immobilization devices
DESCRIPTION
A presentation regarding the Immobilization devices used in positioning the patient during radiotherapy treatment for cancer.TRANSCRIPT
Immobilization devicesDr. Nikhil S.
DefinitionAny device that helps to establish and
maintain the patient in a fixed, well defined position from treatment to treatment over a course of radiotherapy or prevent the patient from moving during a single treatment session.
ObjectivesMain: to limit the patient movementto reduce the probability of positioning errorsIncidental benefits:Redn in daily set up timeRedn in pt s fear and worryNo need for pt to be awake, alert & co-opConversion into a rigid body
Desirable characteristics
Ease of useEase of constructing the device Patient Comfort: Fully supported in a comfortable
and relaxed positionTactile reminder to the pt of how it feelsAll movements be constrainedDevice conforms to the pt’s external surface
contours(H&N)The device be appropriate to the particular
patient(e.g. obese) and anatomy(e.g. abdomen) under trtmt.
The device should optimally position the patient so as to minimize the normal tissue complications
It should not obstruct the path for beamDevice be usable on simulator, CT/MRI and
other trtmt planning imaging systemsSurface dose should not be altered.Adequate space for reference marks.Rigid & holds its shape over time
Cost considerations:Of materials and device itselfStaff time 4 construction of deviceStaff time 4 each patient set upNecessary suppliesRe-usabilityStorage space
History of Immobilization methods.
Early Days: Plastic head cups(doggy dish)Standardized neck rollsMasking tapesNot to move during T/ tHold the breath
1960 -1970sSkin marksPlaster of Paris castBite blocksVacuum molded plastic masksPolyurethane foam molds
Early 1980s and onwards:LaserBase plateIndexerHead supports: timosAcrylic mould/ Cobex castThermoplastic mouldVacuum mouldGill Thompson frame
In detail about...Adhesive tapesVelcro tapesGeneric body
supports- indexed and non- indexed
POP castsVacuum molded
plastic masksAcrylic mould/ cobex
casts
Polyurethane foam casts
Vacuum bagsThermoplastic
masks
Adhesive tapes:
with paper, cloth, masking tapes
To discourage movt. Eg. Tape across pt s
forehead attached to couch side rails
Straps with velcro backing
Strips of adhesive velcro tapes with hook facing outwards can be permanently fixed to the side rails.
Padded and re usableHelps to keep hand at
side and feet togetherNo pain
GENERIC BODY SUPPORTSFoam rubber wedgesOther foam rubber
supportsOne-size-fits-all plastic
head cups/ doggie bowlsNeck rollsKnee and lumbar
supportsThigh and heel stirrupsProne face holders with
cut outs for nose and mouth
Do not offer guidance for inter treatment set up reproducibility
But gives added comfort and stability
Foam wedges- used for patient comfort.
Indexed supportsSimple improvement of generic body
supports
provide means to facilitate inter trtmt set up reproducibility.
Head cups, H&N supports, Foam rubber wedges which are carefully indexed by size, shape, elevation above the trtmt couch.
Head & Neck supports- Clear- plastic Opaque- foam rubber or polyurethane foamIndexed supports provide Head & Neck height or
slant info for setup duplicationTo support the head during trtmt of1. lungs2. Scln3. oesophagus4. any trtmt which necessitates securing
Head&Neck.
Body Cast techniques1960s- Complete body
supports or helmets were cast from POP.
Labor intensive and time consuming
Immobilization helmet required initially creation of a model of patient’s head.
POP casts lose shape over time & become flexible
Mostly used in children for
-- craniospinal irradiation for medulloblastoma
-- CNS leukemia.
Vacuum moulded plastic masks or bubble packs… 1970s- “bubble pack”. A transparent form-fitting plastic shell
fabricated using a special vacuum forming device - Vacu-Former.
polyvinyl chloride sheet electrically heated to soften the plastic and then formed over a plaster model of the patient by creating a vacuum between them.
quite stablelabor intensive.
Acrylic Mould / Cobex cast
Made from perspex sheetsIt forms hard nonmalleable material when
mixed and allowed to set.Materials required : POP bandage & powderPerspex sheetVaseline base plate head rest
Advantages :Effective fixationClose conformity
between body surfaceand mould.Portals can be marked.Windows may be cut.Can be used for
CT/MRI without causing
any distortion of image.
Disadvantages:Difficult and
cumbersome to make .
Relatively delicate, with use / rough
handling it may get fractured.
expensive.Cannot be reused.
