Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
96 Cards in this Set
 Front
 Back
 3rd side (hint)
In soft tissue, the greatest backscatter factor is associated with: 
e) 1mm Cu HVL xrays

Scatter is associated w/COMPTON INTERACTIONS.
@2mm Al HVL= mainly Photo Electric Interactions. @about 1m Cu HVL and above =mainly Compton. As photon E increases, more energy is transferred to the e and less to the scattered photon. The max BSF is~0.7mm Cu HVL. 

The TMR depends on:
a) Energy, SAD, Depth & Field Size b) Energy, SAD & Field Size c) SAD, Depth & Field Size d) Energy, Depth & Field Size e) SSD only 
d) Energy, Depth & Field Size

TMR, like TAR, is independent of SAD


TAR is:
a) Equal to the BSF @ dmax b) Independent of SAD c) Used in calc of timer settings in rotational therapy d) all the above e) none of the above 
d) all the above

The timer or MU setting for rotation uses the ave TAR, averaged over all depths for the area of rotation


A single PA spine field is tx'd @130cm SSD. Compared to tx @ 80cm SSD, the exit dose will be:
a) Greater b) Smaller c) the same 
a) Greater

As SSD increases, PDD (and thus Exit Dose) increase  per Mayneord's ffactor


Which is true:
a) TAR Increases as SSD Increases b) BSF Increases as beam Energy Increases above 1 MV c) PDD Increases with Increasing SSD d) TMR can NOT be measured for Co60 
c) PDD Increases with Increasing SSD

a) TAR is INDEPENDENT of SSD and SAD.
b) BSF increases with increasing energy up to~1mm Cu HVL, then Decreases as Energy increases. d) Historically, TARs measured for Co60 & TMRs measured for Higher Energy beams. *But, TMRs can be measured & used for calcing timer settings AT ANY MEGAVOLTAGE ENERGY* 

TMR:
Dependent/Independent of SAD 
TMR, like TAR, is INDEPENDENT of SAD (and SSD).



TAR:
Dependent/Independent of SAD 
TAR, like TMR, is INDEPENDENT of SAD (and SSD).



TAR:
Dependent/Independent of SSD 
TAR is INDEPENDENT of SSD (and SAD).



TMR, formula:
a) (dose rate at dmax) / (dose rate at depth) at SSD b) (dose rate at depth) / (dose rate at dmax) at SSD c) (dose rate at dmax) / (dose rate at depth) at SAD d) (dose rate at depth) / (dose rate at dmax) at SAD e) (dose rate at dmax) / (dose rate in air) at SAD 
d) (dose rate at depth) / (dose rate at dmax) at SAD



BSF, formula:
a) (dose rate at dmax) / (dose rate at depth) at SSD b) (dose rate at depth) / (dose rate at dmax) at SSD c) (dose rate at dmax) / (dose rate at depth) at SAD d) (dose rate at depth) / (dose rate at dmax) at SAD e) (dose rate at dmax) / (dose rate in air) at SAD 
e) (dose rate at dmax) / (dose rate in air) at SAD



PDD/100, formula:
a) (dose rate at dmax) / (dose rate at depth) at SSD b) (dose rate at depth) / (dose rate at dmax) at SSD c) (dose rate at dmax) / (dose rate at depth) at SAD d) (dose rate at depth) / (dose rate at dmax) at SAD e) (dose rate at dmax) / (dose rate in air) at SAD 
b) (dose rate at depth) / (dose rate at dmax) at SSD



TMR:
a) stands for Tumormaximum ratio b) is the ratio of dose at dmax to dose at depth c) Increases as SSD Increases d) can NOT be measured on a Co60 unit e) NONE of the above 
e) NONE of the above.

TMR=Tissuemaximum ratio.
It is the ratio of two dose rates measured in a phantom, at the SAME distance from the source (one w/a chosen thickness of overlaying phantom, the other w/only the rhicness rquired to attain dmax. It is Independent of SSD. It can be measured on any megavoltage xray or gamma ray unit. 

