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