Planning. Clinical Aspects. Radiobiological Aspects. Delivery. Arthur Boyer Stanford University School of Medicine Stanford, California. Verification. Conventional planning. Time. IMRT planning. Complexity. Establish the Correspondence Between Output and Input. Output. Input.
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Delivery
Arthur Boyer
Stanford University School of Medicine
Stanford, California
Conventional planning
Time
IMRT planning
Complexity
Establish the Correspondence Between Output and Input
Output
Input
Specify quantities that describe a patient’s
quality of life (e.g., Karnofsky status)
Desired
output
Specify TCP and NTCPbiological model
Specify a dose distributiondose based model
Procedures of Inverse Planning Computation
Optimal Input
Output
Construct an objective function
F = F (input parameters) = F (w1,w2,w3,….,wJ)
Optimize F and find the optimal beam profiles
Convert beam profiles into MLC leaf sequences
Dosimetric:
F = [Dc(1)D0(1)]2 +[Dc(2)D0(2)]2 + ...
w1
Beam profile
Dc(1)
D0(1)
Dc(2)
D0(2)
n=4
F = S [Dc(n)D0(n)]2
Calculated dose
n=1
w3
w4
Prescribed dose
3
4
D3
D4
1.0
0.5
w2
1
2
D1
D2
w1
1.0
1.0
w4
w3
n=4
F = S [Dc(n)D0(n)]2
n=1
D3
D4
w2
D1
D2
w1
D1= w1 d11+ w2 d21 + w3 d31 + w4 d41
D2= w1 d12+ w2 d22 + w3 d32 + w4 d42
D3= w1 d13+ w2 d23 + w3 d33 + w4 d43
D4= w1 d14+ w2 d24 + w3 d34 + w4 d44
A Simple Iterative Algorithm
Dose to point n:
1
dn = w1d1n + w2d2n + w3d3n
target
organ
2
3
Algebraic Iterative Method:
Initial beam profiles
Calculate dose at a voxel n
Compare Dc(n) with D0(n)
n+1
Dc(n) > D0(n) ?
Yes
No
Decrease wi
Increase wi
Algebraic Iterative Method:
n=6
F = S [Dc(n)D0(n)]2
Calculated dose
n=1
0.5
0.5
Prescribed dose
1.0
1.0
1.0
1.0
0.5
1.0
0.5
1.0
1.0
0.5
1.0
1.0
1.0
1.0
0.5
Algebraic Iterative Method:
Iteration step = 5
Iteration step = 1
0.51
0.45
0.50
0.49
1.01
0.95
0.50
0.99
1.00
0.50
0.95
0.99
0.90
0.44
0.97
0.49
1.02
1.01
0.99
1.00
0.50
0.50
Objective function
Iteration step = 10
i=6
F = S [Dc(i)D0(i)]2
0.30
0.51
0.42
i=1
0.25
0.20
0.15
0.10
0.51
1.02
0.92
0.05
0.91
0.41
0.82
0
20
40
80
60
1.02
0.92
100
0
0.51
Iteration step
Algebraic Iterative Method:
9 equispaced beams
9 selected beams
180o collimator angle
Collimator angle
Isocenter in geometric center of targets
Isocenter in geometric center of GTV
Yi et al. 2000
Lehmann et al. 2000
Verification
Planning System Commissioning
a
b
c
d
e
f
specially designed intensity patterns
Planning System Commissioning
90%
90%
50%
50%
40%
10%
20%
20%
40%
70%
70%
10%
80%
80%
90%
90%
30%
50%
30%
10%
10%
50%
90%
90%
Calculated Measured
specially designed intensity patterns
Patient Specific Field Verification
Quantitative Comparison of Two Fluence Maps
Film
Courtesy, Tim Solbert
Quantitative Film Analysis
White = measurement
Red = calculation
Courtesy, Tim Solberg
Calculated
Measured
Horizontal and vertical profiles of measured data, calculated data, and index.
Courtesy, Tim Solberg
40 cm
1.5 cm
4.5 cm
30 cm
Measurement Tissue Equivalent Phantom
50%
70%
90%
1.8%
1mm
3.5%
2mm
Cylindrical Phantom Dose Verification
Measured in Plane of Isocenter
BANG gel Dosimetry
Courtesy, Tim Solberg
Periodic IMRT QA
Periodic IMRT QA
Test Pattern with Leaf Error
Test Pattern after leaf replacement and MLC calibration
