W
Waldeyer’s ring a lymphoid tissue circle surrounding the pharynx. See also tonsils.
WAN (Wide Area Network) the connection of a group of computer networks.
WAP (Wireless Application Protocol) a standard to allow text messages from the web to be available to mobile phones.
washing in film processing is to remove fixer solution and the remaining soluble silver complex salts from the film surface.
water phantom a water tank containing a small ionization chamber; the radiation beam can enter the tank either horizontally or vertically. The signal is displayed on a television monitor and the image is analysed for radiotherapy treatment planning.
watt (W) derived SI unit (International System of Units) for electrical power, watts equal volts times amps (W=VI).
waveguide a series of chambers with small iris diaphragms between them and varying distance apart. The function is to control the velocity of the electron beam that passes through it. See also magnetron, klystron.
wavelength (λ) the distance travelled in one complete cycle, usually expressed in millimetres; it is dependent on the frequency and propagation of speed. The term can refer to electricity or ultrasound. See also propagation speed.
wave theory the theory of electromagnetic radiation which considers that the radiation is produced as a sinusoidal wave consisting of an electrical field with a magnetic field at right angles to it.
web server a computer which fetches or stores images or web pages and makes them available over the internet or intranet on request.
wedge a wedge-shape piece of metal used to attenuate the beam over part of the field during radiotherapy treatment.
wedge angle for a particular wedge is the angle that the 50% isodose line makes with the central axis of the X-ray beam. The angle defined at a specific depth of tissue in a patient, usually 10 cm.
wedged pair dose distribution when two beams of the same wedge angle are used to produce an ideal dose distribution when used with a hinge angle of (180–200) degrees.
wedge factor the increase in set monitor units required to the same dose at Dmax
