate to contact us (support@econtour.org) with questions or suggestions!
Dr. Erin Gillespie, Chief Resident at UC San Diego, eContour Co-Founder and ROECSG Member
Dr. Jill Gunther, Resident at MD Anderson Cancer Center, ROECSG Member
Grant Larson, BS, Medical Student at University of North Dakota, eContour Contributor and ROECSG Member
Neil Panjwani, BSE, Medical Student at UC San Diego, eContour Co-Founder and ROECSG Member
It is often best to start with contouring the OARs (check they are accurately delineated if a dosimetrist contoured them for you!)
GTV/CTV/ITV/PTV
start with GTV = gross tumor volume (can be primary tumor and/or lymph nodes), if present*
*NOTE: most post-op cases will not have gross tumor remaining
then contour CTV = clinical target volume
includes direct microscopic extension of primary tumor (apparent normal tissue on imaging) - can be created by an automatic expansion (aka margin, often 5-10mm), though usually "carving out" bone or air that is not at risk of tumor invasion (but this depends on tumor type)
include lymph node regions at risk
of tumor spread - sometimes called "elective" lymph node regions if no
nodes are involved with tumor in that region (called "levels" in the
H&N)
sometimes divided into multiple subdivisions (CTV1, CTV2,
etc) in order to allow differential margins for internal or physiologic
organ motion (ITV) or setup error (PTV)
lastly PTV = planning target volume
usually an automatic expansion based on predicted error in daily setup which depends on:
immobilization devices (ie H&N masks hold skull much more reliably than vac lock bag for pelvis)
extent of daily imaging (ie daily CBCT will be more exact than a weekly MV port film)
NOTE: daily setup starts with lasers and tattoos! ....then adjustments are made from imaging...
"Window/Level" the CT scan --> treatment planning systems have pre-set ranges that optimize your view based on the tissue of interest.
Select "abdomen" or "pelvis" or "mediastinum" for best soft tissue contrast (fat/muscle/vessels)
Select "bone" (highest density) to view abnormalities within the bone or skull base
Select "lung" (lowest density) to view lung parenchyma
NOTE: You can always switch between them while contouring to
determine which window/level allows you to best delineate your target.
Use your 3D views --> align your sagittal and coronal images over your contour to check your contour in all three dimensions.
Fused images - diagnostic images that have been fused to the simulation CT to help contour delineation.
MRI is most useful for differentiating different soft tissues
PET is most useful for identifying abnormal lymph nodes - be
sure to correlate with tissue on the CT scan to ensure the size of your
area of interest, since PET windowing can significantly affect the
apparent size of the tumor.
MORE: For case-specific tips, see Modules above and "Pearls" within each eContour case
Resources
Management
NCCN Clinical Practice Guidelines in Oncology (NCCN.org)
- expert consensus recommendations for work-up and management organized
by disease site including reference to studies that guide the standard
of care (FREE to register)
AP/PA = opposing radiation fields in 2D or 3D-CRT in which an one
beam treats anterior-to-posterior and a second beam treats
posterior-to-anterior in relation to the patient
BED = biologically equivalent dose --> check out "BED calc" for iPhone or "RBApp" for Android
BID = latin for "bis in die", which means twice per day; in
radiation therapy, usually in regards to two fractions separated by at
least 6 hours