By Vi Nhan Nguyen University of Arizona Outlines Background Projects Objectives Calculate the dose distributions to the tumor and the eye Procedures Matlab code to calculate the dose ID: 749300
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Slide1
Evaluate and improve tumor dose calculation for eye plaques loaded with radioactive seeds
By: Vi
Nhan
Nguyen
University of ArizonaSlide2
Outlines
Background
Project’s Objectives
Calculate the dose distributions to the tumor and the eye.
Procedures
Matlab
code to calculate the dose
Verification:
Monte Carlo simulation
Radiochromic
Film
RESULTS?????????????Slide3
BACKGROUND
Eye Plaque is used to
t
reat tumors locate on the eye
M
elanoma is a deadly cancerPain and Vision LossMortality is 31% at 5 yearCURRENT TREATMENTS – 2 Options: Option 1 : Enucleation to prevent metastasis Option 2: Radiotherapy: brachytherapy using a radioactive plaque. Slide4
THE EYE PLAQUE
Clinical Results show that:
Irradiation using the
Eye
Plaques could
Reduce the mortality rate to 18% at 5 yearsSaving visionSpare the eyeDesigned by COMS (Collaborative Ocular Melanoma Study)Different sizes8mm-25mmEach eye plaque has between 8 and 24 seeds, depending upon the diameter of the plaque.The seeds are inserted into a silastic mold according to a defined patternSlide5Slide6
Background
Who are the patients
?
Select by the
opthalmologist
Consults with the radiation oncologistsUsually Patients with tumors from 2.5 mm to 10 mm in apical height and a basal diameter of 16 mm or lessTumor geometry is determined using ultrasound and then send to a medical physicistsThe Treatment Plan:85 Gray -total doseThe radioactive plaque will be left in place for 5 to 7 days (A prostate implant will use about 100 seeds which are left in permanently)Slide7
Eye Plaque
Physics staff does most of the radiation work
Select the radiation sources
Calculate the dose distributions to the tumor
Sources
Exampleiodine 125 (IAI-125A)IsoAid Advantageabout 4.5 mm long0.8 mm in diameterstrength of each seed is about 5 U or 4 mCi (which is about 10 times stronger than used for Prostate Seed Implants).ruthenium 106Slide8
BackgroundSlide9Slide10
Project’s Objectives
To develop a program using
matlab
to calculate the dose to the tumor and to these Critical Structures.
Sclera
RetinaLensMacula and optic nerveSlide11
Dose Calculation
Dose Calculation
L
ine source Approximation
Sum up all the dose distribution of each seed
Assume that the eye is homogenous and ignore backscatters.AAPM TG 43 2-D formalism to find the DOSE RATE:AAPM TG 43 – Line Source approximationSk – seed strength (given)^ - dose rate constant (given)g(r) – radial dose function F -- anisotropy functionG – geometry factor Slide12
Dose Calculation
g(r)
is the radial dose function, and accounts for radial dependence of photon absorption and scatter in the medium along the transverse axis with the geometric factor removed
.Slide13
Dose Calculation
F(r,) is the anisotropy factor normalized at θ = π/2 (transverse axis), with the geometric factor factored out. The anisotropy factor accounts for the angular dependence of photon absorption and scatter in the encapsulation and the medium. Slide14
Dose Calculation
G(r,) is the geometry factor (cm-2) that accounts for the geometric falloff of the photon
fluence
with distance from the source and depends on the distribution of radioactive material. For a point source, G(r, θ) = 1/r2, and for uniformly distributed line source, G(r, θ) = (θ2 - θ1)/
LrSlide15
Methods
Verification:
Radiochromic
film
dosimetry
Monte Carlo simulationMCNP5Measurements: Along the plaque’s central axis Off axis direction at depths of 5 and 10 mm Homogenous and heterogeneity dose correctionSlide16
Questions?