1
Q
1 Gray is equal to how many Sieverts?
A
0.01
B
0.10
C
1
D
10
A
C
1
2
Q
The interaction that occurs when an incoming electron is slowed and changes direction near the nucleus is known as:
A
Bremsstrahlung
B
Compton
C
Pair Production
D
Coherent
A
A
Bremsstrahlung
- Bremsstrahlung interactions = projectile electron completely avoids all orbital electrons. The electron interacts with nuclear field of atom (because of its electric field) and the closer the electron gets = more likely to interact
3
Q
Which of the following is NOT one of the 5 stages of grief defined by Elisabeth Kübler-Ross?
A
Denial
B
Anxiety
C
Bargaining
D
Acceptance
A
B
Anxiety
“DABDA” 5 stages of grief = denial, anger, bargaining, depression, acceptance
4
Q
Which interaction occurs between a photon and atomic nucleus?
A
Photoelectric Effect
B
Compton Scattering
C
Coherent Scattering
D
Pair Production
A
D
Pair Production
- Photon interactions can occur with orbiting shells or the nucleus. Pair production and photodisintegration occur with the atomic nucleus.
5
Q
The star shot test on a linear accelerator checks the rotation of:
A
Collimator
B
Couch
C
Gantry
D
All the above
A
D
All the above
- The “star-shot” pattern is used to check the collimator, couch, and gantry rotation isocenters. It is checked using the EPIDs while rotation collimator, couch or gantry individually.
6
Q
The measurement of ionizations in air is referred to as:
A
Absorbed dose
B
Exposure
C
Quality factor
D
Equivalent dose
A
B
Exposure
- Exposure (Roentgen): measures the total number of ionizations produced by photons and occur in a unit mass of air (C/kg).
7
Q
What is the purpose of klystrons and Magnetrons?
A
Supply power
B
Bend and shape the beam
C
Spread out the beam
D
Provide a source of microwaves
A
D
Provide a source of microwaves
- Klystrons and magnetrons provide a source of microwaves. The klystron amplifies microwaves which are used to accelerate electrons (requires a microwave oscillator). Magnetrons can generate microwaves. Machines have either a klystron or a magnetron, but never both.
8
Q
Prostate cancers are most likely to metastasize to the:
A
Brain
B
Bone
C
Liver
D
Lung
A
B
Bone
- Distant metastasis of the prostate is rare, but if it does occur it includes bones (more specifically the spine, which is the most common location). Other locations include liver and lungs
9
Q
Flattening filters are used to:
A
Increase the beams penetrability
B
Filter out low energy x-rays
C
Spread out the photon beam
D
Decrease beam intensity along the central axis
A
D
Decrease beam intensity along the central axis
10
Q
The intensity of a radiation beam is 150 cGy/min at a distance of 100 cm. What is the intensity of this beam at 105 cm?
A
136 cGy/min
B
143 cGy/min
C
157 cGy/min
D
165 cGy/min
A
A
136 cGy/min
Inverse square law: 150/x= (105/100)^2 x=136 cGy/min
11
Q
The carina is the bifurcation of:
A
Trachea
B
superior vena cava
C
Aorta
D
Circle of Willis
A
A
Trachea
The carina is the division or bifurcation of the primary bronchi and is located at T4-T5.
12
Q
A picket fence test is used to test:
A
Electron gun
B
MLCs
C
Klystron
D
Isocenter
A
B
MLCs
- Picket Fence Test = verifies MLC leaf position and is checked annually.
13
Q
Machine output is most frequently measured by:
A
Pocket dosimeters
B
Thimble Chambers
C
OSLs
D
Ion chambers
A
D
Ion chambers
- Ion chambers monitor beam output, beam symmetry and flatness for each treatment beam/field delivered and for every patient, which makes it the most frequent method of measurement.
14
Q
A ring badge worn by a physicist handling radioactive sources is a type of:
A
TLD
B
OSL
C
Diode
D
Pocket dosimeter
A
A
TLD
- TLD (thermoluminescent dosimeters) give an “in vivo” dose verification for personnel monitoring. Ring badges are specifically used by those who handle radioactive sources.
15
Q
Pancreatic tumors most commonly arise in the:
A
Head
B
Body
C
Tail
D
Fundus
A
A
Head
- The head of the pancreas is the widest portion and sits to the right side of the abdomen within the duodenal loop and this is where most cancers of the pancreas arise.
