Class Notes from Treatment Planning
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. What would you like to do?
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?
- A beam modifier blocks critical stuctures
- A FBL is a focus block has attenuation 15% less than PB
- Photon blocks have 5HVL
What is a photon block 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
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 is not situated at mid-depth , it is usually beneficial to deliver a(higher/lower) dose from the field where the 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)
Why is it important to use a mask with H&N cancers?
small margins and to protect nearby critical structures
What kind of H&N is a tongue blade used for?
- maxillary antrum
- the tongue blade blocks the lower half of mouth and the tongue
What is a 3-field technique for H&N?
- POP lat +AP SCV
- borders are matched with a couch kick and collimator angle or closing independent jaw half-way for each field at junction
Describe 5-field technique for H&N
- POP lats -photons
- POP lats(overlay photon POP lasts)-electrons for posterior cervical nodes
What is a typical dose structure for H&N?
- 4500 cGy
- reduce off cord-1000 cGy
- BOOST-1500 cGy
- TOTAL -7000 cGy
How many isos are typical for 3 field H&N?
2 isos are typical- the LAN field would be SSD(SSD-100) technique
When 1 iso used-it is at matchline and LAN is no longer an SSD technique. Patient(or table) is not moved between fields. Independent jaws may be used to close opposite halves of field for each field
What position is the patient in for a CSI?
What is the field arrangement for a CSI?
- 3 field-2 POP lats +
- posterior spinal field matched at the C-spine(2 fingers below base of skull)
matchline is "feathered"
What are the 3 whole brain techniques?
- 1)POP lats-borders are at superior orbital bone, EAM, and base of skull, collimator is turned-flash on 3 sides
- 2) Same borders, flash, and collimator angle as #1 but field is larger in order to include C1
- 3)"German Helmet" whole head is included with no collimator angle-face(face-including eyes blocked)
what are the typical field sizes, energy, and dose for a whole brain?
- FS: 21x16
- Energy: 6-MV
- Dose: 3000 CgY/ 10 fx (300 cGy/fx)
For an SSD technique the beams are weighted at the isocenter or Dmax ?
For a isocentric technique, the beams are weighted at the isocenter or Dmax?
If you have two opposed beams and one has a shorter distance to travel, which one should be weighted heavier?
The one that has a shorter distance
What cancers are included in the thorax?(list 5)
- 1)Lung(MOST COMMON)
- 2)germ cell tumors
Thymomas arise in the ______ in the _____mediastinum and _____metastasize.
- Thymomas arise in the thymus in the
- anterior mediastinum and rarely metastasize.
Mediastinal germ cell tumors are located in the ___, _____ mediastinum where they usually originate. However, sometimes mediastinal germ cell tumors are metastasis from _______cancer.
- Mediastinal germ cell tumors are located in the anterior, superior mediastinum
- where they usually originate. However, sometimes mediastinal germ cell
- tumors are metastasis from testicular cancer.
What are the fields for a tumor in the thorax?
- AP/PA opposed fields + (possibly)
- Obliques(off cord)
What are the lymph nodes in the thorax that are important in RT?
What is the dose gradient disadvantage in the thorax, and how is is overcome?
The slope of the chest causes differences in separation-The AP beam can be weighted heavier, or a wedge can be added on the AP beam with the heal towards the neck(think of it as filling in the missing tissue)
What is the Rx for a classic lung?
- 4500 cGy AP/PA
- 2000 cGy Obliques -offcord
- 1000 cGy boost-usually AP/PA(sometimes obliques depending on where the tumor is) field is smaller
7500 cGy total
Describe a 3-field esophagus for the lower 1/3.
2 obliques with wedges, equally weighted + PA
(when patient is PRONE the field arrangement looks like a "Y")
The medial and lateral tangents for the breast are separated by ______ degrees in order to match the divergence so that they don't overlap and cause hot spots.
The inferior border of the medial breast tangent is ____cm below the breast tissue(infra-mammary fold).
- 2 cm
The breast patient's arm is always ___.
When treating a breast cancer patient whose treatment includes the SCV, always ___ the head to the _______in order to avoid inclusion of the ____(name 3)
- turn the head to the opposite side
- trachea, esophagus, spinal cord
The left SCV is treated with a gantry angle of ____, and a right SCV is treated with a gantry angle of_____.
- left SCV- RAO-345 degrees
- right SCV- LAO-15 degreees
The PAB is treated using a (SSD/isocentric) technique?
Post axillary boost
An electron boost for a post-lumpectomy patient treats the ____, and for a post-mastectomy patient it treats the _______.
- tumor bed
- chestwall (with bolus to bring dose to surface)
A ____cm margin is usually required around a lumpectomy scar for a boost.
If the correct electron energy is not available for a boost for breast, then _______ can be used.
mini photon tangents
The nodes important for RT of breast cancer are?
- internal mammary
What device is used to shift breast back onto chest for RT?
- breast board??
- I think-help me here-I found the question in my notes with no answer
What does CT-compatible mean?
It is made out of a material which does nto cause scatter(artifacts)
How is a CT sim done for a breast?
- patient place on CT compatible breast board with arms over head
- wire is placed on:
- 3)around breast to define where breast tissue is located(doctor can also draw in)
- 3)To make reference marks-BB's are place in middle of anterior skin surface and on each lateral surface(all should be stable surfaces) so that they will all show up on same CT slice
Shifts from reference marks to isocenter are determined from CT
What are the possible fields for breast?
Tangents-Medial and Lateral
-angled 185-6 degrees apart
Tangents + SCV(angled 15 degrees) and matched to tangents
- 4 field: Tangents +SCV + PAB
*Internal Mammary usually included in tangents
Chestwall treatment is for a postlumpectomy patient or a _____. It must include a ___.
- Medial and lateral tangents include a BOLUS
- (wet towel is good-if superflab is used, make sure it conforms to skin surface)
2000 cGy will cause pericarditis
4500-5000 transverse myelitis
5000 cGy will cause esophagitis
Define a DVH?
A dose volume histogram is a graph that plots relative volume of structures contoured in a radiation treatment plan to how much dose they receive.
What techniques are used for pituitary? How is the head positioned?
- POP lats + vertex, AP, or PA
- (usually IMRT)
The head is tilted forward in order to keep the beam sup and post of eyes
What is the dose/fx for Gliomas?
What is the most common glioma?
Who developed SRS and when?
Lars Leksell in 1951(Sweden)
How many holes are there in the Pb sphere used in GammaKnife? What is the source?
When feathering a field junction the matchline should move ____times.
20 percent of all childhood brain tumors are _______.
- *they are treated with CSI
The pituitary is located in the ______.
What is Lermitte's sign?
- Lhermitte's sign, sometimes called the Barber Chair phenomenon, is an electrical sensation that runs down the back and into the limbs.
- It is a sign of RADIATION INDUCED TRANSVERSE MYELITIS(OR IT CAN ALSO BE A SIGN OF MYELOPATHY)
- 50% OF PATIENTS DIE OF SECONDARY COMPLICATIONS!!!
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