2. Contents of the Lecture :
Types of radiotherapy
Notion of Simulator
EBRT - treatment approaches
Brachytherapy Sources and Equipment
1. Clinical brachytherapy applications
2. Implant techniques and applicators
3. Delivery modes and equipment
4. Special techniques
– A. Prostate seed implants
– B. Endovascular brachytherapy
– C. Ophthalmic applicators
3. Radiation therapy given before surgery is called pre-
operative or neoadjuvant radiation. Neoadjuvant
radiation may be given to shrink a tumor so it can be
removed by surgery and be less likely to return after
surgery.
Radiation therapy given during surgery is called
intraoperative radiation therapy (IORT). IORT can be
external-beam radiation therapy (with photons or
electrons) or brachytherapy. When radiation is given
during surgery, nearby normal tissues can be
physically shielded from radiation exposure. IORT is
sometimes used when normal structures are too
close to a tumor to allow the use of external-beam
radiation therapy.
4. •Radiation therapy given after surgery
is called post-operative or adjuvant
radiation therapy.
•Radiation therapy given after some
types of complicated surgery
(especially in the abdomen or pelvis)
may produce too many side effects;
therefore, it may be safely if given
before surgery in these cases
6. External Beam Therapy (EBT)
Non-invasive
Target localization important and beam
placement may be tricky
Usually multiple beams to place target
in the focus of all beams
patient
Single beam Three coplanar beam
Multiple non-
coplanar beams
9. Simulator
Important to mimic
isocentric treatment
environment
However, some
functions can be
replaced by other
diagnostic X Ray units
provided the location
of the X Ray field can
be marked on the
patient
unambiguously
Other functions
(isocentricity) can then
be mimicked on the
treatment unit
10. Radiotherapy simulator
A diagnostic X Ray unit mimicking the
geometry of a treatment unit
Diagnostic aspects covered in course of
diagnostic radiology
Additional features:
– field defining wires
– centre of field indication
– couch matches treatment couch
12. Virtual simulation
All aspects of simulator work are
performed on a 3D data set of the patient
This requires high quality 3D CT data of
the patient in treatment position
Verification can be performed using
digitally reconstructed radiographs (DRRs)
14. Digitally Reconstructed Radiographs
as reference image for verification
View and print
DRRs for all
planned fields:
Improved
confidence for
planning and
reference for
verification
18. Target delineation
Treated Volume =
volume that receives
dose considered
adequate for clinical
objective
Irradiated volume =
dose considered not
negligible for normal
tissues
21. Customization of blocks
Pour low melting
alloy into foam
Customized blocks
include divergence
of the beam
Blocks are mounted
on trays
22. Conformal radiotherapy
Conform the
treated volume
(receiving a
therapeutic dose)
to the planning
target volume
shield all areas
surrounding it
micrologic circuit is
an option for this
23. Compensator manufacturing
Sheets of lead
glued together
Automatic
milling into
foam - this can
be filled with
low melting
alloy or steel
shot
24. Volume effects
The more normal tissue is irradiated in
parallel organs
– the greater the pain for the patient
– the more chance that a whole organ fails
Rule of thumb - the greater the volume the
smaller the dose should be
In serial organs even a small volume
irradiated beyond a threshold can lead to
whole organ failure (e.g. spinal cord)
25. 2. External beam radiotherapy
(EBRT) treatment approaches
Superficial X Rays
Orthovoltage X Rays
Telecurie units
Megavoltage X Rays
Electrons
Heavy charged particles
Others
26. Superficial radiotherapy
50 to 120kVp - similar to diagnostic X Ray
qualities
Low penetration
Limited to skin lesions treated with single
beam
Typically small field sizes
Applicators required to collimate beam on
patient’s skin
Short distance between X Ray focus and skin
28. A kV X Ray unit
Two independent timers:
elapsed time and time
29. Operator control
kV and mA
indicator
Selection
of filter
Radiation on
indicator
Dual timer
Key for
lock-up
Emergency
off button
30. Orthovoltage radiotherapy
150 - 400kVp
Penetration sufficient for palliative
treatment of bone lesions relatively close
to the surface (ribs, spinal cord)
Largely replaced by other treatment
modalities
32. Megavoltage radiotherapy
60-Cobalt (energy 1.25MeV)
Linear accelerators (4 to
25MVp)
Skin sparing in photon
beams
Typical focus to skin
distance 80 to 100cm
Isocentrically mounted
33. Isocentric set-up
Result of the large
FSDs possible with
modern equipment
Places the tumour
in the centre -
multiple radiation
beams are easily
set-up to deliver
radiation from many
directions to the
target
Image from
VARIAN webpage
34. Other radiation types
Neutrons
– Complex radiobiology
– Complex interactions
– Potential advantages for hypoxic and
radioresistant tumors
– Not widely used
Protons - probably the most promising
other radiation type
35. Intensity modulation
Optimize the dose distribution
Make dose in the target homogenous
Minimize dose out of the target
Different techniques
– physical compensators
– intensity modulation using multileaf
collimators
37. Total body irradiation (TBI)
Target: Bone marrow
Different techniques available
– 2 lateral fields at extended focus
– AP and PA
– moving of patient through the beam
Typically impossible to do a
computerized treatment plan
Need many measurements
38. TBI: one possible patient position
Couch top
Breast board
Rice bags
Angle of breast board
adjusted for individual
patients
Placed all around body
to achieve two distinct
separations
Radiation field
at >3m FSD;
collimator rotated
40. Image registration
Variety of systems
Many frame
attachments to
allow for different
diagnostic
modalities (MRI,
CT, angiography)
41. Stereotactic procedures
Spatial accuracy around 1mm
High dose single fraction (e.g. for
arterio-venous malformations) =
stereotactic radiosurgery using an
invasively mounted head frame
Multiple fractions for tumour
treatment = stereotactic radiotherapy
using a re-locatable head
immobilisation
42. EBT verification tools
Correct location
– portal films
– electronic portal imaging
Correct dose
– phantom measurements
– in vivo dosimetry
43. Gammaknife
Used for stereotactic brain irradiations
201 sources of Co-60 around a patients
head - only sources which shall contribute
to the irradiation are ‘unplugged’
alignment crucial
46. Brachytherapy overview
Brachytherapy uses encapsulated
radioactive sources to deliver a
high dose to tissues near the
source
brachys (Greek) = short (distance)
Inverse square law determines
most of the dose distribution
Per patient treated the number of
accidents in brachytherapy is
considerably higher than in EBT
47. Sealed sources
Closed radiopharmaceutical it is a radioactive drug,
which is located in capsule and at the cost of it the
spreading of ionizing chemical agent into surroundings is
absent. There are used the chemicals of radium drug,
caesium, iridium, radioactive gold and gamma ray (for
intracavitary gamma-therapy, contact gamma-therapy
and interstitial radiotherapy).
