Radiation Protection in Radiotherapy Part 5 Properties and
safety of radiotherapy sources and equipment used for external beam
radiotherapy IAEA Training Material on Radiation Protection in
Radiotherapy Slide 2 IAEA Safety Series 120, Safety Fundamentals
(1996) Source: Anything that may cause radiation exposure an X-ray
unit may be a source Slide 3 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques3
External Beam Radiotherapy patient tumour Beam 3 Beam 2 Beam 1
Slide 4 Radiation Protection in RadiotherapyPart 5, lecture 1:
Radiation types and techniques4 External Beam Therapy (EBT) l
Non-invasive l Target localization important and beam placement may
be tricky l Usually multiple beams to place target in the focus of
all beams patient Single beam Three coplanar beam Multiple non-
coplanar beams Slide 5 Radiation Protection in RadiotherapyPart 5,
lecture 1: Radiation types and techniques5 External Beam
Radiotherapy l More than 90% of all radiotherapy patients are
treated using EBT l Most of these are treated using X Rays ranging
from 20keV to 20MeV in peak-energy l Other EBT treatment options
include telecurie units (60-Co and 137-Cs), electrons from linear
accelerators and accelerators for heavy charged particles such as
protons Slide 6 Radiation Protection in RadiotherapyPart 5, lecture
1: Radiation types and techniques6 Objectives l To become familiar
with different radiation types used for external beam radiotherapy
l To understand the function of different equipment used for EBT
delivery l To appreciate the implications of different treatment
units and their design l To be familiar with auxiliary equipment
required and used for EBT l To understand the measures used in this
equipment to ensure radiation safety Slide 7 Radiation Protection
in RadiotherapyPart 5, lecture 1: Radiation types and techniques7
Contents l Lecture 1: Radiation types and techniques l Lecture 2:
Equipment and safe design Slide 8 Radiation Protection in
Radiotherapy Part 5 External Beam RT Lecture 1: Radiation types and
techniques IAEA Training Material on Radiation Protection in
Radiotherapy Slide 9 Radiation Protection in RadiotherapyPart 5,
lecture 1: Radiation types and techniques9 Objectives l To be
familiar with different radiation types used in EBT l To appreciate
the technical needs to make these radiation types applicable to
radiotherapy l To understand common external beam radiotherapy
techniques Slide 10 Radiation Protection in RadiotherapyPart 5,
lecture 1: Radiation types and techniques10 Contents 1. External
Beam Radiotherapy process 2. Radiation qualities in use 3. Delivery
techniques 4. Prescription and reporting 5. Special procedures
Slide 11 Radiation Protection in RadiotherapyPart 5, lecture 1:
Radiation types and techniques11 1. EBT process Slide 12 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques12 EBT process: Use of radiation Slide 13 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques13 Note on the role of diagnosis l The responsibility of
clinicians l Without appropriate diagnosis the justification of the
treatment is doubtful l Diagnosis is important for target design
and the dose required for cure or palliation Slide 14 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques14 Note on the role of simulation l Simulator is often
used twice in the radiotherapy process n Patient data acquisition -
target localization, contours, outlines n Verification - can the
plan be put into practice? Acquisition of reference images for
verification l Simulator may be replaced by other diagnostic
equipment or virtual simulation Slide 15 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques15
Simulator l Important to mimic isocentric treatment environment l
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 l Other functions (isocentricity) can then be
mimicked on the treatment unit Slide 16 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques16
Virtual simulation l All aspects of simulator work are performed on
a 3D data set of the patient l This requires high quality 3D CT
data of the patient in treatment position l Verification can be
performed using digitally reconstructed radiographs (DRRs) Slide 17
Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation
types and techniques17 CT Simulation (Thanks to ADAC) Marking the
Patient already during CT Slide 18 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques18
Virtual Simulation 3D Model of the patient and the Treatment
Devices Slide 19 Radiation Protection in RadiotherapyPart 5,
lecture 1: Radiation types and techniques19 Digitally Reconstructed
Radiographs as reference image for verification View and print DRRs
for all planned fields: Improved confidence for planning and
reference for verification Slide 20 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques20
Note on the role of treatment planning l Links prescription to
reality l The center piece of radiotherapy l Becomes more and more
sophisticated and complex l Extensive discussion in part 10 Slide
21 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation
types and techniques21 2. External beam radiotherapy (EBT)
treatment approaches l Superficial X Rays l Orthovoltage X Rays l
Telecurie units l Megavoltage X Rays l Electrons l Heavy charged
particles l Others Slide 22 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques22
External beam radiotherapy (EBT) treatment approaches l Superficial
X Rays l Orthovoltage X Rays l Telecurie units l Megavoltage X Rays
l Electrons l Heavy charged particles l Others +40 to 120kVp +150
to 400kVp +137-Cs and 60-Co +Linear accelerators +Protons from
cyclotron, C, Ar,... +Neutrons, pions Slide 23 Radiation Protection
in RadiotherapyPart 5, lecture 1: Radiation types and techniques23
