SRS & SBRT - Unflattened Beam
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Transcript of SRS & SBRT - Unflattened Beam
11 October 2014
Outline
� SRS and SBRT
� History of SRS
� Recent advances in SRS and SBRT
� Advantage of Flattening Filter Free(FFF) beam
� Characteristic of Flattening Filter Free beam
� Recommendation of AERB & AAPM TG 101
Introduction
�Stereotactic Radiosurgery (SRS)
– SRS is a precise and focused delivery of a single, high dose
of irradiation to a small and critically located intracranial
volume while sparing normal structure
�Stereotactic Body Radiation Therapy (SBRT)
– SBRT is a treatment procedure similar to SRS, except that
it deals extra-cranial radiosurgery
SRS and SBRT Definition
1. High doses of radiation via multiple beams
2. Limited number of treatment session (1-5)
3. Image guided treatment (CT, PET, MRI)
4. Computer assisted robotic delivery4. Computer assisted robotic delivery
5. Real time respiratory motion accommodation
SRS and SBRT
The challenge for SRS and SBRT
is to accurately deliver is to accurately deliver
conformal high dose radiation
to the target and minimize
normal tissue damage.
Differences between Conventional and Stereotactic
Historical Background
� The first one to combine stereotactic methodology with
radiation therapy was the Swedish neurosurgeon Lars
Leksell. Leksel performed the first treatment in 1951, at the
Karolinska Institute, and called the new therapy approach
radiosurgery (RS)
� Leksel continued his work and built the first isotope � Leksel continued his work and built the first isotope
radiation machine, in 1968, the Gamma knife
� The stereotactic radiation therapy with LINAC started in the
early 1980s: the Swedish physicist Larsson proposed to use
the LINAC instead Co 60 or protons (Larsson et al. 1974)
Radiosurgery Machines
Gamma Knife Proton Therapy
Cyberknife Tomotherapy Brainlab Vero Varian-Truebeam
SBRT Work Flow
Immobilization &
Simulation
Motion Management PlanningSimulation
IGRTMotion VerificationDelivery
How LINAC Radiosurgery Works
� The gantry of the LINAC rotates around
the patient, producing an arc of radiation
focused on the target. The couch in
which the patient rests is then rotated in
the horizontal plane, and another arc is the horizontal plane, and another arc is
performed. In this manner, multiple non-
coplanar arcs of radiation intersect at the
target volume and produce a high target
dose, resulting in minimal radiation
affecting the surrounding brain and
normal tissue.
How Gamma Knife Radiosurgery Works
� The GammaKnife is used to treat brain
tumors. The procedure begins with the
patient receiving anesthesia and a frame
is attached to the head to hold it in place.
� The patient lays on their back and moved
head first into the machine, where 201
beams of cobalt – 60 radiation target the
diseased tissue, without damaging the
surrounding tissue.
Recent Advances in SBRT and SRS
�VMAT� Volumetric Modulated Arc Therapy (VMAT)
was first introduced in 2007 and described as a
novel radiation technique
� VMAT is the simultaneous variation of three
parameters during treatment
delivery, i.e. gantry rotation speed, treatment
aperture shape via movement of MLC leaves
and dose rate
Recent Advances in SBRT and SRS
� Flattening Filter Free (FFF) mode� FFF beam is produced without the use of
flattening Filter
� In the 1990s, several groups studied about FFF
high-energy photon beams. The main interesthigh-energy photon beams. The main interest
for that, is to increase the dose rate for
radiosurgery or the "physics interest”.
� Need of increase in dose rate from traditional
300-600 to 1400-2400MU/min to overcome
time-inefficiency and to improve patients
comfort specially in SRS/SBRT
Dosimetric advantages of FFF beams
� FFF has increased dose rate, e.g., 1400 MU/min for 6 MV,
2400 MU/min for 10 MV.
� FFF beams have less variation of off-axis beam hardening.
� FFF has less photon head scatter and thus less field size
dependence.
� FFF has less leakage outside of beam collimation
Potential advantages of FFF beams
� Fast treatment for Stereotactic Radiotherapy (SRT) and SRT
plans between FB and FFF beams should be similar for small
fields.
� FFF is especially useful for SBRT, where respiration controlled� FFF is especially useful for SBRT, where respiration controlled
treatment delivery is compromised by the large number of MU
to delivery high fraction doses.
