modern radiotherapy
TRANSCRIPT
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