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