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Evaluate and improve tumor dose calculation for eye plaques loaded with radioactive seeds Evaluate and improve tumor dose calculation for eye plaques loaded with radioactive seeds

Evaluate and improve tumor dose calculation for eye plaques loaded with radioactive seeds - PowerPoint Presentation

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Uploaded On 2019-01-31

Evaluate and improve tumor dose calculation for eye plaques loaded with radioactive seeds - PPT Presentation

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

eye dose factor plaque dose eye plaque factor calculation source tumor background radioactive seeds calculate axis seed radial accounts

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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 patternSlide5
Slide6

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

BackgroundSlide9
Slide10

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?