Opened radiopharmaceutical it is a radioactive drug
where the spreading of ionizing chemical agent into
surroundings is possible. Radiopharmaceuticals may be
taken inside (iodine 131), also may be used
intravenously (phosphorus 32) and implanted within the
organ (colloidal solution of radioactive yttrium).
49. Brachytherapy Sources
A variety of source shapes and forms:
– pellets = balls of approximately 3 mm diameter
– seeds = small cylinders about 1 mm diameter and 4 mm
length
– needles = between 15 and 45 mm active length
– tubes = about 14 mm length, used for gynaecological
implants
– hairpins = shaped as ‘hairpins’, approximately 60 mm active
length
– wire = any length, usually customised in the hospital -
inactive ends may be added
– HDR sources = high activity miniature cylinder sources
approximately 1mm diameter, 10mm length
51. Source form examples
Seeds:
– small containers for activity
– usually 125-I, 103-Pd or 198-Au for permanent
implant such as prostate cancer
Needles and hairpins:
– for ‘life’ implants in the operating theatre - activity
is directly introduced in the target region of the
patient
– usually 192-Ir for temporary implants e.g. of the
tongue
Scale in mm
53. A. Surface moulds
Treatment of superficial lesions with
radioactive sources in close contact
with the skin
A mould for the back
of a hand including
shielding designed to
protect the patient
during treatment
Hand
Catheters for
source transfer
63. Breast implants
Typically a boost
Often utilizes templates to improve source
positioning
Catheters or needles
64. Special techniques
A. Prostate seed implants
B. Endovascular brachytherapy
C. Ophthalmic applicators
D. Other special techniques
Both point B and C are examples for the use
of brachytherapy for non-oncological purposes
65. A. 125-I seeds for
prostate implants
Relatively new technique
Indicated for localized early stage prostate
cancer
Permanent implant
Preferred by many patients as it only
requires one day in hospital
69. HDR brachytherapy procedure
Implant of applicators, catheters or needles in theatre
For prostate implants as shown here use transrectal
ultrasound guidance
70. CT post-planning after 4 weeks
Swelling is gone - CT provides true three dimensional
information on the implant geometry
72. The issue: re-stenosis
After opening of a blocked blood vessel
there is a high (60%+) likelihood that the
vessel is blocked again: Re-stenosis
Radiation is a proven agent to prevent
growth of cells
Radiation has been shown to be effective
in preventing re-stenosis
73. Radioactive stents
Stents are used to
keep blood vessels
open
Can be impregnated
with radioactive
material (typically 32-
P) to help prevention
of re-stenosis
75. Isotopes for endovascular
brachytherapy
Gamma sources: 192-Ir
– the first source which has been clinically used
(Terstein et al. N Eng J Med 1996)
Beta sources: 32-P, 90-Sr/Y, 188-Rh
(Rhenium)
Activity around 1Ci
Dose calculation
76. Radiation safety in theatre
Application of
radiation in theatre:
– time is of the essence
- planning in situ
– shielding would be
difficult
– physicists must be
present
78. C. Ophthalmic applicators
Treatment of pterigiums
and corneal vasculations,
a non-oncological
application of
radiotherapy
Use of beta sources -
mostly 90-Sr/Y
Typical activity 40 to
200MBq (10-50mCi)
79. Ophthalmic applicators
Activity covered by thin plated gold or
platinum
Curvature to fit the ball of the eye
Diameter 12 to 18mm
Activity may only be applied to parts of
the applicator
Typical treatment time for several Gy
less than 1min
80. Intra-operative brachytherapy
In practice not often used because
– not always possible to predict if radiation
will be needed during the operation
– requires radiation oncologist to be
available
– radiation safety issues
shielded theatre costly
patient must be left alone during irradiation
even if less than 5min this is a risk due to
anesthetics