IMRT MU Checks
QUALITY ASSURANCE OF IMRT TREATMENT PLAN
DEPARTMENT OF RADIATION ONCOLOGY ,STANFORD UNIVERSITY SCHOOL OF MEDICINE
PATIENT NAME: xxx, xxxxxxx
PATIENT ID: xxxxxxx
TPS PLAN #: 2512
Treatment Machine: LA7
Beam Energy: 15 MV
Calibration Setup: SSD
Delivery Mode: Step and Shoot
Beamlet Size: 1.0 x 1.0 (cm x cm)
Calibration Factor: 1.000
Isocenter Dose Verification Report
Field MU x1 x2 y1 y2 SSD beamdose
F 180000 170 7.80 6.80 4.20 16.20 88.79 50.2
F 180080 118 4.80 6.80 4.20 17.20 82.03 40.6
F 180145 108 8.00 1.00 5.00 18.00 90.87 24.0
F 180145a 101 1.00 8.00 4.00 18.00 90.87 17.9
F 180215 80 9.00 0.00 3.00 18.00 90.49 1.6
F 180215a 107 2.00 7.00 5.00 18.00 90.49 48.7
F 180280 115 6.80 5.80 4.20 17.20 81.68 41.2
IMRT MU Checks
Calculated Isocenter Dose: 224.2 cGy
TPS Isocenter Dose: 221.3 cGy
Percentage Difference: 1.3 (%).
Leaf Sequence Verification Report
Field ID Gantry Angle Correlation Coefficient Maximum Difference
1 0 1.0000 0.5112 (%)
2 80 1.0000 0.4017 (%)
3 145 1.0000 0.6799 (%)
4 215 1.0000 0.7275 (%)
5 280 1.0000 0.4034 (%)
Physicist: _________________________
DATE: 7/20/2001
Isocenter Setup Verification with DRRs
Anterior Isocenter Verification
Isocenter Setup Verification with DRRs
Lateral Isocenter Verification
Align DRR with EPID Image To Verify Patient Positioning
DRR Image
AmSi EPID Image
DELIVERY OF IMRT BY COMPUTER CONTROLLED MLC
1 cm
m
1 cm
Tl,m,k
Beam Modulation Patterns
Velocity Modulation
Fluence Profile Required for IMCRT
Velocity Modulation
.
(x) = (x) [tA(x)  tB(x)]
B
A
Velocity Modulation
.
(x) = (x) [tA(x)  tB(x)]
(x)
.
(x) =
(x)
(x) = tA(x)  tB(x) > 0
Gradient Regions Between Extrema
“Velocity” leaf sequencing
250
200
Leaf A
(x)
150
100
50
0
Leaf B
0
5
10
15
20
25
30
35
40
Position, X (cm)
Interpretation as Trajectories
“Velocity” leaf sequencing
250
200
150
(x)
100
50
0
0
5
10
15
20
25
30
35
40
Position, X (cm)
Reflection Operation to Remove Time Reversals
(x) = (x) 
“Velocity” leaf sequencing
250
200
150
(x)
100
50
0
0
5
10
15
20
25
30
35
40
Position, X (cm)
Translation Operation to Remove Discontinuities
(x) = (x) + (x)
“Velocity” leaf sequencing
Reflection Operation to Remove Time Reversal
250
200
150
(x)
100
50
0
0
5
10
15
20
25
30
35
40
Position, X (cm)
“Velocity” leaf sequencing
250
Leaf A
200
150
(x)
100
Leaf B
50
0
0
5
10
15
20
25
30
35
40
Position, X (cm)
Shear Operation to Remove Infinite Velocity
(x) = (x) + x/vmax
“Velocity” leaf sequencing
(x)
.
(x) =
(x)
d(x) =
dx
d (x)/dx
.
(x)
Differentiation of Opening Time
“Velocity” leaf sequencing
Differentiation of Shear Operation
(x) = (x) + x/vmax
d(x) = d(x) + 1
dx dx vmax
d(x) = 1
dx v(x)
“Velocity” leaf sequencing
d (x)/dx
1
1
.
+
=
vmax
v(x)
(x)
vmax
=
v(x)
d (x)/dx
.
vmax
1
(x)
Substitutions to Obtain Velocity Relation
“Velocity” leaf sequencing
80
70
Leaf A
60
50
Time (sec)
40
30
20
Leaf B
10
0
0
5
10
15
20
25
30
35
Position (cm)
“Velocity” leaf sequencing
Step and Shoot
“StepandShoot” leaf sequencing
5.0
4.0
3.0
Intensity Level
2.0
1.0
12
13
0.0
14
3
Leaf Pair
15
2
1
0
+1
+2
+3
xPosition
3 2 1 0 +1 +2 +3
3 2 1 0 +1 +2 +3
Leaf Pair 12
Leaf Pair 13
3 2 1 0 +1 +2 +3
3 2 1 0 +1 +2 +3
Leaf Pair 14
Leaf Pair 15
A
B
5
5
1
4
8
4
4
2
5
7
3
Levels
3
3
6
6
2
2
7
1
1
8
0
3 2 1 0 +1 +2 +3



