Modern Radiotherapy

DR :- Omer Hashim

Conformal &IMRT

In two-dimensional (2D) radiotherapy singlebeams from one or two directions were used. Beam setups were usually quite simple and treatment plans frequently consisted of opposed lateral fields [1, 2].

three-dimensional (3D) conformal radiation therapy is a technique where the beams of radiation used in treatment are shaped to match the tumor. Previously, radiation treatment matched the height and width of the tumor, meaning that healthy tissue was exposed to the beams.

In 3D & IMRT With the advent of CT imaging, which took into account axial Anatomical and complex tissue contours, three-dimensional conformal radiotherapy (3D-CRT) had arrived

Conformal 3D:-The technique aiming to geometrical shaping of the fields alone

IMRT :-The technique to modulate the intensity of the fluency acrossThe geometrically shaped fields

Planning steps :-

CT scanning Refer

image

Volume delineati

on

3D image Dose

analysis

Treatment QA

Positioning

Treatment delivery

1) Positioning &immobilization

This is the two most important steps in planningOf the 3D. Should be include the following :-1)Comfortable2)Reproducible3)Minimal beam attenuating 4)Affordable

Positioning

supine prone

Immobilization Frame base

Invasive

Nom invasive

Frame less

Data acquisition

CT scanning is the corner stone in the conformal RT CT scanning provides detailed cross-sectional anatomy of the

normal organs, as wellas 3D tumor information. These images provide density data for

radiation dose calculation It different from diagnosis CT in the:_1)wider borne70—85 cms 2) CT couch must be flat3) using supporting aids and immobilization devices andaligned using tattoos and midline and lateral laser

In the ct room we do after position fixation of pts specify the organ to be treated thenContrast – laser -- tech SSD or SAD then we takeCT cut 3—5 cms according to part to scanning

Volume delineation

Then referring data to the planning room and Target Volume delineation take place (contouring) common international language for describing target volumes is found in International Commission on Radiation Unit (ICRU) . Report 50 (1993), 62 (1999) and 71 (2004 )

GTV(Gross tumor volume) :-The primary tumor or other tumor mass shown by clinical examination or images

CTV (Clinical target volume) :- consist of the GTV + Margin for subclinical microscopic disease. The GTV - CTV margin depend on the site of the tumors and alsoderived from biological characteristics of the tumor in

head &neck5—10 mms. LNs CTV = 3—5 mms.PTV (Planning target volume) :- this margin for

physiological organ motion (internal margin). variations in patient positioning. alignment of treatment beams (set-up

• margin)

ITV:- additional margin CTV/GTV for physiological organ movement .OAR Organs at risk :- organs around the treated Volume that will be affected by radiation and have limited dose e.g- spinal cord .

Drawing

Usually done in planning room by doctors with Special program. Selection for the color then drown GTV – add margin to CTV – add margin to PTV . THE drown OAR

MRI

Also most drown program done for CT .MRI have the following:-Superior soft tissue resolution.Ability to assist neural and bone morrow infiltration .Ability to obtain image in any position coronal seggitallMetabolic effect of tumor – vascular effect -No radiation during scanning

Image Registration & fusion

The techniques in which two identical point in imageIs determined (CT&MRI). Then fusion of MRI &CTBenefit form MRI advantage

MRI-CT image fusion

MRI :- show soft tissue & tumor will CT :- show bone structure will

CT/MR registration

Fusing of the CT & MRI volumes,

Dose objective Total dose

Total time

Total fraction /N

Organ at risk dose

Number of beam

Beam &couch angle

planning techqunlogy

Forwardplanning inverse

planning

Virtual simulation

type of simulation in which we use the data obtain by CT . Determine of the field then beam entering Is done in simulation room but not 3D

IMRT

IMRT not depend on the shaping of the tumor Only as done by 3D but also use MLC to define the beam intensity independently in different regions of each incident beam by use of micro leaf lead to Creating of micro beam with different density

Process of IMRT

Target delineation

Treatment planning and optimization

Quality assurance

Treatment deliver

to produce the desired uniform distributionof dose, or a deliberate non-uniform dose distribution, in the target volume. Theposition of the leaves of the MLC can be varied in time with a fixed or movinggantry. IMRT can be delivered using dose compensation, multiple static fields, step-and-shoot, dynamic MLC or tomotherapy

Dynamic IMRT

Type Intensity modulation method

Segmental MLC (step and shoot) Multiple MLC segments delivered from each treatment direction

Dynamic MLC (slidingwindow)

Leaves slide across the field at different rates

Intensity-modulated arc therapy (IMAT) Leaves move while the gantry is rotating. Can require multiple rotation arcs.

