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.