Role of immobilisation and devices in radiotherapy
1. ROLE OF IMMOBILISATION
AND
DEVICES IN RADIOTHERAPY
DR. SWARNITA SAHU
RADIATION ONCOLOGY
BATRA HOSPITAL AND MEDICAL RESEARCH CENTRE
NEW DELHI.
2. WHY IT IS IMPORTANT??
• To position target accurately.
• To minimise the dose to surrounding normal tissue as
far as possible.
• Reduces the time in daily patient setup .
• Makes the patient feel more secure and less
apprehensive.
• Especially in CNS tumours (small fields, critical adjacent
structures).
• Reduces the reliance on patient cooperation and
alertness.
• Immobilisation techniques can influence PTV.
3. PROPERTIES OF AN IMMOBILISATION DEVICE
• Lightweight
• Strong and durable
• Minimally affect the megavoltage treatment
beam
• Do not cause CT imaging artifacts
4. PREREQUISITES OF IMMOBILISATION
• Fully supported in a comfortable and relaxed
position
• Device conforms to patients body contour.
• Should be sturdy and maintain shape over time.
• See the target Volume to be treated and
structures to be spared.
• Treatment portal arrangement.
• General condition of patient.
11. Thermoplastic moulds
• Is a heat sensitive material
(cellulose acetate /
polyvinyl chloride).
• Available in form of various
precut shapes, size and
thickness(1.6-4.2mm).
• Soften by heating in water
bath at minimum 70 degree
Celsius.
12. • Advantages :
• can be used practically for all body parts
• Can achieve very close conformity between body surface and mould.
• Relatively easy to make and less time consuming.
• Portals can be marked on surface with ease
• Treatment windows can be cut.
• Wax bolus can be fixed to surface.
• Can be used with CT/MRI scan
• Disadvantages-
• Windows cut can not be reused
• When old becomes brittle and too soft when activated
13. Bite block system
• Claustrophobic
• Anxiety
• Custom dental mould is
formed for each patient
and is suctioned to
patients hard palate.
• The dental mould is
attached to the frame.
14. Body conformal immobilization devices
• Vaccum lock-
• Bag filled with plastic minispheres.
• Bag is first conformed to the patients
body contour by pushing the
minispheres accordingly.
• Vaccum pump connected and air is
evacuated.
• Plastic minispheres lock together to
retain the shape.
• During the evacuation the minispheres
are maneuvered to provide optimal fit
and body contour.
15. Alpha cradle
• Forms are available for treatment of patients
with a variety of disease sites.
• Appropiate body form is chosen and placed
in a polyvinyl bag
• Two part chemical foaming agents are mixed
together-----chemical reaction-----foam
expands.
• Mixed foaming agent isdistributed evenly
throughout the body form and sealed inside
the polyvinyl bag.
• Patient is positioned inside the form as the
foaming agent expands and conforms the
body contour.
16. PRONE POSITION
• PRONE BELLY BOARD (for treating pelvis)
Aid of gravity-small bowel falls into board’s cut out
ADV-reduce the dose to the small bowel
DISADV-patient dependant
17. Breast cancer patients:-
• Large pendulous breasts-
• larger tissue separation
• larger treatment volumes
• worse surface irregularity
• accentuated inframammary fold
• Higher rates of acute and late toxicities(high grade
dermatitis,fibrosis)
• Prone position improves dose homogenecity and
hence reduces toxicities.
• Face resting in a donut shaped cushion
• Hold the hand posts(helpful in arthritis patients who
cant keep their hand above their head for long time)
• DIASADV-cumbersome for elderly and obese patients
• limit visual alignment of an anterior
supraclavicular field.
18. TOTAL BODY IRRADIATION
• BONE MARROW TRANSPLANTATION
PREPARATION
• MYCOSIS FUNGOIDES
• 10 TO 40 MINS
• BICYCLE SEAT,HANDGRIPS,SHOULDER
STABILIZER
• SOME HAVE HARNESS
19. Dosimetric effects-
• Any material placed between the patient and the
radiation source
Modify characteristics of the treatment beam
• Electron liberated within the immobilization devices-
increase in surface dose—bolusing effect(depends on
composition, density, thickness)
• Modern devices---low density materials --- less impact
20.
