This document discusses immobilization devices used in radiotherapy. It begins by explaining the goals of immobilization which are to limit patient motion and reduce positioning errors. It then describes various immobilization devices for different body sites including masks, supports, straps, and indexing systems. Thermoplastic masks are discussed in detail as effective head and neck immobilization devices. The document also notes some dosimetric considerations and ideal properties for immobilization devices.

1. IMMOBILISATION IN
RADIOTHERAPY
YAMINI BAVISKAR JR2
SABHEEN BUSHRA SR1

2. FLOW OF SEMINAR
1. INTRODUCTION
o Rationale
o Definition
o History
2. IMMOBILISATION DEVICES
o Miscellaneous
o Head Neck
o SRS
o Thorax Abdomen
o Breast
o Pelvis
o TBI & extremities
3. DOSIMETRIC CONSIDERATIONS
4. SUMMARY

3. RATIONALE
o GEOMETRIC MISS : Missing the
intended target volume AND
irradiating some (excess) volume of
normal tissue instead.
o ↓ TCP & ↑ NTCP, ↓↓ therapeutic
ratio
o ACCURACY of radiation delivery
o REPRODUCIBILITY : Patient’s
anatomical geometry at the time of
simulation reproduced for all
subsequent treatment fractions.
GOAL OF
RADIOTHERAPY:
Maximum desirable
dose to the tumour
with maximal sparing of
OARs
GOAL OF
IMMOBILISATION:
Limit patient motion
and reduce positioning
errors

4. GEOMETRIC UNCERTAINITIES
MECHANICAL
Light & radiation field
coincidence
Couch stability
Laser alignment
Quality Assurance
LOCALIZATION
Defining extent of
target volume
Image registration,
Contrast
enhancement
POSITIONING
Patient motion
Internal organ motion
Immobilization Devices
Motion management
techniques

5. IMMOBILISATION DEVICE
o Any device that helps to establish and maintain
the patient in a fixed and well defined position
from treatment to treatment over the course of
radiotherapy & prevent the patient from moving
during a single treatment session.
o INTERFRACTION & INTRAFRACTION STABILITY
o Precise positioning of the target to avoid geographical miss
o Immobilisation can influence PTV!

6. IDEAL IMMOBILISATION DEVICE
1. Comfortable for the patient
2. Simple to implement.
3. Must not interfere with the delivery of radiotherapy
4. Must not cause radiation beam attenuation
5. Must not cause artifacts in radiographic images used for planning and
treatment verification.
6. Transparency for easy visualization of beam field lights, crosshair, and
distance indicator scale at the patient’s skin.
7. Ability to retain marks

7. HISTORY
EARLY DAYS
PLASTIC HEAD CUPS
STANDARDIZED NECK ROLLS
MASKING TAPES
1980s
LASER
INDEXER
BASE PLATE
HEAD SUPPORTS
PRESENT ERA
BODY CONFORMAL DEVICES
STEREOTACIC DEVICES
IMPROVED IMAGE
GUIDANCE
1960 – 70S
SKIN MARKS
POP CASTS
POLYURETHAN FOAM
MOULDS
BITE BLOCKS

8. PATIENT POSITIONING AND
ALIGNMENT
 Comfortable
 Practical position
 Consideration of anticipated beam arrangement.
Supine/Prone/ Lateral
Arm position

9. ALIGNMENT MARKS
o External marks placed on either the patient’s skin or the
immobilization devices
o For initial laser alignment as a surrogate for internal target anatomy.
o In-room laser system in the simulator suite
o Should give coordinates in 3 dimensions.
o Preferably made on the immobilization device as it is more reliable as
opposed to the patient’s skin (soft tissue & mobile).
o If on skin, preferably marked on bony landmark for a relatively fixed
geometry
o Issues - Motion of soft tissue with relation to immobilization device,
Marks washing off, Wearing off or migration.

