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Dosimetry... |
 The
accurate delivery of the correct radiation dose is of vital importance
in the treatment of disease using radiotherapy. Too small a dose, and
cancerous cells may survive, leading to a recurrence of the disease. Too
large a dose and healthy organs may be damaged, leading to unacceptable
side effects.
With radiotherapy, one is not able to buy a meter "of the shelf" which
will immediately give you an acceptably accurate measurement of dose.
Dosimeter must be calibrated in-house for each type of radiation beam in
use, against a secondary standard dosimeter, which itself is calibrated
against the UK primary standard at the National Physical Laboratory in
Teddington. Calibrations of dosimeters must be performed independantly
by two suitably trained and experienced physicists before they can be
used to calibrate the treatment units.
The distribution of dose is measured in a variety of ways. The Hull
department uses a Scanditronix plotting tank system (with 24 channel
diode array), a Vidar film scanner, a Harshaw automatic TLD reader and
Rando anthropomorphic phantom, and is developing a 3-D optically read
gel scanner in collaboration with the University of Hull departments of
Physics and Chemistry.
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