21. STEREOTACTICIMMOBILIZATION AND STABILIZATION
HIGH DOSE PER FRACTION
TARGET VOLUME IN CLOSE PROXIMITY TO VITAL STRUCTURES
PATIENT IMMOBILIZATION BECOMES A MAJOR CHALLENGE TO
OVERCOME INTER AND INTRA FRACTIONAL VARIATION IN
PATIENT SETUP.
22. INVASIVE CRANIAL-for single fraction radiosurgery
• Metal pins driven into the skull which are
attached to a frame usually via metal
posts(2 long anteriorly,2 short posteriorly)
• The head frame is connected to either a
floor mounted stand or the treatment table.
• Adv-accuracy of 1 mm.
• Disadv-sedation,infection,bleeding.
• ring placement,image
acquisition,planning,implementation-all in
same day
23. NONINVASIVE CRANIAL:FRAME BASED
3 pieces of thermoplastic material custom
molded to the patient’s head
Attached to the vertical posts on either side of
patients head
Posts attached to U-SHAPED frame
Frame attached to the treatment couch
24. NONINVASIVE CRANIAL:FRAMELESS
• Thermoplastic masks with daily pretreatment
image guidance.
• Optically guided fiducial markers as a
surrogate for daily target localisation and to
monitor patient motion in real time.
26. IMMOBILISATION AND INTERNAL MOTION MANAGEMENT
• INTERNAL TARGET MOTION due to breathing
is a major concern in SBRT particularly in lung
and liver tumors.
Multiple stratigies -
• Deep inspiration breath hold
• Active breathing control
• Respiratory gating
• Real time tumor tracking
• Abdominal compression devices.
27. ABDOMINAL COMPRESSIONDEVICES
• TO CONTROL RESPIRATORY
EXCURSION.
• ALSO REFERRED TO AS
FORCED SHALLOW
BREATHING.
• PLATE (FEW CMS BELOW THE
XIPHOID PROCESS)IS
ATTACHED TO THE ARCH.
• ARCH ATTACHED TO THE
STEREOTACTIC
FRAME/TREATMENT COUCH.
• STEREOTACTIC FRAME AND
ARCH –BOTH ARE INDEXED.
29. GYNECOLOGIC MALIGNANCIES:
• Vaginal packing and waistbands –immobilise
applicators
PHYSICIAN DEPENDANT:-
AN EARLY STUDY SHOWED-DISPLACEMENT OF TANDEM AND
OVOID APPLICATORS OF UPTO 5 mm DUE TO MOVEMENT OF
THE PATIENT FROM SIMULATION TO THE TREATMENT ROOM
SOLUTION-Integrated brachytherapy suits:-
(SCAN PLAN AND TREAT THE PATIENT IN THE SAME ROOM)
• Nucletron integrated brachytherapy unit(elekta)
• Varian acuity suite
30. IMMOBILISATION FOR BREAST BRACHYTHERAPY
BREAST IS IMMOBILISED BETWEEN 2 MAMMOGRAPHIC
PADDLES
MAMMOGRAM
LUMPECTOMY CAVITY IS DELINEATED
BRACHYTHERAPY IS DELIVERED
31. IMMOBILISATIONSTRATEGIES FOR INTRAOPERATIVE RADIOTHERAPY
THE CONE IS PLACED DIRECTLY
OVER THE TARGET TISSUE
FOLLOWING LUMPECTOMY.
THE LINEAR ACCELERATOR IS THEN
POSITIONED ABOVE THE CONE
AND AUTOMATICALLY ALIGNED
USING LASER GUIDANCE WITH THE
MIRROR ON THE CONE.
32. CONCLUSION
With advanced methods like-HYPOFRACTIONATED STEREOTACTIC
BODY RADIATION THERAPY & IMAGE GUIDED BRACHYTHERAPY
Patient be comfortably immobilised to ensure-
Radiation is properly delivered to the tumor.
This is necessary as the dose per fraction is increased ,which could lead to serious
complications if the normal tissues surrounding the tumor receive excessive dose due to poor
localization and immobilization.