10. DEVICES
o Devices for SRS
o Thermoplastic moulds
o Neck supports, base plate
o Body conformal devices
o Breast Boards
o Belly Board
o Tapes, Straps
o Wedges and rolls
IMMOBILISATION
DEVICES
FRAME BASED
INVASIVE
NON INVASIVE
FRAMELESS

11. TAPES AND STRAPS
o Straps of adhesive Velcro tapes or plain tapes
o Stretched over patient’s forehead, shoulders,
arms and attached to couch side rails
o Simple to use , Re – usable
o Less robust
o Mainly to "remind“ patient to hold still during
treatment.
BITE BLOCKS

12. ARM STRAPS
o Allows patients to hold their arms in a comfortable
position by the side
o Requires no effort from patient’s side.
o Increased comfort  decreased motion more
accurate treatment
o Indicated for patients with paralysis, patients that
cannot lie still or obese patients
o One-size-fits all with velcro that allows adjustment
THORACIC ARM REST
o Supine with arms
above the head.
o In a comfortable,
reproducible position
to allow a greater
choice of beam angle.

13. ROLLS AND WEDGES
Wedges - To support arms and outstretched thighs(frog leg)
Knee rest
Ankle rest / Feet rest
Equipped with marking for alignment.

14. INDEXING SYSTEM
o The indexing bar (indexer) placed at the desired indexing
indents of the couch. Locked by rotating the levers.
o Allows devices to be rigidly affixed in concert to both the
simulator and treatment tables with high accuracy.
o The base plates then positioned below its pins
o Records the geometry used for each patient at the time of
simulation.
o Improves interfraction reproducibility
o Decreases the setup time
o Flat couches preferred to accommodate wide range of patient
sizes, treatment setup positions & immobilization devices

15. HEAD AND NECK
INVASIVE
• Mouth bite block
• Thermoplastic Mould
• GTC frame
NON INVASIVE/ BODY CONFORMAL
• Leksell Coordinate frame
• BRW frame

16. PERSPEX MASKS
o Made from perspex sheets in 2 stages
o First, a plaster mould is made with wet strips of POP bandages
o After the POP mask is set, Perspex mould is made over it.
o It forms hard nonmalleable material when mixed and allowed to set.
o Cumbersome for both technologist & patient, time consuming

17. o FRAME MADE OF CARBON FIBRE
o Stand-alone bite block systems
o Setup accuracy similar to
thermoplastic masks (1 to 3 mm)
o Can be used in patients not
tolerating thermoplast due to
claustrophobia
o Require a high level of patient
compliance
o Not suitable for patients with poor
dentition or with edentulism.
HeadFIX

18. THERMOPLASTIC MOULDS
o Thermoplastic material - Polymer of styrene acrylonitrile copolymer and
polycaprolactone (HMW)
o Thickness of 1.6 – 4.2 mm
o The polymer chains associate through intermolecular forces - weaken rapidly
with ↑ temperature (Heated to ~ 70°C in water bath or dry heat oven)
o Becomes malleable, can be stretched and shaped to conform to the body part
and maintain it on cooling after initial shrinkage (in first 24- hour period)
o The mask is connected to a base plate, which is attached to the couch via the
indexing system
o Systematic & random errors have standard deviations ranging from 1 to 4 mm

19. COMMERCIALLY
AVAILABLE
THERMOPLASTIC
MOULDS

21. Steps in Making a
Thermoplastic Mask
1. Temperature of water bath between 65 °C and 70 °C (149°F – 158°F).
2. Heating time in the water bath approximately 3-4 minutes
3. Ensure proper patient positioning and instructions.
4. Dry the mask sufficiently to avoid hot water from dripping on the patient.
5. Position the mask over patient’s body part and clamp it to base plate
6. Mold the mask over patient’s bony parts, ensuring alignment throughout
molding (e.g. – chin contour, nasal bridge, head tilt, roll)
7. Leave the mask on the patient for at least 10 minutes to allow it to harden
completely.
8. Label it with patient’s ID, name, date and simulation details.

22. Gilbeau et al, 2001
o N=30
o Randomized to 3, 4 & 5 clamp mask
o Weekly portal images acquired for 3 fictitious isocentres –
at the level of head, the neck and the shoulders
o For HN isocentres, No substantial difference in the setup deviation amongst
the masks.
o Setup reproducibility significantly worse at the shoulders with 3 cl. mask.
o 1 SD of 2.3 mm vs 0.8 mm vs 1.2 mm for 3, 4 & 5 PF masks
o Conclusions:
o Thermoplastic masks provide an accurate patient immobilization.
o At the shoulder level, setup variations are reduced with 4 or 5 PF masks
Systematic 3D error mean (mm) (SD) Random 3D error (mm)
Head Neck Shoulder Head Neck Shoulder
3 Clamp mask 3.1 (1.0) 2.3 (0.8) 2.5 (1.2) 0.7 0.9 2.3
4 clamp mask 2.4 (0.8) 1.7 (1.0) 3.7 (1.1) 0.9 1.0 0.8
5 clamp mask 2.4 (0.9) 2.2 (1.0) 2.8 (1.1) 1.0 1.0 1.2