TMR:
a) Tissuemaximum ratio. b) the ratio of two dose rates measured in a phantom, at the SAME distance from the source c) Independent of SSD. d) can be measured on any megavoltage xray or gamma ray unit. e) all of the above 
e) all of the above

TMR=Tissuemaximum ratio.
It is the ratio of two dose rates measured in a phantom, at the SAME distance from the source (one w/a chosen thickness of overlaying phantom, the other w/only the rhicness rquired to attain dmax. It is Independent of SSD. It can be measured on any megavoltage xray or gamma ray unit. 

BSF:
a) is the TAR @ dmax b) Increases as energy Increases over 1MV c) is the PDD @ dmax d) is the ratio of dose in air to dose in tissue e) All the above 
a) is the TAR @ dmax

a) TAR is the dose rate at depth / dose rate in air at the same point.
The TAR @ dmax is called the Back Scatter Factor. BSF DECREASES as Energy INCREASES above 1 MV 

All of the following are INDEPENDENT of SSD  EXCEPT:
a) TMR b) TAR c) PDD d) BSF 
c) PDD

c) PDD:
PDD INCREASES with INCREASING SSD  since it contains an inverse square (IVS) component as well as attenuation. TMR, TAR and BSF measure attenuation only, and are INDEPENDENT of SSD 

BSF: Increases/Decreases as Energy Increases above 1 MV

BSF DECREASES as Energy INCREASES above 1 MV



TAR (definition)

TAR is:
the dose rate at depth / dose rate in air at the same point 


BSF (definition)

TAR @ dmax

At Energies > 1MV:
BSF DECREASES 

PDD vs SSD:
a) Proportional b) Inversely Proportional c) Independent 
PDD and SSD are:
PROPORTIONAL 
PDD vs SSD, example:
PDD INCREASES with INCREASING SSD 

TMR, TAR and BSF measure (?) only

TMR, TAR and BSF measure ATTENUATION Only

TMR, TAR and BSF measure attenuation only, and are INDEPENDENT of SSD


TMR vs SSD
a) Proportional b) Inversely Proportional c) Independent 
TMR is INDEPENDENT of SSD

TMR, TAR and BSF measure attenuation only, and are INDEPENDENT of SSD


TAR vs SSD
a) Proportional b) Inversely Proportional c) Independent 
TAR is INDEPENDENT of SSD

TMR, TAR and BSF measure attenuation only, and are INDEPENDENT of SSD


BSF vs SSD
a) Proportional b) Inversely Proportional c) Independent 
BSF is INDEPENDENT of SSD

TMR, TAR and BSF measure attenuation only, and are INDEPENDENT of SSD


10x10 field, Superficial (2.5mm Al HVL); BSF= (?)
a) 1.0 b) 1.02 c) 1.035 d) 1.15 e) 1.26 
e) Superficial (2.5mm Al HVL); BSF= 1.26

The BSF is a function of:
Beam Quality AND Field Size. BSF can NOT have a value of 1.0 (Because that would imply that there is NO difference between the dose rare in air & that at dmax in tissue). BSF Increases to a value of ~1.5 for a large field @ ~1mm Cu HVL, then falls to a negligable value > 10 MV. 

10x10 field, Co60; BSF= (?)
a) 1.0 b) 1.02 c) 1.035 d) 1.15 e) 1.26 
e) Co60; BSF= 1.035

The BSF is a function of:
Beam Quality AND Field Size. BSF can NOT have a value of 1.0 (Because that would imply that there is NO difference between the dose rare in air & that at dmax in tissue). BSF Increases to a value of ~1.5 for a large field @ ~1mm Cu HVL, then falls to a negligable value > 10 MV. 