16
Q
The change in beam’s intensity as the distance changes is a definition of:
A
Half-Value Layer
B
Inverse Square Law
C
Beam Quality
D
Exponential Attenuation
A
B
Inverse Square Law
- Radiation beam intensity will decrease as distance increases due to beam divergence. This is known as the inverse square law. At increased distances, the radiation beam will be spread over a greater area and the intensity will be decreased.
17
Q
What is the maximum dose permitted to the lens of the eye to someone who does NOT work in radiation oncology or radiology?
A
0.15 rem
B
1.5 rem
C
5 rem
D
15 rem
A
B
1.5 rem
- The recommended dose limit for the lens of the eye for the public exposure is <15 mSv or 1.5 rem.
King Henry Died By Drinking Chocolate Milk
18
Q
What is the maximum annual dose permitted to the hands of a physicist who handles radioactive materials?
A
5 mSv
B
50 mSv
C
500 mSv
D
5000 mSv
A
C
500 mSv
- The recommended dose limit for a radiation worker’s skin, hands, and feet is 500 mSv or 50 rem.
19
Q
The proper order of each subdivision of the pharynx from superior to inferior is:
A
Nasopharynx, hypopharynx, laryngopharynx
B
Hypopharynx, Nasopharynx, Oropharynx
C
Oropharynx, Laryngopharynx, Nasopharynx
D
Nasopharynx, Oropharynx, Hypopharynx
A
D
Nasopharynx, Oropharynx, Hypopharynx
- The pharynx consists of (from superior to inferior for anatomical purposes) nasopharynx, oropharynx and laryngopharynx/Hypopharynx.
20
Q
The gantry angle indicator on the linac tolerance is within _____ degrees.
A
1
B
2
C
3
D
5
A
A
1
21
Q
Which of the following is NOT a common site for lung cancer metastasis?
A
Brain
B
Pancreas
C
Adrenal Glands
D
Bone
A
B
Pancreas
- Distant spread of the lungs can occur to the liver, brain, bones, bone marrow, adrenal glands, and/or kidneys.
22
Q
The component of the linear accelerator that is used to create a homogenous spread out beam for electron therapy is?
A
Bending magnet
B
Scattering foil
C
Hooded anode
D
flattening filter
A
B
Scattering foil
- When electrons are used for treatment, the target and flattening filter are moved out of the beam’s path and instead a scattering foil is used to spread out the electron beam.
23
Q
All of the following are located within the oral cavity EXCEPT?
A
Base of tongue
B
Gingiva
C
Alveolar ridge
D
Retromolar trigone
A
A
Base of tongue
- The oral cavity anatomy includes the lips, buccal mucosa, teeth, gums, alveolar ridge, anterior or front 2/3 of the tongue, floor of mouth below the tongue, hard palate, and the retromolar trigone. The base of the tongue is located in the oropharynx
24
Q
Epinephrine is produced by what organ?
A
Brain
B
Kidney
C
Heart
D
Adrenal glands
A
D
Adrenal glands
- The inner part of the adrenal gland is called the medulla creates norepinephrine and epinephrine
25
The ethical principle that follows the principle to do no harm is:
A
Beneficience
B
Autonomy
C
Malpractice
D
Patient's Bill of Rights
A
Beneficience
31. Beneficience: act of charity, good, or kindness. Doing good to others and doing no harm. This is a moral principle of all healthcare workers.
26
The Mayneord's F factor is a correction for which of the following:
A
Depth
B
Field size
C
Beam energy
D
Distance
D
Distance
The Mayneord F Factor makes up for the change in dose at different depths of the central axis due to the inverse square law.
27
The spinal cord ends at the level of:
A
T12
B
L2
C
L5
D
S1
B
L2
28
The point which the gantry, collimator, and couch rotate around is called:
A
Midplane
B
Central Axis
C
Isocenter
D
ITV
C
Isocenter
34. The isocenter is the calibration point of the gantry, collimator, and couch.
29
The most common location for distant metastasis of sarcomas is to:
A
Lung
B
Bone
C
Liver
D
Brain
A
Lung
35. The lungs are the most common site of distant metastasis of sarcomas, followed by the bone, lymph nodes, liver, brain, and subcutaneous tissue.
