1. ABC system, Free Breath 4DCT &
Symmetry
Dr Sanjeet Mandal
Assistant Professor, Radiation Oncology
Kidwai Memorial Institute of Oncology, Bengaluru
2. Introduction
The advancements in Radiation Oncology is always to aim
higher dose to tumour and less dose to normal tissues.
ICRU 62 defines Internal Target
Volume (ITV) as CTV with internal
margin
Planning Risk Volume (PRV) as OAR
with internal margin
3. Organ Motion
Intra – fraction motion
- Swallowing
- Coughing
- Eye movement
- Heartbeat
Inter – fraction motion
- Tumour change
- Weight gain/loss
- Positioning changes
- Respiration
- Bowel and Rectal filling
- Bladder filling
4. Respiration is most relevant source of motion for lung, breast,
liver and pancreatic cancers.
Respiratory motion is patient specific
It may vary between fractions and even within a fraction
Lung tumours, typically 5-10mm, but in lower lobe ≥5cm
Breast tumours, typically 5-10mm, more in pendulous type
Abdominal tumours (Liver, Pancreas), typically > 10mm
5. Problems from respiration
Inter and Intraobserver variation in GTV & CTV delineation
Motion artefacts in CT simulation – target delineation errors
Daily variation of respiratory motion
Treatment related anatomic changes, reduction in bronchiole
obstructions and changes in atelectasis
RT planning & delivery limitations
6. Motion artefact due to respiration
RT planning limitations due to respiration
Free Breath versus Respiratory Gated scan
7. Tumour motion is complex
Some tumour move in AP predominantly
Some tumour move in SI predominantly
Sometimes hysterical
Ref: AAPM TG 76
8. Methods to account for Respiratory motion
Motion encompassing methods – Slow CT, Inhalation & Exhalation
Breath Hold CT, 4DCT (Symmetry, Bellows belt)
Respiratory gating methods
External fiducials– RPM system, ExacTrac gating, Anzai belt
Internal fiducials – Hokkaido university & Mitsubishi
Gated IMRT
Breath hold methods
DIBH – VMAX Spectra 20C, SpiroDyn’RX
mDIBH - Active Breathing Control (ABC) system
Forced shallow breathing with abdominal compression
Real time tumour tracking methods
10. Free Breath 4DCT
Patient Selection
- Tumour motion ≥ 5mm or OAR sparing can be increased
Preparation
- Inform regarding the Immobilisation steps & CT simulation
process (120s slow CT)
- No coaching required
- Patient must be not move during image acquisition (due to
pain or any other discomfort)
11. 4DCT Image Acquisition - Prospective
Images are acquired & sorted during a portion of respiratory
cycle
12. 4DCT Image Acquisition - Retrospective
Images are acquired during entire phase of respiratory cycle &
sorted later
13. Free Breath 4DCT – Bellows belt
Pulmonary tool kit by Phillips
It consists of a deformable belt with pneumatic sensors
(placed on patient) with a cable connected to CT gantry
Image during CT simulation
It generates breathing signals corresponding to respiration
during all phases (retrospective 4DCT)
Entire image sets (usually 10) are created – used to create ITV,
average or MIP
15. Free Breath 4D CBCT – Symmetry
4D CBCT feature within linac by Elekta (VersaHD)
No external belt or IR marker required
Image during treatment
It generates breathing signals corresponding to respiration
during all phases (retrospective 4DCT)
Entire image sets (usually 10) are created – used to create ITV,
average or MIP
18. mDIBH by ABC system
Patient Selection
- Tumour motion ≥ 5mm or OAR sparing can be increased
- Good cardiopulmonary function
- No dental issues
- No facial muscle / upper limb weakness
- No hearing problems
- Able to follow commands
19. mDIBH by ABC system
Preparation
- Inform regarding the Immobilisation steps, mDIBH by ABC
system training, CT simulation & Radiation Therapy process
- Coaching required (Usually 5-7days)
- Patient must be not move during image acquisition (due to
pain or any other discomfort)
- Spirometer exercise
20. mDIBH by ABC system
- A reproducible breath hold method developed at William
Beaumount Hospital and commercialized by Elekta
- It consists of digital spirometer connected to balloon valve
- The valve is inflated to pre-defined tidal volume & duration
- Moderate DIBH, usually 75% of deep inspiratory capacity
(reproducible & comfort)
- Deep Expiration Breath Hold can also be done
24. Take home message
Tumour motion ≥ 5mm or OAR sparing may be increased
Proper patient selection criteria
Patient should comply throughout radiation treatment
Choose motion management method appropriately (ABC
system has less ITV volume BUT Free breath 4DCT has better
patient comfort)