10x10 field, 10MV xrays; BSF= (?)
a) 1.0 b) 1.02 c) 1.035 d) 1.15 e) 1.26 
b) 10MV xrays; BSF= 1.02

The BSF is a function of:
Beam Quality AND Field Size. BSF can NOT have a value of 1.0 (Because that would imply that there is NO difference between the dose rare in air & that at dmax in tissue). BSF Increases to a value of ~1.5 for a large field @ ~1mm Cu HVL, then falls to a negligable value > 10 MV. 

The BSF is a function of:
(?) AND (?). 
The BSF is a function of:
Beam Quality AND Field Size. 
The BSF is a function of:
Beam Quality AND Field Size. BSF can NOT have a value of 1.0 (Because that would imply that there is NO difference between the dose rare in air & that at dmax in tissue). BSF Increases to a value of ~1.5 for a large field @ ~1mm Cu HVL, then falls to a negligable value > 10 MV. 

BSF:
Can/Can NOT be=1.00 
BSF can NOT have a value of 1.0 (Because that would imply that there is NO difference between the dose rare in air & that at dmax in tissue).

The BSF is a function of:
Beam Quality AND Field Size. BSF can NOT have a value of 1.0 (Because that would imply that there is NO difference between the dose rare in air & that at dmax in tissue). BSF Increases to a value of ~1.5 for a large field @ ~1mm Cu HVL, then falls to a negligable value > 10 MV. 

BSF Increases to a value of ~ (?) for a large field @ ~1mm Cu HVL

BSF Increases to a value of ~1.5 for a large field @ ~1mm Cu HVL, (then falls to a negligable value > 10 MV)

BSF Increases to a value of ~1.5 for a large field @ ~1mm Cu HVL, then falls to a negligable value > 10 MV


BSF Increases to a value of ~1.5 for a large field @ ~1mm Cu HVL, then falls to a negligable value > (? energy)

(BSF Increases to a value of ~1.5 for a large field @ ~1mm Cu HVL), then falls to a negligable value > 10 MV

BSF Increases to a value of ~1.5 for a large field @ ~1mm Cu HVL, then falls to a negligable value > 10 MV


Which is FALSE about TMR:
a) it is = TAR/BSF b) it is ~ related to the %DD by Inverse Square factor c) it is the ratio of the dose at depth / the dose at dmax, both measured at the isocenter d) it is Dependent on SSD e) it Increases with Increasing Field Size 
d) it is Dependent on SSD  is FALSE.

TMR is INDEPENDENT of SSD (since the dose at depth and the dose at dmax are measured at the same distance from the source)


True/False, TMR is = TAR/BSF

TRUE:
TMR is = TAR/BSF 


True/False, TMR is approximately related to the %DD by Inverse Square factor

TRUE:
TMR is approximately related to the %DD by Inverse Square factor 


True/False, TMR is the ratio of the dose at depth / the dose at dmax, both measured at the isocenter

TRUE:
TMR is the ratio of the dose at depth / the dose at dmax, both measured at the isocenter 


True/False, TMR Increases with Increasing Field Size

TRUE:
TMR Increases with Increasing Field Size 


TMR is: Dependent/Independent of SSD? (BONUS: Why?)

TMR is INDEPENDENT of SSD (since the dose at depth and the dose at dmax are measured at the same distance from the source)

TMR is INDEPENDENT of SSD (since the dose at depth and the dose at dmax are measured at the same distance from the source)


TAR @ dmax can be calculated from the BSF by:
a) multiplying by the SAR b) dividing BSF by the collimator output factor c) applying Inverse Square correction to the BSF d) no need to calculate; they are the SAME @ dmax 
d) no need to calculate; they are the SAME @ dmax



TAR = BSF in what situation?

TAR = BSF @ dmax



For megavoltage photons, TMR has replaced TAR because:
a) TMR is INDEPENDENT for Field Size b) TAR is difficult to measure at high energies c) TMR is preferable to TAR for rotation calculations d) TMR is independent of depth of mazimum dose 
b) TAR is difficult to measure at high energies

As the beam energy ↑, the depth of dmax also ↑. A large size buildup cap will start to act as a "mini" phantom.


