RADIATION UNITS MODERATOR :- Mr. TEERTHRAJ SIR

PRESENTER :- DR.VIJAY.P.RATURI

KGMU , RADIATION ONCOLOGY DEPTT.

RADIOACTIVITY & DISINTEGRATION

EXCESS ENERGY IN FORM OF E.M RADIATION

ANOTHER NUCLEUS + CHARGED PARTICLE DAUGHTER

ONE NUCLEUS PARENT

DISINTEGRATION

Co Ni + e 60

27

60

28

0

-1

GAMMA RAY EMISSION

PHOTON

NEED OF MEASURING SYSTEM

• MAGNITUDE OF BIOLOGICAL EFFECT IN RADIOTHERAPY & RADIODIAGNOSIS.

• DIRECT MEASUREMENT IMPRACTICABLE

CRITERIA FOR MEASURING SYSTEM• REPRODUCIBLE

• REPEATABLE

• SENSITIVE

• OBJECTIVE

• LINEAR

• IONIZATION OF AIR, IS NOW INTERNATIONALLY ACCEPTED BASIS OF

STANDARD X-RAY DOSIMETRY

• IONIZATION IS MAJOR PRODUCT OF ENERGY ABSORPTION PROCESS

• DEPENDS UPON ENERGY OF RADIATION & ON ATOMIC NUMBER OF MATERIAL

UNITS OF RADIOACTIVITY Curie Becquerel

UNITS OF RADIATION DOSES 1) Units of Exposure Roentgen 2) Units of Absorption Physical dose – Rad/ Gray Biological dose – rem/seivert

RADIATION UNITS

DECAY CONSTANT • No of atom disintegrating / time ( dN/dt) is proportional to No of radioactive atoms (N)

dN dt N - N

• Rate of disintegration dN/dt is called activity

• Unit of activity is curie (Ci)

• 1 Curie = 3.7 x 10 disintegration/sec ( or Bq)

• SI unit is Becquerel

• 1 Bq = 1 radioactive decay per second = 2.703 x 10 Ci

UNITS OF RADIOACTIVITY

-11

10

THE ROENTGEN

• AMOUNT OF X, OR GAMMA RADIATION SUCH THAT ASSOCIATED CORPUSCULAR EMISSION PER 0.001293 GM( 1CC) OF AIR PRODUCES IN AIR IONS CARRYING 1 ELECTRO STATIC UNIT OF CHARGE OF EITHER SIGN.

• Roentgen is unit of X or GAMMA ray & can’t be used for other ionizing radiation like BETA ray or NEUTRON.

• For these, an additional unit the RAD was introduced in 1956

• In 1962 , it was decide roentgen -- unit of exposure. rad unit -- unit of absorbed dose.

• 1 R = 2.58 * 10 c/kg of air-4

THE RAD

• Absorbed dose is what we want to measure

Defined by I.C.R.U, D= Ed m Ed ( energy imparted by ionizing radiation to the matter )

m ( mass of matter)

• 1 rad = 100 erg per gram

THE GRAY

• In JUNE 1975 , International committee on weights & measures adopted the gray (sym G) as S.I unit of absorbed dose ( named after Dr.L.H.Gray)

1 gray = 1 joule /kg = 100 rad

CONVERSION FACTORS FOR ROENTGEN TO RAD

Absorbed energy/gram = energy in the beam* mass absorption coefficient

= E ( mass abs coefficient) After some calculation we get

Absorbed energy /gram = f R rads

factor f , for converting roentgen into rads. factors varies with the material & with radiation energy .

• 0.87• 0.94• 0.96• 0.96

WATER

• 0.91• 0.94• 0.95• 0.955

MUSCLE

• 4.23• 1.46• 0.91• 0.92

BONE

ROENTGEN TO RAD CONVERSION FACTOR ( f ) FOR WATER ,MUSCLE & BONE

100KV200KV1 MEV4 MEV

ENERGY

RADS ( PER ROENTGEN)

MUSCLE

9294

95.695.7

BONE

41419192.192

VOLTAGE OF RADIO-ACTIVE SOURCE

100KV200KV4 MVC0 60

ABSORBED DOSES IN MUSCLE & BONE

Radiation increases the risk of cancer and other stochastic effects at any dose.

The ICRP maintains a model of these risks as a function of absorbed dose and other factors. That model calculates an effective radiation dose, measured units of rem, which is more representative of the stochastic risk.

THE REM • Dose of any ionizing radiation which will produce

the same biological effect as 1 rad of Co 60 gamma ray ( for which the Q.F is 1)

• Dosimetric quantity relevant to radiation protection is dose equivalent (H)

• Rem is designed to represent stochastic biological effect of ionizing radition

H = D * Q ( D – Absorbed dose Q – Quality factor )

ICRP officially adopted the rem as the unit of equivalent dose in 1962 to measure the way different types of radiation distribute energy in tissue

Dose equivalent in rem = (dose in rad * QF) + ( dose in rad * QF) + …

QUALITY FACTOR(QF) :- value based on range of RBE related to LET of radiation .

Radiation 2

Radiation 1

QUALITY FACTOR

X RAY , GAMMA RAYELECTRON

THERMAL SLOW NEUTRON

FAST NEUTRON , PROTONS

1

3

10

L.E.T

• The S.I unit of dose equivalent is Sievert (Sv)

1 Sv = 1 joule /kg

• It is a measure of the health effect of low levels of ionizing radiation on the human body.

Quantities that are measured in sieverts are intended to represent the stochastic health risk, which for radiation dose assessment is defined as the probability of cancer induction and genetic damage.

The ICRP calculation provides two weighting factors to enable the calculation of protection quantities.

1. The radiation factor WR, which is specific for radiation type R - This is used in calculating the equivalent dose HT which can be for the whole body or for individual organs.

2. The tissue weighting factor WT, which is specific for tissue type T being irradiated. This is used with WR to calculate the contributory organ doses to arrive at an effective dose E..

When a whole body is irradiated uniformly only the radiation weighting factor WR is used, and the effective dose equals the whole body equivalent dose.

If the irradiation of a body is partial or non-uniform the tissue factor WT is used to calculate dose to each organ or tissue.

RADIATION WEIGHtING FACTOR (WR)

"The 2007 Recommendations of the International Commission on Radiological Protection". Annals of the ICRP. ICRP publication 103 37 (2–4). 2007. ISBN 978-0-7020-3048-2. Retrieved 17 May 2012.

TISSUE WEIGHTING FACTOR (WT)

"1990 Recommendations of the International Commission on Radiological Protection". Annals of the ICRP. ICRP publication 60 21 (1-3). 1991. ISBN 978-0-08-041144-6. Retrieved 17 May 2012.

• Acronym for Kinetic Energy released per unit mass

• K = sum of kinetic energy all charged particle liberated by ionizing radiation per unit weight of matter

dE dm • It is different from absorbed dose as some of

the kinetic energy escapes from the absorbing volume

KERMA

K = Unit – j/kg (gray)

THANK YOU…