� Patient beam on time can be reduced for IMRT
FFF Mode Machines
Cyberknife Tomotherapy BrainLab Vero
Varian -Truebeam Elekta – Versa HD
Two Different FFF machines
at RGCI
Varian – Truebeam
� Dose rate :
1400MU/min 6MV FFF &
2400MU/min 10MV FFF
Siemens – Artiste
� Dose rate:
• 2000MU/min - 6MV_FFF
� 120Leaf HD – MLC
Center - 2.5 mm width x 32 pairs
Peripheral 5.0 mm width x 28 pairs
� Modulation Area 22x40 cm 2
� Speed of MLC 2.5cm/sec
� 160Leaf MLC
Resolution 5.0 mm, 40cm wide
� Modulation Area 40x40 cm2
� Speed of MLC 4.0cm/sec
Comparison between 6X FB and FFF (Varian
TrueBeamTM) - Profiles
FB Profiles FFF Profiles
Comparison of PDD for FB&FFF for 10cmX10cm
10XFB
10XFFF
6XFFF
6XFB
1.0000
1.0100
1.0200
1.0300
1.0400
1.0500
He
ad
Sca
tte
r F
act
or
( S
c)
Variation of Output factor in air with field size
0.9400
0.9500
0.9600
0.9700
0.9800
0.9900
0 5 10 15 20 25 30 35 40
He
ad
Sca
tte
r F
act
or
( S
c)
Field Size in cm2
6MV-FB Varian True Beam
6MV-FFF True Beam
10MV-FB Varian True Beam
10MV-FFF True Beam
Dosimetry concern of FFF
• Due to the above changes, the Dosimetric parameters like field size
definition, beam quality, surface dose, off axis ratio (OAR), flatness,
symmetry, degree of un-flatness, penumbra and depth dose profiles differs
from standard Linac with Flat beam.
• There is no international standard/acceptance test protocol available for
FFF beam, AERB constituted a Task Group to evolve the acceptance
criteria for FFF beam
AERB Recommendations for FFF
Treatment should be
implemented with TPS
through Record & Verify
system, Manual system, Manual
planning and calculation
shall not be adopted in
clinical use of FFF
beam.
AERB Recommendations for FFF
Measurements should cover
� Beam Energy:
TPR20/10 for 10 cm x 10 cm Field Size for all FFF energies
� Surface dose:� Surface dose:
10cm x 10cm and 20cm x 20cm compared with the corresponding
nominal flat beam energy
� OAR
At ±3 cm from central axis at the depth of 10 cm for 10 cm x 10 cm
collimator setting shall be measured for all available FFF energies
–
•
AERB Recommendations for FFF
� Depth dose profiles
�Dose profile for field size 5cm x 5cm, 10cm x 10cm and 20cm x
20cm at depth of Dmax and 10cm shall be recorded for all available
energies
�FS ≤10 cm x 10 cm, the Dosimetric parameters such as field size,�FS ≤10 cm x 10 cm, the Dosimetric parameters such as field size,
penumbra, flatness, symmetry shall be measured and evaluated the
methods applied for flat beam
� If flatness is > ± 3%, the evaluation criteria of unflattend beam shall
be adopted
AERB Recommendations for FFF
� Depth dose profiles
�Flatness: As per IEC
976 (IEC 60976), the
flat region for field
sizes less than 10cm x
10cm along major10cm along major
axes defined by
subtracting 1cm from
the beam profiles.
Eg. For F.S 5cm x 5cm
flat region is central
3cm.
AERB Recommendations for FFF
� Depth dose profiles
� Inflection Point: Inflection
Point can be identified as per
its mathematical definition.
However, for practical
purposes it can be
approximated as the midapproximated as the mid
point on either side of the
high gradient region (sharply
descending part) of the beam
profile. IP is located at h/2.
� Penumbra:Lateral Separation
beween either side of profile
will be measured for the
penumbra
AERB Recommendations for FFF
� Degree of un-flatness:
• To quantify the degree of un-
flatness, lateral distance from
the central axis at 90%, 75%
and 60% dose points onand 60% dose points on
either side of the beam
profile shall be recorded
along major axes.