As Beam Energy ↑, Depth of dmax:
a) Increases b) Decreases c) Unchanged 
a) As the beam energy ↑, the depth of dmax also ↑.



Given a square & rectangle of the same area, which would have the greater % DD for Co60:
a) square b) rectangle c) they have the SAME depth dose 
a) square

Scatter from the corners of the retangle has FARTHER to travel tha from the periphery of the square & will contribute less to the depth dose.


The TAR for a 10x10cm field @ 100cm SAD for a 4 MB photons is 0.8 at a depth of 7cm. What change would you expect in the TAR by extending the SSD from 93 cm to 193 (200cm from the source), for the same field size @ SAD:
a) 5% Increase in TAR b) 10% Increase in TAR c) 15% Increase in TAR d) NO Change in TAR 
d) NO Change in TAR

TAR is INDEPENDENT of SSD


As Photon Energy ↑, the TMR @ dmax:
a) Increases b) Decreases c) Remains Unchanged 
c) Remains Unchanged

TMR @ dmax is 1.0 by definition for ANY photon energy


As Photon Energy ↑, the % transmission thru a 1cm Lucite blocking tray:
a) Increases b) Decreases c) Remains Unchanged 
a) Increases



Which of the follwing is CORRECT:
a) TAR = TMR x BSF b) TAR = TMR / BSF c) TMR = BSF / TAR d) TMR = TAR x BSF e) BSF = TAR x TMR 
a) TAR = TMR x BSF

TMR
= (dose rate @ depth) / (dose rate @ dmax) = (dose rate @ depth) / (dose rate in air x BSF) = TAR/BSF; therfore TAR = TMR x BSF 

% DD in photon beams:
1. Increases w/Increasing SSD 2. Increases w/Increasing Field Size 3. Increases w/Increasing beam Energy 4. Decreases exponentially (not including inverse square effect & scattering) beyond dmax: a) 1 only b) 1, 2, 3 c) 2, 4 d) 4 only e) All are correct 
e) All are correct

% DD Increases w/Increasing SSD, according to Mayneord's ffactor, because the Inverse Square Factor becomes relatively less important at greater SSD


True/False:
% DD in photon beams Increases w/Increasing SSD 
True:
% DD in photon beams Increases w/Increasing SSD 
% DD Increases w/Increasing SSD, according to Mayneord's ffactor, because the Inverse Square Factor becomes relatively less important at greater SSD


True/False:
% DD in photon beams Increases w/Increasing Field Size 
True:
% DD in photon beams Increases w/Increasing Field Size 
% DD Increases w/Increasing SSD, according to Mayneord's ffactor, because the Inverse Square Factor becomes relatively less important at greater SSD


True/False:
% DD in photon beams Increases w/Increasing beam Energy 
True:
% DD in photon beams Increases w/Increasing beam Energy 
% DD Increases w/Increasing SSD, according to Mayneord's ffactor, because the Inverse Square Factor becomes relatively less important at greater SSD


True/False:
% DD in photon beams Decreases exponentially (not including inverse square effect & scattering) beyond dmax 
True:
% DD in photon beams Decreases exponentially (not including inverse square effect & scattering) beyond dmax: 
% DD Increases w/Increasing SSD, according to Mayneord's ffactor, because the Inverse Square Factor becomes relatively less important at greater SSD


Relative Output Factor of Co60 for a 5x5 Field Size is (?)

Relative Output Factor of Co60 for a 5x5 Field Size is: 0.96

The relative Output Factor for Co60 range from ~ 0.96 (5x5 field) to 1.07 (30x30 field)


Relative Output Factor of Co60 for a 30x30 Field Size is (?)