Newer body casts techniques
1. polyurethane foam casts2. vacuum bags3. thermoplastics
Polyurethane foam casts(alpha cradle)2 component chemical systems Patient placed in the treatment position on top of a
plastic bag. The bag rests within a specialized form constructed of
solid Styrofoam blocks. When two chemicals are combined in the bag, they begin
to expand into a polyurethane foam. As the foam rises, technician maneuvers it around the
patient . Support given to anatomic structures that do not lie flat
on the treatment couch. Once the foam hardens, the customized device is ready
for use.
used in combination with other patient support systems for
ca breast ca prostatelower extremities lung pituitary gland head and neck region Hodgkin's disease.
ADVANTAGESrigid stable radiolucent. comfortable
DISADVANTAGES do not prevent
patient movement and rotation when used by themselves.
cannot conform completely to changes in body contour as other methods.
Vacuum bags
Radiolucent plastic cushions filled with tiny polystyrene ball.
Semi-deflated cushion moulded around the patient's gross body contours.
Using vacuum pump air is pumped out and the balls come together to form a firm solid support.
The cushion becomes an entirely rigid and comfortable mold of the patient's body.
advantages disadvantages shape maintained
through out REUSABLEcomfortable and secure for support of --1. head 2. upper thorax 3.the pelvis 4. breast. .
conforms well to gross
surface changes
less well to the finer
details.
strict immobilization
possible in combination
with other devices only
ThermoplasticsLow-temperature
orthopedic plastics.PolycaprolactoneSoftens at 60 C
(working temp)Melts at 150 C
(melting pt)solid sheets or a flat
plastic mesh of diff thicknesses.
precut thermoplastic mesh softened by soaking in warm water for a few
minutes.Then mask stretched around the topside of a
patient who is already in the treatment position
soft thermoplastic moulded to the patient's
facial contours, and in a few minutes the mask hardens.
no strength or cushioning properties
wont support the patient's weight.
easy to use.allow treatments
with few skin marks.
Reference lines drawn on the plastic sheet.
some loss of skin sparing through the material.
Other materials used are: different hardening tapes such as 1. fiberglass tape 2. light-cast tape (a thermoplastic that
hardens under ultraviolet light).
LaserUsed for aligning
the patient for immobilisation
Base Plate• The plate onto which the
head immobilization systems are secured is usually referred to as a base plate.
• Its material should be strong ,yet it should minimally attenuate the radiation beam.
• Most base plates are acrylic and recently carbon fiber base plates are hugely devolped
Indexer• The indexing bar can
be placed at the desired indexing indents of the couch and it can be locked down by rotating the levers.
• The base plates then can be positioned over the pins of the two pin indexing bar.
Positioning devicesAll immobilization devices in some sense are
positioning devices.
positioning devices are ancillary devices which maintain the patient in a nonstandard treatment position.
Need for positioning devicesset up the patient in a special position designed
to improve the therapeutic ratio and patient's comfort.
optimal beam access is limited by external anatomic features such as the extremities, a large belly, or a pendulous breast.
proximity of the target (PTV) to the surrounding radiosensitive structures.
List of positioning devicesNeck rollsFoam wedgesHead holdersTimos
Arm boardKnee saddleThigh stirrups
Hand GripOver head arm positionerShoulder retractor
PATIENT ELEVATION SYSTEMS
Breast boardProne breast platform
supportThermoplastic brassiere,
breast ringBelly board
Neck Roll, Foam wedge, Head holder and Timoused to maneuver
body parts out of the way of the beam or into a better position
maxillary antrum tumors-
- patient's head positioned with chin hyper extended to include the superior extent of the maxillary antrum in the anterior field without including the eye.
pituitary or small brain tumors -- head positioned with neck in extreme flexion .
anterior beam can avoid the dose-limiting structures such as the optic chiasm, the retina, and much of the brain tissue
Arm board, knee saddle, and thigh stirrupsDesigned to position the extremities in a
comfortable and reproducible manner.Used for soft tissue sarcomas in the arms or
legs.Necessary to remove the uninvolved arm or
leg from the path of the radiation beam.
Upper limb positioning Arm best treated
with 90 degree extension & treatment couch rotated 90 degrees.
Axis of the arm aligned with the axis of gantry rotation for planning & delivering precise isocentric treatment
overhead arm positionerUsed to position the
extremities if interfering with treatment of some other region.
Positioned above the head or at the sides with either:
1)couch rail mounted or tilt board mounted hand grips and arm supports .
2) or an overhead arm positioner hand grip device.
(e.g., the butterfly or the T-bar)
T bar hand grip T-bar hand grip mounted
on a horizontal plastic board.
Used in combination with head and neck support device.
adjustable hand grip positions available.
Maintains the patient in a reproducible arms-up position.
Used for treating various lesions in the thorax and abdomen.
Shoulder retractors Patient nudged into a
position with arms and shoulders down.