1
2
3
Position
Instance 1
A
B
5
5
1
4
8
4
4
2
5
7
3
Levels
3
3
6
6
2
2
7
1
1
8
0
3 2 1 0 +1 +2 +3



1
2
3
Position
Instance 2
B
A
5
5
1
4
8
4
2
4
7
5
3
3
Levels
3
6
7
6
2
2
7
1
1
8
0
3 2 1 0 +1 +2 +3



1
2
3
3
2
1
Position
Instance 3
B
A
5
5
1
4
8
4
2
4
7
5
3
3
Levels
3
6
7
6
2
2
7
1
1
8
0
3 2 1 0 +1 +2 +3



1
2
3
3
2
1
Position
Instance 4
B
A
8
5
7
6
6
7
5
5
1
4
4
2
4
7
3
3
Levels
3
2
2
1
1
8
0
3 2 1 0 +1 +2 +3



1
2
3
3
2
1
Position
Instance 5
B
A
5
5
1
4
8
4
2
4
7
5
3
3
Levels
3
7
6
6
2
2
7
1
1
8
0
3 2 1 0 +1 +2 +3



1
2
3
3
2
1
Position
Instance 6
B
A
5
5
1
4
8
4
2
4
7
5
3
3
Levels
3
7
6
6
2
2
7
1
1
8
0
3 2 1 0 +1 +2 +3



1
2
3
3
2
1
Position
Instance 7
B
A
5
5
1
4
8
4
2
4
7
5
3
3
Levels
3
7
6
6
2
2
7
1
1
8
0
3 2 1 0 +1 +2 +3



1
2
3
3
2
1
Position
Instance 8
B
A
8
5
7
6
6
7
5
1
4
4
5
2
4
7
3
3
Levels
3
2
2
1
1
8
0
3 2 1 0 +1 +2 +3



1
2
3
3
2
1
Position
Instance 9
B
A
5
1
4
8
4
5
2
4
7
5
3
3
Levels
3
7
6
6
2
2
7
1
1
8
0
3 2 1 0 +1 +2 +3



1
2
3
3
2
1
Position
Instance 10
B
A
5
5
1
4
8
4
2
4
7
5
3
3
Levels
3
7
6
6
2
2
7
1
1
8
0
3 2 1 0 +1 +2 +3



1
2
3
3
2
1
Position
Instance 11
B
A
5
5
1
4
8
4
2
4
7
5
3
3
Levels
3
7
6
6
2
2
7
1
1
8
0
3 2 1 0 +1 +2 +3



1
2
3
3
2
1
Position
Instance 12
B
A
5
5
1
4
8
4
2
4
7
5
3
3
Levels
3
7
6
6
2
2
7
1
1
8
0
3 2 1 0 +1 +2 +3



1
2
3
Position
Instance 13
B
A
5
5
1
4
8
4
2
4
7
5
3
3
Levels
3
7
6
6
2
2
7
1
1
8
0
3 2 1 0 +1 +2 +3



1
2
3
Position
Instance 14
B
A
5
5
1
4
8
4
2
4
7
5
3
3
Levels
3
7
6
6
2
2
7
1
1
8
0
3 2 1 0 +1 +2 +3



1
2
3
3
2
1
Position
Instance 15
B
A
5
5
1
4
8
4
2
4
7
5
3
3
Levels
3
7
6
6
2
2
7
1
1
8
0
3 2 1 0 +1 +2 +3