Trubeam FB and FFF beam Stereotactic Plan
comparison – Liver
6 MV_FFF
1400MU/M
6 MV_FB
600MU/M
Trubeam FB and FFF beam Stereotactic Plan
comparison – Brain
6 MV_FB
600MU/M
6 MV_FFF
1400MU/M
Comparison of FFF and FB for SBRT
� Similar Dose distribution and DVH for FB and FFF
�Treatment plan strategies are similar between FB and
FFF beams since the beam profile are similar for field FFF beams since the beam profile are similar for field
size < 4 cm
AAPM TG 101 Recommendation for SBRT
� SBRT Patient Selection Criteria:
� When appropriate protocols are not available, clinicians must decide
whether they will treat patients in accordance with published guidelines
or develop new SBRT guidelines. At a minimum, an institutional
treatment protocol or set of guidelines should be developed by
radiation oncologists and physicists.radiation oncologists and physicists.
� Simulation imaging:
� The simulation study should cover the target and all organs at risk to
obtain geometric and Dosimetric information for the treatment setup
� Slice thickness: < 3 mm near clinically important organs
AAPM TG 101 Recommendation for SBRT
� Planning Recommendation:
� The adequacy of target margins i.e., GTV, CTV, ITV, in SBRT should
be based on from information in the current literature available
� Dose Calculation Algorithm:
� Algorithms that account for 3D scatter integration such as convolution/superposition� Algorithms that account for 3D scatter integration such as convolution/superposition
have been found to perform adequately in most clinical situations, including in many
cases circumstances where there is a loss of electronic equilibrium such as the lung tissue
interface or tumor margin in low-density medium.
� Calculation algorithms accounting for better photon and electron transport such as Monte
Carlo would be ideal for the most demanding circumstances, such as a small lesion
entirely surrounded by a low-density medium.
AAPM TG 101 Recommendation for SBRT
� Special Dosimetry Recommendation:
� Due to the small dimensions and steep dose gradients of photon beams
used in SRS/SBRT and IMRT, an appropriate dosimeter with a spatial
resolution of approximately 1 mm or better stereotactic detectors is
required to measure the basic dosimetry data, e.g., the total scatter
factor or relative output factor, tissue maximum ratio, and off-axisfactor or relative output factor, tissue maximum ratio, and off-axis
ratios.
Accuracy of SRS & SBRT depends on
� Linac Mechanical – Iso
� Accuracy of SRS frame & Immobilization
� Positional accuracy� Positional accuracy
� Dosimetry accuracy
Conclusions
� Advanced treatment techniques such as SBRT and IMRT have stimulated
interest in FFF beam, which provides higher dose rate, and reduced head
scatter, leaf transmission, and head radiation leakage.
� Clinical utilities of FFF beam include a treatment time reduction for SRT,
SBRT, and IMRT.SBRT, and IMRT.
� More studies are needed for FFF beam to specify and quantify the clinical
advantages, especially with respect to treatment plan quality and quality
assurance.
Conclusions
� Several aspects related to standardization, dosimetry, treatment planning,
and optimization need to be addressed in more detail in order to facilitate
the clinical implementation of FFF beams.
Our Publications & Abstracts of FFF beam
� “Comparison of Head Scatter Factor for 6MV and 10MV flattened (FB) and
Unflattened (FFF) Photon Beam using indigenously Designed Columnar Mini
Phantom”
– Journal of Medical Physics, July-September 2014
� A Comparison of Out-Of-Field Dose and Its Constituent Components for 6MV
Flattened and 7MV Unflattened
– AAPM 55th Annual Meeting - 2013– AAPM 55th Annual Meeting - 2013
� Comparison of the Depth Dose in the Build-Up Region and Surface Dose for 6MV
Flattened and 7MV
– AAPM 55th Annual Meeting - 2013
� Scatter Factors Comparison of 6MV Flattened and 7MV Unflattened Beams
– AAPM 54th Annual Meeting - 2012
� Effect of Surface Dose and Depth of Maximum Dose with Physical Wedge Filters
for 6MV Flattened and 7MV
– AAPM 54th Annual Meeting - 2012
�Our Medical Physics team
�Dr. Girigesh Yadav
�Mr. Manindra Mishra�Mr. Manindra Mishra
�Mr. T. Suresh
�Mr. Lalit Kumar
�Mr. Pavan Singh