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When a linear accelerator with one independently moving leaf is used with a wedge in the beam, there is a chance that the independent jaw cannot be used because...
The COLLIMATOR may have to be turned in a direction such that the independent jaw cannot be used
The attenuation if Cerrobend is about ___% (less than/ greater) than lead.
Cerrobend attenuates 15% less than lead
The potential hazards of working in the mold room where alloy shields are made consist of-(list 4)
- 1) inhalation of vapors and dust particles
- 2)ingestion of small fragments of the metal
- 3)skin penetration
To reduce the risks of ingestion fragments of the alloy in the block room, the following precautions should be taken-
Practice good hand hygiene before eating, drinking and smoking
Multilevel collimators are different from custom shaped blocks because-
The produce step like edges, leakage can occur between leaves, and they can only be used with limited field sizes
Custom made electron locks are different from custom blocks for photon beams because -
They have NO FOCUSED EDGE and are much thinner; also, the size of of the opening is practically the same as the field on the skin surface.
When a skin lesion is treated using an electron or orthovoltage beam, the shielding -
Should be placed directly on the patient, covering a large area surrounding the lesion
Secondary scatter in the tissue-metal interface can cause____ dose in the adjacent tissues but can be ______by.....
- placing 2-4mm of tissue equivalent material over the teeth
When a lip lesion is treated, it is possible to reduce mucosal reaction by
Placing an internal shield distal to the tumor and covering the shield with a coating of wax
When a missing tissue compensator is used in a photon beam, the compensator should be placed....
At some distance from the skin surface.
The most practical material to use when making a compensator for a photon beam is(name 5)
(NOT LEAD or other higH Z materials!)
- 4)brass(like DOT DECIMAL)
Bolus material is used to
Reduce the depth of maximum dose when PHOTON beam is used
????doesn't it do the same for an electron beam or is it just used for surface irregularities?????
The function of the Radiologic Physics Center(RPC) is to
- Review patient treatment records, Dosimetry calibration of equipment use in treatment of patients enrolled in clinical trials, and communicate instructive findings to the clinical study groups.
- *Note- even though the RPC is for QA for CLINICAL TRIALS, it has a spillover effect towards ALL treatments.
Departmental weekly chart rounds should include verifying( name 6 things )
- 1)presence of diagnoses
- 2) histology
- 4) presence of consent to treatment
- 5)presence of pathology report
- 6) evidence that patient is making progress
The frequency of port films varies, but they
Should always be taken on the first day of treatment
Electronic portal imaging is a method whereby the patient/beam alignment is checked
after only a few MU have been delivered
Various methods of documenting the treatment parameters include( list 3)
- 2) photograph of each treatment field
- 3)port film of treatment field
???Ask about difference between port film and "isos"??????
If a 30 degree wedge is left out of the treatment during 1-5 treatments,
the central axis dose is increased and the isodose curve is affected
*the MOST IMPORTANT Thomas g is when a mistake is discovered to REPORT it to the PHYSICIAN so that he can decide if adjustments are needed
When an error in dose delivery is discovered
THE ATTENDING RADIATION ONCOLOGIST SHOULD BE NOTIFIED
Treatment fields should be labeled in the chart with reference to......