Footboard attached to hand grips through nylon ropes with adjustable tension.
Reproducible. very useful for
treating head and neck cancers with lateral fields.
lower limb positioningPosition the uninvolved leg sufficiently
outside the radiation field.
Knee saddles or stirrups mounted on the couch rail used with a customized solid foam or vacuum bag support.
Patient elevation systems1. tilt board
severe obesity lung disease Built-in hand grips or arm supports that provide
comfortable and reproducible arms-up support. Used for treating lung cancer through lateral fields without the
interference of arms or shoulders. severe sloping chest by positioning the
patient so that the antero-posterior vertical beam impinges orthogonally .
breast board
Used in the treatment of breast cancer with parallel opposed tangential fields.
Advntg:Provides arm support to bring the arm above
the shoulders and out of the way of the lateral field.
Allows the patient to be positioned with the chest wall horizontal avoiding angulation of the collimator.
Takes advantage of gravity to pull the large breast down into a better treatment position.
Modern breast boardRigid plastic.wide range of indexed tilt angles .The back support includes a head holder. It is cut away to prevent interference with
the tangential field for steep beam angles. Also contains an arm support system.
Wing boardIt comfortably
supports the patients arms during trtmt of breast, lung and thorax.
thermoplastic brassiere or breast ring Treatment of women
with large, flaccid, or pendulous breasts.
Prevents severe skin reactions resulting from the skin overlap in the infra-mammary fold.
Prone breast platform support patient lies prone
rigid trough-like supporting device mounted on top of the treatment couch.
Involved breast hangs under its own weight through a window in the bottom of the trough.
.
provides improved separation between the target and the normal tissues.
Lateral tangential beams are used for treatment.
Reduces pulmonary ,cardiac, skin complications .
Belly board Thick mattress for
supporting the patient prone with a window cutout for the patient's belly.
provide more comfort and stability in the prone position (obese patient) .
Reduces the amount of intestine in the lateral radiation fields.
Treatment chair.Not popular.
Made of carbon fiber grids .
Chair can be mounted on the treatment couch.
Contain head and neck supports as well as arm rests.
Patients with troubled breathing and cannot be placed in a recumbent position.
Advantageous for treatment of mediastinal disease.
Reduces the amount of irradiated normal tissue.
Head Fixation Devices
Stereotactic radio surgery(SRS) immobilization requires greater precision and accuracy.
Stereotactic frame bolted to the patient's skull before the target localization procedure and attached until treatment is complete.
Single-fraction technique.Impractical for fractionated radiotherapy
1. Gill-Thomas-Cosman system
frame fixed to the head with a dental mold.
occipital tray with a cast of the occiput.
strap that holds the device tightly to the head.
2nd device consist of a rod
in each external auditory canal and a clip molded to the bridge of the nose
3. invasiveFor IMRT of head&
neckbone screws set
into the inner table of the skull.
screws have internal threads and can receive the standoffs which remain in place during the course of therapy.
SRS using thermoplastic shell
Traditional bite block Dental impression
mouthpiece. Rigidly supported by and
referenced to a solid base plate placed under the patient's head and fastened to the treatment couch.
The patient's reproducible head position is recorded according to the reference numbers
Modern bite block systemsHas optical tracking
systems that verify correct placement of fiducial markers incorporated within the bite block apparatus.
Positions of the fiducial markers relative to the isocenter compared at the time of the acquisition of the planning CT scan.
Graphical user interface suggests shifts in patient position as per the plan.
Site Technique Trtmt to trtmt(mm)
alignment
Pelvis, abdomen
Alpha cradle 3 to 4 Laser
Un-immobilized 6 to 8 Laser
breast Alpha cradle/ vacuum bags
3 Light field
thorax Un-immobilized 4 Laser
Head and neck
Face mask with neck
2.5 to 4 Laser
Mechanical 3 Laser
Bite block 4 Laser
Intracranial Un-immobilized 3 Laser
Face mask with neck
2 to 2.5 Laser
Stereotactic non- invasive
1 to 1.5 Mechanical
Stereotactic-invasive
<1 Mechanical
Individual malignancy immobilisation
Head and Neckproximity of tumor to critical normal tissues.good immobilization will enable smaller
treatment margins and reduce side effects.Most accurate: Perspex shellPatient supine with head on a customized
head rest and as flat as possible to maintain the spinal cord parallel to the couch top.
Neck chin distance
Fixed to the couch top in at least five places.
mouth bitepull the shoulders
inferiorly.anterior and lateral
reference marks made on the shell.
selected parts can be cut out to reduce skin dose
Ear Patient is immobilised lying supine in a
custom-made shell. Neck extended to move the orbit superiorly
out of the treated volume.