Relative Output Factor of Co60 for a 30x30 Field Size is: 1.07

The relative Output Factor for Co60 range from ~ 0.96 (5x5 field) to 1.07 (30x30 field)


At 80cm SAD, the dose rate for a 10x10cm field using Co60 is 100cGy/min in air. The dose rate in air for a 30x30cm field would be (cGy/min):
a) 101 b) 103 c) 107 d) 115 e) 125 
c) 107

The relative Output Factor for Co60 range from ~ 0.96 (5x5 field) to 1.07 (30x30 field)


True/False:
The Relative Output Factor range for a Linac is > the relative Output Factor range for Co60 
True:
The Relative Output Factor range for a Linac is > the relative Output Factor range for Co60 
The Relative Output Factor range for a Linac is > the relative Output Factor range for Co60  DUE TO SCATTER INTO THE ION CHAMBER FROM THE COLLIMATORS


A 6MV linac is calibrated @ the iso @ depth dmax (D). To calculate the MUs, MU = (dose@depth)/x, where x = (?)
a) D x BSF x TAR b) D x TAR c) D x TMR d) D x BSF x TMR e) none of the above 
c) D x TMR

The general timeon formula is: time = (dose @depth)/dose rate @ depth).


True/False 
Dose Rate at depth can be found by either using: Dose Rate in Air (SAD x TAR) or Dose Rate in Tissue at SAD (dmax x TMR) 
True.
(NOTE: BSF x TMR = TAR) 
Dose Rate at depth can be found by either using:
Dose Rate in Air (SAD x TAR) or Dose Rate in Tissue at SAD (dmax x TMR) 

BSF x TMR = ?

BSF x TMR = TAR



To calculate Dose Rate at depth, Dose Rate in Air = ? x ?

Dose Rate in Air = SAD x TAR



To calculate Dose Rate at depth,
Dose Rate in Tissue at SAD = ? x ? 
Dose Rate in Tissue at SAD = dmax x TMR



The dose @ dmax, for an SSD calculation, (formula):
D= ? / ? 
The dose @ dmax, for an SSD calculation:
D = Prescribed dose / %DD 


10x10 Field Size @ 80cm SSD. Depth=7cm. %DD=65%. Dose Rate @ dmax=100cgy/min. Presc dose=150cGy@d7cm, dose@dmax= (?)

D = Prescribed dose / %DD
D = 150cGy / 65% D = 150 / 0.65 D = 231cGy 
The dose @ dmax, for an SSD calculation:
D = Prescribed dose / %DD 

A patient was previously tx'd (single AP sclav field, SSD setup). Before treating an adjacent spine field, what data is needed to figure prior cord dose:
1. Given dose to s'clav field 2. Field Size 3. Depth to cord 4. %DD tables 5. Timer error 6. Dose rate in tissue a) 1, 2, 3, 4 b) 1, 2, 3, 4, 5 c) 2, 3, 4 d) 1, 2, 4, 5, 6 e) 3, 4, 6 
a) 1, 2, 3, 4

Exit to cord = given dose to s'clav x %DD. (%DD is a function of field size & cord depth)


True/False:
The Equivalent Square of a rectangular field  Has the Same Area as the Rectangle 
False
(The Eq Sq of a rectangle has a SMALLER area than the rectangle) 
*The Eq Sq of a rectangular field is that square field which has the same scatter contribution on the axis  and therfore the same %DD and TAR. (One sq cm near the axis contributes MORE scatter than the same area at the corner of the field  therfore the Eq Sq of a rectangle has a SMALLER area than the rectangle)


True/False:
The Equivalent Square of a rectangular field  Is approx twice the area divided by the perimeter 
False

An approx rule for the side of the Eq Sq ~ (4xA)/P, where A=Area & P=Perimeter


True/False:
The Equivalent Square of a rectangular field  Has the same %DD on the axis as the Rectangular field 
True



True/False:
The Equivalent Square of a rectangular field  Has the same backscatter factor as the Rectangular field 
True

