Brachytherapy, Radionuclide Therapy Medical...

Brachytherapy, Radionuclide Therapy

Medical Physics in the Clinic

Raymond K. Wu, PhD

Chairman

AAPM Exchange Scientist Program

TG 43 of 1995

New dose calculation formalism for

brachytherapy

Consensus data for Pd-103 and I-125

seeds

Resolution of the 17% discrepancy for

some seed types

Significant improvements in dosimetry

methodologies

Med. Phys. 22 (2), February 1995 pp.209-234

AAPM Exchange Scientist Program – Wuhan China 2015

After TG 43

Source Activity or Apparent Activity => Source Strength (unit is U

or cGy per hour at 1 cm) Sk

Milligram Radium Equivalent => U

Exposure Rate Constant => Dose Rate Constant Λ

Tissue Attenuation Coefficient => Tabulated data

Ignoring source construction and design => Radial Dose

Function, Anisotropy Factor, Anisotropy Function Table Clinical work not standardized for source design except as a point

source => Standardized for radioactive sources of various

size, shape, and construction


TG 43 U1 - 2004

Revised definition of Air Kerma Strength

Elimination of Apparent Activity as source

strength

Elimination of Anisotropy Constant and

replaced by Anisotropy Functions 1D and

2D

Other minor improvements

Med. Phys. 31 „3…, March 2004, pp.633-674


SK is Source Strength in U

Λ is Dose Rate Constant

gL(r) is Radial dose function

F(r,θ) is Anisotropy function

r0 is 1 cm, and θ0 is 90°


ρ(r’) is density of radioactivity at r’

r’ is (x’, y’, z’) within the integrated volume V


It may be shown for a point source, the TG 43

equation becomes

F(r,θ) may be simplified as a function of r,

which becomes the Anisotropy factor Φan(r)


Example for

Cs 131 (IsoRay Medical)®



Dose Rate Constant (cGy/h-U) 1.06

Anisotropy Constant 0.964

Half Life (days) 9.689

Active Length (cm) 0.40

Physical Length (cm) 0.45

Physical Diameter (cm) 0.08




Point source approximation



Line source

approximation

Prostate Seed implants

I-125 seeds

Pd-103 seeds

LDR Implants

Ir-192 ribbons

Cs-137 sources

HDR Sources

Ir-192

Co-60


Common Radionuclides in Rad Onc

Symbol Primary Emission

Energy (or max energy) keV

Half-life 10 half-lives

60Co gamma 1170-1330 5.26yrs 53 yrs

89Sr beta Ave 1.463 MeV 50.5 days 1.4 yrs

90Sr beta/gamma 546 (up to 2.27 MeV) 28.5 yrs 285 yrs

103Pd gamma 21 17 days 170 days

125I gamma 27-36 60.2 days 20 months

131I gamma 364, 637 8.04 days 2.7 months

131Cs beta/gamma EC 29 9.7 days 3.25 months

137Cs gamma 510, 1180, 662 30 yrs 300 yrs

192Ir gamma/beta 380 73.83 days 2 yrs

223Ra alpha 5.78 MeV 11.43 days 114 days

Radionuclide Therapy

I 131 Thyroid Ablation


I-131 Thyroid Ablation

Limit of Removable

contamination

< 2000 dpm/100cm2

•Washable chair covers

•Disposable absorbing

padding material


• Liquid form of I-131

• In house radiopharmacist

• Urine storage for decay

• Decontamination tasks

• Fume hood

• Bioassays


Inhaled or Ingested

Radioactive Material


ACPSEM Summer School 2014 – Melbourne

Committed dose equivalent (HT,50)

The dose equivalent to organs or

tissues of reference (T) that will be

received from an intake of radioactive

material by an individual during the 50-

year period following the intake.

Committed effective dose equivalent

(HE,50)

