lesson 4 Flashcards
A technique in which the source of radiation is at some distance from the patient
TELETHERAPY METHOD OR EXTERNAL BEAM RADIATION THERAPY (EBRT)
Placement of radioactive substance or nuclides in or on neoplasm to deliver cancercidal dose
BRACHYTHERAPY OR PLESIOTHERAPY
- Refers to the old techniques of radiation therapy where treatments would be planned by defining a limited
number of beams with the boundaries delineated on orthogonal x-rays of the patient. - It has been largely replaced by other highly conformal external beam radiation therapies, which use CT
images to plan the treatment.
CONVENTIONAL (2D) RADIATION THERAPY
- Is a radiation therapy technique that involves CT planning where the volume to be treated is defined on a 3D
data set. - Therefore, organs at risk can also be delineated to shield these and reduce treatment side effects.
3D CONFORMAL RADIATION THERAPY (3D-CRT)
is used to design complicated beam arrangements and to assess dose-volume histograms for the tumor and organs at risk.
Radiotherapy planning software
- Is a type of cancer treatment that uses advanced computer programs to calculate and deliver radiation directly to cancer cells from different angles.
- It allows people with cancer to receive higher, more effective doses of radiation while limiting damage to the healthy tissues and organs around it
INTENSITY-MODULATED RADIATION THERAPY (IMRT)
is the gross palpable or visible/ demonstrable extent and location of malignant growth” (ICRU Report No. 50)
GROSS TUMOR VOLUME (GTV)
- Is the tissue volume that contains a demonstrable GTV
and/or sub-clinical microscopic malignant disease, which has
to be eliminated. - This volume thus has to be treated adequately to achieve the aim of therapy, cure or palliation” (ICRU report no. 50).
CLINICAL TARGET VOLUME (CTV)
- Consists of the CTV plus an internal margin.
- The internal margin is designed to take into account the variations in the size and position of the CTV relative to the patient’s reference frame (usually defined by the bony anatomy); that is, variations due to organ motions such as breathing and bladder or rectal contents (ICRU report no. 62).
INTERNAL TARGET VOLUME (ITV)
- Is a geometrical concept, and it is defined to select appropriate beam arrangements
- taking into consideration the net effect of all possible geometrical variations, to ensure that the prescribed dose is absorbed in the CTV” (ICRU Report No. 50)
PLANNING TARGET VOLUME (PTV)
– Uses very soft (low-energy) x-rays produced at potentials below 20kV.
– Because of the very low depth of penetration, such radiations are no longer used in radiotherapy
– For skin lesions
Grenz Ray Therapy
– Operates at potentials of 40 to 50 kV
– Facilitates irradiation of accessible lesions at very short source (focal spot) to the surface of the skin (SSD of 2cms.)
– It operates with a tube current of 2 mA
Contact Therapy or Endocavitary
– The term BLANK applies to treatment with X-rays produced at potentials ranging from 50 to 150 kV.
– This equipment produces a large amount of soft (low energy) x-rays which can produce severe skin reactions thus, it is useful for irradiating tumors to about 5mm depth.
– The Source-to-Skin Distance (SSD) typically ranges from 15 to 20 cm.
– The machine usually operates at a tube current of 5 to 8 mA.
Superficial Therapy Units
– is used to describe treatment with X-rays produced at potentials ranging from 150-500 kV.
– Reasonable tissue penetration of the resultant X-ray beam is achieved with this equipment, which also must be operated with filters to reduce the soft X-rays
Orthovoltage Therapy or Deep Therapy Unit
– X-ray therapy in the range of 500 to 1,000 kV has been designated as high-voltage therapy or BLANK.
– Since the electron attains high energies before striking the target, a transmission-type target may be used to obtain the x-ray beam on the other side of the target
Supervoltage Therapy Unit
– X-ray beams of energy 1 MV or greater can be classified as BLANK.
– Although the term strictly applies to X-ray beams, the gamma-ray beams produced by radionuclides are also commonly included in the category if their energy is 1 MeV or greater.
Megavoltage Therapy Unit
- An electrostatic accelerator designed to accelerate charged particles.
- The unit accelerates electrons to produced high energy x-rays typically at 2MV
Van de Graaf Generator
The operation of a BLANK is based on the principle that an electron in a changing magnetic field experiences acceleration in a circular orbit.
- Were first used for radiotherapy in the early 1950s
Betatron
The BLANK is shaped like a hollow doughnut and is placed between the poles of an alternating current magnet.
Accelerating tube
A type of PARTICLE ACCELERATOR concept originating from the CYCLOTRON in which the accelerating field is not applied through large D-shaped electrodes but through a linear accelerator structure.
- Developed by VLADIMIR VEKSLER in 1944
MICROTRON
– Source irradiating ordinary stable Co-59 with neutrons in a reactor produces a BLANK source.
– The BLANK source is usually in the form of solid cylinders, discs, or pellets.
– The beta decay energy is 2.824 MeV, and the Gamma rays are produced at 1, 173,210 and
1,332,470 Ev (1.17MeV & 1.33 MeV) energies with nearly 100% frequency of occurrence.
– Half-life: 5.27 years
– Energy: Ave. 1.25 MV gamma ray
– SAD: 80cm
COBALT – 60 UNIT (Co-60)
The housing for the source is called the SOURCEHEAD. It consists of a steel shell filled with lead for shielding purposes and a device for bringing the source in front of an opening in the head from which the useful beam emerges
Source Housing