23. o Patient receiving adjuvant RT for a head and neck cancer EPID
equipped LA
o 4 clamp HN orfit
o 99 % of the displacements were within 5 mm in all three cardinal
directions.
o Systematic component represents the displacement that was
present during the entire course of treatment.
o Random errors represent day-to-day variation in the set-up of
the patient.
Mean displacements
AP - 0.25 mm
ML - 0.48 mm
SI + 0.45 mm
Systematic
Errors
Random
Errors
AP 0.96 mm 1.97 mm
ML 0.98 mm 1.97 mm
SI 1.2 mm 2.48 mm

24. o N = 260
o RCT 3 clamp head mask (HM) vs 4 clamp head-and-shoulder mask (HSM)
o 3DCRT
o Compared actual treatment table positions, Patient tolerability and comfort, radiation-induced
skin toxicity weekly
o No statistically significant difference in terms of reproducibility.
o Patients using HSM
- Experienced significantly more claustrophobia (p = 0.023)
- Receiving ≥60 Gy had more skin reactions
o Conclusion : Smaller HM reduced claustrophobia and skin reactions, for patients receiving ≥60
Gy & did not compromise the reproducibility of the setup.
Sharp L et al, IJROBP, 2005 3 Clamp
4 Clamp

25. MERITS
1. Versatile
2. Easy to make and use
3. Compatible with imaging
modalities
4. Compatible with beam
modifiers
5. Good reproducibility of setup
ISSUES
1. Expensive
2. Re-use difficult
3. Storage
THERMOPLASTIC MOULDS

26. HEAD AND NECK SUPPORT
o Low Density foam head supports made of polyethylene foam covered
with a Polyurethane coating resulting in a good dimensional stability.
o Shape comfortably cradles the patient’s head & the cranial stop allows
a correct and reproducible position within the head support
o Dosimetric properties per cm of material through which the beam
passes:
o Attenuation at 6 MV: 0.15 %/ cm.
o Attenuation at 15 MV: 0.05 %/ cm.
o Available in variety of sizes (adult/ paediatric) and lengths

27. Flexion/extension as per individual patient
anatomy, tumour location and target volume.

28. Budrukkar et al. – JCRT 2008

29. SHOULDER
TRACTION
o Proper depression of shoulder
using rubber traction/grip bars
for exposure of lower neck for
beam entry.

30. BASE PLATE
o The plate onto which the immobilization systems are secured
o Material - Strong AND minimally attenuating the radiation
beam.
o Acrylic, Carbon fibre
o Low attenuation index
ALL IN ONE BASE PLATE

31. IMMOBILISATION DEVICES FOR SRS
o Invasive :
1. Leksell Stereotactic coordinate Frame G
2. Brown Roberts Wells (BRW) frame system
3. Talon system - Relocatable
o Non Invasive:
1. Brainlab Non Invasive Mask System
2. Gill Thomas Cosman (GTC) Relocatable
Head Ring
3. Tarbell Loeffler Cosman (TLC) Pediatric
Head Ring

32. LEKSELL STEREOTACTIC
COORDINATE FRAME G
o Compatible with linear accelerator and gamma knife, by ELEKTA
o The frame is attached to 4 adjustable posts, and 4 self tapping screws are
driven into the skull to fix the device to the head
o A CT/MRI Indicator is then attached to the frame for treatment planning
o At the time of treatment, head ring is attached to the couch for rigid
immobilisation and is shifted into position based on the stereotactic
coordinates determined from planning.
o Overall accuracy (mean ± SD)
o MR-defined target 0.2 ± 0.3 mm
o CT-based target 0.05 ± 0.1 mm