BSF = TAR @ dmax


Given a circle and a rectangle of the same area, which would have the greater %DD?
a) the circle b) the rectangle c) they have the SAME depth dose 
a) the circle

Scatter from the corners of the rectangle has farther to travel than from the periphery of the circle  and therefore will contribute LESS to the to the depth dose


The % of dose @ dmax will be:
Greater/Less for Smaller fields. Bonus: Why? 
The % of dose @ dmax will be:
GREATER for Smaller fields. (Due to the change of %DD w/Field Size) 


The % of dose @ dmax will be:
Greater/Less for Larger fields. Bonus: Why? 
The % of dose @ dmax will be:
LESS for Larger fields. (Due to the change of %DD w/Field Size) 


Lowest cord dose results from:
Higher/Lower energy AND Smaller/Larger SSD? 
HIGHEST Energy and LARGEST SSD

The lowest dose to points between midplane and the surface results from using the HIGHEST Energy and LARGEST SSD (ex: SSD setup would be larger than Isocentric), to maximize %DD.


The LOWEST dose to points between midplane & the surface results from using the (Highest/Lowest) energy and the (Largest/Smallest) SSD.
Bonus: Why? 
The LOWEST dose to points between midplane & the surface results from using the HIGHEST energy and the LARGEST SSD.
Bonus: To maximize %DD 


Total dose delivered @ d=dmax from a pair of parallel opposed fields, expressed as a % of the total dose at midplane:
a) Decreases as photon energy Increases b) Decreases as Field Size Increases c) Increases as patient thickness increases d) is slightly less for an SSD setup than for an SAD setup e) All of the Above f) None of the above 
e) All of the Above

Any factor that INCREASES %DD will DECREASE the total dose @dmax, compared w/the Total Dose at midplane. Treating at SSD rather than SAD gives slightly higher %DDs.


Any factor that INCREASES %DD will (INCREASE/DECREASE the total dose @dmax, compared w/the Total Dose at midplane.

Any factor that INCREASES %DD will DECREASE the total dose @dmax, compared w/the Total Dose at midplane.



?? In order to keep the total dose @ dmax<110% of the midplane dose (for Co60 unit, parallel opposed fields, 80 SSD), AP sep should not be greater than:
a) 8cm b) 14cm c) 20cm d) 24cm e) 28cm 
c) 20cm

Note: the % at dmax will be GREATER for SMALLER fields, and LESS for LARGER fields  due to the change of %DD with field size


Rule of thumb for Co60 is (?)% extra dose @dmax for (?)cm separation (for SSD setup).

(10%) extra dose @dmax for (20cm) separation (for SSD setup).

Rule of thumb for Co60 is (10%) extra dose @dmax for (20cm) separation (for SSD setup).


The Mayneord
factor is used for, correction of: 
The Mayneord
factor is used for, correction of: PDDs from one SSD to another 
the inverse square law correction component is the main component of
the correction, and is referred to as the Mayneord factor. The second factor, represented by the ratio of TARs or PSFs, is often ignored, because its effect is much smaller than that produced by the Mayneord factor, and the Mayneord factor alone is used for correction of PDDs from one SSD to another 

True/False  Using 2 wedged fields, a uniform dose distribution is usually obtained:
Only when the wedges are used at 90degrees to each other 
FALSE

Positioning is NOT limited to 90 degrees


True/False  Using 2 wedged fields, a uniform dose distribution is usually obtained:
Only when a 3rd open field is added 
FALSE

Uniform dose distributions can be obtained in many cases w/only 2 wedged fields. a 3rd unwedged field is sometimes ued to good effect w/a pair of wedges


True/False  Using 2 wedged fields, a uniform dose distribution is usually obtained:
When the wedge angle is approx 90degrees minus half the hinge angle 
TRUE

This is the ideal relation between Hinge Angle & Wedge Angle


True/False  Using 2 wedged fields, a uniform dose distribution is usually obtained:
When the thick ends of the wedges are adjacent to each other 
TRUE

For most treatments, the "heels" should be together


The angle between the beam axis in a wedged pair is 60degrees. The appropriate wedge angle would be:
a) 15 b) 30 c) 45 d) 60 
d) 60degree wedge

Wedge Angle (WA) = 90degrees  (Hinge angle/2).
90  (60/2) = 90  30 = 60 

Wedge Angle (WA), formula is (?)

