The Impact of Magnetic Stresses and Inhomogeneities on Accretion Disk Spectra
St Luke’s Radiation Oncology Network€¦ · Rapidarc plan verification Prostate Head & Neck 2....
Transcript of St Luke’s Radiation Oncology Network€¦ · Rapidarc plan verification Prostate Head & Neck 2....
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St Luke’s Radiation Oncology Network
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1. Rapidarc plan verification Prostate Head & Neck
2 Commissioning2. Commissioning Treatment plan verification Algorithm tests – inhomogeneities Measurement of interleaf leakage
3. Research Cell survival study Cell survival study
4. Future work Commissioning of stereotactic systemg Investigation into out-of-field doses A study on small field dosimetry
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Increased degrees of modulation present in Increased degrees of modulation present in RapidArc delivery:◦ MLC are continuously moving◦ MLC are continuously moving◦ Gantry speed & dose rate are variably modulated
New methods and tools are required for patient specific QAp p Q1. ArcCHECK2. Gafchromic film measurements for validation and
as a backup for arcCHECK.
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ArcCHECK is a commercial diode array designed ArcCHECK is a commercial diode array designed specifically for rotational measurements. ◦ 1386 diodes, depth = 3.3cm, 10mm spacing, spiral
d idesign
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ArcCHECK – plan assessment
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ArcCHECK – confidence limitF h i i i l h fid li i i 96 2% From the commissioning plans the confidence limit is 96.2%. (for gamma criteria of 3% 3mm, Threshold =10%)
101
m 98
99
100
ma
3% 3
mm
96
97
98Average = 97.7%
Gam
m
94
95
Pass rate should equal 96 2% for 95% of the measurementsArc
93
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Pass rate should equal 96.2%, for 95% of the measurements.Ezzell et al., 2009
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Gafchromic film Advantages:
High spatial resolution Weak energy dependence Near-tissue equivalence
Disadvantages:I ff f ‘l l’ if d h Images suffer from a ‘lateral’ artifact and other problems related to scanning
Other non dose-dependent artifacts includingOther non dose dependent artifacts including variations in thickness of film active layer
Solution: Use triple channel dosimetry to separate dose-dependentSolution: Use triple channel dosimetry to separate dose dependent and dose-independent parts of scanned film
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Axial dose planes
Coronal dose planesCoronal dose planes
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Treatment plan Assessment using FilmQA Pro softwarep
Treatment plan & Film
Assessment using FilmQA Pro software
Film
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105.00
Gafchromic results
100.00
m
Prostate Head & Neck
Average95.00
ndex
1% 2mm Average
97%
85 00
90.00
Gam
ma in
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 2080.00
85.00
arc 97. 98. 99. 99. 96. 95. 98. 95. 97. 87. 93. 99. 95. 95. 98. 98. 97. 95. 99. 99.
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Prostate plan Prostate plan 4 field 3D conformal plan
with MLC and EDWs.
Measurement set-up A 20cm block of WEP was
set to SSD = 90cm. EBT3 Gafchromic film was EBT3 Gafchromic film was
placed at isocentre (10cm depth). Plan delivered at l d lplanned gantry angles.
Analysis was performed using FilmQA Pro software.using FilmQA Pro software.
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Profiles through the central axis Profiles through the central axis.
Horizontal Vertical
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The ability of the AAA algorithm to account The ability of the AAA algorithm to account for inhomogeneities was tested using Gafchromic EBT3 film in the CIRS phantomGafchromic EBT3 film in the CIRS phantom.
Chamber
Film
Lung insert
Isocentre
Bone insert
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Gamma analysis was used in order to ensure film was aligned with dose plane from TPSfilm was aligned with dose plane from TPS.
Water
Bone Lung
Disagreement is evident in build-up region and at inhomogeneity interfaces.and at inhomogeneity interfaces.
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Validation of absolute dose Validation of absolute dose◦ To validate the calibration of the film, a 0.125cc
semiflex chamber was used.semiflex chamber was used. Dose of 150.1cGy was measured at 10cm deep in
water equivalent part of phantom. Dose values of 142.0cGy and 133.2cGy were calculated
for the beams which traversed the bone and lung inserts respectively.inserts respectively.
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Cirs Phantom ‐ Bone insertGafchromic film Treatment plan Chamber measurement
Chamber at 10cm = 142.0cGy2.8% higher than film
2 0220230
dose point Gafchromic adjusted
g1.4% higher than TPS
Film at dmax = 208.1 cGyTPS at dmax = 210.6 cGy%difference = 1.2%
160170180190200210
% difference 1.2%Film inside bone = 198.6TPS inside bone = 188.3% difference = 5.1%
110120130140150160
se (cGy)
60708090100D
os ← Bone insert →
01020304050
0
0 20 40 60 80 100 120 140
Depth (mm)
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Film inside lung1 = 171.1 cGyTPS inside lung1= 171.3 cGy
% difference = 0.1%Film inside lung2 = 90.2 cGyTPS inside lung2= 89.4 cGy
% difference = 0.9%
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Summary We observed an overestimation of dose beyond
inhomogeneities for 10MV: Bone ~1%Bone 1% Lung ~3%
Previous commissioning work for 6MV gave similarly overestimated doses beyond inhomogeneities:overestimated doses beyond inhomogeneities: bone ~1.5% Lung ~3.5%
Van Esch et al measured point doses beyond Van Esch et al., measured point doses beyond lung and cork: Dose overestimated beyond lung by 4.7% and 3.4% for 6MV
and 15MVand 15MV Dose overestimated beyond cork by 7% and 2.5% for 6MV
and 18MV
Van Esch et al., 2006. Testing of AAA for photon dose calculation. Med. Phys. 33 (11)
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Recommended measurement:
C t l i l fil◦ Central axis cross-plane profile for T-shaped field shown here
Measurement conditions:◦ Gafchromic Film (EBT2)◦ 90 cm SSD, 10 cm deep◦ 1000 MU irradiation◦ 1000 MU irradiation◦ Backscatter > 10 cm ◦ Gantry 0o, Collimator 90o
Analysis software:◦ FilmQA Pro
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Values of ILL = 0 0 012 0 015 0 016 0 017 0 018Values of ILL = 0, 0.012, 0.015, 0.016, 0.017, 0.018
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A study focussing on the ‘Bystander effect’ A study focussing on the Bystander effect led by DIT◦ Tissue and blood samples from treated cancer◦ Tissue and blood samples from treated cancer
patients are irradiated to low dose levels (0.05Gy and 0.5Gy)◦ Individual patient radiosensitivity can be
investigatedG f h i fil i d Gafchromic film is used:◦ To help us design the experimental set up.
T d t i th t d l l b i d li d◦ To determine the exact dose level being delivered to the cells.
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Varian Trilogy linac commissioning for stereotactic treatments◦ Accurate measurement of small fields (0.5cm x
0.5cm) is required We propose to use gafchromic film in a water tank. We will need a specialised holder in order to be able to
accurately place the film within the tank.y p
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Accurate measurement of out-of-field doses◦ Using Gafchromic to measure out-of-field doses g
(<2Gy) and compare to TPS and Monte Carlo
Small field dosimetry◦ Using Gafchromic to measure small fields (<0.5cm)
d TPS d M C land compare to TPS and Monte Carlo
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All staff at St Luke’s in Rathgar Beaumont All staff at St Luke s in Rathgar, Beaumont and James’s.
Andre Micke and David Lewis for all their Andre Micke and David Lewis for all their work on gafchromic film and FilmQA Pro softwaresoftware.
Ann Martindale from Perlamar for organising the workshopthe workshop.
Thanks for listening !