1. What is Digitally Reconstructed Radiograph (DRR)?
Based on acquired CT information, these are images that render a beam's eye view display of the treatment field anatomy and areas of treatment interest. These images resemble conventional radiographs and can be used in conjunction with patient Port Films to check patient treatment setup prior to irradiation.
A cylindrical phantom, 30 cm in diameter and 18 cm long, made of Solid Water. For patient QA, it separates into two hemispheres to place film and can have an ion chamber within 5 mm or film.
3. What is intraoperative Radiation Therapy (IORT)?
A boost technique in which a single dose of 10-20 Gy is delivered directly to the tumor bed with electrons or photons. The tumor bed has been surgically exposed, allowing critical normal structures to be shielded or displaced out of the radiation beam.
4. What is conformal Radiation Therapy?
Therapy that, with the use of 3D treatment planning, allows the delivery of higher tumor doses to selected target volume without increasing treatment morbidity. Requires a CT Simulator, 3D Treatment Planning System (TPS) and usually Multi-Leaf Collimators (MLCs) on the linear accelerator.
5. What is Electronic Portal Imaging Devices (EPID)?
A system producing near real-time portal images on a computer screen for evaluation. This is attached to the linear accelerator and is composed of amorphous Silicon (aSi) crystals. They receive MV x-rays that images the patients setup and is used to compare to the DRR's from the Treatment Planning System (TPS). These are done almost universally on all patients now.
6. What is characteristic Radiation?
Photon radiation that is emitted in discrete energies when an outer shell electron fills an inner shell position after the original inner shell electron is ionized. The binding energy difference between residing in the outer shell compared to the inner shell is the energy of the photon emitted.
7. What is Digital Imaging and Communications In Medicine (DICOM)?
A standard for handling, storing, printing, and transmitting information in medical imaging. This protocol was formed to provide communication standards for sharing image information regardless of manufacturer and has included radiation therapy treatment information. This facilitates the use of picture archival and communications systems (PACS) and allows diagnostic images to be widely distributed.
8. Do you know how Is Radiation Emitted From The Body?
The body radiates energy through thermal conduction through the skin to the air, clothes, etc, around the body. A small amount of energy would also be radiated as electromagnetic radiation with a peak wavelength directly related to the Kelvin temperature of the skin.
Also very small amounts of other radiation are emitted due to naturally occurring radioactive isotopes in the body (i.e. Carbon-14).
9. What is Intensity Modulated Radiation Therapy (IMRT)?
Therapy that delivers non-uniform exposure across the beam's eye view (BEV) rather than an open field. This type of treatment can be delivered with a machined compensator (rare outside of community clinics), linear accelerator Multi-Leaf Collimator (MLC) leaves or Tomotherapy binary leaves. The IMRT plan is usually (but not alwaysi.e. breast tangents with control points) developed with an inverse treatment planning system. While it can deliver a more conformal plan to the patient, extra care and quality checks must be done to ensure proper delivery due to its increased complexity..
10. What is clinical Target Volume (CTV)?
The visible (imaged) or palpable tumor plus any margin of subclinical disease that needs to be eliminated through the treatment planning and delivery process.
Used in the gantry head of high-energy linear accelerators to bend the electrons that will either be used directly for electron radiation treatments or will hit a target and produce photons for photon radiation treatment. Bending magnets are used along with an energy slit that physically limits the energy of the electron beam to within a desired range. Two models are in primary use 270degree (Varian), slolom method (Seimens) 3 magnets used to do slights bends.
12. What is alpha-1 antitrypsin deficiency (A1AD)?
A genetic disorder caused by low levels of alpha-1 antitrypsin, a protein that protects the lungs. Alpha-1 antitrypsin deficiency (A1AD) puts a person at risk of developing emphysema or chronic obstructive pulmonary disease (COPD).
13. What is electron Binding Energy?
The amount of energy required to remove an electron from its orbit in an atom. This amount is subtracted from the initial energy acquired by the photon or electron once it leaves the proximity of the atom.
14. What is blocked Field Size?
The equivalent rectangular field dimensions of the open treated area. The blocked field size is the actual area treated. Therefore the blocked field size is normally smaller than the collimator field size. Blocked field size dimensions are used when determining TMRs and PDDs. Collimator field size dimensions are used to determine Output Factors.
Particulate radiation, positively charged, which consists of two protons and two neutrons (effectively a He nucleus). It has a high Radiobiological Effectiveness (RBE) compared to photons, and thus will cause significant damage to tissue, but it has a short track length (a piece of paper will shield most of it).
An early version of IMRT that is still used today in centers without Multi-Leaf Collimators (MLCs). It is a beam modifier that allows known non-uniformities within the irradiated field to better conform to the target volume. It is made of tungsten and is machined
Product of the absorbed dose and a quality factor (QF), which takes into account the biologic effects of different types of radiation on humans; units are the rem (1 rem = 1 rad x QF = 1 cGy x QF = 1 cSv). Photons and electrons have a QF of 1 for instance where as protons have a QF of 3 and neutron 5-20.