An anatomical description, and it should have a unique number
The angle of beam divergence is
Larger farther from the central axis
When parallel opposed fields are used and the isocenter is at mid depth in the chest, the length of the spinal cord is
Longer on the anterior field than the posterior
When parallel opposed fields are used and the isocenter is at mid depth in the chest, the
The anterior port film should appear exactly as the anterior sim film with respect to anatomy
The size of the magnification device is important because a ______ device is more likely to lead to errors in the magnification factor
A circular magnification device, which is 5 cm in diameter, is placed on the patient's anterior surface where the SSD is 100 cm. the sim film is at 135 cm from the target(TFD). The magnification factor is
135/100=1.35 mag factor
A 3D coordinate system is used in RT to describe a point in the patient in respect to the origin. +2 cm on the Y-axis would be located
2 cm cephelad to the origin
The most commonly used beam energy to treat head and neck cancer is
- 4-MV and 6-MV photons
The following techniques can be used to deliver a boost dose in the treatment of carcinoma of the base of the tongue
small external beam fields or an interstitial implant
The majority of cancer in the head and neck region is
squamous cell carcinoma
A bite block is sometimes inserted between a patient's teeth because
It help's the patient keep his or her mouth open during the treatment so more of the oral mucosa can be excluded from the radiation field
To make patients more comfortable during treatment, it is a good idea to
provide supports under head, knees, and arms
Xerostomia is caused by irradiation to the
- salivary glands
The functions of the saliva are to
- 1)Moisten food
- 2)promote swallowing
- 3)prevent tooth decay
In the treatment of head and neck cancer, immobilization is particularly important because
- 1)the proximity of several radiosensitive organs
- 2)often small tumor margins
When carcinoma of the oropharynx is treated, the field junction between opposed lateral and an inferior border should be set-
Cephalad to the thyroid notch
*In book it says to match AT the thyroid notch
When a patient, immobilized in the supine position, is treated for Graves' opthalmopathy, half-beam blocked opposed lateral fields centered on the lateral canthus are usually used. Both lenses of the eyes are excluded from the beam when rotating the gantry to
An angle when both lead markers placed on the eyelids of the closed eyes are superimposed
To place a large patient so the head is in the neutral positition
a high support is needed under the head
To include the entire maxillary antrum without also including the eye when a patient is treated for a maxillary antrum tumor
The chin is extended and the head tilted back
To avoid overlap between the opposed lateral and anterior fields used in treatment of head and neck cancer
A full-length midline block can be used over the spinal cord in the anterior fields
The junction between the lateral and the anterior fields is chosen so that, when a full-length midline block is used, the larynx is also blocked in an effort to
Prior to starting the treatment of boost fields, it is good idea to take port films because
skin and seed markers may have shifted and margins are small
When the boost field is given and the central axis is moved the dose in the midplane on the central axis of the boost fields is added to the dose received at the ________from the previous fields.
When the true vocal chords tumors are treated
- A 15 or 30 wedge is often used, but the dose in the anterior commissure could be compromised.
Early vocal cord cancers with normal cord motility are cured by radiation therapy alone in about ______% of cases.
Retinoblastoma is a tumor of the eye that usually occurs in _________.
Parotid tumors are often treated using
mixed electron and photon fields
The most common of all intracranial malignancies is
*remember to be careful how this question is asked... If it asks what is the most common PRIMARY brain tumor the answer would be GLIOMAS
A stereotactic frame is intended for use in(single/multiple) fraction treatments.
- Leksell stereotactic frame
When adjacent fields are matched, it is more important to
Match the fields precisely during a GIVEN treatment than reproduce the LOCATION
*In other words, the fields might move slighty but they always need to be MATCHED PRECISELY
To appreciate the position of the eyes relative to the beam
A radiopaque marker is placed on the lateral canthus of each eye
Dose heterogeneities within the brain when parallel opposed fields are used
are increased when lower energy photon beam is used
*However, when higher energy beams are used then the lateral aspect of the brain is compromised
The vertex field is difficult to treat because
there is no way to obtain a port film
*couch is kicked 90 degree(along with gantry)make it possible to have beam vertex(come in through top of head) but then there is no place to put port film(and flat panel can not be raised into table or in the middle of the body)
To minimize the beam divergence into the eye on the opposite side, when treating a brain through opposed lateral fields
the beam is centered on the lateral canthus of the eye
*Block for anterior portion of eye, beam anlged posteriorly
When the entire spinal axis must be treated, the patient's posterior surface should be as flat as possible in order to
make the dose more uniform
Lateral brain fields and a posterior spinal field are matched by
- rotating the collimator and rotating the couch when treating lateral fields
To trace the tumor volume onto a lateral sim film, a sagittally reconstructed CT or MRI image of the patient's head
CANNOT be used because they may not represent the midsaggital plane
When a 3-field technique(vertex and opposed lateral) is used to treat pituitary lesion
Wedges are used in the lateral fields
When 6-MV photon beam is used in a 180 degree arc technique to treat a pituitary lesion
a wedge is used a reversed midway in the arc
The disadvantage of a vertex field is that
it often exits in the pharynx and spinal cord
*also inability to take port film
Field gaps are often shifted 2-3 times during a course of treatment to
- to reduce the risk of overdosage in the spinal cord
*Clinical Endocrine Oncology edited by Ian D. Hay, John A. H. Wass
When the lateral cranial fields are treated and the couch is turned to facilitate the gap with the posterior spinal field then the SSD becomes(shorter/longer)in the ________spine segment when both lateral fields are treated.
