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 - bartosz.bak@wco.pl

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


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



TUMOUR LOCALISATION
– DIFFERENT PROBLEMS

USE OF PRE-TREATMENT IMAGING PROTOCOLS FOR MOTION ESTIMATION

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!

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


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


Chest
  Movement compensation:
  Free breathing gating technique:
Temporal tracking by
detecting the breathing
phase and gating the
beam on and off
Synchronously with
the breathing cycle.

  Tumour tracking:
  By detecting tumour posision and shifting the alignment of the
beam synchronously.


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

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)



THE DIAGNOSTIC LEVEL
- TO DEFINE TARGET BETTER

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


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.;

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)
B.Bak MSc,respiratory-gated PET -(RGPET)
  Greater Poland Cancer Center bartosz.bak@wco.pl


THE DELIVERY LEVEL


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

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

What do we have?

Siemens CT-on- Elekta kv CBCT Varian kv CBCT
rails (Synergy) (OBI)

Siemens MV TomoTherapy
CBCT MVCT

What do we have?

  EPID
  kV

  CT on rails

  CBCT
 kV
 MV

  MVCT

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


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)

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)


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


3D KV Imaging

The Synergy system from Elekta Inc (Norcross, Varian Trilogy with On-Board Imager features Elekta Axesse™ unique capabilities include
Ga) also features a kV imaging system retractable arms with which to image the true 3D imaging which gives target and
deployed with retractable arms to image the patient using a cone beam of kV energy. critical structure visualization at the time of
patient in the treatment position. treatment and enables 6D remote robotic
automatic position corrections.

BrainLab ExacTrack CyberKnife


CT on rails
  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


CBCT
Elekta Synergy

Varian Trilogy


KV CBCT
  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


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

MVCT - Tomotherapy


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

  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)



IMAGING PROTOCOLS

Imaging protocols

NAL or NAL3
NAL5 Weekly
NO ACTION LEVEL

eNAL FFFs ALT


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


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


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

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


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


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


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.

Thank You

Use of pre treatment protocols

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