33. BROWN-ROBERTS-WELLS
(BRW) FRAME
o Linear accelerator based frame by Integra
o The frame is connected to 4 posts fixated to skull by 4 pins
o Has set of vertical and diagonal indicator rods to facilitate
stereotactic localization within the image set
o For treatment, the ring and BRW frame are attached with an
adapter to the treatment couch or to a floor mounted stand
o Mean deviation between frame - based and image-guided
positioning of 1.0 ± 0.5 mm
o Mean intra-fraction deviation 0.4 ± 0.3 mm

34. BRAINLAB NON INVASIVE
MASK SYSTEM
o Non invasive rigid cranial immobilisation
o U-shaped frame, two vertical posts, 3 piece thermoplastic mask,
optional bite block attachment
o Thermoplastic shells are custom shaped to the anterior and
posterior aspect of the patient’s head
o The shells are fastened to the vertical posts, and attached to the
head ring
o The ring is attached to the CT couch by an adapter
o Optional bite block can be connected to the anterior part of the
frame to provide additional support.

35. GILL – THOMAS- COSMAN
(GTC) FRAME
o Non invasive and relocatable
o Compatible with the BRW frame

36. o Invasive frame based immobilization may be considered for single fraction treatment of
small targets < 5mm
BrainLAB mask system Invasive head frame
Mean intra-fraction shift 0.7 mm (SD = 0.5 mm)
(vertical component more)
0.4 mm (SD = 0.3 mm)
Intra-fraction shift
percentage of >/ = 1 mm
22 % 3 %

37. BODY CONFORMAL SYSTEMS
(CRADLE – TYPE DEVICES)
o These devices are placed between couch top and the
patient , and are custom moulded to patient's body
o Mainly used for thorax, abdomen and pelvis.
o E.g: Alpha cradle
o Vac-Loc bag
o BodyFIX

38. ALPHA CRADLE
o Two-part chemical foaming agents are mixed together, initiating the
chemical reaction that causes Polyurethane foam to expand.
o The mixed foaming agent is distributed evenly throughout the body
form and sealed inside the polyvinyl bag,
o Patient is positioned in the treatment position on top of a polyvinyl bag
as the foaming agent expands 10 to 15 mins and conforms to the
patient’s body contour
o As the foam rises, technician maneuvers it around the patient .
o Once the foam hardens, the customized device is ready for use.
o Used in Ca breast, Prostate, Hodgkin’s lymphoma, Lower extremities,
Thorax, etc.
Registered trademark of
Smithers Medical Products, Inc., US

39. VACUUM - LOCK BAGS
o A durable nylon material bag filled with plastic mini-spheres (polystyrene
confetti)
o Variety of sizes : to accommodate different treatment sites and patient
positioning techniques.
o After positioning the patient over the bag, it is first conformed to the
patient’s body contour by pushing the mini-spheres to fill in around the
patient.
o A vacuum pump is then connected to the bag and the air is evacuated
causing the confetti to lock together to rigidly retain the device’s shape,
while maneuvering to provide optimal fit of the patient’s body contour.
o Longer devices need longer setup marks to be made in the superior–inferior
direction to help detect rotational setup errors
o Should be placed outside treatment field whenever possible to keep skin
dose to a minimum level.

40. ADVANTAGES
o Resists tears or punctures
o Expected to retain their shape for 6
weeks or more.
o Reusable
o Require less time to generate a
customized mold than the expanding
foam systems.
o Can be re-inflated and remolded to
achieve the desired shape as many
times as necessary
DISADVANTAGES
o If a tore or punctured during the
course of treatment, a new vacuum-
lock bag needs to be made and
treatment planning process may need
to be repeated to deliver the
remaining fractions
o Less well conformed to the finer
details.
o Patient setup in vacloc and alignment
time consuming
VACUUM - LOCK BAGS

41. BodyFIX
o Vacuum lock bag with a vacuum sealed total body plastic cover sheet
o Patient first placed in a vacloc bag system
o A thin plastic cover sheet is then placed over the patient, attached to
the vacloc bag via special adhesive strips.
o Vacuum pump evacuates the air under the cover sheet, creating a
continuous pressure of up to 0.6 atm.
o The additional pressure by the cover-sheet vacuum system helps the
patient settle into the vacloc bag, which is molded to the patient and
then evacuated with a second vacuum system to create body
conformal device.
o For all subsequent treatment fractions, the pressure from the cover-
sheet vacuum system helps the patient settle reproducibly in the
vacuum-lock bag.
1. Better alignment and
fixed geometry of the
patient with respect to
couch and the
immobilization device
2. Can also provide a
degree of abdominal
compression
3. Adhesive attachments
present on cover sheet
for infrared markers
for special techniques
– DIBH/ DEBH
Elekta

