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Source axis distance is measure from the _____to a _____around which the gantry rotates 360 degrees.
focal spot, point
Name the three modalities that can be used in a fusion study:
MRI, CT, PET
Thinner CT slices (increase/decrease) resolution on DRRs.
The contour of a CT simulator tabletop should be:
TRUE or FALSE?
IMRT is a sophisticated method of radiation delivery to a target area and does not require port films verification.
- Badly worded and confusing!!
- Unlike conventional RT, each IMRT port or gantry stop contains a number of beamlets. In most cases the beamlets are so numerous that filming each one would not be feasible. Instead, QA is chosen to compare output and fluence provided by the treatment planning computer. Usually, orthogonal films("isos") are taken to verify isocenter placement.
A good method for breast immobilization that affords the best reproducibility is:
nothing (let breast find it's natural shape)
When looking up the PDD or TMR for a given field size and depth, ______should be used when there are blocks or MLC.
(what is difference in effective and equivalent square)
List pros and cons of SSD setup:
- 1)more clearance between gantry and patient
- 2)larger field size possible
- 3)Less collimator scatter
- 1)Pt must be moved between fields(less reproducibility)
What invention allowed IMRT to become a reality?
When an extended distance is required for a nonisocentric treatment technique, what changes are needed in the calculation(name 3)?
- 1)Include Mayneord factor in denominator
- 2)Change inverse square to reflect new SSD
- 3)Find new PDD for the field size at the extended distance
Which is not an advantage of using a multifield approach?
(In other words: what is a disadvantage of a multifield approach)
Increases integral dose
Field size determinations should be done(dosimetrically/geometrically).
Dmax is defined as(name 2):
- 1)point of peak dose in an irradiated medium
- 2) Depth of electronic equilibrium
TRUE or FALSE?
Standard wedges can have a beam hardening effect when the radiation is monoenergetic.
- (the key word here is MONOENERGETIC)
- Wedges filter out lower energy photons in a POLYENERGETIC beam in order to harden the beam.
TD 5/5 means:
5% chance of complications in 5 years
In 10-MV photons where used to treat a GTV(prostate) to 100 cGy, then compared to a 4-MV beam treatment plan, the rectum would get a _____dose and the bladder would get ____dose.
- 1)rectum will get higher dose(because it is more posterior,or deeper,the 10 MV beam which has a higher dmax will give more dose than the 4 MV beam)
- 2)bladder will get a lower dose (because the bladder is more anterior, or shallower, the 10MV beam which has a higher dmax will give less dose to it than the 4 MV beam)
Concerning 6x and 18x beams: The depth of maximum dose for ____MV beam is 1.5 cm and 3.5 cm for the ___MV beam. At 10 cm depth, the ____MV beam will have greater %DD.
The depth of maximum dose for 6 MV beam is 1.5 cm and 3.5 cm for the 18 MV beam. At 10 cm depth, the 18 MV beam will have greater %DD.
A pt i delivered a dose of 150 cGy at a depth of 13 cm with 10 MV photons at 100 SSD. The %DD is 60%. Calculate the dose delivered at depth of maximum dose.
- Two ways to solve:
- 1)use a direct proportion (easy if you forget the formula)
- 2)Use the formula:(the way the book does it)
- 150/.60= 250
Electron arc therapy has what effect on dmax position, as compared with a stationary electron field of the same energy?
Moves dmax away from the surface
*electron arc is more skin sparing than stationary arc
prostate seed implant is considered:(interstitial, intraluminal, or intracavitary) CHOOSE ONE
An accelerated partial breast treatment such as Mammosite is considered: (interstitial, intraluminal, or intracavitary) CHOOSE ONE
intraluminal (because the sources are put into the a balloon which is in the tumor cavity)
Au 198 seeds imbedded into the tongue are considered: (interstitial, intraluminal, or intracavitary) CHOOSE ONE
What is the generic formula for calculating an exposure at a specific distance from a particular isotope?
When planning a GYN implant, what point is dose calculated to?
When an element has an excessive number of neutrons, in order to achieve stability, it is likely to experience______decay.
Alpha particles are similar to the ____nucleus. It has a ___charge.
The radioactive decay that results in the ejection of a positive or negative electron is called___decay.
Considering the weight/size and charge of alpha, beta, and gamma particle, what simple device could be used to separate them?
Prostate implants are preplanned on a treatment planning computer using a ____database.
HDR isotopes deliver a dose rate =_____cGy/min.
isotopes deliver a dose rate =20cGy/min
LDR isotopes deliver a dose rate of between ___ and_____cGy/min.
isotopes deliver a dose rate of between 0.5
and 2 cGy/min.
Once it has been discovered that too many fractions have been delivered to the preliminary fields, the therapist should:
Document error and submit to physics for necessary adjustments
Your pt has been hospitalized for blood transfusion and infection and has missed three consecutive weeks of treatments. When pt returns, the therapist should:
Remeasure, relocalize, remark, and ask for BED
A spinal cord compression at the level of T5-6 is being treated emergently. The most likely field arrangement is:
A single posterior low energy photon field
What would likely be the field arrangement be for a primary brain tumor in the right temporal lobe?
A wedged pair consisting of a vertex and right lateral fields
Manual contouring can be achieved by using all the following tools but:
3)plaster of paris
The optimal hinge angle for a 45 degree wedged pair is:
A suitable wedge angle for two fields separated by 90 degrees is:
An entire spine is treated at 100 cm SSD. Filed number 1 measure 8x20, and field 2 measures 8x25. In order to match at a depth of 5 cm, what would the skin gap be?
10(5/100) + 12.5(5/100)= 1.1
1/2 field length1(d/SSD)+ 1/2 field length2(d/SSD)
On the plan data sheet,
X1: +4.2 cm
X2: +5.0 cm
Y1: +3.0 cm
Y2: +4.8 cm
What is the field size?
9.2 X 7.8 cm
(add the x's and add y's)
Assuming the pt is positioned supine with head toward gantry if plan data sheet says:
Isocenter Z -2cm
what is the shift?
The isocenter moves 2 cm posterior (raise table 2 cm)
Negative (PATIENT) shifts=LIU
(Live it Up!
- -x= PATIENT left
- -y= PATIENT in
- -z= PATIENT up
The removable grids used in therapeutic linacs to broadcast crosshairs onto portal images are referred to as all of the following EXCEPT:
For treatments in the chest, Head, and Neck regions, ___straightens the lordotic curvature of the spine, making the pt more comfortable during treatment.
For nonisocentric treatment techniques, _______is the factor of choice to demonstrate central axis dose at a given depth.
What are the advantages of a SAD treatment over a SSD one?
pt is does not need to be moved between angles: this minimizes setup errors
How can the treatment planner see treatment marks when viewing axial images on TPS computer?
What are 2 reasons for using a bolus?
- 1)brings dose closer to surface
- 2)fills in surface irregularities, making dose more homogeneous
The energy loss of megavoltage electron beams in water is aprx _____MeV per cm
2 MeV per cm
- So, when you want to find the range of an electron beam in water, divide the energy by 2
- (i.e. a 12 MeV beam has a range of 6 cm in water)
Which brachy system havs sources of uniform strength spaced 1 cm apart?
Which brachy system have a uniform source distribution, but a nonuniform dose distribution?
Which brachy systems have a nonuniform source distribution with a uniform dose distribution?
Which brachy system is often used for calculating line sources?
The wedge angle is determined by the tilt of the isodose lines at the ___% isodose line and at a depth of ___cm for high energy beams.
The wedge angle is determined by the tilt of the isodose lines at the 50% isodose line and at a depth of 10 cm for high energy beams.