View
233
Download
0
Category
Preview:
Citation preview
8/10/2019 Principles Radiotherapy
1/71
Basic Principles ofRadiotherapy
8/10/2019 Principles Radiotherapy
2/71
Objectives
At the end of this presentation, you
should be able to answer the followingquestions:1) What 3 basic principles need to be
considered when recommendingradiotherapy (RT)
2) What are the 3 basic RT approaches forcancer treatment (ie. When and why is itused)
8/10/2019 Principles Radiotherapy
3/71
3) What are some of the radiation treatment
modalities (list 5) available4) How is radiation treatment delivered (be
able to describe a standard approach)5) What are some site specific side effects
(describe 3 side effects for each of brain,head&neck, chest, breast, abdomen andpelvis)
8/10/2019 Principles Radiotherapy
4/71
Some general background
Radiation has been available as a treatment for
cancer for over 100 years. Ionizing radiation (X-rays) is a type of energyfound within the electromagnetic spectrum
(which also includes microwaves, radio wavesand visible light). The goal of radiation treatment is to deliver a
precisely measured dose of radiation to a target(tumour) with minimal damage to surroundingnormal tissue.
8/10/2019 Principles Radiotherapy
5/71
At the Clinic or Bedside
Consultation with Radiation Oncologist History & Physical Exam (the patient factors) Staging (the tumour factors) Diagnosis Recommend treatment (the treatment factors)
8/10/2019 Principles Radiotherapy
6/71
Pre-Treatment Planning
Should this patient be treated withradiation? Patient Factors:
Previous therapy Relevant past medical history
Performance status and age Social situation Wishes / likelihood of compliance
8/10/2019 Principles Radiotherapy
7/71
Pre-Treatment Planning
Should this patient be treated withradiation? Tumour Factors:
Type Extent
Natural history Treatment intent Treatment options, expected toxicities and
results
8/10/2019 Principles Radiotherapy
8/71
Pre-treatment Planning
What are 3 radiotherapeutic treatmentintentions ? (part A of treatmentfactors)
8/10/2019 Principles Radiotherapy
9/71
What are the 3 basic RT
approaches to cancer treatment1) Curative requires high doses, typically
above 60 Gy (the exceptionis lymphomas)2) Adjuvant requires intermediate doses,
typically in the range of 30-50Gy
3) Palliative low doses effective, notgreater than 30 Gy in mostcases
8/10/2019 Principles Radiotherapy
10/71
8/10/2019 Principles Radiotherapy
11/71
Dose fractionation
Curative Usually delivered as 2 Gy once
daily, but there can be smaller fractionsizes (1.2-1.8 Gy) or slightly larger fractionsizes (2.2 Gy).
Adjuvant Also usually delivered as 2 Gyonce daily, but there can be the samevariations as for curative.
Palliative Much larger fraction size (3-8Gy) is standard.
8/10/2019 Principles Radiotherapy
12/71
Examples of treatment delivery
Curative most often think of H&N
cancers where RT is theprimary treatment modality The patient requires an immobilization mask. The RO outlines the various target volumes
on CT images, and also outlines normalstructures that are in proximity to the tumour
Treatment planning can be very sophisticatedusing IMRT to target tumour and minimizedose to normal tissue.
8/10/2019 Principles Radiotherapy
13/71
Adjuvant Typically think of breast
treatment. In these cases,the gross tumour has beenremoved. The RO outlinesthe CTV/PTV and treatmentvolume, using standard X-ray(fluoroscopy) or CT imaging.Treatment planning can be2D or 3D.
8/10/2019 Principles Radiotherapy
14/71
Palliative Covers a wide range of sites.
The set-up is kept as simple as possible. Volume delineation may be done using
surface landmarks (eg. Ribs, clavicle,brain), fluoroscopic imaging (eg, spine,hips) or CT (lung, H&N, pelvis)
Planning is kept as simple as possible toexpedite initiation of treatment.
8/10/2019 Principles Radiotherapy
15/71
Questions/comments so far?
8/10/2019 Principles Radiotherapy
16/71
What are some RTmodalities for treatment of
cancer?
8/10/2019 Principles Radiotherapy
17/71
What are some RT modalities for
treatment of cancer 1) External beam
The commonest external beam utilizes photons Electrons are another type of external beam.