Photon percentage depth dose comparison for photon beams
Superficial beam Orthovoltage beam Slide 24 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques24
Superficial radiotherapy l 50 to 120kVp - similar to diagnostic X
Ray qualities l Low penetration l Limited to skin lesions treated
with single beam l Typically small field sizes l Applicators
required to collimate beam on patients skin l Short distance
between X Ray focus and skin Slide 25 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques25
Superficial radiotherapy Philips RT 100 Slide 26 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques26 Superficial radiotherapy issues l Due to short FSD
high output and large influence of inverse square law l Calibration
difficult (strong dose gradient, electron contamination) l Dose
determined by a timer - on/off effects must be considered l Photon
beams may be contaminated with electrons from the applicator Slide
27 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation
types and techniques27 Orthovoltage radiotherapy l 150 - 400kVp l
Penetration sufficient for palliative treatment of bone lesions
relatively close to the surface (ribs, spinal cord) l Largely
replaced by other treatment modalities Slide 28 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques28 Orthovoltage Equipment (150 - 400 kVp) l Depth dose
dramatically affected by the FSD FSD 6cm, HVL 6.8mm Cu FSD 30cm,
HVL 4.4mm Cu Slide 29 Radiation Protection in RadiotherapyPart 5,
lecture 1: Radiation types and techniques29 Orthovoltage patient
set-up l Like for superficial irradiation units the beam is set- up
with cones directly on the patients skin Slide 30 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques30 Megavoltage radiotherapy l 60-Cobalt (energy 1.25MeV)
l Linear accelerators (4 to 25MVp) l Skin sparing in photon beams l
Typical focus to skin distance 80 to 100cm l Isocentrically mounted
Slide 31 Radiation Protection in RadiotherapyPart 5, lecture 1:
Radiation types and techniques31 Photon percentage depth dose
comparison l PHOTONS l ELECTRONS Slide 32 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques32
Typical locations of tumor and normal tissues l PHOTONS l ELECTRONS
Slide 33 Radiation Protection in RadiotherapyPart 5, lecture 1:
Radiation types and techniques33 Build-up effect Result of the
forward direction of secondary electrons - they deposit energy down
stream from the original interaction point Slide 34 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques34 Build-up effect l Clinically important as all
radiation beams in external radiotherapy go through the skin l Is
reduced in large field sizes and oblique incidence and when trays
are placed in the beam l Can be avoided by the use of bolus on the
patient if skin or scar shall be treated Slide 35 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques35 Isocentric set-up Slide 36 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques36
Isocentric set-up l Result of the large FSDs possible with modern
equipment l 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 Slide 37 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques37 Common photon treatment techniques l Two parallel
opposed fields n lung n breast n head and neck Slide 38 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques38 Common photon treatment techniques l Four field box n
cervix n prostate Slide 39 Radiation Protection in RadiotherapyPart
5, lecture 1: Radiation types and techniques39 Isocentric or not? l
All the beam arrangements discussed so far can be set-up with a
fixed distance (e.g. 80cm) to the patients skin or isocentrically
with a fixed distance to the centre of the target. Slide 40
Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation
types and techniques40 Photon beam modification l Blocks l Wedges l
Compensators Slide 41 Radiation Protection in RadiotherapyPart 5,
lecture 1: Radiation types and techniques41 Shielding blocks l Beam
shaping l Conform the high dose region to the target n Fixed blocks
n Customized blocks made from low melting alloy (LMA) l Partially
replaced now by Multi Leaf Collimator (MLC) Siemens MLC Customized
shielding block Slide 42 Radiation Protection in RadiotherapyPart
5, lecture 1: Radiation types and techniques42 Physical wedge Slide
43 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation
types and techniques43 Wedges l One dimensional dose modification l
Different realizations l Now often a dynamic wedge Slide 44
Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation
types and techniques44 Use of wedges l Wedged pair l Three field
techniques patient Isodose lines patientTypical isodose lines Slide
45 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation
types and techniques45 Compensators l Physical compensators n lead
sheets n brass blocks n customized milling l Intensity modulation n
multiple static fields n arcs n dynamic MLC Slide 46 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques46 Intensity modulation l Can be shown to allow
optimization of the dose distribution l Make dose in the target
homogenous l Minimize dose outside the target l Different
techniques n physical compensators n intensity modulation using
multileaf collimators Slide 47 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques47
Intensity Modulation l Achieved using a Multi Leaf Collimator (MLC)
l The field shape can be altered n either step-by-step or n
dynamically while dose is delivered MLC pattern 1 MLC pattern 3 MLC
pattern 2 Intensity map Slide 48 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques48
Dynamic treatment techniques l Arcs l Dynamic wedge l Dynamic MLC
increasing complexity with increasing flexibility in dose delivery.
