Dosimetry Test 2
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What is the equation used when there is a change in PDD?
- Maynoerd's F Factor:
The attenuation of Cerrobend is about _______ less than lead.
What is make-up of Cerrobend?
(percentage of each material)
- BLT with Cheese
- Bismuth: 50%
- Lead: 26.7%
- Tin: 13.3%
- Cadmium: 10%
The field size when using an SSD technique & a photon beam is usually defined at the ____________ of the machine
The goal of _________ procedures is to identify the precise position of relevant internal structures with respect to external landmarks
How are MLC's different from custom-shaped blocks?
- 1. Steplike field edges
- 2. Leakage between the leaves
- 3. Limited field sizes
How are electron blocks different from blocks for photon beams?
- 1. No focused edges
- 2. Much thinner
- 3. The size of the opening is approx. the same as the field size on the skin
Secondary scatter in the metal-tissue interface can cause high dose in the adjacent tissues but can be reduced by placing ___________ over the teeth.
2 to 4 mm of tissue-equivalent material
When a lip lesion is treated, it is possible to reduce the mucosal reaction by placing an internal shield _______ to the tumor and covering the shield with ________.
DISTAL to the tumor
The most practical materials to use when making a compensator for photon beams are:
________ material is used to reduce the depth of the maximum dose when photon beams are used.
Weekly chart rounds check for:
- 1. Diagnosis, histology & stage
- 2. Consent for treatment
- 3. Pathology report
- 4. Prescription (dated & signed)
- 5. Weekly port films of each field (approved, signed & dated by the RadOnc)
The frequency of port films varies, but they should always be taken on the _______ day of treatment.
If a 30° wedge is left out of the treatment during two of five treatments, the central axis dose is ________ (increased/decreased) and the isodose distribution ______ (is/is not) affected.
- central axis does is INCREASED
- isodose distribution IS affected
Treatment fields should be labeled in the chart with reference to:
- 1. Anatomic description
- 2. Unique number assigned to each field
The term "oblique" in a dose calculation word problem indicates there will be ________ fields.
The most commonly used beam energy to treat head & neck cancer is:
- Cobalt 60
- 4 MV photons
- 6 MV photons
What are two techniques used to deliver a boost dose in base of the tongue cancer?
- External beam (small fields)
- Interstitial Implant
The majority of cancer in the head & neck region is:
Squamous cell carcinoma
Xerostomia is caused by irradiation of the
In the treatment of head & neck cancer, immobilization is particularly important because of:
- 1. proximity of several radiosensitive organs
- 2. small tumor margins
When treating carcinoma of the oropharynx, the field junction between opposed lateral and an inferior field should be set _________ of the thyroid notch.
CEPHALAD of the thyroid notch
When a patient is treated for Graves' ophthalmopathy, half-beam blocked opposed lateral fields centered on the lateral canthus are generally used. Both lenses of the eyes are excluded from the beam by rotating the gantry to an angle when:
BOTH lead markers on the eyelids are superimposed
(pt's eyes closed)
To avoid overlap between the opposed lateral and anterior fields used in treatment of head & neck cancer, a ____________ can be used over the spinal cord in the anterior field.
Full-length midline block
The junction between the lateral and anterior fields is chosen so that, when a full-length spinal cord block is used, the larynx is also blocked in an effort to avoid __________.
When the final boost is given and the central axis is moved, the dose in the midplane on the central axis of the boost field is added to the dose received at ____________ from the previous fields.
the dose in the midplane on the central axis of the boost field is added to the dose received at the SAME POINT from the previous fields.
When ___________ are treated, wedges are never needed because a higher dose posteriorly is an advantage.
True Vocal Cord Tumors
Early vocal cord cancers with normal cord mobility are cured by radiation therapy alone in about ______% of cases.
Retinoblastoma is a tumor of the eye that usually occurs in:
(what age group?)
(weeks to months old)
Parotid tumors are often treated using:
(what type of energy)
Mixed ELECTRONS & PHOTON beams
The most common of all intracranial malignancies is:
Dose heterogeneities within the brain when opposed lateral fields are used are _________ when lower-energy photon beams are used.
To minimize the beam divergence into the eye on the opposite side when treating a brain through opposed lateral fields, the beam is centered at the ___________
Lateral brain fields and a posterior spinal field are matched by turning the _________ and the ___________ when the treating the lateral fields.
COLLIMATOR and the COUCH
When a three-field technique (vertex & opposed lateral) is used to treat a pituitary lesion wedges are used in the _________ fields.
wedges are used in the LATERAL fields
When a 6 MV photon beam is used in a 180° arc technique to treat a pituitary lesion a ________ is used and is _________ midway through to arc.
WEDGE is used and REVERSED midway through the arc
The disadvantages of a vertex field is that it often exits in the _________ and the ___________.
exits in the PHARYNX & SPINAL CORD
When the lateral cranial fields are treated and the couch is turned to facilitate the gap with the posterior spinal field the SSD becomes ________ in the cervical spine segment when both lateral fields are treated.