2) Sealed sources
- These are inserted into the patient and can betemporary or permanent (eg, gynecologic tumours aretreated with temporary insertions while prostatetumours are treated with permanent seed implants)
3) Unsealed sources- These are radionuclides such as iodine which are
ingested or injected.
8/10/2019 Principles Radiotherapy
18/71
Pre-Treatment Planning
Patient Education:
Rationale for treatment Expected toxicities of treatment
Process of treatment planning Rough time frame for starting treatment
8/10/2019 Principles Radiotherapy
19/71
Treatment Planning
Goal:
Evaluate possible treatment approaches, andchoose one that:
Gives the best (or at least an acceptable) dosedistribution
Is reproducible Is verifiable
8/10/2019 Principles Radiotherapy
20/71
Treatment Planning:
Simulation Mark-up
typically used for planning of RT ofsuperficial lesions (skin CA, breast boost,
palliative DXR for rib / sternal mets) also used for planning of palliative brain RT
Conventional Simulation CT-Simulation
8/10/2019 Principles Radiotherapy
21/71
Treatment Planning:
Simulation Get patient in optimal / acceptable
treatment position Allows reproducible and verifiable treatment of tumour Possible additional benefit: allows / increases sparing of
normal tissues Patient comfort is critical Pain control Use support devices and immobilization devices liberally
Can patient maintain desired position for 15 30 minuteswithout difficulty?
For a given site, avoid treating same patient in different
positions
8/10/2019 Principles Radiotherapy
22/71
Treatment Planning: Simulation
8/10/2019 Principles Radiotherapy
23/71
8/10/2019 Principles Radiotherapy
24/71
Treatment Planning: Simulation
CT-MRI fusion
used for planning of treatment of brain lesionsfairly routinely, as MRI and CT arecomplementary imaging modalities
8/10/2019 Principles Radiotherapy
25/71
8/10/2019 Principles Radiotherapy
26/71
8/10/2019 Principles Radiotherapy
27/71
Beam Choices
Orthovoltage
Photons Co-60 MV
Electrons Exotica (you cant do that here)
Neutrons Protons
8/10/2019 Principles Radiotherapy
28/71
Basic Beam Characteristics Orthovoltage Beam:
characteristics (PDD curve): full dose at surface rapid attenuation in tissue (~8%/cm with 250 kVp)
slightly slower with higher energy beams
compared to higher energy photons: increased absorption in bone increased scatter when bone in way of path to
tumour (i.e. decreased dose to tissue beyond) shorter SSD (typically 50 cm) Slow delivery (typically 10-15 minutes/field)
8/10/2019 Principles Radiotherapy
29/71
TBCC Orthovoltage PDD Curves(8 x 10 cm field)
020406080
100120
0 5 10 15
depth (cm)
d o s e (
% )
75 kVp225 kVp250 kVp
8/10/2019 Principles Radiotherapy
30/71
Clin RT Phys, 2nd ed, Fig. 15-2
Orthovoltage
8/10/2019 Principles Radiotherapy
31/71
Absorption in BoneClin RT Phys, 2nd ed,Table 14-3:
ratio of mass-energyabsorption coefficientsfor bone/muscle showsimpact of photoelectriceffect at low energiesseen with orthovoltage
radiation
8/10/2019 Principles Radiotherapy
32/71
Basic Beam Characteristics
Cobalt-60 beam:
characteristics (PDD curve): ~50% surface dose, with d max at 0.5 cm depth slower attenuation in tissue than orthovoltage
(~5%/cm) not a point source
geometric penumbra
contributes to total penumbra Treatment time typically 2-4 minutes
8/10/2019 Principles Radiotherapy
33/71
Co-60 Beam
Clin RT Phys, 2nd ed, Fig. 15-3
8/10/2019 Principles Radiotherapy
34/71
Basic Beam Characteristics
Megavoltage Photon Beam:
characteristics (PDD curve): decreased surface dose with gradual build-up to
dmax surface dose decreases as increase photon energy depth of d max increases as increase photon energy
slower attenuation in tissue than Co-60
rate of attenuation decreases as increase photon energy
Treatment delivery time typically 1-2 minutes/field
8/10/2019 Principles Radiotherapy
35/71
Megavoltage Beam
Clin RT Phys, 2nd ed, Fig. 15-4
8/10/2019 Principles Radiotherapy
36/71
PDD Curves, 10 x 10 cm field
02040
6080
100120
0 10 20
depth (cm)
%
d o s e Co-60
6 MV
18 MV
Co-60: past dmax (0.5 cm), lose ~ 5%/cm
6 MV: past dmax (1.5 cm), lose ~ 4%/cm
18 MV:past dmax (3 cm), lose ~ 3%/cm
8/10/2019 Principles Radiotherapy
37/71
Switching Horses
8/10/2019 Principles Radiotherapy
38/71
8/10/2019 Principles Radiotherapy
39/71
TBCC Electron PDD Curves, 10 x 10 cm field
0
20