30
The most aggressive of these skin cancers is:
A
Kaposi sarcoma
B
Melanoma
C
Basal Cell
D
Squamous Cell
B
Melanoma
36. Melanoma is often called the most serious skin cancer because it has a high chance of spreading.
31
To find the therapeutic range of electrons, divide the energy by:
A
2.0
B
3.0
C
4.0
D
5.0
C
4.0
37. The therapeutic range of electrons is the 90% isodose line. A common formula used is E/4 to find the range.
32
PDD has a direct relationship with:
1. Energy
2. Depth
3. Field Size
4. SSD
A
1 & 2
B
1, 2 & 4
C
1, 3 & 4
D
1, 2, 3, & 4
C
1, 3 & 4
38. PDD has a direct relationship with energy, SSD, and field size. PDD has an indirect relationship with depth.
33
What is the therapeutic ratio if the lethal tumor dose is 5500cGy and the normal tissue tolerance is 6500 cGy?
A
0.72
B
0.85
C
1.18
D
1.40
C
1.18
39. Therapeutic ratio = normal tissue tolerance/lethal tumor dose = 6500/5500 = 1.18
34
Pancoast tumors are typically found in the:
A
Lining of the lung
B
Apex of the lung
C
Brain
D
CSF
B
Apex of the lung
35
The most radioresistant cell cycle is the _____ phase
A
G1
B
G2
C
M
D
S
D
S
41. The radioresistant cell cycle is the S phase.
S phase is chemosensetive
36
When treating a chest wall with a supraclavicular field, which of the following techniques would be best to avoid beam overlap?
1. Half Beam Block
2. Cast Block
3. Couch angles
4. Electron cone
A
1 & 2
B
1 & 3
C
1, 2, & 3
D
1, 3, & 4
B
1 & 3
42. For 3 or 4 field breast treatments (tangents with supraclavicular nodes), in order to avoid beam overlap the patient must be treated with a half-beam block and monoisocentric technique OR dual isocenters and couch rotations.
37
What is the tolerance dose (TD 5/5) for the whole brain defined by Emami et. al.
A
1750 cGy
B
2300 cGy
C
4500 cGy
D
5500 cGy
C
4500 cGy
38
The largest gland in the human body is the:
A
Pancreas
B
Liver
C
Spleen
D
Adrenals
B
Liver
39
The most common pathology for bladder tumors would be:
A
Transitional
B
Squamous
C
Adenocarcinoma
D
Sarcoma
A
Transitional
40
In relation to the glottis, the false vocal cords are located:
A
Anterior
B
Posterior
C
Superior
D
Inferior
C
Superior
46. False vocal folds are a pair of thick folds of mucous membrane that are located in the supra-glottal space in the larynx, which is superior to the glottis.
41
The depth of dose equilibrium is most dependent on:
A
Field Size
B
Beam Energy
C
SSD
D
Patient separation
B
Beam Energy
47. Dose equilibrium = dmax. Dmax changes depending on beam energy.
42
We will be treating an AP/PA spine at midplane. A patient has a separation of 32 cm. What is the field size on the skin surface if the field size measures 6x10cm at 100 SAD?
A
2.7 x 6.8 cm
B
5.0 x 8.4 cm
C
4.7 x 11.9 cm
D
5.9 x 14.7 cm
B
5.0 x 8.4 cm
Direct proportion. First find depth 32/2 = 16. 100 – 16 = 84 SSD. 6/100= x/84 and 10/100= x/84 = 5 x 8.4cm
43
Which type of photon interaction is most likely to occur during kV imaging?
A
Coherent scattering
B
Photoelectric effect
C
Compton Scattering
D
Pair Production
B
Photoelectric effect
49. Photoelectric is more predominant in diagnostic ranges (KV ranges).
44
When the radiation hits DNA in the cell, this is said to be a(n):
A
Direct effect
B
Indirect effect
C
Bremmstrahlung
D
Characteristic
50. A direct effect is when radiation interacts with DNA first.
45
As field sizes ______, scatter will ______.
A
Increase, Decrease
B
Increase, Increase
C
Decrease, Increase
D
Decrease, Decrease
E
Both A & C
F
Both B & D
F
Both B & D
51. As field size increases, scatter increases. As field size decreases, scatter decreases. As field size increases, there is more surface area for the beam to interact with causing more scatter. This will affect MU.
46
Where are the adenoids located?
A
On top of each kidney
B
In the oral cavity
C
In the oropharynx
D
In the nasopharynx
D
In the nasopharynx
52. The adenoids are located within the nasopharynx.
47
A patient was accidentally treated at 90 cm SSD instead of 100 cm. The prescribed dose was 2.5 Gy. What did the patient actually receive?