SSD becomes SHORTER in the CERVICAL spine segment when both lateral fields are treated
In a typical CSI setup, to avoid having the caudal margin of the lateral brain fields diverge into the cephalad aspect of the posterior spinal field, the foot of the couch is turned:
in TOWARD the collimator
CSI: table kicked In towards the gantry
Of all childhood brain tumors, medulloblastoma represents about ______%
The most commonly occurring cancer in the US is ________ cancer.
Opposed anterior and posterior fields in the chest invariably causes a higher dose near the _________ margin than at the ___________.
higher dose near the CEPHALAD MARGIN than at the CENTRAL AXIS
A lung boost is often delivered via:
Opposed Oblique Fields
Tumors in the lower two-thirds of the esophagus can be boosted via a _______ and two _________ oblique fields.
Anterior & two Posterior oblique fields
In setting up opposed oblique boost fields to treat a lung tumor it is important to know the isocenter _________ in each field.
The number of US women who will develop breast cancer is approximately:
The regional lymph nodes in breast cancer are the:
- Internal Mammary LN
- Supraclavicular LN
- Axillary LN
In most breast treatment techniques, field matching is a problem between the ______ & _______ fields and the ________ & ________ fields.
Internal Mammary & Tangential
Tangential & Supraclavicular
To avoid beam divergence from the tangential fields into the supraclavicular field, the foot of the couch is turned (kicked) ________ from the collimator/gantry.
AWAY from the gantry
kick table Away from the gantry for tAngents
The couch angle necessary to avoid beam divergence from the tangential fields into the supraclavicular field depends on the ________ of the _________ field in the direction of the supraclavicular field and the ________.
LENGTH of the TANGENTIAL field
To avoid beam divergence into the lung by the tangential fields, the central axes of the tangential fields can be separated by slightly more than ______ until the deep margins become _________.
A boost is sometimes delivered to the tumor bed in breast cancer using a _________ beam or an interstitial implant.
The __________ lymph nodes are sometimes treated in a separate field using a photon and an electron beam or are included in the tangentials.
________ toxicity from breast irradiation is sometimes a serious problem.
The most important considerations to avoid radiation-induced pneumonitis are:
DFV = Dose, Fractionation, Volume
- 1. Total Dose
- 2. Fractionation schedule
- 3. Volume of irradiated lung
What is the most common type of glioma?
(side note: 50-60 Gy)
What is the origin of gliomas?
What are the average stats for a generic whole brain treatment?
(field size, dose, energy, fractions)
- Fields Size: 21x16
- Dose: 300 cGy*
- Energy: 6 mv
- Fractions: 10
*right & left lateral beams*
What is the formula used to determine how many degrees the table will need to be kicked?
Tan θ =
What are the 3 traditional whole brain set-ups?
- 1. Classic/Traditional borders with some collimation, not to include C-1
- 2. Includes C-1 by angling or turning the collimator
- 3. German Helmet- includes while head with blocks over the eyes, no collimator angling, C-1 not included
What are the borders of a generic whole brain set-up?
- 1. Orbital Ridge
- 2. EAM or Tragus
- 3. Base of Skull
1-2 cm of flash on all sides
Craniospinal fields are often used to treat:
Primitive Neuroectodermal Tumors
Other than transverse myelitis, name another radiation induced spinal injury:
The term "single field" in dose calculation word problems indicates that it is a _______ treatment, so the ______ should be used to calculate the monitor units.
When treating a whole brain, dose heterogeneity is greater when _______ beams are used.
Lower energy beams
Which type of CNS malignancy represents approx 20% of all primary brain tumors and are considered to be benign in overall nature, but locally malignant?
The gantry angles for tangent fields are usually separated by _______°.
When treating the supraclavicular LN of a breast cancer patient, the gantry is angled _____° away from the side of the cancer.
A ________ is a plot of target or normal structure volume as a function of dose.
Represents the amount of dose (an absolute value) received by a percentage or fraction of a structure like an organ (a relative value)
Dose Volume Histogram (DVH)
What are the 3 classic phases of lung cancer treatment?
1. AP/PA fields ⇨ 45Gy
2. Offcord Boost ⇒ 20Gy
- 3. Primary lesion boost → 10Gy
- (often via AP/PA)
Name that fractionation:
Irradiating a patient twice daily with a smaller than normal daily dose, making it possible to deliver 15-20% more dose over the same period of time.
Name that fractionation:
Delivering the same dose over a shorter period of time.
- Accelerated Fractionation
- (canadian fractionation)
What are the treatment techniques for Posterior Pharyngeal Wall cancer?
- Lateral POP fields ⇄
- Treated to 45 Gy reduced off-cord w/ shrinking field boost
- Total Doses: 65-75Gy
- (once daily 65-70Gy / bid 75Gy)
What are the treatment techniques for Subglottis cancer?
- Lateral POP fields ⇄
- treat to 40 Gy
- 65 Gy w/ boost
- (to larynx & upper trachea)
What are the treatment techniques for Glottis cancer?
- Lateral POP fields ⇆ω↯
- Early lesions treated to 64-66 Gy
- Fields centered on the Vocal Cords
- -Flash (↯) over the anterior skin surface
- 15° or 30° wedges (ω)
What are the treatment techniques for the Pyriform sinus?
- Lateral POP fields ⇄
- Treat to 45 Gy reduce off-cord
- 65 Gy to primary lesion
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