First Long Examination Flashcards
Defined as the quantity of radioactive substance that gives rise to a decay rate of 1 decay per second.
Becquerel (Bq)
Traditional unit of radioactivity; It is the amount of radioactive substance which gives rise to a decay rate of 3.7 x 1010 decays per second.
Curie (Ci)
Expresses how much ionization the beam causes in the air through which it travels; It is the quantity of X-rays or gamma-rays such that the associated electrons emitted per kilogram of air at S.T.P produce ions carrying 1 coulomb of electric charge.
Radiation Exposure
What is the SI unit for radiation exposure?
C/kg
What is the traditional unit for radiation exposure?
Roentgen
Defined as the quantity of X- or gamma rays such that the associated electrons emitted per kilogram of air at S.T.P produce ions carrying 2.58 x 10-4 coulombs of electric charge.
Roentgen
Energy deposited in the absorber when radiation interacts with it.
Absorbed Dose (D)
What is the SI unit for absorbed dose?
Gy
What is the traditional unit for absorbed dose?
rad
Defined as the absorption of 1 joule of radiation energy per kilogram of material.
Gray
Defined as the absorption of 10-2 joules of radiation energy per kilogram of material.
rad
Based on estimates of the ionization capability of the different types of radiation
Equivalent Dose (H)
What is the formula for equivalent dose and what factors are considered?
H = WrD
where Wr is the radiation weighting factors and D is the absorbed dose
Includes radiation weighting factors as well as estimates of the sensitivity of different tissues.
Effective Dose (E)
What is the formula for effective dose and what factors are considered?
E = ΣWtH
where Wt is the tissue weighting factors and H is the equivalent dose
Derived unit of ionizing radiation dose in the International System of Units (SI) and is a measure of the health effect of low levels of ionizing radiation on the human body.
Sievert
Expresses the exposure rate produced by the gamma-rays emitted from a radioisotope; It is defined as the exposure rate per unit activity at a certain distance from a source.
Specific Gamma Ray Constant
What is the SI unit for specific gamma ray constant?
C/kg/s/Bq at 1 m
What is the traditional unit for specific gamma ray constant?
R/hr/mCi at 1 cm
Law on the influence of distance on the intensity of radiation beam; It states that radiation intensity will decrease with the square of the distance from the source
Inverse Square Law
A very destructive process which occurs in some heavy nuclei which split into 2 or 3 fragments plus some neutrons
Spontaneous Fission
Which phase of the cell cycle is radioresistant?
S phase
Which phase of the cell cycle is radiosensitive?
G2 and M phases
Type of radiation damage wherein photons physically break one or both of the sugar phosphate backbones or break the base pairs of the DNA.
Direct Action or Damage
Photons are absorbed in the water of an organism causing excitation and ionization in the water molecules
Indirect Action or Damage
Type of break in the sugar phosphate backbone wherein only one of the sugar phosphate backbones is broken; It is readily repaired using the opposite strand as a template; Base pair substitutions and frameshift mutations can still occur
Single Strand Break
Most detrimental lesions in chromosomes; Difficult to repair, they can cause mutations and cell death
Double Strand Breaks
What is the process of DNA repair?
Excision
Enzyme that recognizes damaged DNA
Glycosylase
Enzyme that cuts out damaged DNA
Endonuclease
Enzyme that resynthesizes the original DNA
DNA Polymerase
Enzyme that repairs the sugar phosphate backbone
DNA Ligase
Sequence of Radiation Injury
1) Exposure
2) Latent Period
3) Period of Injury
4) Recovery Period
Factors Affecting Biologic Response to Radiation
1) Tissue Radiosensitivity
2) Dose
3) Duration of Exposure
4) Age of the Patient
Types of Radiation Effects
1) Acute and Late Effects
2) Somatic and Genetic Effects
3) Deterministic and Stochastic Effects
Type of effect wherein the probability of occurrence increases with increasing dose but the severity does not depend on the dose.
Stochastic Effects
Type of effect wherein there is a threshold dose, below which the effect does not occur. However, once the threshold is reached, the severity of an effect increases with dose.
Deterministic Effects
Irradiation of the entire body by a high dose of ionizing radiation in a very short period of time.
Acute Radiation Syndrome (ARS)
What is the major cause of ARS?
Depletion of parenchymal stem cells
What are the stages of ARS?