- the cervical spine section SSD becomes SHORTER
*Leibel and Phillips Textbook of Radiation Oncology: Expert Consult By Richard Hoppe, Theodore L. Phillips, Mack Roach III
The typical CSI setup, to avoid having the caudal margin of the lateral brain fields diverge into the cephalad aspect of the posterior spinal fields, the foot of the couch is turned
In towards the collimator
To determine depth of the spinal cord
Measure the depth on a lateral radiograph with a lead wire over spine
Of all childhood tumors, medullablastoma represents____%
Symptoms or myelopathy are (reversible/irreversible)
The most commonly occurring cancer in the United States is
When an immobilization device is needed, it is best to first determine the _______, and then________.
first determine beam orientation THEN build the device
It is important to reproduce the patient's position as it was during________.
the simulation procedure
Opposed anterior and posterior fields in the chest invariably cause a (higher/lower?) dose near the (cephalad/caudal) margin of than at the ______.
higher dose near the cephalad margin of the CAX
A lung boost is often delivered via_____
opposed oblique fields
Treatment fields in the chest should be designed with_______in mind.
Tumors in the lower 2/3 of the esophagus can be boosted via_________
An anterior and two posterior obliques
Aligning two points separated by a long distance (is/is not?) a reliable method to reproduce a patient's position.
Is a reliable method
In setting up opposed oblique fields to treat a lung tumor it is important to know_______.
The SSD for each field
The number of US women who will develop breast cancer is approximately one in ______.
The regional lymph nodes in breast cancer are:
- internal mammary
In most breast treatment techniques, field matching is a problem between:
- Between the internal mammary and the tangential field
- Between the tangential and the supraclavicular fields
The couch angle necessary to avoid bean divergence from the tangential fields into the SCV field depends on the(list 2 things)
- 1)length of the tangential field in the direction of the SCV field
- *Use Heinz-57 formula
To avoid beam divergence into the tangential fields into the SCV field the (foot/head) of the couch is turned(towards/away) from the collimator(gantry).
foot of couch is turned AWAY from the collimator
To avoid beam divergence into the lung by tangential fields the CAXs can be separated by slightly(more/less?) than _______degrees.
separated by slightly MORE than 180 degrees
Multiple adjacent electron fields to treat a chest wall recurrence should be considered ONLY if _______is available.
A boost is sometimes delivered to the tumor bed in breast cancer using
- an electron beam or an interstitial implant
- (also Accuboost)
Cardiac toxicity from breast irradiation is __________.
sometimes a serious problem
The internal mammary nodes are sometimes treated in a separate field using an electron or photon beam or are_______;
included in the tangential fields
The most important considerations to avoid radiation-induced pneumonitis is(name 3):
- 10total dose
- 2)fractionation schedule
- 3)volume of irradiated lung
What should be contoured?
- external surface
Multiple level contours show what?
Change in separation along the proposed treatment area
Besides using a CT based treatment planning software how can a patient's external surface be contoured?
plaster of paris
How is the field contoured?
