Immobilization in radiotherapy

1. IMMOBILIZATION
IN
RADIOTHERAPY
DR KIRAN KUMAR BR

2. Role of immobilization
• Patient positioning and immobilization are said to be
the most crucial parts of radiation therapy treatment.
• For accurate delivery of a prescribed radiation dose
to a target volume,while sparing sourrounding
normal and critical tissues.
• Without proper immobilization,the patient is at risk
for improper treatment and unwanted side effects
• Immobilization such as molds,casts,headrests,and
other devices are constructed to reduce setup error
and patient movement during treatment.

3. Contd..
• Although the primary goal of immobilization system
is to limit patient motion and reduce the probability
of major positioning errors, there are other benefits
as well..
• A well constructed immobilizing system can reduce
the time for daily patient set up.
• It can make the patient feel more secure and less
apprehensive.
• It can reduce the reliance on patient co-operation
and alertness, and it can help to stabilize the
relationship between external skin marks and
internal structures.

4. Desirable characteristics of
immobilization devices
• Ease of use.
• Ease of making the device.
• Comfort for the patient.
• Minimal space requirement for storage.
• Resistance to bending and streching.
• Minimal perturbation of the beam so as not to
produce artefacts in image acquisition.

5. HEAD,NECK AND BRAIN IMMOBILIZATION
• Initial construction and selection of proper
immobilization for head and neck cancer is one of the
most important parts of ensuring proper treatment of
the patient.
• In the past,patients for head&neck cancers were taped
to the table across their forehead.a bite block was
occasionally used in order to tilt the neck in a
reproducible manner.
• Current methods for head&neck and brain tumours
include a variety of masks,molds and frame systems.In
some instances,shoulder straps are used to pull the
shoulders out of the treatment field for the neck.

6. Contd..
• The most common
immobilization device used
to treat head&neck cancers
is an aquaplast.
• This device is made from a
rigid plastic that becomes
pliable when placed in
warm water.
• When it is wet ,it is placed
over the patients body and
conforms to the contour of
the treatment area.

7. contd…
• Advantages: Aquaplast provide great reproducibility
in daily treatments,lightweight and easy to use.
• Additionally modifications can be made to the mask
if the patient experiences swelling or weight loss
during the treatment.
• Disadvantages: windows cut cannot be reused.
when old becomes brittle and too soft when
activated.

8. Contd…
• 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

9. Contd..
• Indexing bar: the two pin
indexing bar is designed for
reproducible positioning and
stable fixation of base plates
on the treatment couch.
• 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.

10. Contd..
• Shoulder retraction: in patients with short neck or in
patients where opp lateral fields are used to treat the
neck, the shoulders need to be retracted caudally to
avoid entrance and exit doses.
• An elastic strap ,equipped with handles and attached
to each side of the treatment couch,can be used for
the patient to pull on.

11. IMMOBILIZATION IN BRAIN TUMORS
• Immobilization becomes more complex for
radiosurgery or gamma knife procedures,because the
requirements for positional and numerical accuracy
in dose delivery are ±1mm and 5% respectively.
• Hence highly precised and accurate reproducibility is
needed.
• Two types of fixation systems are used in
radiosurgery
1)GTC frame for fractionated therapy 2)BRW system
for single fraction radiosurgery.

12. Contd..
• 1)GTC relocatable head
ring is a non invasive
device that can be
repeatedly fixed to the
patient’s head in precisely
the same position.
• It has an impression taken
of the patients upper
dentition and the mold is
then mounted to the head
ring.
• An impression is also taken
of the occiput to conform
to the shape of the
patient’s head.

13. Contd..
• A biasing strap holds these
two components firmly in
place,so that precise
repositioning can be
achieved in each treatment
session
• The depth helmet provides
quality assurance.it allows
to conform the positional
accuracy.
• A depth probe with mm
scale can be passed in to
the guide tubes on the
helmet,so that the distance
from the hole to the
patient’s head can be
measured to mm accuracy.

14. Contd..
• 2)In single fraction radiosurgery,invasive procedure is
followed,the patient is fitted with a BRW system and
then bolted to the treatment table.Bolts are fitted
and screwed into the patients skull to minimize any
movement during treatment.

15. THORAX AND BREAST IMMOBILIZATION
• There are two common
immobilization systems used
when treating tumors in
chest cavity.
• 1)VACLOK:these are
custom,beanbag type pillows
that are placed around the
patients upper body.
• The air is then vaccumed out
of the bag for a custom fit
and sealed in order to retain
its shape.
• vacloks are
radiotranslucent.,almost air
equivalent. they are washable
and reusable.

16. Contd..
• 2)BREAST BOARD: is used
specifically for the
treatment of breast cancer.
• It has several adjustable
features to allow for the
manipulation of patients
arms,wrists,head and
shoulders.
• Breast boards are generally
constructed of carbon
fiber,allowing the device to
be lightweight and
durable.

17. Contd..
• Carbon fiber boards have lower attenuation
levels,which permit maximum beam penetration.
• The breast can also be immobilized using a
thermoplastic breast support system,the aquaplast
mold is taken of the breast to aid in placement when
lying supine on a breast board.
• Vacloks can also be used to improve patient set-ups
for the breast field.This type of treatment can involve
the simultaneous use of the vaclok system with
breast board.

18. PELVIC IMMOBILIZATION
• There are two different crucial aspects in the
immobilization of pelvic region.
1)to properly maintain patients outer contour during
treatment..with respect to isocentre.
2)other is related to variation of internal structures
during daily treatments.
• Immobilization systems such as vacloks,belly
boards,and the hip-fix(using aquaplast) system are
commonly used during treatments of pelvic region

19. Contd..
• Most of the pelvic
malignancies are treated
with partial body casts.
• A mask from the patient’s
mid thorax to upper thighs
is made by streching
warm, pliable thermoplast
over the patient and then
securing that mask to the
pelvic board by a locking
system.
• Windows on either sides
can be cut on the mask, so
that skin tattoos are visible
and can be used for
alignment.

20. Contd..
• A vaclok can also be
used for immobilization
in pelvic treatments.
• It should extend from
the lower thoracic area
to the mid thigh.
• Vacloks are popular
choice for hip and pelvic
positioning due to
patient comfort and set
up reproducibility.

21. Contd..
• Advantages: easy to use,
very little time to prepare,
comfortable for the patient,
and can be reused.
• Disadvantages: contour and shape may change with
handling and use.
• Expensive.

22. Contd..
• Belly boards are used
when the patient is
treated prone.
• Belly boards allow the
small bowel to drop
below the lateral field to
avoid severe side effects
of irradiation.
• Use of the belly board
significantly decreases
the average volume of
small bowel that would
otherwise be within the
lateral field during
standard box technique
treatment.

23. IMPROVED IMMOBILIZATION
TECHNIQUES
SMALLER TREATMENTVOLUME HIGHER CONTROLLED DOSES HIGHLY PRECISED TREATMENT
HIGHER CURE RATE

24. THANK YOU