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


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



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:

 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.


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.; 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



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


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


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) 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)


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, 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


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 B.Bak MSc, Greater Poland Cancer Center - [email protected]

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 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)


IMAGING PROTOCOLS USE OF PRE-TREATMENT IMAGING PROTOCOLS FOR MOTION ESTIMATION


Imaging protocols

NAL or NAL3

NO ACTION LEVEL NAL5 Weekly

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 IMAGING PROTOCOLS FOR MOTION ESTIMATION

use of pre treatment protocols

Health & Medicine