- 1) contoured CAX
- 2)1 cm below superior border(sup -1cm)
- 3)1 cm above inferior border(inferior -1cm)
Why is field placement so important?
- see pg 185(more to follow!)
- to avoid missing target and irradiating dose limiting structures
How often are lasers checked?
Where are the lasers placed for a whole brain?
What is failure of localization?
failure to determine the extent of the disease
What happens when patient is not positioned correctly?
The treatment field is displaced compared to intended position.(that's why we take port films)
How much is the tumor margin(usually?)?
- most fields include a margin of 0.5 cm(5mm)
- the PTV has 1.5 cm
Why is the patient immobilized?
What is a beam modifier why is it needed?
BEAM MODIFIER CHANGES THE SHAPE OF THE FIELD
- A beam modifier blocks critical structures
- A FBL is a focus block has attenuation 15% less than PB
- Photon blocks have 5HVL
What is a photon block cutter called?
A Heuster block cutter
What is the makeup of Cerrobend?
BLT with Cheese
What is an internal shield and where is it used?
- It is used in the mouth because photons interact with teeth causing secondary electron scatter
- Seconday electron scatter can cause high dose in the tissue/metal interface and cause ulcers in the mouth
- Gauze in the ear is another internal shied to eliminate electron scatter
What is a tissue compensator?
A tissue compensator compensates for "missing tissue" which are caused by irregularities in the patient's surface
*Only used for photons
What is QA and what does it included?(generally)
Quality assurance is written policies(or rules) and procedures(steps to follow) which are done daily, weekly, monthly, etc.
- Chart rounds are an example of QA
- Verifying patient name and birthdate
*A misadministration leads to new policies and procedures
What are tattoos for?
- 1)They locate previous tx field(so we don't overlap fields and over-treat)
- 2)locate current treatment field
*Before tattooing a patient be sure to ask them if it is okay after explaining the purpose of the tattoo(VERBAL CONSENT)
What is and EPID?
- i.e. the "flat panel"
- On board imaging
What is a record and verify system?
It is a system in the computer that confirms and records everything from data acquired from the VB on first day.(gantry angles, wedges,MUs, xyz)
How much must a mistreat be before the doctor is notified? The state?
- Doctor is ALWAYS notified when there is a mistreat.
- State is notified when it is more than 20%
What are the three methods of shielding?
- 1)LESS time
- 2)MORE shielding
- 3)MORE distance
- Percentage Depth Dose
- Dose at depth/Dose at dmax x 100%
The ratio of absorbed dose at a specified depth to the absorbed dose at dmax expressed as a percentage
What does ARRT, R.T. (T) stand for?
The American Registry of Radiologic Technologists, Registered Technologist in Radiation Therapy
When is Mayneord's F Factor used?
Mayneord F Factor is used to calculate the change in PDD for a treatment with an extended distance.
21, 12 dmax before depth
- ***used to correct for depth dose at an SSD other than 100cm for SSD type set ups.
- MF = [(f₂+dmax)/(f₁+dmax)]²⋅[(f₁+d)/(f₂+d)]²
- and then DD = DD₀ x MF
- REMEMBER MAYNEORD'S IS FOR FINDING THE NEW PDD WHEN THE SSD IS CHANGED-USE THE FACTOR TO MULTIPLY BY THE OLD PDD TO GET THE NEW PDD
What are the limitations of an isodose chart(list 3)
- 1)represent dose distribution in only one plane
- 2)are only for square or rectangular fields
- 3)depict dose distribution from only one field
What is a single field typically used to treat?
When the tumor si not situated at mid-depth , it is usually beneficial to deliver a(higher/lower) dose from the field wherethe tumor is shallower.
This is called______the beam.
- Higher dose from the side where tumor is shallower
WHAT IS DOSE NORMALIZATION?
It is the dose at some point that has been forced to 1)00%.
MU(of 100% ISL)/ISL(of volume covered)