1
2
3
3
2
1
Position
Instance 16
Leaf Pair 12
Leaf Pair 13
Leaf Pair 14
Leaf Pair 15
15
1&2
14
13
12
15
3&4
14
13
12
15
5&6
14
13
12
15
14
13
7&8
12
15
14
13
9&10
12
15
14
13
11&12
12
15
14
13
12
13&14
15
14
13
12
15&16
15
14
13
12
17&18
15
14
12
13
19&20
File Structure
Static File Structure
File Rev = G
Treatment = Static
Last Name = Collimator
First Name = M.L.
Patient ID = 5551212
Number of Fields = 13
Number of Leaves = 52
Tolerance = 0.3
Field = Left Lung
Index = 0.0
Carriage Group = 1
Operator = DNR
Collimator = 0.0
Leaf 1A = 0.00
Leaf 2A = 1.00
Leaf 3A = 2.00
Leaf 4A = 3.00
Leaf 5A = 4.00
Leaf 6A = 5.00
Leaf ...
For conventional MLC treatments, the STATIC mode is used.
Dynamic Treatment Files
File Rev = G
Treatment = Dynamic dose
Last Name = Patient
First Name = QA
Patient ID = 5551212
Number of Fields = 12
Number of Leaves = 120
Tolerance = 0.3
Field = Shape1
Index = 0.000
Carriage Group = 1
Operator = DNR
Collimator = 0.0
Leaf 1A = 0.00
Leaf 2A = 1.00
Leaf 3A = 2.00
Leaf 4A = 3.00
Leaf 5A = 4.00
Leaf 6A = 5.00
Leaf ...
Field = Shape2
Index = 0.050
Carriage Group = 1
Operator = DNR
Collimator = 0.0
Leaf 1A = 0.00
Leaf 2A = 1.00
Leaf 3A = 2.00
Leaf 4A = 3.00
Leaf 5A = 4.00
Leaf 6A = 5.00
Leaf ...
Field = Shape3
Index = 0.072
Carriage Group = 1
Operator = DNR
Collimator = 0.0
Leaf 1A = 0.00
Leaf 2A = 1.00
Leaf 3A = 2.00
Leaf 4A = 3.00
Leaf 5A = 4.00
Leaf 6A = 5.00
Leaf ...
Treatment Field Index
File Rev = G
Treatment = Dynamic Dose
Last Name = John
First Name = Smith
Patient ID = 1234
Number of Fields = 20
Number of Leaves = 80
Tolerance = 0.1
Field = 1 of 20
Index = 0.0000
Carriage Group = 1
Operator = Physicist
Collimator = 180.0
Leaf 1A = 0.00
Leaf 2A = 0.00
Leaf 3A = 3.00
The file must specify the total number of instances that will be used.
Treatment Field Index
File Rev = G
Treatment = Dynamic Dose
Last Name = John
First Name = Smith
Patient ID = 1234
Number of Fields = 20
Number of Leaves = 80
Tolerance = 0.1
Field = 1 of 20
Index = 0.0000
Carriage Group = 1
Operator = Physicist
Collimator = 180.0
Leaf 1A = 0.00
Leaf 2A = 0.00
Leaf 3A = 3.00
Varian has 52leaf, 80leaf, and 120leaf MLCs. The file must identify the MLC.
Treatment Field Index
File Rev = G
Treatment = Dynamic Dose
Last Name = John
First Name = Smith
Patient ID = 1234
Number of Fields = 20
Number of Leaves = 80
Tolerance = 0.1
Field = 1 of 20
Index = 0.0000
Carriage Group = 1
Operator = Physicist
Collimator = 180.0
Leaf 1A = 0.00
Leaf 2A = 0.00
Leaf 3A = 3.00
Tolerance parameter is in units of centimeters.
Treatment Field Index
File Rev = G
Treatment = Dynamic Dose
Last Name = John
First Name = Smith
Patient ID = 1234
Number of Fields = 20
Number of Leaves = 80
Tolerance = 0.1
Field = 1 of 20
Index = 0.0000
Carriage Group = 1
Operator = Physicist
Collimator = 180.0
Leaf 1A = 0.00
Leaf 2A = 0.00
Leaf 3A = 3.00
Dose (MU) fraction ranging from 0.0 (beginning of treatment) to 1.0 (end of treatment).
Treatment Field Index
File Rev = G
Treatment = Dynamic Dose
Last Name = John
First Name = Smith
Patient ID = 1234
Number of Fields = 20
Number of Leaves = 80
Tolerance = 0.1
Field = 1 of 20
