Treatment Planning

The maximum acceptable amount of dose transmitted throught the MLCs is:

5%

Partial breast irradiation may involve treatment techniques that employ all of the following EXCEPT: - 5-field breast technique - brachytherapy - 3-D conformal IMRT - intraoperative XRT

5-field breast (partial breast irradiation)

The field size of an xray or gamma ray beam is defined as the area enclosed within the boundary of the _______% depth dose line.

50%

The most likely photon beam energy used to treat areas in the head and neck would be:

6 MV

Brain tissue tolerance

60 Gy

The skin dose, in the case of electron beams, is:

80-90%

The expected total dose to point A for treatment of the cervix from both external beam radiation and brachytherapy is approximately:

90 Gy

Bone metastasis to the thoracic spine is often managed using ________ treatment field(s)

A single posterior

Positron Emission Tomography (PET) is based on imaging with photons produced in: - pair production - annihilation of positrons by electrons - fluorescence caused by positrons in certain screens - Compton scattering of photons

Annihilation of positrons by electrons

Wedge angle refers to: A. the angle of the actual wedge filter B. the angle at which an isodose curve at a specific depth is tilted as a result of the wedge being inserted in the beam C. the angle at which the isodose curve at a specific depth is tilted with respect to the central axis of the beam

B. the angle at which as isodose curve at a specfic depth is tilted as a result of wedge being inserted in the beam

Overall, most intracranial malignancies are: A. Glioblastoma multiforme B. Astrocytoma C. Metastatic D. Pituitary adenoma

C. Metastatic

A volume that consists of the demonstrated tumor and any other tissue presumed to contain tumor is called the: A. integral volume B. treatment volume C. target volume D. irradiated volume

C. target volume

In the maintenance phase of managing ALL, whole brain radiation may be given with the inferior border of the treatment field at:

C2

When preparing to assist with the administration of iodine based contrast the therapist should inspect the contrast container and use only when the content is:

CLEAR not discolored or cloudy, and has current date

DRRs can be generated from:

CT images

The best head/chin position for treating the vertex field is:

Chin flexed (this position makes the field easy to image)

A good surface landmark to approximate the apex of the lung is the:

Clavicle (apex is 3 cm superior to the clavicle)

Which radioisotope is commonly used for permanent, interstitial implants of the prostate gland?

Gold-198

Electron beams are useful in radiation therapy because they: - have a greater biological effect than x-rays - provide more skin sparing than gamma rays - have a definite range in tissue - have maximum LET at electronic equilibrium

Have a definite range in tissue

When treating the maxillary antrum, the organ at the greatest risk for damage is the: - pituitary - brain - lens - sphenoid

Lens the floor of the orbit is the superior edge of the maxillary sinus.

In order to reduce the potential for electron contamination, the preferred material for custom block and compensator holders is:

Lucite

What type of image would yield the poorest contrast quality when visualizing soft tissue? - CT image - MRI image - mega-voltage portal image - diagnostic x-ray image

MV portal image (too penetrating)

The therapeutic ratio is:

Normal tissue tolerance / tumor lethal dose

For patients with bladder cancer, the preoperative radiation treatment fields should be large enough to include the bladder and regional nodes such as:

Obturator External iliac & Internal iliac (EIO)

The ratio of dose at depth in tissue to dose at electronic equilibrium on the beam axis is known as:

PDD

When treating adjacent multiple fields on a patient:

Patient position should remain the same for all fields

magnification = ________/_________

SFD/ SOD

The width of penumbra increases with increasing

SSD

Posterior cervical nodes need to be treated and the patient's shoulder will only allow a treatment distance of 115 cm SSD on the 100 cm SAD linac. The inverse square correction factor needed in the MU calculation would be:

(100/115)^2 (SAD/SSD + Dmax)^2 gives the inverse square factor for extended distance tx

Which of the following is not a neccesary step in tumor volume definition? - contour of the tumor highlighted throughout the patient volume - measurements of anatomical separation - staging of the disease - identification of adjacent normal tissue

- staging of the disease

Anatomical data for CT imaging and reconstruction is acquired through the _______ plane.

Transverse

T/F: Increasing FS increases backscatter

True

CT number of water (HU)

0

The normal range for LDR brachytherapy is ____ to ____ Gy/minute.

