Download - Use of pre treatment protocols
USE OF PRE-TREATMENT IMAGING PROTOCOLS FOR MOTION ESTIMATION
Bartosz Bak MSc Greater Poland Cancer Center
Introduction
With the introduction of IMRT and SBRT we have reached a point where the radiation dose can be shaped to the target volume with steep dose gradients to surrouding normal tissues.
These new treatment techniques introduce an enormous inherent risk, to quote J. Rosenman:
“We are at increased risk of missing very precisely”
B.Bak MSc, Greater Poland Cancer Center - [email protected]
Introduction
Increasing precision and accuracy in radiotherapy PLANNING and radiation DELIVERY will lead to reduced toxicity with the potential for
dose escalation and improved tumour control
B.Bak MSc, Greater Poland Cancer Center - [email protected]
Accuracy
... for safe daily treatment is achieved by: ensuring reliable and reproducible patient immobilization, planning and treatment correlation, pre-treatment quality assurance using daily imaging (and possibly) a method of accounting for tumour motion during treatment
B.Bak MSc, Greater Poland Cancer Center - [email protected]
TUMOUR LOCALISATION – DIFFERENT PROBLEMS
USE OF PRE-TREATMENT IMAGING PROTOCOLS FOR MOTION ESTIMATION
B.Bak MSc, Greater Poland Cancer Center - [email protected]
Head and Neck
Small or negligible intra-treatment organ movement
Main problem are changes in location, form and size of disease and normal anatomy:
Tumour shrinkage, nodal regression Oedema Changes in the H&N posture, weight loss Alterations in normal glands and mucosa
Leading to significant dose changes in the target and OARs Tumor can shrink volumetrically by up to 90%! Parotid glands can involute and shift medially (towards high-dose coverage in the
oropharynx) by up to a centimeter during a treatment course!
B.Bak MSc, Greater Poland Cancer Center - [email protected]
Chest
Main problem: Breathing motion
Organ displacements during normal breathing may occur in all directions of about 5,5-20mm
Lung target motion can amount to 3cm when no movement reduction methods are used
B.Bak MSc, Greater Poland Cancer Center - [email protected]
Chest
Movement reduction methods: Active breath control (ABC) device Cheung et al: the average (SD) displacement of GTV centres was 0.3 mm (1.8 mm),
1.2 mm (2.3 mm), and 1.1 mm (3.5 mm) in LR, AP and CC
Voluntary breath-hold methods using spirometer-based monitoring Kimura et al: 1.3 1.3)mm, 1.4(1.8)mm, 2.1(1.6)mm and 3.3(2.2)mm in CC, LR and AP
DIBH (Deep Inspiratory Breath Hold) technique Mah et al: the inferred displacement of the centroid GTV was 0.2(+/- 1.4mm) (mean
and SD)
Abdominal compression
B.Bak MSc, Greater Poland Cancer Center - [email protected]
Chest
Movement compensation: Free breathing gating technique:
Tumour tracking: By detecting tumour posision and shifting the alignment of the
beam synchronously.
Temporal tracking by detecting the breathing phase and gating the beam on and off Synchronously with the breathing cycle.
B.Bak MSc, Greater Poland Cancer Center - [email protected]
Pelvis
Main problem: Inter- and Intra-fraction prostate motion
Shimizu et al.: shifts < 3mm (81%), < 5mm (98%); Nederveen et al.: greatest motion in CC and AP 2-3 mm; Fiducial makers Madsen et al.: mean prostate motion < 2mm
Kron et al.: intrafraction prostate displacement - after a relatively short interval of 3 min, the vector displacement is likely to exceed 1.5 mm BUT Even in relatively short times there is a significant probability that the prostate has moved more than 3 mm.
Kron et al
B.Bak MSc, Greater Poland Cancer Center - [email protected]
Pelvis
Prostate motion is a result due to: Different fillings of hollow organs (rectum and bladder) Breathing Pelvic muscle constriction and relaxation
Different protocols of rectal and bladder preparation intend to limit prostate motion
Ghilezan et al.: shifts >3mm in full rectum group, only small shifts after 20minutes in empty rectum group (cine MRI)
B.Bak MSc, Greater Poland Cancer Center - [email protected]
THE DIAGNOSTIC LEVEL - TO DEFINE TARGET BETTER
USE OF PRE-TREATMENT IMAGING PROTOCOLS FOR MOTION ESTIMATION
B.Bak MSc, Greater Poland Cancer Center - [email protected]
To define target better
The identification of the target volume is potentially the largest source of systematic error
Multimodality imaging and the ability to co-register images have the potential to improve tumour volume
identification
B.Bak MSc, Greater Poland Cancer Center - [email protected]
Imaging modalities
For all patient planning CT is a golden standard CT can provide accurate information on size, position
and density of the tumour and other anatomy in 3D
Moreover, the HUs give information on electron density distribution in the
patient, readily useful for calculation of the absorbed dose in
the patient.
