Formulas Flashcards
Wavelength in formula with speed of light
- c=w * f
- c=wavelength x freq
work unit
J
kinetic E formula
(1/2)(mass) * velocity^2
energy formula
E=mc^2
E in ev
1.24 x 10^-6/wavelength
E in kev
1.24 x 10^-9/wavelength
E in mev
1.24 x 10^-12/wavelength
transmission intensity formula
I/I0–> final intensity/initial intensity
transmission lin atten coef
- I- I0e^-ux –> I0e^-.693x/HVL
- I= intensity after passing thru filter
- I0=inten b4 passing thru filter (100)
- x= thickness of filter
- u=lin atten coef
- e= inverse nat log
HC (homogeneity coefficient) formula
1st HVL/2nd HVL
exposure formula
exposure rate * time
X= Q/m (units stand for)
- X= exposure
- Q= charge
- m= mass
1R= ? C/kg
2.58 x 10^-4 C/kg air
1R= ? rad
0.876 rad in air
1 rad=? R
1.15 R
1 rem= ? rad
1 rad
1 rem= ? Sv
0.01Sv
100 rem= ? Sv
1 Sv
1 rad= ? erg/g
100 ergs/g
1 rad=J/kg
10^-2 J/kg
100 rad= ? Gy
1 Gy
1 rad= ? cGy
1 cGy
1 rad = ? Gy
0.01 Gy
0.876 rad = ? R
1 R
1 Gy =? J/kg
1 J/kg
1 Gy = ? rad
100 rad
1 Gy=? Sv/QF
1 Sv/QF
absorbed dose in air formula
exposure in R * 0.876 rad/R
absorbed dose in medium formula
exposure in R * f-med factor
dose equivalent formula
absorbed dose * QF
answer in rem if question in ?
rad
answer in Sv if question in ?
Gy
geometric penumbra formula
- SS * [(SSD + depth)- SDD)]/SDD
- ex: SS= 2.5 cm, SSD= 78cm, d= 5 cm, SDD= 40 (if no d assume 0)—> 2.5 * [(78+5)-40]/40
fs directly prop to
distance
mag factor formula (field size)
fs on film/fs @ coll
mag factor formula (object size)
size of object on image or film/actual size of object
mag factor formula (distance)
source to film distance or source to image distance/source to object distance
abutting flds (gap calc)
- depth/2 * L1/SSD1 + L2/SSD2)
- SAD if fs defined @ SAD
over or underdose formula with distance
- (correct SSD/incorrect SSD)^2
- ex: 90cGy Rx @ 92cm SSD mistake s/u @ 95 SSD–> (92/95)^2= 0.94= 94%= 6% underdose (further away or bigger #= underdose)
- what was dose delivered as result? 90 cGy * 0.94= 84.6cGy
Celsius=
5/9 (F-32)
Fahrenheit=
9/5 C + 32
e- R100=
depth @ Dmax
e- R90 =
- 90% isodose
- MeV/4
e- R80 =
- 80% isodose
- D or R80= MeV/3
e- R50 =
depth at which dose is 50% of maximum
e- Rp =
- practical range
- E (MeV)/2 or 1/2 nominal E
average E e-
depth of R50 x 2.33
MU calc for e- beam
- MU= Rx dose/depth dose * mach calib factor * fs corr factor (cCAL)
- if depth dose is %- use decimal
beam atten formula
dose with device/dose without device
mean life
tavg = 1 / λ = 1.44 * t1/2
exposure rate for change in distance
X(d)= gamma factor * A/d^2 (cm)
OER (oxygen enhanced ratio)
absence of O2/presence of O2
1 AMU = ? kg
1.66 x 10^-27 kg
E equiv of 1 AMU=
931 MeV
Planck’s constant (h)
- 6.62 x 10^-34 J-sec
- E= hv (v=velocity)
Avogadro’s #
6.0228 x 10^23
TMR=
TAR/BSF
activity formula
A = A0 * e-λt
SMR=
TMR-TMR(0x0)
SAR=
TAR-TAR(0x0)
%DD=
- TAR/BSF * (SSD+Dmax/SSD + d)^2 * 100
- absorbed dose at any depth in phantom div by dose at depth of max dose
dose rate @ point =
exposure rate constant * f-med * activity * 1/r
exposure (x)=
X = Γ * Α / d2
mean free path formula
I/u (u=lin atten coef)
uncertainty formula
square root of sum (error)^2
1/Te=
- 1/Tp + 1/Tb (calc eff T1/2 from physical & biolog T1/2
- if Tp is much smaller than Tb, Teff= Tp
iso shift=
PDD2= PDD * (SSD + dmax/SSD + d + dmax)^2
equivalent square for blocked field formula
equiv square open * square root of unblocked
dose correction=
Do (TAReff/TARphy)
given dose
- tumor dose/PDD * 100
- aka dose @ dmax, applied dose, entrance dose, peak absorbed dose
back scatter factor (BSF) formula
- dose @ dmax in phantom/dose without backscatter (free space)
