CT scan in Radiotherapy Planning · accurately reproduce treatment conditions. Wide aperture (e.g.,...
Transcript of CT scan in Radiotherapy Planning · accurately reproduce treatment conditions. Wide aperture (e.g.,...
CT scan in
Radiotherapy
Planning
Ashraf Hamed Hassouna
Professor of Radiation Oncology
NCI, Cairo University
Contents
Introduction
CT in RT planning
CT in IGRT
CT in ART
Role of CT scan in RT planning & Treatment:
Patient contour.
Delineation of target volumes.
Delineation of OARs.
CT index and dose calculation.
RT plan evaluation and optimization.
Adaptive RT (ART).
Image Guided RT (IGRT).
Simulation
CT Simulator
Immobilization
(1) Sidewall containing oblique and horizontal copper wires for CT-based measurement
of longitudinal stereotactic coordinate. (2) Longitudinal stereotactic scale. (3)
Stereotactic arc for lateral and AP coordinates. (4) Arc and scaled screw for diaphragm
control. (5) Level control. (6,7) SBF attached laser system (leg and trunk) for assistance
at patient repositioning. (8) Vacuum pillow.
ELEKTA stereotactic body frame (SBF)
Stereotactic body frame
CT number or Hounsfield units
The density of a structure is represented by CT
number or Hounsfield units (HU).
HU range from +1000 (bright white) to −1000
(dark black).
Dense bone (+1000), water (0), air (−1000).
CT Simulator vs Conventional Simulator
Image patient anatomy and gross tumor,
slice by slice. These data can be processed
to view images in any plane or in 3D.
CT numbers can be correlated with tissue
density, allowing heterogeneity corrections
in treatment planning.
CT Simulator vs Conventional CT
Accessories (e.g., flat table, laser light for positioning,
immobilization, and image registration devices, etc.):
accurately reproduce treatment conditions.
Wide aperture (e.g., 80 cm diameter): provide flexibility in
patient positioning for a variety of treatment setups.
CT image data set, with precise localization of patient
anatomy and tissue density information, is not only useful in
generating an accurate treatment plan but also providing a
reference for setting up treatment plan parameters.
Image fusion with CT
MRI
PET
Angiography
Others
Good CT Simulation
Positioning and fixation.
Complete patient contour.
Upper and lower tissue margin.
Contrast.
CT slice thickness.
Artifacts.
CT Simulation can be used for:
2D
3DCRT
IMRT
SRS and SBRT
Brachytherapy
Bone Metastases
Brain Metastases
Breast Cancer
Wh
ole
Bre
ast
• CTV: based on wired breast tissue, limited 5 mm from skin and ant to pectoralis.
• PTVeval: CTV + 7mm, excluding heart, taken 5 mm from skin and ant to ribs/lung (include pectoralis).
Lum
pec
tom
y
• GTV: seroma and clips.
• CTV: GTV + 1 cm, excluding pectoralis and taken 5 mm from skin.
• PTVeval: CTV + 7mm, excluding pectoralis, lung and taken 5 mm from skin.
Accelerated Partial Breast
Irradiation
EBRT
APBI
Multicatheter Interstitial Brachytherapy
Mammosite
34Gy/10f/5d at 1 cm depth
Brain Tumors
Head & Neck Tumors
LN Contouring
2D
IMRT
Cancer Cervix
CRT
IMRT
IMRT
Brachytherapy
CT
artifacts
Fletcher-Suit-Delclos-style Applicator Set
CT & MR Compatible
SBRT
Axial slice of HCC SBRT plan showing a conformal isodose distribution. The red and
blue solid lines represent GTV and PTV. The HCC was treated with 42 Gy in six
fractions (pink line), which tightly surrounds the PTV, with a rapid dose falloff.
Typical RT plan with GTV and PTV delineated
by red and blue lines respectively
33Gy/6F
HCC with PVT
45Gy/5F
Recurrent HCC
after TACE
Image Guided RadioTherapy
(IGRT)
Portal Imaging
DRR EPI
CBCT
Adaptive RadioTherapy
(ART)
LN metastasis from NPC on CT before
RT
After 36 Gy/18 f LN shifted 1 cm medially
(body weight loss and tumor shrinkage)
Dose distributions on CT-1
and the same plan
transferred onto CT-2. Most
of both parotid glands is
included in the 70 % dose
level (blue color).
Shrinkage of the neck
diameter and the LN is
evident on CT-2 obtained
after 38Gy/19f for NPC
patient.
CT-1 CT-2