Korreman et al.; B.Bak MSc, Greater Poland Cancer Center - [email protected]
Improvements of imaging modalities
Morphological: Fast CT (every tumour site) MRI (H&N, prostate)
Functional: MRS – Magnetic Resonance Spectroscopy (H&N, prostate) PET/CT (H&N, lung)
Reduction of respiratory motion 4D CT:
respiratory-gated CT (RGCT)
4D PET/CT: one of the most recent technological progresses for accurate imaging of tumors, particularly those located in the thorax and in the upper abdomen
respiratory-correlated dynamic PET (RCDPET) respiratory-gated PET (RGPET) B.Bak MSc, Greater Poland Cancer Center - [email protected]
THE DELIVERY LEVEL
USE OF PRE-TREATMENT IMAGING PROTOCOLS FOR MOTION ESTIMATION
B.Bak MSc, Greater Poland Cancer Center - [email protected]
Image Guided Radiation Therapy
IGRT can be performed either statically or dynamically (in real time)
IGRT concept : Allows for tighter margins around the tumour Minimizing the volume healthy tissue exposed to the treatment beam
reducing geometrical uncertainly by evaluating the patient geometry at treatment
Altering the patient position Adapting the treatment plan with respect to anatomical changes that occur
during the RT
Uncertainties: Technical precision provided by IGRT also includes a potential danger as to
reducing margins to levels that are inadequate B.Bak MSc, Greater Poland Cancer Center - [email protected]
What do we have?
Radiation therapy evolved from 2D to 3D in the treatment-planning process, in the same way a similar evolution can be observed in IGRT.
DRR and EPI for planning and verification have replaced radiographic films.
Volumetric imaging techniques nowadays provide the soft-tissues contrast required for daily pre-treatment positioning, providing online information concerning OAR as well as tumours and identifying anatomical changes during the course of RT
B.Bak MSc, Greater Poland Cancer Center - [email protected]
What do we have?
Siemens CT-on-rails
Elekta kv CBCT (Synergy)
Varian kv CBCT (OBI)
Siemens MV CBCT
TomoTherapy MVCT B.Bak MSc, Greater Poland Cancer Center - [email protected]
What do we have?
EPID kV CT on rails CBCT
kV MV
MVCT
B.Bak MSc, Greater Poland Cancer Center - [email protected]
EPID - Electronic Portal Imaging Device
Established as a gold standard for on-line verification of patient’s set-up
Portal images from 2 or more directions aquired immediately before the radiation delivery and compared to reference images
Uses bony landmarks for the reference Adequate for H&N Requires gold markers implanted in or near the tumour for
other sites
B.Bak MSc, Greater Poland Cancer Center - [email protected]
EPID - Electronic Portal Imaging Device
Technique: MV treatment beam
Time: 10 min
Dose: 2 – 8 cGy
Advantages: Management of interfractional geometric uncertainties
(reduction of set-up margin) Moderate cost, Electronic data, Real-time display, Cine mode
Limitations: 2D, Large dose, Low contrast Requires surrogates for the target volume (bony landmarks or
implanted radio-opaque fiducial markers) B.Bak MSc, Greater Poland Cancer Center - [email protected]
kV
In-room kV imaging replaces MV portal imaging for set-up
kV images have better resolution and contrast than MV (allowing for more accurate rigid registration to determine the patient’s pose correction)
Require independent x-ray sources and detectors (uncertainty between the imaging and beam isocenters)
B.Bak MSc, Greater Poland Cancer Center - [email protected]
kV
Technique: kV x-rays
Time: <5 min
Dose: < 1 cGy
Advantages: Management of interfractional geometric uncertainties (reduction of set-up
margin) Electronic data, real-time display, Excellent contrast, Remote couch shift,
Fluoroscopic mode (motion assesment), Very quick, very low dose
Limitations: Expensive, 2D, No treatment port, No soft tissue information
B.Bak MSc, Greater Poland Cancer Center - [email protected]
3D KV Imaging
The Synergy system from Elekta Inc (Norcross, Ga) also features a kV imaging system
deployed with retractable arms to image the patient in the treatment position.
Varian Trilogy with On-Board Imager features retractable arms with which to image the patient using a cone beam of kV energy.
Elekta Axesse™ unique capabilities include true 3D imaging which gives target and
critical structure visualization at the time of treatment and enables 6D remote robotic
automatic position corrections.
