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80 Cards in this Set

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What is the transmission formula?

HVL = 1/2ⁿ

What is the field size on the skin (surface) formula?

SAD - depth/ SAD

answer x field size at SAD

Transmission formula = attenuation

It = Iₒ e- 0.693 x thickness/ HVL

HINT use 100 for Iₒ if original intensity is not given

TVL formula

TVL = 3.32 x HVL

Linear coefficient

ɥ = 0.693 / HVL cm-1

Given dose (or dmax dose)

(tumor dose/Pdd) X 100
TPC
(273.2 + Cᵒ/ 295.2)(760/P)

760 is in mmgh
use 1013.2 mbar
Celsius conversion to farenheit

C = 5/9 (F - 32)

Mayneord Factor (Big F)

(New + dmax/ Old SSD + dmax) X (Old SSD + depth/ New SSd + depth)
multiply the answer by the original pdd

Decay formula
A = Aₒ e - 0.693 x time /T 1/2
Penumbra

GP = s(SSD + depth -SDD)/SDD

If no given depth use 0

source size must be converted to cm by s/10mm

Magnification

Img distance/ Object distance
or
Img size/ Object size
Exposure to dose conversion

Exposure x dose = rads

Dose to exposure conversion

Dose / exposure = R
Dmax or Given dose

(tumor dose / pdd)x 100

Inverse Square

I₁D ₁²= I₂D₂²

Old /New

Scatter to Air Ratio = SAR

Scattered dose at given point in phantom / dose in free space at same point

Independent of SSD
Dependant on Energy, depth, field size

Equivalnt Square = EQSQ

2A / P

or
2 (L X W) / (L + W)

Wedge factor

dose with wedge / dose without the wedge

measured at 10cm

RX given dose or dose to a point

RX dose @ depth / Pdd @ RX dose
X Pdd @ depth of interest

Equivalent Radius = EQRA

2A / square root of pi *P


2 (l x w) / square root of pi * (l + w)

# e- per gram formula

NA x Z / A

OR

6.02205 x Z# / A

TAR

Dose in the phantom / dose in air at the same point

Pdd
Depth / dmax X 100
Electron density formula

Pe = Pm Na Z /A

Avogados number (number of atoms)

Na = 6.02205 X 10²³ atoms

Atoms per gram formula

NA / A

OR

6.02205 10^23 / A

As Pdd increases
E↑ Field Size↑ depth↓ SSD↑
As TAR increases
E↑ Field Size↑ depth↓
Independent of SSD or SAD
As TMR increases
E↑ Field Size↑ depth↓
Independent of SSD or SAD
Wedge factor is dependant on
Energy, Field size, depth
GTV
CTV
PTV

Gross tumor volume,


clinical tumor volume,


planning target volume

Which one of these is most important .
GTV
CTV
PTV

PTV

Back scatter factor = BSF

dose at dmax / dose in air
at the same point

OD = optical density

log lₒ / lᵻ

or
log without film / with film
divide first then log

GAP formula

(L₁x d /2SSD₁) + (L₂x d/2SSD₂)

Collimator formula

(1/2 L₁x 1/SSD) -1 tan
OR
(L/2/SSD) -1 tan

Couch formula

(1/2 L₁x 1/SAD) -1 tan
OR
FIELD LENGTH/2/SAD) -1 TAN

TPR = tissue phantom ratio

dose in tissue at a point / dose in phantom at referenced depth

IF that depth is dmax then it is TMR

Atomic # Z what is the division between #protons and e- and neutrons
number of protons + number of e- = Z
Atomic mass A
number of protons + # neutrons = A atomic mass
What is 2n²?

n is the quantum number

MU formula
TD/Junk

T or F
BSF and TAR @dmax are the same?

True

Calculate the MU of a 6 MV e- beam with a 15 x 15 cm cone.


RX dose is 200 cGy at 95 % isodose line. The output of a 15 x 15 cm cone is 1.042.

MU =TD/Junk



OR



SAD Technique


{MU=cGy / C F×(OF×TPR×WF)}

200/ 1.042 x 0.95 = 202MU

Calculate the MU of a 6 MV e- beam with a 15 x 15 cm cone. RX dose is 200 cGy at 95 % isodose line. The output of a 15 x 15 cm cone is 1.042. If there is a 1cm bolus what is MU?

MU =TD/Junk

200/ 1.042 x 0.95 x (100/99)²
= 198 MU



Fixed SAD Technique


MU=cGy / CF×(OF×TPR×WF)



Fixed SSD Technique


MU=cGy.SSD / CF×(OF×PDD×WF)

Rule of thumb
How far will your energy travel?