40
60
80100
120
0 5 10 15
depth (cm)
d o s e
( % ) 6 MeV e-
9 MeV e-12 MeV e-16 MeV e-20 MeV e-
8/10/2019 Principles Radiotherapy
40/71
8/10/2019 Principles Radiotherapy
41/71
Exotica
Available in a few highly specialized centers
only
8/10/2019 Principles Radiotherapy
42/71
Protons
8/10/2019 Principles Radiotherapy
43/71
Neutrons
Finally have ability to build treatment machineswhich would be suitable for clinical use, butinterest in neutrons has waned because: no additional benefit over traditional photon or
electron radiation for most tumours depth-dose characteristics are at best like 6 MV
photons (most like DXR 4 MV) Only rationale for neutrons = radiobiological
late effects often far worse than expected for givendose neutrons
8/10/2019 Principles Radiotherapy
44/71
8/10/2019 Principles Radiotherapy
45/71
Designing the treatment
8/10/2019 Principles Radiotherapy
46/71
2D-RT
Conventional simulator used to design
beam portals based on standardized beamarrangement techniques and bonylandmarks visualized on planarradiographs
8/10/2019 Principles Radiotherapy
47/71
Volume delineation for external
beam and sealed sources The gross tumour volume (GTV) is outlined A margin is included around the GTV to include
areas at risk for microscopic involvement, this isthe clinical target volume (CTV)
A margin is added onto the CTV to allow fordifferences in internal organ motion or day-to-day set up variations, this is the planning targetvolume (PTV)
There is a margin added to the PTV to allow forphysical characteristics of the beam (penumbra),this is the actual treatment volume.
8/10/2019 Principles Radiotherapy
48/71
8/10/2019 Principles Radiotherapy
49/71
Organs At Risk
(Part B of treatment factors) organs at risk := normal tissues whose
radiation sensitivity may significantlyinfluence treatment planning and / orprescribed dose
class I organs : radiation lesions are fatal orresult in severe morbidity (spinal cord) class II organs : radiation lesions result in
mild to moderate morbidity (bowel) class III organs : radiation lesions are mild,transient and reversible, or result in nosignificant morbidity (muscle)
8/10/2019 Principles Radiotherapy
50/71
8/10/2019 Principles Radiotherapy
51/71
8/10/2019 Principles Radiotherapy
52/71
3D - Conformal Radiotherapy
3D-CRT: method of irradiating target volume(defined in 3D imaging study) using array ofbeams individually shaped to conform to 2Dprojection of target
Beam orientations selected to minimizeoverlap with neighbouring OARs
Beam characteristics and modifiers selectedto produce dose distribution that is uniformthroughout target(s) and as conformal as
possible, consistent with dose constraints tonormal tissue
8/10/2019 Principles Radiotherapy
53/71
3D - Conformal Radiotherapy
Iterative changes to weights, beam modifiers,
number and directions of beams untilsatisfactorily uniform dose to target is achievedwithout exceeding dose tolerance of
neighbouring OARs Allows safe escalation of dose to targets in a
variety of areas in the body (prostate,nasopharynx) that is expected to result inincreased local tumour control probability
ConformalConformal
8/10/2019 Principles Radiotherapy
54/71
ConformalConformalTreatmentTreatment
vs.vs.ConformalConformal
Avoidance Avoidance
8/10/2019 Principles Radiotherapy
55/71
Treatment Planning: DVH Can extract dose stats from this data,
for both targets and normal tissues: Maximum or minimum point dose Mean dose, standard deviation Vx (e.g., V 20 for both lungs PTV)
Can compare DVHs generated forcompeting plans to try to decide on
best plan Can look at DVHs for individual plan to
assess if acceptable Does not provide any spatial
information therefore complementary todose distribution information
Perez, 4th
ed, Fig 8.20 A& B
8/10/2019 Principles Radiotherapy
56/71
Limitations of 3D-CRT
3D-CRT cannot conform well to 3D shape oftarget unless: Large numbers of beams are used Target has relatively simple shape
3D-CRT cannot give a satisfactory treatmentplan if: Concave tumour wrapped around sensitive
structure Angles required to avoid / minimize dose tonormal tissues are difficult or impossible toachieve clinically
target surrounded by different OARs:e.g., nasopharyngeal cancer
Wh t i I t it M d l t d
8/10/2019 Principles Radiotherapy
57/71
What is Intensity Modulated
Radiotherapy (IMRT)?