Index = 0.0000
Carriage Group = 1
Operator = Physicist
Collimator = 180.0
Leaf 1A = 0.00
Leaf 2A = 0.00
Leaf 3A = 3.00
Dose (MU) fraction ranging from 0.0 (beginning of treatment) to 1.0 (end of treatment).Leaf positions (cm) are specified as a function of dose fraction.
File Footer  CRC
Leaf 51B = 2.25
Leaf 52B = 2.25
Leaf 53B = 1.75
Leaf 54B = 6.20
Leaf 55B = 6.20
Leaf 56B = 6.20
Leaf 57B = 6.20
Leaf 58B = 6.20
Leaf 59B = 6.20
Leaf 60B = 6.20
Note = 0
Shape = 0
Magnification = 0.00
CRC = CF95
â
File Structure
CRC
Stepandshoot
Dynamic delivery
fMU=0.0
1st MLC
position
fMU=0.0
1st MLC
position
step
fMU=0.14
1st MLC
position
fMU=0.14
2nd MLC
position
shoot
fMU=0.14
2nd MLC
position
fMU=0.25
3rd MLC
position
step
fMU=0.25
2nd MLC
position
fMU=0.33
4th MLC
position
shoot
Clinical Applications of IMRT
Planning
180o
140o
Immobilization
Aquaplast
Position Verification
Ximatron
Network File Management
Varis
Plan Verification
Wellhöfer
Structure Segmentation
AcQsim
Inverse Planning
Corvus
CT/MRI Acquisition
PQ 5000
240o
100o
260o
60o
300o
Delivery
20o
340o
Treatment Delivery
CSeries Clinac Dynamic MLC
IMRT Process
180o
140o
220o
100o
260o
60o
300o
20o
340o
Example
9field Head and neck Treatment
80%
90%
55%
85%
90%
55%
55%
80%
90%
80%
90%
55%
90%
55%
85%
80%
80%
90%
55%
80o
280o
320o
40o
0o
Prostate
Nodes
Irradiate Prostate and Nodal Region in Pelvis
SV
CTV
Rectum
Bladder
GU or GI Toxicity
80
70
60
IMRTProstate and
50
Nodes
40
3DProstate and Nodes
30
20
10
0
0
1
2
3
P = 0.002
Maximum RTOG Score
Steven Hancock, 2002
IMRT: Prostate and Nodes
Intensity Modulated Plan
Field Intensity Maps
70%
50%
60%
80%
30%
20%
40%
10%
90%
40%
80%
50%
70%
30%
60%
20%
90%
10%
40%
80%
50%
70%
60%
90%
40%
30%
20%
10%
Organ3D CRTIMRT
Mean±SDMeanMax Min
Small field:
Prostate: 74.0 ± 1.5 75.7 82.8 65.3
Seminal Vesicles:50.0 ± 1.0 63.5 79.1 50.1
Large field:
Prostate:50.0 ± 1.0 55.1 61.8
+ Boost:70.0 ± 1.4 77.3 87.7
Nodes:50.0 ± 1.0 54.2 63.5
Steven Hancock, 2002
P = 0.05
Steven Hancock, 2002
MSKCC: Dose to 98 ± 2% of CTV: 81. Gy
Dose to 95% of PTV:78. Gy
5% of Bladder > 83. Gy
2530% Rectum> 75.6 Gy
Dose per fraction 1.8 Gy
2 yr risk of GI bleeding: 2% IMRT v. 10% 3DCRT
Zelefsky et al. Radiother & Oncol 55:241
IMRT for Gynecological Cancers
Mundt, 2002
Intensity ModulatedWPRT
100%
90%
70%
50%
Mundt, 2002
100
90
80
70
60
50
40
30
20
10
0
Grade 0
Grade 1
Grade 2
Grade 3
Acute GI toxicity IMWPRT vs. WPRT
IMWPRT
WPRT
P = 0.002
Mundt et al. Int J Radiat Oncol Biol Phys 52:13301337, 2002
Chronic GI Toxicity IMWPRT vs. WPRT
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
0
1
2
3
IMWPRT
WPRT
Multivariate analysis controlling for age, chemo, stage and site,
IMRT remained statistically significant ( p = 0.002)
Mundt et al. ASTRO 2002 (New Orleans)
SPECTCT Image Fusion
Based on image fusion, highest intensity BM was contoured and used in planning process
Mundt, 2002
Isodose Comparison – Mid Pelvis
BMSparing Plan
100%
90%
70%
50%
100%
90%
70%
50%
IMWPRT Plan
Mundt, 2002
Localization of the prostate can also be achieved with conebeam CT.
Tumor Motion During Respiraton
Courtesy, David Faffray