Verification becomes essential patient Slide 49 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques49 Electron radiotherapy l Finite range l Rapid dose fall
off Slide 50 Radiation Protection in RadiotherapyPart 5, lecture 1:
Radiation types and techniques50 Characteristics of an electron
beam RpRp d max 50 0 10 20 30 40 60 70 80 90 100 0123456789101112
Depth (cm) %DD R 100 R 50 Surface dose Therapeutic range x-ray
component Slide 51 Radiation Protection in RadiotherapyPart 5,
lecture 1: Radiation types and techniques51 Electron beam isodoses
(20MeV) Watch bulging of isodoses at depth Watch dose increase
(115%!) due to oblique incidence Slide 52 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques52
Other issues with electron beams Dose distribution significantly
affected by surface contour changes - this must be considered when
using bolus to shape dose distribution at depth. Slide 53 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques53 Inhomogeneities affect the dose distribution Air
cavity Monte Carlo Calculations Slide 54 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques54 Use
of electrons l Skin lesions l Scar boosting l Avoidance of deep
lying sensitive structures (e.g. spinal cord) Slide 55 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques55 More issues with the use of electrons for radiotherapy
l Computer prediction of dose distribution more difficult l Small
fields difficult to predict l Dosimetry somewhat more difficult
than in photons due to strong dose gradients and variation of
electron energy with depth Slide 56 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques56
Other radiation types l Neutrons n Complex radiobiology n Complex
interactions n Potential advantages for hypoxic and radioresistant
tumors n Not widely used l Protons - probably the most promising
other radiation type Slide 57 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques57
Comparison to other radiation types Slide 58 Radiation Protection
in RadiotherapyPart 5, lecture 1: Radiation types and techniques58
Potential Advantage of Proton radiotherapy: dose sparing before and
behind the target due to Bragg peak Slide 59 Radiation Protection
in RadiotherapyPart 5, lecture 1: Radiation types and techniques59
Slide 60 Radiation Protection in RadiotherapyPart 5, lecture 1:
Radiation types and techniques60 X Rays versus protons Slide 61
Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation
types and techniques61 4. Prescription and reporting l Prescription
is the responsibility of individual clinicians, depending on the
patients condition, equipment available, experience and training. l
The prescription should follow protocols which are established by
professional organizations and modified and adopted by radiotherapy
departments. l The prescription must be informed - as far as
possible - by clinical evidence Slide 62 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques62
Prescription and reporting l Prescription may vary within reason
depending on equipment available l Reporting must be uniform - any
adequately educated person must be able to understand what happened
to the patient in case of: n need for a different clinician to
continue treatment n re-treatment of the patient n clinical trials
n potential litigation Slide 63 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques63
Recommendations by the ICRU l International Commission on Radiation
Units and Measurements l ICRU reports provide guidance on
prescribing, recording and reporting Slide 64 Radiation Protection
in RadiotherapyPart 5, lecture 1: Radiation types and techniques64
Target delineation l ICRU report 50 Slide 65 Radiation Protection
in RadiotherapyPart 5, lecture 1: Radiation types and techniques65
Definitions form ICRU 50 l Gross Tumour Volume (GTV) = clinically
demonstrated tumour l Clinical Target Volume (CTV) = GTV + area at
risk (e.g. potentially involved lymph nodes) Slide 66 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques66 Definitions form ICRU 50 l Planning Target Volume
(PTV) = volume planned to be treated = CTV + margin for set-up
uncertainties and potential of organ movement Slide 67 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques67 Strategies for margins l Margins are most important
for clinical radiotherapy - they depend on: n organ motion -
internal margin n patient set-up and beam alignment - external
margin l Margins can be non-uniform but should be three dimensional
l A reasonable way of thinking would be: Choose margins so that the
target is in the treated field at least 95% of the time Slide 68
Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation
types and techniques68 Definitions form ICRU 50 l Treated Volume =
volume that receives dose considered adequate for clinical
objective l Irradiated volume = dose considered not negligible for
normal tissues Slide 69 Radiation Protection in RadiotherapyPart 5,
lecture 1: Radiation types and techniques69 l The concept of
margins was expanded on by ICRU report 62 n Internal margin = due
to organ motion n Set-up margin l The two are often combined as
independent uncertainties Slide 70 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques70 5.