IMRT: method of irradiating target volume(defined in 3D imaging study) using array ofbeams, where the intensity of the beams
varies across each treatment field
Does this really help?
Wh t B k d Ab t
8/10/2019 Principles Radiotherapy
58/71
Traditional
forward planning:
Whats Backwards About
Inverse Planning?
Choose treatment parametersChoose treatment parameters
Produce dose distributionProduce dose distribution
Assess dose distribution Assess dose distribution Satisfied ?Satisfied ?
Accept treatment plan Accept treatment plan
Yes Yes
NoNo
Wh t B k d Ab t
8/10/2019 Principles Radiotherapy
59/71
Inverse planning:
Whats Backwards About
Inverse Planning?
ChooseChoose dose volume constraintsdose volume constraints
for target &for target & OARsOARs
Set treatment parametersSet treatment parameters
Create dose distributionCreate dose distribution Satisfies constraints ?Satisfies constraints ?
Accept treatment plan Accept treatment plan Yes Yes
No
8/10/2019 Principles Radiotherapy
60/71
IMRT- 9 Beams
8/10/2019 Principles Radiotherapy
61/71
Coronal & Sagittal Slices at Iso
8/10/2019 Principles Radiotherapy
62/71
8/10/2019 Principles Radiotherapy
63/71
Side effects from radiation
Side effects are grouped into acute, delayed andlate; severity is related to overall dose as well aspatient factors.
1) Acute (fatigue is common to all)
Brain: Headache, nausea, alopecia H&N: Xerostomia, mucositis, dysphagia Lung and esophagus: Dysphagia, cough, hoarseness Breast: skin erythema, breast discomfort Abdomen or pelvis: nausea, diarrhea, dysuria
8/10/2019 Principles Radiotherapy
64/71
2) Delayed Lung is the classic organ for a delayed response
(pneumonitis) 2-6 months post RT3) Late
Brain: Necrosis, pituitary dysfunction, hearing loss
H&N: Xerostomia, dental decay, thyroid dysfunctionLung/esophagus : Esophageal stricture, lungfibrosis/dyspnea, coronary artery disease
Breast: Altered skin pigmentation, firmness of breast,arm edema Abdomen or pelvis: Bowel obstruction, infertility,proctitis
8/10/2019 Principles Radiotherapy
65/71
8/10/2019 Principles Radiotherapy
66/71
8/10/2019 Principles Radiotherapy
67/71
Objectives
At the end of this presentation, you
should be able to answer the followingquestions:1) What 3 basic principles need to be
considered when recommendingradiotherapy (RT)
2) What are the 3 basic RT approaches forcancer treatment (ie. When and why is itused)
What factors need to be considered
8/10/2019 Principles Radiotherapy
68/71
What factors need to be considered
when recommending RT 1) Patient factors (age, performance
status, co-morbidities [particularlyconnective tissue diseases], surgery) 2) Tumour factors (extent of disease [ie.
stage] 3) Treatment factors (has there been
previous RT, what normal structures are inproximity to the tumour)
8/10/2019 Principles Radiotherapy
69/71
8/10/2019 Principles Radiotherapy
70/71
3) What are some of the radiation treatment
modalities (list 5) available4) How is radiation treatment delivered (be
able to describe a standard approach)5) What are some site specific side effects
(describe 3 side effects for each of brain,head&neck, chest, breast, abdomen andpelvis)
8/10/2019 Principles Radiotherapy
71/71
Thank you. Any questions?
Recommended