Wedge Angle (WA) = 90degrees  (Hinge angle/2).



Wedge Angle (definition)

The angle through which the 50% isodose curve is turned (from its position in the open field)



Given:
Output, WTF (wedge factor), TAR, Dose (per beam)  what's the formula to calc MUs? 
MU=Dose/(output x WTF x TAR)

ex:
Dose per field=60cGy Output in air @ iso=0.90cGy/MU TAR=0.782 WTF=0.58 MU=60/(.9 x .58 x .782) MU=150/0.59 MU=254 

Surface Dose:
(Increases/Decreases) as Photon Energy Increases? 
Surface Dose DECREASES as Photon energy INCREASES

Surface Dose DECREASES as Photon energy INCREASES.
The opposite is true for Electrons. 

Surface Dose:
(Increases/Decreases) with the addition of a blocking tray? 
Surface dose INCREASES with the addition of a blocking tray

Surface dose INCREASES with the addition of a blocking tray


Surface Dose:
(Increases/Decreases) as the SSD Increases for the same field size on the skin? 
Surface Dose DECREASES as the SSD INCREASES for the same field size on the skin

Surface Dose DECREASES as the SSD INCREASES for the same field size on the skin


Surface Dose:
(Depends/does NOT Depend) on the obliquity of the patient's skin surface? 
Surface Dose DEPENDS on the obliquity of the patient's skin surface

Surface Dose DEPENDS on the obliquity of the patient's skin surface


Surface Dose is primarily due to electrons generated in materials between the (?) & (?)

the Source & the Patient

Surface Dose is primarily due to electrons generated in materials between the (SOURCE) & (PATIENT)


For Co60 unit:
The skin dose will (Increase/Decrease) when the SSD is Decreased? 
The skin dose will (INCREASE) when the SSD is Decreased

As SSD Decreases, scatter from the collimators will INCREASE


For Co60 unit:
The skin dose will (Increase/Decrease) when the field size is Decreased? 
The skin dose will (DECREASE) when the field size is Decreased

Similarly, skin dose will INCREASE as the Field Size INCREASES


For Co60 unit:
The skin dose will (Increase/Decrease) when bolus is used? 
The skin dose will (INCREASE) when bolus is used

Bolus generallly used to decrease skin sparing & bring the skin dose up to 100%


For Co60 unit:
The skin dose will (Increase/Decrease) when fields are treated at oblique incidence? 
The skin dose will (INCREASE) when fields are treated at oblique incidence

Oblq incidence causes secondary electrons to travel in a more parallel (rather than perpendicular) direction to the skin. The buildup depth is reduced and the skin dose INCREASES


Skin dose:
The skin dose is (Higher/Lower) for Larger Field Size? 
Skin dose increases w/Larger field size



True/False:
2 AP/PA adjacent photon fields are needed, it's a good idea to have the same collimator settings for both fields because...a larger field size will diverge into a smaller field size & create hot and cold spots 
TRUE:
With 2 adjacent AP/PA fields, a larger field size will diverge into a smaller field size & create hot and cold spots 


The formula used to caluclate the gap on the skin between adjacent fields, matched @ depth, relies on the fact that:
a) the projection of the edge of the light field shows the 50% decrement line of the radiation field b) both beams must be treated w/the same energy xray beam c) the angle of divergence of adjacent beams is the same d) both fields must be treated simultaneously e) the depth at the junction <10cm 
a) the projection of the edge of the light field shows the 50% decrement line of the radiation field

