Technological Advances in Radiotherapy€¦ · 1. High precision & sophisticated treatment planning...
Transcript of Technological Advances in Radiotherapy€¦ · 1. High precision & sophisticated treatment planning...
Technological Advances in Radiotherapy
Samuel ChiuDepartment of Clinical Oncology
Prince of Wales HospitalHong Kong
HA Convention
May 2007
Discovery of X ray1895• German Physics Professor
Wilhem Conrad Roentgen discovered X ray when he noticed that only the bones of his hand was shown on the fluorescent screen placed at the path of a beam produced by the Crooke’s tube
1901• Get the Nobel Prize
The beginning of Radiotherapy
1904• Thomas Edison’s assistant died of
repeated exposure to x rays causing severe burns with several amputations
• Noticed the harmful effects of x rays and marks the beginning of the potential use of x rays in radiotherapy
Development of Radiotherapy Machines
Early half of twentieth century
• Orthovoltage machines • low energy (200-300kv) x-rays
machines for treatment of cancer
• Low penetration• High toxicities
Development of Radiotherapy Machines
1951-The first high energy Cobalt 60 machines
• gamma rays, high energy.
• Deep penetration• Allows more widely
use of x rays in treatment of cancers
Development of Radiotherapy Machines
1970’s• Development of Linear
accelerators • accelerate electrons,
then slow them down through their collision with a metal target, causing high energy x-rays to be released
• Marks the beginning of technological development of teletherapy and widely use of external beam irradiation in treatment of cancers
Two dimensional radiotherapy in 80’s
Two dimensional RTTwo fields Three fields
HIGH DOSE to SURROUNDING NORMAL TISSUE
HIGH TOXICITIES LIMITING RADIATION DOSE
RT late toxicityBrain as an example
• Focal injury Necrosis (related to the high dose region)– Optic neuropathy– Pituitary dysfunction
• Neuropsychologic/cognitive (related to the whole brain dose)– Volume, fraction, size dose, age
dependent
How to decrease late toxicities
• Focal injury (Better Conformity to decrease volume and dose to critical organs)
• Neuropsychologic/cognitive (Increase conformity and number of beams to decrease volume of high dose zone)
Three dimensional Conformal Radiotherapy
(3DCRT)
Computer Planning
CT scan
MultileafCollimator
PWH RTPWH RT
ImmobilisationDevice
3 dimensional conformal RT (3DCRT) – 90’s
•Imaged guided target localisation•Computer 3D planning•Multiple beams•High conformity•Spare surrounding critical organs•Less dose to surrounding brain
2DCRT 3DCRT
High conformity decrease risk of focal injuries
Decrease high dose volume
Decrease cognitive impact
3-DCRTConventional 2-D
3D CRT treatment Dosimetric advantage over 2D
LimitationSuboptimal for irregular Targets (Concave shape)
Brainstem
60Gy Tumour
50Gy Chiasm
54Gy brainstem
3DCRT cannot produce an isodose distribution to exactly to what we want ?
70Gy Highly proliferativetumour
Limitation
The planner starts with a set of beam weights and profiles to obtain a plan by trial-and-error process.
3DCRT - Conventional (Forward) Planning
Based on two new principles:
1. Inverse treatment planning
2. Intensity modulated treatment beams
Intensity Modulated Radiotherapy (IMRT)
•The planner define the required dose & dose distribution
•The computer can calculate and optimized the beam intensity patterns of the individual IMRT beams.
Principle of Inverse Planning
70Gy to tumor
54Gy to Brainstem
90Gy to visible tumour by imaging
81Gy to subclinicaldisease
60Gy to urethra to prevent stenosis
Intensity modulated radiotherapy (IMRT)-the use of optimised multiple non uniform radiation beam intensities with multiple small beamlets
IMRTDynamic Multileaf Collimator
Methods of IMRT Treatment Delivery
3-DCRT IMRTConventional 2-D
IMRT Dosimetric advantage over 2D and 3D CRT treatment
High conformity
IMRT Dosimetric AdvantageNon uniform dose
Higher dose to Tumor
Lower dose to subclinical diseae
Potential Benefits of IMRT
1 Deliver treatments with better dose conformity and coverage to the target,hence reducing the probability of in-field recurrence.
2 Better sparing and protection of normal tissue, hence minimise the degree of morbidity associated with treatment.
3 Facilitating the escalation of dose to improve local control.
Gy
2DRT IMRT
Gy 1. 2D-Ho’s2. 3DCRT3. IMRT
Cumulative Dose Volume HistogramStructure :Rt Parotid
Parotid Gland
Kam et al, Asco 2006
Clinical Oncology, PWH
Parotid Sparing
RTOG/EORTC Xerostomia Grade
Grade ≧2 (%) Chi-Square
2DRT IMRT p-value
6 week 85.7 46.4 0.0019
6 month 92.9 75 0.0689
1 year 82.1 39.3 0.0010
85.7
46.4
92.9
7582.1
39.3
0102030405060708090
100
Xer
osto
mia
Gra
de ≧
2(%
)
6 week 6 month 1yearTime after RT
2DRTIMRT
Dose Escalation For Ca prostate
Decrease in biochemical failure with increase dose
Decrease Grade 2 rectal complications using IMRT
Alan Pollack et al.
World J Urol (2003)
Problems & Challenges - IMRT
1. High precision & sophisticated treatment planning procedures
2. High cost 3. Radiation safety- higher x ray exposure 4. Higher integral dose- Increases the probability
of radiation induced secondary cancer in the irradiated volumes.