Special procedures l Total body irradiation l Total electron skin
irradiation l Stereotactic radiosurgery Slide 71 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques71 Total body irradiation (TBI) l Target: Bone marrow l
Different techniques available n 2 lateral fields at extended FSD n
AP and PA n moving of patient through the beam l Typically
impossible to do a computerized treatment plan l Need many
measurements Slide 72 Radiation Protection in RadiotherapyPart 5,
lecture 1: Radiation types and techniques72 TBI: one possible
patient position Radiation field at >3m FSD; collimator rotated
Slide 73 Radiation Protection in RadiotherapyPart 5, lecture 1:
Radiation types and techniques73 Issues with TBI l In vivo
dosimetry essential l May need low dose rate treatment l Shielding
of critical organs (e.g. lung) and thin body parts may be required
n this can be only for parts of the treatment to achieve the best
possible dose uniformity Slide 74 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques74
Total electron skin irradiation l Treat all skin to very shallow
depth l Different techniques available n 4 or 6 fields n rotating
patient l Impossible to plan using a computer l Requires many
measurements for beam characterization Slide 75 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques75 Total Body Skin Irradiation l Multiple electron fields
at extended FSD l Whole body skin as target Slide 76 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques76 Issues with TBSI l Use low energy electrons (4 or
6MeV) l Spoiler in front of patient improves dose distribution l in
vivo dosimetry required l shielding of nails and eyes l boost of
some areas (e.g. under arms) may be required Slide 77 Radiation
Protection in RadiotherapyPart 5, lecture 1: Radiation types and
techniques77 Stereotactic procedures l Target usually brain lesions
l External head frame used to ensure accurate patient positioning l
Invasive or l Re-locatable Slide 78 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques78
Image registration l Variety of systems l Many frame attachments to
allow for different diagnostic modalities (MRI, CT, angiography)
Slide 79 Radiation Protection in RadiotherapyPart 5, lecture 1:
Radiation types and techniques79 Image registration CT scan MRI
Leksell fiducial markers on both Slide 80 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques80
Stereotactic procedures l Spatial accuracy around 1mm l High dose
single fraction (e.g. for arterio-venous malformations) =
stereotactic radiosurgery using an invasively mounted head frame l
Multiple fractions for tumour treatment = stereotactic radiotherapy
using a re-locatable head immobilisation Both systems MedTec Slide
81 Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation
types and techniques81 EBT verification tools l Correct location n
portal films n electronic portal imaging l Correct dose n phantom
measurements n in vivo dosimetry Slide 82 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques82 EBT
verification tools l Correct location n portal films n electronic
portal imaging l Correct dose n phantom measurements n in vivo
dosimetry l Part 10 with some comments in second lecture part 5
(now) l Parts 2 and 10 Slide 83 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques83
Summary l A wide variety of radiation qualities are available for
the optimization of radiotherapy for individual patients l The
choice depends on patient and availability of equipment l Given
adequate understanding of radiation properties and patient
requirements many highly specialized procedures have been developed
to address problems in radiotherapy Slide 84 Radiation Protection
in RadiotherapyPart 5, lecture 1: Radiation types and techniques84
Have we achieved the objectives? l To be familiar with different
radiation types used in EBT l To appreciate the technical needs to
make these radiation types applicable to radiotherapy l To
understand common external beam radiotherapy techniques Slide 85
Radiation Protection in RadiotherapyPart 5, lecture 1: Radiation
types and techniques85 Where to Get More Information l Part 10
relates directly to this part l References: sKarzmark, C, Nunan C
and Tanabe E. Medical electron accelerators. McGraw Hill, New York,
1993. l Site visit of... Slide 86 Any questions? Slide 87 Question:
Please put together a table comparing electron and X Rays produced
by linear accelerators Slide 88 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques88 X
Rays and electrons in EBT Slide 89 Radiation Protection in
RadiotherapyPart 5, lecture 1: Radiation types and techniques89
Acknowledgments l John Drew, Westmead Hospital, Sydney l Patricia
Ostwald, Newcastle Mater Hospital