A
2.03 Gy
B
2.77 Gy
C
3.09 Gy
D
3.76
C
3.09 Gy
Inverse square law: x/2.5= (100/90)^2 x=3.09 cGy
48
Which type of lung CAlarcinoma is connected to asbestos exposure?
A
Non-small cell
B
Small Cell
C
Mesothelioma
D
Adenocarcinoma
C
Mesothelioma
54. Mesothelioma is a lung cancer associated with asbestos exposure.
49
A treatment of 152 monitor units requires that a blocking tray factor of 0.942 be included in the calculation. What should the monitor units be if the tray is added to the treatment?
A
143 MU
B
152 MU
C
161 MU
D
171 MU
C
161 MU
55. 152/0.942 = 161 MU
50
The largest salivary gland is called:
A
Submental
B
Submandibular
C
Pretracheal
D
Parotid
D
Parotid
51
Which side effect is MOST likely to occur after partial brain treatments of 6000 cGy?
A
Cystitis
B
Laryngitis
C
Epilation
D
Pruritus
C
Epilation
58. Radiation side effects are local to treatment areas. When treating the brain, cystitis 3000-4000 cGy, laryngitis 4000 cGy and pruritus is not likely. Epilation (hair loss) occurs at doses as low as 2000 cGy and is the best possible answer.
52
To reduce the size of the PTV for bladder cancer treatments, the bladder should be ______ for treatments.
A
Empty
B
Partially full
C
Filled with 8 oz of water
D
Filled with contrast media
A
Empty
53
The tonsillar lymph nodes that surround the nasopharynx & oropharynx are known as:
A
Waldeyer's ring
B
Peyer's patches
C
Circle of Willis
D
Obturator
A
Waldeyer's ring
61. Waldeyer’s ring is a ring of lymphoid tissue found in the throat and surrounds the nasopharynx and orpharynx. The Waldeyer's ring is made up of the tonsils, adenoids, and other lymphoid tissue.
54
Which of the following structures is MOST radioresistant when irradiating the entire organ?
A
Lens of the eye
B
Lung
C
Kidney
D
Small Intestine
D
Small Intestine
According to the TD 5/5 chart (by Emami et. Al.) the most radioresistant organ listed is the small intestine. The lung tolerance dose (3/3 organ) is 1750 cGy. The lens of the eye tolerance dose (3/3 organ) is 1000 cGy. The small intenstine tolerance dose (3/3 organ) is 4000 cGy. The kidney tolerance dose (3/3 organ) is 2300 cGy
55
What is the tolerance dose when irradiating 3/3 of the kidney?
A
2300 cGy
B
3000 cGy
C
4200 cGy
D
5000 cGy
A
2300 cGy
56
What is the equivalent square of a 6x15cm field size?
A
6 x 15 cm
B
7.2 x 7.2 cm
C
8.6 x 8.6 cm
D
10.5 x 10.5 cm
C
8.6 x 8.6 cm
Equivalent Square can be found by the equation 2ab/(a+b)= 2x6x15/(6+15) = 8.6 x 8.6 cm
57
Which of the following lung cancer pathologies has a higher incidence of metastatic spread?
A
Small cell
B
Large cell
C
Mesothelioma
D
Adenocarcinoma
A
Small cell
58
After what dose to the head and neck should the treatment plan be altered to go "off cord"?
A
3000 cGy
B
4500cGy
C
5500 cGy
D
6000 cGy
B
4500cGy
66. Off cord adjustments are new beam arrangements to avoid the spinal cord. The spinal cord has a tolerance of 4500-4700 cGy. After a dose of 4500 cGy, a cone down/second phase should be planned to avoid the spinal cord (if not using IMRT).
59
What is the material that is used for OSLs?
A
Film
B
Lithium fluoride
C
Aluminum oxide
D
Tungsten
C
Aluminum oxide
OSL (optically stimulated lumi nescent dosimeters)
TLDs are made of Lithium fluoride (LiF) because this material has an atomic number that is very similar to human tissue
60
What is the most potent radiosensitizer for x-rays?
A
Oxygen
B
Adriamycin
C
Bleomycin
D
Carboplatin
A
Oxygen
Oxygen is the potent radiosensitizer.
61
Which type of radiation travels the furthers through matter?