Rt Lung
heart
cord
Lt Lung
Radiobiology for IMRT and SRT
Phenomenological Lyman Model for NTCP
(Note: The Lyman model does not explicitly take fraction size into consideration.)
Lyman Model for NTCP
For a biological target uniformly irradiated to dose D, the upper limit of integration is expressed as
where is the dose at which the complication probability is 50%, and m is a slope parameter.
Lyman Model for NTCP
For a uniformly irradiated partial volume,
define
then the upper limit of integration is
Lyman Model for NTCP
for n > 0
The ntcp curve moves to the right vs. D for partial volume irradiation.
Lyman Model : nonuniform irradiation
[Kutcher–Burman]
Equivalent Uniform Dose
Equivalent Uniform Dose (EUD) is the uniform dose that gives the same cell kill as a nonuniformly irradiated target.
(Niemierko, Med Phys. 24:103110; 1997.)
For the simplest model of exponential cell kill, and uniformly distributed cells,
where really means the surviving fraction at dose Dref , which is often taken as 2 Gy
climbing the TCP curve
where we should be
Tumor Control Probability
where we are
complication curve
Dose
the unique biology of CaP
Striking similarities with slowly proliferating normal tissues
Extremely low proportion of cycling cells (< 2.5%)
Regression following RT is very slow
• PSA nadir times > 1 year
• regression of postRT biopsies up to 3 years
Potential doubling times
• median 40 days (range 15 – 170 days)
PSA doubling times of untreated CaP
• median 4 years
Radiobiology 101
LinearQuadratic equation
s = exp(adbd2)
s
cell survival curve
dose
Radiobiology 101
Fractionated radiotherapy: n x d = D
S s…s = s n
S = exp(adbd2) n
S = exp(aBED)
BED = D(1+ d/(a/b))
Biologic
Equivalent
Dose
Radiobiology 101
BED = D(1+ d/(a/b))units of Gy
aintrinsic radiosensitivity
brepair of sublethal damage
a/bsensitivity to doseperfraction
Radiobiology 101
BED = D(1+ d/(a/b))
a/btumors > a/bNTLE
tumors a/b ~ 10
normal tissue late effects a/b ~ 3
tumors vs. NTLE
Tumors & early
responding tissues
a/b ~ 10
Normal
Tissue late
effects
a/b ~ 3
surviving fraction
dose
tumor vs. NTLE
BED (Gy) = D(1+ d/(a/b))
D / d / n (Gy)BED a/b=10BED a/b=3
tumorNTLE
74 / 2 / 3788.8123.3
70 / 2.5 / 2887.5128.3
69 / 3 / 2389.7138
64 / 4 / 1689.6149.3
NTLE: Normal Tissue Late Effects
the a/b ratio for CaP
seriesmethoda/b95% CI
Brenner & Hall (1999)LDR / EBRT data1.5[0.8 – 2.2]
King & Fowler (2001)LDR / EBRT model1.8/2
Fowler et al. (2001)LDR / EBRT data1.49[1.25 – 1.76]
Brenner et al. (2002)HDR data1.2[0.03 – 4.1]
36.25 / 7.25 / 5211.5123.862.5
90 / 2 / 45210150108
what if a/b is that low?
D (Gy) / d / nBEDa/b=1.5BEDa/b=3BEDa/b=10
tumorNTLEacute effects
74 / 2 / 37172.6123.388.8
NTLE: Normal Tissue Late Effects
why hypofractionate?
Hypofractionation for CaP will:
escalate dose biologically
reduce acute sequelae
keep same normal tissue lateeffects
reduce overall treatment course
potential tumor control
100
90%
62%
SRS
hypofractionation
50
Tumor Control Probability
43%
0
50
60
70
80
90
100
Dose (Gy)
Radiobiology
Sensitivity to dose
fraction size
Other Tumorsa/b ~ 10
Normal Tissuesa/b ~ 3
Prostate cancera/b ~ 1.5