Electromagnetic radiation emitted from decaying isotopes and used for external beam and brachytherapy treatments. Since it is electromagnetic radiation it is a photon and has no mass and no charge. Gamma Rays typically have similar energies to X-rays but are distinguished from these radiations by the origin of emanation. Gamma Rays are from the nucleus of the atom whereas X-Rays come from the electron shells outside of the nucleus.
19. Explain me what Is Neutral Buoyancy?
Buoyancy is the net upward force experienced by an object submersed in a fluid. Pascal's principle dictates that fluid pressure on an object increases with depth, so there is greater pressure on the bottom of the object than the top, resulting in a net upward force. When an object's buoyancy is greater than its weight, the object will float.
An object with neutral buoyancy has a density such that when it is fully submerged the upward force due to buoyancy is exactly equal to the downward force due to the weight of the object.
In pure water this is a density of 1000 kg/m3 (1kg/litre)
In seawater, this is a density of about 1025 kg/m3 (1.025kg/litre)
A radioactive isotope with a half life of 30.2 years and an average energy of 662 keV. It is a pure beta emitter and is used for Low Dose Rate (LDR) Brachytherapy especially for use in tandem and ovoid treatments for gynecological cancers.
A type of simulation that operates along with a 3D geometric planning computer. The extension of a CT system allows the single acquisition of many thin slices over a required treatment area. After scanning, radiation beams, isocenter, and blocks can be visualized and placed on the three dimension CT images set. CT simulation also allows for the construction of a Digitally Reconstructed Radiograph (DRR) that is helpful for verifying patient setup when compared to port films with a film cassette or Electronic Portal Image Device (EPID).
The section of the target at which radiation is produced. The smaller the focal spot, the sharper the field produced (very defined penumbra), however the smaller the focal spot also means the hotter the target material gets and can cause damage. Therefore, a compromise must be struck between sharper fields and adequate and reasonable heat loading of the target.
23. What is inverse Square Law?
A mathematical relationship that describes the change in beam intensity as the distance from the source changes. The change in intensity is primarily caused by the divergence of the beam. The mathematical formula states that the intensity decreases inversely proportional to the square of the distance. (Intensity = 1/r2). Example: Triple the Distance (r), the Intensity drops by a factor of 9.
24. What is sedation, non-pharmacological?
Approaches that guide a patient to a state of relaxation by focusing attention on pleasant thoughts. Guidance is provided by specially trained radiology or other medical personnel. This condition may be achieved via distraction techniques or self-hypnotic relaxation.
25. What is accelerated Hyperfractionation?
The technique in which there are more treatment days than accelerated fractionation. The total dose (cGy) of primary radiation is more than conventional fractionation, hyperfractionation, or accelerated fractionation.
The region between the skin surface and the depth of Dmax. A buildup region is a characteristic of MV irradiation. In this region the dose increases with depth until it reaches a maximum at the depth of Dmax.
An inverse treatment planning system for creating intensity modulate fields (IMRT). It was the first system used for IMRT in this department and has since been largely replaced by other TPS.
28. What is effective Dose Equivalent?
The dose equivalent weighted by the proportionate risk for various tissues. For example, the gonads are more sensitive to radiation than the fingers so there weighting of effective dose is higher. Thus for equal equivalent dose to the gonads and the fingers, the gonads would be more adversely affected.
29. What is craniospinal Irradiation (CSI)?
Complex irradiation of all central nervous system and cerebrospinal fluid regions from behind the eye down to the midsacrum for treatment of medulloblastoma and other cerebrospinal fluid seeding tumors.
A recent addition to the stable of radionucleotides used for Prostate brachytherapy, it has a half life of 10 days and an average energy of 30.4 keV.
In Brachytherapy, the length of the area in which the radioactivity lies in the source. This is usually a little shorter than the physical length of the source.
32. What is subarachnoid hemorrhage?
Blood collection between middle (arachnoid) and inner (pia mater) linings of the brain. It can be a result of trauma, or a bursting (ruptured) aneurysm. An aneurysm is a small area of weakness of the wall of an artery, which may be congenital, or less commonly, due to other causes, such as an infection.
The rotational delivery of modulated beams. This machine is similar in physical appearance to a CT Scanner, however instead of delivering keV X-rays to garner diagnostic information, it delivers MV (therapeutic) beam and is outfitted with a collimator with two sets of binary leaves that either open and close and deliver modulated dose patterns to the patient.
34. What is equivalent Square?
The square field that has the same percentage depth dose and output of a rectangular field. An equation is (4A/P) = 4 times the Area of the field divided by the perimeter of the field.
ivergence is the spreading out of the beam of radiation. The farther from the source, the more the beam has spread. We need to be aware of beam divergence when setting up adjacent fields or where field edges are near critical structures. The divergence of the beam is taken into account when performing field size calculation and many dose calculations.
