Issues caused by respiratory motion
- Causes displacement of tumour location
- 12-16 respiratory cycles every minute
- SI direction up to 2-2.5cms
- Ant-post and lat directions 5mm to 1cm
Causes difficulty localising tumour - overdose normal tissue, underdose tumour
How can motion be controlled
Motion compensation: Respiratoy gating and tumour tracking
Motion Suppression: Abdominal compression and deep inspiration breath hold
Respiratory gating
Imaging and delivery of RT during a portion of the breathing cycle or “gate”
Tumour tracking
radiation beam follows the tumours changing position
Abdominal compression
use of compression plate to limit breathing. Originally designed for SBRT of lung and liver. Limits air intake of patient, therefore reducing amount the diaphragm can move. Smaller margins achievable
Abdominal compression advantages
simplicity, minimal technological devices, easy to use, reduce respiratory motion, reusable
Abdominal compression disadvantages
increased setup time, slight discomfort, difficult for patients with claustrophobia
Deep inspiration breath hold
assist patient in holding his own breath at a pre-determined position. Commonly used for LT breast and lung tumours
ELEKTA - ACTIVE BREATHING CONTROL (ABC)
- Apparatus can suspend breathing at any predetermined position
- Used to avoid dose to healthy lung and heart
- During a deep breath, the heart moves away from breast and chest wall, reducing the amount of heart tissue within the treatment area
ABC eligibility criteria
Able to follow prompts from staff
Able to establish a reproduceable breathing pattern
Able to hold breath for a min of 20seconds - multiple times
ABC process
- mouthpiece placed in patient’s mouth
- Hooked up to ABC machine
- Continously monitors lung volume
- When lung volume is at the ideal level, the valve on the mouthpiece is closed of (usually set at 70-80% of maximum inspiration and prevents the patient from inhaling and exhaling)
5.Radiation beam is turned on and once beam is delivered, the valve re-opens
Components of ABC
- Spirometer
- Tubing
- Filter
- Mouth piece
- Nose peg
- Patient control switch
Advantages of ABC
- reproduceable breath holds
- reduces tumour motion and cardiac treatment volumes
- Allows a reduction in margin sizes
can treat more complex volumes
ABC Disadvantages
-more invasive
- patient needs to hold breath for min 15sec
- requires verbal training by therapist
VARIAN RPM (real position management)
- Audio-visual feedback option used to assist patient in holding own breath at a pre-determined position
Patient instructed to breathe when beam turns off
Advantages and disadvantages of VARIAN RPM
- Less invasive
- Reduces tumour motion and cardiac treatment volumes
Disadvantages:
Difficult for many elderky and frail patients or those with pulmonary disease
What to discuss during patient education:
- Familiarise patient with equipment
- Taking a lung volume level to establish an immune breath threshold
- Breathing routine reharsed to ensure patient can comfortably hold breath for required time
- Patient returns next day for planning CT scan
General health and side effect disccussion
RPM method
Free breathing breath hold
Utilises an infra-red camera and marker block placed on the patient to track movement of their chest and breathing
Abches monitors breathing pattern
Patient is instructed to hold the breath at a specified breathing position. By viewing a breathing level indicator
Components of VARIAN RPM
Camera, marker block
Infra-red systems
camera sends signals, reflected off the markers, markers learn the patients breathing pattern
Components of abdominal compression
Stereotactc body frame
pressure plate
screw