A
Alpha particles
B
Beta particles
C
X-Rays
C
X-Rays
X-rays travel further through matter than alpha particles and beta particles.
62
The treatment volume that encompasses the tumor and microscopic disease is:
A
GTV
B
CTV
C
PTV
D
ITV
B
CTV
70. CTV (clinical target volume) = GTV + margin for microscopic disease
63
A craniospinal irradiation treatment has two posterior spine fields. One is 8x20cm and the other is 8x15cm. Both are treated to 100cm SSD. What is the gap needed to match the fields at an 10cm depth?
A
0.61
B
1.23
C
1.75
D
2.4
C
1.75
Gap calculations: Gap= d/2( L1/SSD1 + L2/SSD2))
64
Imaging on the linear accelerator that shows anatomy in three planes is known as:
A
Portal Imaging
B
IMRT
C
KV-KV
D
CBCT
D
CBCT
CBCTs are volumetric imaging that can show the images in axial, sagittal, and coronal views. Portal imaging is one plane. KVKV imaging can show two planes.
65
Which isodose curve is used to define the physical radiation field for a 15 MV beam?
A
25%
B
50%
C
80%
D
90%
B
50%
The physical radiation field is defined by the 50% isodose line regardless of beam energy.
66
The person a patient chose to make decisions on the patient's healthcare plan is called:
A
Power of Attorney
B
DNR
C
Bill of Rights
D
HIPAA
A
Power of Attorney
The power of attorney is the person chosen by the patient to make decisions when the patient I no longer able to do so.
67
Another term for a slow heart beat would be:
A
Tachycardia
B
Bradycardia
C
Anaphylaxis
D
Leukoplakia
B
Bradycardia
Bradycardia = slow heart rate. Tachycardia = high heart rate.
68
A patient is to be treated isocentrically to his midline on the 6 MV linear accelerator at 100 cm SAD. Calipers were used to measure the patient thickness of 21 cm. No immobilization was used. What SSD is required for isocentric treatment to the patient's midline?
A
79 cm
B
89.5 cm
C
100 cm
D
110.5 cm
B
89.5 cm
Using the thickness of the patient (aka patient separation), we can then determine the depth at midline (middle of separation). 21/2 = 10.5 cm. Next, we subtract the depth from 100: 100-10.5 = 89.5
69
The x-ray interaction in which the photon's energy is completely absorbed is:
A
Coherent
B
Photoelectric
C
Compton
D
Differential
B
Photoelectric
X-rays or photons can be completely absorbed, transmitted, or scattered when interacting with matter
70
Calculate the monitor units to deliver 200 cGy to the 90% isodose line using 12 MeV electrons at 100 SSD & the cutout factor is 0.787
A
255 MU
B
229 MU
C
282 MU
D
301 MU
C
282 MU
MU calculation: 200/(0.9 x 0.787) = 282 MU
71
Which of the following are possible x-ray interactions with tissue
A
Absorption
B
Transmission
C
Scattering
D
All of the above
D
All of the above
X-rays or photons can be completely absorbed, transmitted, or scattered when interacting with matter.
72
Frequency is measured in:
A
Hertz
B
Ohms
C
Curie
D
mR/min
A
Hertz
Ohms?
73
The predominant photon interaction during portal imaging would be:
A
Coherent scattering
B
Photoelectric effect
C
Compton scattering
D
Pair production
C
Compton scattering
Portal imaging occurs from the MV source, which has more Compton scattering
74
The physician's objective finding of the patient is a(an):
A
Sign
B
Symptom (Subjective)
C
Etiology
D
Epidemiology
A
Sign
84. A sign is an indication of disease observed by someone who is examining the patient (objective)
75
To preserve the skin sparing properties of the MV photon beams, the compensator must be placed at least ____ from the skin.
A
1-5 cm
B
5-10 cm
C
10-15 cm
D
15-20 cm
D
15-20 cm
85. During photon therapy, beam modifiers such as compensators, should be placed at least 15-20 cm from the patient’s skin. Otherwise, scatter would contribute to patient skin dose
76
A 10 MV beam is calibrated to 100 cm SSD. The location of the maximum dose is at a depth of?
A
0.25 cm
B
0.5 cm
C
1.5 cm
D
2.5 cm
D
2.5 cm
4 MV = 1cm
6 MV = 1.5cm
15 MV = 3cm
18 MV = 3.2cm
20 MV = 3.5
25 MV = 5cm
6 MEV = 15cm
9 MEV = 2.2cm
12 MEV = 2.8cm
77
Which of the following are TRUE about lead & cerrobend?
