Chapter 14 Brachytherapy W/L pgs 293-309
The external beam portion of treatment of cervical cancer precedes the brachytherapy portion of the treatment, and serves two purposes:
(1) to treat parametrial disease and pelvic lymph nodes that cannot be treated with brachytherapy, and (2) to reduce the tumor volume, thereby reducing the treatment volume and the toxicity associated with the brachytherapy treatment that follows.
Paris system for intracavitary brachy delivery
- Specifies fixed # mg-hrs for given tumor - Constant dose rate to Rx point
Quimby System
- Uniform loading - Non-uniform dose - Crossing needles - Along & Away - Higher dose in center than periphery
Paterson-Parker Method for interstitial brachy
- aka Manchester system - needles arranged either in 1 or more planes or needles embedded in a volume of tissue
air kerma strength, is denoted by the symbol SK, and has the units of U, where:
1 U = 1 cGy/h cm2
Two methods are used in conjunction with TRUS for prostate implantation
1. Intraoperative 2. a gunlike applicator can deliver the seeds according to the treatment plan
Brachytherapy implants for breast cancer treatment fall into three categories:
1. interstitial catheter-based implants, 2. balloon- based implants, and 3. intraoperative radiation therapy-based treatments.
Why are Remote brachytherapy procedures part of today's standard of care in brachytherapy?
1.reduction of exposures of medical personnel to radiation, 2. the ability to reduce costs through outpatient treatment, and 3. the benefits of consistent customized treatments
At 15 cm from an 192Ir source, the exposure rate is 313 mR/hr (0.313 R/hr). What is the activity of this source?
15.0 mCi
One curie equals (='s)
3.7 × 10 to the 10 disintegrations per second.
The charge per ion pair produced is constant ='s
33.97 j/coulomb (C).
What is the AAPM?
American Association of Physicists in Medicine
Which of the categories of the brachytherapy implants for breast cancer the most popular and Why?
Balloon based implants - because of 1. its simplicity, 2. favorable cosmetic results, and 3. patient comfort.
The unit for activity, recommended by the International System of Units (SI) is the
Becquerel (Bq), named after the French scientist, Henri Becquerel.
intracavitary therapy
Brachytherapy in which the radioactive substance is placed in a cavity or near a cancerous lesion
decay constant equation
Decay Constant = Change in Number of Atoms / Change in Time
What is the basis of all dose calculations in classic brachytherapy?
Dose distribution from radium-226 is the basis of all dose calculations
The dose profile (depth dose curve) around a brachytherapy source depends on the source's:
Energy
The most commonly used isotopes for permanent implants are:
I-125 and Pd-103
Packing in gynecologic implants serves which of the following purposes? I. Spaces sources to even out dose distributions. II. Aids in pushing dose-sensitive structures farther from the sources. III. Provides stability of applicator placement.
II and III
Decay constant
Probability of decay of a nucleus per unit time
Which system relies on a uniform distribution of seeds but achieves a non-uniform distribution?
Quimby system
Photon-emitting isotopes
Radium-226 Cobalt-60 Cesium-137 Iridium-192 Gold-198 Iodine-125 Palladium-103
unit for exposure intensity in the air
Roentgen (R) - roentgen, denoted by R: 1 R = 2.58 × 10 − 4 C/kg of air
Intravascular brachytherapy
Similiar to intraluminal - intravascular brachytherapy. Widely used in the past to reduce the rate of restenosis after angioplasty and the placement of stents in blood vessels, it has ceded its popularity to drug alluding stents.
Beta-emitting isotopes
Strontium-90/Yttrium-90 Phosphorus-32 Ruthenium-106/Rhodium-106
Which of the following statements about radioactivity is true?
The change in the number of atoms per unit time is proportional to the number of atoms present
What is the basis for current dose calculations in clinical brachytherapy treatment planning systems?