- aka peak scatter factor
- BSF= TAR at Dmax
output calc formula
Cfs * Ccal (SSD1 + dmax/SSD2 + dmax)^2
equiv square fld formula
2 (L*W)/L+W or 4 (area/perimeter)
TAR formula
dose at a given point in medium/dose at same point in air
TMR formula
dose @ depth/dose @ dmax
TPR formula
dose at specified point in tissue/dose at same distance at ref depth in phantom (usu 5 cm)
mayneord’s factor formula
(SSD2 + dmax/SSD1 + dmax)^2 x (SSD1 + d/SSD2 + d)^2
new PDD
PDD1 * mayneord factor
dose rate formula
mach output (Ccal) * fmed * BSF
beam on time formula
dose per fx/dose rate
time setting formula
beam on time (min) + timer error
wedge angle formula
90 deg - (hinge angle/2)
hinge angle formula
180 deg - (2 * wedge angle)
ISCF for PDD formula
[(ref SSD + depth of dmax)/(tx SSD + depth of dmax)]^2
ISCF for TMR formula
[(source calib distance)/(SSD + depth)]^2
normalization formula
new iso line/old iso line * 100
weighting formula
- ex: ap, pa , rt, lt 1:1:1.3:1.3 for 180cGy–> 1+1+1.3+1.3= 4.6
- ap/pa= 180/4.6= 39*1= 39cGy each
- lt/rt= 180/4.6=39*1.3= 51 cGy each
exposure rate for chg in distance
X(d)= gamma factor x A/d^2
gamma factor unit
R * cm^2/mi * hr
Sc or output factor
- ratio of output in air for given fs to that of std fld
- most often measured @ SAD
evaluation of PDD assumes variation of
beam intensity along CAX of beam
Sp or phantom scatter factor
- ratio of dose in phantom of a given fs, @ depth of max dose, to dose at same depth, to that of std fs
- if can accurately measure BSF, Sp is also known as Sp= BSF(r)/BSF(o)
TMR concept
fractional scatter contribution @ given depth is indep of beam divergence & depends only on field size & depth of overlying tissue for a beam of given E
SAR concept
-calc scatter dose in medium
linear atten coef (u)
prob per unit thickness that any 1 photon will be atten
mass atten coef
u/density
equivalent square
- same Pdd & TMR as rect fld
- smaller area than rect fld
ESF have same
output factor, scatter effects, & DD as rect fld
OAR/OCR
- off axis ratio/off center ratio
- ratio of dose at any pt on dose profile/dose at central ray of profile
output factors (Sc, Sp)
dose rate @ given fld/dose rate of std 10x10 fs
beam attenuation formula
dose with device/dose without device
BSF formula
- dose @ pt @ dmax w/scatter div by dose @ same pt in air w/o scatter
- dose dmax/dose free air
- dose on CAX @ dmax/dose in air
exposure rate for change in distance
- X(d)= gamma factor x A/d^2
- A= activity
- d= distance
- ex: expos rate @ 5 cm from 10mCi Cs-137–> X= (3.27R x cm^2/mCi x hr) x 10mCi div by 5cm^2= 32.7/25=1.308=1.31 R/hr
decay constant
0.693/t 1/2
cumulative implant dose
dose= 1.44 x t1/2 x Do
Sc
ratio of output in air for given fs to exposure for ref fs
inverse square factor
(SSD1/SSD2)^2
I1/I2= (d2/d1)^2
SMR
ratio of scattered dose @ point in phantom to the effective primary dose @ same point @ ref depth of max dose
value of c
3 x 10^8 m/s OR 3 x 10^10 cm/s
force unit
Newtons= 1 kg x m/sec^2
kinetic E unit
J
gravitation acceleration unit
9.8 m/sec^2
potential E unit
J
1 J = ? kg m^2/sec^2
1 kg m^2/sec^2
1 N-m
SAR formula
scatter @ given pt in med/dose in air @ same pt (w/o scatter)
linear atten coef depends on
- nature of material
- energy
- Z impacts lin atten coef
linear atten coef formula
-0.693/HVL
mass atten coef depends on
- E of beam
- material
mass atten coef independent of
density
increase E = ? BSF
decrease
increase field size = ? BSF
increase
Measure of ionization produced in air by photons, X =
dQ/dm
Exposure rate
A x exp rate constant/ distance^2
F factor is
0.876 rads/R
Z/A for all elements is approx
0.5