1. Lead has a lower melting point.
2. Cerrobend has a lower melting point.
3. Lead blocks are thicker.
4. Cerrobend blocks are thicker.
5. Allowable transmission is <0.5%
6. Allowable Transmission is <5%
A
1, 3, 5
B
1, 3, 6
C
2, 4, 5
D
2, 4, 6
D
2, 4, 6
Cerrobend has a lower melting point than lead. Cerrobend blocks need to be thicker than lead alone for the same allowed transmission of 5%.
78
Which type of test is a PSA?
A
Incisional biopsy
B
Excisional biopsy
C
Fecal test
D
Blood test
D
Blood test
Prostate-specific antigen (PSA) test: a blood test that measures amount of PSA in blood.
79
The patient is positioned supine, head first. The AP SSD is 88cm. Calculate the new SSD after performing a 2 cm posterior iso shift.
A
86 cm
B
88 cm
C
90 cm
D
Unable to determine
A
86 cm
80
A procedure that removes skin cancers one layer at a time is called:
A
Curettage
B
Cryosurgery
C
Moh's surgery
D
Dermabrasion
C
Moh's surgery
81
A patient is treated on the 6 MV linear accelerator. The patient is setup to 94 cm SSD. The TAR at 6 cm depth is 0.87 and the output is 1.02 cGy/MU for the required field size. How many monitor units will it take to deliver 100 cGy to a depth of 6 cm?
A
88 MU
B
102 MU
C
113 MU
D
116 MU
C
113 MU
MU calculation: 100/(0.87 x 1.02) = 112.68 = 113 MU
82
The deficiency in the number of circulating white blood cells is called:
A
Anemia
B
Leukopenia
C
Polycythemia
D
Thrombocytopenia
B
Leukopenia
93. Leukopenia is a deficiency of circulating white blood cells, especially the granulocytes. AKA: neutropenia.
83
A patient receiving chemotherapy treatments becomes immunosuppressed. The best isolation technique for this patient would be:
A
Airborne
B
Droplet
C
Contact
D
Reverse
D
Reverse
94. Reverse isolation is used for immunosuppressed/neutropenic patients. Neutropenia can occur from chemotherapy, radiation therapy and other medications
84
Which number represents the angle of the wedge?
There are a variety of definitions of where the wedge angle is found: At the 50 percent isodose curve (for low energy beams). At the 80 percent isodose curve. At a depth of 10 cm (for high energy beams). Regardless of depth or isodose line, to find the angle in tis figure, it is at a line drawn perpendicularly to the central axis at one of these depths (#4).
85
Backscatter has a direct relationship with:
A
Distance
B
Beam quantity
C
Field size
D
Depth
C
Field size
Backscatter factor (BSF) is used for low energy beams. BSF is independent of SSD and depends only on beam quality (energy) and field size.
86
Which is the correct definition of an excisional biopsy?
A
Removal of a portion of the tumor
B
Removal of the entire tumor
C
Collects a sample of tumor
D
Place clips or markers inside tumor
B
Removal of the entire tumor
87
Which of the following is least likely to affect isodose curve distributions?
A
SSD
B
Geometric field size
C
Beam energy
D
Barometric pressure
D
Barometric pressure
Isodose lines can be affected by beam energy, beam type, source to surface distance, field weighting, beam modifiers, and field size.
88
he ratio of a dose at a given point within a phantom compared to the dose at the same point in free space is called:
A
Tissue-air ratio
B
Tissue maximum ratio
C
Dmax
D
Scatter air ratio
A
Tissue-air ratio
99. Tissue-Air ratio (TAR) is the ratio of an absorbed dose at a depth within the phantom at a given distance compared to the absorbed dose in free space at the same distance.
89
If a partial arc is utilized for a treatment & the tumor is located 8 cm below the skin surface, where should the beam be aimed?
A
Distal to the tumor
B
At the tumor
C
Closer to the skin surface
D
At the skin surface
100. Partial arcs require the use of past-pointing techniques. For partial arcs, meaning the gantry moves less than 360 degrees, dmax gets displaced. It winds up somewhere in the middle of the irradiated area. Past pointing is a technique that corrects this displacement. The treatment is planned to treat past the tumor depth so that dmax actually lands on the tumor/desired depth.
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