E/2
E/3 = 80%
E/4 = 90%

T or F
If a lesion is on the skin you will have to use dmax thickness of bolus of that Energy?

True
4 MV use 1cm bolus
6 MV use 1.5 cm bolus

Compton and photoelectric interactions are produced by what machine energy ranges

Compton by Mega (bone- high Z)
Photoelectric by Orthovolt

T or F you can use MLCs with Island blocks?
False you cannot

Calculate the gap of 2 adjacent fields which are
10 x 10 cm 100 SSD
15 x15 cm 100 SSD
The matchline depth should be 7 cm

gap = L₁*d/2SSD + L₂*d/2SSD

10*7/200 + 15*7/200 =

%dd for a 10 x 10 field at 10cm with 80cm SSd (dmax at 1cm) using a 4 MV photon is 62.2. Find the %dd for the same field size and depth at 100 cm

(NEW SSD +dmax/OLD SSD +dmax)²*(OLD SSD + depth/ NEW SSD +depth)² x original pdd

(100 +1cm/80+1cm)² *(80+10/100+10)² x 62.2 = 64.73 %

What is the collimator angle if the spine field is 18 cm long at 80 SSD?
(1/2 L* 1/ssd) arc tan -1

(18/2 * 1/80 )*tan -1 = 6.4
What is the couch angle if the brain field is 16 cm in length at 100 SAD?

(1/2 L* 1/sad) arc tan -1

(16/2 * 1/100) *tan-1 = 4.57

T or F
For orthovoltage (E up to 400 kvp) and lower E xrays the dmax is on the skin and always 100%?
True because dmax is always on the skin

Calculate the Hvl of a material if the thickness to produce 60% transmission is 7cm.

It = I₀ e- 0.693*t / HVL
60 = 100 e- 0.693*7 / HVL
60/100 = e- 4.851 / HVL
ln .6 = -4.851/ HVL
-0.51082 = -4.851/HVL
HVL = -4.851 / -.51082
HVL = 9.49

During a 2.5 minute fluoroscopy exam a tech was exposed to 250 mR/hr. What is the exposure?

Exposure = Rate x Time
250 mR/hr * 2.5 min/ 60 min
250 mR * .04166
= 10.4 mR

What is Tar at 5 cm depth if dose at 5cm is 180 cGy and dose in freespace is 210 cGy?
180cGy / 210 cGy = .857 or .86

Definition
The thickness of material required to reduce the intensity of the beam to 1/2 its original value

HVL

Definition
Thickness of material required to reduce the intensity of the beam to 1/10th its original value

TVL

Hinge Angle

180/2 - wedge angle

HELP ME LIZ I THINK I AM LOSING IT

Wedge Angle

90- hinge angle / 2

Tray factor

Dose with tray / dose without the tray
Exposure
exposure rate X time
Radium Equivalent - brachy
『A/『ra
OR
source * activity / Ra source
Exposue at distance - brachy

『A /d²

Exposure time - brachy
『 A t/『ra
Mghr -- perm implant
RaEq *1.44 * T1/2 *24 hrs
Mghr -- temp implant
RaEq * T1/2 * 24 hrs

Field weighting

When beams are weight equally each field receives the same amount of dose --180/4 = 45 cGy per field

As weight is increased the hot spot moves toward the surface of that beam

AP/PA field weighted 3:1 with a dose of 200

200/4 = 50
3 * 50 = 150
1 * 50 = 50
What is image size of a block if magnification is 3.2 cm and object size is 1.25?
mag = img size/obj size

3.2cm = image size/ 1.25
3.2 * 1.25 = 4
What is the depth of 50% of a 10 MeV e- energy?
E/2 = 10/2 = 5

????

The atom is neutral provided the # of e- and the # of protons is the same.


If the atom has more e-, is the atom neg or positive?
more protons?
more neutrons?
WHY???

more e- = neg atom b/cuz e- are neg

more protons = positive atom b/cuz protons are positive

more neutrons nothing, b/cuz nuetrons are nuetral

AMU

atomic mass unit
atomic weight is measured in atomic mass unit

Isotopes (ZA)

Nuclear with the same # of protons and different # of neutrons
Same Z but different A


12 13
C C
6 6

same chemical reaction because of same Z (6)

q
Isobar (AZ)
have the same atomic weight A different Z

do not have same chemical reaction

Isotone (N)

Isotone have the same # neutrons different Z and different A

Annealing

heating to remove radiation from ionization chambers

How is absolute dose measured?

Ion chambers and Fricke dosimetry.
absolite dose means 1 rad is 1 rad
Who calibrates ion chambers and how often

Calibrated by ADCL or NIST
Survey meters calibrated once a year