42. 2017
o N = 45
o Randomized to Q fix arm shuttle, BodyFIX without wrap or BodyFIX with wrap.
o Patients were imaged before and after treatment to ascertain intra-fraction and inter-fraction
motion.
o Bony anatomy was used for matching to determine the positional accuracy of each device.
o The BodyFIX without wrap was the more accurate device, BUT not statistically significant.
o BodyFIX with wrap was found to take significantly longer to set up and set down time
o Patients (37%) marginally preferred the BodyFIX with wrap.
o Most (81%) staff preferred the BodyFIX without wrap

43. Navarro-Martin et al.
Radiation Oncology
(2015)
Thermoplastic masks
offers better
reproducibility with
significantly less inter-
fractional set up
displacement than
vacuum cushions.

44. ABDOMINAL COMPRESSION
o Liver SBRT
o Low pressure foil vs Abdominal compression
o Significant decrease in cranial movement of
tumour in 4DCT
o Stomach Adjuvant RT:
o Mean ML displacements
o without compression - 5.92 mm
with compression - 4.15 mm
o Mean CC displacements
o without compression - 11.3 mm
with compression - 7.2 mm
o Range of reduction
o 29.85% in ML
o 36.86% in CC direction.
o Placed 3 to 4 cm below the costal margin and inferior to the xiphoid
process.
o High compression levels achieved reduction of tumor motion to <1 cm
o Abdominal compression significantly reduced tumor motion in the lateral,
SI direction and overall.

46. ACTIVE BREATH CONTROL
o Breath hold at a predefined lung
volume
o Non invasive
o Immobilizes target anatomy during
planning, imaging and treatment
delivery
o Reduces dose to OARs, enables
dose escalation in SBRT
o Reduces treatment time by
instantaneous beam on & off as
patients holds his breath

47. BREAST
o Supine with arms overhead
o Head turned to opposite side if
including SCF
o Modern Breast Board:
Wide range of indexed tilt angles ,
cut –away head holder to prevent
interference with the tangential
beam at steep angles and Arm
support system
T BAR
WEDGE
ACTREC BREAST BOARD
MEDTECH BREAST BOARD

48. PRONE BREAST
PLATFORM
o Patients with large, pendulous breast
o Goal - To minimize the lateral tissue separation
o Decreased entrance dose needed to provide target coverage at depth
 decreases the overall hot spot for the treatment plan, particularly at
the skin surface
o Produces more homogeneous dose distribution.
o Decreased rate of late toxicities like fibrosis better cosmetic outcome
o Also reduces mean lung and cardiac doses
o Risks under-dosage at the medial and lateral borders of the PTV close
to the chest wall, and should be avoided for primary tumours in these
situations.

49. Q FIX (WINGED
BOARD) Single‐pole position
more comfortable and
can reduce dose
coverage to heart as
compared to double -
pole in
postmastectomy
radiation

50. OMNIBOARD

51. PELVIS o A randomized trial of Supine vs Prone simulation &
treatment for Ca Prostate
o Less prostate motion in Supine Position
o Prone position required larger PTV
o Stastistically significant improvement in small bowel,
bladder & rectum doses in supine position
o Patient comfort & technologist’s convenience better
with Supine.
Bayley et al, 2003

52. BELLY BOARD
o Set up: Prone position
o Ca Rectum, 3DCRT
o With the aid of gravity, the small bowel will fall into the
board’s cutout
o Reduces the volume of small bowel at all dose levels in
the treatment fields
o A comfortably full bladder protocol is used for planning
and treatment as this displaces small bowel superiorly
o Modern belly board devices are more comfortable,
improve immobilisation, have calibration and reduce set-
up errors in the prone position.