Serial tomotherapy Gantry rotates around the patient with the couch fixed. Binary leaves modulate a fan beam. Upon completion of each rotation, the couch ismoved in a step-wise fashion

Helical tomotherapy Gantry and couch move synchronously. Binary leaves modulate a fan beam

Forward planning

The technology where the planner will try to variety of companion of the beam Engle .couch angle, beam weight and beam modifying to reach to the optimum dose destitution .all trial done manually Until reach to the optimum solution is reach

Inverse planning

Planning when selection of the beam, couch angle, beam weight and beam modifying to reach to the optimum dose destitution done by the computer. Inverse planning requires specification of doseprescription to GTV, PTV and PRV in terms of dose–volume constraints, fluence

The Magic Bullet“Conformality”

Prostate

Rectum

Prostate

Rectum

Prostate

Rectum

Pre-IMRT IMRT IGRT

Radiation Field •Improved Outcome•Reduced Side effects

avnatage of IMRT• Conformality• Concave shaped dose distribution

• Decreased penumbra• OAR sparing with sharp dose fall-off• Dose escalation• Lower rate of complication• Reduced cost of patient care

• Multiple simultaneous treatments• Least sensitive to physical planning

parameters• Only secondary field shaping devices-MLCs

Delineation of OARs

OAR

: parallel

series

parotids, ears, TMJs, duodenum, liver, GI

: spinal cod, brainstem, optic chiasm, nerves, lens, brain, eyes, mandible, temporal lobes

For serial organs, Planning organ at risk volume(PRV) should be delineated

9 beams

80

120

150180210

240

280

7 beams

•Depends on target shape and location

Beam Placement

• Optimum beam angles can be derived by using beam angle optimization available with TPS

Beam Angle Optimization

Planning Objectives (Constraints)

• Required by the inverse planning process – dose or dose-volume constraints for all structures• A trial and error process to come up with the proper dose

or dose-volume constraints.• Don’t ask the impossible – set realistic goals – improperly

specified constraints will result in inferior plans.• Create site-specific protocols which can be used for

similar cases.

Optimization

Definition:Systematic computerized process to generate a large number of plans rapidly and to evaluate and rank them according to some specified criteria

2D fluence profiles of various beam ports is the free treatment parameterOther parameters like beam entry angles, beam energy, the type of radiation, number of beams are decided by the planner and are fixedEach treatment field is divided into independent spatial subunits called as ‘bixels’No of bixels depend on

Size of lesion to be irradiatedChoice of resolution of the fluence mapsSelected to correlate with the width of MLC usedFor MLC width of 10mm at isocentre, bixel 10 mmX10mm

Traditional Optimization

Contour regions of interest

Define constraints and select beam parameters

Compute dose

Plan accepted

IMRT Optimization

No

Contour regions of interest

Define constraints and establish an objective function

Compute beamlet weights or beam segment shapes and weights

Optimization requirement meet

Plan acceptedNo

No

IGRT The process of frequency image (2D, 3D) before and

During course of radiotherapy .high accurateAnd Precise treatment.IGRT is use because of organ movement:-Interfraction motionIntrafraction motion – Reduce severity and risk of therapy-induced

complications.– Increase both quality and probability of success.

RT Targeting Uncertainty in RT plan • Setup Variation• Internal Organ Displacement• Volume Change and

et up error :-Patient position out of plan –wt loss Un voluntary movement as reparation –patient

discomfort –boil gas motionOrgan motion :-bladder rectum filling . Intra abd-

pressure

IGRT

USG

BETSonoarray

I-beamResitu

Video based

Align RTPhotogrammetryReal 2 video G

IMRTVideo subtraction

Planner xray

KV xray OBI

Gantry mounted Room mounted

CT

Fan beam Cone beam

MRI

Mv CT KV CTSiemens Mobile CT arm

Varian OBI

Eelekta

Siemens inline