Medical physics Interview Preparation Guide

A system in Brachytherapy that allows the applicators to be placed at the treatment site, then loaded remotely without personnel in the room. This reduces dose to the staff and since done via computers, should ensure a more accurate placement provided the applicators are correctly placed. Usually associated with High Dose Rate Brachytherapy (HDR)

A sharp increase in the dose distribution curve of a charged particle at a particular depth. It is this physical phenomenon that is exploited in proton radiation treatments.

An arrangement of shielding material in the linear accelerator designed to define the dimension of the beam of radiation. The collimators are located in the treatment head and are usually made of tungsten alloy.

A geometrical principle describing two radiation fields configured in such a way that the beam edges lie in the same plane. An example of a non coplanar field would be delivering one beam at one couch angle, and then kicking (rotating) the couch and delivering a second beam.

The area in the 3D treatment planning system that dose is calculated. It is split into units called voxels (indicating a volume, hence 3D). The higher the resolution (smaller the voxel size) the more accurate the dose calculation, however, the trade off is a longer period of time to make the calculation as there are now more voxels to calculate.

A device for measuring dose. It makes use of the following phenomenon: when film is exposed to radiation and subsequently developed, the amount of blackening (AKA Optical Density) is proportional to the dose delivered to the film. By measuring this darkening, it is possible to determine the amount of dose the badge received. These are worn by all radiation workers to document the dose received during their time at work.

Brachytherapy The delivery of brachytherapy on an outpatient basis using HDR brachytherapy equipment. The actual treatment delivery last approximately 5-10 minutes in contrast to a hospital stay that might take several days for low-dose rate (LDR) brachytherapy. HDR is almost always done with remote afterloader devices due to the high exposures hospital personnel would receive if they stayed in the room with the patient during administration.

Dose is recorded by a material that is read by a LASER. The LASER stimulates the emission of photons relating to the total dose recorded. The benifit is that only part of the chip is read at a time, one can re-read the same chip many times.

A wave front is an imaginary surface joining all points in space that are reached at the same instant by a wave propagating through a medium.

Let's try some examples. When a rock is tossed into a calm lake, a surface disturbance radiates from the point where the rock broke the water. The leading edge of that entire wave forms a circle, and that circle is the wave front for that event. It is moving outward at a constant speed in all directions. Note that it's two-dimensional (2D). Want 3D? You got it.

In a burst of chemical energy, a star shell explodes at a fireworks display. The light moves away from the origin in all directions at the same speed - the speed of light. And the 3D surface of this wave front is a sphere, and it is expands around the origin at the speed of light. Pick an arbitrary distance, say, 1 kilometer. Anyone at a distance of 1 km from the event in any direction will find that the wave front reaches him at the same instant of time as anyone else in any direction who is that 1 km from the event. Even someone in an airplane that is 1 km away will be on the wave front for an instant - that same instant as any other observers 1 km away. Note that the sound will arrive later - but it, too, radiates forming a spherical wave front. Our observers at 1 km distance from the event all experience the arrival of the sound wave at the same time.

Doctors who oversee the care of each cancer patient undergoing radiation treatment. They develop and prescribe each cancer patient's treatment plan, they make sure that every treatment is accurately given, and they monitor the patient's progress and adjust treatment to make sure patients get quality care throughout treatment. Radiation oncologists also help identify and treat any side effects of radiation therapy and work closely with all members of the radiation oncology team. Radiation oncologists have completed four years of college, four years of medical school, one year of general medical internship, then four years of residency (specialty training in radiation oncology). They have extensive training in the safe use of radiation to treat disease. If they pass a special examination, they are certified by the American Board of Radiology. Patients should ask if their doctor is board certified.