1) Prodromal Stage
2) Latent Stage
3) Manifest Illness Stage
4) Recovery or Death
Types of Radiotherapy According to Aim
1) Curative
2) Palliative
3) Prophylactic
4) Total Body Irradiation
Type of radiotherapy that prevents possible metastases or recurrences
Prophylactic
Type of radiotherapy that involves ablation of bone marrow in order to suppress the immune system
Total Body Irradiation
Types of Radiotherapy According to Timing
1) Adjuvant Radiotherapy
2) Neoadjuvant Radiotherapy
3) Radiochemotherapy
Radiotherapy given after any kind of treatment modality
Adjuvant Radiotherapy
Radiotherapy given before any kind of treatment modality
Neoadjuvant Radiotherapy
Radiotherapy given concurrently with chemotherapy
Radiochemotherapy
Types of Radiotherapy According to Mode
1) External Beam Radiation Therapy
2) Internal Beam Radiation Therapy
Type of radiotherapy wherein the radioactive material is placed in the body near the cancer cells
Internal Beam Radiation Therapy
Sealed source of radiotherapy
Brachytherapy
Unsealed source of radiotherapy; Delivered through ingestion or intravenous route
Systemic Radioisotope Therapy
Type of radiotherapy wherein radiation is delivered by a machine outside of the body
External Beam Radiation Therapy
Delivers radiation beams from different directions designed to match the shape of the tumor through the use of 3D anatomical data from CT or MRI; Aim is to apply the maximum dose to the target; Helps to reduce radiation damage to normal tissues.
Three-Dimensional Conformal Radiation Therapy (3D-CRT)
Form of 3D-CRT where imaging (eg CT scan) are done before each treatment; This allows the radiation oncologist to adjust the position of the patient or refocus radiation as needed to hit the tumor; Accounts for target volume changes during RT such as tumor volume decrease or weight loss.
Image-Guided Conformal Radiation Therapy (IGRT)
Similar to 3D-CRT but changes the strength of some of the beams in certain areas, therefore, certain parts of the tumor have higher doses and help lessen damage to nearby normal body tissues.
Intensity Modulated Radiation Therapy (IMRT)
Form of IMRT that delivers radiation inside a large “donut”; Delivers many small beams of radiation at the tumor from different angles around the body
Helical-tomotherapy
Administer large dose of radiation to a small tumor area and is very precisely aimed; Used for brain tumors and other tumors inside the head; Brain imaging are done to determine exact location of the tumor and radiation is sent to the area from many different angles; Given in more than five fractions
Stereotactic Radiotherapy (SRT)
Administer large dose of radiation to a small tumor area and is very precisely aimed; Used for brain tumors and other tumors inside the head; Brain imaging are done to determine exact location of the tumor and radiation is sent to the area from many different angles; Given in one to five fractions in ablative doses
Stereotactic Radiosurgery (SRS)
Administer large dose of radiation to a small tumor area and is very precisely aimed; Used for treatment outside the brain
Stereotactic Body Radiation Therapy (SBRT)
Given directly to the tumor during surgery; Used when tumors cannot be removed completely or risk of cancer recurrence is high; Can give large dose of radiation which limits effects on nearby tissues
Intraoperative Radiation Therapy (IORT)
Radioisotopes used for brachytherapy
1) Ir-192
2) I-125
3) Pd-103
What type of decay does cobalt-60 undergo?
Beta- decay
What energy is emitted by the decay of cobalt-60?
Two gamma emissions
What is the half life of cobalt-60?
5.27 years
What collimator is often used for EBRT?
Multileaf Collimator
What are the 5 R’s of Fractionation?
1) Repopulation
2) Repair
3) Redistribution
4) Reoxygenation
5) Radiosensitivity
What are the three types of cell damage caused by ionizing radiation?
1) Lethal Damage
2) Sublethal Damage
3) Potentially Lethal Damage
Gross palpable or visible/demonstrable extent and location of malignant growth
Gross Tumor Volume
Tissue volume that contains demonstrable GTV and/or subclinical microscopic malignant disease, which has to be eliminated; May contain microscopic disease and other areas considered to be at risk and requiring treatment (eg positive lymph nodes)
Clinical Tumor Volume
Consists of the CTV plus an internal margin; Designed to take into account variations in the size and position of the CTV relative to the patient’s frame (e.g. breathing)
Internal Tumor Volume
Geometrical concept defined to select appropriate beam arrangements, taking into consideration the net effect of all geometrical variations, in order to ensure that the prescribed dose is actually absorbed in the CTV
Planning Target Volume
Type of photon beam wherein there is a higher dose near the entrance at the depth of dose maximum.
Single Photon Beams
Requires adjusting the patient such that the skin is at the correct distance from each beam orientation
Fixed SSD Technique
Requires placing the patient such that the target is usually at the isocenter
Isocentric Techniques
This beam combination is well suited to a large variety of treatment sites (eg. lung, brain, head and neck)
Parallel Opposed Beams
Allow for a higher dose in the beam intersection region;
Multiple Coplanar Beams
Isodose curves for two bilateral arcs of 120° each; Produce a relatively concentrated region of high dose near the isocenter but they also irradiate a greater amount of normal tissue to lower doses than fixed-field techniques
Rotational Technique
Most often used for treatments of brain as well as head and neck; Useful to get more adequate critical structure sparing compared to conventional coplanar
Multiple Non-coplanar Beams
Used to evaluate treatment plans along a single plane or over several planes in the patient
Isodose Curves
Most commonly used as a plan evaluation tool and to compare doses from different plans or to structures
Dose-Volume Histogram