BrainLab ExacTrack CyberKnife
B.Bak MSc, Greater Poland Cancer Center - [email protected]
CT on rails
Technique: kV x-rays
Time: 10 – 15 min
Dose: 5 cGy
Advantages: Electronic data, real-time display, Excellent contrast and image quality,
Remote couch shift, 3D images, Volume information
Limitations: Expensive, large couch motion between CT and treatment
cannot be used for the detection of intra-fractional patient or organ motion
This type of CT requires a lot of space in the treatment room
B.Bak MSc, Greater Poland Cancer Center - [email protected]
KV CBCT
Technique: kV x-rays
Time: 10 – 15 min
Dose: 3 – 11 cGy
Advantages: Management of interfractional geometric uncertainties (reduction of
set-up margin) Electronic data, Real-time display, Excellent contrast, Remote couch
shift, 3D images, Volume information
Limitations: Expensive, Longer aquisition, Collision clearance, No treatment port
B.Bak MSc, Greater Poland Cancer Center - [email protected]
MV CBCT
Technique: MV x-rays MV beam is used for treatment and imaging so Imaging dose is easily incorporated into the dose calculation
algorithm
Time: 10 – 15 min
Dose: 2 cGy
Advantages: Management of interfractional geometric uncertainties (reduction of set-up
margin) Electronic data, Real-time display, Remote couch shift, 3D images, Volume
information MV-based CT images can be used to complement or replace diagnostic KV
CT images when high density objects introduce severe artifacts
Limitations: Expensive, Longer aquisition, No treatment port B.Bak MSc, Greater Poland Cancer Center - [email protected]
MVCT - Tomotherapy
B.Bak MSc, Greater Poland Cancer Center - [email protected]
MVCT
Fusion of a MV linac with a helical CT scanner Allows DAILY patient set-up verification and
repositioning Provides less soft tissue contrast but suffers less from
beam hardening and the artifacts induced by highly attenuating high-Z materials
Technique: MV treatment beam
Time: 5 – 10 min
Dose: 1 – 3 cGy, enables daily veryfication B.Bak MSc, Greater Poland Cancer Center - [email protected]
Advantages: Management of interfractional geometric uncertainties (reduction of set-up
margin) Estimation the tumour response and adaptation the treatment plan during the
same course of radiotherapy (ART) Automated target localization and positioning prior to the treatment
The set up correction can be implemented by moving the patient, or by modifying the IMRT delivery to account for the patient’s actual geometric offset
Electronic data, Real-time display, Excellent contrast – less scatter than CBCT, 3D images, Volume information, Dose verification
Limitations: Expensive, Time consuming, not suitable for large respiratory motion (Chest)
B.Bak MSc, Greater Poland Cancer Center - [email protected]
IMAGING PROTOCOLS USE OF PRE-TREATMENT IMAGING PROTOCOLS FOR MOTION ESTIMATION
B.Bak MSc, Greater Poland Cancer Center - [email protected]
Imaging protocols
NAL or NAL3
NO ACTION LEVEL NAL5 Weekly
eNAL FFFs ALT
B.Bak MSc, Greater Poland Cancer Center - [email protected]
NAL/NAL3 (No Action Level) Protocol
Based on H.C. De Boer
Imaging is done on the first three treatment days No positional correction is applied for the first three
fractions when imaging data is being collected The targets location and set-up optimization shifts
are averaged over these 3 days, and all subsequent set-ups are adjusted for those shifts.
No additional image-guidance studies are obtained
B.Bak MSc, Greater Poland Cancer Center - [email protected]
NAL5 Protocol
NAL5 is similar to the NAL (NAL3) protocol except the first five fractions are imaged instead of the first three
No positional correction is applied for the first 5 fractions
B.Bak MSc, Greater Poland Cancer Center - [email protected]
Weekly
corresponds to once a week imaging (every 5th fx) Shifts derived from each imaging instance are
applied to the subsequent 4 fractions Weekly set-ups are typically only corrected for
subsequent fractions when a defined threshold (5mm) of set-up uncertainty is exceeded
This reflects typical clinical practice in which imaging is acquired on the first day of treatment, and then once weekly
B.Bak MSc, Greater Poland Cancer Center - [email protected]
eNAL imaging protocol
eNAL is a combination of the NAL3 and Weekly protocol With this protocol, imaging is done for the first three days,
followed by weekly imaging If the patient set-up during weekly imaging would be within 5
mm of the simulation set-up, no further correction would be made
Set-up corrections larger than 5 mm would be averaged with the shifts of the first 3 fractions, and constitute a new baseline correction for all subsequent fractions
B.Bak MSc, Greater Poland Cancer Center - [email protected]
First Five Fractions (FFFs) - protocol
Pre-treatment MVCTs are acquired during the patient’s first five fractions allowing for patient set-up verification and correction on those particular days.
This protocol closely resembles the previously described NAL protocol with five imaged fractions described byDeBoer et al.,
Although MVCT imaging provides more anatomical information than electronic portal imaging
B.Bak MSc, Greater Poland Cancer Center - [email protected]
Alternate week (ALT)- protocol
Pre-treatment MVCTs are acquired for fractions 1 to 5 allowing for patient setup correction.
deviations are then averaged and automatically corrected for during the subsequent 5 fractions (fraction 6–10).
MVCTs are re-performed during the third week of treatment (fractions 11–15), and averaged and corrected for during the subsequent five fractions (fractions 16–20).
The process is repeated until the end of the patient’s treatment course
B.Bak MSc, Greater Poland Cancer Center - [email protected]
MVCTs protocol: FFFs vs. ALT
Conclussions:
The ALT protocol resulted in slightly smaller residual deviations, particularly in the a–p direction, compared to the FFF protocol.
B.Bak MSc, Greater Poland Cancer Center - [email protected]
Thank You USE OF PRE-TREATMENT IMAGING PROTOCOLS FOR MOTION ESTIMATION