Medical physics

Monitor chambers are located following the flattening filter. Used in several of the LINACs feedback systems to monitor and correct for dose rate, symmetry, and total dose delivered. The physicist is responsible for setting the dose calibration of the monitor chamber (ex. 1 monitor unit = 1cGy/MU at dmax on CAX 100SSD setup.

Equipment that converts kinetic energy to microwave energy in the linear accelerator. Klystrons are high-vacuum devices that use a well-focused pencil electron beam that directs the stream through a number of microwave cavities, which are tuned at or near operating frequency of the tube. Conversion takes place as a result of the amplified RF input signal, causing the electron beam to form "bunches". These "bunches" give up their energy to the high-level induced RF fields at the output cavity. The simplified signal is extracted from the output cavity through a vacuum window.

Administration of a local anesthetic into the subarachnoid space surrounding the spinal cord. Generally used to prevent pain and movement in areas below the chest and extending to the feet.

The technique in which the overall treatment time is shortened through the use of doses per fraction less than conventional doses two to three times a day

A special treatment procedure that utilizes the irradiation of a target with sealed radioactive sources placed at short distances from the target and inside the patient's body. Typically, the sources are implanted in the target tissue directly (interstitial brachytherapy) or are placed at distances of the order of a few mm from the target tissue, in body cavities such as the uterus, mouth, etc. (intracavitary brachytherapy)

A radioactive isotope with a half life of 5.26 years that was heavily used for external radiation therapy before the popularization of linear accelerators. It is a beta emitter that decays to Ni-60 and gives off two gamma rays of average energy 1.25 MeV in the process. This is the therapeutic part of the beam. One major disadvantage of Cobalt compared to Linear Accelerators is a wider penumbra at the field edge. It is seldom used for external beam treatments but is still employed in the Gamma Knife stereotactic system.

Fractionation in which the total dose of radiation is typically divided into 180 or 200 cGy increments and delivered once a day, 5 days a week.

Pro Software used to compare doses measured with film to doses computed by a treatment planning system. These comparisons are typically performed for every IMRT plan, as required by billing.

The process of combining images from different modalities with a CT image. Properly fused images combine the enhanced contrast imaging capabilities of MRI and/or the enhanced functional/physiological capabilities of PET with the spatial accuracy of CT. Usually the anatomy or Tumor Volume is defined on either the MRI or PET and then placed onto the CT which is then used to plan the treatment.

A group of hormones produced by both men and women. They are present in much higher levels in men and govern the growth and development of the male reproductive system. In women, they are converted to hormones called estrogens.

Radiation Safety term that stands for As Low As Reasonably Achievable. It states that radiation exposure should be kept to a minimum within reasonable effort.

Tissue equivalent material that is usually placed on the patient to increase the skin dose and/or even out irregular contours in the patients. When bolus is placed on the skin surface for megavoltage irradiation, skin sparing is lost.

A decrease of dose to an area significantly under the prescribed dose. While there is no hard fast rule as to what quantifies a cold spot, numbers greater than 5-10% below prescription should be scrutinized.

Teletherapy delivered through a beam with independently variable gantry angle and aperture opening, in which MLC leaves do not occlude the target.

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.

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.

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.

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.

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.

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.