53. PELVIS
 Fiorino et al. (1998) compared pelvic alpha cradle, leg immobilisation,
and no immobilisation. Reduction in random error in the patients
immobilised at the ankle compared to pelvic/no immobilisation.
 Retrospective study immobilization with a leg separator, whole body
vacuum bag cushion (VBC) & 6 point aquaplast immobilization system
o Orthogonal EPID for first five #  once weekly
o VBC - position, alignment of tattoos to lasers, fine adjustments
difficult
VBC Aquaplast Leg separator
Systematic error (mm Mean ± 1SD) 4.31 ± 3.84 3.39 ± 1.71 2.42 ± 0.97

54. PELVIS
o N = 30
o Randomised cross over trial (after 3 weeks)
o Portal images of each field acquired daily for 1st 5 #  twice weekly later
o Weekly patient and technologist questionnnaire
Radiotherapy & Oncology, 2000
Conventional treatment position (CTP) Immobilisation system (IMS)
Simulation &
treatment position
Supine, Pillow, Ankle stock, Tattoed Supine, VAC FIX (from iliac crest to upper thigh) on
customized couch top, Pillow, Ankle stock, Tattoed
Median sim. time 22.5 min (range 20±30 min) 25 min (range 15±40 min)
Median t/t time 9 min (range 8±10 min) 10 min (range 8.5±13.5 min)
CONCLUSION : IMS showed no improvement in treatment accuracy, with increase in both
treatment and planning times and difficult patient set up

55. o Rectal Displacement Device improves prostate and rectal intrafraction stability as
assessed by cine MRI. This improvement increases with treatment time.
o Rectal dosimetry was significantly improved with the RDD.
o The improvement in stability could potentially translate into reduced margins,
further sparing OARs.
BRACHYTHERAPY

56. EXTREMITIES
o Thermoplastic
moulds
o Vacuum casts
o POP moulds
TOTAL BODY IRRADIATION
Harness

57. DOSIMETRIC CONSIDERATIONS
AAPM TG 176
o Any material placed between the patient and radiation source can modify dosimetric characteristics of
the treatment beam.
o Modern immobilization devices made of low-density materials - little impact on the depth-dose
characteristics of MV energy treatment beams
o Electrons liberated within the immobilization device can lead to a measurable increase in patient’s
surface dose by a bolusing effect.
o Magnitude depends on composition, density, and thickness of the immobilization device & beam
energy, field size, and geometric arrangement.
o Hadley et al. – Increase in surface dose from 16% without mask to 61% with thermoplastic mask using
6-MV photons
o Body conformal immobilization devices exhibit dosimetric behavior of additional 0.2 cm of water
equivalent thickness for physical device thickness of 2 cm (1:10 ratio for low-density vacloc bags)

58. Jabbari K, Almasi T, Rostampour N, Tavakoli MB, Amouheidari A. Evaluating the effect of the
vacuum bag on the dose distribution in radiation therapy. J Can Res Ther 2018;14:1245-50

59. o Considerable reduction in prescription dose coverage rate and mean dose to the
target volumes
o Increase in the skin dose could be up to 53% on average.
o The immobilization device should be included within external body contour to
account for the dose attenuation and skin dose increment in the TPS calculation
Dosimetric Effects of Head and Neck Immobilization
Devices on Multi-field Intensity Modulated Radiation
Therapy for Nasopharyngeal Carcinoma
Li Chen et al, 2018

60. ADVANTAGES OF
IMMOBILISATION DEVICES
1. Limits patient movement - Rotational and Translational
2. Reduce the probability of non-rigid body rotation of one portion
of the patient relative to another
3. Stabilizes the relationship between external skin marks/surface
fiducials, couch and internal structures
4. Reduce the time for daily patient setup
5. Make the patient feel more secure and less apprehensive
6. Reduce the reliance on patient cooperation and alertness

61. DRAWBACKS
Does not address
1. Movement of the target with respect to other
tissues
2. Change of shape or size of the target during the
course of radiotherapy
3. Change in position of surface marks relative to
internal organs during the course of radiotherapy
4. Deformation of the immobilization device
5. Dosimetric effect – Attenuation and Bolusing

62. CHOOSE WISELY,
TREAT WELLImmobilization
Device
Displacement
Invasive frame 0.05 – 0.5 mm
Non invasive frame 0.7 - 1 mm
Thermoplast 1 - 4 mm
Bite block 1 - 4 mm
Body conformal 3 - 6 mm

63. THANK YOU