0.5 - 2.0 Gy/min

A 6 MV photon beam on the linac has an output at isocenter of 1.2 cGy/MU. What would be the inverse square factor used in the MU calc for an extended distance treatment at 120 cm SSD?

0.677

A tumor lethal dose is 5000 cGy. The spinal cord is adjacent to the tumor. The approximate therapeutic ratio is:

0.9

The shape of the isodose curves depends largely on: 1. field size 2. depth dose 3. flattening filters 4. SSD

1 & 3 only FS & filters (and accessories/cones)

In order to make custom Cerrobend blocks, the following information is needed: 1. Target to film distance 2. Beam energy 3. Patient thickness

1, 2

The factors that determine the number of treatment fields to be used includes: 1. beam quality 2. adjacent normal tissue 3. tumor depth 4. tumor shape

1, 2, 3, 4

Tissue inhomogeneities that may alter dose distribution would include: 1. air cavities 2. lung 3. fat 4. bone

1, 2, 3, and 4

The use of a wedgde filter helps to: 1. achieve more homogenous dose distribution 2. compensate for the presence or absence of tissue 3. avoid hot spots

1, 2, 3.

RT to treat medullary thyroid cancer requires large treatment portals that include: 1. the lesion 2. bilateral supraclavicular nodes 3. superior mediastinum

1, 2, and 3

PDD varies with which of the following: 1. depth 2. fractionation 3. field size 4. radiation quality

1, 3, 4.

When comparing an isodose profile from a linear accelerator with one from an orthovoltage machine, the linear accelerator isodose will have the following characteristics: 1. greater penetration 2. greater side scatter 3. higher %DD at depth 4. flatter isodose lines

1, 3, 4.

The backscatter factor depends on these two things:

1. Field size & 2. Energy of the beam

Dmax of a 4 MV photon beam

1.0 cm

A midline brain tumor will be treated to 4500 cGy, through right and left lateral ports. Of concern is the normal brain tissue. The therapeutic ratio is approximately:

1.33 (60/45)

Dmax for 6 MV photon beam

1.5 cm

Which of the following therapeutic ratios would be expected to provide the highest probability of cure? a. 0.85 b. 1.0 c. 1.45 d. 1.75

1.75 The highest probability of cure is expected with the highest therapeutic ratio

depth of the 80% isodose line for electron beams is given by:

1/3 the energy

A wedge transmission factor of 0.895 indicates a wedge attenuation of the beam by:

10.5%

Standard wedges are designed for use in high voltage beams and vary in angle from _____ to ______ degrees.

15 to 60 degrees

The attenuation of Cerrobend is less dense than lead by about:

15%

The energy loss of Megavoltage (MeV) electron beams in water is approximately ____ MeV/cm.

2

Depth of inguinal nodes can range from __ to __ cm depending on _______________.

2 - 18 cm. depending on patient size

for breast irradiation, IM nodes would be best treated using: -an AP 10 MV photon field - widened tangents - an AP electron field - a PA electron field

an anterior electron field

External beam radiation for cancers of the mid-esophagus is best delivered using:

anterior and two posterior obliques

When a missing tissue compensator is used, it should be placed:

at some distance from the skin surface

During CT simulation, laser alignment marks should be placed:

at the level of anticipated isocenter

All thermoplastics need some kind of base plate on the couch top. The preferable plate material is:

carbon fiber material

when treating the whole brain with opposing laterals, one way to minimize beam divergence into the eye opposite the entrance port would be to:

center the axis near the lateral canthus (since no divergence along cax, plus beam shaping)

When using lateral and anterior supraclavicular fields to treat a tumor in the oropharynx, the field junction should be placed:

cephalad of the thyroid notch

Custom tissue compensators are used to:

compensate for surface irregularity

Which of the following radioisotopes is sometimes administered into the *peritoneal cavity* in the treatment of gynecological malignancies? a. cesium-137 b. iridium-192 c. iodine-131 d. phosphorus-32

d. Phosphorus-32 can be suspended in liquid and administered intracavitarily for management of GYN cancers *that have spread to the abdominal cavity*