NoseThe patient is immobilised in a thermoplastic
or Perspex shell. Wax nostril plugs to help produce a more
homogeneous dose distribution.
Oral cavity Patient supine with a straight spine.Immobilized in a Perspex or thermoplastic
shell.custom-made mouth bite -- pushing the tongue inferiorly when
irradiating the hard palate or upper alveolus. -- separate the roof of the mouth from the
inferior oral cavity when irradiating the tongue
Pts may find it difficult to tolerate.may precipitate swallowing and thus cause
movement of critical structures.distort the anatomy and make volumes on CT
more difficult to define.
oropharynxThe patient lies supine with the spine as
straight as possible and no mouth bite,but any dentures should be left in place. A shell with at least five fixation points is
constructed to ensure immobilization
hypopharynxThe treated volume will usually extend
inferior to the level of the shoulders which should be as low as possible to facilitate beam entry.
No mouth bite is required.
nasopharynxThe chin is elevated to spare the oral cavity
and orbitthe spine should be kept as straight as
possible if posterior neck nodes are present, to facilitate matching of an electron boost.
A mouth bite may be used to depress the tongue away from the treated volume.
larynxshoulders are immobilized in the shell as
inferiorly as possible shoulder tips should be inferior to the lower
border of the cricoid cartilage thus permitting lateral radiation beams to
treat the larynx without the need to angle them inferiorly.
Grip bars on the side of the couch may help to achieve this.
Salivary glandsneck slightly extended to move the orbits
superiorly and reduce the chance of beams exiting through the eye.
sinusesPatients should be immobilised supine in a
Perspex or thermoplastic shell. If the neck is not irradiated, the shoulders do
not need to be immobilised.If the low neck nodes are to be treated (level
III–V) the neck should be extended to allow treatment of most of the neck nodes with an anterior beam, avoiding the oral cavity and pharynx where possible.
mouth bitePatients should be asked to look straight
ahead to avoid rotating the lens or retina, particularly if the orbital cavity is included in the treated volume.
Wax plugs in the nostrils are used if the tumour extended inferiorly in the nasal cavity to enable a more uniform dose distribution.
orbitThe proximity several critical normal
structures excellent immobilisation is vital. A custom-made thermoplastic or Perspex
shell is created with the patient supinethe chin in a neutral position.
CNS GLIOMASThe patient lies supine with the head
immobilized in an individual Perspex or thermoplastic shell.
More rigorous immobilization with a stereotactic frame and mouth bite is possible.
MedulloblastomaCONVENTIONALPt treated prone
with indvdl facial support and a shell down over the shoulders to immobilize head, neck and shoulders.
CONFORMALPt treated supine on
carbon fiber couch top, neck extended
Vacuum molded bag to support head and shoulders.
Thermoplastic shell covers face and shoulders
Indexed knee rest(spine)Hips fixed in foam formsArm rests
Pituitary tumors Thyroid tumorsPerspex shell or
relocatable frameNeutral position
Perspex shellNeck extendedShoulders as low as
possible
LUNGPt supine with arms above headPt holds on to T bar device with their elbows
supported laterallyIf treatment delivery is prolonged, vacuum
bag should be used to reduce movement.
BreastPatient treated supineWith an immobilization
device which secures both arms above the head
Head rest, elbow and arm rests, knee supports and a foot board provides stability
Large pendulous- breast support either with thermoplastic shell or breast cup.
ProneReduces mean lung
and cardiac doseMore homogenous
dose distribution
Esophagus & stomachPatient treated supine with arms above the
head.Ideally immobilized with a vacuum formed
polystyrene bag.Cervical esophagus tumors- thermoplastic or
perspex shell
Pancreas & liver rectumPatient lies supine in a
vacuum molded bag with arms above the head in arm rest
Prone positionBelly board usedWhich allows small
bowel to be displaced anteriorly
prostate
Patient treated SupineHead pad combinedwith individually adjustable knee and ankle supports used
Urinary bladderPt supineWith arms folded across the chestWith ankle supports to stabilize the leg and
pelvis
CERVIXPatient supine with arms on the chestKnee and lower leg immobilization or alpha
cradles to prevent pelvic rotationObese- belly board
Anal canalTreated prone to displace bowels superiorlyBelly board– displaces the bowels anteriorly
into the blly-board aperture.
Cyber knifeIntegrates a compact robotically positioned
linac with image guided stereotactic localization
Basic components:Robotic linacImage guidance hardware:--a pair of orthogonal x ray sources-- imaging panel
Implantation of fiducial markers in or around the tumors
Patient stabilizationBody length vacuum
bagCT and PET imagesThin cuts 1.25mm-->
HR DRR
DRR compared with images acquired by orthogonal X ray sources.