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.
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Delivery
Arthur Boyer
Stanford University School of Medicine
Stanford, California
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
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
w “measurement” of radiation treatment.4
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 “measurement” of radiation treatment.
Dose to point n:
1
dn = w1d1n + w2d2n + w3d3n
target
organ
2
3
Algebraic Iterative Method: “measurement” of radiation treatment.
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: “measurement” of radiation treatment.
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: “measurement” of radiation treatment.
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 “measurement” of radiation treatment.
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 “measurement” of radiation treatment.
Planning System Commissioning “measurement” of radiation treatment.
a
b
c
d
e
f
specially designed intensity patterns
Planning System Commissioning “measurement” of radiation treatment.
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 “measurement” of radiation treatment.
Quantitative Comparison of Two Fluence Maps
Quantitative Film Analysis “measurement” of radiation treatment.
White = measurement
Red = calculation
Courtesy, Tim Solberg
Calculated “measurement” of radiation treatment.
Measured
Quantitative Film Analysis  ProfilesHorizontal and vertical profiles of measured data, calculated data, and index.
Courtesy, Tim Solberg
40 cm “measurement” of radiation treatment.
1.5 cm
4.5 cm
30 cm
Measurement Tissue Equivalent Phantom
50% “measurement” of radiation treatment.
70%
90%
1.8%
1mm
3.5%
2mm
Cylindrical Phantom Dose Verification
Measured in Plane of Isocenter
BANG gel Dosimetry “measurement” of radiation treatment.
Courtesy, Tim Solberg
Periodic IMRT QA “measurement” of radiation treatment.
Periodic IMRT QA “measurement” of radiation treatment.
Test Pattern with Leaf Error
Test Pattern after leaf replacement and MLC calibration
IMRT MU Checks “measurement” of radiation treatment.
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 “measurement” of radiation treatment.
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 “measurement” of radiation treatment.
Anterior Isocenter Verification
Isocenter Setup Verification with DRRs “measurement” of radiation treatment.
Lateral Isocenter Verification
Align DRR with EPID Image To Verify Patient Positioning “measurement” of radiation treatment.
DRR Image
AmSi EPID Image
DELIVERY OF IMRT BY COMPUTER CONTROLLED MLC “measurement” of radiation treatment.
Velocity Modulation “measurement” of radiation treatment.
Fluence Profile Required for IMCRT
Velocity Modulation “measurement” of radiation treatment.
.
(x) = (x) [tA(x)  tB(x)]
(x)
.
(x) =
(x)
(x) = tA(x)  tB(x) > 0
Gradient Regions Between Extrema “measurement” of radiation treatment.
“Velocity” leaf sequencing
250 “measurement” of radiation treatment.
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 “measurement” of radiation treatment.
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 “measurement” of radiation treatment.
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 “measurement” of radiation treatment.
250
200
150
(x)
100
50
0
0
5
10
15
20
25
30
35
40
Position, X (cm)
“Velocity” leaf sequencing
250 “measurement” of radiation treatment.
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
“measurement” of radiation treatment. (x)
.
(x) =
(x)
d(x) =
dx
d (x)/dx
.
(x)
Differentiation of Opening Time
“Velocity” leaf sequencing
Differentiation of Shear Operation “measurement” of radiation treatment.
(x) = (x) + x/vmax
d(x) = d(x) + 1
dx dx vmax
d(x) = 1
dx v(x)
“Velocity” leaf sequencing
d “measurement” of radiation treatment. (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 “measurement” of radiation treatment.
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 “measurement” of radiation treatment.
“StepandShoot” leaf sequencing
5.0 “measurement” of radiation treatment.
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
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 +3
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 +3
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 +3
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 +3
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 +3
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 +3
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 +3
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 +3
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 +3
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 +3
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 +3
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 +3
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 +3
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 +3
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 +3
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 +3
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
File +3Structure
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.
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 ...
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.
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.
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.
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).
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.
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
CRC
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
Planning +3
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
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
Organ 3D CRT IMRT
Mean±SD Mean Max 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 +3
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 +3
Mundt, 2002
100 +3
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 +3 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)
Based on image fusion, highest intensity BM was contoured and used in planning process
Mundt, 2002
Isodose Comparison – Mid Pelvis +3
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 conebeam CT.
Courtesy, David Faffray
Radiobiology for IMRT and SRT conebeam CT.
Phenomenological Lyman Model for NTCP conebeam CT.
(Note: The Lyman model does not explicitly take fraction size into consideration.)
Lyman Model for NTCP conebeam CT.
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 conebeam CT.
For a uniformly irradiated partial volume,
define
then the upper limit of integration is
Lyman Model for NTCP conebeam CT.
for n > 0
The ntcp curve moves to the right vs. D for partial volume irradiation.
Lyman Model : nonuniform irradiation conebeam CT.
[Kutcher–Burman]
Equivalent Uniform Dose conebeam CT.
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 uniformly distributed cells,
where we should be
Tumor Control Probability
where we are
complication curve
Dose
the unique biology of CaP uniformly distributed cells,
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 uniformly distributed cells,
LinearQuadratic equation
s = exp(adbd2)
s
cell survival curve
dose
Radiobiology 101 uniformly distributed cells,
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 uniformly distributed cells,
BED = D(1+ d/(a/b))units of Gy
a intrinsic radiosensitivity
b repair of sublethal damage
a/b sensitivity to doseperfraction
Radiobiology 101 uniformly distributed cells,
BED = D(1+ d/(a/b))
a/btumors > a/bNTLE
tumors a/b ~ 10
normal tissue late effects a/b ~ 3
tumors vs. NTLE uniformly distributed cells,
Tumors & early
responding tissues
a/b ~ 10
Normal
Tissue late
effects
a/b ~ 3
surviving fraction
dose
tumor vs. NTLE uniformly distributed cells,
BED (Gy) = D(1+ d/(a/b))
D / d / n (Gy) BED a/b=10 BED a/b=3
tumorNTLE
74 / 2 / 37 88.8 123.3
70 / 2.5 / 28 87.5 128.3
69 / 3 / 23 89.7 138
64 / 4 / 16 89.6 149.3
NTLE: Normal Tissue Late Effects
the uniformly distributed cells,a/b ratio for CaP
series method a/b 95% CI
Brenner & Hall (1999) LDR / EBRT data 1.5 [0.8 – 2.2]
King & Fowler (2001) LDR / EBRT model 1.8/2
Fowler et al. (2001) LDR / EBRT data 1.49 [1.25 – 1.76]
Brenner et al. (2002) HDR data 1.2 [0.03 – 4.1]
36.25 / 7.25 / 5 211.5 123.8 62.5 uniformly distributed cells,
90 / 2 / 45 210 150 108
what if a/b is that low?
D (Gy) / d / n BEDa/b=1.5BEDa/b=3BEDa/b=10
tumorNTLE acute effects
74 / 2 / 37 172.6 123.3 88.8
NTLE: Normal Tissue Late Effects
why hypofractionate? uniformly distributed cells,
Hypofractionation for CaP will:
escalate dose biologically
reduce acute sequelae
keep same normal tissue lateeffects
reduce overall treatment course
potential tumor control uniformly distributed cells,
100
90%
62%
SRS
hypofractionation
50
Tumor Control Probability
43%
0
50
60
70
80
90
100
Dose (Gy)
Radiobiology uniformly distributed cells,
Sensitivity to dose
fraction size
Other Tumors a/b ~ 10
Normal Tissues a/b ~ 3
Prostate cancer a/b ~ 1.5