In radiation therapy planning, the x, y, z coordinate system is used to:

describe a point in space relative to isocenter

When an immobilization device is needed, the therapist should:

determine beam orientation, then make the device

The posterior surface of the patient should be flat when treating the entire spine so that:

dose is more uniform

A representation of the dose in an irradiated volume, as a function of spatial position along a single line is known as:

dose profile

The equivalent square field size must be determined in order to calculate the:

dose to be delivered to the central axis of an irregular field

The term used to define the area on the surface of the patient on which radiation is incident is the:

entrance point

The hypogastric lymph nodes are part of the ______________ chain of nodes.

external iliac

Because electrons scatter so readily in air, they are:

focused by cones extending close to isocenter

CTV includes:

gross target and subclinical disease

Increasing the field size from 5 x 5 to 20 x 20, with all other factors remaining the same, the PDD will:

increase

With all other factors remaining the same, increasing the field size from 6 x 6 to 10 x 10, backscatter would:

increase

As SSD increases, depth dose:

increases

The volume larger than the treatment volume receiving some significant dose is the:

irradiated volume

For patients with pancreatic cancer, extra care is taken to limit dose to the radiosensitive:

liver, kidney & spinal cord

What type of tissue will appear darkest on a CT image?

lung/ air

Surface mold brachytherapy is appropriate for ____________ tumors located in the ____________, _____________, or ______.

mold therapy is for superficial tumors in the: oral cavity skin or eye

The volume of lung within an anterior supraclav field can be reduced when treating breast carcinoma by: - elevating the arm - treating the scv field every other day - placing an angl board under the chest - moving the breast down on the chest wall and making the match line as superior as possible

moving the breast down on the chest wall and *making the match line as superior as possible*

Indian club needles have: - gold seed - one hot end - two hot ends - even activity

one hot end

If a patient has a large pelvic tumor involving the bladder and prostate, and there is a presacral mass, the best arrangement would be: -opposed anterior and posterior fields - opposed lateral fields - 4-field box - 90 degree wedged pair

opposed AP/PA fields due to the extent of the disease, AP/PA ports would be used (at least at first) to ensure dose to the entire area while sparing pelvic bones.

Depth of electronic equilibrium for a 10 MV beam (Dmax)

2.0 cm

When treating an extremity, the limb should be positioned:

parallel to the horizontal axis of the beam

One disadvantage of using a vertex field to treat primary brain malignancies is that the field exits through:

pharynx & spinal cord

An advantage of using custom compensators for missing tissue over bolus in MV therapy is:

preservation of skin sparing

Shoulder retractors are important for:

pulling the shoulders out of the treatment field.

A tumor that can be completely eradicated by radiation is known to be:

radiocurable

An advantage of using the wedged pair technique is that beyond the point of beam intersection, there is:

rapid dose falloff

If the pituitary gland is treated using a three-field technique including laterals and vertex fields, wedges will be used in:

the lateral fields

Perforated thermoplastics are better than nonperforated thermoplastics because:

they reduce the average skin dose

when using rotational arc therapy, MUs or treatment time should be calculated using which of the following methods? - Mayneord's factor - Paterson-Parker - tissue air ratio - Clarkson's

tissue air ratio TAR method for arc-therapy

When treating lateral brain fields in the tx of craniospinal axis, to avoid having the caudal margin of the lateral fields diverge into the posterior spine field, the couch should be rotated:

toward the collimator

During verification placement imaging for radioactive needles the image receptor is located 120 cm from the source. The 3 cm needles measure 4 cm on the film. How far away were the needles from the image receptor?

30 cm 4/3 = 120/SAD SAD=90 120-90 = 30 cm from needles to receptor

A dose of 3000 cGy is to be delivered at a depth of 5 cm with a PDD of 85%. What is the applied dose?

3529 cGy

An 8 MeV electron beam is used to deliver 300 cGy to the 90% isodose line. The cone size is 15 x 15 and the SSD is 100 cm. The cone factor is 0.872, and the reference dose rate is 1.0 cGy/MU. What MU setting should be used to deliver this treatment?

382 MU SSD treatment: MU = dose/ cone factor x dose rate x *PDD*

Total dose to the lumpectomy site following accelerated partial breast irradiation utilizing high dose rate brachytherapy will be approximately:

45 Gy

The average life of a radioactive source with a half-life of 32 minutes is:

46 minutes Avg life = 1.44 x T1/2

The 50% isodose line for a 12 MeV electron beam would be at an *approximate* depth of:

5 cm Energy/ 2.5 = 50% isodose depth (cm)