The sum of the products of the weighting

factors applicable to each of the body organs

or tissues that are irradiated and the

committed dose equivalent to these organs

or tissues

HE,50 = ΣWTHT.50


Historical dose information for

Radiation Oncology staff

Radiation Oncology staff 2011

maximum 2-month whole body dose was 0.08 mSv

maximum whole body yearly total was 0.08 mSv

maximum annual extremity exposure was 0.17 mSv

Radiation Oncology staff 2012

maximum 2-month whole body dose was 0.041 mSv

maximum whole body yearly total was 0.041 mSv

maximum annual extremity exposure was 0.070 mSv


Other Radiation Oncology Procedures

Cyberknife X-sight Lung, X-sight Spine

Image Guided RT

Cs-131 brain implant

Prostate seed implant

LDR cervix endometrium implants

Zevalin, SIR sphere procedures

Xofigo, Metastron procedures



Let us focus on HDR

High Doserate

Remote Afterloader

HDR

High Doserate

Remote-afterloader


Nucletron Microselectron – Version 2

One single source

4 mm long

Iridium – 192

Emits 350 kV ɤ ray

Half Life 73.8 days

Max activity allowed – 10 Ci

Source replacement 3-4 time per year

When activity becomes 3-4 Ci


Popular because

• Drastically reduces exposure to staff

• Can reduce unnecessary dose to patient

• Can minimize risk of source inadvertently

left in patient

• Can produce desirable dose distribution

• Greatly increases throughput-Outpatient

• Allows for adjustment of applicators

• Computerized documentation



The Devil is in the

Applicators

MammoSite


Contura


Tandem & Ovoid

CT/MR Applicator


Esophageal

Applicator


Multi-purpose

Applicator



Source Location Simulator

Misadministration USNRC

Delivering treatment to the wrong patient

Using the wrong radioisotope

Treating the wrong site

Using leaking sources

Failing to remove a temporary implant

Delivering a radiation dose differing more than

20% from the prescribed dose


Risks

Very High dose rate affords little time to correct

problem

Intrinsically complicated system takes longer to

learn

Radiation biology different from external beam

Sharp dose gradient requires better anatomical

data

High risk to staff if failure of unit occurs



PermaDoc by Mick


Transfer Tubes


Rotte Applicator -

Radiochromic film

exposed by HDR

source and by 6e


Dummy Sources


Global Threat

Reduction Initiative

GTRI

Security of Radioactive

Material – GTRI program


Security of Radioactive Material – GTRI program


Men and women are

created to take care

of the necessity AAPM Exchange Scientist Program – Wuhan China 2015

When necessary we

may apply the law

inconsistently AAPM Exchange Scientist Program – Wuhan China 2015

We may overkill if we

just want to deliver


Pay proper attention

No need to be afraid


BEIR VII


NCRP 116 Public Dose Limits

0.25 mSv/yr per site

Annual background radiation doses in

USA 4.1 mSv / yr

1 mSv

Cosmic background (5%)

0.34 mSv

Indoor Radon

(37%) 2.45 mSv

Radiography/fluoroscopy

(5%) 0.35 mSv

Interventional fluoroscopy (7%) 0.47 mSv

Nuclear Medicine

(12%) 0.8 mSv

CT (24%)

1.6 mSv

Internal (5%) 0.33

Terrestrial (3%) 0.2mSv


0

0.1 mSv

0.06

Extremity x-ray

Trans-continental

flight

Chest x-ray

0.02

0.04

1-week dose in

US, all sources

Annual dose

from building

materials

Transpolar

flight

0

1 mSv

0.6

0.2

0.4

0.8

0

10 mSv

6

2

4

8

Radiation Doses in Perspective

Annual

terrestrial dose

in Maryland

Annual cosmic

rays

Internal to body

Annual dose from

medical exams

Annual

terrestrial dose

in Denver

BSS annual

limit to public

US Annual

dose from

natural

background

Apollo XVI

astronauts

Modern

CAT scan

0.08

Annual dose

natural bkgd:

Kerala 15 mSv

Denver 6 mSv


As Low as Reasonably

Achievable (ALARA)


Radiation Hormesis

Case of a Taiwan high rise apartment built with

contaminated reinforcement steel, published in 2007

• 1700 apartment units, 10,000 occupied building

• 40 mSv average dose received

• Cancer death only 3% of natural incidence

• Congenital malformation only 7% of general public


IOMP Policy Statement No. 3 http://www.iomp.org/?q=node/5

This policy statement addresses predictions of

induced cancers and cancer deaths in a

population of patients exposed to low doses

(<100 mSv) of ionizing radiation during medical

imaging procedures.


Prospective estimates of cancers and cancer deaths induced

by medical radiation should include a statement that the

estimates are highly speculative because of various random

and systematic uncertainties embedded in them. These

uncertainties include dosimetric uncertainties; epidemiological

and methodological uncertainties; uncertainties from low

statistical power and precision in epidemiology studies of

radiation risk; uncertainties in modeling radiation risk data;

generalization of risk estimates across different populations;

and reliance of epidemiological studies on observational

rather than experimental data. Such uncertainties cause

predictions of radiation-induced cancers and cancer deaths to

be susceptible to biases and confounding influences that are

unidentifiable.



Paragraph A86 of Report 103 of the International

Commission on Radiological Protection (ICRP)

states that “There is, however, general

agreement that epidemiological methods used

for the estimation of cancer risk do not have the

power to directly reveal cancer risks in the dose

range up to around 100 mSv”.



Further, UNSCEAR Report A-67-46, approved in

May, 2012, states that “The United Nations

Scientific Committee on the Effects of Atomic

Radiation (UNSCEAR) does not recommend

multiplying very low doses by large numbers of

individuals to estimate numbers of radiation-

induced health effects within a population

exposed to incremental doses at levels

equivalent to or lower than natural background

levels.”


IOMP Policy Statement No. 3

Paragraph 151 of ICRP Report 103 states: “The

use of effective dose for assessing the exposure

of patients has severe limitations that must be

considered when quantifying medical exposure”,

and “The assessment and interpretation of

effective dose from medical exposure of patients

is very problematic when organs and tissues

receive only partial exposure or a very

heterogeneous exposure which is the case

especially with x-ray diagnostics.”



Predictions of radiation-induced cancers and

cancer deaths from medical imaging procedures

should be accompanied by estimates of

reductions in patient morbidity, mortality and cost

resulting from the same medical imaging

procedures


ACPSEM Summer School 2014 – Melbourne


If effective dose is used to generate predictions

of cancers and cancer deaths, a statement

should be included that the ICRP has expressed

caution in the use of effective dose for purposes

of estimating risks to individuals or populations

exposed to ionizing radiation.

The End

[email protected]

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