Medical physics related Frequently Asked Questions by expert members with job experience as Medical physics. These questions and answers will help you strengthen your technical skills, prepare for the new job interview and quickly revise your concepts

## 69 Medical physics Questions and Answers:

### 1 :: What is afterloader?

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)

### 2 :: What is bragg Peak?

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.

### 3 :: What is collimator?

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.

### 4 :: Explain me what is coplanar?

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.

### 5 :: What is dose Calculation Matrix?

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.

### 6 :: Suppose film Badge?

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.

### 7 :: What is High Dose Rate (HDR)?

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.

### 8 :: What is optically Stimulated Luminescence Dosimeter (OSLD)?

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.

### 9 :: Please explain what Are Wave Fronts?

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.