The formalism introduced by TG-43 has been applied to all photon radiation sources (1 U = 1 cGy/h cm2 = source strength)
Define classical brachytherapy
The initial experience gained with the therapeutic use of radium sources
Intraluminal Brachytherapy
This type of brachytherapy places the radioactive sources into the body tubes. Such as the esophagus, trachea, and bronchus
Mick Applicator
a gunlike applicator is used for seed placement according to the treatment plan. This device, allows the practitioners to make on-the-fly adjustments to the seed loading to achieve optimal implants.
Brachytherapy may be used alone, as monotherapy, or as ______________________________________
adjuvant therapy, often referred to as a boost, to external beam irradiation
low-dose rate (LDR) treatments refer to dose rates of
as high as 2 Gy/h,
Define specific activity
as the activity per unit mass of a radioactive material (e.g., Ci/g).
Source activity
as the number of disintegrations per unit time for a particular source.
Why is a source's activity easy to calculate but difficult to measure?
because some of the emitted radiation interacts with the source material and encapsulation.
The storage of the sources should facilitate source identification ______________________
by type and strength.
The most common use of intercavitary therapy is for
cervical cancer
The historic unit of activity is the
curie (Ci), named after Marie Curie and assigned the activity of one gram of radium.
Define Brachytherapy
derived from the Greek words 'brachy' meaning short and 'therapy' meaning treatment.
Afterloading techniques were developed primarily to reduce:
exposure to personnel
high-dose rate (HDR) brachytherapy treatments refer to dose rates
greater than 12 Gy/h.
Intracavitary brachytherapy has been a mainstay
in treatment of cervical cancer for more than 50 years
Brachytherapy dose distributions are inherently ___________
inhomogenous.
Appropriate documentation should be kept for source control from ________________________
initial receipt through calibration, inventory, treatment, and disposal.
A source's activity is:
inversely proportional to treatment time
One Becquerel (Bq)
is one disintegration per second. Thus: 3.7 × 10 to the 10 Bq = 1 Ci
A combination treatment provides the benefits of
localized high-dose brachytherapy and the treatment of more distal but a well-defined volume of disease by using external beam irradiation.
Electronic Brachytherapy
makes use of miniature X-ray devices instead of radioactive sources
The average lifetime of radioactive atoms is the definition of:
mean life
TRUS enabled visualization
of the prostate, critical organs such as the urethra, rectum, and bladder, as well as the needles inserted.
Surface Brachytherapy
places the radioactive sources on top of the area to be treated. Most commonly used for the treatment of nonmelanoma skin cancer
The most common use of permanent brachytherapy today is for the treatment of ____________________________
prostate cancer.
An authorized ______________ _______________ and a qualified ______________ ________________ must be physically present for each HDR treatment delivery.
radiation oncologist and medical physicist
Define Stochastic
randomly determined
medium-dose rate (MDR) treatments refer to dose rates
ranging from 2 Gy/h to 12 Gy/h,
Temporary Brachytherapy
refers to the placement of radiation sources in or next to a target volume for a limited amount of time, before they are removed from the patient.
interstitial brachytherapy
refers to the placement of radioactive sources directly into a tumor or tumor bed for a period of time
Permanent Brachytherapy (or seed implantation)
refers to the placement of small radioactive sources directly in the targeted tissue where they are left to decay.
Sources used for brachytherapy are usually
sealed sources, in which the radioactive isotope is encased and sealed within a small metal structure, usually titanium or stainless steel tubes that are welded shut at the ends
The AAPM Task Group (TG-43) recommend the ______________________ for dose calculations
source strength (specification air kerma strength)
Radioactive decay is a __________________________
stochastic process.
The decay constant describes
the fraction of the number of atoms that decay per unit time.
One of the more common GYN brachytherapy applications is ____________________________
the prophylactic treatment of posthysterectomy endometrial cancer
Afterloading
the source is placed in the applicator after the applicator is placed in or on the patient
Brachytherapy is the standard treatment modalities for many malignancies including
those of the uterus and uterine cervix, lung, prostate, and breast.
Interstitial brachytherapy is commonly used in
treatments of the neck, breast, prostate, and soft tissue sarcomas.
transrectal ultrasound (TRUS)
ultrasound imaging of the prostate done through the rectum; used to diagnose prostate cancer