5. The effect of geometrical errors on treatment dosimetry is more serious then conventional treatments.
Geometric Errors in RadiotherapyInter-fraction treatment errors1 Set up errors2 Organ positional changes3 Integrity of immobilization cast4 Changes in patient physical conditions 5 Machine errors
Intra-fraction treatment errors 1 Patient movement2 Organ movement caused by e.g. breathing
Conventional setup only relies on laser to line up surface markers on skin/cast disregard the positions of internal organs and the targetInter-fraction treatment errors
Better Immobilization DeviceHelp to decrease setup errors but not the ultimate solution
PWH RTPWH RT
Irradiated VolumeTreated Volume
PTV
ITV
CTV
GTV
ICRU Report 50 & 62
Internal margin
Setup margin
Penumbra
Geometrical Uncertainties
Definition of Target Volumes Definition of Critical Normal Structures
OAR
PRV
Image-Guided Radiation Therapy (IGRT)
What is IGRT?
• Measure and correct target and critical structure positional errors immediately prior to or duringtreatment delivery
• To reduce ITV and / or Setup inaccuracy thus decrease RT related toxicity and allow tumourdose escalation
IGRT
• Positioning of patient based on internal bone landmark or implanted marker using X rays
IGRT – Acquisition of CT scan images
Allow reconstruction of images in different planes
IGRT
1st set of X ray images
2nd set of X ray images
IGRT
•Fusion of x ray images to the digitally reconstructed images from planning CT
•Patient aligned to correct position based on bony landmarks/implanted markers
IGRTPositioning of patient based on internal bone landmark or
implanted marker using X rays
Courtesy of BrainLab
IGRT
Positioning of patient with CT guided
Helical Tomotherapy
LINAC and CT Scan in the same machine
Multileafcollimator with IMRT
No limitation on field size and field matching
On-line treatment verification by matching of the planning CT image (bottom left) with the tomotherapy treatment set up image (top left) immediately before treatment delivery without moving the patient.
TomotherapyCT image guided treatment delivery
Courtesy of Peter Teo, HKS & Hospital
Intra-fraction Errors
Tumour moves with respiration. Range: 0.5 ~3cm
Convention RT: Need extra margin for tumour motion – Internal Target Volume (ITV)
What is IGRT?
• Measure and correct target and critical structure positional errors immediately prior to or duringtreatment delivery
• To reduce ITV and / or Setup inaccuracy thus decrease RT related toxicity and allow tumourdose escalation
Respiratory Gated RT: Less extra margin for tumour motion – Decreased ITV
IGRT Equipments – PWH – Respiratory Gating
• Real-time Positioning Management (RPM) system (Varian)
• 4D-CT
• Respiratory Gated RT
Gating of radiotherapy treatment beams by respiratory motion waveform to compensate for target movement
Beam On
Beam On Window
Beam off
Breathing signal
Liver Volume: 1010 cm3
GTV= 119 cm3
Liver Volume: 1010 cm3
GTV= 119 cm3
PTV = 684 cm3
without Gating Txmargins: SI=2.5cm, circumferential=1.5cm
Liver Volume: 1010 cm3
GTV= 119 cm3
PTV = 684 cm3
without Gating Txmargins: SI=2.5cm, circumferential=1.5cm
PTV = 286 cm3
with Gating Txmargins: 0.75cm for all
Liver Volume: 1010 cm3
GTV= 119 cm3
PTV = 684 cm3
without Gating Txmargins: SI=2.5cm, circumferential=1.5cm
PTV = 286 cm3
with Gating Txmargins: 0.75cm for all
PTV VolumeReduction: 58%
Gating of respiratory motionExternal infrared markers and internal implanted markers
Courtesy of BrainLab
REAL-TIME tumor-tracking - CyberknifeCorrect for respiratory tumor motion
Robot motion is steered by external fiducial motion
Internal tumor motionX-ray images
The Synchrony™ Respiratory Tracking SystemBuilding the correspondence model
Implanted gold seeds
External fiducial motionInfrared LED-camera system
The Synchrony™ Respiratory Tracking System
Building the correspondence model
The Synchrony™ Respiratory Tracking System
Robot follows internal fiducials using a correspondence modelbetweenmeasured internal fiducial motion (implanted gold markers)
andmeasured external fiducial motion (LEDs)Correspondence model is build prior to the start of treatmentCorrespondence model is verified and updated during the treatment
LED position
Inte
rnal
fidu
cial
x,y,
z (m
m)
Correspondencemodel
Surgery
Multidisciplinary Management of Cancers
Radiotherapy
Department of Clinical Oncology, PWH
Chemotherapy Biological Therapy
Pathology
Radiology
Clinical Psychology Palliative Medicine
Conclusion
• The rapid technological advancement brings radiotherapy to a new era
• Development of radiotherapy from two dimensional to three dimensional conformal radiotherapy achieve high conformity of radiation to the target with sparing of surrounding normal tissue and allow dose escalation with improvement in tumor control
Conclusion• Intensity modulated radiotherapy (IMRT)
further improves the conformity of radiation especially for the irregular targets, allows the delivery of differential doses within the target according to the tumor characteristics and dose limitations of critical organs
• The development of these highly conformed radiotherapy further facilitated by the development of imaged guided radiotherapy (IGRT) with or without respiratory gating and assures accurate setup, decrease margins and decrease volume of irradiation
Conclusion
• Treatment of cancers require multidisciplinary management. Good coordination among the different disciplines and careful selection of patient will allow provision of best services to our patients.
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